Scientific principles of present-day and future technologies of synthesis and processing polycondensation polymers. Review

PolymerScienceVol. 33, No. 11, pp. 2135-2160, 1991 Printed in Great Britain.

0965--545X/91 $15.00+.00 (~) 1992 Pergamon Press Ltd

SCIENTIFIC PRINCIPLES OF PRESENT-DAY AND FUTURE TECHNOLOGIES OF SYNTHESIS AND PROCESSING POLYCONDENSATION POLYMERS. REVIEW* A. YA. MALKIN and M. I. SILING "Plastmassy" Science-Production Association

The scientific principles of the current and future technologies of polycondensation polymers are examined and a critical review presented of new ideas in this field. It is assumed that in the creation of the scientific basis of the new generation polymer technologies an important role will be played by research into the physicochemical basis and mathematical modelling of the processes of polymer synthesis, the use of methods of artificial intelligence and also the concepts and methods of other (non-chemical) sciences. The status and prospects of work along these lines are reviewed. In analysing the basis of the technology of processing polycondensation polymers the authors start from the idea of them as "living" systems capable in the course of the process of changing in composition and structure. This is particularly important for the realization of the path for regulating the properties of the material by obtaining copolymers and blends and also for the development of the technology of "chemical" shaping when the stages of synthesis of the polymer and obtaining the product of a set form are combined.

INTRODUCTION POLYCONDENSATIONpolymers (PCPs) continue t o occupy an important place in industry both in terms of the volume of production and the variety and significance of the areas of application. Thus, in the progress of the leading branches of modern technology an important role is played by constructional and heat-resistant PCPs. The significance of the criteria characterizing chemicotechnological processes is now the subject of reappraisal. Pushing aside the traditional technico-economic indicators, pride of place is now being occupied by such requirements for technology as ecological soundness, little waste, reliability of control, safety of the process, flexibility and meanoeuvrability. This tendency largely governing the face of tomorrow's chemical technology also applies fully to the technology of PCPs. The problems of creating a new generation of polymer technologies cannot be solved on an empirical basis for its price is too high and the results are not reliable. Therefore, the problems associated with the development of the scientific basis and principles for obtaining and processing PCPs remain acute and topical. The present review critically scrutinizes the situation in this field, attention being focused on unresolved and debatable issues in order to draw the attention of specialists to them. The authors have not sought to cover fully the published material since the paper is rather not a literature review but a r6sum6 of current ideas. For this reason preference was given to work done in the last three to five years which highlights the characteristic features of the development of polymer *Vysokomol. soyed. A33: No. 11, 2275-2299, 1991.

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science. Although the review is mainly devoted to PCPs included are several references to work on polymerization reflecting the tendencies and ideas common to the science of high molecular mass compounds.

PROCESSES OF POLYMER SYNTHESIS In the development and renewal of the scientific basis of polymer technology an important role will, in our view, be played by scientific research along the following lines: the physicochemical basis of the processes of synthesis of polymers; mathematical modelling of these processes; the use of artificial intelligence methods; and the use of the concepts and methods of other (non-chemical) sciences.

Physicochemicalbasis of the processes of polymer synthesis The physicochemical patterns of the processes of polymer synthesis include problems of thermodynamics, catalysis, kinetics and macrokinetics. The interest in research in this field is determined by the following motives. Firstly, the results of research traditionally provide knowledge of the mechanism of the process. Secondly, they are directly used to solve technological tasks. Thirdly, the physicochemical data are the basis for constructing mathematical models of the processes. In the epoch of computerization, mathematical models are becoming one of the main channels whereby the results of scientific research come into practical use [1].

Thermodynamics The thermodynamic characteristics determine the very possibility of synthesis of a polymer---on them, primarily, depends the composition of the equilibrium polycondensation systems. To construct a sufficiently complete mathematical model of the process of polycondensation it is necessary to know the thermodynamics of the main and side reactions; this is particularly important for reversible processes. The traditional use of thermodynamic data refers to heat calculations of the apparatus and devising energy-saving technologies. The latter not only raise the efficiency of the use of energy but also lower the heat contamination of the environment. One of main modern ideas on energy saving is to look for the optimum organization of heat flow in which the need for heat at the energy-consuming stages is completely or partially met through the exothermal stages of the process [2-4]. To find the optimum organization of large chemicotechnological systems one recommends the information-thermodynamic method [2] in which the concepts of information theory are used to evaluate the efficiency of transformation of the energy flows. The thermodynamic analysis of the processes in polymer technology is, as a rule, based on use of the first law of thermodynamics. Such an approach does not allow for the qualitative difference in the forms of energy involved in the process and does not always allow one to say where and why the energy is lost. The shortcomings of this approach are more obvious the greater the role played in the process being analysed by the conversions of some forms of energy to others. More refined methods of analysis are based on the use not only of the first but also the second and third laws of thermodynamics and the concept of energy which measures the ability of a system to perform work [2, 5-7]. Such methods have still not found appropriate use in polymer technology. Yet the character of polymer technology, in which an important place is occupied by heat and mass

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exchange processes, creates the prerequisites for the effective use of the exergetic approach. Evidently this is of particular importance for high energy-consuming processes such as, for example, obtaining the copolymer of trioxane with dioxalane which is comparable in energy expenditure with the production of steel. The introduction of the exergetic analysis into the practice of scientific and engineering work is promoted by the notable progress in the methodological and information backing of this approach [5, 7, 8]. The advances in computerization have given a fresh impetus to the use of thermometry and calorimetry in the study of chemicotechnological processes. These methods in their current technical form combined with the use of kinetic data and mathematical models [9] are becoming a convenient instrument of scientific and technological developments of the processes of synthesis and curing of polymers [10, 11]. In this respect of interest are the possibilities of the reaction calorimetric system backed by computer real-time treatment of the incoming data for controlling periodic and semicontinuous processes of emulsion polymerization [12]. The prospects for the wider use in polymer technology of measurements of the dynamics of heat release and raising the temperature in the reactor in combination with spectral, rheological, conductometric and other methods are obvious. The proper scientific validation of such procedures makes them a useful means for the timely detection of deviations from the normal regime of the process and for damage prevention. In the investigations of the process of obtaining polymers the ideas and concepts of non-linear thermodynamics or irreversible processes are beginning to be used. At the centre of attention of this scientific trend, in contrast to classical thermodynamics, are systems far from equilibrium to describe which non-linear mathematical models are necessary. According to the ideas of the Prigogine school [13, 14] for a system the non-equilibrium of which exceeds a certain critical value, not a single but several steady states of a particular space-time structure may prove possible. An important factor in the advent and maintenance of such structures called dissipative is the openness of the system, i.e. the possibility of the exchange of energy, matter and information with the ambient medium. The forms of dissipative structures may be vibrations and waves [15]. The mathematical image of dissipative structures constitutes a set of steady solutions of the equations of the mathematical model. The formation in the processes of polymer synthesis of several steady states, vibratory or wave structures has been confirmed experimentally in the study of radical polymerization of methylmethacrylate in a flow reactor [16]. The copolymerization of nonylacrylate with methacrylic acid [17, 18], anionic polymerization of caprolactam in the frontal regime [19] and curing of carbamidoformaldehyde oligomers [20, 21]. In research into radical polymerization [16, 22-26] from calculations from mathematical models conclusions have been drawn that in certain conditions a multiplicity of steady states may appear in the system. The condition for this is that certain parameters such as, for example, temperature, concentration of initiator and the rate of its consumption, concentration of solvent, the Damkeller criterion, etc., reach critical values. The practical significance of such research is obvious: it brings out new possibilities for the use in the technology of polymers of such factors as distance from equilibrium, the non-isothermal regime, the openness of the reaction system, the non-monotonic influence of catalysts or initiators and the complex mechanism of the process due to autocatalysis, substrate inhibition, heterophasicity or other factors. These factors and especially combinations of them may serve as the source of strong and sometimes unexpected effects. An important practical aspect of research in the field of non-linear thermodynamics is provided by the problems of the stability and incident-free technological processes. The authors of the monograph [26] believe that for a detailed judgement of the character of instability of the work of a

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polymerization reactor, the theory of bifurcations appears promising. The investigations [22, 23] laid down the foundations for work in this direction. From the common standpoints of the thermodynamics of irreversible processes it may be said that the further the state of the system from equilibrium the less determined and predictable the behaviour of the system and the more sensitive it is to external factors. In terms of the stability and resistance of the process, the polymer should be synthesized in a reaction mixture the composition of which is close to equilibrium, for example, on reversible polycondensation* the rate of removal of the low molecular mass product must not very greatly exceed the rate of its formation as a result of the condensation reaction. At the same time this does not exclude the possibility of the existence, far from equilibrium, of the steady regimes of polymer synthesis of undoubted interest for technology (see, for example, reference [27]). We would note that research in the field of irreversible thermodynamics of the processes of polymer synthesis closely joins study of the macrokinetics and mathematical modelling of these processes. The non-equilibrium and open character of the system is not an obligatory condition for the advent of vibratory regimes. Thus, it proved possible to understand the vibratory process of curing carbamidoformaldehyde resins within the framework of the thermodynamics of reversible processes in a closed system [21, 28]. The mathematical model of the process with vibratory solutions is based on the following propositions: the cured system contains regions with an unordered and ordered structure--domains; domains are stable for oligomers above a critical chain length; in the domains the equilibrium constant of the reversible reaction of curing is far lower than in the unordered regions. In reference [28] it was concluded that during curing of carbamidoformaldehyde resins there may be fluctuations in the structures both in time and space. It was shown that in such systems there may be fluctuations in time in the parameters at fixed points although the experimental data on the parameters average by volume do not show fluctuations. In the scientific validation of technological developments concerned with reversible processes of polymer synthesis a key place is occupied by data on the dependence of the equilibrium constants of the reactions on temperature, composition and the phase state of the medium. A general perusal of these dependences is given in references [29, 30]. There is growing interest in the thermodynamics of polymer synthesis in the solid phase in view of the prospects of creating on this basis resource-saving and ecologically sound technologies. An instructive example is the synthesis of PA-6 by hydrolytic polymerization of caprolactam. The conduct of the process in the melt at 250-270°C, because of thermodynamic constraints (insufficiently large equilibrium constant), does not give a product with a content of free caprolactam and oligomers <9-10%. To remove them it is necessary to introduce an extraction stage. The reactions of synthesis of PA-6 are exothermic and therefore, the equilibrium constants may be increased by reducing the temperature of the reaction, the process being brought into the solid phase. As shown in references [31, 32] the temperature dependences of the equilibrium constants in the amorphous phase of PA are close to those for the process in the melt. This then validates the conduct of the final stage of the process of synthesis at a temperature 30-40°C below the melting point of PA-6. Such

*For the correct thermodynamicanalysisof the processesof obtainingpolymersof no littleimportanceis the accuracyand definitionof terminology.Often the terms "equilibrium"and "non-equilibrium"are used as synonymsof the conceptsof reversible and irreversible polycondensation.Yet these concepts are not equivalent [1]. The reversibilityof the polycondensation reactionsis determinedby the valueof the equilibriumconstantand the equilibriumor non-equilibriumcharacter of the process may also depend on macrokineticfactors, for example, on the rate of removal of the low molecularmass product or the temperature fieldin the reactor.

