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On the high temperature relaxation transitions in cis-1,4-polyisoprene
Polymer Science U.S.S.R. Vol. 25, No. 2, pp. 388-395, 1983 Printed in Poland
0032-3950]83 $10.00-1-.00 © 1984 Pergamon PreM Ltd.
ON THE HIGH TEMPERATURE RELAXATION TRANSITIONS IN e/s-I,4-POLYISOPRENE* L. V. SOKOLOVA, V. A. SHERSHNEV and YE. A. GAVRILINA M. V. Lomonosov Institute of Fine Chemical Technology, Moscow
(Received 26 Augus$ 1981) A comparative study has been made of the diffusion properties of fihns of c/s1,4-polyisoprene (PI) and P I blended with trioxyethylene-~,(o-dimethaerylate. The character of the mieroheterogeneous structure of the P I m a t r i x depends on the amount of the additive: when 0.1 wt. ~o of the latter is used, the most ordered microdomains are formed in the matrix. When the P I film is prepared from solution in heptane the microdomains are for the most part more ordered in character, compared with the large fraction of less ordered mierodomains appearing i~ the film prepared from toluene solution.
THE presence of microdomains with a higher degree of density [1] in the volume of amorphous polymers may- be detected b y the introduction of plasticizers of a particular t y p e which alter the level of intermoleeular interaction in the polymer matrix. Relaxation times for the microdomains of higher density are significantly higher than for the rest of the matrix [2], and so it would appear that the plasticizer influence is most marked in the region of one or other of the high temperature transitions related to decay of these mierodomains. This paper is based on our use of the plasticization effect as a means of analyzing the microheterogeneous structure of the cis-l,4-polyisoprene (PI) matrix b y a diffusion-sorption method. The study object was synthetic P I (grade Cariflex-IR-305) t h a t had first been purified by precipitation from solution in toluene by m e t h y l alcohol. P I films were prepared b y slow evaporation of the solvent (toluene or heptane} on a glass support. Films were dried to constant weight at 50 ° in vaeuo. The additive used in the investigation was trioxyethylene-~,o)-dimethacrylate (TGM-3) which was introduced to the P I m a t r i x on a micromill. The viscosity of the TGM-3 was 7.8 cP. Preheating of the films and blends of P I with TGM-3 was performed at 65 ° for 2 hr. As a molecular probe for the m a t r i x we used sulphur t h a t had first been purified by two recrystallizations from solution in benzene. Its rate of dissolution was determined by a diffusion-sorption method [3]. The error is 1 5 ~ o for this method.
It is known [4] that a relaxation transition that m a y well be due to breakdown of ordered microdomains has been observed for P I and natural rubber at c a . 43 °. The data in [5, 6] show t h a t ordered microdomains of size 15-20 A * Vysokomol. soyed. A25: No. 2, 333-338, 1983. 388
On t h e high t e m p e r a t u r e r e l a x a t i o n transitions in
cis-1,4-polyisoprene
389
are present in N R melts and matrices. To obtain more a c c u r a ~ data on the high-temperature relaxation transition occurring in P I we investigated features of the dissolution of a crystalline substance (sulphur) in a polymer maVrix containing TGM-3. It is known from [7] that small amours of TGM-3 (0.1-0.5 wt.~)) lead to the formation of structural elements that are more ordered than in the original elastomer. Figure 1 shows the influence of TGM-3 on the rate of sulphur dissolution in PI. The rate of dissolution is characterized by the reciproc~d of the time in which 10% of the sulphur dissolves r~.~. The value of r~.~ determined at 45 ° decreases at first as the TGM-3 concentration increases (up to o.2 wt. o~),
6o L_ 2
zlO ,<
18-
5" o
I
1
I
I
3 5,0, wf. %
I
I
5
lq'm. ]. I n f l u e n c e o f t h e c o n c e n t r a t i o n (0 o f T G M - 3 on t h e r a t e o f s u l p h u r dissolut i o n in P I at 45 (1) and 60 ° (2).
then (up to I wt.~/o) it increases, and at TGM-3 concentrations exceeding l wt. % a slight and practically linear increase is observed. As the measurement temperature is increased to 60 °, the clear-cut extremal character of the concentration dependence of the rate of sulphur dissolution degenerates gradually (Fig. 1), indicating the kinetic character of structural changes occurring in the polymer maVrix in the presence of TGM-3. The complex character of the concentraVion dependence of the rate of sulphur dissolution, as well as the influence of temperature on the rate are in accord with the data in [7, 8] on the TGM-3 influence on the viscosity of diene elastomer melts. The authors think t h a t in concentrations up to 1 wt.°//o, TGM-3 plays the role of an antiplasticizer, at 1.5-4% concentrations that of interstrucCural plasticizer, and of a molecular plasticizer in the case of concentrations exceeding 4 w~.%.
390
L. V. SoxoLovA et al.
In terms of free volume theory the data in Fig. 1 suggest that a change in the free volume of the polymer matrix takes place in the presence of TGM-3. With TGM-3 concentrations of 0.1-0.2 w t . % a marked reduction in the free volume of the P I matrix could occur as a result of consolidated packing of fragments of the polymer chains [7]. Then an increase in the free volume of the polymer matrix is observed, as the TGM-3 concentration increases.
lo3 co E.g/ cm l
!og~ ~cm2/secT.
