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The Kargin Lectures
Polymer Science U.S.S.R. Vol. 28, No. 7, pp. 1740-1743, 1986 Printed in Poland
0032-3950/86 $10.00+ .00 © 1987 Pergamon Journals
THE KARGIN LECTURES* P. V. KOZLOV On "rm8 23 January 1986 the large chemical auditorium in memory of N. D. Zelinskii was the setting in which the XVI Kargin Lectures took place under the auspices of the Chemistry Faculty at the Lomonosov State University Moscow. The lecture progra~ included four independent reports dealing with various aspects of polymer science. These reports highlighted not only the basic and pioneering character of the research, but also the usefulness of the results obtained and their value in several branches of the Soviet economy. Opening these Lectures the president of the orgkomitet, P. V. Kozlov, remarked that their organization had by now acquired its own systematic character and undoubtedly reflected successful progress in Soviet polymer science, to whose organization and development such a great contribution had been made by Valentin AIekseyevich Kargin. P. V. Kozlov recalled that in the case of all the preceding fifteen events (from 1971 to 1985) there had been 145 lectures (of which 28 were outstandingly memorable) reflecting the creative work of V. A. Kargin relating to various branches of polymer science and their further development. This was indeed a fitting memorial and tribute to the very eminent Soviet scientist. As regards the fifteen previous Kargin Lectures P. V. Kozlov referred to the seventh in honour of the 70th Anniversary of the birthday of V. A. Kargin, which took place in 1977. On this occasion 21 papers were read, and there was also a report on the creative work of V. A. Kargin and two speeches in which he was specially remembered. The next speaker after P. V. Kozlov was V. A. Kabanov, whose report entitled "The polymeric effects and biological activity of functional synthetic macromolecules" dealt with features of chemical reactions involving the participation of synthetic polyelectrolytes in aqueous solutions, and examined these in relation to the physiological activity of polyelectrolytes, with special reference to their immunostimul'ating action. Given the presence of charged functional groups in polyelectrolyte macromolecules it folliows that these may be linked to various oppositely charged functional groups forming part of natural polymers or included in cage membranes. The polymeric nature of a polyelectrolyte determnes the cooperative character of linking with biopolymers and cage membranes, thereby ensuring o n the one hand good bond strength, and on the other hand opening the way towards intermacromolecular reactions of exchange and substitution discovered in the high polymer department at the Moscow State University. It is such substitution reactions, that underlie the fact that macromolecules of synthetic polyelectrolytes introduced into living organisms on a "trial and error" basis are able to find for themselves macromolecular partners with which to form the most stable bonds. This principle is of fundamental importance in the development of synthetic vaccines of a novel type based on polyelectrolytes. A vaccine of this type is a polyelectrolyte macromolecule to which is covalently added an antigenic determinant isolated from a bacterium or virus giving rise to a particular illness. Mice that have been treated with vaccines of this type and have then been infected with germs causing influenze or typhus have demonstrated 100 Yo survivability, compared with practically 100% mortality in control tests without the use of vaccines. A group of immunologists and chemists headed by academician R. V. Petrov is now working on the development of a novel type of man-made vaccine based on synthetic polyelectrolytes. This is leading to fresh and encouraging hopes relating to the propylaxis and treatment of many infectious illnesses.