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technology yields high molecular mass PA which is directly (without the demonomerization stage) suitable for processing to fibres and plastics. In some cases, with the thermodynamics is directly linked the important ecological problem of protecting humans and the environment from the harmful influence of polymeric materials. The question concerns the toxic action of monomer impurities such as, for example, phenols, formaldehyde, diamines. The presence of monomers in the polymer may be due to three factors. The first is kinetic: synthesis cannot be conducted to high conversion of the monomer because of the low reaction rate. The second is thermodynamic: the equilibrium constants of the reactions of monomer expenditure are too small. The third is operational: the thermodynamic and kinetic characteristics of the polymeric system are such that in conditions of processing and/or use of the polymeric material chemical conversions of the polymer become possible with release of monomer. Evidently thermodynamic data are necessary for an understanding of the significance of these factors and, consequently, for searching for effective ways of reducing the release of monomer. In the last few years the ecological aspect of the problem of chipboard and other materials obtained with use of carbamidoformaldehyde resins has come into sharper focus. The reason lies in the establishment of the carcinogenic and mutagenic properties of formaldehyde with the result that the public health-hygiene requirements on the formaldehyde content in the human environment have become more stringent. It has been shown that the release of CH20 from cured resins in the course of processing and use of materials far exceeds the content of formaldehyde in the starting resins. Thus, in this case the main reason for the isolation of the monomer is its use. Analysis of the thermodynamic data [1, p. 33; 51; 52] points to the possibility of isolating CH20 from cured carbamide resins through the reactions of demethylolation and also hydrolysis of the dimethylene ether and methylene bonds. Hydrolysis is promoted by the presence of moisture in the board. These results largely determine the future paths of solving the problem touched upon.

Catalysis The use of a particular catalyst largely determines the whole technology of polymer synthesis. On the efficacy of the catalyst depends both the technico-economic and ecological indicators of the process. An active catalyst helps to raise the productivity of the reactor and/or lower the temperature of synthesis. The result is lower energy expenditure and improved quality of the polymer since with fall in temperature, as a rule, the importance of side and destructive reactions drops. Further, the quality of the polymer is strongly affected by the selectivity of the catalytic action determining the composition and structure of the chain molecules and also the influence of the catalyst remaining in the polymer or the products of its chemical conversions [34-36]. To eliminate the last factor the polymeric product is often subjected to special purification. However, in some cases a better technological procedure may be the use of additives inhibiting the harmful action of the catalyst. Such an additive must at least not worsen the activity and selectivity of the catalyst and, naturally, the properties of the polymer. Examples of a positive effect of additives to catalysts are given in references [34, 35]. One of them relates to the synthesis of polyalkylene terephthalates in the presence of titanium-containing catalysts and an organophosphorous compound which stabilizes the polymer [35]. The influence of catalysts on the ecological characteristics of a polymer in the course of its synthesis is manifest along several lines. In the first place the fall in temperature of the reaction with use of a more active catalyst or initiator helps to lessen the volatility of the monomers and solvents. An ecological effect is also given by replacing an organic reaction medium by an aqueous one. In references [37, 38] new initiating systems are proposed permitting a number of processes of

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polymerization and copolymerization of the derivatives of acrylic acid, vinyl acetate and other vinyl monomers at low temperatures in an aqueous medium. A selective catalyst may run the process in a direction ensuring the formation of polymers more acceptable ecologically. For example, the nature of the catalyst influences the release of formaldehyde from a carbamidoformaldehyde binder: maximum release is observed with the use of oxalic acid and less in the case of ammonium phosphate and minimal for hydrogen peroxide [39]. There is no doubt that research aimed at finding highly active and selective catalysts will continue to remain highly topical. It is pertinent to raise the question, what guide points for the search are given by the modern science of catalysis? It is important to bear in mind the absence of fundamental differences in the theoretical interpretation of catalysis of the reactions of synthesis of polymers and the reactions of low molecular mass compounds with the same functional groups. Current approaches to the prediction of catalytic activity are based on particular notions of the character of the intermediate chemical catalyst-reactant interaction (CRI). These notions are determined primarily by the type of reaction to be catalysed. Thus, polycondensation reactions unlike polymerization are, as a rule, heterolytic. From this it follows that catalysts of polycondensation will be compounds capable of interaction, of the acid-base type, with the functional groups of the monomers. An important role in the shaping of the high activity of a catalytic system is assigned to its polyfunctionality, i.e. the capacity for CRIs of varied type. Thus, for a number of catalytic conversions the coupled action of the acidic and basic centres and the rupture of old and the formation of new bonds with the realization, because of the diversity of the CRIs of energetically advantageous concerted (synchronous) mechanisms of the reaction, have been proposed [40-42]. The diversity of the CRIs underlies polyfunctional systems each component of which accelerates one or more stages of the process [43]. The following principle has been proposed [1]: the preferential routes of the catalytic reaction are those which ensure activation, via a catalytic system, of all the substances entering the reaction. Examples of the fulfilment of this principle are given below. With regard to monomers for polycondensation their activation may occur as a result of the CRIs of four main types: protonation by the acid of an electrophilic reagent; deprotonation of the nucleophile by the base; coordination interaction of the monomer with the atom (ion) of a metal; and the formation of a hydrogen bond. Let us go into some new ideas concerning the CRIs of the last two types. In reference [44] the results of investigations into outer sphere coordination occurring through the H-bonds, donoracceptor and electrostatic interactions are analysed. The authors arrive at the conclusion that the interaction between the ligands of the inner and outer spheres of a complex compound leading to the formation of outer sphere complexes may play a crucial role in the mechanism of catalysis by metallocomplexes. The monomers for polycondensation, as a rule, are O- and/or N-containing compounds capable both of coordination interaction and the formation of H-bonds which is undoubtedly important for the mechanism of catalytic polycondensation. The formation of outer sphere complexes through the H-bond of the molecule of an alcohol with the ligand of the inner sphere is demonstrated in reference [45] dealing with the catalysis of the reaction of formation of urethanes by the triacetylacetonate iron. In the view of the authors, the process occurs through the coordination of the isocyanate in the inner sphere of the complex and of the alcohol in the outer. Evidently the electrophilicity of the isocyanate and the nucleophilicity of the alcohol are enhanced here, i.e. both reactants are activated. The assumption of the direct participation of inner sphere ligands in the activation of the reactants

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helped to explain the patterns of esterification of mono-2-ethylhexylphthalate by ethylhexyl alcohol catalysed by a tetraalkyl titanate [46]. Activation of the electrophilic agent (mono-ester) is explained by the coordination interaction of the carboxyl group with titanium leading to a shift of the electron density to the metal, while the reactivity of the nucleophile (alcohol) grows as a result of the formation of the H-bond with the proton acceptors which are oxygen-containing ligands of the inner sphere. This reaction underlying the synthesis of dioctylphthalate may be regarded as a model for the polycondensation of aromatic dicarboxylic acids with glycols. The last examples demonstrate the fulfilment of the principle of activation of both reactants of the catalytic reaction. Other similar examples relating to polycondensation of phenol with formaldehyde are given in the monograph [1]. A general feature of all these cases is that increase in the reactivity of the monomer which is not directly activated by the effect of the main (principal) catalyst is achieved through the formation of H-bonds. A tendency of the recent period which will probably move ahead consists of the construction of complex catalytic systems, the use of which is widening the possibilities of intensifying the processes of obtaining polymers, control of the selectivity of synthesis reactions and the properties of the polymers. Thus, the use for catalysis of polyesterification instead of protonic of aprotonic acids in the form of complexes and other metal compounds helps to reduce considerably the role of the side reactions, to exclude the neutralization stage and, consequently, also the amount of waste and to facilitate solution of the problems of protecting the plant against corrosion [34]. This tendency encompasses work on multicomponent catalysts of polymer synthesis [34, 35, 47], the use of heteropolyacids in the polymerization of THF and oligomerization of vinyl monomers [48, 49], catalysis of the polymerization of olefins by fixed metallocomplexes [50] and the use of gel-immobilized catalytic systems [51, 52]. It is not hard to see the closeness in ideas of the concepts of the important role of polyfunctionality of the catalytic system and the tendency towards the creation of complex catalysts. Such approaches also agree with the results of analysis of catalysis in terms of control and information theories [1, 35]. From the results it follows that the activity and selectivity of a catalyst largely depend on the diversity of the CRIs. The ideas outlined and their development provide a scientific base for constructing catalytic systems for the reactions of polymer synthesis. Another path is linked with the use of computer prediction of the catalytic action. Here, two main directions may be singled out [53]. The first is based on a study of the mechanism of catalysis and the use of quantochemical calculations. The importance of this direction will grow with the introduction of supercomputers into the practice of catalytic research and the most important advances here are still awaited. The second direction is based on current methods of treating the experimental material such as optimum planning of the experiment, the theory of decision making, the theory of image recognition, the methods of logical modelling, uneven multiplicities and artificial intelligence. One example is provided by reference [54] in which logical modelling with use of a computer was employed to choose the conditions of synthesis of a catalyst for obtaining PP. Kinetics and macrokinetics The data on the kinetics of synthesis of a polymer provide the base for constructing a mathematical model of the process. Lack of reliable and full kinetic material is primarily holding back the mathematical modelling of the processes of polymer production. This applies, in particular, to the kinetic data for wide intervals of varying the conditions of synthesis and also the kinetics of the side reactions. Here, there is a favourable field for future research.

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The creation of new technologies with little or no waste requires study of the kinetics of the corresponding processes. Thus, in obtaining phenolic and carbamide resins it is possible to reduce considerably the quantity of waste water, if as the formaldehyde component of the raw material, not formalin but concentrated solutions of CH20 or its solutions in phenol or carbamide are used. On synthesis of esterified resins such an effect is given by the use of alcoholic solutions of formaldehyde. The kinetics of such a variant of synthesis was studied in references [55, 56]. The advances in the experimental study of the kinetics of synthesis of polymers will be furthered by achievement in working out new sensitive sensors, the use of the possibilities of fibre optics and computerization of the instrumental methods for analysing reaction mixtures. To raise the reliability of determining the kinetic parameters of polymerization it is natural to use a range of methods. An interesting comparison of different current methods for determining the chain propagation and termination rate constants in radical polymerization as a function of conversion of the monomers, the efficiency of initiation, the share of the polymeric fraction and the degree of polymerization is proposed in reference [57]. The close relationship between the kinetics and mathematical modelling is expressed in the fact that a model constructed from the kinetic data is itself used as an important source of information on the kinetic patterns of the process. This applies in the first place to macrokinetics. The main way of identifying macrokinetic patterns of the complex processes of polymer synthesis is becoming, not the natural, but the computational experiment on a mathematical model. The importance of macrokinetics for a real process of obtaining a polymer depends on such interrelated factors as the ratio of the rates of the chemical reactions and heat release, on the one hand, and the processes of mass and heat transfer, on the other, and also on the viscosity of the reaction system and its phase state. In the case of very fast polymerization processes lasting <1 s the rates of mass and heat transfer, as a rule, are considerably less than those of chemical reactions. Such processes required essentially new approaches to their investigation and to technological developments [58]. Experimental and theoretical research into the kinetics of the processes of synthesis of polymers with the stages of chain propagation and termination controlled by diffusion remain very important for technology [59]. In reversible polycondensation the macrokinetic effects are linked with the influence of the rate of removal of the low molecular mass product. The authors of reference [60] proposed that the role of this factor can be characterized by the dimensionless parameter A = f(v/K, where K is the equilibrium constant and A'P is the number average degree of polycondensation. With increase in A the role of the reversibility of the reaction grows. Polycondensation for A~>1 is called polycondensation with a weak influence of reversibility. A typical example of the first case is polyamidation (Xp < 102, K ~ 500, A ~<0.1) and of the second the deep stages of full esterification (A'p = 102, K ~ 1, A -- 102). This paper considers the kinetics of reversible polycondensation for a different ratio of the rates of the chemical reaction and removal of the low molecular mass product from the reaction mixture. The increase of viscosity in the course of polymer synthesis largely determines the macrokinetics of the process through the influence on heat and mass exchange, dissipative heat release due to viscous friction and the energy consumption characteristics of the reactor. On change in viscosity of the reaction mass depends the hydrodynamic picture in the polymerization reactor and, consequently, the productivity of the reactor, the MMD and properties of the polymer obtained [61-64]. The heterophasicity of the process of polymer synthesis, as a rule, entails the need to consider a

