International symposium on macromolecular chemistry

~olymer Science U.S.S.R, VoL 21, pp. 2102-1216. O Pergamon Pre~ Ltd. 1980. Printed in Poland

0032-3950/79/0801-2102507.50/0

REPORTS INTERNATIONAL SYMPOSIUM ON MACROMOLECULAR CHEMISTRY* (Tashkent, 0ktober 1878) V. A . VASlfEV a I l d A . A . -~t_SKADSKII

TKE International Symposium on Macromolecular Chemistry was organized within t h e

framework of the International Association of Theoretical and Applied Chemistry (IUPAC) from 17 to 21 October, 1978 in Tashkent. The U.S.S.R. A c a d e m y of Sciences, the Scientific Council on High Molecular Weight Compounds, U.S.S.R. A c a d e m y of Sciences, the A c a d e m y o f Sciences of the Uzbek.S.S.R., the U.S.S.R. Ministry of Chemical Industry, the Ministry of Oil Refining and Petrochemical I n d u s t r y and the U.S.S.R. Ministry of higher and specialized secondary Education took p a r t in the organization of the Symposium. Opening the Symposium Acad. V. V. Korshak, Chairman of the Organizing Committee o f t h e Symposium reported t h a t a message of goodwill had been received b y the Symposium from L. I. Brezhnev, General Secretary of the CC of CPSU, Chairman o f the Presidium o f t h e U.S.S.R. Supreme Soviet. L. I. Brezhnev announced t h a t Sh. R. Rashidov is to be the candidate member of the Political Bureau of the CC CPSU, who is first Secretary of the CC of the CP of Uzbekistan. I n his message L. I. Brezhnev noted t h e importance of polymer science in industry as i t is linked to the "solution of complicated problems concerning the development of highly efficient technical processes, the efficient use of minerals, the protection of the environment a n d the more satisfactory fulfillment of human requirements". L. I. Brezhnev expressed confidence t h a t the "work of the Symposium, creative discussion of scientific problems a n d extensive exchange of opinion will contribute to further development of chemical science, intensify the scientific and technical link between specialists of various governments, in order to achieve a full understanding between nations in their fight for a lasting peace a n d social progress". L. I. Brezhnev's message was greeted with enormous interest among the participants of the Symposium. I n his opening address Acad. V. V. Korshak briefly dealt with the progress achieved in chemical science in the field of synthesis and investigation of properties of polymers. H e also noted the significant role of chemists of Uzbekistan in the development of this field a n d wished the Symposium and all its participants success on the hospitable soil of Uzbekistan. L. A Kostandov, Minister of Chemical I n d u s t r y greeted the participants of the Symposiren on behalf of the Ministry. Prof. G. Smets (Belgium), President of I U P A C spoke on behalf of his Organization and Acad. 1~. M. Emanuel' Acad. Secretary of the Dept. of General a n d Technical Chemistry, U.S.S.R. Academy of Sciences spoke for Soviet chemists, participants and guests of the Symposium. Over 2500 scientists and specialists from 28 countries took p a r t in the work of the Symposium, among them ministers of chemical i n d u s t r y in socialist countries. Six plenary papers were read at the Symposium b y eminent Soviet and foreign scientists (2 of the U.S.S.R. * Vysokomol. soyed. A21: No. 8, 1902-1915, 1979. 2102

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m~d 4 o f foreign countrles), 29 introductory sectional papers (11 of the U.S.S.R. a n d 18 for0ign) a n d 550 brief reports (324 of the U.S.S.R. and 226 from abroad) presented. T h e s ~ o f all papers a n d reports read a t the Symposium were published in the Proceedings. Some o f theSe reports a n d papers were the result of direct scientific contact between scientists o f various countries and results of joint studies b y scientists a n d specialists of these eountrlos such as Poland a n d Czechoslovakia, German Democratic Republic a n d the U.S.S.R., H u n g a r y a n d the U.S.S.R., U.S.A. and Belgium, Bulgaria and the U.S.S.R., etc. were reflee~ed in them. The work of the Symposium was carried out at the meetings of 10 sections. I. Radical polymerization. 2. Ionic and coordination polymerization. 3. Polycondensation. 4. Synthesis of now polymers. 5. Chemical conversions in polymer chains. 6. Breakdown and stabilization of polymers. 7. Structure and physical properties of polymers. 8. P o l y m e r solutions. 9. Scientific principles of developing composition. 10. Cellulose and cellulose derivatives. Furthermore, " R o u n d Table" discussions were organized concerning the following problems. 1. Modification of h e a v y - d u t y polymers: cellulose, polyolefias, polydienes, p o l y v i n y l chloride (condition and prospects). 2. Mechanism of stereor~gulation during polymerization and eopolymerization, including the alternating process (experimental approach). 3. H e a t resistant polymers (synthesis, role of organic a n d heteroorganic fragment s). 4. Physiologically active polymers (possibilities and restrictions of methods of synthesis a n d application). 5. Structure of amorphous polymers and mesophases (new methods of investigation a n d new ideas). 6. Mechanical breakdown of polymers (role of structure). 7. Compositions (structure of oligomers and topology of crosslinked polymers). Discussions on the fifth and sixth problems were combined. The p a p e r b y Prof. G. Smets (Belgium) entitled °Dissociation and Recombination i n Solid Polymers" compared dissociation and recombination processes in solid polymers and in solutions; main attention was given to three points: photochemical processes of complex formation and dissociation; dissociation and radical decomposition in polymer systems; equilibrium in reactions of dissociation a n d recombination. W h e n analysing the first aspect as a limiting case of the effect of a m~trix on the course of reactions a s t u d y was made of photochemical processes including the formation of iut~rmediate products, the life time of which is considerably shorter t h a n the tim0 required for processes preceding photochemical processes. Problems of dissociation and radical decomposition in polymgr systems were a n a l y s e d using thermal dissociation of organic compounds in solutions and "cells" from solid polymers. As a result of the investigations it was established t h a t reactions of dissociation a n d recombination in polymers take place a t a much lower rate t h a n in solutions. The paper b y Acad. K. A. Andrianov (U.S.S.R.) entitled "Progress in t h e F i e l d of Hetero-organie High Molecular Weight Compounds" read b y Prof. A. A. Zhdauov a n a l y s e d the main achievements in the'field of synthesis of organosilicon polymers. At generalization o f results of fundamental research in this field enabled us to deal with several m a j o r p r o b l e m s , t h e solution of which defines to ~ considerable extent the level of the chemistry a n d tochno'logy of organosilic0n p o l y m ors.