7
-B.q
b
2 -20
-7B
2"9
J'l
3"3
lo /r,K -,
2-9
~
3"3
FIO. 2. Temperature dependences of the diffusion coefficient D (a) and of the equilibrium solubility Co (b) of sulphur in PI containing 0.1 (1) and 5 wt. % TGM-3 (2). Here and in Fig. 3 the pointers show the positions of the transition temperatures, Let us now turn to features of the diffusion of sulphur in P I containing 0.1 and 5 we.% TGM-3. In the interval 30-80 ° the temperature dependences of the rate of sulphur dissolution obey the Arrhenius equation. For the TGM-3 concentrations selected the apparent activiaton energies for sulphur dissolution differ only insignificantly (see the Table). I t should be noted that the temperature dependences of the dissolution rate and of the coefficient of diffusion of hexachloro-p-xylene [4] and sulphur [9] in a P I matrix have a discontinuity in the region of 40 ° owing to the high-temperature relaxation transition. The temperature dependences of the coefficient of sulphur diffusion in P I containing TGM-3 obey the Arrhenius equation, and have a discontinuity in the region of 60 ° at a TGM-3 concentration of 0-1 wt.%, and in the region of 46 ° at 5 w t . % (Fig. 2). Thus the addition of 5 w t . % TGM-3 to the P I matrix leads to a 6° displacement of the realxation transition temperature, whereas a t 0.1 w t . % TGIVI-3 the relaxation transition temperature is displaced b y 20 °. In both cases the activation energy for sulphur diffusion is lowered as a result of the relaxation transition, b u t in the case of a TGM-3 concentration of 0.1 w¢.% this reduction is more marked, and amounts ¢o 38 instead of the 14 kJ/mole for 5 we.% TGM-3 (see Table). For bulk P I the reducotin in the activation
On the high temperature relaxation transitions in
cis-l,4-polyisoproao|
391
1JA/%AMETERSCH)~RACTERIZINGTIIE DIFFUSION AND SOLUBILITYOF SULPHURIN PI Transit iotl tempera-
Polymes
T°
Ed
40
PI fihn prepared from solution in heptane PI fihn prepared from solution in toluene
D × lOs, OoX 10~, g/cm ~ cmS/sec
30"2 30.2
7 46
1"17 3"09
4.3 1"3
2 14 56
0"90 0"98 0"99
71 81 114
15.1
2 9 64
1"38 0"92
35 70
88 63
58 33
46 6O
35 55 70
70 76
69 109
47 6O
35 55 70
83 88 73
J
Ha
k J/mole
t 4 tl"O ~ o C
Bulk PI [9]
Eal~
5"5
1"78
PI containing 0-I wt.~o TGM-3
6O
35 70
71
52 15
3"9 10'6
3-2 17
1"07 2"78
P I containing 5 wt.% TGM-3
46
35 70
72
65 51
9.4 17.6
5 45
0"98 1"79
Note. Ea is the apparent activation energy for the dissolution process, Ba~t is the activation energy for diffusion, Ha is the heat of dissolution, D is the diffusion coefficient, a n d G0 is the equilibrium solubility.
e n e r g y for sulphur diffusion as a result of the r e l a x a t i o n transition is 25 k J / m o l e
[9]. T h e r e is likewise a d i s c o n t i n u i t y on t e m p e r a t u r e dependences of t h e equilibr i u m solubility of sulphur (Fig. 2). I n t h e t e m p e r a t u r e region a b o v e t h e r e l a x a t i o n transition t h e equilibrium solubility of sulphur increases t o a g r e a t e r e x t e n t in t h e case o f P I containing 0.1 w&°/o TGM-3. According t o B o y e r [10] this points t o a greater increase in t h e free v o l u m e o f t h e p o l y m e r m a t r i x as a result o f t h e r e l a x a t i o n transition. Comparing t h e e n e r g y p a r a m e t e r s for sulphur dissolution in P I a n d in its blends with TGM-3 (Table) it is seen t h a t a t a 5 v~. % concentration o f TGM-3 t h e microdomains f o r m e d in t h e p o l y m e r m a t r i x h a v e a more c o m p a c t packing o f chain f r a g m e n t s c o m p a r e d with t h e initial PI. A r e d u c t i o n in t h e TGM-3 c o n c e n t r a t i o n to 0.1 w t . % leads to the f o r m a t i o n of microdomains with t h e d e n s e s t packing of chain fragments. I t is possible t h a t as TGM-3 is t h e r m o d y namically incompatible with P I [ l l ] it m a y act as a kinetic s t i m u l a t o r of conformational transitions m a k i n g for the f o r m a t i o n of microdomains with a denser packing of chain fragments. We would e x p e c t these microdomains t o be o r d e r e d f o r m a t i o n s serving as centres of crystallization o f PI. I n this connection it was of interest to c o m p a r e t h e diffusion p a r a m e t e r s o f films o f P I a n d P I - T G M - 3 blends with differing TGM-3 concentrations. I t is well k n o w n t h a t in t h e crystallization of polymers in t h i n films p r e p a r e d b y e v a p o r a t i o n o f t h e solvent t h e l a t t e r acts as a kinetic p r o m o t e r of crystallizatiom Moreover t h e " p o o r e r " the t h e r m o d y n a m i c quality of the solvent, the stronger
392
L.V.