* Vysokomol. soyed. A28: No. 7, 1560-1562, 1986. 1740
The Kargin lectures
1741
The report of A. I. D'yachkov was based on fresh data on the kinetics and mechanism of radi¢.al polymerization of (meth)acrylates. The report relates to the kinetics of polymerization and postpolymerization of MMA in the 'temperature interval 20-70 °. The results of investigation of bcqrl m©thacrylate, methacrylate and MMA-dibutyl phthalate (up to 40 Yo DBP) show that the mechanism of chain growth limitation in the area of conversions corresponding to a steady rate of polymerization js invariably a bimolecular ~one. In the region where the onset of autoacceleration appears two mechanisms of limitation of chain growth are detectable, viz a bimolecular mechanism and a monomolecular one. In the conversion region where rapid autoacceleration occurs a monomolecular mechanism of limitation of chain growth is observed, and is apparently the result of diffusion limitations hindering access of monomer to growing centres. On the basis of the kinetic data the author expressed the view that systems palymerizing with autoacceleration become nonequilibrium ones in the conversion area for autoacceleration, and become nonuniform from a concentration standpoint. This assumption is borne out by experimental " results. The use of light acattering methods makes it possible to detect the formation of (concentrationwise) nonuniform areas in the region of the onset of autoacceleration, the characteristic lengths of the areas being 10-50/zm, their intensity increasing with the increase in conversion. If polymerization is stopped with conversions in this region the system relaxes and a state of equilibrium is established. The fact that a sterically nonuniform distribution of monomer and polymer is involved means that distribution of components of polymerizing systems will be nonuniform. In the case of initiators this factor may provide a means of controlling polymerization rates at advanced degrees of conversion. Certainly,2dnetic studies of polymerization in the presence of initiators such as cyclohexylperoxydicarbonate, azobisisobutyronitrile (ABN), lauryl peroxide and benzoyl peroxide have shown that, initial rates of polymerization being equal, there are marked differences in the rates at high degrees of conversion. In the case of initiators that dissolve more readily in polymer the reduction in rates at high degrees of conversion is more marked. It was found that when the polymerization rate decreases, the MW of the polymer, far from decreasing, is actually slightly increased. It was also found that where polymerization temperatures are in the range of high degrees of conversion autodegradation of the high molecular mass fraction of a polymer takes place. This effect is more marked in cases where the initiator happens to be one that dissolves readily in the polymer. The report presented by S. S. Ivanchev related to polymerization systems containing polyfunctional components. This report was based on an analysis of the extent to which the polyfunctional nature of the components of polymerization systems influences the kinetics and mechanism of radical polymerization of vinyl monomers and affect the structure, molecular characteristics and mechanical properties of the resulting polymer products. In the view of the author the use of polyfunctional components plays a definite role in development of polymerization theory, and is the dominant direction of research in the search for novel polymeric materials. The author proposed that polyfunctional components should be classified according to their main uses, taking account of the nature and amount of functional groups forming part of the composition of a single molecule. With this in view a study was made of the properties of polyfunctional monomers, initiators, emulsifiers and fillers. This was followed by an analysis .of the polymerization of diene compounds with conjugated and unconjugated double bonds, as well as polymerization of alkene-alkyl monomers and m o n o mers containing other functional groups, particularly peroxide groups. Copolymerization conditions were determined for vinyl monomers with peroxide-containing monomers, viz. conditions whereby in the first stage transformation of peroxide groups could be kept to a minimum, and where the second stage would result in block copolymers, comb-like polymers, high-impact weather-reaisrant ABS copolymers, heterofunctional reactive oligomers, and polymers and latices for finishing leather and textile goods, as well as adhesives and complex erosslinking agents.
