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Association in dilute solutions of polyblock copolymers based on polydimethylsiloxane and polyarylates
Association in dilute solutions of polyblock copolymers
401
vanced stage of cure (see Fig. 3, curves 7, 8). In view of the low values of the diffusion coefficient of D B P micro-heterogeneity increases at the degrees of conversion in question [6], which leads to a widening of the transition regions. In the state of maximum cure the D B P concentration in polymeric phase is quite high, and is sufficient to ensure an appreciable reduction in Tg~ (Fig. 1, curve 1), i.e. there is a well defined plasticizing effect in the case of DBP. Thus the system E D - 2 0 - P O E P arrives at the onset of gelation with a minimal P O E P concentration, while with DBP, the concentration is practically equal to the original. This means that from the effect of dilution of an epoxy system b y an inert component, a maximum reduction in reaction rate is observed where D B P and P O E P are used as modifiers. Translated by R. J. A. HENDR¥ REFERENCES 1. P. G. BABAYEVSKII and J. K. GILLtIAM, J. Appl. Polymer Sci. 17: 2067, 1973 2. D. van KREVELEN, Svoistva i khimicheskoye stroyeniye polimerov (Properties and Chemical Structure of Polymers). p. 135, Izd. " K h i m i y a " , 1976 3. A. Ye. CItAL~](~I, Fiziko-khimicheskoye m e t o d y issledovaniya polimerov (Physicochemical Methods for Polymer Investigations). p. 30, I z d "Znaniye", No. 8, 1975 4. A. Ye. CHAL~vdE[, Vysokomol. soyed. A17: 2603, 1975 (Translated in Polymer Sci. U.S.S.R. 17: 11, 2997, 1975) 5. P. J. ~w_,ORY, Principles of Polymer Chemistry, N. Y., p. 13, 1953 6. S. A. NENAKIIOV, Candidate's dissertation, Moscow A. V. Topehiyev Chemical Physics Institute, 1978
Polymer ScienceU.S.S.R.Vol. 23, No. 2, pp. 401--409,1981 Printed in Poland
0032-39501811020401-09507.50]0 1982 Pergamon Press Ltd.
ASSOCIATION IN DILUTE SOLUTIONS OF POLYBLOCK COPOLYMERS BASED ON POLYDIMETHYLSILOXANE AND POLYARYLATES* S.-S. A . PAVLOVA, L . V. DVBROVI~A, YE. M. BELAVTSEVA,
M. A. PO~OMAREVAand S. I. SENKEVICtI Heteroorganic Compotmds Institute, U.S.S.R. Academy of Sciences (Received 6 November 1979) Very high scattering intensity values were obtained in an investigation of the properties of block copolymer solutions, using light scattering. These very high values due to the presence of maeromolecular associates were observed not only in * Vysokomol. soyed. A23: No. 2, 359-365, 1981.
402
S.-S. A. PAVLOVA et a~.
selective solvents, such as tetrachloroethylene or benzene, but also in dioxan, which is a solvent for both of the block copolymer components. Dimensions of the associates calculated from the light scattering data are in agreement with the results of the electron microscope investigations. F o ~ a long t i m e n o w t h e p h e n o m e n o n o f association o f p o l y m e r m a c r o m o l e e u l e s in dilute solutions h a s claimed t h e a t t e n t i o n of investigators. I t was s h o w n in [1-3] t h a t t h e e x t r a o r d i n a r i l y high molecular weight values p e r t a i n n o t to m a c r o molecules b u t to m a c r o m o l e c u l a r associates. T h e r e are several m e t h o d s t h a t m a y be used to d e t e c t t h e presence of associates in solutions. T h e m e t h o d m o s t sensitive is light scattering, where a m a r k e d increase in t h e s c a t t e r i n g i n t e n s i t y u n d e r p a r t i c u l a r conditions (in solvents) is due to t h e presence of associates in p o l y m e r a n d c o p o l y m e r solutions. F o r instance, c o p o l y m e r s o f s t y r e n e w i t h m e t h a c r y l i c acid f o r m associates in CC]4 a n d in t e t r a c h l o r o e t h a n e (TCE) [4], as do b l o c k c o p o l y m c r s of s t y r e n e a n d m e t h a c r y l a t e , in a c e t o n e a n d trichlorobenzene [5], while c o p o l y m e r s of s t y r e n e w i t h p o l y d i m e t h y l s i l o x a n e f o r m associates in n - a l k a n e s [6]. I t h a s b e e n suggested in p a p e r s b y M e r r e t t [7]. a n d K r a u s e [5] t h a t block e o p o l y m e r s in dilute solutions m a y f o r m i n t e r m o l e c u l a r , mice[les in solvents in which one of t h e r e s p e c t i v e h o m o p o l y m e r s dissolves, i.e. in selective solvents. T h u s b l o c k c o p o l y m e r s o f s t y r e n e a n d p o l y d i m e t h y l siloxane form, in n-alkanes, micelles whose nuclei consist of insoluble p o l y s t y r e n e blocks a n d are s u r r o u n d e d b y a shell of p o l y d i m e t h y l s i l o x a n e blocks t h a t h a v e swollen in solvents. F r o m a s t u d y o f p h o t o m i c r o g r a p h s t h e cited a u t h o r s w e r e able to calculate t h e nuclear radii o f t h e micelles, a n d to c o m p a r e t h e l a t t e r w i t h radii b a s e d on spherulitic models of t h e micelles. "Silar" type block copolymers were prepared from polydimethylsiloxane and polyarylates (polyesters} [8]. An investigation of the properties of these block copolymers brought up the problem of estimating their molecular weights and their eompositiona~ inhomogeneity. In view of this our aim in the present instance was to find a group of solvents in which it would be possible to carry out measurement of light scattering intensities so as to determine 2tlw values in solvents in which association of copolymer macromolecules may take place. "Silar" block copolymers were prepared by heterofunctional polycondensation of oligoarylates (polyesters based on dichlorides of terephthalic acid and 3,3-bis-(4-hydroxyphenyl}phthalide) and oligodimethylsiloxanes [8]. The two block eopolymer specimens under study differed in respect to the degree of polymerization n ~ 105 (specimen 1) and 200 (specimen 2). The degree of polymerization of the oligoarylate was 10 for both specimens. All the solvents in which measurements were carried out (chloroform, cyclohexanone, THF, dioxan, benzene, TCE, methyl ethyl ketone (MEK) were painstakingly purified by standard methods [9]. The degree of purity was verified through the absence of asymmetrical light scattering. Before measurements were carried out solutions were filtered through glass porous filters or were centrifuged at 15,000 g for 1 hr. Light scattering intensity measurements were done with a " F i t s " photogoniodiffusometer with 2.=546 nm, temperature 25:t:0.1 °. In addition molecular weights were calculated from the sedimentation diagrams obtained by the Archibald method of approximation to equilibrium, using an lYIOM-3170 type ultracentrifuge (produced in Hungary) Do].