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number of macrokinetic problems. These are the establishment of the region in which the process takes place (internal kinetic or diffusional, external kinetic or diffusional), the location of the reaction zone, the determination of the type of disperse system, measurement of the size of the interphacial surface and establishment of the mechanism of the process with determination of the stages controlling its rate. The range of the corresponding problems is considered in the monograph [1, pp. 145-166]. The hydrodynamic aspects and mass transfer on interphacial polycondensation were recently explored in reference [65]. The different current approaches to a description of the kinetics and macrokinetics of polymer synthesis in the solid phase are presented in references [32, 66--68]. At the same time further development of theoretical notions in this field combining analysis of microkinetic phenomena such as diffusion, heat transfer, crystallization, etc., with allowance for the features of the kinetics of chemical reactions in the solid phase is highly topical. The importance of kinetic factors is indicated, in particular, by data on the catalysis of solid phase reactions of polymer synthesis, for example, the process of polyamidation [69]. In our view characteristic of the current and future stages in the development of the kinetics is the tendency towards staging wide physicochemical investigations including, not only determination of how the composition of the reaction mixture changes in time, but also study of the whole complex of coupled phenomena. Such an approach is important for constructing effective mathematical models of the process. One characteristic example is the investigation of the macrokinetics of heterophase polycondensation of oligocarbonates [70-73]. This is a fairly complex process developing in a mixed system consisting of two phases---water-alkaline and methylene chloride; besides the chain propagation reactions an important role is played by hydrolysis of the chloroformate end groups, the catalysts of the reactions are the alkali and triethylamine. To understand the mechanism of the process and its quantitative description it was necessary to obtain, together with the kinetic information, details on the type of emulsions formed in different conditions of synthesis, the size of the interphacial surface, the distribution of the reactants and catalysts between the phases, adsorption of the oligo- and polycarbonates at the interface, the viscosity of the polycarbonate solutions as a function of the MM and the concentration of the polymer and the specific power of mixing.

Mathematical modelling The problems of polymer technology are becoming ever more complex. Firstly, because of complications of the technological processes themselves and, secondly, because of the considerable rise in the demands placed on the level of solving the problems. The more complex the object the greater the role of mathematical methods and computers in investigating it. Therefore, nowadays the computer is becoming an essential tool for investigating and exploring the processes of obtaining polymers. But there is a real danger of divorce between the advances in computer techniques and the level of readiness for their use. The accumulated experience of computerization indicates that the rational use of the possibilities of the computer (enormous today and fantastic tomorrow) requires scientific validation and, in the first place, profound knowledge of the object of mathematical modelling. A purely empirical approach to complex tasks has few chances of success even when it is combined with the application of a potent computational technique. This raises the need for grasping and closer exploration of those aspects of the sciences of high molecular mass compounds which will ensure effective use of computers of the future. The problems of constructing and using mathematical models of the processes for obtaining

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polymers are considered in many publications [1, 26, 27, 29, 58, 74-77]. We shall confine ourselves to a few remarks on this score. The choice of the model is determined by its purpose: the model must ensure the greatest possible exact calculation of those parameters of the process or polymer for which it was created. For example, the aim of mathematical modelling of the process of oxidative polymerization of coatings consisted of intensification of the process [78]. It was established that this can be done without lowering the quality of the coating, by shortening the final period of the process in which the spatial-network polymer is shaped. Further research had a clear direction--to construct a model for calculating the duration of this period as a function of temperature and partial oxygen pressure. In the case of a complex process the construction, not of a universal model, but of a set of models, for example, one for calculating the conversion of the monomers and another for determining the characteristics of the polymer and a third for controlling the process may turn out to be preferable. The completeness of our knowledge of the process determines the soundness of the assumptions used for constructing a mathematical model. A classical example is the assumption of fulfilment of the Flory principle, i.e. the independence of the reactivity of the functional groups of the macromolecule from the chain length. In many cases of mathematical modelling this principle serves as a good approximation. The deviations observed from the principle of equal reactivity are considered in reference [79]. Effective methods for calculating the MMD for systems not obeying the Flory principle are proposed in references [80, 81]. To describe heterophase reaction systems, assumptions are usually made on the applicability of the ideal gas laws; Henry's law and the Flory-Huggins equation [82, 83], although there are significant deviations from these rules. Thus, on polycondensation of adipic acid with triethylene glycol the Flory-Huggins parameter was found to depend closely on the concentration of the end groups [84]. Often it is assumed that the establishment of the equilibrium distribution of the components of a mixture between phases occurs instantly and does not affect the rate of the process [82]. However, in the case of fast reactions this may not be the case, for example, the diffusional character of heterophase polycondensation of oligocarbonates is largely determined by the stage of mass transfer of catalyst between phases [70, 73]. The successful identification (finding the parameters) of the mathematical model also essentially depends on the soundness of the physicochemical investigation of the process. In the often encountered case when the problem has not one but several solutions roughly equivalent in adequacy to the experimental material, the independent additional information on the thermodynamic and kinetic constants may provide a basis for choosing the true set of parameters. A model with such parameters having a clear physical meaning must possess high predictive powers. Mathematical models are used as a powerful instrument for solving the diverse tasks of polymer technology. These are the tasks of investigating the process of polymer synthesis: establishing the relations between the parameters of the technological regime and the rate of the process and also the structural characteristics of the polymer; and analysis of the influence of the type of reactor, its design features, the hydrodynamic regime and passage from a periodic to a continuous process. Next, come the tasks of designing and calculating reactors and other equipment; optimization of the process and synthesis of the chemicotechnological system. The next group of tasks includes investigation of the parametric sensitivity and stability of the operation of the reactor, the creation of control and monitoring systems and guarantees of the safety of the process. Developing the thesis that the efficacy of mathematical modelling is largely determined by the degree of knowledge on the process to be modelled, let us look at the tasks of optimization and also

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of monitoring and control. A deep understanding of the process is a necessary prerequisite for the correct formulation of the tasks of optimization--choice of the criterion of optimality and the system of constraints in the case of a multicriterial task--mode of convolution and evaluation of the weight coefficients reflecting the importance of a given criterion. It has been proposed [85] that four groups of criteria of optimality be distinguished--economic, quality of production, ecological and failure proof. The criteria characterizing the process are interrelated and the requirements corresponding to them may be concordant or contradictory. In general, the task of optimization has no clearcut formalized solution. Much depends on the knowledge and practical experience of the specialist. Examples of different approaches to the optimization of the processes of obtaining polymers may be found in references [26, 27, 74, 78, 86, 87]. The requirements for monitoring and control systems in polymer technology are growing, in the first place through complication of the problems of ecology and more stringent criteria of the quality of production. In line with this we see a tendency towards the closer control of the processes of synthesis: modern plant is equipped with a full instrumental backing. The efficiency of the measuring technique rises sharply when monitoring and control are based on a qualitative mathematical model of the process. In this case the control strategy is based on a knowledge of the process as a whole with all its interrelations and multidiversity. A number of publications of a reviewing character have appeared dealing with the use of mathematical models for the monitoring and control of technological processes including polymer synthesis [27, 88-92]. In particular, it has been proposed that mathematical models are used to ensure trouble-free work of a reactor. Thus, in reference [93] for the polycondensation of phenol with formaldehyde in a batch reactor a model describing the system of protection should the process get out of control is proposed. The original mode of control of a process was validated with the aid of a mathematical model of a radical polymerization reactor [94]. The aim of the control is to stabilize the unstable steady state in the continuous reactor through periodic change in pressure. The predicted feasibility of such stabilization was confirmed experimentally on a pilot reactor for ths polymerization of ethylene. Effective control must be based on sufficiently complete, reliable and operational information on the process. The practice of polymer production indicates that it is often not possible to obtain such information by traditional methods, the reasons being the absence of express methods of analysis of the reaction mixtures, insufficient precision of the analytical techniques, the difficulties of selecting representative samples and the high sensitivity of a number of methods to the presence of impurities and byproducts. The use of mathematical models provides the necessary information on the process including data on variables practically not amenable to rapid measurement. These may be the concentrations of certain reagents and the functional groups, the activity of the catalyst, isomeric composition, MMD, the amount of polymer formed, etc. [27, 89, 90, 95]. We would note that non-measurable variables are usually of the utmost interest for controlling the process. Success is being achieved in the ASU TP "Polymer" polyethylene production plant [27] in which the current productivity of the reactor is calculated on the basis of a mathematical model of the process working in real-time. Another example is the system of monitoring the periodic process of obtaining PA by hydrolytic polymerization of lactams created in the Plastmassy Science-Production Association. In the course of synthesis, the signals from the temperature and pressure sensors in the reactor enter the computer memory every 3 min. Using these data and information on the starting conditions the computer in line with the mathematical model of the process calculates the ongoing indicators of the reaction system, such as the degree of conversion of the lactam, the concentrations of the amino- and carboxyl-groups, low molecular mass and cyclic oligomers, water, the molecular mass of the polyamide formed and so on.

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Since calculation occurs practically at the same pace as the process its results may be used for operational monitoring and control. Evidently the approach considered to monitoring sets high requirements on the adequacy of the mathematical model to the process of polymer synthesis.