1742
P . V . KozLov
It is shown that when polyfunctional initiators are used the formation of macromolecules takes place by a polymerization-polyrecombination type process. Macromolecules formed at the start of the process contain initiating groups whereby it is possible to regulate MW, MWD, degrees o f branching, compositional heterogeneity and accordingly the properties of the resulting polymers and copolymers. Moreover it i s shown that reactions of formation of macromolecules may be localized within particular zones, and the importance of this as a means of obtaining microheterogeneous polymer systems during the synthesis of materials is highlighted. A quantitative theory of polymerization is proposed for ~ases where polyfunctional initiators of various types are being used. It is pointed out that polyfunctional emulsifiers include compounds of two types, namely emulsifier-monomers and emulsifier-initiators. In the case of emulsifiers of the first type, specific features of the kinetics of emulsion polymerization are determined by the local concentration of monomers in associates and by reduction in the termination rate constant accompanying increased packing density in micelles, by reduction in the mobility of vinyl groups on going from spherical micelles to anisotropic ones, and by a change in the mutual orientation of molecules and double bonds in the latter accompanying formation of multilayer lamellar type structures. It is proposed that emulsifier-monomers could be used for the preparation of lattices containing no free emulsifier in the aqueous phase, as well as for the preparation of extra-stable, heat-sensitive, and practically monodisperse latices. By means of the second type of polyfunctional emulsifiers it is possible to localize initiation reactions in the adsorption layers, which results in a higher rate of decompoSition of peroxide groups, and in the appearance of peculiarities appearing in the course of elementary termination steps. Radical polymerization of vinyl monomers conducted on solid dispersed particles, having on their surface peroxide initiating groups or polymerizable double bonds was discussed as a means of development of novel polymeric materials. Special features of the initiation of polymerization on a solid-phase surface were analyzed, as well as some peculiarities of the copolymerization of vinyl monomers in the presence of a reactive surface. In addition methods for the preparation of filled polymer systems were examined, as well as the properties of the systems. Composite materials with enhanced service properties have been prepared through the presence of chemical bonds between disperse phase and polymer matrices, and also through the uniform and extremely narrow size distribution of filler particles in polymer matrices. The resulting materials have higher strength and elasticity in addition to enhanced heat stability and conductivity. The final report was that contributed by Yu. A. Zubov, S. N. Chvalun and N. F. Bakeyev, entitled "Special characteristics of the structure of highly oriented polyethylene". The latter line of research is of great practical value as well as being of interest from a scientific standpoint. In "The main directions of economic and social development in the USSR in the years 1986-1990 and in the period up to 2000" it is not without reason that the section entitled " P r o duction of Constructional Materials and Chemical Products" refers directly to "The Need to Develop and Introduce Production of Novel Types of High-Strength and High-Modulus Chemical Fibres and Filaments". It is known that at present the strength properties of chemical fibres amount to only several percentages of the theoretical possible levels. This means that a detailed structural investigation of chemical fibres that have undergone orientation should lead to the discovery o f methods whereby the strength properties of these polymer products may be increased. The report is in the form of a brief review of work in this field, including work in the Soviet Union and elsewhere, and on this basis information covering the present state of affairs is provided. It is known that structural anomalies are often found in hihgly oriented samples - the longitudinal crystallite dimensions may well exceed the length of the long periods. In view of this one has been able to deduce that reinforcement of high-modulus and high-strength samples stems from the formation of crystallites with straightened chains. Various structural models have been proposed for polymers of this type and are based either on a carcass of crystals with streightened chains,~ or on a filler (in the matrix) consisting of crystals with folded chains. On the basis of an analysis
The Kargin lectures
1743
~of basis structural features of these polymer together with a study of their mechanical properties o n e may advance another idea as to the mechanism whereby reinforcement of highly oriented fiexible-chain polymers takes place, as proposed by N. F. Bakeev. He takes the view that as the draw ratio increases the n u m b e r of tie chains in amorphous regions of microfibrils grows larger, a n d these are straightened out. This will result in the appearance of bundles of straightened tie chains leading to a marked increase in the strength of the flexible-chain polymers, and likewise in their elastic moduli. One-dimensional diffraction investigations carried out by the authors of the present report have confirmed that there are indeed linear systems of this type in the highly oriented samples. These linear systems consisting of straightened tie chains would account for the main structural peculiarities, and the behaviour, of highly oriented flexible crystallizing polymers. Principles underlying reinforcement of flexible polymers based on structural modification of a m o r p h o u s regions were utilized by the authors of the present report in their collaboration with coworkers at the Moscow State University and at the All-Union Synthetic Fibre Research Institute (Kalinin) and also at the High. Polymer Institute, U.S.S.R. (Leningrad). Their aim was that of developing methods of reinforcement for polypropylene and polycaproamide. Procedures thus developed have now been introduced into working routines at several works and factories of the Ministry of Chemical Industries.