Association in dilute solutions of polybloek copolymers
403:
Specific partial volume determinations were carried out pyenomertically at a temperature of 254-0.1 ° . Refractive index increments were measured with a Pulfrieh type refractometer provided with a differential cell. Intrinsic viscosities were measured by a standard method, using a suspended level viscosimeter. Specimens intended for electron microscope investigations were prepared from dilute solutions (concentration 0.01 g/100 ml) by removing solvents in a desiccator or by sublimation of solvents from rapidly prefrozen specimens under vacuum (10-5-10 -6 tort) at --40 °, and in individual cases, at --80 °, for 6 hr. A drop of the solution being investigated was coated on a carbon film-support. Investigations were made with the aid of an EMV-100L eleeron microscope (magnification × 10,000). The microscopic magnification was verified with the aid of strictly calibrated particles of polystyrene latex measuring 850 /~. Shading was done with a platinum-palladium alloy, using a VUP-2 vacuum apparatus. Of t h e solvents in T a b l e 1 a g r o u p in which t h e m o l e c u l a r w e i g h t v a l u e s are v e r y high m a y be seen. T h u s values of Atapp for specimen 1 in T C E a n d in b e n z e n e a m o u n t to several millions a n d t h e curred c h a r a c t e r of t h e Z i m m diag r a m s is seen in Fig. la. Values of t h e second virial coefficient are below zero in t h e s e cases. T e t r a c h l o r o e t h a n e a n d b e n z e n e are selective solvents w i t h r e s p e c t to one of t h e t w o b l o c k c o p o l y m e r c o m p o n e n t s : T C E is a good s o l v e n t for t h e p o l y a r y l a t e only, a n d likewise b e n z e n e for t h e oligodimethylsiloxane. T h e d a t a in T a b l e 1 a n d Fig. l a evidence t h e presence of associates in t h e b l o c k c o p o l y m e r solutions.
go .^8 -~-'IU I0
~
c=O O'Zl
8
0'18:
G
ko/u
O.J2
0~.5
0~.8
/.I
b
OL.J
0'-5
v 0.@
J 1.2
S~,nz[~)+iOOc FIG: 1. Ke/Ro vs. sin 2(~-) plot for specimens 1 (a) and 2 (b); the solvent was benzene. I t is k n o w n [11, 12] t h a t u n d e r a p p r o p r i a t e conditions associates m a y g r o w w i t h t i m e or m a y d i s i n t e g r a t e u n d e r t h e influence of t e m p e r a t u r e . On v e r i f y i n g changes in t h e i n t e n s i t y of light s c a t t e r i n g b y solutions of s p e c i m e n 1 in T C E it w a s f o u n d t h a t t h e i n t e n s i t y r e m a i n s c o n s t a n t o v e r 4 - d a y period (Fitg. 2), i.e. t h e d i m e n s i o n s of associates r e m a i n c o n s t a n t w i t h time.
404
S.-S. A. PAVI,OVAeta/.
As is seen from Table 1, the/~w value for specimens 1 is 100,000, and molecular weight measurements may be carried out in TttF, chloroform and cyclohexanone. However, as was noted in [131, identical refractive indices for polydimethylsiloxane and the solvent in THF result in an absence of scattering by siloxane blocks, and molecular weight is determined solely for the polyarylate component. Compositional inhomogeneity calculated in accordance with equations ~14] for specimen 1 proved to be only slight. ~x/g
FO
~, t
.__1 /
:
--
.
