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Morphological properties of rubber-oligomer compositions and their effect on the strength of vulcanizates
Morphological properties of rubbor-oligomer compositions
1267
t h e difference in values of a c t u a l a n d e x p e r i m e n t a l p a r a m e t e r s o f M W D a n d o f glycol m i x t u r e s does n o t exceed 2 - 3 % a n d 1.5-2.5~/o, respectively. T h e m e t h o d p r o p o s e d for calibrating a n d calculating absolute M W was used with success for i n v e s t i g a t i n g a n u m b e r of p o l y m e r i c systems, including industrial o l i g o m e r s - p h e n o l - f o r m a l d e h y d e a n d e p o x y resins. R e s u l t s concerning t h o s y s t e m s m e n t i o n e d deserve a separate investigations. Translated by E. S~.~ERE REFERENCES
1. G. DETERMAN, ~el-khromatografiya (Gel-Chromatography). Izd. "Mir", 1970 2. Sb. Gel-pronikayushchaya khromatografiya (Gel-Permeation Chromatography). IKhF A_N SSSR, Chernogolovka, 1974 3. V. G. BELEN'KII and L. Z. VILENCHIK, Khromatografiya polimerov (Chromatography of Polymers}. Zzd. "Khimiya", 1978 4. Z. CRUBISIC, P. REMPP and H. BENOIT, J. Polymer Sci. B5: 753, 1967 5. C. STRZEIELLE and H. BENOIT, Pure Appl. Chem. 26: 451, 1971 6. S. B. MAKAROVA, Ye. A. GUKASOVA, A. I. KUZAYEV and S. P. DAVTYAN, Vysoko, mol. soyed. A18: 2747, 1976 (Translated in Polymer Sci. U.S.S.R. 18: 12, 3141, 1976) 7. A. I. KUZAYEV, S. D. KOLESNIKOVA and A. A. BRIKENSHTEIN, Vysokomol. soyed. AI7: 1327, 1975 (Translated in Polymer Sei. U.S.S.R. 17: 6, 1524. 1975) 8. A. I. KUZAYEV, G. A. MIRONTSEVA and Ye. N. SUSLOVA, Sb. Sintez i fizikokhimiya polimerov (Synthesis and Physico-chemistry of Polymers). Izd. "Naukova dumka", 1975
Polymer Science U.S.S.R.
Vol. 22,
No. 5, pp.
1207-1273, 1980
Printed in Poland
0032-3950/80/051287-07507.5010 © 1981 Pergamon Press Ltd.
MORPHOLOGICAL PROPERTIES OF RUBBER-OLIGOMER COMPOSITIONS AND THEIR EFFECT ON THE STRENGTH VULCANIZATES * T. D.
OF
MAL'CHEVSKAYA, A. A. BERLIN, A. A. DONTSOV, R. P. IVANOVA, A . S . KUZ'lVI-INSKII, A. V. REBROV a n d M. N. KHOTIMSKII Scientific Research Institute of the Rubber Industry (Received 27 March 1979)
I t was shown that a globular formation of three-dimensional crosslinked oligoester acrylate of a dimension of 0.02-0-04 tzm is the smallest structural element of the dispersed phase of vuleamzates based on rubber-oligomer compositions. The distribution of particles of the dispersed phase in a rubber matrix is determined by the type~ of rubber and has a marked effect on the tensile strength of vulcanizates. * Vysokomol. soyod. A22: No. 5, 1153-1157, 1980.