Use of artificial intelligence methods Despite the wide possibilities of the methods of mathematical modelling, they are not limitless. In mathematical models, it is difficult to allow for non-formalized information and even more so the unconscious experience of the specialist. Moreover, the predictions given by models far from always possess sufficient completeness and accuracy. Thus, the mathematical models of the processes of polymer synthesis allow one usually to calculate the productivity of the reactor, the MM and MMD of the polymer and the quantity of the main byproducts. This is far from always sufficient, for example, for evaluating the quality of a polymer or the diagnosis of disturbances of the technological process. These limitations can be largely circumvented by the artificial intelligence methods. This trend in science, swiftly developing in the last few years, is oriented to a computer solution of creative tasks previously amenable only to human intelligence [53, 96, 97]. Wide currency has been gained by expert systems representing programs for a computer, the work of which is based on knowledge received from specialists in a particular field [53, 96-100]. Expert systems are used in the chemical industry for the control of technological processes including the diagnosis of the course of the process and the state of the equipment, for production planning and instructing and training the personnel [53, 96, 101-103]. The use of expert systems working in real-time as an adviser to the operative appears highly promising. Such systems can take into account a large number (hundreds and thousands) of measured variables, sufficiently rapidly undertake expertise and recommend measures to ensure the optimum regime of the process and the prevention of troublesome situations. This is of particular importance for dangerous production. Apparently to improve the safety of such a production, parallel independent control systems may find use, one of them being based on the use of the mathematical model of the process and the other on expert systems. These systems will differ from each other not so much in that they can use discordant masses of measured variables but chiefly in the fundamental difference in the modes of processing the incoming information. In polymer technology the use of artificial intelligence is making inroads, the bulk of the work in this direction relating to composites and processing of polymers [104-106]. The shortcomings and limitations, peculiar to expert systems, are due to their very nature and mode of construction. These are primarily the inability to make recommendations on the basis of axioms or theoretical knowledge. The system cannot go beyond the direct experience of the experts, it being hard for it, at the same time, to recognize the limits of its competence. Considerable difficulties arise in the work of expert systems with contradictory or erroneous data. The complete elimination of these drawbacks is a matter for the future. A highly promising trend is the development of intellectual systems in which theoretical knowledge is rationally combined in the form of determined mathematical models and practical experience in the form of expert information. The realization of such an approach has already begun [96, 103, 107,108]. Evidently the effectiveness of any system of artificial intelligence will be firstly determined by the knowledge embodied in it. A decisive role in obtaining, evaluating, organizing and harmonically combining knowledge of different types remains with man. In our case this makes it necessary for specialists in high molecular mass compounds to enter a sphere of ideas and methods of artificial intelligence new to them.

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Application of the concepts and methods of other sciences Nowadays the interaction of the sciences is being converted from an episodic phenomenon gradually into a global process [109, 110] promoted by awareness of the limitations of describing reality within the framework of one science and also the numerous examples of the birth of original ideas at the junction of difference branches of knowledge and the successful application in a science of the procedures and methods of other sciences. l~ractically, from any science, including humanitarian, one may draw something useful for the science of polymers. However, the most promising appears to be the interaction of the science of high molecular mass compounds with physics, biology and informatics. Physical methods are considerably enriching the arsenal of the means of acting upon the processes of chemical technology especially if this is based on the latest achievements of physics and technology [111]. The "physicalization" (to use the expression of V. A. Legasov) of chemical technology is proceeding via the use of ultra-high and low pressures, acoustic, mechanical and electrochemical methods, electromagnetic fields and the processes of laser, photo-, plasma- and radiation chemistry. Physical influences on a polymer system are most often used to initiate and intensify the processes. Such effects are achieved by raising the temperature or pressure, by the influence of heat and mass transfer and also by selective action on the elementary acts of chemical reactions. Successes in radiation chemistry in the field of synthesis, modification and curing of polymers are known [112, 113]. Electrochemical initiation of polymerization is the subject of the monograph [114], photodegradation and photostabilization of polymers are considered in the monograph [115]. Physical methods of clearing the production waste of polymers are assuming great importance as can be seen in reference [116]. Naturally, the effective use of physical methods is impossible without a thorough knowledge of the properties of polymeric systems attending the method such as, for example, the thermophysical, optical, magnetic and electrophysical properties. Polymer technology cannot stand aside from the achievements of modern biotechnology. Biological clearance has become one of the most universal methods for rendering harmless the runoffs in polymer production [116]. An important role is played by biological methods in solving the problems of decomposing the wastes of polymeric materials. These problems are far more easily solved for polymers obtained by reversible polycondensation than for those of the PE, PS or PVC type. One promising line of work in the creation of polymers with a defined "lifetime" is the synthesis of complex polymers, the macromolecules of which contain together with units of traditional polycondensation polymers also units of natural polymers [116, 117]. These may be residues of amino acids, carbohydrates, some polyols and carboxylic acids. Together with work on biodegradation, research into biological polymer stabilizers is moving ahead. It is of interest to study the possibilities of synthesizing polycondensation polymers using microorganisms. Such an approach is based on the ability of a number of enzymes, notably hydrolases, to speed up the reactions ensuring polycondensation. Reference [118] describes the enzymatic polycondensation of an amino acid--methyl-L-tyrosine--in an aqueous buffer solution. A high degree of conversion was achieved on polycondensation of hydroxyacids catalysed by lipase [119]. The structure and properties of the copolyesters obtained with the aid of bacteria from glucose and propionic acid are examined in reference [120]. Other examples of polymer synthesis using enzymes can be found in reference [121]. Some technological problems of enzymatic synthesis of esters are discussed in references [34, 122]. The high activity and selectivity of the action of enzymes combined with the mild conditions of

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synthesis make work in the field of enzymatic polycondensation attractive. Such investigations may play an important role in future polymer technology. One may speak of two aspects of the application of informatics in polymer chemistry and technology. In the first case we have in mind the use of computers for collection of information, its processing and decision taking. With this are connected such concepts as the mathematical model and the computational experiment, knowledge base, automated design system, automated system of scientific research, artificial intelligence including intelligence information search systems, intelligence packets of applied programs and expert systems. The use of such means underlies the so-called information technologies. The second aspect reflects the tendency observed in the methodology of modern science towards the supplementation of the physical description of the test object by its description in terms of control and information [123]. This is a matter of identifying the informational mechanism of the phenomenon, looking at it from different angles and so seeking to clarify new aspects of the phenomenon. Such an approach has been used in relation to catalysis [1, 35]. The reaction system was regarded as a control object and the catalyst as a controlling device and the reaction rate as the controlled magnitude. The catalyst, as it were, drives the reaction system along a path differing fundamentally from the non-catalytic. Any control is based on transmission of information. In the given case the question concerns the transmission of information from the catalyst to the reactants, the CRI serving as the material base of information transmission. Information transmission is, as a rule, accompanied by errors (noise) which may be expressed, for example, in the omission of the necessary CRI, its replacement by another or the appearance of a "superfluous" CRI. While the transmission of undistorted information governs the progress of the main reaction, noise may be the cause of secondary reactions. Such a view served as the basis for using the information transmission theory over a channel with noise [124] for analysing the problem of the selectivity of the catalytic reaction. The result was establishment of some factors enhancing selectivity [35]. The first is the occurrence in the system of a large number of fast CRIs. Such systems are characteristic, in particular, of enzyme catalysis. The second is reduction in the amount of transmitted information which may be relatively low if in the course of the reaction there is rupture and formation of a small number of links as a result of which considerable diversity of the CRI is not required. It is worth noting that for the enzymatic catalysis of complex conversions it is common to use a system of enzymes each of which speeds up the simple chemical conversion. The third factor is the union of the individual signals into long blocks. To such a mode of information coding in catalysis corresponds synchronous mechanisms when the rupture of the old and the formation of new links occurs simultaneously in a single activated complex. In the light of the approach outlined titanium-containing catalysts for the synthesis of polyalkylene terephthalates are considered [35]. As assumed by the authors the high activity and selectivity of these catalysts are linked with the wide variety of CRIs through coordination and exchange reactions and also with the fact that these are fast reactions. There are grounds for expecting interesting results in examining, from the standpoint of information and control theories, other aspects of the processes of polymer synthesis. In conclusion, we would note that the use of the achievements of other sciences influences, not only the methodological equipment of the scientist, but also the style of thinking, help to overcome stereotypes and psychological barriers.

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PROCESSING OF POLYCONDENSATION POLYMERS

General problems The creation of a modem highly effective technology of shaping (processing) PCP products requires the solution of a number of fundamental scientific problems specific to the materials of this class. The position here is more complicated than in the case of such classicial plastics as, for example, the polyolefins. The extensive group of PCPs in terms of a basic technological scheme may be divided into two--thermoplastic PCPs (typical examples are different PAs or PCs) and reactive oligomers (ROs) forming at the shaping stage a three-dimensional, dense (in relation to the size of the kinetic segment) network. An intermediate position is taken by some heat-resistant linear polymers acquiring the final chemical structure at the stage of shaping the product (for example, on passing from the polyamido acid to the polyimide). Characteristics of all these materials (this is very clearly marked for the ROs and less clearly for the thermoplasts) is that they "live" during processing undergoing particular chemical conversions so that the material in the product is always different (more or less) from the starting substance. Consequently, the technological characterization of PCPs must rest on evaluation of their kinetic stability at raised temperatures corresponding to the region of processing. Therefore, together with the traditional problem of evaluating (and regulating) the technological properties of the materials for processing, for PCPs analysis of the kinetic aspects of the chemical conversions comes to the fore among the scientific problems arising in the creation of materials based on PCPs and validation of the permissible or optimum regimes of their processing. The problem may be posed in two ways. Firstly, of scientific interest are the kinetics of the chemical conversions proper which may be judged from change in the content of the end or other reactive groups in the chain, the heat effect of the reaction, etc. Secondly, and of crucial importance are the kinetics of change in the technological and, primarily, rheological properties of the material. Of course a link exists between the first and second, but unfortunately it is not always known and its establishment is a task for research in its own right.

Chemical conversions during processing Let us consider some characteristic situations associated with the kinetics of chemical conversions during processing of linear PCPs.

Fullpolycondensation and depolymerization. In the course of processing linear PCPs reactions of partial degradation or depolymerization (fall in MM) and/or full polycondensation (rise in the MM) may take place. The direction of the reaction depends on temperature and the presence of some low molecular mass compounds shifting condensation equilibrium. Regulation of the MM in the case of equilibrium polycondensation through change in temperature is a quite widespread technological procedure. An example is solid phase complete polycondensation of PA-6, dealt with above. Of decisive importance here is the relation between the rate of the chemical process, where it is necessary to use higher temperatures in order to raise, and the desirable MM values, where the temperature must be lowered to give the content of low molecular mass products. This raises the optimizational problem of establishing the temperature profile, the solution of which would allow one to realize the most advantageous technological regime of synthesis of a polymer with the requisite characteristics. Another known (and technically probably the most important) case referring to this group of PS 33:11-B

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problems is the behaviour of a PA in the presence of different (very small) amounts of residual moisture. Although the temperature of the processing of a PA is far higher than the boiling point of water, moisture is present in the melt possibly in a state bound by physical interactions and plays an enormous role in the processing of a PA. This role is dual. Firstly, the Presence of moisture as such lowers very sharply the viscosity of the melt and the presence of appreciable amounts of moisture adversely affects the properties of the end product. Secondly, depending on the moisture content not only do the kinetics change but also the direction of the change in the viscosity of the melt (and hence the MM of the polymer). The dependence of the viscosity of the melt on the moisture concentration is expressed by an exponential law [125] 7/= ~oe -k~, a curious feature being that the value of the constant k depends not only on the type but also on the origin of the PA. Thus, for "anionic" PA-12 k ~ 0.3 while for "hydrolytic" PA-12 k ~ 2-3; it is worth noting that this very high k value is significantly higher than those usually observed in describing the dependence of the effective viscosity on the content of low molecular mass additives on plasticization of polymers pointing to the special role of moisture interacting with the PA. Next, for hydrolytic PAs dried to the limit, or samples with very low moisture content, the viscosity (and hence the MM) rises with time; with increase in the moisture content this effect weakens and in the region ~p> 0.2% gives way to a drop in viscosity with time while the viscosity of "anionic" PA-12 decreases with time whatever the moisture content although material of this type is less sensitive to the presence of moisture. The general technological recommendation stemming from the known observations on the influence of moisture on the behaviour of a PA is quite obvious---the need to keep the moisture content of the material from the moment of completion of its synthesis to processing at a certain fixed very low level. However, the concrete patterns of the rheokinetic changes occurring in PAs of different types, the nature of their link with the features of the synthetic scheme used for obtaining them and the physics of the interaction of water with the PAs at high temperatures remain unclear. The exponential dependence of the viscosity of PCP melts on the moisture content has also been observed for PET [126] here again moisture inducing hydrolysis of the polymer [127]. Therefore, the role of moisture is identical for the different PCPs; possibly a similar picture also applies to other PCPs. The kinetics of change in the MM and the rheological properties of other PCPs has practically not been investigated. However, recently with the development of the processes of reaction shaping, special interest has been aroused by the new method devised by General Electric (U.S.A.) of obtaining high molecular mass PC starting from cyclic oligomeric products [128]. With the aid of this method and using a catalyst of the amine type (triethylamine) it was possible to obtain PC samples with M ~- 4 x 105 which surpasses by an order the MM of typical commercial PC grades. With the proper choice of catalyst the opening of the cycle with sharp rise in the MM (observed by the rheokinetic method from the sharp growth in viscosity) can be achieved directly in the course of processing PC at 280°C in 5 min which actually meets the technological requirements [129]. The idea of using cyclic compounds for the fundamental modification of the properties of the end product is not confined to PC. Functional macrocyclic polysulphones have been obtained in the same way starting from aminomethylpolysulphone [130].