I
,I ,y
i
Cgaz 1 5
T/me~d a y s FIQ. 2. Relations between the light scattering intensity Rg0 and time for specimen 1; the solvent was TCE. Benzene is a better solvent for specimen 2 (with a ~75% concentration v f the dimethysiloxane component) than for specimen 1 (61% PDMS). This is apparent from the Zimm diagram (Fig. lb) and from the positive value of As. In contradistinction to specimen 1 the molecular weight of specimen 2, determined in THF, was found to be 300,000. Moreover molecular weight values determined from the light scattering and the sedimentation data coincide. Undoubtedly the foregoing molecular weight does not refer to the polyarylate component, but is the MW of the block eopolymer as a whole. The true MW of the specimen in question is 270,000, and, as one would have expected, the compositional inhomogeneity is more marked than in the case of specimen 1, in view of the greater length of the siloxane block, while the block factor is of the same order for both specimens. Dioxan is a slightly unusual solvent. Although dioxan is a good solvent for both the block copolymer components, Mapp for specimens 1 and 2 exceeded Mu, by factors of 2 and 7 respecitively. Moreover, molecular weight increases with time in dioxan, and there is a simultaneous reduction in the value of As (Table 2). We assume that association takes place in dioxan, and that growth of the associates proceeds with time. However, calculation of the particle sizes based on the Zimm diagram showed that R~ for specimen 2 remains constant with time, and is equal to ~400 _~. A similar fact was observed in [15] where the size of a~sociates remained constant while the MW increased. This was attributed by the authors to a gradual consolidation of supermolecular formations. The appearance of associates with time in thermodynamically good solvents
THF
Does not dissolve Dissolves
Dissolves
polydimethylsiloxane
Specimen, No.
Time, days
1 "00
1'50
4-00
A~X 104
TABLE
3.62 0.39
12.0 1.7
0"20 0"60
0"15 0"33
4.5 1.4 1-1 --0.9
1200 - - 0"05
20 10" 10 10 10" 200
0.43
8.3
0"47
specimen 1 (10 : 105)
ku
A~xlO4l[t/]'dl/g[
4.5
M a p1p0X- x4
20 29 32
~app X 1 0 -4
180 180 170
Specimen No.
(Solvent : dioxan) Time, days
)~app X 1O- 4
200 280
A2 X 104
0"54 0.43
450 400
(R;),/,,
h
0"85
10"34 0'158 0"459
0"14 0"846 9.0
48
0"75
7"56 0"130 0.54
7O
1 "38
1"38
0"755
0-380
12.5
-- 7'8
specimen 2 (10 : 200)
k~r
30 30* 200
80
Mapp X
2. V A R I A T I O N S I N M O L E C U L A R W E I G H T P A R A M E T E R S VITITH TIME
* Molecular weight based on results of sedimentation analysis.
Benzene
T CE
Chloroform Cyelohexmlone
Does not dissolve
dissolve Dissolves
Dioxan
Does not
polyarylate
MEK
Solvents
Solubility of the homopolymer
TABLE 1. C H A R A C T E R I S T I C S OF T H E S P E C I M E N S U N D E R s T U D Y
O
O
8
o
o
406
S.-S. A. PAVLOVAeta/,
(As>0) is accounted for by crystalline phase forming from blocks of one of the components. It is known [16] tha~ polyarylates in dioxan form crystalline phase, so this process may well take place in a polyblock polymer containing polyarylate. The value of As is an indicator of the solvent quality. As was noted above, TCE, benzene and MEK are thermodynamically poor solvents for the block eopolymers under study. Formation of associates takes place for specimen 1 in TCE and benzene, and the values ofA 2 are negative. At the same time Elias has shown that positive values of A~ may appear if associates are present in solutions [17]. This proved to be so in the present instance is solutions of the block eopolymers in dioxan (see Table 1). It is the view of the authors of [18-20] that the Huggins constant may provide a further reasonably sensitive criterion for association or even for aggregation. The value of Huggins constant for most polymeric systems is kH~0"5. It was shown in [19, 20] that a marked increase in kH appears in the case of association. At the same time, however, the authors say that viscosimetric measurements alone do not provide adequate grounds for deciding whether or not association has taken place. It is clear from Table 1 that it is precisely in those solvents where we would assume (from scattering data) that association has taken place that the value of kH is significantly higher than in a good solvent (chloroform). To substantiate our observations we carried out electron microscope investigations. This method has been successfully used by authors investigating dilute polymer solutions, given appropriate conditions of preparation of the compounds under study [21-23]. Obviously the conditions must be such as will preclude the association of polymer in a solution taking place as a result of a low rate of solvent evaporation or through the solution concentration increasing during the drying process. Such difficulties can only be eliminated by way of a constant refinement of methods used for preparation of the compounds. For instance it was shown in [22, 23] that certain disadvantages occur in the case of freeze=drying, and accordingly a novel method has been proposed, which allows the use of a larger number of solvent. Preliminary preparation was carried out by solvent evaporation from a dilute solution, making it possible to obtain a statistical distribution of molecules according to size on the support. The formation of associates was prevented by keeping the solution concentration low, and the drying rate high. The electron microscope reveals spherical particles of size 350-800/~ (photomicrographs in Fig. 3b); these would presumably correspond to individual macromo]ecules and to associates of the block copolymer (specimen 2) in dioxan. Dimensions of the associates accord with those calculated on the basis of the light scattering data, where the radius of inertia (R~)~ for the specimen was ,,,400 ~. Spherical particles of the order of 350 A (Fig. 3¢) were also found, in benzene (a good solvent for specimen 2) by electron microscopy, and it appears from the light scattering data that the radius of inertia
Association in dilute solutions of polyblock copolymers
407
FIG. 3. Photomicrographs of specimens 1 (a} and 2 (b-d). Solvents: TCE (a), dioxan (b} and benzene, removed by drying (c) and freezing (d); x 30,000.