1268
T. D. M.AL'CHEVSKAYAe t a / .
tT WAS shown previously [1, 2] t h a t mixing of rubber with oligoester acrylates produces a system with dispersion of the liquid oligoester acrylate (OEA) in a rubber matrix fixed by vulcaxization in the presence free-radical initiators. I t was assumed t h a t a crosslirrked S E A polymer with particle size ranging from 0.02 to 10-20 gm exists in similar vulcanizates and strength properties were linked with a variation of the dispersed phase of S E A in various rubbers. This investigation was carried out, in order to develop a theory concerning morphological features of rubber-oligomer compositions and study their effect on the reinforcement of vulcanizates in various deformation intervals. Untreated rubber mixtures and vulcamzates of different polarities, combined with oIigoester acrylate TM-HF-11 (tetramethacrylate-(bis-glycerol)phthalate, M = 586) were investigated. The mixtures were vulcanized in a curing press in the presence of a peroxide initiator. Characteristics of the samples examined are tabulated. The morphology of systems examined was studied by electron microscopy (EM-V-100L microscope) using carbon-palladinm replicas obtained in a VUP-1 apparatus. Replicas were prepared by a two-stage method using an intermediate replica on gelatin obtained of the shearing surface of samples in liquid nitrogen. Stress-elongation diagrams of vulcanizates up to rupture were obtained by stretching samples using a "Zwick" tensile testing machine at a rate of movement of the clamps of 200 mm[min. Instantaneous actual stress values were calculated at given deformations. _Average instantaneous stress and actual tensile strength were calculated by statistical analysis of results obtained when testing 50 samples.
Electron-microscope photographs of the mixtures and vulcanizates studied are shown in Fig. 1. Before vulcanization (system A) the liquid OEA is distributed in an SKMS-30ARK rubber matrix in the form of drops of different size. The same distribution of S E A has been observed previously [1] when studying ~he same systems using a microscope. After vulcanization globular formations of polymeric S E A particles are observed, which are apparently grouped in the region of initial S E A particles and separated by rubber layers (systems B and C, respectively). For vulcanizates based on SKN-26m polar rubber distribution of three-dimensional S E A in the form of individual globules is the most typical. Globules are only accumulated with amounts of S E A over 18 vol. ~/o (systems D and E, respectively). I t may be assumed t h a t the morphology of the vulcanizates studied reflects special features of forming the systems both at the stage of mixing and vulcanization. Theories concerning the mechanism of forming rubber-oligomer compositions cannot be developed without considering at the mixing stage the associative nature of OEA [3], its surface-active properties and the polarity of rubber, which determine the intensity of the process of solubilization [4] and at the stage of vulcanization -- features of three-dimensional polymerization of OEA taking place as a heterogeneous process with the formation of a crosslinl~ed polymer of globular structure [5-7].
Morphological properties of rubber.oligomer compositions
1269
I n t h e absence of c o m p a t i b i l i t y * in m e c h a n i c a l dispersion o f O E A in nonp o l a r r u b b e r t w o - p h a s e colloidal s y s t e m s are f o r m e d in e v e r y case. On c o m b i n i n g T M H F - 1 1 w i t h nitrile r u b b e r O E A is o n l y f o r m e d as a s e p a r a t e p h a s e w i t h high c o n c e n t r a t i o n s of t h e oligomer [1].
FIG. 1. Microphotographs of rubber-oligomer compositions and vulcanizates based oil them: a-f--systems A - F , respectively. * The SKMS-30ARK (SKD)TTMHF-I I system is defined as incompatible and SK_N--26 shows limited compatibility w~th TMHF-11 [ 1, 8].
1270
T.D. MAL'CS:EVSKAYAel al.