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Possibly this approach is of general importance for PCPs and the sharp rise in their MM, attainable with much difficulty for PCPs, undoubtedly improves their use characteristics. The situation here is similar to that observed for polymerization plastics for example, on passing from the usual PE grades to ultrahigh molecular mass PE. But in the case of PCPs the kinetics of change in the rheological properties with rise in the MM gives grounds for the successful realization of the promising technology of "chemical" reaction shaping.

Exchange reactions. The fact that interchain exchange reactions take place on processing PCPs is quite obvious. But specific investigations into this problem are confined to individual qualitative observations. Here, two cases are to be distinguished---mixing of two batches of one polymer with different mean MM values and contact of the melts of two heterogeneous polymers also leading to interchain exchange. To describe the ongoing MMD resulting from the interaction of two polymeric samples with different MMs it is necessary to allow at least for the reactions of complete condensation occurring over the end groups and the interchain exchange reactions. This problem to our knowledge has not been considered at a quantitative level although there is a fundamental monograph [131] dealing especially with different aspects of interchain exchange in polymers where numerous and diverse situations associated with this problem are examined. Here, one may try to formulate the usual approach to the experimental evaluation of the relation between the rate constants of complete polycondensation k~: and interchain exchange kM. Let two samples of the same polymer with fundamentally different MM values and known MMDs be mixed. Let us follow the change in the content of some fractions with degrees of polymerization Ni. For any of them one may write a kinetic equation of the form

d[N,]

d-----~-

kKXl[Ni]-kMX2[Ni](Ni- 1)"[-kKX3X4-I-kMXsX6,

where X1 is the number of chains of any type in the mixture; X2 is the number of bonds with which exchange of the chains may occur with N~; X3 and X4 are the number of chains on interaction between which a polymer forms with N/; Xs and X6 are the number of chains the interchain exchange between which forms a polymer with N~. Such equations for a certain set Ni form a redundant system. Next, it is necessary to study the functions Ni(t) which it is, in principle, easy to do, for example, by the GPC method. The result is a typical back kinetic problem quite similar to those solved, for example, for the synthesis of an oligomide [132] or polysulphone [133] with two unknown constants. Minimizing the divergence between the experimental and calculated (for different pairs of values kK and kM) one may find the most probable values of the kinetic constants and, thereby, evaluate the relative role of interchain exchange. The same approach may also be applied to the quantitative description of interchain exchange of heterogeneous polymers although here additional difficulties arise associated with the analytical determination of the content of heterogeneous-unit exchange products. Nevertheless, direct experimental evidence of the reality and notable role of interchain exchange in PCPs exists apparently described for the first time in reference [134]. Numerous studies of this trend are reviewed in the already mentioned monograph [131] and recently for the investigation of the products of interchain exchange of heterogeneous polymers and the kinetics of their accumulation (but without quantitative determination of the kinetic constants) the calorimetric method was successfully employed for the systems PA-polybutylene terephthalate [135] and PA-6--PCA [136]. Here, it is particularly interesting to emphasize the general scheme of this process. As shown in

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reference [135] at first block copolymers form and then the blocks cleave and in the end a statistical copolymer is formed. This means that in real technological conditions products may be obtained with different molecular structures and, accordingly, variable properties. Intrachain reactions. The most important of the intrachain reactions in PCPs must be considered to be cyclization of the polyamido acids which is determined by the greatest spread of these polymers in the class of heat resistant polymers. Therefore, the appearance of a quite large number of publications concerned with the study of the kinetics of cyclization is not surprising. A review of the relevant publications is contained in the monograph [137, pp, 65-81]. For the present discussion it is important to stress the established drop in the reaction rate constant with increase in the extent of conversion and/or the macroscopic viscosity of the material, this also being characteristic of other polyheteroarylenes, for example, polyhydrazide, i.e. this effect is of general significance. Hence, the standard technological recommendation for the use of raised temperatures for obtaining the final product. At the same time a more general problem would be optimization of the temperature regime of cyclization since at extremely high temperatures different, including unwanted, reactions develop. The task of determining the kinetics of the intrachain reaction remains topical also in relation to catalytic cyclization with the existence here of a fairly wide field for research since diverse compositions of the reaction systems are possible (for the case of conducting reactions in solution). Another open question is the establishment of general patterns which would allow one to approach the choice of the composition of the reactants on firm grounds.

RHEOLOGICAL PROPERTIES The rheological of PCPs do not, in principle, differ from those of any polymers [138]. The pecularities of the rheological properties of a PCP are determined by the following factors: their comparatively low chemical stability, fairly high energy of interaction with the ingredients introduced into the melt, a not very high mean MM of most commercial PCP grades and a practically identical MMD. The first of these factors was already discussed above. The second, i.e. the character of the interaction of the PCP with different components of the composition, was also touched upon in connection with the behaviour of the PCP-water system. This problem is a particular case of the more general task of plasticization of polymers. Plasticization is, in effect, the most important procedure of regulating both the use and technological, in particular, rheological, properties of polymers which is well known for example, for PVC. But for a PCP this path appears rather to be the exception although it is possible [139]. The reason is that the use of ionic compounds, for example, water, is realistic as plasticizers for PCPs with an extremely strong influence being exerted by such additives as already noted for the PA-water system. This makes it difficult to reproduce technologically the optimum formulations and excludes the mass use of plasticization as an industrial means of regulating the rheological properties of PCP melts. A kind of exception here still remains, plasticization of PA-6 by its now oligomeric products: it is known that the removal of the oligomers (low molecular mass fractions) worsens the technological properties of PA-6. All this does not deny the possibility of using plasticization for modifying the end properties of PCPs but the scale of employing this method of regulating the rheological properties is very modest. More important is another quite traditional procedure of regulating the rheological properties---

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variation in chain length. This question relates to the problem of the influence of the MM and MMD on the rheological properties of PCP melts. Because of the reduced MM the viscosity of PCP melts is, as a rule, lower than for thermoplastic polymers and even more so elastomers. The effect of the viscosity anomaly (non-Newtonian behaviour of the melt) for a PCP is also much more weakly marked than for polymers of other classes. These conclusions hold for traditional mass PCPs of the type PA, PC, PET, etc. but do not apply, on the one hand, to rigid chain polymers of the polyheteroarylene type and, on the other, to PCPs (of the aromatic PA type) forming a LC phase. In addition, because of the not very wide and essentially identical MMD, the elasticity of PCP melts is low and is practically identically marked in different materials. To consider a sufficiently wide MM range the dependence of viscosity on the MM for a PCP is described by the same equations as for any other polymers, i.e. in the high molecular mass region •/ ~ M 35. But in very many cases of practical importance the PCP series considered lies in a transitional region--from low molecular mass samples where 7/- M, to a high molecular mass where in effect 7 / - M 3"5. Therefore, not infrequently for a comparatively narrow MM range of practical interest, the experimental data are satisfactorily described by the empirical relation 7/~ M a where 1 . 0 < a < 3 . 5 . A clearcut link exists (though different in form for different PCPs) between the behaviour of the solution diluted to the limit, i.e. values of specific or intrinsic viscosity, and the viscosity of the melt as has been demonstrated for different PAs [140]. This fact reflects the absence of a significant influence of the MMD of commercial PCPs on the patterns of the change in their viscosity which is readily explained by the narrow range of variation in the MMD observed in many cases for a PCP. The endeavour to raise the MM and hence the viscosity of the PCP is inherently contradictory. On the one hand, this endeavour corresponds to the task of improving the use of properties of PCP products and, on the other, growth of viscosity complicates the technological process of shaping the products and makes the equipment more expensive since it requires the use of raised pressures and temperatures. This problem is particularly important in relation to the development of a new generation of constructional (engineering) plastics--reinforced plastics with a thermoplastic binder. Unlike the RSOs traditionally used for this purpose with a comparatively low initial viscosity, that of PCP melts, especially if one takes the high molecular mass analogues, is still higher. It creates certain technological difficulties: it impedes uniform impregnation and requires high pressures. A possible and promising way of overcoming these difficulties is linked with the peculiarities of the rheological properties of PCPs---with the reality of changing their MM in the course of the technological process. Above we discussed the means of obtaining high molecular mass (and very highly viscous) PCA by using, at the initial stage of the process, a comparatively low viscous macrocyclic oligomer followed by opening of the ring. As well as traditional and well understood means of regulating the rheological properties of PCPs by varying the MM, definite prospects are held out by change in the chain structure both by copolymerization (in particular, by the above discussed means of interchain exchange) and by introducing branches into the linear chain. It is known that long chain branching promotes fall in viscosity which is also true of a PCP. However, although the effects themselves, due to copolymerization and the introduction of long chain branching into the linear chain are unquestionable at present only their qualitative illustrations are known and this direction, as a whole, is weakly developed: in particular, there are no generalizing links (if only empirical) between the chain geometry (extent and type of branches, the content and size of the intramolecular macrocycles) and the rheological properties of PCP melts. Particularly important is the possibility of regulating the rheological properties of melts through

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copolymerization (or in a more general sense by creating unit heterogeneity of the backbone) for rigid chain polymers. Thus, PCPs of the polyamidoimide type have become fairly customary permitting radical improvement in the technological properties of thermally stable polymers (without appreciable loss in their use characteristics) and allowing one to move towards the use for their processing of the modem highly effective technology of injection moulding. However, the possibilities of regulating the chain structure for achieving particular goals are not confined to this. As well as the case of copolymerization of amido-forming compounds classical and long used in industry, the recent period has seen the appearance of such new materials as polyimidosulphonamides [141], multiblock PA copolymers with polyoxymethylene [142], polysulphones with pendant side functional groups [143] or containing thiophene groups in the backbone [144], mixtures of maleimide with PA with heat stability to 280°C [145], block copolymers of polyarylates [146], block copolymers of polyetherether ketones with PDMS [147], polyimides based on new monomers [148], polyarylether-b/s-sulphones [149], polyketones [150] and many others. Also of future interest are PCPs obtained from modified monomers, in particular, fluorinecontaining aromatic PCPs [151], polyethersulphones [152] and polyarylates [153]. Naturally such modification of the chemical structure of the backbone influences not only the use but also the rheological and technological properties of the material.