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A n i m p o r t a n t place is given in the paper to the synthesis of linear polyorganosiloxanee (first polymers with inorganic main chaln~ of molecules) corresponding to the increased requirements of m a n y branches of modern technology. I n particular, detailed studies were m a d e of catalytic (anionic and cationic) polymerization of organocyclosiloxanes--the main m e t h o d of synthesis of these polymers. A promising t r e n d which opens up extensive possibilities for the control of composition a n d properties of polymers is the synthesis of linear and branched oligomers which as a result of polycondensation are able to change into high molecular weight compounds with given properties; this can be cffected directly in the products. A significant p a r t of the paper was concerned with problems of breakdown of polysiloxanes. Methods were outlined for the stabilization of linear polysiloxanes and a critical analysis made of the possibility of increasing the heat stability of the polymers examined as a result of modifying structure, particularly b y transition from linear to cyclolinear structures. I n addition to polysiloxanes, considerable attention was given in the paper to an extensive group of polymer compounds containing nitrogen and silicon in main chains of macromoleeules--polyorganosilazanes and polyorganosiloxazanes. The paper b y Prof. G. Still (U.S.A.) "New Reactions of Crosslinking of H e a t Resistant P o l y m e r s " was concerned with one of the methods of solving the problem of producing polymers t h a t can be readily processed and can be used for a long period of time at increased .temperatures, namely cresslinking heat resistant systems after processing into products. Bifunctional diphenylene and hexaphenylbenzene derivatives were used as crosslinking agents a n d polyquinohnes, polyamides, po]ybenzimidazoles and polyphenyl quinoxa]ines, as polymer systems t h a t can be solidified. These crosslinking agents are characterized b y t h e fact that, in contrast to systems previously used, t h e y do not introduce in the solidifying p o l y m e r s bonds t h a t are weak from a thermal point of view, since even a small amount o f biphenylene group introduced in polymers determines the effective crosslinking of heretocyclic polymers. The proposed approach m a y be regarded as very effective in increasing t h e operating temperatures of polymers without any deterioration in processing properties. The paper b y Prof. G. F u r n k a w a (Japan) (Recent Progress in the Field of Polymerization) resulting in the folmation of regularly alternating copolymers' examined five aspects of this p r o b k m : the dependence of glass temperatures of copolymers on composition and t h e sequence of arrangement of units in the chains, rubbery properties of copolymers, copolymers as systems with functional groups, synthesis of regularly alternating copolymers on modified Ziegler catalysts and bssed on monomers of donor-accepter type. Analysis o f m a i n results dealt with in the paper shows t h a t regularly alternating copolymers behave in a specific manner in the region of glass temperature or during elongation, which is due t o t h e orientation or aggregation of segments. Among copolymers with functional groups greatest interest is attached to systems characterized b y the cooperative effect of adjacent groups. I n the paper b y Aead. G. Klare of the Academy of Sciences, German I)emocratic l~epublic, entitled "Sti~cture and Properties of Polyalkylene Terephthalates" a detailed s t u d y was made of various aspects of physics, chemistry and technology of a class of polyesters i m p o r t a n t from a practical point of view, which are based on alkyleneglycols a n d terephthalic acid derivatives. A considerable p a r t of the paper was cGncerned with polyethylene t e r e p h t h a l a t e as an initial polymer used for fibre formation and properties of fibres made frcm it. A v e r y detailed s t u d y was made of results of physical investigations carried out in the I n s t i t u t e of Polymer Chemistry, Academy of Sciences, German Democratic Republic a n d directed to solve problems related to the structure and structural dynamics in solid polymers based on polyethylene terephthalate. P a r t of the paper was concerned with the technology of polyalkylene terephthalato

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materials and a report was given of the fibrillation method developed in the German I)emo. cratie Republic for polyethylene terephthalate-polyolefin mixtures used for film making, followed b y the direct processing of film threads into textile products using k n i t t i n g a n d • sewing machines. Among other chemical aspects of the problem a n analysis was made of the correlation between the chemical structure of substances used for the synthesis of polyalkylene terephthalates a n d their reactivity and between the structure of catalysts and rates of polycondensation. I n a basic paper b y Acad. N. M. Emunuel (U.S.S.R.) entitled 'Some Problems of Ch emical Physics of Ageing and Stabilization of Polymers" results of a n u m b e r of investigations dealing with detailed mechanisms and ageing kinetics of polymers and the development of efficient methods of stabilization, were generalized. I n the light of existing results ageing of polymers was examined as a multifactoral problem which c a n be solved in a general form using modern computer technology. A detailed analysis was made of. the effect o f external conditions on three main stages of ageing of polymers; initiation, ageing and the loss of active centres of ageing, which enabled optimum methods of controlling t h e rate of ageing to be forecast. I n his r a p e r N. M. E m a n u e l made a detailed study of elementary reactions in polymers. The measurement of elementary reaction constants in solid polymers b y methods used for liquid phase processes made it possible to develop a detailed kinetic pattern of ageing o f polymers. Part of the paper dealing with the stabilization of polymeric materials from the point, of view of ageing mechanisms, illustrating the possibility of classifying methods of stabilization of polymer materials according to the stage of ageing they influence, is of u n d o u b t e d interest. Another aspect of the paper b y N. M. E m a n u e l ' was concerned with a problem of everincreasing i n t e r e s t - - t h e breakdown of polymers in tissues of live organisms. Polymers used in medicine, as a result of contact with tissues of organisms change their properties to ~ome extent, which m a y be reflected in the activity of man. U n d o u b t e d interest is attached to the point of view concerning chemical degradation as a method of modifying polymer surface which in m a n y cases determines the operational properties of polymers. Finally, there is another aspect of the paper which is very pressing; this concerns the combustion of polymers: main mechanisms of inhibition and the most effective methods o f introducting inhibitors into polymers were examined in detail. The complexity of the problem of reducing the combustibility of polymers and the need for intensifying studies in t h i s direction were noted in the paper. At the first section of the Symposium entitled "Radical Polymerization" 4 introduction sectional papers were read. One of the most eminent scientists in the field of radical polymerization, C. Bamford (Great Britain) devoted his paper to the problem of developing new, highly efficient initiating systems. He examined the synthesis and conversions of macromolecules with two types of end group: those containing covalent derivatives of transition metal carbonyls and t h o s e able to form intermolecular crosslinks by the action of radiation. A description was given of the breakdown mechanism of end groups of the first type to form macrore~licals able to initiate polymerization of vinyl compounds. This enables these macro-initiators to be used for the synthesis of block copolymers. Very important problems of polymerization in crosslinked a n d ordered systems were examined in a paper by G. Ringsdorf (German Federal Republic), where a brief review is given of the synthesis and properties of liquid crystalline polymers. As a result of t h e s e studies it was established that to synthesize polymers with properties of liquid crystals it.