Differences in colloid-chemical characteristics of the systems studied are due at this stage, to a higher level of interaction in SK_N-26M polar rubber mixtures with 0EA, which accounts for the formation of micro-heterogeneous systems with a high degree oi dispersion of the 0 E A phase, determined by the size of associative formations. During vulcanization as a result of radical-initiated three-dimensional polymerization transfer of structural order takes place in the initial heterogeneous system, in the crosslinked copolymer formed of nitrile rubber and 0EA. FORMULATION AND
System A B C D E F
TECHlqOLOGICALCHARACTERISTICSOF RUBBER--OLIOOMERCOMPOSITIONS* Rubber
SKMS-30ARK SKD SKN-26m
[OEA] vel. °/o 18 18 18 18 27 31
Conditions of Conditions of pre- vulcanization paring the mixture of samples Mill mixing Same wp
Swelling of rubber in OEA
Untreated 150°; 60 min 150°; 60 rain 150°; 60 min 150°; 60 rain 150°; 50 rain
Micro-regions of globular structure were also observed when studying the morphology of vulcanizates prepared from mixtures by spontaneous swelling of nitrile rubber in OEA (system F). Interaction of rubber with associated OEA molecules in this case probably results in the formation of micro-heterogeneous "intermediate products" observed during vulcanization. When polymerization of OEA takes place in the micro-volume of OEA drops dispersed in a rubber matrix during mixing, the associative nature of liquid OEA and the unsually high rate of polymerization in associates, as with bulk polymerization [5, 6], predetermines the heterogeneous structure of crosslinked polymers. Globular formation of OEA in a rubber matrix appear, in the initial stage of vulcanization of rubber-oligomer systems (~ 15 sec) and their dimensions and the distances between them remain subsequently unchanged. [9] Variation of molecular interaction caused by the formation of a phase interface contributes to the penetration of rubber macromolecules in the region between primary structural elements of the OEA phase. As a result initial drops "distintegrate" during vulcanization to form polymer globules surrounded by rubber. Chemical and physical interaction takes place between rubber macromolecules and the surface of crosslinked OEA formation. I t may therefore be assumed t h a t three-dimensional crosslinked OEA formations are the smallest structural element of the OEA phase which, according to the type of rubber and the method of mixing components by various methods, a r e distributed in the rubber matrix.
Morphological properties of rubber-oligomer compositions
1271
As a consequence of the varying distribution of the OEA phase in the rubber matrix effects of reinforcement in vulcanizates based on polar and non-polar rubber differ from a quantitative point of view. As a result of the formation of particles of the OEA solidified phase structural heterogeneities and internal stress are formed evidently which take the form of defects [10], as observed in filled vulcanizates [10]. During elongation unevenly distributed stress increases which, according to the Volkov theory [11], explains the variation of results of strength tests. A widening of curves of actual stress distribution on increasing deformation proves increased damage in rubber during dynamic elongation in deformatidn close to the point, causing failure. ]OL*~Plflll~x
0.8
l-O-
f
h x6
/
a
"~ 0.6 c,.
$
2
~ o-4 i
0-6
I
,
1"0
I
l.q
~: 0.2
,..~ ×/x~ \x"x"-x--x--× Acfua/ afnes8 , PlPa
55
Fzo. 2. Effect of tensile strain (a) and the concentration of OEA (b) on curves of distribution of actual tensile strength and actual stress values: a: 1--SKMS-30ARK; 2-4--system B; 5--SKN-26m; 6-9--system D. 1, 4, 5, 9--~e. Elongation, °/o: 2, 6--100; 3, 7--50 and 8--100; b: /--system B; 2--D; 3-E. As an example Fig. 2a compares instantaneous actual stress with different tensile strain values of unfilled vulcanizates and vulcanizates containing 18 vol. °/o OEA. The latter are characterized by a wider (compared with unfilled vulcanizates) and asymmetric distribution. The existence of asymmetry is, no doubt, due to an increase during elongation of the heterogeneity of internal stress. The higher the stress value, the lower the average tensile strength and the higher the asymmetry of the distribution curve in the range of lower strength values.
1272
T.D. MaL'OH~VSg~YAeta/.
In valeanizates based on SKMS-30ARK the existence of mieroregions o f varying size, which represent globular formations (these regions, apparently, emerge during deformation as single formations) results in a higher heterogeneity of stress distribution, compared with vulcanizates based on SKN-26M, in which the corresponding amount of OEA is more evenly distributed in the form of individual globules. The variation in defects in rubber is particularly clear when plotting results of tensile strength of samples in relative coordinates "(. (ap,
P~-~, where pmax] %m~x is the most likely strength corresponding to pm~x; Jp, is strength at a relative frequency of p~ (Fig. 2b). I t is obvious t h a t the existence of a relatively large number of low strength values for vulcanizates based on SKMS-30ARK (system B) and SKN-26 rubber (system E) (left-hand side of curve 1 and 3) is due to the presence of defects, which are practically absent from rubber which is based on SKN-26m with a lower OEA content (system D) (curve 2). Comparison of results with microscopic data suggests t h a t macro-regions consisting of globular formations are such defects. As a result of this investigation it was therefore shown t h a t the type of interaction of components, the associative nature and properties of three-dimensional polymerization of OEA are decisive factors in the formation of the morphology of rubber-oligomer compositions and vulcanizates. The differences in the morphology of polar and non-polar rubber mixtures with OEA and of vulcanizates prepared from them determine the differences in strength characteristics of the systems examined.
