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An investigation of structure formation in polystyrene sodium sulphonate
2032
V . A . KARGI~ et al.
REFERENCES
1. V. A. KARGIN, V. G. ZI~URAVLEVA and Z. Ya. BERESTNEVA, DokJ. Akad. Nauk SSSR 144: 1089, 1962 2. Yu. K. OVCHINNIKOV, G. S. MARKOVA and V. A. KARGIN, Vysokomol. soyed. Ag: 449, 1967 (Translated in Polymer Sci. U.S.S.R. 9: 2, 505, 1967) 3. Yu. K. OVCHINNIKOV, G. S. MARKOVA and V. A. KARGIN, Vysokomol. soyed. Al1: 329, 1969 (Translated in Polymer Sci. U.S.S.R. 11: 2, 369, 1969) 4. V. K. KALASHNIKOVA, Dissertation, 1965 5. A. F. SKRYSHEVSKII, Rentgenografiya zhidkostei (The X-ray Scattering by Liquids). Kiev, 1966 6. B. K. VAINSHTEIN, Strukturnaya elektronografiya (Structural Electron Scattering). Izd. Akad. Nauk SSSR, 1956 7. L. I. MIRKIN, Spravochnik po rentgenostrukturnomu analizu polikristallov (Handbook for the X-ray Structural Analysis of Polycrystals). Fiz. Mat. Gos. Izd., 1961 8. C. W. BUNN, Proc. Royal Soc. 180: 40, 1942 9. C. S. FULLER, J. Am. Chem. Soc. 62: 1905, 1940 10. A. I. MAREI and G. E. NOVIKOVA, Kuchuk i rezina No. 10, 7. 1964 11. G. BARRON, Sovremennye sinteticheskie kauchuki (Modern Synthetic Rubbers). Gos. Khim. Izd., 1948
AN INVESTIGATION OF STRUCTURE FORMATION IN POLYSTYRENE SODIUM SULPHONATE* V. A. KARGIN (dec.), T. A. KORETSKAYA, A. M. KHARLAMOVA, G. S. MARKOVA a n d Y v . K . 0VCHII~NIKOV L. Ya. Karpov Physicochemical Research Institute
(Received 23 February 1970) POLYELECTROLYTES h a v e b e e n of considerable interest to a u t h o r s in r e c e n t y e a r s in v i e w of t h e i m p o r t a n c e o f these p o l y m e r s b o t h f r o m a p r a c t i c a l a n d f r o m a scientific s t a n d p o i n t . P o l y e l e c t r o l y t e s are e n c o u n t e r e d in studies o f t h e tissues o f living organisms; m o r e o v e r t h e y are used as i o n - e x c h a n g e m a t e r i a l s in m e d i cine a n d biology [1-3], as s o r b e n t s [4], a n d also as m a t r i c e s in p o l y m e r i z a t i o n processes [5] etc. M a n y of t h e p r o p e r t i e s of p o l y m e r i c m a t e r i a l s are r e l a t e d to t h e chemical s t r u c t u r e of t h e p o l y m e r chain a n d t h e configuration a n d c o n f o r m a t i o n o f t h e macromolecules, as well as to t h e s u p e r m o l e c u l a r s t r u c t u r e s f o r m e d in t h e p r e p a r a t i o n of p o l y m e r i c materials. I o n o g e n i e g r o u p s in p o l y m e r i c electrolytes are of m a j o r i m p o r t a n c e in t h e f o r m a t i o n of materials. W i t h c o p o l y m e r s o f a-olefins w i t h c a r b o x y l i c acids as e x a m p l e s it was s h o w n t h a t i n t e r m o l e c u l a r ionic b o n d s * Vysokomol. soyed. A13: No. 8, 1811-1818, 1971.
Investigation of structure formation in polystyrene sodium sulphonate
2033
reduce the ability of polyelectrolytes to form crystalline supermolecular struotures, while at the same time t h e y enhance the tensile strength and the elastic properties of the materials, and increase the rigidity of the polymer chains [6]. Of particular interest are strong polyelectrolytes containing ionogenic sulpho-groups completely dissociated in a wide pH interval. Crosslinked strong polyelectrolytes are used inter alia as ion-exchange resins and membranes. There is very little information in the literature in regard to the structure of linear strong polyelectrolytes [7, 8], and a study of these polymers should therefore be of interest. The present investigation was carried out with samples of linear polystyrene sodium sulphonate (PSSNa). EXPERIMENTAL
The investigated polymer was of medium molecular weight (300,000), and was prepared by radical polymerization initiated by ~ light in an aqueous solution of the p-styrene sodium sulphonate monomer. The polymer was purified by reprecipitation ~om aqueous solution by methanol. The molecular weight was determined from the viscometric measurements using the formula [~] =5-75 × 10-~ P (in 0.5 N l~aC1) [9]. The melting point of the polymer is higher than the degradation temperature, and could not be determined. The polymer decomposes at temperatures of around 330°. In this investigation we studied structure formation processes in PSSNa using a polarizing microscope together with electron microscopic and X-ray analysis. The samples used in the experiments were prepared by applying aqueous solutions of the polymer to a substrate (from 0.02 to 1.5 g of the investigated substance in 100 ml water). The substrates were provided by amorphous polymers of different chemical natures such as atactic polystyrene, chlorosulphonated polyethylene, polymethylmethacrylate, cellulose nitrate, and also glass. The polymer films for the optical experiments were prepared on glass, and on the substrates referred to above which had first been coated on glass. The samples for the electron microscope studies were prepared on mesh supports which had first been coated with the substrates. The original polymer subjected to X-ray structural analysis was either in powder form or in the form of isotropic films (thickness 240 p) or films oriented by 3-3.5-fold extension. The isotropic translucent film was obtained from aqueous solution on a glass surface. The oriented film was prepared by placing a portion of the isotropic film in an atmosphere of water vapour at 25 °, where it was kept for 5 hr, and then stretched. On drying the oriented structure of this film was preserved. Optical investigations Optical microscope studies of the PSSNa showed t h a t structure formation* in the latter was accompanied by the emergence of dendrites and spherulitic formations of radial, ring-shaped and mixed structures. Figure la-c shows the results of examination of PSSNa on the glass substrates. The particular nature of the polymeric substrates has no great effect on the morpho* The process of structure-formation does not cover the entire film; there is apparently some disordered fraction in the polymer.