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is essential t h a t mesog'enic Side groups were combined with the main chain b y fairly 10ng a n d fiexible aliphatie fragments. Using radical polymerization of oetadecylmethacrylate and a n u m b e r of diacetylenedicarboxylic acids an analysis was made of kinetic a n d topechemical regularities of the formation of polymers in mono- a n d poly-layers on the wa~er-gas interface. These systmms are regarded as models of biomembranes. V. A. Kabanov's (U.S.S.R0 paper was concerned with interesting possibilities of using complex formation to control radical polymerization. He examined the structure of monomers combined in a complex m a n n e r and the effect of complex formation on the activity of monomers and corresponding radicals; As a result of analysing kinetic aspects of coordination-radical polymerization it was found possible to use complex formation to control elementary stages of radical homo- a n d copolymerization. General problems of radical polymerization, particularly the effect of inert solvents on process kinetics were examined in a paper by F. Tfid6s (Hungary). The author carried out a detailed analysis of kinetic anomalies of radical polymerization as a result of which he came to the conclusion that of the two alternative approaches--the theory of hot radicals and the theory Of radicals combined in a complex m a n n e r - - the former appears to be correct. The work of the section showed that there are several trends in the field of radical polymerization which arouse considerable interest and stimulate the further development of this field of the chemistry of high molecular weight compounds. At the first section alone :33 brief reports were read a n d 4 papers presented. At the second section of the Symposium entitled "Ionic a n d Coordinatior~ P o l y merization" 4 introductory sectional papers were read. The paper b y B. A. Dotgoplosk (U.S.S.R.) dealt with a new trend in polymer chemistry -the initiation of chain processes by carbene complexes of transition metals. Using polymerization of cyclo-olefins and the metathesis of olefins taking place in the presence of metal compounds a study was made of the stage of chain initiation, extension and rupture. Using the decomposition of diazo-compounds b y the action of tungsten halides made it possible to confirm experimentally the carbene nature of active centres in polymerization of cycloolefins. I n addition to chain extension, taking place b y the action of the centres mentioned linear unsaturated polymers undergo cycle-degradation, resulting in" the formation of cyclic oligomer molecules. The formation of carbene eyelo-olefins more stable t h a n active centres of a growing macromolecule during polymerization ruptures the chain. Finally, the author gave some information concerning properties of polymers obtained from cyclo-olefins. I n his paper S. Penchek (Poland) reported interesting results concerning the mechanism of polymerization of cyclic phosphates and showed that it is possible, in principle, to prepare polymers similar to biological objects, particularly nucleic acids. He examined the synthesis and polymerization of some monomers of this type. I m p o r t a n t problems of synthesis of block and graft copolymers of a given structure were examined b y P. Rempy (France). He showed that anionic copolymerization, compared with cationic polymerization, is more often used for the synthesis of graft and block copolymers and t h a t this method is based on the use of "live" macromolecules. A method has recently been developed for the synthesis of block copolymers which involves the step-by-step polymerization of monomers b y various mechanisms, for example, anionic and cationic mechanisms. A promising trend of synthesis of block copolymers is by the condensation of polymers with different functional end groups which m a y be prepared b y anionic, cationic, or radical polymerization. I n his paper T. Tsuruta (Japan) examined the mechanism of stereoselective polymerization of oxiranes b y the action of catalysts containing zinc. The author used complex comp o u n d s of zinc of known molecular weight for polymerization of methyloxirane and showed t h a t the formation of zinc methoxy propanolate is the first stage of ohain extension. Results

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o f investigation of the polymer obtained point to a relation between the activity a n d stereospecific properties of zinc catalysts. The work of the second section demonstrated considerable interest in ionic a n d coordination polymerization among scientists of different countries. Altogether 33 brief r e p o r t s a n d 30 papers were read which showed a high level of investigations in this field. Two introductory sectional papers were read at the third section of the Symposium entitled "Polycondensation". I n his paper V. V. Korshak (U.S.S.R.) analysed main problems facing scientists engaged in the field of polycondensation. Using m a n y examples the author showed that as a result of secondary reactions polymers containing different units are formed under conditions of polyeondensation. The presence of unusual units has a marked effect on properties of polymers, a study of conditions resulting in the formation of polymers containing "different units" is therefore one of the most important problems in polymer chemistry. Catalysts, \ which not only enable technology of polymer synthesis to be modernized, b u t also polymers of different structures to be prepared, are of considerable significance in polyeondensation. The use of new chemical reactions and new monomers in polycondensation widens the scope of this process a n d enables polymers of a new type to be prepared with a specific complex of properties or known polymers to be synthesized using new technology. M." M. K o t o n ' s (U.S.S.R.) paper is concerned with urgent problems of synthesis a n d properties of aromatic polyimides. The author proved it convincingly that properties of polyamido-acids formed at the first stage of the process determine to a large extent properties of final polyimides. The second stage of the reaction -- solid phase thermal dehydroeyelization of polyamido-acids is a very complex process, which is influenced b y chemical a n d structural factors. The dependence of the structure and properties of polyimides on the structure of initial compounds, reaction conditions and other factors enables polyimides of t h e required quality to be prepared, which makes it possible to solve important practical problems. The work of the third section showed that studies in the field of polyeondensation a r e of considerable practical significance, as well as being able to solve important f u n d a m e n t a l problems of the chemistry of high molecular weight compounds. F o r t y brief reports w e r e read at the section in all. Three introductory sectional lectures were given at the fourth section entitled "Synthesis of New Polymers". Z. Yedlinskii (Poland) devoted his lecture to polymerization of asymmetrically substituted epoxide compounds. Results of controlling the mechanism of polymerization a n d the structure of polymers b y changing factors such as the type of catalyst a n d reaction conditions were of particular interest. These results provide further information about the mechanism of ionic polymerization of alkene oxides in the presence of various catalysts. A comprehensive review was made of the synthesis and properties of polymers containing sulphur in a paper by S. R. Rafikov (U.S.S.R.). He examined and classified various types of polymer with sulphur atoms in the main or side chains, showed the considerable effect of fragments containing sulphur on thermal, photochemical, radiation stability a n d other properties of polymers. Principles of polymer stabilization using compounds containing sulphur and described by the author are of considerable interest. I n his paper N. A. Plate (U.S.S.R.) examined results of investigations into the synthesis, structure and properties of thermotropic liquid crystalline polymers. A new approach was proposed and introduced to prepare these polymers, which involves the synthesis of comblike polymers, in which fragments of molecular-analogues of classical low molec~ar weight liquid crystals and chain fragments, capable of undergoing local selective interaction with each other, take the form of lateral chains. As a result of investigating monomers, polymers