\ ap~ u
Translated by E. SEI~ERE REFERENCES 1. T. D. MAL'CHEVSKAYA, S. N. ARKINA, A. S. KUZ'MINSKII, A. A. BERLIN, M. F.
2. 3. 4. 5. 6.
7. 8. 9.
BUgHINA and N. M. GAL'PERINA, Vysokomol. soyed. AI8: 390, 1976 (Translated in Polymer Sei. U.S.S.R. 18: 2, 447, 1976) V. N. KULEZNEV, V. D. KLYKOVA,Ye. I. VASIL'CHENKO,A. A. BERLIN and S. M. MEZI-E[KOVSKII~Kolloidl~. zh. 37: 176, 1976 A. A. BERLIN, Vysokomol. soyed. A12: 2313, 1970 (Translated in Polymer Sci. U.S.S.R. 12: 10, 2619, ]970) A. A. DONTSOV, Protsessy strukturirovaniya elastomerov (Structure Formation in Elastomers). Izd. "Khimiya", 1978 N. G. MATVEYEVA, M. R. KISELEV, A. A. BERLIN and P. I. ZUBOV, Dokl. AN SSSR 231: 385, 1976 A. A. BERLIN, S. M. KIREYEVA, Yu. M. SIVERGIN and A. A. SUKHAREVA, Dokl. AN SSSR 213: 109, 1973 A. A. BERLIN, Vysokomol. soyed. A20: 483, 1978 (Translated in Polymor Sci. U.S.S.R 20: 3, 541, 1978) T. B. MAL'CHEVSKAYA, N. A. NOVIKOV, S. N. ARKINA, A. S. KUZ'MINSI~IIand A. A. BERLIN, Vysokomol. soyed. BI8: 289, 1976 (Not translated in Polymer Sci. U.S.S.R.) A. V. REBROV, Yu. K. OVCHINNIKOV, T. D. MAL'CHEVSKA~A, S. N. ARKINA,
Conformation characteristics of polymers in solid state
1273
G. S. MARKOVA, N. F. BAKEYEV and A. S. KUZ'MINSKII, Vysokomol. soyed. B19: 684, 1977 (Not translated in Polymer Sci. U.S.S.R.) 10. G. M. BARTENEV and Yu. S. ZUYEV, Prochnost' i razrusheniye vysokoelasticheskikh materialov (Strength and Decomposition of High-elastic Materials). Izd. " K h i m i y a " , 1964 ' I I. S. D. VOLKOV, Statisticheskaya teoriya prochnosti (Statistical Strength Theory). Mashgiz, 1960
Polymer Science U.S.S.R. Vol. 22, No. 5, pp.
1273-1280, 1980
Printed in Poland
0032-3950/80]051273-08507.50]0 1981 Pergamon Press Ltd.