408
S.:S. A. PAVLOVAeta/.
is 160 A. A n analysis o f p h o t o m i c r o g r a p h s o f t h e specimens in this solvent s h o w t h a t t h e spherical particles are o f u n i f o r m dimensions. T h e particles are d i s c r e t e ones; t h e distance separating one f r o m a n o t h e r varies. T h e elimination of b e n z e n e in this case was b r o u g h t a b o u t in t h e same w a y as t h e elimination of dioxan. W h e n a n o t h e r m e t h o d o f p r e p a r a t i o n was used (freezing and: drying) spherical particles likewise a p p e a r in t h e p h o t o m i c r o g r a p h s for specimen 2 (solution in benzene, Fig. 3d). I t appears f r o m a n analysis o f t h e p h o t o m i c r o g r a p h s t h a t in this instance b o t h m e t h o d s o f solvent elimination produce similar results a n d shed light on t h e shape o f t h e copolymer macromolecules. F i g u r e 3a shows t h e f o r m a t i o n of supermolecular structures, of t h e o r d e r o f 1600 A or more, in T C E for specimen 1. T h u s it appears f r o m this i n v e s t i g a t i o n o f polyblock c o p o l y m e r solutions t h a t a g r e e m e n t exists between the light scattering d a t a a n d t h e results o f electron microscopy investigations. I t was f o u n d b y light s c a t t e r i n g t h a t s u p e r m o l e c u l a r f o r m a t i o n s m a y a p p e a r in selective solvents, and, in some cases, in c o m m o n solvents, direct confirmation o f which was o b t a i n e d b y electron microscopy. Translat~ by R. J. A. HENDRY REFERENCES
1. H. G. ELIAS, Light Scattering by Polymer Solutions, (Ed. M. B. Huglin), p. 397~ London-New York, 1972 2. M. BOHDANESKY, V. PETRUS and P, KRATO~rHVIL, Collect. Czechosl. Chem. Commun. 34: 1168, 1968 3. H. MORAWETZ and R. H. GORBAN, J. Polymer Sci. 12: 133, 1954 4. JEW CHANG and H. MORAWETZ, J. Phys. Chem. 60: 782, 1956 5. S. KRAUSE, J. Phys. Chem. 68: 1948, 1964 6. J. V. DAWKINS and G. TAULOV, Makromolek. Chem. 180: 1737, 1979 7. E. M. MEERETT, J. Polymer Sci. 24: 467, 1957 8. S. B. DOLGOPLOSK, V. P. MILESHKEVICH, P. M. VALETSKII, V. V. KORSHAK~ S. V. VINOGRADOVA, Ye. Yu. PACHOGINA, N. G. SVIRIDOVA, G. V. GRYAZNOVA, Ye. I. LEVIN, L. B. SHIROKOVA and L. K. YEREMINA, Vysokomol, soyed. BI9~ 748, 1977 (Not translated in Polymer Sei. U.S.S.R.) 9. A. WAISBERGER, E. PROSKAUER, J. RIDDICK and E. TUPPS, Organieheskie rastvoriteli, Izd. inostr, lit, 1958 10. W. J. ARCHIBALD, J. Appl. Phys. 18: 362, 1974 11. H. G. ELIAS and H. DIETSHY, Makromolek. Chem. 105: 102, 1967 12. H. A. DIEN J. Polymer Sci. 12: 417, 1954 13. Ye. P. PISKAREVA, Ye. G. ERENBURG and I. Ya. PODDUBNYI Vysokomol. soyed. ,%20: 784, 1978 (Translated in Poylmer Sci. U.S.S.R. 20: 4, 883, 1978) 14. W. BUSHUK and H. BENOIT, Canad. J. Chem. 86: 1616, 1958 15. I. Ya. PODDUBNYI, Ye. G. ERENBURG, Ire. P. CHERNOVA-IVANOVA and G. G. KARTASHOVA, Dokl. AN SSSR I48: 384, 1963 16. N. V. I¢L1MANOVA, L. V. DUBROVINA, S.-S. A. PAVLOVA, T. M. BABCHINITSER, Ira. V. GENIN and V. V. KORSHAK, Vysokomol. soyed. A19: 2309, 1977 (Translated in Polymer Sci. U.S.S.R. 19: 2649, 1977) 17. H. G. ELIAS and H. LYS, Makromolek. Chem. 92: 1, 1966 18. W. KUHN and P. MOSER, Makromolek. Chem. 44-46: 71, 1961
Chemical structure and glass transition temperatures of polyarimides
408
19. J. C. WATI~ERSON and H. G. ET.TAS,Makromolek. Chem. 157: 237, 1972 20. O. WOLF, A. SIUIERBERG, Z. PRIEL and M. N. LAYEC-RAPHLEN, Polymer 20: 281, 1979 21. L. KOSZTERSZITZ, W. K. R. RAVNIKOL and L. V. SCHULZ, Makromolek. Chem. 178: 1133, 1977 22. L. KOSZTERSZITZ and G. V. SCHULZ, Makromolek. Chem. 178: 2434, 1977 23. H. REIMI.INGER, lqaturwissenschaften 63: 574, 1976
Polymer Science U.S.S.R.Vol.23, No. 2, pp. 409-418,1981 Printed in Poland
0032-3950/81/020409-10507.50/O 1982Pergamonpress Ltd.