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and copolymers boundaries of phase transitions of crystal-liquid crystal-isotropie m e l t were established and possibilities of controlling the structure of liquid crystalline polymers,

analysed. The work of the fourth section showed t h a t scientists of various countries attach considerable interest a t the present time to the synthesis of heat resistant polymers, p o l y m e r s with special properties, including ion exchange, semi-conductor, catalytic, biological, etc. properties. 35 brief reports were read at the section. I m p o r t a n t problems of investigating reactions of polymers and developing physiologically active polymer preparations a n d immobilized fragments were dealt with a t ~h~ fifth section "Chemical Conversions in P~lymer Chains". F o u r introductory sectional p a p e r s were devoted to these trends. I n his paper P. A. Kirpichnikov (U.S.S.R.) examined the synthesis and chemical conversions of these reactive oligomers with functional groups such as oligoisobutylenes a n d oligosulphides. Oligoisobutylenes with given functionality and t y p e of end group e.g. carb o x y l groups, were obtained b y the breakdown of isobutylene copolymers with dienes b y the action of ozone. Using oligoisobutylenes with functional groups polymer materials were developed with given structure and properties. Reducing separation of polymers with disulphide bridges in macromolecules is an efficient method for the synthesis of polysulphide oligomers with mercapto-groups. Industrial oligothiols were used as separating agents. As a consequence of interchain exchange reactions products of chemical modification a r ~ formed. The p a p e r b y G. Manecke (West. Berlin) was concerned with the synthesis of polymers with reactive groups, which are used for the immobilization of ferments (papain, chymo. trypsin, urease, etc.). Polymers with active groups m a y be prepared b y polymerization o f corresponding monomers, e.g. cationic copolymerization of azyridine derivatives or v i n y l ethers, l~owever, these polymers are often obtained b y polymer-analogue conversions. Polyethylene-imines, polyvinyl alcohol, a styrene-acrylic acid and styrene-butadiene benzene copolymer were used for this purpose. I n the latter case the copolymer was processed b y the Friedel-Crafts reaction using N-chloromethylmaleimide. The copolymer formed w i t h t h e maleimide groups can combine ferments with mereapto-groups at the double bond. I m p o r t a n t problems of synthesis and investigation of polymers for medical p u r p o s e s were dealt with in a paper b y Ya. • a l a l a (Czechoslovakia). Soluble polymethemrylic acid derivatives and polypeptide derivatives of poly-aspartic acid were evaluated from this p o i n t of view. The t y p e of lateral group determines to a large extent properties of polymers: their reactivity, physiological activity, ability to undergo breakdown b y ferments, etc. These characteristics of the polymer are also greatly influenced b y conformation, which was examined b y the author using the spin label method. The t y p e of distribution in t h e organism is of enormous importance in the practical use of soluble polymers. Fluorescence a n d scintographic methods were therefore used with success. Insoluble polymers ar~ 'used for the preparation of prostheses as their surface m a y be modified b y chemical t r e a t m e n t . Results are given concerning natural r u b b e r , covulcanized with copolymers containing functional groups. I n his paper D. H u m m e l (German Federal Republic ) examined problems of r a d i a t i o n synthesis and modification of polymers, interesting from a practical point of view. Low velocity electron- and ~,-radiation and electric discharge were used for this purpose. W e indicated possibilities of using radiation for alternating, block and graft copolymerLzation and for other purposes. The work of the fifth section showed t h a t theoretical investigations in the field of chemical conversions of polymers are further develol~d in the synthesis of high molecular ~-eight compounds valuable from an applied point of view, chiefly polymers used in medicine~ $2 brief reports were read and 23 lectures given.

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At the sixth section entitled "Breakdown and Stabilization of Polymers" a n introductory sectional paper was read b y S. Sz6kely (Hungary). The author described the the rmal decomposition of high tnolecular weight compounds a n d used complex thermal analysis a n d mathematical simulation of the reaction mechanism. Interesting methods were developed for this purpose to investigate the mechanism of thermal reactions and determine the h e a l stability of polymers during rapid heating to high temperatures, which is based on t h e continuous measurement of sample weight and the continuous analysis of volatile breakdown products using a chromate-mass-spectrometer. As a result of these investigations a system was proposed for the thermal breakdown of polypropylene, polyimides, polyquinones a n d their copolymers; it was established in particular which of the mechanisms of thermal decomposition is responsible for the formation of breakdown products of polymers. The 47 brief reports and 7 papers read at the sixth section showed that new fields were added to traditional trends of investigations: comprehensive study of oxidation in a solid polymer, relation between kinetics a n d mechanism and the mobility of a polymer m a t r i x a n d consideration of the specific properties of the solid "polymer state". The seventh section of the Symposium entitled "'Structure a n d Physical Properties of Polymers" was concerned with the structure and physical properties of polymers. Fourintroductory sectional papers were read at this section. I n his paper C. Simoneseu (Rumunia) gave results of the effect of c/s- and trans-conformation of polyarylacetylenes on physical a n d physico-chemical properties of these s u b s t a n ces. I t was established that the cis-tra~s-transition is accompanied b y a significant variation, in properties of polymers, specific volume resistance in particular varies b y eight orders~ of magnitude. Methods were developed for preparing polyarylacetylenes mainly in cis- or ~ tra~s-form. Analysis of chain conformation and the structure of amorphous polymers were d e a l t with b y G. Iech (U.S.A.). He noted that based on direct structural investigations carried out in 1967 a structural model of an amorphous polymer was later proposed (1977) which contains small (15-50 ~) ordered paracrystalline regions, with ordered packing of individual chain segments which, however, form irregular folds. "Statistical sphere" type disorder exists in this model for macromolectfles which link one ordered region with another. This model, which is based on results of direct structural investigations of polyethylene terephthalate, atactic and isotactic polystyrene, n a t u r a l rubber and other polymers in the glassy or high elastic state, was accepted by a n u m b e r of scientists as incompatible with new result~ of small angle neutron scattering, depolarized light scattering, etc. I n his paper the a u t h o r tried to show that if existing information is examined more critically, including experimenta}' results of small angle scattering of neutrons by crystalline polymers and wide anglo X - r a y scattering by glassy a n d viscous polymers, it m a y be stated that the model described d o e s not conflict with results available (listed above and results of electron microscopy, including transmission and dark field microscopy and diffraction). I n this sense structural models of amorphous polymers previously proposed in the form of random spheres on the one h a n d a n d in the form of highly elongated ordered regions, on the other should be modified if existing results obtained when investigating amorphous polymers by direct structural methods are more strictly considered. A paper b y P. Corradini (Italy) dealt with some results of conformation analysis of polymer chains. This analysis was carried out b y investigating the interaction between atomic of free valency for the partially crystalline and amorphous state of polymers. D u r i n g conformation analysis of chains in the crystalline state calculations were made related t o energy bearing in mind variations of internal rotation angles along the chain and in the s i d e chains. Therefore, it became possible to predict geometrical chain parameters for p o l y m e r s based on olefins and diolefins. I t was shown for partially crystalline polymers (using polytetrafluoroethylene) that in