LOW-TEMPERATURE SPECIFIC HEAT AND CONFORMATION CHARACTERISTICS OF POLYMERS IN SOLID STATE* E. Z. FAIlCBERG(dec.) Scientific Industrial Association "Khimvolokno" (Received 28 March 1979) Based on the analysis of data concerning low-temperature specific heat of polymers methods were proposed for the comparative evaluation of the rigidity (flexibility) of polymers in the solid condensed state. The standard "effective" weight of the polymer is the most valid criterion of rigidity (flexibility) of polymer macromolecules in the solid state from a physical point of view. SPECIFIC heats of polymers show a direct dependence on the conformation state of macromolecules, i.e. on rigidity (flexibility). It is known that the rigidity (flexibility) of molecular chains m a y be fairly accurately and theoretically correctly determined by studying dilute polymer solutions in 0-solvents, which enable the size of the K u h n segment characterizing intramolecular rigidity to be determined. This problem was examined in detail in a review paper by Tsvetkov [1]. Transferring these theories to the solid condensed state of the polymer is a very remote extrapolation. Intensive molecular interaction, no doubt, involves significant amendments to this index. Glass temperature Tg m a y now be the only qualitative index of rigidity (flexibility) of molecular chains of the polymer in the solid state. It is, of course, essential to complement this index of the conformation state of polymer macromolecules by another independent criterion. A study is made in this paper of the possible use of specific heat values for the evaluation of the rigidity (flexibility) of polymers. When finding the standard rigidity of molecular chains of the polymer in the solid state it is advisable to use the quantum theory of specific heat, which requires data concerning the low* Vysokomol. soyed. A22: No. 5, 1158-1164, 1980.
1267
t h e difference in values of a c t u a l a n d e x p e r i m e n t a l p a r a m e t e r s o f M W D a n d o f glycol m i x t u r e s does n o t exceed 2 - 3 % a n d 1.5-2.5~/o, respectively. T h e m e t h o d p r o p o s e d for calibrating a n d calculating absolute M W was used with success for i n v e s t i g a t i n g a n u m b e r of p o l y m e r i c systems, including industrial o l i g o m e r s - p h e n o l - f o r m a l d e h y d e a n d e p o x y resins. R e s u l t s concerning t h o s y s t e m s m e n t i o n e d deserve a separate investigations. Translated by E. S~.~ERE REFERENCES
1. G. DETERMAN, ~el-khromatografiya (Gel-Chromatography). Izd. "Mir", 1970 2. Sb. Gel-pronikayushchaya khromatografiya (Gel-Permeation Chromatography). IKhF A_N SSSR, Chernogolovka, 1974 3. V. G. BELEN'KII and L. Z. VILENCHIK, Khromatografiya polimerov (Chromatography of Polymers}. Zzd. "Khimiya", 1978 4. Z. CRUBISIC, P. REMPP and H. BENOIT, J. Polymer Sci. B5: 753, 1967 5. C. STRZEIELLE and H. BENOIT, Pure Appl. Chem. 26: 451, 1971 6. S. B. MAKAROVA, Ye. A. GUKASOVA, A. I. KUZAYEV and S. P. DAVTYAN, Vysoko, mol. soyed. A18: 2747, 1976 (Translated in Polymer Sci. U.S.S.R. 18: 12, 3141, 1976) 7. A. I. KUZAYEV, S. D. KOLESNIKOVA and A. A. BRIKENSHTEIN, Vysokomol. soyed. AI7: 1327, 1975 (Translated in Polymer Sei. U.S.S.R. 17: 6, 1524. 1975) 8. A. I. KUZAYEV, G. A. MIRONTSEVA and Ye. N. SUSLOVA, Sb. Sintez i fizikokhimiya polimerov (Synthesis and Physico-chemistry of Polymers). Izd. "Naukova dumka", 1975
Polymer Science U.S.S.R.
Vol. 22,
No. 5, pp.
1207-1273, 1980
Printed in Poland
0032-3950/80/051287-07507.5010 © 1981 Pergamon Press Ltd.
MORPHOLOGICAL PROPERTIES OF RUBBER-OLIGOMER COMPOSITIONS AND THEIR EFFECT ON THE STRENGTH VULCANIZATES * T. D.
OF
MAL'CHEVSKAYA, A. A. BERLIN, A. A. DONTSOV, R. P. IVANOVA, A . S . KUZ'lVI-INSKII, A. V. REBROV a n d M. N. KHOTIMSKII Scientific Research Institute of the Rubber Industry (Received 27 March 1979)
I t was shown that a globular formation of three-dimensional crosslinked oligoester acrylate of a dimension of 0.02-0-04 tzm is the smallest structural element of the dispersed phase of vuleamzates based on rubber-oligomer compositions. The distribution of particles of the dispersed phase in a rubber matrix is determined by the type~ of rubber and has a marked effect on the tensile strength of vulcanizates. * Vysokomol. soyod. A22: No. 5, 1153-1157, 1980.