THE CHEMICAL STRUCTURE AND GLASS TRANSITION TEMPERATURES OF POLYARIMIDES* L. N. KORZHAVII~, S. V. BRONNIKOVand S. YA. FRENKEL' High Polymer Institute, U.S.S.R. Academy of Sciences
(Received 16 Nowmber 1979) Glass transition temperature have been calculated for 48 polyarimides, using the Askadskii--Slonimskii relation. A relationship has been found between glass transition temperatures, and the chain flexibility and number of imide rings providing for intermolecular interaction. I t was found that the critical chain rigidity value is 0.67. If the rigidity exceeds 0.67, the glass transition temperatures of the polymers are determined solely by forces of intermolecular interaction between adjacent chains.
INTERMOLECULARinteractions between adjacent macromolecules are one of t h e main factors determining the physical properties of polymers. Intermolecular forces act as pseudo network points inhibiting free rotation of individual chain segments and are responsible for major limitations in the number of chain conformations possible for maeromolecules in bulk. The introduction of bridge groups as loops between maeromolecules leads to increased kinetic and thermodynamic flexibility levels, a n d increased molecular mobility. The increased flexibility leads, in t u r n , to a r e d u c t i o n in the glass t r a n s i t i o n t e m p e r a t u r e o f t h e p o l y m e r s [1]. I n the p r e s e n t instance we t o o k as an example the following series of polyarimides, w i t h oligomerization coefficients n = 1-8 a n d i n v e s t i g a t e d intermoleeular i n t e r a c t i o n a n d chain flexibility in relation to the glass t r a n s i t i o n t e m p e r a t u r e of the polymers * Vysokomol. soyed. A23: 1~o. 2, 366-374, 1981.
401
vanced stage of cure (see Fig. 3, curves 7, 8). In view of the low values of the diffusion coefficient of D B P micro-heterogeneity increases at the degrees of conversion in question [6], which leads to a widening of the transition regions. In the state of maximum cure the D B P concentration in polymeric phase is quite high, and is sufficient to ensure an appreciable reduction in Tg~ (Fig. 1, curve 1), i.e. there is a well defined plasticizing effect in the case of DBP. Thus the system E D - 2 0 - P O E P arrives at the onset of gelation with a minimal P O E P concentration, while with DBP, the concentration is practically equal to the original. This means that from the effect of dilution of an epoxy system b y an inert component, a maximum reduction in reaction rate is observed where D B P and P O E P are used as modifiers. Translated by R. J. A. HENDR¥ REFERENCES 1. P. G. BABAYEVSKII and J. K. GILLtIAM, J. Appl. Polymer Sci. 17: 2067, 1973 2. D. van KREVELEN, Svoistva i khimicheskoye stroyeniye polimerov (Properties and Chemical Structure of Polymers). p. 135, Izd. " K h i m i y a " , 1976 3. A. Ye. CItAL~](~I, Fiziko-khimicheskoye m e t o d y issledovaniya polimerov (Physicochemical Methods for Polymer Investigations). p. 30, I z d "Znaniye", No. 8, 1975 4. A. Ye. CHAL~vdE[, Vysokomol. soyed. A17: 2603, 1975 (Translated in Polymer Sci. U.S.S.R. 17: 11, 2997, 1975) 5. P. J. ~w_,ORY, Principles of Polymer Chemistry, N. Y., p. 13, 1953 6. S. A. NENAKIIOV, Candidate's dissertation, Moscow A. V. Topehiyev Chemical Physics Institute, 1978
Polymer ScienceU.S.S.R.Vol. 23, No. 2, pp. 401--409,1981 Printed in Poland
0032-39501811020401-09507.50]0 1982 Pergamon Press Ltd.
ASSOCIATION IN DILUTE SOLUTIONS OF POLYBLOCK COPOLYMERS BASED ON POLYDIMETHYLSILOXANE AND POLYARYLATES* S.-S. A . PAVLOVA, L . V. DVBROVI~A, YE. M. BELAVTSEVA,
M. A. PO~OMAREVAand S. I. SENKEVICtI Heteroorganic Compotmds Institute, U.S.S.R. Academy of Sciences (Received 6 November 1979) Very high scattering intensity values were obtained in an investigation of the properties of block copolymer solutions, using light scattering. These very high values due to the presence of maeromolecular associates were observed not only in * Vysokomol. soyed. A23: No. 2, 359-365, 1981.
402
S.-S. A. PAVLOVA et a~.