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V . A . KARGIN et al.
FIG. 1. Optical investigations of PSSNa; in polarized light with crossed nicols: a - c - - g l a s s substrate; d--chlorosulphonated polyethylene substrate, t e m p e r a t u r e for p r e p a r a t i o n a n d dissolution of the samples, 5°;e-j--glass substrate, t e m p e r a t u r e of sample preparation, 25 °, dissolution temperature, 25 ° (e, f ), -- 55 ° (g, h) a n d -- 92 ° (i, j).
Investigation of structure formation in polystyrene sodium sulphonate
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•!I¸,~i~ FIG. 2. Electron microscopic investigations of PSSNa: a , b - - q u a r t z substrate, freshly-prepared samples; c - e - - g u a r t z substrate after structure formation for two months a t 25 °, temperature of preparation and dissolution of samples, 5°; f--cellulose nitrate substrate, temperature of preparation and dissolution of samples, 5°; g-/--ceUulose nitrate substrate; after structure formation at 25 ° for one (g) and two (h, i) months, temperature of preparation a n d dissolution of samples, 25 ° .
logy of the structural formations. All the photographs show spherulites, sometimes as large as 500/~. Figure ld corresponds to PSSNa investigated on substrates of chlorosulphonated polyethylene; similar structures were obtained on other polymeric substrates also. However, on glass, as was shown above (Fig. 1) a great variety of more clearly defined structures is formed. One m a y assume that glass provides the nuclei of structure-formation in PSSI~a. The nucleating properties of glass would probably also account for the large forces of polymerglass interaction observed in the experiment. As was shown in investigations with other polymers [10] the prehistory of the solution has a marked effect upon processes of structure formation. PSSNa
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V.A. KARG~ et al.
was structurized from solutions prepared at different temperatures. With solutions in the region of 5 to 55 ° the nuclei are apparently not completely destroyed, and so the morphology and the size of the structures formed from these solutions differ only to an inconsiderable extent (see Fig. le-h, and similarly Fig. la-c). At temperatures of the order of 92 ° it is probable t h a t the nuclei are completely destroyed, with the result t h a t structure-formation in the films takes rather a long time, e.g. 30 days at 25 °. As is seen from Fig. 1i, j, smaller structures of a rather different morphological type are formed under these conditions. A rise in the dissolution temperature therefore results in destruction of the nuclei in polyelectrolyte solutions also. The viscosity of the solution alters the mobility of the molecules and their associates, and in this way has a direct effect on the structure-formation processes. Virtually no structure-formation takes place with solutions containing 5 g of PSSNa in 100 ml of water. The experiments showed that the optimal concentrations would be 0.1-1.2 g of polymer in 100 ml of water. Electron microscopic investigations. Electron microscopic analysis was carried out to determine the fine structure of PSSI~a. I t was found t h a t ff the structure formation took place at a temperature of the order of 5 °, the polymer separating from solution on the quartz substrate (see Fig. 2a, b) was in the form of a structureless film containing well-defined fibril-clusters sometimes covering the entire viewing field. In the course of two months (the samples were kept at 25 °) spherulitic and crystalline structures were found as well as the fibril-clusters (Fig. 2, c-e). Moreover it is noteworthy t h a t the structures of type 2b remained constant with time. Far fewer fibril-clusters appear on the cellulose nitrate substrates, and t h e y are not very well defined. More frequently one finds branched fibrils growing along the edges of the structureless film, or covering the entire viewing field (Fig. 2]). Similarly on the cellulose nitrate substrates, structure formation takes place progressively with time. In 1-3.5 months (the samples were kept at 25 °) structuration takes place in PSSNa; as is seen from Fig. 2g-/ there are spherulitic and laminar crystalline structures which are morphologically somewhat different from those shown in Fig. 2c-e, and this is probably due to the nature of the substrate. In the light of the electron microscopic analysis it appears therefore that structuration takes place in polystyrene sodium sulphonate, and that a large number of different structures are formed. On a glass or quartz substrate the structuration process is more rapid, and the assumption made on the basis of optical studies t h a t glass is the structuration nucleus in PSSNa is confirmed by the electron microscope experiments. X-ray structural investigations. The photographing was done with a planecassette camera, CuK, radiation, 1~i filter. The X-ray patterns obtained for the isotropic original sample in powder form, and for the optically translucent (unstructurized) film consisted of a single very sharp peak corresponding to a distance of 16.7/~, and two diffuse peakscorres ponding to distances of ~5.1 and 3.3 A.