1268
T. D. M.AL'CHEVSKAYAe t a / .
tT WAS shown previously [1, 2] t h a t mixing of rubber with oligoester acrylates produces a system with dispersion of the liquid oligoester acrylate (OEA) in a rubber matrix fixed by vulcaxization in the presence free-radical initiators. I t was assumed t h a t a crosslirrked S E A polymer with particle size ranging from 0.02 to 10-20 gm exists in similar vulcanizates and strength properties were linked with a variation of the dispersed phase of S E A in various rubbers. This investigation was carried out, in order to develop a theory concerning morphological features of rubber-oligomer compositions and study their effect on the reinforcement of vulcanizates in various deformation intervals. Untreated rubber mixtures and vulcamzates of different polarities, combined with oIigoester acrylate TM-HF-11 (tetramethacrylate-(bis-glycerol)phthalate, M = 586) were investigated. The mixtures were vulcanized in a curing press in the presence of a peroxide initiator. Characteristics of the samples examined are tabulated. The morphology of systems examined was studied by electron microscopy (EM-V-100L microscope) using carbon-palladinm replicas obtained in a VUP-1 apparatus. Replicas were prepared by a two-stage method using an intermediate replica on gelatin obtained of the shearing surface of samples in liquid nitrogen. Stress-elongation diagrams of vulcanizates up to rupture were obtained by stretching samples using a "Zwick" tensile testing machine at a rate of movement of the clamps of 200 mm[min. Instantaneous actual stress values were calculated at given deformations. _Average instantaneous stress and actual tensile strength were calculated by statistical analysis of results obtained when testing 50 samples.
Electron-microscope photographs of the mixtures and vulcanizates studied are shown in Fig. 1. Before vulcanization (system A) the liquid OEA is distributed in an SKMS-30ARK rubber matrix in the form of drops of different size. The same distribution of S E A has been observed previously [1] when studying ~he same systems using a microscope. After vulcanization globular formations of polymeric S E A particles are observed, which are apparently grouped in the region of initial S E A particles and separated by rubber layers (systems B and C, respectively). For vulcanizates based on SKN-26m polar rubber distribution of three-dimensional S E A in the form of individual globules is the most typical. Globules are only accumulated with amounts of S E A over 18 vol. ~/o (systems D and E, respectively). I t may be assumed t h a t the morphology of the vulcanizates studied reflects special features of forming the systems both at the stage of mixing and vulcanization. Theories concerning the mechanism of forming rubber-oligomer compositions cannot be developed without considering at the mixing stage the associative nature of OEA [3], its surface-active properties and the polarity of rubber, which determine the intensity of the process of solubilization [4] and at the stage of vulcanization -- features of three-dimensional polymerization of OEA taking place as a heterogeneous process with the formation of a crosslinl~ed polymer of globular structure [5-7].
Morphological properties of rubber.oligomer compositions
1269
I n t h e absence of c o m p a t i b i l i t y * in m e c h a n i c a l dispersion o f O E A in nonp o l a r r u b b e r t w o - p h a s e colloidal s y s t e m s are f o r m e d in e v e r y case. On c o m b i n i n g T M H F - 1 1 w i t h nitrile r u b b e r O E A is o n l y f o r m e d as a s e p a r a t e p h a s e w i t h high c o n c e n t r a t i o n s of t h e oligomer [1].
FIG. 1. Microphotographs of rubber-oligomer compositions and vulcanizates based oil them: a-f--systems A - F , respectively. * The SKMS-30ARK (SKD)TTMHF-I I system is defined as incompatible and SK_N--26 shows limited compatibility w~th TMHF-11 [ 1, 8].
1270
T.D. MAL'CS:EVSKAYAel al.