SO~OLOVA et al.
will be its influence on crystallization processes [12]. It would seem that for a crystalline polymer such as P I the type of solvent will be the primary factor determining the structural character of an amorphous film. The moulding of polymer films is accompanied b y the formation of ordered microdomains, which are centres of crystallization. Let us now turn to features of the dissolution of sulphur in P I films prepared from solutions in different solvents. Toluene was used as thermodynamically good solvent, and heptane as a poor one. The temperature dependences of the dissolution rate of sulphur in P I films in the region of 30-80 ° obey the Arrhenius equation and a staggered character is observed for the curve of change in the rate of sulphur dissolution at 6 0 ± 3 ° in the case of the P I film prepared from solution in heptane, and at 47 and 60 ° in the case of the film prepared from solution in toluene (Fig. 3). A staggered increase in the apparent activation for the dissolution of sulphur in the P I film prepared from heptane solution is due to the relaxation transition, whereas in the case of the P I film prepared
log
log0[crnYsec] h
Esec7
-/-5~-
-2.Sl
>jt
-3"51
I
-7
I
I
logco[g/cmJ] 2.9
I
3"1
I 3"3
2"8
3"I
8"J
C
-2.0
I
2.9
I
I
3.1
I
I
3.3 10J/T,K-r
FIG. 3. Temperature dependences of the dissolution rate (a), the diffusion coefficient (b) a n d the equilibrium solubility (c) of sulphur in P I films prepared from solution in toluen~ (1) and in heptane (2).
On the high temperature relaxation transitions it~ cis-1,4-polyisopren,,
393
from toluene solution there is but an insignificant increase in the above parameter as a result of the first transition, and its value is reduced as a result of the second (see the Table). The coefficient of diffusion of sulphur in the P I fihn prepared from solution in heptane is markedly higher in the vicinity of the relaxation transition ~Lt 60 ° (Fig. 3). The activation energy for sulphur diffusion increases in this case from 69 to 109 kJ/mole. As the temperature rises the coefficient of sulphur diffusion for the P I film obtained from toluene solution increases twice in staggered fashion at ca. 47 and 60 °. At the same time the activation energy of SUll)hur diffusion likewise increases in a staggered manner: in the case of the first relaxation transition from 71 to 81 kJ/mole and during the second to 114 kJ/mole (Fig. 3). It should be noted that at temperature above 60 ° the diffusion parameters for both types of P I film are fairly similar as regards sulphur (Fig. 3), i.e. there is similarity in the structure of the matrices. Thus the activation energy of sulphur diffusion is significantly increased in the case of the P I films as a result of high-temperature relaxat, ion transitions. On the other hand, the activation energy of diffusion is reduced from 58 to 33 kJ/mole [9] in the case of the bulk P I as a result of the relaxation transition (40°). I t appears that the preparation of P I films from solution is accompanied b y the formation of a microheterogeneous structure differing appreciably from t h a t found in the bulk state. This assumption is further supported by the t y p e of change occurring in the temperature dependence of the equilibrium solubility of sulphur (Fig. 3). In the case of the bulk P I the equilibrium solubility of sulphur increases linearly with temperature in the interval 30-80 ° . The heat of sulphur dissolution is 30.2 kJ/mole [9]. In the case of the P I films of both t)Tes the temperature dependence of the equilibrium solubility of sulphur has a discontinuity in the region of the first relaxation transition and is reduced in staggered fashion as a result of the second (Fig. 3). On analyzhlg the results obtained (Fig. 2) it is seen in the light of free volume theory that the preparation of P I films from solution is accompanied by l,he formation of structure with a smaller amount of free volume than in the initial P[. In addition, features of sulphur dissolution in the P I films show that P I chains m a y form microdomains of two types differing in their packing density. The use of a poor solvent for P I film preparation leads mainly to the formation of more compact microdomains: the relaxation transition in the region of 60 -~ is clear-cut, whereas that at around 47 ° is less so (Fig. 2), Microdomains of two types are formed in the case of thermodynamically good solvent: tlmre are ~:learcut relaxation transitions at around 47 and 60 °. In view of the more perfect crystalline formations in the films prepared from solution in heptane [11] on the one hand, and the more densely packed microdomains in these films on the other hand, we surmise that the latter have an ordered structure, arid are centres of crystallization. Comparing the diffusion data for P I films with features of the influence of