Investigation of structure formation in polystyrene sodium sulphonate
2037
A texture-gram was also obtained for the same polymer; it resembles the X-ray patterns of proteins (keratin, myosin, etc.) [11] and consisted of a sharp equatorial reflection corresponding to 16.7 •, and a very diffuse meridional reflection cor-
FIG. 3. Model of PSSNa molecule along (a) and perpendicular to (b) the molecular axis. responding to 5.1 A: the third reflection remains practically isotropic. Possible models of the PSSNa molecule were investigated to account for the X-ray pattern. The concept of an isotactic configuration for the PSSI~a molecule is bound to involve the latter having a helical conformation, which would mean that the helical axis period will be not less than 6.65 A. The X-ray pattern has a peak corresponding to a distance of 5.1 A in respect to the molecular axis, which is possible only in the case of a planar zigzag conformation for the main chain. This means that the molecule could only have a syndiotactic configuration: an isotactic arrangement of benzene rings would be sterically impossible in the case of a planar zigzag. Figure 3a, b is a photograph of the P S S N a molecule with a syndiotactic configuration taken along (cross section) and perpendicular to the molecular axis. An arrangement of the P S S N a molecules as seen in Fig. 4 was designed to explain the observed diffraction pattern on the basi~ of compact packing. The mutual contact of the long sides of the molecules probably ensures good Van der Waals interaction between them, leading to the formation of monomolecular layers with a thickness of 16.7/~. With this type of packing the sulpho-groups appear on the surface. To some extent the behaviour of these layers resembles that of the smectic layers in liquid crystals (in contrast to liquid crystals the P S S N a molecules are parallel to the layers). The monomolecular layers m a y be displaced relative to one another and sag, with consequent loss of long-range ordering in the layer itself and also between the layers, leading to the loss of crystalline diffraction. However, a period corresponding to a layer thickness of 16.7 A is plainly evident in the isotropic X-ray patterns. The spacing between adjacent molecules in the same layer was measured, and found to be 7.4 A. The calculated value of the density for this type of packing was 1.1 g/cm a. I n the calculations it was assumed that the benzene rings were in the base plane. Some
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V . A . I r ~ c t i ~ eta/.
dogree of rotation of the benzene rings about their single bond with the molecular skeleton could bring the molecules in the layers closer together, and this in the final analysis could lead to higher density.
FIG. 4. Packing of PSSNa molecules. As was shown above the texture-gram has not only a sharp equatorial reflection but also a weakly oriented meridional one corresponding to 5-1 A, i.e. along with the very good orientation of the layers along the direction of stretch there is also poorly defined orientation of the molecules along the texture axis. This could be explained ff we begin by assuming that in the stretching process there m a y be some slipping of the layers relative to one another in practically any direction covered by the glide plane; this could be due to the large amount of water in the space between the layers. At the same time there is only very slight preference for slipping .of layers in the direction in which the molecules are arranged in the layers, and this leads to the slight meridional orientation of the reflection corresponding to the period along the molecular axis.
r(p) L
"'EA 01~
I,I
,
/,AV
",'~'~#~..i
I.
#'%. A I .
F~e. 5. Difference curve of radial dislbribution for PSSNa, 18°. difference curve for PSSNa was also obtained (see Fig. 5) for the radial distribution of electrons using the formula F ( r ) ~ 4ur2[p (r)--po]. In view of the fact t h a t the experimental intensity curve was plotted on a DRON-1 diffracto-
Investigation of structure formation in polystyrene sodium sulphonate
2039
meter up to angles ibased on S=~ 3-4 A a short-range at 1 _~ maximum appeared on the radial distribution curve corresponding to poorly resolved C--C and C--It basic bonds. An intramolecular maximum then appeared at 2.6 A corresponding to the C--C--C spacing along the chain and to the spacing between single Catoms in the benzene ring. Two intramolecular peaks characteristic of polystyrene appeared at distances of 4.7 and 6.95 A. In the region of 9.5 to 13 A a peak appeared which in all probability is of an intermolecular ,aature and corresponds to adjacent molecules lying in the same layer. The second order of the inter-layer intermolecular maximum, where it exists, may be superimposed on the first order for the inter-layer maximum, together resulting in an extremely broad peak in the region of 18 to 28 A. On analysing the radial distribution curve one may conclude that the molecules in the layers themselves and in the spaces between the layers are interrelated right up to considerable distances of 30 A, which is unquestionably due to the good mutual ordering of the molecules in the layers and of the layers in respect to one another. DISCUSSION OF RESULTS
Structure formation processes in polystyrene sodium sulphonate were investigated by different methods (optical polarizing microscopy, electron microscopy) and a great variety of morphological structures were found, ranging from fibrils to spherulitic and crystalline-like lameUar formations. The experiments showed that the nature of the investigated polymeric substrates has no significant effect on the morphology of the structural formations; on glass the process of structure formation takes place more rapidly, and this is attributed to the nucleating action of glass. The structuration of PSSI~a proceeds progressively with time. In the process of film preparation the optimal concentration of polymer in solution is n.ot more than 1-2-1.5 g per 100 ml of water. The films prepared from viscous solutions show practically no structuration (3-5 g in 100 ml of water). It was shown that dissolution of the polymer in the temperature range from 5 to 55 ° does not cause complete loss of the nuclei, and the structuration of the polymer takes place at an accelerated rate. At temperatures of the order of 92 ° there is apparently complete destruction of the nuclei, and a longer period is necessary (30 days) for the formation of structures in the films prepared from these solutions. Structuration processes in PSSNa films therefore obey the usual laws pertaining to polymers. As the decomposition temperature for PSSI~a is lower than the melting point heat treatment has no effect on the structuration processes. The main factors governing structure-formation in PSSNa are the prehistory of the solution, the concentration of the solution, and the type of substrate. X-ray structural investigations of PSSNa showed that the polymer molecules have syndiotactic structure and are packed in monomolecular layers with good mutual ordering, with the sulpho-groups appearing on the surface of the layers, thus facilitating the diffusion of H~O molecules into the spaces (inter-layers)
2040
V.A. KARGINet al.