Differences in colloid-chemical characteristics of the systems studied are due at this stage, to a higher level of interaction in SK_N-26M polar rubber mixtures with 0EA, which accounts for the formation of micro-heterogeneous systems with a high degree oi dispersion of the 0 E A phase, determined by the size of associative formations. During vulcanization as a result of radical-initiated three-dimensional polymerization transfer of structural order takes place in the initial heterogeneous system, in the crosslinked copolymer formed of nitrile rubber and 0EA. FORMULATION AND
System A B C D E F
TECHlqOLOGICALCHARACTERISTICSOF RUBBER--OLIOOMERCOMPOSITIONS* Rubber
SKMS-30ARK SKD SKN-26m
[OEA] vel. °/o 18 18 18 18 27 31
Conditions of Conditions of pre- vulcanization paring the mixture of samples Mill mixing Same wp
Swelling of rubber in OEA
Untreated 150°; 60 min 150°; 60 rain 150°; 60 min 150°; 60 rain 150°; 50 rain
Micro-regions of globular structure were also observed when studying the morphology of vulcanizates prepared from mixtures by spontaneous swelling of nitrile rubber in OEA (system F). Interaction of rubber with associated OEA molecules in this case probably results in the formation of micro-heterogeneous "intermediate products" observed during vulcanization. When polymerization of OEA takes place in the micro-volume of OEA drops dispersed in a rubber matrix during mixing, the associative nature of liquid OEA and the unsually high rate of polymerization in associates, as with bulk polymerization [5, 6], predetermines the heterogeneous structure of crosslinked polymers. Globular formation of OEA in a rubber matrix appear, in the initial stage of vulcanization of rubber-oligomer systems (~ 15 sec) and their dimensions and the distances between them remain subsequently unchanged. [9] Variation of molecular interaction caused by the formation of a phase interface contributes to the penetration of rubber macromolecules in the region between primary structural elements of the OEA phase. As a result initial drops "distintegrate" during vulcanization to form polymer globules surrounded by rubber. Chemical and physical interaction takes place between rubber macromolecules and the surface of crosslinked OEA formation. I t may therefore be assumed t h a t three-dimensional crosslinked OEA formations are the smallest structural element of the OEA phase which, according to the type of rubber and the method of mixing components by various methods, a r e distributed in the rubber matrix.
Morphological properties of rubber-oligomer compositions
1271
As a consequence of the varying distribution of the OEA phase in the rubber matrix effects of reinforcement in vulcanizates based on polar and non-polar rubber differ from a quantitative point of view. As a result of the formation of particles of the OEA solidified phase structural heterogeneities and internal stress are formed evidently which take the form of defects [10], as observed in filled vulcanizates [10]. During elongation unevenly distributed stress increases which, according to the Volkov theory [11], explains the variation of results of strength tests. A widening of curves of actual stress distribution on increasing deformation proves increased damage in rubber during dynamic elongation in deformatidn close to the point, causing failure. ]OL*~Plflll~x
0.8
l-O-
f
h x6
/
a
"~ 0.6 c,.
$
2
~ o-4 i
0-6
I
,
1"0
I
l.q
~: 0.2
,..~ ×/x~ \x"x"-x--x--× Acfua/ afnes8 , PlPa
55
Fzo. 2. Effect of tensile strain (a) and the concentration of OEA (b) on curves of distribution of actual tensile strength and actual stress values: a: 1--SKMS-30ARK; 2-4--system B; 5--SKN-26m; 6-9--system D. 1, 4, 5, 9--~e. Elongation, °/o: 2, 6--100; 3, 7--50 and 8--100; b: /--system B; 2--D; 3-E. As an example Fig. 2a compares instantaneous actual stress with different tensile strain values of unfilled vulcanizates and vulcanizates containing 18 vol. °/o OEA. The latter are characterized by a wider (compared with unfilled vulcanizates) and asymmetric distribution. The existence of asymmetry is, no doubt, due to an increase during elongation of the heterogeneity of internal stress. The higher the stress value, the lower the average tensile strength and the higher the asymmetry of the distribution curve in the range of lower strength values.
1272
T.D. MaL'OH~VSg~YAeta/.