FEATURES OF THE TECHNOLOGY OF PROCESSING OF PCPs

The features of the technology of the processing of PCPs are predetermined by the specifics of their behaviour at high temperatures and the pecularities of the rheological properties. Thus, the comparatively low chemical stability of PCPs determines the need for very stringent requirements for maintaining an optimum technological regime, narrow permissible ranges of the content of impurities (moisture), etc. Naturally, the permissible boundaries must be scientifically substantiated, i.e. must be the result of investigation of the behaviour of these materials in strictly controlled laboratory conditions. If the necessary tough requirements are observed, the main linear PCPs may be processed by traditional highly productive means on existing plants, for example, injection moulding on serial machines. However, certain limitations arise from the comparatively low viscosity and low elasticity of the melts of most PCPs. Thus, it is very difficult (if at all technologically rational) to obtain a film from traditional PCPs by the highly productive "sleeve" method since the PCP melt cannot be subjected to stretching without destruction. (It may be said that the "strength of the melt" of a PCP on stretching is low [154].) The specifics of the technological properties of a PCP also has, however, a reverse side. The instability of PCPs allows them or the monomers (oligomers) of a PCP to be actively utilized for undertaking a variety of processes of "chemical" shaping when the stages of the formation of the polymer and moulding of the product are combined. In fact, in the recent period different variants of carrying out the processes relating to technologies of this type--from slow (of the order of one hour) polycondensation in continuous machines [155], for example, the double worm extruder of the Werner-Pfleiderer type, to the comparatively fast (of the order 10 min) process of "monomeric" moulding (on anionic polymerization of lactams) right up to the very fast reaction injection moulding (RIM process), lasting <1 min, have become increasingly popular. Fundamentally new constructive schemes of designing rapidly developing processes of reaction moulding have also been proposed [156]. The introduction into the reaction mixture of additives and reinforcing elements of different types and reactive groups into the

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molecule is proposed as a promising technological variant in any engineering design of the process. Their interaction with the filler or intermolecular contacts are capable, within very wide limits, of changing the properties of the final product giving the technology an unprecedented flexibility. All these possibilities are a feature of the technological properties of a PCP determining the specifics of its processing. The future importance of this field is such that according to some estimations reaction moulding may be regarded as the "beginning of a new era in the production of plastics" [157]. Among the typical reactive polymeric systems (which are often and quite rightly called "alloys") already finding to a varying degree commercial use are the bicomponent mixtures PA-carboxylated SREP, PA-polyphenylene oxide and PC-polybutylene terephthalate or PETP. To these mixtures are added, in small amounts, b/s-maleimide to run the reactions directly in the extruder [158]. This class of compounds includes copolymers containing cyclic anhydride groups capable of reacting with the hydroxyl groups present, for example, at the ends of the oligomeric chains [159]. Although many publications are known dealing with this theme, it is curious that most of the new results in this field are described in promotional materials and patents. Evidently in this field there is now active accumulation of empirical material which will inevitably raise the need for systematization, validation and optimization of the technological processes. This calls for intense scientific research. For the validated choice of the regime and means of processing a PCP, it is necessary to study the basic characteristics of the process--its chemical kinetics, quantitative description of the rheokinetics and the rate of crystallization of the product obtained and establish the correspondence between the composition, properties and quality of the end product. These tasks taken as a whole go to make up the problem of the mathematical modelling of the basic technology of PCP processing which is at present solved only in relation to some traditional PCPs, primarily PA [160], and must on each occasion be considered anew (on the basis of the known and partially outlined above general principles) to obtain quantitative information on the behaviour of particular systems. The technological features of PCPs at the stage of processing include the very wide possibilities of moulding mixtures based on heterogeneous PCPs. This is a comparatively new scientific and technical line allowing one to obtain and introduce into industry a number of highly valuable constructional polymeric materials. Of course, the problem of optimizing the structure, composition and properties of multicomponent polymeric systems is a huge independent field of research meriting separate consideration. However, it is important to emphasize that the development of this field is essentially based on PCPs. It is possible that this is linked with their already repeatedly noted lability and the possibility of reactions of interchain exchange which might stabilize a multicompnent system, keeping it from total breakdown into phases and thereby promoting the achievement of optimum use properties of the material. The recent period has seen the very active development of the so-called "macromolecular" technology of obtaining mixtures from thermodynamically incompatible polymers, in particular, from mixtures of a PCP (for example, PA and PC) with ABS or polyphenylene oxide by introducing into the composition "compatibles"--substances capable of chemical or physical interaction with both components of the pair and of thereby promoting the creation of a stable technical material [161,162]. A few words on the specifics of processing and the technological properties of a PCP with raised chain rigidity which either do not pass at all into the melt state, or possess extremely high viscosity and may exist in the molten state in a very narrow temperature range for a limited time. The general principles of processing such PCPs are quite well known and the recent period has here not seen any fundamental changes although close attention continues to be paid to improving the technological

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properties of these materials, in particular, by copolymerization, for example, passage from a polyimide to a polyetherimide or polyamidimide [163]. Only one aspect of the problem to which comparatively little attention is paid in practice deserves special mention. This is the choice of the solvent on moulding products from solutions of polymers of this type. Some time ago it was shown [164, 165] and later confirmed in a series of examples [166, 167] that the behaviour and, in particular, the long term properties of the final material depend very closely on the nature of the solvent used. Since new thermally stable materials are appearing all the time moulded from solution, it is important to bear in mind that the results are by no means immaterial to the nature of the solvent used even after its complete removal so that the choice of the solvent optimal for each of them plays a role in achieving the best properties of the product to be moulded.

Translated by A. CRozv

REFERENCES 1. M. I. SILING, Polikondensatsiya. Fiziko-khimicheskiye osnovy i matematicheskoye modelirovaniye (Polycondensation. Physicochemical Bases and Mathematical Modelling) 256 pp. Moscow, 1988. 2. V. V. KAFAROV, V. L. PEROV and D. A. BOBROV, Itogi nauki i tekhniki. Protsessy i apparaty khimicheskoi tekhnolgii (Processes and Apparatus of Chemical Technology) Vol. 11, p. 3. Moscow, 1983. 3. Chem. Plants + Process, Vol. 21, p. 4. March, 1988. 4. V. D. MOISEYEV, Yu. V. VINOKUROV, T. I. PEREPELKOVA, A. M. LIBYENZON and Ye. Ye. YAKOPSON, Hast. massy No. 4, 3, 1989. 5. H. VOIGT, Intern. Inst. Applied Systems, Analysis RM-78-60. November, 1978. 6. W. F. KENNEY, Chem. Engng. Prog. 85, 57, 1989. 7. V. S. STEPANOV, Khimicheskaya energiya i eksergiya veshchestv. (Chemical Energy and Exergy of Substances), 263 pp. Novosibirsk, 1990. 8. J. SZARGNT and D. R. MORRIS, Bull. Pol. Acad. Sci. Techn. Sci. 33: 293, 1985. 9. D. BONVIN and U. SANER, Comput. Chem. Engng. 12: 371, 1988. 10. A. Ya. MALKIN, Usp. khim. 54: 509, 1985. 11. CHANG DAE HAN and DAI-SO LEE, J. Appl. Polymer Sci. 33: 2859, 1987. 12. H.-U. MORITZ, Proc. III Berlin Intern. Workshop on Polymer "Reaction Engineering", p. 248. Berlin, 1989. 13. I. PRIGOGINE, Ot sushchestvuyushchego k voznikayushchemu (From Being to Becoming) 314 pp. Moscow, 1985. 14. 1. PRIGODINE and I. STENGERS, Poryadok iz khaosa (Order out of Chaos) 432 pp. Moscow, 1986. 15. Kolebaniya i byegushchiye volny v khimicheskikh sistemakh (Vibrations and Running Waves in Chemical Systems) (Edited by R. Field and M. Burger) 720 pp. Moscow, 1988. 16. A. D. SCHMIDT and W. H. RAY, Chem. Engng. Sci. 36: 1401, 1981. 17. B. V. OZERKOVSKII and N. N. DREMOVA, Dokl. Akad. Nauk SSSR 273: 147, 1983. 18. V. P. ROSHCHUPKIN and L. I. MAKHONINA, Tez. dokl. I Vsesoyuz. simpoz. IX) makroskopicheskoi kinetike i khimicheskoi gazodinamike (Summaries of Reports to First All-Union Symposium on Macroscopic Kinetics and Chemical Gas Dynamics) Vol. II, p. 73. Chernogolovka, 1984. 19. V. A. VOL'PERT, I. N. MEGRABOVA, S. P. DAVTYAN and V. P. BEGISHEV, Fizika goreniya i vzryva 21: 69, 1985. 20. V. P. PSHENITSYNA, N. N. MOLOTKOVA and A. N. SHABADASH, Vysokomol. soyed. B28: 403, 1986 (not translated in Polymer Sci. U.S.S.R.). 21. V. V. KUZNETSOV, O. S. MATYUIKHINA, I. M. GURMAN and M. I. SILING, Ibid. B31: 168, 1989 (not translated in Polymer Sci. U.S.S.R.). 22. A. UPPAL, W. H. RAY and A. B. POORE, Chem. Engng. Sci. 29: 967, 1974. 23. R. JAISINGHANI and W. H. RAY, Ibid. 32: 811, 1977. 24. J. W. HAMER, T. A. AKRAMOV and W. H. RAY, Ibid. 36: 1897, 1981. 25. V. V. KAFAROV, A. I. CHEREPANOV, A. G. SHUMIKHIN and S. V. SHCHERBAKOVA, Dokl. Akad. Nauk SSSR 297: 144, 1987.