between the monomolecular layers. This special type of structure enables the polymer molecules to absorb and give off large amounts of water. This also accounts for the peculiar behaviour of the polymer under deformation (stretching) giving rise to good orientation of the layers relative to one another with a practically complete absence of orientation in the arrangement of the molecules in adjacent layers. I t is this type of highly-ordered system which probably accounts for the formation of highly organized structures (fibrils, spherulitic and crystallinelike formations) which were revealed in the course of the optical and electron microscope studies of investigated polymer. The syndiotactic regular structure of polystyrene sodium sulphonate is probably due to preferential addition of the monomer in the "head-to-tail" manner as a result of the electrostatic interaction and the steric hindrances that appear in aqueous solution in the radical polymerization of p-styrene sodium sulphonate
[12]. CONCLUSIONS
(1) A study has been made of structuration processes and of the chain configuration and conformation of polystyrene sodium sulphonate, which is a strong polyeleetrolyte. (2) Optical microscopy and electron microscopy were used to analyse the effect of the substrates, the dissolution temperature and the time factor on structure-forming processes in PSSI~a. (3) A great variety of structures ranging from fibrillar formations to spherulitic and crystal-like lamellar structures were discovered. (4) The X-ray diffraction patterns showed that the polymer molecules have a syndiotactic structure and a planar zigzag conformation. (5) The radial distribution curve calculated for PSSI~a confirmed the good mutual ordering of the polymer molecules. (6) On the basis of the X-ray structural analysis and the radial distribution curve it is shown that PSSNa is a well-ordered system and this would account for the formation of the highly ordered structures observed b y optical microscopy and b y electron microscopic analysis. Translated by R. J. A. HENDRr REFERENCES
1. K. P. KHOMYAKOV, A. D. VIRNIK and Z. A. ROGOVIN, Uspekhi khimii 33: 1061, 1964 2. I. B. ADEL and S. A. DMITRIEV, Ioanyi obmen in yego primenenie (Ion Exchange and its Uses). Izd. AN SSSR, p. 307, 1959 3. A. KHAMENGI and G. FLANACHAK, The Medical Use of Ion-exchange Resins, 1956 4 . V. A. KARGIN, M. E. BOGDANOV and E. P. CHERNEVA, Vysokomol. soyed. A10: 429, 1968 (Translated in Polymer Sci. U.S.S.R. 1O: 2, 500, 1968) 5. V. A. KARGIN, V. A. KABANOV and O. V. KARGINA, ]:)ok]. AN SSSR 161: 1131, 1965 6. R. REdS and D. VAUGHAN, Polymer Preprints 6: 287, 1965
Comparison of acetylation of cellulose and a polysaceharide
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7. V. A. KARGIN, Z. Ya. BERESTNEVA, E. P. CHERNEVA, T. D. IGNATOVICH and G. S. POTAPOVA, Dok]. A N SSSR 175: 1318, 1967 8. A. M. gHARLAMOVA, E. P. CHERNEVA and Z. Ya. BERESTNEVA, Vysokomo].
soyed. Bg: 635, 1967 (Not translated in Polymer Sci. U.S.S.R.) 9. M. KATO, T. NAKAGAWA and H. AKAMATU, Bull. Chem. Soe. Japan 33: 322, 1960 10. V. A. KARGIN, T. A. KORETSKAYA and T. A. BOGAYEVSKAYA, Vysokomol. soyed. 6: 441, ]964 (Translated in Polymer Sci. U.S.S.R. 6: 3, 489, 1964) 11. B. K. VAINSHTEIN, Difraktsiya rentgenovskikh luehei na tsepnykh molekulakh (X-ray Diffraction by Chain Molecules). Izd. AN SSSR, p. 328, 1963 12. S. E. BRESLER and B. L. YERUSALIMSKII, Fizika i khimiya makromolekul (Chemistry and Physics of Macromolecules). Izd. "Nauka", 234, 1965
A COMPARISON OF THE ACETYLATION OF CELLULOSE AND A POLYSACCHARIDE CONTAINING BOTH GLUCOSE AND 3,6-ANHYDROGLUCOSE UNITS* L. P. TKACHEVA, E. L. AKn~ a n d L. S. GAL'BRAIKH Moscow Textile Institute S. M. Kirov Leningrad Light Industry and Textile Institute
(Received 24 February 1970) O ~ L ¥ a r e l a t i v e l y small n u m b e r of p a p e r s has b e e n p u b l i s h e d concerning t h e s y n t h e s i s o f m i x e d p o l y s a e c h a r i d e s containing glucose a n d 3,6-anhydroglucose units [1-3]. N o s y s t e m a t i c s t u d y o f t h e p r o p e r t i e s o f a m i x e d p o l y s a c c h a r i d e of t h i s t y p e has y e t b e e n m a d e , t h o u g h t h e effect of fine s t r u c t u r a l differences in t h e e l e m e n t a r y u n i t s o f p o l y s a c c h a r i d e s on t h e p r o p e r t i e s o f t h e l a t t e r w o u l d d o u b t l e s s be o f considerable i n t e r e s t to investigators. O u r a i m in this i n v e s t i g a t i o n w a s t o m a k e a c o m p a r a t i v e s t u d y o f t h e rea c t i v i t y o f cellulose a n d a m i x e d p o l y s a c c h a r i d e containing glucose a n d 3,6a n h y d r o g l u c o s e units in a c e t y l a t i o n reactions. The mixed polysaccharide was synthesized by the method used in reference [4] by a l l , line saponification of cellulose tosylates. The monosaccharide composition of the mixed polysaceharide compounds with different contents of 3,6-anhydroglucose, and also of the products of aeetylation of these compounds, was determined by quantitative paper chromatographic analysis of the products of complete hydrolysis [5]. The acetylation of cellulose and mixed polysaeeharides was investigated in homo- and heterogeneous media. Cotton cellulose and mixed polysaccharide compounds containing 17 (I) and 70 (II) mole~o of 3,6-anhydroglueose were subjected to acetylation in a homogeneous medium. The study of the acetylation process in a homogeneous medium was based on the changes in the electrical conductivity of the system [6]. * Vysokomol. soyed. A13: No. 8, 1819-1824, 1971.