In valeanizates based on SKMS-30ARK the existence of mieroregions o f varying size, which represent globular formations (these regions, apparently, emerge during deformation as single formations) results in a higher heterogeneity of stress distribution, compared with vulcanizates based on SKN-26M, in which the corresponding amount of OEA is more evenly distributed in the form of individual globules. The variation in defects in rubber is particularly clear when plotting results of tensile strength of samples in relative coordinates "(. (ap,
P~-~, where pmax] %m~x is the most likely strength corresponding to pm~x; Jp, is strength at a relative frequency of p~ (Fig. 2b). I t is obvious t h a t the existence of a relatively large number of low strength values for vulcanizates based on SKMS-30ARK (system B) and SKN-26 rubber (system E) (left-hand side of curve 1 and 3) is due to the presence of defects, which are practically absent from rubber which is based on SKN-26m with a lower OEA content (system D) (curve 2). Comparison of results with microscopic data suggests t h a t macro-regions consisting of globular formations are such defects. As a result of this investigation it was therefore shown t h a t the type of interaction of components, the associative nature and properties of three-dimensional polymerization of OEA are decisive factors in the formation of the morphology of rubber-oligomer compositions and vulcanizates. The differences in the morphology of polar and non-polar rubber mixtures with OEA and of vulcanizates prepared from them determine the differences in strength characteristics of the systems examined.
\ ap~ u
Translated by E. SEI~ERE REFERENCES 1. T. D. MAL'CHEVSKAYA, S. N. ARKINA, A. S. KUZ'MINSKII, A. A. BERLIN, M. F.
2. 3. 4. 5. 6.
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Conformation characteristics of polymers in solid state
1273
G. S. MARKOVA, N. F. BAKEYEV and A. S. KUZ'MINSKII, Vysokomol. soyed. B19: 684, 1977 (Not translated in Polymer Sci. U.S.S.R.) 10. G. M. BARTENEV and Yu. S. ZUYEV, Prochnost' i razrusheniye vysokoelasticheskikh materialov (Strength and Decomposition of High-elastic Materials). Izd. " K h i m i y a " , 1964 ' I I. S. D. VOLKOV, Statisticheskaya teoriya prochnosti (Statistical Strength Theory). Mashgiz, 1960
Polymer Science U.S.S.R. Vol. 22, No. 5, pp.
1273-1280, 1980
Printed in Poland
0032-3950/80]051273-08507.50]0 1981 Pergamon Press Ltd.
LOW-TEMPERATURE SPECIFIC HEAT AND CONFORMATION CHARACTERISTICS OF POLYMERS IN SOLID STATE* E. Z. FAIlCBERG(dec.) Scientific Industrial Association "Khimvolokno" (Received 28 March 1979) Based on the analysis of data concerning low-temperature specific heat of polymers methods were proposed for the comparative evaluation of the rigidity (flexibility) of polymers in the solid condensed state. The standard "effective" weight of the polymer is the most valid criterion of rigidity (flexibility) of polymer macromolecules in the solid state from a physical point of view. SPECIFIC heats of polymers show a direct dependence on the conformation state of macromolecules, i.e. on rigidity (flexibility). It is known that the rigidity (flexibility) of molecular chains m a y be fairly accurately and theoretically correctly determined by studying dilute polymer solutions in 0-solvents, which enable the size of the K u h n segment characterizing intramolecular rigidity to be determined. This problem was examined in detail in a review paper by Tsvetkov [1]. Transferring these theories to the solid condensed state of the polymer is a very remote extrapolation. Intensive molecular interaction, no doubt, involves significant amendments to this index. Glass temperature Tg m a y now be the only qualitative index of rigidity (flexibility) of molecular chains of the polymer in the solid state. It is, of course, essential to complement this index of the conformation state of polymer macromolecules by another independent criterion. A study is made in this paper of the possible use of specific heat values for the evaluation of the rigidity (flexibility) of polymers. When finding the standard rigidity of molecular chains of the polymer in the solid state it is advisable to use the quantum theory of specific heat, which requires data concerning the low* Vysokomol. soyed. A22: No. 5, 1158-1164, 1980.