394
L. V. SOKOLOVAet al.
TGM-3 oll the dissolution of sulphur in PI, it is seen t h a t TGM-3 in the polymer matrix causes formation of microheterogeneities of one type only. Moreover the character of the microdomains depends on the TGM-3 concentration in %he matrix: at a TGM-3 concentration of 0.1 w t . % we obtain the most ordered microdomains, giving rise to a relaxation transition at 60 °, whereas with a TGM-3 concentration of 5 w t . % the ordered microdomains are less ordered (relaxation • ransition at around 46°), but their diffusion parameters differ from those of P I in the bulk state. The selectivity of TGM-3 during formation of the microheterogeneous structure of the P I matrix m a y be the result of its incompatibility with polymer and its influence on retardation of the motion of kinetic chain segments :[13] and this selectivity is a function of the TGM-3 concentration in the matrix. The character of change in the activation energy for sulphur diffusion following relaxation transitions also points to a stTuctural difference in the structure of a P I matrix containing TGM-3, and those of films prepared from solutions in toluene and heptane. In the case of the P I films the activation energy of sulphur diffusion is higher (Fig. 3), whereas it is lower for the P I containing TGM-3, as it is for P I in the bulk state (Fig. 2). A reduction in the activation of sulphur diffusion in P I (with or without TGM-3) at temperatures above the relaxation transition is attributable to the fact t h a t breakdown of ordered microdomains of the matrix facilitates cooperative movements of chain segments during diffusion displacements of large molecules of a diffusing substance such as sulphur. A similar change in the activation energy of diffusion of penetrating substances as a result of a Tu-relaxation transition was also reported for PS in [14]. An increase in the activation energy of sulphur diffusion in P I films at temperatures above 60 ° m a y be the result of partial preservation of the microheterogeneous structure of the matrix. However, the present data are insufficient to provide more definite information in this connection. Translated by R. J. A. t:[..E17DRY REFERENCES
1. V. I. LEBEDEV, Uspekhi khimii 47: 1, 127, 1976 2. G. M. BARTENEV, Struktura i relaksatsiomlye svoistva elastomerov (Structure and Relaxation Behaviour of Elastomers). p. 177, Moscow, Khimiya, 1979 3. B. S. GRISHIN, I. A. TUTORSKII and Ye. E. POTAPOV, Vysokomol. soyed. 16: 130, 1974 (Translated in Polymer Sci. U.S.S.R. 16: 1, 156, 1974) ~. L. V. SOKOLOVA and V. A. SttERSHNEV, In: Abstrs. Reports III All-Union Conf. "Diffuzionnye yavleniya v polimerakh" (Diffusion Effects in Polymers). p. 105, Riga, 1977 5. E. B. BOKHYAN, Yu. K. OVCHINNIKOV, G. S. ~ O V A and V. A. KARGIN, Vysokomol, soyed. A13: 1805, 1971 (Translated in Polymer Sci. U.S.S.R. 13: 8, 2026, 1971) 6. G. S. IEKH, Vysokomol. soyed. A21: 2233, 1979 (Translated in Polymer Sci. U.S.S.R. 21: 10, 2467, 1979)
Liquid and amorphous-crystalline phase ~ p a r a t i o n processes
395
7. A. A. BERLIN, S. M. MEZHIKOVSKII, Ye. I. VASIL'CHENKO, N. V. PROZORO¥SKAYA, I. K. CHURAI~OVA, R. Sh. FRENKEL' and Ye. V. KHAVAROVA, Kolloidn. zh. 36: 3, 537, 1976 ~. N. N. SCHASTLIVAYA, S. M. MEZIIIKOVSKII, Ye. I. LOTAKOVA, Ye. I. VASIL'CHENKO, I. I. TUGOV, G. A. BLOKtt a n d A. A. BERLIN, Vysokomol. soyed. A20: 175, 1978 (Translated in Polymer Sci. U.S.S.R. 20: 1, 203, 1978) 9. I. S. YUROVSKAYA, Disc. at Chem. Sci. Contest (Cand. Degree), Moscow, Lomonosov Inst. of Fine Chem, Technology, 1979 I0. R. F. BOYER and J. B. ENNS, Polymer Pveprints 18: 2, 461, 1977 l I. A. Ye. CHALYKI~, N. N. AVDEYEV a n d S. M. MEZHIKOVSKII, Vysokomol. soyed. B22: 464, 1980 (Not translated in Polymer Sei. U.S.S.R.) l~°. L. M. MANDELKERN, Kristallizatsiya polimerov (Crystallization of Polymers). p. 128, Moscow, Khimiya, 1966 13. G. I. BORISOVA, S. M. MEZHIKOVSKII, S. V. GLADCHENKO, Ye. I. VASIL'CHENKO and A. A. BERLIN, Vysokomol. soyed. 21: 900, 1979 (Translated in Polymer Sei. U.S.S.R. 21: 4, 1017, 1979) 14. J. L. DUDA a n d J. S. VRENTAS, J. Polymer Sci. A-2, 6: 2, 675, 1968
]F(~lymerSciem:eU.S.S.t¢. Vo|. °.5, No. 2, pp. 395-404, 1983 ])tintedin Poland
0032-3950/83 $10.00+.00 © 1984PergainonPreas Ltd.
FEATURES OF LIQUID AND AMORPHOUS-CRYSTALLINE PHASE SEPARATION PROCESSES IN BLOCK COPOLYMERS AND IN MIXTURES WITH VARIABLE MOLECULAR WEIGHTS* ¥1~. D. SHIBAI~OV and Yr. K. GoDovsI(II L. Ya. Karpov Physico-ehemical Research Institute
(Received 27 August 1981) C~Lrves of brightening (clearing) in polymer-polyiimr systems with variable MW of the components are discussed from a geometrical standpoint. Anomalies in the form of mb~ima are possible because curves of brightening in these systems are determined by th(:, polynodal, whereas ill the systems where composition and MW arc m u t u a l l y indep~ndent the curve is determined by the binodal. The curves measured for P E O polyarylate systems b y an optical method, where changes in composition occur as a result of a change in MW, are similar to curves for systems with an upper critical temperature of dissolution. However, no anomalies appear on these curves. Preheating of the mixture of 5 : 90 composition above the binodal results in crystallization taking place, olt subsequent cooling to 290 K, spontaneously from single phase solution without a n y preliminary separation into two amorphous phases.