V . A . KARGI~ et al.
REFERENCES
1. V. A. KARGIN, V. G. ZI~URAVLEVA and Z. Ya. BERESTNEVA, DokJ. Akad. Nauk SSSR 144: 1089, 1962 2. Yu. K. OVCHINNIKOV, G. S. MARKOVA and V. A. KARGIN, Vysokomol. soyed. Ag: 449, 1967 (Translated in Polymer Sci. U.S.S.R. 9: 2, 505, 1967) 3. Yu. K. OVCHINNIKOV, G. S. MARKOVA and V. A. KARGIN, Vysokomol. soyed. Al1: 329, 1969 (Translated in Polymer Sci. U.S.S.R. 11: 2, 369, 1969) 4. V. K. KALASHNIKOVA, Dissertation, 1965 5. A. F. SKRYSHEVSKII, Rentgenografiya zhidkostei (The X-ray Scattering by Liquids). Kiev, 1966 6. B. K. VAINSHTEIN, Strukturnaya elektronografiya (Structural Electron Scattering). Izd. Akad. Nauk SSSR, 1956 7. L. I. MIRKIN, Spravochnik po rentgenostrukturnomu analizu polikristallov (Handbook for the X-ray Structural Analysis of Polycrystals). Fiz. Mat. Gos. Izd., 1961 8. C. W. BUNN, Proc. Royal Soc. 180: 40, 1942 9. C. S. FULLER, J. Am. Chem. Soc. 62: 1905, 1940 10. A. I. MAREI and G. E. NOVIKOVA, Kuchuk i rezina No. 10, 7. 1964 11. G. BARRON, Sovremennye sinteticheskie kauchuki (Modern Synthetic Rubbers). Gos. Khim. Izd., 1948
AN INVESTIGATION OF STRUCTURE FORMATION IN POLYSTYRENE SODIUM SULPHONATE* V. A. KARGIN (dec.), T. A. KORETSKAYA, A. M. KHARLAMOVA, G. S. MARKOVA a n d Y v . K . 0VCHII~NIKOV L. Ya. Karpov Physicochemical Research Institute
(Received 23 February 1970) POLYELECTROLYTES h a v e b e e n of considerable interest to a u t h o r s in r e c e n t y e a r s in v i e w of t h e i m p o r t a n c e o f these p o l y m e r s b o t h f r o m a p r a c t i c a l a n d f r o m a scientific s t a n d p o i n t . P o l y e l e c t r o l y t e s are e n c o u n t e r e d in studies o f t h e tissues o f living organisms; m o r e o v e r t h e y are used as i o n - e x c h a n g e m a t e r i a l s in m e d i cine a n d biology [1-3], as s o r b e n t s [4], a n d also as m a t r i c e s in p o l y m e r i z a t i o n processes [5] etc. M a n y of t h e p r o p e r t i e s of p o l y m e r i c m a t e r i a l s are r e l a t e d to t h e chemical s t r u c t u r e of t h e p o l y m e r chain a n d t h e configuration a n d c o n f o r m a t i o n o f t h e macromolecules, as well as to t h e s u p e r m o l e c u l a r s t r u c t u r e s f o r m e d in t h e p r e p a r a t i o n of p o l y m e r i c materials. I o n o g e n i e g r o u p s in p o l y m e r i c electrolytes are of m a j o r i m p o r t a n c e in t h e f o r m a t i o n of materials. W i t h c o p o l y m e r s o f a-olefins w i t h c a r b o x y l i c acids as e x a m p l e s it was s h o w n t h a t i n t e r m o l e c u l a r ionic b o n d s * Vysokomol. soyed. A13: No. 8, 1811-1818, 1971.
Investigation of structure formation in polystyrene sodium sulphonate
2033
reduce the ability of polyelectrolytes to form crystalline supermolecular struotures, while at the same time t h e y enhance the tensile strength and the elastic properties of the materials, and increase the rigidity of the polymer chains [6]. Of particular interest are strong polyelectrolytes containing ionogenic sulpho-groups completely dissociated in a wide pH interval. Crosslinked strong polyelectrolytes are used inter alia as ion-exchange resins and membranes. There is very little information in the literature in regard to the structure of linear strong polyelectrolytes [7, 8], and a study of these polymers should therefore be of interest. The present investigation was carried out with samples of linear polystyrene sodium sulphonate (PSSNa). EXPERIMENTAL
The investigated polymer was of medium molecular weight (300,000), and was prepared by radical polymerization initiated by ~ light in an aqueous solution of the p-styrene sodium sulphonate monomer. The polymer was purified by reprecipitation ~om aqueous solution by methanol. The molecular weight was determined from the viscometric measurements using the formula [~] =5-75 × 10-~ P (in 0.5 N l~aC1) [9]. The melting point of the polymer is higher than the degradation temperature, and could not be determined. The polymer decomposes at temperatures of around 330°. In this investigation we studied structure formation processes in PSSNa using a polarizing microscope together with electron microscopic and X-ray analysis. The samples used in the experiments were prepared by applying aqueous solutions of the polymer to a substrate (from 0.02 to 1.5 g of the investigated substance in 100 ml water). The substrates were provided by amorphous polymers of different chemical natures such as atactic polystyrene, chlorosulphonated polyethylene, polymethylmethacrylate, cellulose nitrate, and also glass. The polymer films for the optical experiments were prepared on glass, and on the substrates referred to above which had first been coated on glass. The samples for the electron microscope studies were prepared on mesh supports which had first been coated with the substrates. The original polymer subjected to X-ray structural analysis was either in powder form or in the form of isotropic films (thickness 240 p) or films oriented by 3-3.5-fold extension. The isotropic translucent film was obtained from aqueous solution on a glass surface. The oriented film was prepared by placing a portion of the isotropic film in an atmosphere of water vapour at 25 °, where it was kept for 5 hr, and then stretched. On drying the oriented structure of this film was preserved. Optical investigations Optical microscope studies of the PSSNa showed t h a t structure formation* in the latter was accompanied by the emergence of dendrites and spherulitic formations of radial, ring-shaped and mixed structures. Figure la-c shows the results of examination of PSSNa on the glass substrates. The particular nature of the polymeric substrates has no great effect on the morpho* The process of structure-formation does not cover the entire film; there is apparently some disordered fraction in the polymer.