Present-day and future technologies of P C P s - - r e v i e w

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26. Dzh. A. BAIZENBYERG and D. Kh. SEBASTIAN, Nizhenernye problemy sinteza polimerov (Engineering Problems in Polymer Synthesis) Chap. 4. Moscow, 1988. 27. Polietilen vysokogo davleniya (High Pressure Polyethylene) Chaps 5 and 6. Leningrad, 1988. 28. V. V. KUZNETSOV, O. S. MATYUKHINA and M. I. SILING, Vysokomol. soyed. A33: 316, 1991 (translated in Polymer Sci. A33: 2, 242, 1991). 29. AI. AI. BYERLIN, S. A. VOL'FSON and N. S. YENIKOLOPYAN, Kinetika polimerizatsionnykh protsessov (Kinetics of Polymerization Processes) Chap. II. Moscow, 1978. 30. H. SAVADA, Termodinamika polimerizatsii (Thermodynamics of Polymerization) p. 294. Moscow, 1979. 31. L. N. MIZEROVSKII, A. K. KUZNETSOV, Yu. M. BAZAROV and A. N. BYKOV, Vysokomol. soyed. A24: 1174, 1982 (translated in Polymer Sci. U.S.S.R. A24: 6, 1319, 1982). 32. A. K. KUZNETSOV, Dissert. Cand. Chem. Sci. (in Russian) 157 pp. MTI im A. N. Kosygina, Moscow, 1984. 33. I. Ya. SLONIM, S. G. ALEKSEYEVA, Ya. G. URMAN, B. M. ARSHAVA, V. Ya. AKSEL'ROD and L. N. SMIRNOVA, Vysokomol. soyed. A20: 1477, 1978 (translated in Polymer Sci. U.S.S.R. A20: 7, 1661, 1978). 34. R. S. BARSHTEIN and I. A. SOROKINA, Kataliticheskaya polikondensatsiya (Catalytic Polycondensation) 288 pp. Moscow, 1988. 35. T. N. LARICHEVA, I. G. RASKINA and M. I. SILING, Katalizatory sinteza polialkilentereftalatov (Catalysts of the Synthesis of Polyalkylene Terephthalates). Series: Proizvodstvo i pererabotka plastmass i sinteticheskikh stool (Production and Processing of Plastics and Synthetic Resins) 67 pp. Moscow, 1988. 36. B. V. PETUKHOV, Poliefirnye volokna (Polyester Fibres) 272 pp. Moscow 1976. 37. N. A. LAVROV, Plast. massy No. 11, 12, 1989. 38. V. G. SHIBALOVICH, K. V. BYELOGORODSKAYA and V. G. KARKOZOV, Ibid. No. 11, 18, 1989. 39. A. A. EL'BYERT, O. V. DOROKHOVA, A. M. SINGURINDI and L. I. KRYUKOVA, Zh. prikl, khim. 61: 2063, 1988. 40. K. I. ZAMARAYEV and G. I. ZHIDOMIROV, Sb. dokl. V. Mezhdunar. simpoz, po svyazi mezhdu. gomogennym i geterogennym katalizom. (Collection of Reports to the Fifth International Symposium on the Link between Homogeneous and Heterogeneous Catalysis) Vol. I, p. 24. Novosibirsk, 1986. 41. A. Ye. SHILOV, Ibid., Vol. I, p. 186. Novosibirsk, 1986. 42. V. B. KAZANSKH, Usp. khim. 57: 1937, 1988. 43. O. N. TEMKIN and S. M. BRAILOVSKII, Tez. dokl. IV Mezhdunar. simp. po gomogennomu katalizu (Summaries of Reports Fourth International Symp. Homogeneous Catalysis) Vol. 1, p. 30. Leningrad, 1984. 44. V. M. NEKIPELOV and K. I. ZAMARAYEV, Zh. strukt, khim. 24: 133, 1983. 45. O. V. NESTEROV, V. M. NEKIPELOV, Yu. N. CHIRKOV, A. N. KITAIGORODSKII and S. G. ENTELIS, Kinetika i kataliz 21: 1238, 1980. 46. M. I. SILING, V. V. KUZNETSOV, Yu. Ye. NOSOVSKII, S. A. OSINTSEVA and A. N. KHARRASOVA, Ibid. 27: 98, 1986. 47. OGATA NAOYA, U.S. Patent 4778873, 1989. 48. I. V. KOZHEVNIKOV, Usp. khim. 56: 1417, 1987. 49. T. JAMAMURA and S. NAKATOMI, J. Catal. 37: 142, 1975. 50. F. HARTLEY, Zakreplennye metallokompleksy (Fixed Metallocomplexes) Chap. 9, Moscow, 1989. 51. V. A. KABANOV and V. I. SMETANYUK, Sb. dokl. V Mezhdunar. simpoz, po svyazi mezhdu. gomogennym i geterogennym katalizom. (Collection of Reports to the Fifth International Symposium on the Link between Homogeneous and Heterogeneous Catalysis) Vol. II, Part 1, p. 3. Novosibirsk, 1986. 52. P. A. BYERLIN, M. A. LEVINA, R. P. TIGER and S. G. ENTELIS, Vysokomol. soyed. A31: 519, 1989 (translated in Polymer Sci. U.S.S.R. A31: 3,566, 1989). 53. I. N. DOROKHOV and V. Ya. V. KAFAROV, Sistemnyi analiz protsessov khimicheskoi tekhnologii (System Analysis of Processing of Chemical Technology) 376 pp. Moscow, 1989. 54. T. V. KREITSER, S. Ye. POLOVETS, L. L. YEZHENKOVA, N. V. IVANOVA and B. S. POLONSKII, Plast. massy No. 5, 6, 1988. 55. G. K. KUCHERENKO, A. P. MOZOLEVA, A. V. MAKOTIN and M. I. SILING, Lakokrasoch. materialy i ikh primeneniye No. 6, 14, 1986. 56. Kh. Z. ZUBAYEROV, V. S. SHAMAYEV, M. I. SILING and Z. M. MESHCHERYAKOVA, Ibid. No. 4, 12, 1987. 57. M. BUBACK, J. Polymer Sci. C26: 293, 1988. 58. Ai. AI. BYERLIN, K. S. MINSKER, Yu. A. PROCHUKHAN and N. S. YENIKOLOPYAN, Vysokomol. soyed. A31: 1779, 1989 (translated in Polymer Sci. U.S.S.R. A31: 9, 1953, 1989).

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A. YA. MALKIN and M. I. StLXNO

59. I. M. VARASKAVITCH, J. L. BRASH and A. E. HAMIELEC, Polymer 28: 489, 1987. 60. V. V. KUZNETSOV and M. I. SILING, Vysokomol. soyed. B29: 263, 1987 (not translated in Polymer Sci. U.S.S.R.). 61. A. Ya. MALKIN and P. V. ZHIRKOV, Teoret. osnovy khim. tekhnolog. 20: 784, 1986. 62. P. V. ZIHRKOV, Dissert. Duct. Chem. Sci. (in Russian) 265 pp. Institute of Chemical Physics. U.S.S.R. Academy of Sciences, Moscow, 1987. 63. M. H. ULRICH, Chem. and Engng. Technol. 12: 71, 1989. 64. A. Ya. MALKIN and S. G. KULICEIIKIiIN, Rheokinetics FRG, 1991. 65. R. G. GRISKEY and C. A. PATEL, J. Appl. Polymer Sci. 38: 351, 1989. 66. M. L TSAPOVETSKII and L. A. LAIUS, Vysokomol. soyed. A24: 979, 1982 (translated in Polymer Sci. U.S.S.R. A24: 5, 1103, 1982). 67. L. N. MIZEROVSKII, A. K. KUZNETSOV, Yu. M. BAZAROV and A. N. BYKOV, Ibid. A25: 1056, 1983 (translated in Polymer Sci. U.S.S.R. A25: 5, 1222, 1983). 68. M. I. SILING, Polikondensatsiya. Fiziko-khimicheskiye osnovy i matematich-eskoye modelirovaniye (Polycondensation. Physicochemical Bases and Mathematical Modelling) p. 126. Moscow, 1988. 69. C. D. PAPASPYRIDES and E. M. KAMPOURIS, Polymer 27: 1433, 1986. 70. A. E. GOLLAND, O. S. MATYUKHINA, M. I. SILING, V. V. GUR'YANOVA, T. N. PRUDSKOVA, A. V. PAVLOV and A. Ya. MAlL,KIN, "Fez. dokl. I Vsesoyuz. simp. po makrokinetike i khim. gazodinanike (Summaries of Reports to First All-Union Symposium on Macrokinetics and Chemical Gas Dynamics) Vol. 1, Pt. 1, p. 118. Alma Ata, 1984. 71. A. E. GOLLAND, O. S. MATYUKHINA, M. I. SILING, N. I. GEL'PERIN, L. A. KARPENKO and G. !. FAIDEL', Vysokomol. soyed. 27: 897, 1985 (not translated in Polymer Sci. U.S.S.R.). 72. Yu. G. FROLOV, M. A. BOGORODSKAYA, V. KIM, O. S. MATYUKIIINA and A. E. GOLLAND, Kolloid. zh. 49: 723, 1987. 73. A. E. GOLLAND, O. S. MATYUKIHNA, O. F. ALAKAYEVA, T. N. PRUDSKOVA, M. I. SILING and V. V. GUR'YANOVA, Plast. massy No. 7, 38, 1987. 74. S. A. VOL'FSON and N. S. YENIKOLOPYAN, Raschety vysokoeffektivnykh polimerizatsionnykh protsessov (Calculations of Highly Effective Polymerization Processes) 312 pp. Moscow, 1980. 75. A. KUMAR, J. Appl. Polymer SCi. 34: 1367, 1987. 76. T. Y. XIE, A. E. HAMIELEC, P. E. WOOD and D. R. WOODS, Ibid. 34: 1749, 1987. 77. Proc. III Berlin Intern. Workshop on Polymer "Reaction Engineering". Berlin, 1989. 78. I.N. TAGANOV and V. P. PILYAVSKH, Khim. tekhnol. No. 2, 59, 1989. 79. V. N. IGNATOV, V. A. VASNEV and S. V. VINOGRADOVA, Vysokomol. soyed. A29: 899, 1987 (translated in Polymer SCi. U.S.S.R. A29: 5,993, 1987). 80. S. I. KUCIIANOV and Ye. S. POVOLOTSKAYA, Ibid. A24: 2179, 1982 (translated in Polymer Sci. U.S.S.R. A24: 10, 2499, 1982). 81. F. D. MAGALllAES and M. R. N. COSTA, Proc. III Berlin Intern. Workshop on Polymer "Reaction Engineering" p. 311. Berlin, 1989. 82. T. V. XIE, A. E. HAMIELEC, P. E. WOOD and D. R. WOODS, J. Appl. Polymer Sci. 34: 1749, 1987. 83. V. V. KUZNETSOV, Ye. S. ARTSIS, M. I. SILING, L. I. VALYSHKINA and T. F. MARYCllEVA, Plast. massy No. 9, 32, 1989. 84. M. R. N. COSTA and J. VILLERMAUX, Industr. and Engng. Chem. Res. 28: 711, 1989. 85. A. I. ROZENFEL'D and G. Ye. KANEVETS, Khim. tekhnologiya No. 6, 56, 1987. 86. S. MOCEIIZUKI and N. ITOII, Chem. Engng. SCi. 33: 1401, 1978. 87. Ye. B. BRUN and S. I. KUCHANOV, Teoret. osnovy khim. tekhnol. 14: 214, 1980. 88. M. R. JUBA and J. W. tlAMER, Proc. Third Intern. Conf. "Chem. Process Contr." p. 139. Asilomar, 1986. 89. E. D. GILLES, Ibid. pp. 689, 738, 1986. 90. ldem, Selected Paper, Tenth Trienn. World Congr. Int. Fed. Autom. Contr. "Autom. contr." Vol. 2, p. 239. Oxford, 1988. 91. G. KREITNER and H. SCItULER, Chem.-Ing.-Techn. 60: 613, 1988. 92. H. RAY, Proc. IlI Berlin Intern. Workshop on Polymer "Reaction Engineering", p. 105, 1989. 93. V. TUFANO, J. Hazardous Mater. 19: 225, 1988. 94. A. E. SOFIYEV and A. M. TRAKHTENVERG, Teoret. osnovy khim. tekhnol. 23: 644, 1989. 95. R. BACHMANN and M. FELDE, Automatisiernngstechn. Prax. 30: 581, 1988. 96. Iskusstvennyi intellekt: primeneniye v khimii (Artificial Intelligence: Applications in Chemistry) (Edited by T. Pierce and B. Hohne) 430 pp. Moscow, 1988.