selective solvents, such as tetrachloroethylene or benzene, but also in dioxan, which is a solvent for both of the block copolymer components. Dimensions of the associates calculated from the light scattering data are in agreement with the results of the electron microscope investigations. F o ~ a long t i m e n o w t h e p h e n o m e n o n o f association o f p o l y m e r m a c r o m o l e e u l e s in dilute solutions h a s claimed t h e a t t e n t i o n of investigators. I t was s h o w n in [1-3] t h a t t h e e x t r a o r d i n a r i l y high molecular weight values p e r t a i n n o t to m a c r o molecules b u t to m a c r o m o l e c u l a r associates. T h e r e are several m e t h o d s t h a t m a y be used to d e t e c t t h e presence of associates in solutions. T h e m e t h o d m o s t sensitive is light scattering, where a m a r k e d increase in t h e s c a t t e r i n g i n t e n s i t y u n d e r p a r t i c u l a r conditions (in solvents) is due to t h e presence of associates in p o l y m e r a n d c o p o l y m e r solutions. F o r instance, c o p o l y m e r s o f s t y r e n e w i t h m e t h a c r y l i c acid f o r m associates in CC]4 a n d in t e t r a c h l o r o e t h a n e (TCE) [4], as do b l o c k c o p o l y m c r s of s t y r e n e a n d m e t h a c r y l a t e , in a c e t o n e a n d trichlorobenzene [5], while c o p o l y m e r s of s t y r e n e w i t h p o l y d i m e t h y l s i l o x a n e f o r m associates in n - a l k a n e s [6]. I t h a s b e e n suggested in p a p e r s b y M e r r e t t [7]. a n d K r a u s e [5] t h a t block e o p o l y m e r s in dilute solutions m a y f o r m i n t e r m o l e c u l a r , mice[les in solvents in which one of t h e r e s p e c t i v e h o m o p o l y m e r s dissolves, i.e. in selective solvents. T h u s b l o c k c o p o l y m e r s o f s t y r e n e a n d p o l y d i m e t h y l siloxane form, in n-alkanes, micelles whose nuclei consist of insoluble p o l y s t y r e n e blocks a n d are s u r r o u n d e d b y a shell of p o l y d i m e t h y l s i l o x a n e blocks t h a t h a v e swollen in solvents. F r o m a s t u d y o f p h o t o m i c r o g r a p h s t h e cited a u t h o r s w e r e able to calculate t h e nuclear radii o f t h e micelles, a n d to c o m p a r e t h e l a t t e r w i t h radii b a s e d on spherulitic models of t h e micelles. "Silar" type block copolymers were prepared from polydimethylsiloxane and polyarylates (polyesters} [8]. An investigation of the properties of these block copolymers brought up the problem of estimating their molecular weights and their eompositiona~ inhomogeneity. In view of this our aim in the present instance was to find a group of solvents in which it would be possible to carry out measurement of light scattering intensities so as to determine 2tlw values in solvents in which association of copolymer macromolecules may take place. "Silar" block copolymers were prepared by heterofunctional polycondensation of oligoarylates (polyesters based on dichlorides of terephthalic acid and 3,3-bis-(4-hydroxyphenyl}phthalide) and oligodimethylsiloxanes [8]. The two block eopolymer specimens under study differed in respect to the degree of polymerization n ~ 105 (specimen 1) and 200 (specimen 2). The degree of polymerization of the oligoarylate was 10 for both specimens. All the solvents in which measurements were carried out (chloroform, cyclohexanone, THF, dioxan, benzene, TCE, methyl ethyl ketone (MEK) were painstakingly purified by standard methods [9]. The degree of purity was verified through the absence of asymmetrical light scattering. Before measurements were carried out solutions were filtered through glass porous filters or were centrifuged at 15,000 g for 1 hr. Light scattering intensity measurements were done with a " F i t s " photogoniodiffusometer with 2.=546 nm, temperature 25:t:0.1 °. In addition molecular weights were calculated from the sedimentation diagrams obtained by the Archibald method of approximation to equilibrium, using an lYIOM-3170 type ultracentrifuge (produced in Hungary) Do].
Association in dilute solutions of polybloek copolymers
403:
Specific partial volume determinations were carried out pyenomertically at a temperature of 254-0.1 ° . Refractive index increments were measured with a Pulfrieh type refractometer provided with a differential cell. Intrinsic viscosities were measured by a standard method, using a suspended level viscosimeter. Specimens intended for electron microscope investigations were prepared from dilute solutions (concentration 0.01 g/100 ml) by removing solvents in a desiccator or by sublimation of solvents from rapidly prefrozen specimens under vacuum (10-5-10 -6 tort) at --40 °, and in individual cases, at --80 °, for 6 hr. A drop of the solution being investigated was coated on a carbon film-support. Investigations were made with the aid of an EMV-100L eleeron microscope (magnification × 10,000). The microscopic magnification was verified with the aid of strictly calibrated particles of polystyrene latex measuring 850 /~. Shading was done with a platinum-palladium alloy, using a VUP-2 vacuum apparatus. Of t h e solvents in T a b l e 1 a g r o u p in which t h e m o l e c u l a r w e i g h t v a l u e s are v e r y high m a y be seen. T h u s values of Atapp for specimen 1 in T C E a n d in b e n z e n e a m o u n t to several millions a n d t h e curred c h a r a c t e r of t h e Z i m m diag r a m s is seen in Fig. la. Values of t h e second virial coefficient are below zero in t h e s e cases. T e t r a c h l o r o e t h a n e a n d b e n z e n e are selective solvents w i t h r e s p e c t to one of t h e t w o b l o c k c o p o l y m e r c o m p o n e n t s : T C E is a good s o l v e n t for t h e p o l y a r y l a t e only, a n d likewise b e n z e n e for t h e oligodimethylsiloxane. T h e d a t a in T a b l e 1 a n d Fig. l a evidence t h e presence of associates in t h e b l o c k c o p o l y m e r solutions.
go .^8 -~-'IU I0
~
c=O O'Zl
8
0'18:
G
ko/u
O.J2
0~.5
0~.8
/.I
b
OL.J
0'-5
v 0.@
J 1.2
S~,nz[~)+iOOc FIG: 1. Ke/Ro vs. sin 2(~-) plot for specimens 1 (a) and 2 (b); the solvent was benzene. I t is k n o w n [11, 12] t h a t u n d e r a p p r o p r i a t e conditions associates m a y g r o w w i t h t i m e or m a y d i s i n t e g r a t e u n d e r t h e influence of t e m p e r a t u r e . On v e r i f y i n g changes in t h e i n t e n s i t y of light s c a t t e r i n g b y solutions of s p e c i m e n 1 in T C E it w a s f o u n d t h a t t h e i n t e n s i t y r e m a i n s c o n s t a n t o v e r 4 - d a y period (Fitg. 2), i.e. t h e d i m e n s i o n s of associates r e m a i n c o n s t a n t w i t h time.