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V . A . KARGIN et al.
FIG. 1. Optical investigations of PSSNa; in polarized light with crossed nicols: a - c - - g l a s s substrate; d--chlorosulphonated polyethylene substrate, t e m p e r a t u r e for p r e p a r a t i o n a n d dissolution of the samples, 5°;e-j--glass substrate, t e m p e r a t u r e of sample preparation, 25 °, dissolution temperature, 25 ° (e, f ), -- 55 ° (g, h) a n d -- 92 ° (i, j).
Investigation of structure formation in polystyrene sodium sulphonate
2035
•!I¸,~i~ FIG. 2. Electron microscopic investigations of PSSNa: a , b - - q u a r t z substrate, freshly-prepared samples; c - e - - g u a r t z substrate after structure formation for two months a t 25 °, temperature of preparation and dissolution of samples, 5°; f--cellulose nitrate substrate, temperature of preparation and dissolution of samples, 5°; g-/--ceUulose nitrate substrate; after structure formation at 25 ° for one (g) and two (h, i) months, temperature of preparation a n d dissolution of samples, 25 ° .
logy of the structural formations. All the photographs show spherulites, sometimes as large as 500/~. Figure ld corresponds to PSSNa investigated on substrates of chlorosulphonated polyethylene; similar structures were obtained on other polymeric substrates also. However, on glass, as was shown above (Fig. 1) a great variety of more clearly defined structures is formed. One m a y assume that glass provides the nuclei of structure-formation in PSSI~a. The nucleating properties of glass would probably also account for the large forces of polymerglass interaction observed in the experiment. As was shown in investigations with other polymers [10] the prehistory of the solution has a marked effect upon processes of structure formation. PSSNa
2036
V.A. KARG~ et al.
was structurized from solutions prepared at different temperatures. With solutions in the region of 5 to 55 ° the nuclei are apparently not completely destroyed, and so the morphology and the size of the structures formed from these solutions differ only to an inconsiderable extent (see Fig. le-h, and similarly Fig. la-c). At temperatures of the order of 92 ° it is probable t h a t the nuclei are completely destroyed, with the result t h a t structure-formation in the films takes rather a long time, e.g. 30 days at 25 °. As is seen from Fig. 1i, j, smaller structures of a rather different morphological type are formed under these conditions. A rise in the dissolution temperature therefore results in destruction of the nuclei in polyelectrolyte solutions also. The viscosity of the solution alters the mobility of the molecules and their associates, and in this way has a direct effect on the structure-formation processes. Virtually no structure-formation takes place with solutions containing 5 g of PSSNa in 100 ml of water. The experiments showed that the optimal concentrations would be 0.1-1.2 g of polymer in 100 ml of water. Electron microscopic investigations. Electron microscopic analysis was carried out to determine the fine structure of PSSI~a. I t was found t h a t ff the structure formation took place at a temperature of the order of 5 °, the polymer separating from solution on the quartz substrate (see Fig. 2a, b) was in the form of a structureless film containing well-defined fibril-clusters sometimes covering the entire viewing field. In the course of two months (the samples were kept at 25 °) spherulitic and crystalline structures were found as well as the fibril-clusters (Fig. 2, c-e). Moreover it is noteworthy t h a t the structures of type 2b remained constant with time. Far fewer fibril-clusters appear on the cellulose nitrate substrates, and t h e y are not very well defined. More frequently one finds branched fibrils growing along the edges of the structureless film, or covering the entire viewing field (Fig. 2]). Similarly on the cellulose nitrate substrates, structure formation takes place progressively with time. In 1-3.5 months (the samples were kept at 25 °) structuration takes place in PSSNa; as is seen from Fig. 2g-/ there are spherulitic and laminar crystalline structures which are morphologically somewhat different from those shown in Fig. 2c-e, and this is probably due to the nature of the substrate. In the light of the electron microscopic analysis it appears therefore that structuration takes place in polystyrene sodium sulphonate, and that a large number of different structures are formed. On a glass or quartz substrate the structuration process is more rapid, and the assumption made on the basis of optical studies t h a t glass is the structuration nucleus in PSSNa is confirmed by the electron microscope experiments. X-ray structural investigations. The photographing was done with a planecassette camera, CuK, radiation, 1~i filter. The X-ray patterns obtained for the isotropic original sample in powder form, and for the optically translucent (unstructurized) film consisted of a single very sharp peak corresponding to a distance of 16.7/~, and two diffuse peakscorres ponding to distances of ~5.1 and 3.3 A.