* Vysokomol. soyed. A25: hTo. 2, 339-345, 1983.
0032-3950]83 $10.00-1-.00 © 1984 Pergamon PreM Ltd.
ON THE HIGH TEMPERATURE RELAXATION TRANSITIONS IN e/s-I,4-POLYISOPRENE* L. V. SOKOLOVA, V. A. SHERSHNEV and YE. A. GAVRILINA M. V. Lomonosov Institute of Fine Chemical Technology, Moscow
(Received 26 Augus$ 1981) A comparative study has been made of the diffusion properties of fihns of c/s1,4-polyisoprene (PI) and P I blended with trioxyethylene-~,(o-dimethaerylate. The character of the mieroheterogeneous structure of the P I m a t r i x depends on the amount of the additive: when 0.1 wt. ~o of the latter is used, the most ordered microdomains are formed in the matrix. When the P I film is prepared from solution in heptane the microdomains are for the most part more ordered in character, compared with the large fraction of less ordered mierodomains appearing i~ the film prepared from toluene solution.
THE presence of microdomains with a higher degree of density [1] in the volume of amorphous polymers may- be detected b y the introduction of plasticizers of a particular t y p e which alter the level of intermoleeular interaction in the polymer matrix. Relaxation times for the microdomains of higher density are significantly higher than for the rest of the matrix [2], and so it would appear that the plasticizer influence is most marked in the region of one or other of the high temperature transitions related to decay of these mierodomains. This paper is based on our use of the plasticization effect as a means of analyzing the microheterogeneous structure of the cis-l,4-polyisoprene (PI) matrix b y a diffusion-sorption method. The study object was synthetic P I (grade Cariflex-IR-305) t h a t had first been purified by precipitation from solution in toluene by m e t h y l alcohol. P I films were prepared b y slow evaporation of the solvent (toluene or heptane} on a glass support. Films were dried to constant weight at 50 ° in vaeuo. The additive used in the investigation was trioxyethylene-~,o)-dimethacrylate (TGM-3) which was introduced to the P I m a t r i x on a micromill. The viscosity of the TGM-3 was 7.8 cP. Preheating of the films and blends of P I with TGM-3 was performed at 65 ° for 2 hr. As a molecular probe for the m a t r i x we used sulphur t h a t had first been purified by two recrystallizations from solution in benzene. Its rate of dissolution was determined by a diffusion-sorption method [3]. The error is 1 5 ~ o for this method.
It is known [4] that a relaxation transition that m a y well be due to breakdown of ordered microdomains has been observed for P I and natural rubber at c a . 43 °. The data in [5, 6] show t h a t ordered microdomains of size 15-20 A * Vysokomol. soyed. A25: No. 2, 333-338, 1983. 388
On t h e high t e m p e r a t u r e r e l a x a t i o n transitions in
cis-1,4-polyisoprene
389
are present in N R melts and matrices. To obtain more a c c u r a ~ data on the high-temperature relaxation transition occurring in P I we investigated features of the dissolution of a crystalline substance (sulphur) in a polymer maVrix containing TGM-3. It is known from [7] that small amours of TGM-3 (0.1-0.5 wt.~)) lead to the formation of structural elements that are more ordered than in the original elastomer. Figure 1 shows the influence of TGM-3 on the rate of sulphur dissolution in PI. The rate of dissolution is characterized by the reciproc~d of the time in which 10% of the sulphur dissolves r~.~. The value of r~.~ determined at 45 ° decreases at first as the TGM-3 concentration increases (up to o.2 wt. o~),
6o L_ 2
zlO ,<
18-
5" o
I
1
I
I
3 5,0, wf. %
I
I
5
lq'm. ]. I n f l u e n c e o f t h e c o n c e n t r a t i o n (0 o f T G M - 3 on t h e r a t e o f s u l p h u r dissolut i o n in P I at 45 (1) and 60 ° (2).
then (up to I wt.~/o) it increases, and at TGM-3 concentrations exceeding l wt. % a slight and practically linear increase is observed. As the measurement temperature is increased to 60 °, the clear-cut extremal character of the concentration dependence of the rate of sulphur dissolution degenerates gradually (Fig. 1), indicating the kinetic character of structural changes occurring in the polymer maVrix in the presence of TGM-3. The complex character of the concentraVion dependence of the rate of sulphur dissolution, as well as the influence of temperature on the rate are in accord with the data in [7, 8] on the TGM-3 influence on the viscosity of diene elastomer melts. The authors think t h a t in concentrations up to 1 wt.°//o, TGM-3 plays the role of an antiplasticizer, at 1.5-4% concentrations that of interstrucCural plasticizer, and of a molecular plasticizer in the case of concentrations exceeding 4 w~.%.
390
L. V. SoxoLovA et al.
In terms of free volume theory the data in Fig. 1 suggest that a change in the free volume of the polymer matrix takes place in the presence of TGM-3. With TGM-3 concentrations of 0.1-0.2 w t . % a marked reduction in the free volume of the P I matrix could occur as a result of consolidated packing of fragments of the polymer chains [7]. Then an increase in the free volume of the polymer matrix is observed, as the TGM-3 concentration increases.
lo3 co E.g/ cm l
!og~ ~cm2/secT.