Translated by R. J. A. HENDRY
0032-3950/86 $10.00+ .00 © 1987 Pergamon Journals
THE KARGIN LECTURES* P. V. KOZLOV On "rm8 23 January 1986 the large chemical auditorium in memory of N. D. Zelinskii was the setting in which the XVI Kargin Lectures took place under the auspices of the Chemistry Faculty at the Lomonosov State University Moscow. The lecture progra~ included four independent reports dealing with various aspects of polymer science. These reports highlighted not only the basic and pioneering character of the research, but also the usefulness of the results obtained and their value in several branches of the Soviet economy. Opening these Lectures the president of the orgkomitet, P. V. Kozlov, remarked that their organization had by now acquired its own systematic character and undoubtedly reflected successful progress in Soviet polymer science, to whose organization and development such a great contribution had been made by Valentin AIekseyevich Kargin. P. V. Kozlov recalled that in the case of all the preceding fifteen events (from 1971 to 1985) there had been 145 lectures (of which 28 were outstandingly memorable) reflecting the creative work of V. A. Kargin relating to various branches of polymer science and their further development. This was indeed a fitting memorial and tribute to the very eminent Soviet scientist. As regards the fifteen previous Kargin Lectures P. V. Kozlov referred to the seventh in honour of the 70th Anniversary of the birthday of V. A. Kargin, which took place in 1977. On this occasion 21 papers were read, and there was also a report on the creative work of V. A. Kargin and two speeches in which he was specially remembered. The next speaker after P. V. Kozlov was V. A. Kabanov, whose report entitled "The polymeric effects and biological activity of functional synthetic macromolecules" dealt with features of chemical reactions involving the participation of synthetic polyelectrolytes in aqueous solutions, and examined these in relation to the physiological activity of polyelectrolytes, with special reference to their immunostimul'ating action. Given the presence of charged functional groups in polyelectrolyte macromolecules it folliows that these may be linked to various oppositely charged functional groups forming part of natural polymers or included in cage membranes. The polymeric nature of a polyelectrolyte determnes the cooperative character of linking with biopolymers and cage membranes, thereby ensuring o n the one hand good bond strength, and on the other hand opening the way towards intermacromolecular reactions of exchange and substitution discovered in the high polymer department at the Moscow State University. It is such substitution reactions, that underlie the fact that macromolecules of synthetic polyelectrolytes introduced into living organisms on a "trial and error" basis are able to find for themselves macromolecular partners with which to form the most stable bonds. This principle is of fundamental importance in the development of synthetic vaccines of a novel type based on polyelectrolytes. A vaccine of this type is a polyelectrolyte macromolecule to which is covalently added an antigenic determinant isolated from a bacterium or virus giving rise to a particular illness. Mice that have been treated with vaccines of this type and have then been infected with germs causing influenze or typhus have demonstrated 100 Yo survivability, compared with practically 100% mortality in control tests without the use of vaccines. A group of immunologists and chemists headed by academician R. V. Petrov is now working on the development of a novel type of man-made vaccine based on synthetic polyelectrolytes. This is leading to fresh and encouraging hopes relating to the propylaxis and treatment of many infectious illnesses.