Investigation of structure formation in polystyrene sodium sulphonate
2037
A texture-gram was also obtained for the same polymer; it resembles the X-ray patterns of proteins (keratin, myosin, etc.) [11] and consisted of a sharp equatorial reflection corresponding to 16.7 •, and a very diffuse meridional reflection cor-
FIG. 3. Model of PSSNa molecule along (a) and perpendicular to (b) the molecular axis. responding to 5.1 A: the third reflection remains practically isotropic. Possible models of the PSSNa molecule were investigated to account for the X-ray pattern. The concept of an isotactic configuration for the PSSI~a molecule is bound to involve the latter having a helical conformation, which would mean that the helical axis period will be not less than 6.65 A. The X-ray pattern has a peak corresponding to a distance of 5.1 A in respect to the molecular axis, which is possible only in the case of a planar zigzag conformation for the main chain. This means that the molecule could only have a syndiotactic configuration: an isotactic arrangement of benzene rings would be sterically impossible in the case of a planar zigzag. Figure 3a, b is a photograph of the P S S N a molecule with a syndiotactic configuration taken along (cross section) and perpendicular to the molecular axis. An arrangement of the P S S N a molecules as seen in Fig. 4 was designed to explain the observed diffraction pattern on the basi~ of compact packing. The mutual contact of the long sides of the molecules probably ensures good Van der Waals interaction between them, leading to the formation of monomolecular layers with a thickness of 16.7/~. With this type of packing the sulpho-groups appear on the surface. To some extent the behaviour of these layers resembles that of the smectic layers in liquid crystals (in contrast to liquid crystals the P S S N a molecules are parallel to the layers). The monomolecular layers m a y be displaced relative to one another and sag, with consequent loss of long-range ordering in the layer itself and also between the layers, leading to the loss of crystalline diffraction. However, a period corresponding to a layer thickness of 16.7 A is plainly evident in the isotropic X-ray patterns. The spacing between adjacent molecules in the same layer was measured, and found to be 7.4 A. The calculated value of the density for this type of packing was 1.1 g/cm a. I n the calculations it was assumed that the benzene rings were in the base plane. Some
2038
V . A . I r ~ c t i ~ eta/.
dogree of rotation of the benzene rings about their single bond with the molecular skeleton could bring the molecules in the layers closer together, and this in the final analysis could lead to higher density.
FIG. 4. Packing of PSSNa molecules. As was shown above the texture-gram has not only a sharp equatorial reflection but also a weakly oriented meridional one corresponding to 5-1 A, i.e. along with the very good orientation of the layers along the direction of stretch there is also poorly defined orientation of the molecules along the texture axis. This could be explained ff we begin by assuming that in the stretching process there m a y be some slipping of the layers relative to one another in practically any direction covered by the glide plane; this could be due to the large amount of water in the space between the layers. At the same time there is only very slight preference for slipping .of layers in the direction in which the molecules are arranged in the layers, and this leads to the slight meridional orientation of the reflection corresponding to the period along the molecular axis.
r(p) L
"'EA 01~
I,I
,
/,AV
",'~'~#~..i
I.
#'%. A I .
F~e. 5. Difference curve of radial dislbribution for PSSNa, 18°. difference curve for PSSNa was also obtained (see Fig. 5) for the radial distribution of electrons using the formula F ( r ) ~ 4ur2[p (r)--po]. In view of the fact t h a t the experimental intensity curve was plotted on a DRON-1 diffracto-
Investigation of structure formation in polystyrene sodium sulphonate
2039
meter up to angles ibased on S=~ 3-4 A a short-range at 1 _~ maximum appeared on the radial distribution curve corresponding to poorly resolved C--C and C--It basic bonds. An intramolecular maximum then appeared at 2.6 A corresponding to the C--C--C spacing along the chain and to the spacing between single Catoms in the benzene ring. Two intramolecular peaks characteristic of polystyrene appeared at distances of 4.7 and 6.95 A. In the region of 9.5 to 13 A a peak appeared which in all probability is of an intermolecular ,aature and corresponds to adjacent molecules lying in the same layer. The second order of the inter-layer intermolecular maximum, where it exists, may be superimposed on the first order for the inter-layer maximum, together resulting in an extremely broad peak in the region of 18 to 28 A. On analysing the radial distribution curve one may conclude that the molecules in the layers themselves and in the spaces between the layers are interrelated right up to considerable distances of 30 A, which is unquestionably due to the good mutual ordering of the molecules in the layers and of the layers in respect to one another. DISCUSSION OF RESULTS
Structure formation processes in polystyrene sodium sulphonate were investigated by different methods (optical polarizing microscopy, electron microscopy) and a great variety of morphological structures were found, ranging from fibrils to spherulitic and crystalline-like lameUar formations. The experiments showed that the nature of the investigated polymeric substrates has no significant effect on the morphology of the structural formations; on glass the process of structure formation takes place more rapidly, and this is attributed to the nucleating action of glass. The structuration of PSSI~a proceeds progressively with time. In the process of film preparation the optimal concentration of polymer in solution is n.ot more than 1-2-1.5 g per 100 ml of water. The films prepared from viscous solutions show practically no structuration (3-5 g in 100 ml of water). It was shown that dissolution of the polymer in the temperature range from 5 to 55 ° does not cause complete loss of the nuclei, and the structuration of the polymer takes place at an accelerated rate. At temperatures of the order of 92 ° there is apparently complete destruction of the nuclei, and a longer period is necessary (30 days) for the formation of structures in the films prepared from these solutions. Structuration processes in PSSNa films therefore obey the usual laws pertaining to polymers. As the decomposition temperature for PSSI~a is lower than the melting point heat treatment has no effect on the structuration processes. The main factors governing structure-formation in PSSNa are the prehistory of the solution, the concentration of the solution, and the type of substrate. X-ray structural investigations of PSSNa showed that the polymer molecules have syndiotactic structure and are packed in monomolecular layers with good mutual ordering, with the sulpho-groups appearing on the surface of the layers, thus facilitating the diffusion of H~O molecules into the spaces (inter-layers)
2040
V.A. KARGINet al.