404
S.-S. A. PAVI,OVAeta/.
As is seen from Table 1, the/~w value for specimens 1 is 100,000, and molecular weight measurements may be carried out in TttF, chloroform and cyclohexanone. However, as was noted in [131, identical refractive indices for polydimethylsiloxane and the solvent in THF result in an absence of scattering by siloxane blocks, and molecular weight is determined solely for the polyarylate component. Compositional inhomogeneity calculated in accordance with equations ~14] for specimen 1 proved to be only slight. ~x/g
FO
~, t
.__1 /
:
--
.
I
,I ,y
i
Cgaz 1 5
T/me~d a y s FIQ. 2. Relations between the light scattering intensity Rg0 and time for specimen 1; the solvent was TCE. Benzene is a better solvent for specimen 2 (with a ~75% concentration v f the dimethysiloxane component) than for specimen 1 (61% PDMS). This is apparent from the Zimm diagram (Fig. lb) and from the positive value of As. In contradistinction to specimen 1 the molecular weight of specimen 2, determined in THF, was found to be 300,000. Moreover molecular weight values determined from the light scattering and the sedimentation data coincide. Undoubtedly the foregoing molecular weight does not refer to the polyarylate component, but is the MW of the block eopolymer as a whole. The true MW of the specimen in question is 270,000, and, as one would have expected, the compositional inhomogeneity is more marked than in the case of specimen 1, in view of the greater length of the siloxane block, while the block factor is of the same order for both specimens. Dioxan is a slightly unusual solvent. Although dioxan is a good solvent for both the block copolymer components, Mapp for specimens 1 and 2 exceeded Mu, by factors of 2 and 7 respecitively. Moreover, molecular weight increases with time in dioxan, and there is a simultaneous reduction in the value of As (Table 2). We assume that association takes place in dioxan, and that growth of the associates proceeds with time. However, calculation of the particle sizes based on the Zimm diagram showed that R~ for specimen 2 remains constant with time, and is equal to ~400 _~. A similar fact was observed in [15] where the size of a~sociates remained constant while the MW increased. This was attributed by the authors to a gradual consolidation of supermolecular formations. The appearance of associates with time in thermodynamically good solvents
THF
Does not dissolve Dissolves
Dissolves
polydimethylsiloxane
Specimen, No.
Time, days
1 "00
1'50
4-00
A~X 104
TABLE
3.62 0.39
12.0 1.7
0"20 0"60
0"15 0"33
4.5 1.4 1-1 --0.9
1200 - - 0"05
20 10" 10 10 10" 200
0.43
8.3
0"47
specimen 1 (10 : 105)
ku
A~xlO4l[t/]'dl/g[
4.5
M a p1p0X- x4
20 29 32
~app X 1 0 -4
180 180 170
Specimen No.
(Solvent : dioxan) Time, days
)~app X 1O- 4
200 280
A2 X 104
0"54 0.43
450 400
(R;),/,,
h
0"85
10"34 0'158 0"459
0"14 0"846 9.0
48
0"75
7"56 0"130 0.54
7O
1 "38
1"38
0"755
0-380
12.5
-- 7'8
specimen 2 (10 : 200)
k~r
30 30* 200
80
Mapp X
2. V A R I A T I O N S I N M O L E C U L A R W E I G H T P A R A M E T E R S VITITH TIME
* Molecular weight based on results of sedimentation analysis.
Benzene
T CE
Chloroform Cyelohexmlone
Does not dissolve
dissolve Dissolves
Dioxan
Does not
polyarylate
MEK
Solvents
Solubility of the homopolymer
TABLE 1. C H A R A C T E R I S T I C S OF T H E S P E C I M E N S U N D E R s T U D Y
O
O
8
o
o
406
S.-S. A. PAVLOVAeta/,
(As>0) is accounted for by crystalline phase forming from blocks of one of the components. It is known [16] tha~ polyarylates in dioxan form crystalline phase, so this process may well take place in a polyblock polymer containing polyarylate. The value of As is an indicator of the solvent quality. As was noted above, TCE, benzene and MEK are thermodynamically poor solvents for the block eopolymers under study. Formation of associates takes place for specimen 1 in TCE and benzene, and the values ofA 2 are negative. At the same time Elias has shown that positive values of A~ may appear if associates are present in solutions [17]. This proved to be so in the present instance is solutions of the block eopolymers in dioxan (see Table 1). It is the view of the authors of [18-20] that the Huggins constant may provide a further reasonably sensitive criterion for association or even for aggregation. The value of Huggins constant for most polymeric systems is kH~0"5. It was shown in [19, 20] that a marked increase in kH appears in the case of association. At the same time, however, the authors say that viscosimetric measurements alone do not provide adequate grounds for deciding whether or not association has taken place. It is clear from Table 1 that it is precisely in those solvents where we would assume (from scattering data) that association has taken place that the value of kH is significantly higher than in a good solvent (chloroform). To substantiate our observations we carried out electron microscope investigations. This method has been successfully used by authors investigating dilute polymer solutions, given appropriate conditions of preparation of the compounds under study [21-23]. Obviously the conditions must be such as will preclude the association of polymer in a solution taking place as a result of a low rate of solvent evaporation or through the solution concentration increasing during the drying process. Such difficulties can only be eliminated by way of a constant refinement of methods used for preparation of the compounds. For instance it was shown in [22, 23] that certain disadvantages occur in the case of freeze=drying, and accordingly a novel method has been proposed, which allows the use of a larger number of solvent. Preliminary preparation was carried out by solvent evaporation from a dilute solution, making it possible to obtain a statistical distribution of molecules according to size on the support. The formation of associates was prevented by keeping the solution concentration low, and the drying rate high. The electron microscope reveals spherical particles of size 350-800/~ (photomicrographs in Fig. 3b); these would presumably correspond to individual macromo]ecules and to associates of the block copolymer (specimen 2) in dioxan. Dimensions of the associates accord with those calculated on the basis of the light scattering data, where the radius of inertia (R~)~ for the specimen was ,,,400 ~. Spherical particles of the order of 350 A (Fig. 3¢) were also found, in benzene (a good solvent for specimen 2) by electron microscopy, and it appears from the light scattering data that the radius of inertia
Association in dilute solutions of polyblock copolymers
407
FIG. 3. Photomicrographs of specimens 1 (a} and 2 (b-d). Solvents: TCE (a), dioxan (b} and benzene, removed by drying (c) and freezing (d); x 30,000.