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crystalline modification which is s t a b l e at a temperature higher t h a n room temperature, • 'based on geometrical and energy considerations fairly frequent variations are possible in the direction of spiralization, which follow each other. Experiment~ carried out using X-ray diffraction confirm results of calculations carried out by the author et al. As far as the amorphous state is concerned, conformation analysis for melts was carried out by examining a n isolated maeromolecule, carrying out calculations of the typical o~ga, nization of linear hydrocarbon molecules in the liquid state and experimentally investigating :the behaviour of melts of model compounds of low molecular weight (using polyamides).. :Results of investigations indicate the existence of m u t u a l o r i e n t a t i o n of adjacent macromolecular fragments in the case of hydrocarbons. For polyamides some order is also observed i n the amorphous state, due to the retention of part of hydrogen bonds in melt. The paper b y M. A. Natov (Bulgaria) is concerned with the effect of the scale factor a n d supermolecular structure on mechanical properties of polymers. Analysing a n u m b e r of results in the literature and experimental information the author of this paper came to the conclusion that increasing the dimensions of polymer samples and changing configuration has a very marked effect on all mechanical indices. This is due to the complex dependence of mechanical indices on chemical and supermolecular polymer structure. I n contrast with m a n y other structural, materials in polymers, the type of supermolecular structure depends on the form and dimensions of the product and this dependence is just as marked as the dependence on production technology. I t is known that the type of supermoleeular structure is due to the thickness of polymer layers, in which this structure is formed. I n a very thin layer a polymer with good crystallization properties m a y even remain uncrystallized. The dimensions of supermolecular formations therefore change in the thickness of the sample. The variation also occurs during using polymer products, particularly on increasing temperature since the material is annealed unde~ these conditions. Considerable interest is therefore a t t a c h e d to results obtained by the author concerning the effect of the seale factor both on limiting strength and deformation and on relaxation properties of polymers. It, was established ~that under constant mechanical stress the rate of deformation decreases with an increase in .cross-sectional dimensions. Limiting deformation also decreases in this case. I t is interesting that decomposition in samples of considerable cross section isn't even accompanied b y "neck" formation. The life time of polymers under constant stress also depends to a marked extent on the scale factor. With an increase in sample dimensions, plastic deformation decreases a n d decomposition takes place, as observed for thermosetting plastics. The use of the Barley criterion under complex stress produces considerable deviations: a change in sample dimensions alone may produce considerable variation in durability. Relaxation properties depend ~)n the cross-sectional dimension of the sample and the type of supermoleeular structure: reduction in dimensions accelerates relaxation processes and changes the relaxation time ~pectrum. Special attention was given in the paper to the effect of the form and dimensions of the 'sample on the type of supermolecular structure in individual parts and therefore, to the complex effect of the structure itself on various mechanical indices. These effects m a y be evaluated quantitatively when considering a number of factors: mechanical breakdown, viseo-elastic deformation and decomposition by the extension of microeracks. The rate of these processes depends on the form and dimensions of the sample, technology of production ,and the type of supermolecular structure in individual parts. 31 brief reports and 52 papers were read at the seventh section. These reports and papers ~¢~ere concerned with problems related to the effect of chemical structure and supermolecular utructure of polymers on various physical properties. Polyolefins, polyamides, polyearbo~ t e s , polyethers a n d polyesters, r u b b e r y polymers, polyphenylacetylenes, polyurethanes, siloxane polymers, etc. were among objects of investigation. Papers were read dealing ~vith properties of polymers in all phase and physical conditions.