between the monomolecular layers. This special type of structure enables the polymer molecules to absorb and give off large amounts of water. This also accounts for the peculiar behaviour of the polymer under deformation (stretching) giving rise to good orientation of the layers relative to one another with a practically complete absence of orientation in the arrangement of the molecules in adjacent layers. I t is this type of highly-ordered system which probably accounts for the formation of highly organized structures (fibrils, spherulitic and crystallinelike formations) which were revealed in the course of the optical and electron microscope studies of investigated polymer. The syndiotactic regular structure of polystyrene sodium sulphonate is probably due to preferential addition of the monomer in the "head-to-tail" manner as a result of the electrostatic interaction and the steric hindrances that appear in aqueous solution in the radical polymerization of p-styrene sodium sulphonate
[12]. CONCLUSIONS
(1) A study has been made of structuration processes and of the chain configuration and conformation of polystyrene sodium sulphonate, which is a strong polyeleetrolyte. (2) Optical microscopy and electron microscopy were used to analyse the effect of the substrates, the dissolution temperature and the time factor on structure-forming processes in PSSI~a. (3) A great variety of structures ranging from fibrillar formations to spherulitic and crystal-like lamellar structures were discovered. (4) The X-ray diffraction patterns showed that the polymer molecules have a syndiotactic structure and a planar zigzag conformation. (5) The radial distribution curve calculated for PSSI~a confirmed the good mutual ordering of the polymer molecules. (6) On the basis of the X-ray structural analysis and the radial distribution curve it is shown that PSSNa is a well-ordered system and this would account for the formation of the highly ordered structures observed b y optical microscopy and b y electron microscopic analysis. Translated by R. J. A. HENDRr REFERENCES
1. K. P. KHOMYAKOV, A. D. VIRNIK and Z. A. ROGOVIN, Uspekhi khimii 33: 1061, 1964 2. I. B. ADEL and S. A. DMITRIEV, Ioanyi obmen in yego primenenie (Ion Exchange and its Uses). Izd. AN SSSR, p. 307, 1959 3. A. KHAMENGI and G. FLANACHAK, The Medical Use of Ion-exchange Resins, 1956 4 . V. A. KARGIN, M. E. BOGDANOV and E. P. CHERNEVA, Vysokomol. soyed. A10: 429, 1968 (Translated in Polymer Sci. U.S.S.R. 1O: 2, 500, 1968) 5. V. A. KARGIN, V. A. KABANOV and O. V. KARGINA, ]:)ok]. AN SSSR 161: 1131, 1965 6. R. REdS and D. VAUGHAN, Polymer Preprints 6: 287, 1965
Comparison of acetylation of cellulose and a polysaceharide
2041
7. V. A. KARGIN, Z. Ya. BERESTNEVA, E. P. CHERNEVA, T. D. IGNATOVICH and G. S. POTAPOVA, Dok]. A N SSSR 175: 1318, 1967 8. A. M. gHARLAMOVA, E. P. CHERNEVA and Z. Ya. BERESTNEVA, Vysokomo].
soyed. Bg: 635, 1967 (Not translated in Polymer Sci. U.S.S.R.) 9. M. KATO, T. NAKAGAWA and H. AKAMATU, Bull. Chem. Soe. Japan 33: 322, 1960 10. V. A. KARGIN, T. A. KORETSKAYA and T. A. BOGAYEVSKAYA, Vysokomol. soyed. 6: 441, ]964 (Translated in Polymer Sci. U.S.S.R. 6: 3, 489, 1964) 11. B. K. VAINSHTEIN, Difraktsiya rentgenovskikh luehei na tsepnykh molekulakh (X-ray Diffraction by Chain Molecules). Izd. AN SSSR, p. 328, 1963 12. S. E. BRESLER and B. L. YERUSALIMSKII, Fizika i khimiya makromolekul (Chemistry and Physics of Macromolecules). Izd. "Nauka", 234, 1965
A COMPARISON OF THE ACETYLATION OF CELLULOSE AND A POLYSACCHARIDE CONTAINING BOTH GLUCOSE AND 3,6-ANHYDROGLUCOSE UNITS* L. P. TKACHEVA, E. L. AKn~ a n d L. S. GAL'BRAIKH Moscow Textile Institute S. M. Kirov Leningrad Light Industry and Textile Institute
(Received 24 February 1970) O ~ L ¥ a r e l a t i v e l y small n u m b e r of p a p e r s has b e e n p u b l i s h e d concerning t h e s y n t h e s i s o f m i x e d p o l y s a e c h a r i d e s containing glucose a n d 3,6-anhydroglucose units [1-3]. N o s y s t e m a t i c s t u d y o f t h e p r o p e r t i e s o f a m i x e d p o l y s a c c h a r i d e of t h i s t y p e has y e t b e e n m a d e , t h o u g h t h e effect of fine s t r u c t u r a l differences in t h e e l e m e n t a r y u n i t s o f p o l y s a c c h a r i d e s on t h e p r o p e r t i e s o f t h e l a t t e r w o u l d d o u b t l e s s be o f considerable i n t e r e s t to investigators. O u r a i m in this i n v e s t i g a t i o n w a s t o m a k e a c o m p a r a t i v e s t u d y o f t h e rea c t i v i t y o f cellulose a n d a m i x e d p o l y s a c c h a r i d e containing glucose a n d 3,6a n h y d r o g l u c o s e units in a c e t y l a t i o n reactions. The mixed polysaccharide was synthesized by the method used in reference [4] by a l l , line saponification of cellulose tosylates. The monosaccharide composition of the mixed polysaceharide compounds with different contents of 3,6-anhydroglucose, and also of the products of aeetylation of these compounds, was determined by quantitative paper chromatographic analysis of the products of complete hydrolysis [5]. The acetylation of cellulose and mixed polysaeeharides was investigated in homo- and heterogeneous media. Cotton cellulose and mixed polysaccharide compounds containing 17 (I) and 70 (II) mole~o of 3,6-anhydroglueose were subjected to acetylation in a homogeneous medium. The study of the acetylation process in a homogeneous medium was based on the changes in the electrical conductivity of the system [6]. * Vysokomol. soyed. A13: No. 8, 1819-1824, 1971.