Present-day and future technologies of PCPs--review

2159

97. Iskusstvennyi intellekt: spravochnik. (Artificial Intelligence: Reference Work) Book 1, (Edited by E. V. Popov) 464 pp., Book 2 (Edited by D. A. Pospelov) 304 pp. Moscow, 1990. 98. D. WATERMAN, Rukovodstvo po ekspertnym sistemam (Guide to Expert Systems) 388 pp. Moscow, 1989. 99. R. LEVIN, D. DRANG and B. EDELSON, Prakticheskoye vvedeniye v tekhnologiyu iskusstvennogo intellekta i ekspertnykh sistem s illyustratsiyami na byeisike (Practical Introduction to the Technology of Artificial Intelligence and Expert Systems with Illustrations in BASIC) 239 pp. Moscow, 1991. 100. Ekspertnye sistemy dlya personal'nykh komp'yuterov: metody sredstv, realizatsii (Expert Systems for Personal Computers: Methods, Means and Realizations) 197 pp. Minsk, 1990. 101. Chemometrics and Intel. Lab. Systems 5: 8, 1988. 102. R. L. MOORE and M. A. KRAMER, Proc. Third Intern. Conf. "Chem Process Contr." p. 839. Asilomar, 1986. 103. A. N. KALMYKOV, Khim. prom-st' za rubezhom. (The Chemical Industry Abroad) No. 2, p. 48. 1989. 104. D.H. KAELBLE, Computer-Aided Design Polymers and Composites. New York, 1985. 105. C. NEDESS and J. PLOG, Kunststoffe 78: 1218, 1988. 106. C. H. LODGE, Plastics World 46: 55, 1988. 107. M. D. DALLE, B. J. KUIPERS and T. F. EDGAR, Comput. and Chem. Engng. 12: 853, 1988. 108. S. OSUGA, Obrabotka znanii (Treatment of Knowledge) 235 pp. Moscow, 1989. 109. Vzaimodeistviye nauk kak faktor ikh razvitiya (Interaction of Sciences as a Factor in their Development) (Edited by A. N. Kochergin) 287 pp. Novosibirsk, 1988. 110. Tez. dokl. Vsesoyuz. konf. "Fundamental'nye problemy sovremennoi nauki o polimerakh" (Summaries of Reports to the All-Union Conference "Fundamental Problems of Current Polymer Science") Part 2, p. 3. Leningrad, 1990. 111. G. A. KARDASHEV, Fizicheskiye metody intensifikatsii protsessov khimicheskoi tekhnologii (Physical Methods for Intensifying the Processes of Chemical Technology) 208 pp. Moscow, 1990. 112. A. K. PIKAYEV, Sovremennaya radiatsionnaya khimiya. Tverdoye telo i polimery. Prikladnye aspekty (Modem Radiation Chemistry. The Solid Body and Polymers. Applied Aspects) 448 pp. Moscow, 1987. 113. V. S. IVANOV, Radiatsonnaya khimiya polimerov (Radiation Polymer Chemistry) 320 pp. Leningrad, 1988. 114. G. S. SHAPOVAL and T. E. LIPATOVA, Elektrokhimicheskoye initsiirovaniye polimerizatsii (Electrochemical Initiation of Polymerization) 235 pp. Kiev, 1977. 115. B. RAMBY and J. RABECK, Fotodestruktsiya, fotookisleniye, fotoostabilizatsiya polimerov (Photodegradation, Photo-Oxidation and Photostabilization of Polymers) 675 pp. Moscow, 1978. 116. G. A. BYSTROV, V. M. GAL'PERIN and B. P. TITOV, Obezvrezhivaniye i utilizatsiya Otkhodov v proizvodstve plastmass (Disposal and Utilization of Plastics Production Wastes) 264 pp. Leningrad, 1982. 117. J. RfJBNER, Spectrum 20: 25, 1989. 118. C. SELVI and M. BABOULENE, Chem. Technol. and Biotechnol. B25: 282, 1985. 119. S. MATSUMURA and J. TAKAHASHI, Makromolekul. Chem. Rapid Communs. 7: 369, 1986. 120. KUNIOKA MASAO, Kagaku to koge 62: 761, 1988. 121. R. D. KATSARAVA, Usp. khim. 58: 1549, 1989. 122. M. L. LYUBAREVA and R. S. BARSHTEIN, Plast. massy No. 7, 30, 1987. 123. Upravleniye informatsiya, intellekt (Control, Information, Intelligence) (Edited by A. M. Byerg) 383 pp. Moscow, 1976. 124. V. I. DMITRIYEV, Prikladnaya teoriya informatsii (Applied Information Theory) 320 pp. Moscow, 1989. 125. A. Ya. MALKIN and B. M. RENDAR, Plast. massy No. 5, 43, 1977. 126. M. B. DUBINSKH, B. M. LAKTIONOV, O. Yu. SABSAI, A. I. MZHEL'SKII and M. L. FRIDMAN, Ibid. No. 3, 20, 1986. 127. M. B. DUBINSKII, Dissert. Cand. Chem. Sci. (in Russian). Moscow Lomonosov Institute of Fine Chemical Technology, Moscow, 1991. 128. D. J. BRUNELL, T. L. EVANS, T. G. SHANNON, E. P. BODEN, K. R. STEWART, L. P. FONTANA and B. K. BONAUTJO, Amer. Chem. Soc. Polymer Preprints 30: 569, 1989. 129. K. R. STEWART, Ibid. 30: 574, 1989. 130. N. KAHANA, R. ARAD-YELLIN, A. DECHE and A. WARSHAWSKY, J. Polymer Sci. Polymer Chem. 28: 3303, 1990. 131. B. A. ROZENBYERG, V. I. IRZHAK and N. S. YENIKOLOPYAN, Mezhtsepnoi obmen v polimerakh (Interchain Exchange in Polymers) 238 pp. Moscow, 1975. 132. A. Ye. TEISHEV, O. M. KARAN'YAN, Z. S. ANDRIANOVA, M. V. CHERKASOV, O. A. AGAPOV,

2160

133.

134. 135.

136. 137. 138. 139. 140. 141. 142. 143. 144. 145. 146. 147. 148. 149. 150. 151. 152. 153. 154. 155. 156. 157. 158. 159. 160. 161. 162. 163. 164. 165.

166. 167.

A. YA. MALKIN and M. I. SILING

V. V. GUR'YANOVA, A. V. PAVLOV and A. Ya. MALKIN, Vysokomol. soyed. A30:578 1988 (translated in Polymer Sci. U.S.S.R. A30: 3,571, 1988). A. Kh. BULAI, V. N. KLUCHNIKOV, Ya. G. URMAN, I. Ya. SLONIM, L. M. BOLOTINA, V. A. KOZHINA, M. M. GOLDER, S. G. KULICHIKHIN, V. P. BEGHISHEV and A. Ya. MALKIN, Polymer 28: 1349, 1987. V. V. KORZHAK, T. M. FRUNZE and LUI.NAN, Vysokomol. soyed. 2: 984, 1960 (not translated in Polymer Sci. U.S.S.R.). Ye. B. KONYUKHOVA, Yu. K. GODOVSKII, Yu. M. MALINSKII, L. V. VOLODINA, F. M. MEDVEDEVA and T. G. FILINA, Ibid. A26: 642, 1984 (translated in Polymer Sci. U.S.S.R. A26: 3,716, 1984). M. CORTAZAR, J. EGUIAZABAL and J. J. TRAIN, Brit. Polymer J. 21: 1989, 1989. M. L BYESSONOV, M. M. KOTON, V. V. KUDRYAVTSEV and L. A. LAIUS, Poliimidy--klass termostoikikh polimerov (Polyimides---A Class of Thermally Stable Polymers) 328 pp. Leningrad, 1983. G. A. VINOGRADOV and A. Ya. MALKIN, Reologiya polimerov (Polymer Rheology). Moscow, 1977. A. Ya. MALl(IN, A. A. DUKOR, V. I. UCHASTKIN and N. Ya. YAKOVLEV, Vysokomol. soyed. A22: 910, 1980 (translated in Polymer Sci. U.S.S.R. A22: 4, 1007, 1980). A. Ya. MALKIN, S. G. KULICHIKHIN and A. V. PAVLOV, Poliamidnye konstruktsionnye materialy (Polyamide Constructional Materials) p. 87. Moscow, 1986. J. M. ADDUCI and E. J. KUSKOFF, J. Appl. Polymer Sci. 41: 129, 1990. T. OTSUKI, M. A. TAKIMOTO and Y. IMAI, Ibid. 40: 1433, 1990. M. BISWAS and P. MITRA, Amer. Chem. Soc. Polymer Preprints No. 2, 488, 1990. K.-J. CHOI, J. C. JUNG, M. N. YI and B. W. LEE, J. Polymer Sci. Polymer Chem. 28: 3179, 1990. Materie Plastiche et Elastomeri No. 11,550, 1989. Y. SAEGUSA, M. KURIKI, A. KAWAI and S. NAKAMURA, J. Polymer Sci. Polymer Chem. 28: 3327, 1990. G. C. COP,FIELD, G. W. WHEATLEY and D. G. PARKER, Ibid. 28: 2821, 1990. S. A. NYE, Ibid. 28: 2633, 1990. P. B. BALANDA, D. CUMMINGS and D. K. MOHANTY, Amer. Chem. Soc. Polymer Preprints No. 2, 671, 1990. A. BHATNAGAR, M. ROBARGE and D. K. BOHANTY, Ibid. No. 2,673, 1990. T.-Y. TSENG, N.-J. CHI and Y.-D. LEE, J. Appl. Polymer Sci. 41: 1651, 1990. A. E. FEIRING, E. R. WONCHOBA and S. D. ARTHUR, J. Polymer Sci. Polymer Chem. 28: 2809, 1990. H. ANDOH and T. TERAMOTO, Amer. Chem. Soc. Polymer Preprints No. 2, 677, 1990. M. L. FREIDMAN and V. D. SEVRUK, Adv. Polymer Sci. 93: 1, 1990. G. MENGES, U. BERGHAUS, M. KULWA and G. SPENSER, Kunststoffe 79: 1344, 1989. B.J. BRISTOE, M. B. KHAN and S. M. RICHARDSON, Polymer Engng. Sci. 30: 162-167, 1990. Modern Plastics Intern. No. 8, 42, 1985. Kobunsi rombunsyu 47: 331, 1990. M. LAMBLA, R.-Z. YU and S. LOREK, Polymer Mat.: Sci. and Engng. Third Chemical Congress N. Amer. Vol. 58, p. 882, Toronto-Washington (D.C.), 1988. A. Ya. MALKIN, Polyamide-Based Plastics. Pt. II. Boca Raton, Florida, U.S.A., 1991. Y. YAMASHITA, Amer. Chem. Soc. Polymer Preprints No. 2, 452, 1990. Purasutikkusu 41: 90, 1990. Ibid. 39: 45, 50, 1990. M. K. KURBANALIYEV, A. A. TAGER and V. Ye. DREVAL', Mekhanika polimerov No. 2, 358, 1968. G. A. SLONIMSKII, V. V. KORSHAK, S. V. VINOGRADOVA, A. I. KITAIGORODSKII, A. A. ASKADSKII, S. I. SALAZKHIN and Ye. M. BYELAYETSEVA, Vysokomol. soyed. Ag: 402, 1967 (translated in Polymer Sci. U.S.S.R. A9: 2,453, 1967). M. K. KURBANALIYEV, I. K. DUSTOV and A. Ya. MALKING, Ibid. A24: 2291, 1982 (translated in Polymer Sci. U.S.S.R. A24: 11, 2626, 1982). A. Ya. MALKIN, M. K. KURBANALIYEV and V. P. BYEGISHEV, Polymer Process. Engng 1: 93, 1983.