7
-B.q
b
2 -20
-7B
2"9
J'l
3"3
lo /r,K -,
2-9
~
3"3
FIO. 2. Temperature dependences of the diffusion coefficient D (a) and of the equilibrium solubility Co (b) of sulphur in PI containing 0.1 (1) and 5 wt. % TGM-3 (2). Here and in Fig. 3 the pointers show the positions of the transition temperatures, Let us now turn to features of the diffusion of sulphur in P I containing 0.1 and 5 we.% TGM-3. In the interval 30-80 ° the temperature dependences of the rate of sulphur dissolution obey the Arrhenius equation. For the TGM-3 concentrations selected the apparent activiaton energies for sulphur dissolution differ only insignificantly (see the Table). I t should be noted that the temperature dependences of the dissolution rate and of the coefficient of diffusion of hexachloro-p-xylene [4] and sulphur [9] in a P I matrix have a discontinuity in the region of 40 ° owing to the high-temperature relaxation transition. The temperature dependences of the coefficient of sulphur diffusion in P I containing TGM-3 obey the Arrhenius equation, and have a discontinuity in the region of 60 ° at a TGM-3 concentration of 0-1 wt.%, and in the region of 46 ° at 5 w t . % (Fig. 2). Thus the addition of 5 w t . % TGM-3 to the P I matrix leads to a 6° displacement of the realxation transition temperature, whereas a t 0.1 w t . % TGIVI-3 the relaxation transition temperature is displaced b y 20 °. In both cases the activation energy for sulphur diffusion is lowered as a result of the relaxation transition, b u t in the case of a TGM-3 concentration of 0.1 w¢.% this reduction is more marked, and amounts ¢o 38 instead of the 14 kJ/mole for 5 we.% TGM-3 (see Table). For bulk P I the reducotin in the activation
On the high temperature relaxation transitions in
cis-l,4-polyisoproao|
391
1JA/%AMETERSCH)~RACTERIZINGTIIE DIFFUSION AND SOLUBILITYOF SULPHURIN PI Transit iotl tempera-
Polymes
T°
Ed
40
PI fihn prepared from solution in heptane PI fihn prepared from solution in toluene
D × lOs, OoX 10~, g/cm ~ cmS/sec
30"2 30.2
7 46
1"17 3"09
4.3 1"3
2 14 56
0"90 0"98 0"99
71 81 114
15.1
2 9 64
1"38 0"92
35 70
88 63
58 33
46 6O
35 55 70
70 76
69 109
47 6O
35 55 70
83 88 73
J
Ha
k J/mole
t 4 tl"O ~ o C
Bulk PI [9]
Eal~
5"5
1"78
PI containing 0-I wt.~o TGM-3
6O
35 70
71
52 15
3"9 10'6
3-2 17
1"07 2"78
P I containing 5 wt.% TGM-3
46
35 70
72
65 51
9.4 17.6
5 45
0"98 1"79
Note. Ea is the apparent activation energy for the dissolution process, Ba~t is the activation energy for diffusion, Ha is the heat of dissolution, D is the diffusion coefficient, a n d G0 is the equilibrium solubility.
e n e r g y for sulphur diffusion as a result of the r e l a x a t i o n transition is 25 k J / m o l e
[9]. T h e r e is likewise a d i s c o n t i n u i t y on t e m p e r a t u r e dependences of t h e equilibr i u m solubility of sulphur (Fig. 2). I n t h e t e m p e r a t u r e region a b o v e t h e r e l a x a t i o n transition t h e equilibrium solubility of sulphur increases t o a g r e a t e r e x t e n t in t h e case o f P I containing 0.1 w&°/o TGM-3. According t o B o y e r [10] this points t o a greater increase in t h e free v o l u m e o f t h e p o l y m e r m a t r i x as a result o f t h e r e l a x a t i o n transition. Comparing t h e e n e r g y p a r a m e t e r s for sulphur dissolution in P I a n d in its blends with TGM-3 (Table) it is seen t h a t a t a 5 v~. % concentration o f TGM-3 t h e microdomains f o r m e d in t h e p o l y m e r m a t r i x h a v e a more c o m p a c t packing o f chain f r a g m e n t s c o m p a r e d with t h e initial PI. A r e d u c t i o n in t h e TGM-3 c o n c e n t r a t i o n to 0.1 w t . % leads to the f o r m a t i o n of microdomains with t h e d e n s e s t packing of chain fragments. I t is possible t h a t as TGM-3 is t h e r m o d y namically incompatible with P I [ l l ] it m a y act as a kinetic s t i m u l a t o r of conformational transitions m a k i n g for the f o r m a t i o n of microdomains with a denser packing of chain fragments. We would e x p e c t these microdomains t o be o r d e r e d f o r m a t i o n s serving as centres of crystallization o f PI. I n this connection it was of interest to c o m p a r e t h e diffusion p a r a m e t e r s o f films o f P I a n d P I - T G M - 3 blends with differing TGM-3 concentrations. I t is well k n o w n t h a t in t h e crystallization of polymers in t h i n films p r e p a r e d b y e v a p o r a t i o n o f t h e solvent t h e l a t t e r acts as a kinetic p r o m o t e r of crystallizatiom Moreover t h e " p o o r e r " the t h e r m o d y n a m i c quality of the solvent, the stronger
392
L.V.