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Special attention was given to three dimensional systems, comb-like polymers and gels.. A tendency to using most modern physical methods of investigation for the analysis of the: structure a n d properties of polymers was clearly shown. Methods of investigation such as rheological a n d thermal methods, various spectroscopic, optical and mechanical methods, statistical approach and m a n y others were extensively represented. At the eight section entitled "Polymer Solutions" a n introductory sectional paper was read by V. N. Tsvetkov (U:S.S.R.). He dealt with the structure and properties of rigid chain polymer molecules in solutions. Interest in rigid chain polymers has suddenly increased in recent years because of their valuable properties retained at high temperatures. A study of the behaviour of rigid chain macromolecules in solution therefore also attracts great attention, especially as properties of dilute solutions of rigid chain polymersd iffer considerably from those of flexible macromolecules. Equilibrium flexibility (or rigidity), characterized b y macromolecular conformation in dilute solution in equilibrium is evaluated by the K u h n segment, which is 15-30 /~ for flexible chain polymers. As shown by investigations carried out by the author et al. for rigid chain macromoleeules, this value represents hundreds and thousands of £ngstr6ms. Kinetic flexibility (or rigidity) is characterized by the time of variation of macromolecular conformation. The author and co-workers developed a special apparatus and proposed methods for investigating properties of dilute rigid chain polymer solutions, namely hydrodynamic, optical and electro-optical properties. These investigations also required the formulation of a relevant theory to describe experimental results. I t appeared that the effect of excluded volume for rigid chain polymers is minimized, whereas the flow effect in the chain is highly significant (the opposite pattern is observed for flexible chain polymers). Flow birefringence provides most information about the conformations of rigid chains in solution. Molecular weight may also be determined from the variation of the characteristic angle of orientation of flow birefringence. Using the Kerr effect (electrical birefringence of solutions) for rigid chain polymers also provides extensive information about conformation characteristics. By studying kinetics of electrical birefringence of solutions the equilibrium and kinetic rigidity of macromolecules may be described. Using the theory, according to which rigid macromolecules are simulated by a worm-like chain, enables the Kerr constant. to be linked with parameters of equilibrium chain rigidity, the dipole moment, anisotropy of the ~ecurrent unit, etc. Using both theories (flow birefringence and electrical birefringence) to describe experimental results suggests that the direction of the dipole moment agrees with the direction of m a x i m u m geometrical extension of the macromolecule, which is also tile optical axis. Examination of a large n u m b e r of polymers by these methods suggests that ring formation in the recurrent unit up to the formation of a ladder type structure, the existence of accurately alternating conjugated bonds, substitution of aromatic nuclei in the para-position, etc. contribute to higher chain rigidity. 38 brief reports and 12 papers were read at the eight section. Considerable a t t e n t i o n was given in these papers to problems of interaction between polymers and solvent, the study of equilibrium and kinetic flexibility of macromolecules in solution, hydrodynamics of dilute solutions, and the development of new and perfection of existing methods of investigating polymer solutions. Problems relating to gel formation, adsorption, diffusion, etc. were also examined. Both traditional systems and new polymers, including polyelectrolytes were among the objects of investigation. The n i n t h section "Scientific Principles of Developing Compositions" was devoted to 3 introductory sectional papers. The paper by N. S. Yenkolopov (U.S.S.R.) dealt with scientific bases of developing compositions. The formation of a complex of mechanical properties of compositions depends on a n u m b e r of factors, the most important one being the properties of the binder (polymer matrix) and filler and the type of packing of the filler in the composite. As noted by th~

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V. A. VAm~rsv and A. A. AS~rAI)SKII

author, glass, carbon, boron fibres and organic fibres a r e used at the present time as reinforcing elements. Conditions of hardening the binder are significant since this way it is possible to regulate molecular packing, the free volume of the system and other parameters influencing mechanical properties in the solid glassy state. Main attention in the paper was given t o e p o x y r e s i n binders and a detailed investigation of hardening of epoxides enabled the f o rm at i o n mechanism of crosslinked polymers to be shown and the role of secondary reuctions, identified. These reactions accompany not only the process of hardening, but also accompany the variation of mechanical properties of compositions over a period of time Mince at increased temperatures and under increased load chemical conversions tuke place in the matrix, which are reflected by properties of composites. Under thermal and mechanical action aliphatic chain elements are the first to break down in epoxide matrices and the radical formed undergo further conversions. Under conditions of thermal oxidative breakdown the amino-group of aromatic diaminc is oxidized in the iminoxyl radical, which accelerates dehydrogenation of aliphatic fragments and results in rapid oxidation. In addition to fine effects of chemical conversions in a polymer binder, results are given i n the paper concerning the decomposition mechanism of compositions. Both the scale factor and the type of artificial incision showed some variation. Various types of deformation, preceding the decomposition of composites were detected and a criterion proposed for the decomposition of thin polymer films by uniaxial elongation confirmed using epoxy resin binders. Considerable attention was also given in the paper to the mutual arrangement of composition elements, the effect of filler concentration and other factors on the formation of a complex of mechanical properties of the composite. A t t e m p t s were made to calculat~ indices of mechanical properties using the law of additivity. The paper by I. M. Ward (England) was concerned with the structure and pioperties o f super-high molecular weight polymers. These polymers are prepared by elongation using high stress and at constant temperatures, or during so-called hydrostatic extrusion. I n the a u t h o r ' s opinion, factors determining conditions of preparing oriented polymers with a super-high modulus of elasticity enable us to understand the structure of polymers in bulk an d explain their mechanism of deformation. The process of hydrostatic extrusion m a y be analysed using results of elongation in the region of forced elasticity at different rates and different pressures. Considerable possibilities are also offered by investigating the structure ,of oriented systems prepared by this method. Results of small angle and wide angle diffraction show satisfactory agreement with results of thermo-meehanical measurements. Furthermore, the non-linear mechanical behaviour of oriented systems with a super-high modulus •under conditions of creep and reduction m a y be explained by results of polymer elongation bearing in mind plastic deformation. I n his paper V. F. Yevstratov (U.S.S.R.) developed an approach to the problem of improving properties of rubber by adding various modifiers, fillers in the form of short fibres and other components. Bearing in mind that rubber is a complex composition containing a large number of components (up to 15-20), the author gave considerable at t en t i o n to the structure of filler and surface effects taking place on the polymer-filler interface. T h e structure and properties of surface layers of the polymer near the filler particles and interaction of the filler with the polymer (rubber), including chemical interaction, determine to a large extent the properties of filled vulcanizates. Among the most important achievements in the field of chemistry and technology of •elastomers in recent years the author noted the use of modifiers of rubber mixtures. Modifiers a r e adhesion active low molecular weight or oligomer substances with functionl groups, which interact with components of the rubber mixture during blending and processing and c r e a t e f ~ r t h e r elastomer-elastomer and elastomer-filler bonds. This results in a change of s t r u c t u r e and properties of filled vulcanizates; strength and deformation properties, electrical ~onductivity, abrasion resistance, etc. change. Abrasion resistance of tyros could be increased