* Vysokomol. soyed. A28: No. 7, 1560-1562, 1986. 1740
The Kargin lectures
1741
The report of A. I. D'yachkov was based on fresh data on the kinetics and mechanism of radi¢.al polymerization of (meth)acrylates. The report relates to the kinetics of polymerization and postpolymerization of MMA in the 'temperature interval 20-70 °. The results of investigation of bcqrl m©thacrylate, methacrylate and MMA-dibutyl phthalate (up to 40 Yo DBP) show that the mechanism of chain growth limitation in the area of conversions corresponding to a steady rate of polymerization js invariably a bimolecular ~one. In the region where the onset of autoacceleration appears two mechanisms of limitation of chain growth are detectable, viz a bimolecular mechanism and a monomolecular one. In the conversion region where rapid autoacceleration occurs a monomolecular mechanism of limitation of chain growth is observed, and is apparently the result of diffusion limitations hindering access of monomer to growing centres. On the basis of the kinetic data the author expressed the view that systems palymerizing with autoacceleration become nonequilibrium ones in the conversion area for autoacceleration, and become nonuniform from a concentration standpoint. This assumption is borne out by experimental " results. The use of light acattering methods makes it possible to detect the formation of (concentrationwise) nonuniform areas in the region of the onset of autoacceleration, the characteristic lengths of the areas being 10-50/zm, their intensity increasing with the increase in conversion. If polymerization is stopped with conversions in this region the system relaxes and a state of equilibrium is established. The fact that a sterically nonuniform distribution of monomer and polymer is involved means that distribution of components of polymerizing systems will be nonuniform. In the case of initiators this factor may provide a means of controlling polymerization rates at advanced degrees of conversion. Certainly,2dnetic studies of polymerization in the presence of initiators such as cyclohexylperoxydicarbonate, azobisisobutyronitrile (ABN), lauryl peroxide and benzoyl peroxide have shown that, initial rates of polymerization being equal, there are marked differences in the rates at high degrees of conversion. In the case of initiators that dissolve more readily in polymer the reduction in rates at high degrees of conversion is more marked. It was found that when the polymerization rate decreases, the MW of the polymer, far from decreasing, is actually slightly increased. It was also found that where polymerization temperatures are in the range of high degrees of conversion autodegradation of the high molecular mass fraction of a polymer takes place. This effect is more marked in cases where the initiator happens to be one that dissolves readily in the polymer. The report presented by S. S. Ivanchev related to polymerization systems containing polyfunctional components. This report was based on an analysis of the extent to which the polyfunctional nature of the components of polymerization systems influences the kinetics and mechanism of radical polymerization of vinyl monomers and affect the structure, molecular characteristics and mechanical properties of the resulting polymer products. In the view of the author the use of polyfunctional components plays a definite role in development of polymerization theory, and is the dominant direction of research in the search for novel polymeric materials. The author proposed that polyfunctional components should be classified according to their main uses, taking account of the nature and amount of functional groups forming part of the composition of a single molecule. With this in view a study was made of the properties of polyfunctional monomers, initiators, emulsifiers and fillers. This was followed by an analysis .of the polymerization of diene compounds with conjugated and unconjugated double bonds, as well as polymerization of alkene-alkyl monomers and m o n o mers containing other functional groups, particularly peroxide groups. Copolymerization conditions were determined for vinyl monomers with peroxide-containing monomers, viz. conditions whereby in the first stage transformation of peroxide groups could be kept to a minimum, and where the second stage would result in block copolymers, comb-like polymers, high-impact weather-reaisrant ABS copolymers, heterofunctional reactive oligomers, and polymers and latices for finishing leather and textile goods, as well as adhesives and complex erosslinking agents.