SO~OLOVA et al.
will be its influence on crystallization processes [12]. It would seem that for a crystalline polymer such as P I the type of solvent will be the primary factor determining the structural character of an amorphous film. The moulding of polymer films is accompanied b y the formation of ordered microdomains, which are centres of crystallization. Let us now turn to features of the dissolution of sulphur in P I films prepared from solutions in different solvents. Toluene was used as thermodynamically good solvent, and heptane as a poor one. The temperature dependences of the dissolution rate of sulphur in P I films in the region of 30-80 ° obey the Arrhenius equation and a staggered character is observed for the curve of change in the rate of sulphur dissolution at 6 0 ± 3 ° in the case of the P I film prepared from solution in heptane, and at 47 and 60 ° in the case of the film prepared from solution in toluene (Fig. 3). A staggered increase in the apparent activation for the dissolution of sulphur in the P I film prepared from heptane solution is due to the relaxation transition, whereas in the case of the P I film prepared
log
log0[crnYsec] h
Esec7
-/-5~-
-2.Sl
>jt
-3"51
I
-7
I
I
logco[g/cmJ] 2.9
I
3"1
I 3"3
2"8
3"I
8"J
C
-2.0
I
2.9
I
I
3.1
I
I
3.3 10J/T,K-r
FIG. 3. Temperature dependences of the dissolution rate (a), the diffusion coefficient (b) a n d the equilibrium solubility (c) of sulphur in P I films prepared from solution in toluen~ (1) and in heptane (2).
On the high temperature relaxation transitions it~ cis-1,4-polyisopren,,
393
from toluene solution there is but an insignificant increase in the above parameter as a result of the first transition, and its value is reduced as a result of the second (see the Table). The coefficient of diffusion of sulphur in the P I fihn prepared from solution in heptane is markedly higher in the vicinity of the relaxation transition ~Lt 60 ° (Fig. 3). The activation energy for sulphur diffusion increases in this case from 69 to 109 kJ/mole. As the temperature rises the coefficient of sulphur diffusion for the P I film obtained from toluene solution increases twice in staggered fashion at ca. 47 and 60 °. At the same time the activation energy of SUll)hur diffusion likewise increases in a staggered manner: in the case of the first relaxation transition from 71 to 81 kJ/mole and during the second to 114 kJ/mole (Fig. 3). It should be noted that at temperature above 60 ° the diffusion parameters for both types of P I film are fairly similar as regards sulphur (Fig. 3), i.e. there is similarity in the structure of the matrices. Thus the activation energy of sulphur diffusion is significantly increased in the case of the P I films as a result of high-temperature relaxat, ion transitions. On the other hand, the activation energy of diffusion is reduced from 58 to 33 kJ/mole [9] in the case of the bulk P I as a result of the relaxation transition (40°). I t appears that the preparation of P I films from solution is accompanied b y the formation of a microheterogeneous structure differing appreciably from t h a t found in the bulk state. This assumption is further supported by the t y p e of change occurring in the temperature dependence of the equilibrium solubility of sulphur (Fig. 3). In the case of the bulk P I the equilibrium solubility of sulphur increases linearly with temperature in the interval 30-80 ° . The heat of sulphur dissolution is 30.2 kJ/mole [9]. In the case of the P I films of both t)Tes the temperature dependence of the equilibrium solubility of sulphur has a discontinuity in the region of the first relaxation transition and is reduced in staggered fashion as a result of the second (Fig. 3). On analyzhlg the results obtained (Fig. 2) it is seen in the light of free volume theory that the preparation of P I films from solution is accompanied by l,he formation of structure with a smaller amount of free volume than in the initial P[. In addition, features of sulphur dissolution in the P I films show that P I chains m a y form microdomains of two types differing in their packing density. The use of a poor solvent for P I film preparation leads mainly to the formation of more compact microdomains: the relaxation transition in the region of 60 -~ is clear-cut, whereas that at around 47 ° is less so (Fig. 2), Microdomains of two types are formed in the case of thermodynamically good solvent: tlmre are ~:learcut relaxation transitions at around 47 and 60 °. In view of the more perfect crystalline formations in the films prepared from solution in heptane [11] on the one hand, and the more densely packed microdomains in these films on the other hand, we surmise that the latter have an ordered structure, arid are centres of crystallization. Comparing the diffusion data for P I films with features of the influence of