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b y 30O/o usLng these measures. C-nitroso-aromatic amines, diatomie phenol compounds, ~ligoesterepoxides and other substances m a y be used as modifiers. Modification is also effective when using two or more different elastomers in the rubber mixture; the distribution of components in elastorners m a y be controlled in this case, phase inversion effected and the structure of transition layers modified. This makes it possible t o improve fatigue characteristics and resistance to corrosive media. The author then dealt with another method of modification of rubbers, when various ~hort fibres--polymeric, metallic and glass fibres--are used as fillers. This increases the hardness and resistance to deformation and also oil and petrol-resistance of rubber. On the whole, modifying properties of technical rubber by these measures, in the author's opinion, is more beneficial from an economic point of view than the development of industrial methods for preparing new elast0mers. 44 brief reports and 9 papers were read at the ninth section. These were devoted to a wide circle of problems including scientific principles of selecting binders and fillers for preparing compositions with the requisite complex of properties. Special attention was given ~o network formation during the solidification of binders. A clear tendency was observed to using the most different types of binder and filler and also polymer mixtures for preparing •compositions and using not only traditional mechanical methods but also several other physical methods--calorimetry, electrophysical methods, mass-spectrometry, thermodynam i c approaches--for preparing compositions. Considerable attention was given to forecasting properties of compositions, effects of hardening, structure and structural modification and a n u m b e r of other important problems such as the development of compositions for special purposes (self-lubricating, shock-resistant, etc.). Three introductory papers were read at the t en t h section "Cellulose and Cellulose Derivatives". The paper by Kh. U. U s m a n o v dealt with results of investigating the structure of concentrated solutions of cellulose derivatives. In view of the development of preparatory methods of evaluating the structure of concentrated solutions by electron microscopy it became possible to change the structure of spinning solutions of cellulose and celluloso d e r i v a t i v e s in the region of high concentrations (between 5 and 25~o). Special attention was ~given in the paper to the structure of real spinning and modified cellulose acetate solutions .and mechanical properties of films and fibres prepared from these solutions. According to results obtained by the author and co-workers, the structure of a concentrated cellulose a c e t a t e solution represents a continuous network, the cells of which contain the solvent. On increasing polymer concentration, the eeUs are redueed and network elements are finally joined to form a solid--fibres or films. The structure of the latter m ay be influenced by t h e addition of a precipitant to the solution, as a result of which fibrils are formed. These additives in many cases improve physical and mechanical properties of films. Direct structural measurements were accompanied by sorption studies and a thermodynamic analysis of the .compatibility of components of the system. The structure and properties of solutions an d fibres and films obtained from them m a y be modified by selecting a solvent, where there is agreement between the structure of the spinning solution and the finished product. Tho correlation between the structure of spinning solutions and the index of mechanical properties, results of thermo-mechanical analysis, the type of isometric heating curve, soft.ening point, etc. was examined. All this, in the author's opinion, makes it possible to modify properties of films and fibres using the information about the structure of concentrated solutions of cellulose derivatives. In his paper R. Manley (Canada) dealt with problems of evaluating the ultra-structure ~)f cellulose fibres. He noted that in spite of numerous investigations in this field, our knowledge of this problem is still insufficient; he put forward certain views about this problem. G. Phflipp's paper (German Democratic Republic) dealt with the very importan~

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V A S T Y and A. A, A s E ~ v a m u

~problem of the dependence of the synthesis of cellulose ethers on structure a n d proces~ contitions. A fundamental relation was established between the mechanism of esterifieation of cellulose, the degree of substitution, type of distribution of functional groups a n d features of supermolecular structure of the initial cellulose material. Considerable attention was given in the paper to increasing the reactivity of cellulose by mercerization and treatment with ammonia. F o r t y brief reports and l0 papers were read at the t e n t h section dealing with most i m p o r t a n t problems in the field of the chemistry and physics of cellulose and its derivatives. Most brief reports and papers contained new, interesting information obtained by modern methods of investigation and are of considerable scientific and practical interest. I t should be noted that these reports and paper~ proved to be correct; reports were received with considerable interest among participants of the Symposium and were accepted for practical examination. Seven "Round Table" sessions were held at the Symposium. These sessions dealt with the following topics. 1. Modification of polymers--cenulose, polyolefins, polydienes, polyvinylchloride (condition and prospects) on a large scale. The discussion was conducted by D. B r a u n (German Federal Republic) and Z. A. Rogovin (U.S.S.R.). I t was noted at the meeting that the main trend in the coming years will be modification o f polymers b y large scale physical and chemical methods. Chief attention was given t ~ cellulose and its derivatives, polyolefins, polyvinylchloride, rubber, etc. Those taking part i n the discussion dealt with methods of modification such as using new solvents when preparing spinning solutions, copolymerization, including graft copolymerization, radiation effects, modification of fibres and rubber, problems of preparing incombustible materials based on traditional polymers. 2, Mechanism of stereoregulation in polymerization and eopolymerization, including alternating processes (experimental approach to the study). The discussion was conducted b y T. Tsuruta (Japan) and B. A. Dolgoplosk (U.S.S.R.). The main problem discussed by the participants of this meeting concerned methods of preparing stereospecific polymers during radical and ionic polymerization and methods of evaluating stereospecific properties. The chief methods of stereoregulation were found to be control of chain extension bearing in mind the structure of growing ends and the use of catalytic complexes, thus anionic polymerization and copolymerization of dienes m a y be controlled b y the action of carbonium complexes. I n radical polymerization stereospeeifie properties m a y be achieved by carrying out the process in the presence of an isotactic polymer. Considerable attention was given to problems of coordination of the monomer and polymer double bonds with a counterion during stereoregulation. Detailed study was made o f the formation of alternating polymers in radical polymerization. Considerable. attention was also given to polymerization of cyclic oxides and N-carboxy anhydrides. 3. Heat resistant polymers (synthesis, role of organic and hetero-organic fragments). The discussion was conducted by G. Butler (U.S.A.) and A. A. Zhdanov (U.S.S.R.). At this meeting the discussion was mainly concerned with the effect of chemical structure of linear a n d crosslinked polymers on heat resistance and heat stability. Considerable attention was given to organosilicon polymers and methods of evaluating heat resistance. Those taking part in the discussion noted that further studies are needed to deteymine characteristics of the concept "heat-stability" according to the name of the polymer. The opinion was expressed that the existence of chemical crosslinks in solid polymers enables heal stability to be increased since glass temperature increases at the same time and breakdown processes are hindered. For elastomers chemical bonds in the main chain have the chief role, they determine the heat stability of the material. For polyorganosiloxanes these characteristics are also considerably influenced b y the type of siloxane chain branch~ with