1742
P . V . KozLov
It is shown that when polyfunctional initiators are used the formation of macromolecules takes place by a polymerization-polyrecombination type process. Macromolecules formed at the start of the process contain initiating groups whereby it is possible to regulate MW, MWD, degrees o f branching, compositional heterogeneity and accordingly the properties of the resulting polymers and copolymers. Moreover it i s shown that reactions of formation of macromolecules may be localized within particular zones, and the importance of this as a means of obtaining microheterogeneous polymer systems during the synthesis of materials is highlighted. A quantitative theory of polymerization is proposed for ~ases where polyfunctional initiators of various types are being used. It is pointed out that polyfunctional emulsifiers include compounds of two types, namely emulsifier-monomers and emulsifier-initiators. In the case of emulsifiers of the first type, specific features of the kinetics of emulsion polymerization are determined by the local concentration of monomers in associates and by reduction in the termination rate constant accompanying increased packing density in micelles, by reduction in the mobility of vinyl groups on going from spherical micelles to anisotropic ones, and by a change in the mutual orientation of molecules and double bonds in the latter accompanying formation of multilayer lamellar type structures. It is proposed that emulsifier-monomers could be used for the preparation of lattices containing no free emulsifier in the aqueous phase, as well as for the preparation of extra-stable, heat-sensitive, and practically monodisperse latices. By means of the second type of polyfunctional emulsifiers it is possible to localize initiation reactions in the adsorption layers, which results in a higher rate of decompoSition of peroxide groups, and in the appearance of peculiarities appearing in the course of elementary termination steps. Radical polymerization of vinyl monomers conducted on solid dispersed particles, having on their surface peroxide initiating groups or polymerizable double bonds was discussed as a means of development of novel polymeric materials. Special features of the initiation of polymerization on a solid-phase surface were analyzed, as well as some peculiarities of the copolymerization of vinyl monomers in the presence of a reactive surface. In addition methods for the preparation of filled polymer systems were examined, as well as the properties of the systems. Composite materials with enhanced service properties have been prepared through the presence of chemical bonds between disperse phase and polymer matrices, and also through the uniform and extremely narrow size distribution of filler particles in polymer matrices. The resulting materials have higher strength and elasticity in addition to enhanced heat stability and conductivity. The final report was that contributed by Yu. A. Zubov, S. N. Chvalun and N. F. Bakeyev, entitled "Special characteristics of the structure of highly oriented polyethylene". The latter line of research is of great practical value as well as being of interest from a scientific standpoint. In "The main directions of economic and social development in the USSR in the years 1986-1990 and in the period up to 2000" it is not without reason that the section entitled " P r o duction of Constructional Materials and Chemical Products" refers directly to "The Need to Develop and Introduce Production of Novel Types of High-Strength and High-Modulus Chemical Fibres and Filaments". It is known that at present the strength properties of chemical fibres amount to only several percentages of the theoretical possible levels. This means that a detailed structural investigation of chemical fibres that have undergone orientation should lead to the discovery o f methods whereby the strength properties of these polymer products may be increased. The report is in the form of a brief review of work in this field, including work in the Soviet Union and elsewhere, and on this basis information covering the present state of affairs is provided. It is known that structural anomalies are often found in hihgly oriented samples - the longitudinal crystallite dimensions may well exceed the length of the long periods. In view of this one has been able to deduce that reinforcement of high-modulus and high-strength samples stems from the formation of crystallites with straightened chains. Various structural models have been proposed for polymers of this type and are based either on a carcass of crystals with streightened chains,~ or on a filler (in the matrix) consisting of crystals with folded chains. On the basis of an analysis
The Kargin lectures
1743
~of basis structural features of these polymer together with a study of their mechanical properties o n e may advance another idea as to the mechanism whereby reinforcement of highly oriented fiexible-chain polymers takes place, as proposed by N. F. Bakeev. He takes the view that as the draw ratio increases the n u m b e r of tie chains in amorphous regions of microfibrils grows larger, a n d these are straightened out. This will result in the appearance of bundles of straightened tie chains leading to a marked increase in the strength of the flexible-chain polymers, and likewise in their elastic moduli. One-dimensional diffraction investigations carried out by the authors of the present report have confirmed that there are indeed linear systems of this type in the highly oriented samples. These linear systems consisting of straightened tie chains would account for the main structural peculiarities, and the behaviour, of highly oriented flexible crystallizing polymers. Principles underlying reinforcement of flexible polymers based on structural modification of a m o r p h o u s regions were utilized by the authors of the present report in their collaboration with coworkers at the Moscow State University and at the All-Union Synthetic Fibre Research Institute (Kalinin) and also at the High. Polymer Institute, U.S.S.R. (Leningrad). Their aim was that of developing methods of reinforcement for polypropylene and polycaproamide. Procedures thus developed have now been introduced into working routines at several works and factories of the Ministry of Chemical Industries.
Translated by R. J. A. HENDRY