394
L. V. SOKOLOVAet al.
TGM-3 oll the dissolution of sulphur in PI, it is seen t h a t TGM-3 in the polymer matrix causes formation of microheterogeneities of one type only. Moreover the character of the microdomains depends on the TGM-3 concentration in %he matrix: at a TGM-3 concentration of 0.1 w t . % we obtain the most ordered microdomains, giving rise to a relaxation transition at 60 °, whereas with a TGM-3 concentration of 5 w t . % the ordered microdomains are less ordered (relaxation • ransition at around 46°), but their diffusion parameters differ from those of P I in the bulk state. The selectivity of TGM-3 during formation of the microheterogeneous structure of the P I matrix m a y be the result of its incompatibility with polymer and its influence on retardation of the motion of kinetic chain segments :[13] and this selectivity is a function of the TGM-3 concentration in the matrix. The character of change in the activation energy for sulphur diffusion following relaxation transitions also points to a stTuctural difference in the structure of a P I matrix containing TGM-3, and those of films prepared from solutions in toluene and heptane. In the case of the P I films the activation energy of sulphur diffusion is higher (Fig. 3), whereas it is lower for the P I containing TGM-3, as it is for P I in the bulk state (Fig. 2). A reduction in the activation of sulphur diffusion in P I (with or without TGM-3) at temperatures above the relaxation transition is attributable to the fact t h a t breakdown of ordered microdomains of the matrix facilitates cooperative movements of chain segments during diffusion displacements of large molecules of a diffusing substance such as sulphur. A similar change in the activation energy of diffusion of penetrating substances as a result of a Tu-relaxation transition was also reported for PS in [14]. An increase in the activation energy of sulphur diffusion in P I films at temperatures above 60 ° m a y be the result of partial preservation of the microheterogeneous structure of the matrix. However, the present data are insufficient to provide more definite information in this connection. Translated by R. J. A. t:[..E17DRY REFERENCES
1. V. I. LEBEDEV, Uspekhi khimii 47: 1, 127, 1976 2. G. M. BARTENEV, Struktura i relaksatsiomlye svoistva elastomerov (Structure and Relaxation Behaviour of Elastomers). p. 177, Moscow, Khimiya, 1979 3. B. S. GRISHIN, I. A. TUTORSKII and Ye. E. POTAPOV, Vysokomol. soyed. 16: 130, 1974 (Translated in Polymer Sci. U.S.S.R. 16: 1, 156, 1974) ~. L. V. SOKOLOVA and V. A. SttERSHNEV, In: Abstrs. Reports III All-Union Conf. "Diffuzionnye yavleniya v polimerakh" (Diffusion Effects in Polymers). p. 105, Riga, 1977 5. E. B. BOKHYAN, Yu. K. OVCHINNIKOV, G. S. ~ O V A and V. A. KARGIN, Vysokomol, soyed. A13: 1805, 1971 (Translated in Polymer Sci. U.S.S.R. 13: 8, 2026, 1971) 6. G. S. IEKH, Vysokomol. soyed. A21: 2233, 1979 (Translated in Polymer Sci. U.S.S.R. 21: 10, 2467, 1979)
Liquid and amorphous-crystalline phase ~ p a r a t i o n processes
395
7. A. A. BERLIN, S. M. MEZHIKOVSKII, Ye. I. VASIL'CHENKO, N. V. PROZORO¥SKAYA, I. K. CHURAI~OVA, R. Sh. FRENKEL' and Ye. V. KHAVAROVA, Kolloidn. zh. 36: 3, 537, 1976 ~. N. N. SCHASTLIVAYA, S. M. MEZIIIKOVSKII, Ye. I. LOTAKOVA, Ye. I. VASIL'CHENKO, I. I. TUGOV, G. A. BLOKtt a n d A. A. BERLIN, Vysokomol. soyed. A20: 175, 1978 (Translated in Polymer Sci. U.S.S.R. 20: 1, 203, 1978) 9. I. S. YUROVSKAYA, Disc. at Chem. Sci. Contest (Cand. Degree), Moscow, Lomonosov Inst. of Fine Chem, Technology, 1979 I0. R. F. BOYER and J. B. ENNS, Polymer Pveprints 18: 2, 461, 1977 l I. A. Ye. CHALYKI~, N. N. AVDEYEV a n d S. M. MEZHIKOVSKII, Vysokomol. soyed. B22: 464, 1980 (Not translated in Polymer Sei. U.S.S.R.) l~°. L. M. MANDELKERN, Kristallizatsiya polimerov (Crystallization of Polymers). p. 128, Moscow, Khimiya, 1966 13. G. I. BORISOVA, S. M. MEZHIKOVSKII, S. V. GLADCHENKO, Ye. I. VASIL'CHENKO and A. A. BERLIN, Vysokomol. soyed. 21: 900, 1979 (Translated in Polymer Sei. U.S.S.R. 21: 4, 1017, 1979) 14. J. L. DUDA a n d J. S. VRENTAS, J. Polymer Sci. A-2, 6: 2, 675, 1968
]F(~lymerSciem:eU.S.S.t¢. Vo|. °.5, No. 2, pp. 395-404, 1983 ])tintedin Poland
0032-3950/83 $10.00+.00 © 1984PergainonPreas Ltd.
FEATURES OF LIQUID AND AMORPHOUS-CRYSTALLINE PHASE SEPARATION PROCESSES IN BLOCK COPOLYMERS AND IN MIXTURES WITH VARIABLE MOLECULAR WEIGHTS* ¥1~. D. SHIBAI~OV and Yr. K. GoDovsI(II L. Ya. Karpov Physico-ehemical Research Institute
(Received 27 August 1981) C~Lrves of brightening (clearing) in polymer-polyiimr systems with variable MW of the components are discussed from a geometrical standpoint. Anomalies in the form of mb~ima are possible because curves of brightening in these systems are determined by th(:, polynodal, whereas ill the systems where composition and MW arc m u t u a l l y indep~ndent the curve is determined by the binodal. The curves measured for P E O polyarylate systems b y an optical method, where changes in composition occur as a result of a change in MW, are similar to curves for systems with an upper critical temperature of dissolution. However, no anomalies appear on these curves. Preheating of the mixture of 5 : 90 composition above the binodal results in crystallization taking place, olt subsequent cooling to 290 K, spontaneously from single phase solution without a n y preliminary separation into two amorphous phases.
* Vysokomol. soyed. A25: hTo. 2, 339-345, 1983.