International symposium on macromolecular chemistry

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functional groups. Polyhe~eroarylenes obtained considerable attention in the discussion. 4. Physiologically active polymers (possibilities and limitations of synthesis and application). The discussion was headed b y G. Ringsdorf (German Federal Republic) and G. V. Samsonov (U.S.S.R.). Main attention in the discussion was given to problems of developing medicinal forms of synthetic polymers. This complex problem is solved at the present time b y various methods a n d covers aspects such as the behaviour of polymers in the organism, methods of addition of medicinal preparations to polymer molecules, methods of supply of medicinal preparations to the required place in the organism, complex formation, etc. The advantages a n d shortcoming of various types of polymer carrier, the effect of molecular weight and MWD on the physiological activity of medicinal preparation combined with the polymer, the effect of physico-chemical properties of macromolcculca on the effectiveness of "polymer ~rugs , etc. were discussed. Some papers were concerned with problems of antigenic properties of physiologically active polymers. Problems such as the effect of relation between medicinal substances and a polymer carrier (chemical bond and electrostatic interaction) on physiological activity, the possibility of using a n u m b e r of proteins and oligopcptides for metal transport in the organism, etc. were discussed. 5-6. Structure of amorphous polymers and mesophase (new methods of investigation and new ideas). Mechanical decomposition of polymers (the role of structure). Organized b y R. Boyer (U.S.A.), Iq. F. Bakeyev and V. R. Regel' (U.S.S.R.). Two extreme points of view were noted in connection with the structure of a m o r p h o u s polymers, one of which denies viscous structure in the amorphous state (P. Flory) and the second, recognizes the existence of ordered structural regions (V. A. Kargin and his followers). I n the course of discussing this problem all those organizing the discussion and those taking part debated various arguments supporting the existence of ordered structural elements in amorphous polymers both in the solid state and in melt. Various physical methods are used to analyse the structure of amorphous polymers: study of radial distribution of curves showing the intensity of X-ray scattering, diffraction methods (large angles), neutron diffraction analysis, optical polarization diffractometry, etc. I t was noted, however, t h a t analysis of results derived b y direct methods is not always simple. Useful information about the structure of amorphous polymers may be provided by indirect methods such as investigation of molecular mobility using paramagnetic tracers, sondes, etc. Although all those addressing the meeting unanimously took the view that amorphous polymers are ordered systems, the urgent problem is to develop new methods of structural investigation in these systems. 7. Compositions (structure of oligomers and topology of crosslinked polymers). The discussion was headed by K. Dushek (U.S.S.R.) and A. A. Berlin (U.S.S.R.). Two main problems were discussed at this meeting- network formation and the structure and properties of polymer mixtures. I n the discussion concerning the first problem c h i e f attention was given to the quantitative criterion of evaluating the point of gel formation a n d parameters of the three dimensional structure. Those addressing the meeting noted that existing simplified views about network formation in polymers do not reflect the enitre complexity of the variety of three dimensional structures formed and the absence of sole definitions hinders the identification of network parameters and the description of three dimensional polymerizatiorr and polycondensation. I n the discussion about the structure and properties of polymer mixtures attention was given to traditional problems such a s thermodynamic equilibrium in mixtures, the effect of heterogeneity and structure of intermediate layers, which determine to a large extent properties of polymer compositions. All " R o u n d Circle" meetings were very active and covered a great n u m b e r of fundamental problems which have to be solved in the field of investigating synthesis, structure and properties of polymers and compositions from them used for the most varied purposes._

~I16

V . A . VASNEV and A. A. As~rAus~

The symposium was closed on 21st October at the Plenary Session. V. A. Kabanov Corr. Member of the U.S.S.R. Academy of Sciences, Chairman of I U P A C addressed the final meeting on behalf of this Organization. O n behalf of foreign participants of the Symposium Prof. G. Klare, President of the Academy of Sciences, German Democratic Republic a n d Prof. R. Boyer, member of the National Academy of Engineers, U.S.A. and on behalf of chemists of Uzbekistan, Acad. A. S. Sadykev, President of the Uz.S.S.R. Academy of Sciences addressed the meeting. The Symposium was closed b y Acad. V. V. Korshak, Chairman of the Organizing Committee, who said. "We were all happy and pleased to receive the exceptional a t t e n t i o n paid to us and our science by the General Secretary Of the CC CPSU, Chairman of the Presidium of the Supreme Soviet of the U.S.S.R., Leonid II'ich Brezhnev. I t is our duty to be worthwile of this high honour and trust and give all our efforts to further develop our po l y m e r science and technology". Summing up the work of the Symposium V. V. Korshak named some of the most important trends in the development of polymer science, among them various aspects of improving the most important forms of polymerization and polyeondensation processes, first of all those, related to heavy polymers. Problems related to new initiating systems a n d .details of kinetics and mechanism of formation of polymers were therefore at the centre of attention of the Symposium. Considerable attention was given to the problem of synthesis of heat resistant polymers, which is particularly important in view of the continuously growing requirements facing these materials in the light of rapidly developing fields of new technology. Papers concerning the synthesis of new polymers with properties such as semiconductor, ion exchange, physiologically active properties and generally concerning polymers used in medicine, were of importance; m a n y branches of industry and public health are very interested in the development of these polymers. A study of problems related to degradation and stabilization and various measures of modification of properties of polymers, in order to improve quality and prolong service life were among significant results of the Symposium. This aspect is linked with an investigation of a number of fine chemical and physico-ehemical mechanisms. Problems related to the link between the structure and properties of polymeric substances, important from a theoretical and practical point of view, were discussed at tile various sections of this Symposium. The work of the section devoted to compositions was of special significance. The technical and economic significance of this problem is very considerable and successful solution requires careful fundamental study of the structure of these materials, its relation to properties, a study of the effect of mineral and organic fillers on properties of materials, etc., which was the aim of discussion at these meetings. At the cellulose section papers and discussions were concerned with modern views about the structure of cellulose and properties of its derivatives and problems which are not only of theoretical, b u t also of practical importance. I n his final address on behalf of the Organizing Committee and all participants of the Symposium Acad. V. V. Korshak thanked Sh. R. Rashidov, candidate member of the Political Bureau of CC of CPSU, first Secretary of the Communist P a r t y of Uzbekistan, the Government of the Republic, Uz.S.S.R. Academy of Sciences and all Republican Organizations for their enormous preparatory work and attention. V. V. Korshak noted the considerable contribution to the preparation of the Symposium of th~ group of Tashkent chemists a n d first of all, A. S. Sadykov, President of the Uz.S.S.R. Academy of Sciences, Acad. Kh. U. Usmanov of the Uz.S.S.R. Academy of Sciences and M.A. Askarov, Corr. Member of the Uz.S.S.R. Academy of Sciences. He also thanked IUPAC and especially its President, ProL 'G. Smets for his kind attention in organizing the Symposium. Trar~late, d by E. SEMEP~