408
S.:S. A. PAVLOVAeta/.
is 160 A. A n analysis o f p h o t o m i c r o g r a p h s o f t h e specimens in this solvent s h o w t h a t t h e spherical particles are o f u n i f o r m dimensions. T h e particles are d i s c r e t e ones; t h e distance separating one f r o m a n o t h e r varies. T h e elimination of b e n z e n e in this case was b r o u g h t a b o u t in t h e same w a y as t h e elimination of dioxan. W h e n a n o t h e r m e t h o d o f p r e p a r a t i o n was used (freezing and: drying) spherical particles likewise a p p e a r in t h e p h o t o m i c r o g r a p h s for specimen 2 (solution in benzene, Fig. 3d). I t appears f r o m a n analysis o f t h e p h o t o m i c r o g r a p h s t h a t in this instance b o t h m e t h o d s o f solvent elimination produce similar results a n d shed light on t h e shape o f t h e copolymer macromolecules. F i g u r e 3a shows t h e f o r m a t i o n of supermolecular structures, of t h e o r d e r o f 1600 A or more, in T C E for specimen 1. T h u s it appears f r o m this i n v e s t i g a t i o n o f polyblock c o p o l y m e r solutions t h a t a g r e e m e n t exists between the light scattering d a t a a n d t h e results o f electron microscopy investigations. I t was f o u n d b y light s c a t t e r i n g t h a t s u p e r m o l e c u l a r f o r m a t i o n s m a y a p p e a r in selective solvents, and, in some cases, in c o m m o n solvents, direct confirmation o f which was o b t a i n e d b y electron microscopy. Translat~ by R. J. A. HENDRY REFERENCES
1. H. G. ELIAS, Light Scattering by Polymer Solutions, (Ed. M. B. Huglin), p. 397~ London-New York, 1972 2. M. BOHDANESKY, V. PETRUS and P, KRATO~rHVIL, Collect. Czechosl. Chem. Commun. 34: 1168, 1968 3. H. MORAWETZ and R. H. GORBAN, J. Polymer Sci. 12: 133, 1954 4. JEW CHANG and H. MORAWETZ, J. Phys. Chem. 60: 782, 1956 5. S. KRAUSE, J. Phys. Chem. 68: 1948, 1964 6. J. V. DAWKINS and G. TAULOV, Makromolek. Chem. 180: 1737, 1979 7. E. M. MEERETT, J. Polymer Sci. 24: 467, 1957 8. S. B. DOLGOPLOSK, V. P. MILESHKEVICH, P. M. VALETSKII, V. V. KORSHAK~ S. V. VINOGRADOVA, Ye. Yu. PACHOGINA, N. G. SVIRIDOVA, G. V. GRYAZNOVA, Ye. I. LEVIN, L. B. SHIROKOVA and L. K. YEREMINA, Vysokomol, soyed. BI9~ 748, 1977 (Not translated in Polymer Sei. U.S.S.R.) 9. A. WAISBERGER, E. PROSKAUER, J. RIDDICK and E. TUPPS, Organieheskie rastvoriteli, Izd. inostr, lit, 1958 10. W. J. ARCHIBALD, J. Appl. Phys. 18: 362, 1974 11. H. G. ELIAS and H. DIETSHY, Makromolek. Chem. 105: 102, 1967 12. H. A. DIEN J. Polymer Sci. 12: 417, 1954 13. Ye. P. PISKAREVA, Ye. G. ERENBURG and I. Ya. PODDUBNYI Vysokomol. soyed. ,%20: 784, 1978 (Translated in Poylmer Sci. U.S.S.R. 20: 4, 883, 1978) 14. W. BUSHUK and H. BENOIT, Canad. J. Chem. 86: 1616, 1958 15. I. Ya. PODDUBNYI, Ye. G. ERENBURG, Ire. P. CHERNOVA-IVANOVA and G. G. KARTASHOVA, Dokl. AN SSSR I48: 384, 1963 16. N. V. I¢L1MANOVA, L. V. DUBROVINA, S.-S. A. PAVLOVA, T. M. BABCHINITSER, Ira. V. GENIN and V. V. KORSHAK, Vysokomol. soyed. A19: 2309, 1977 (Translated in Polymer Sci. U.S.S.R. 19: 2649, 1977) 17. H. G. ELIAS and H. LYS, Makromolek. Chem. 92: 1, 1966 18. W. KUHN and P. MOSER, Makromolek. Chem. 44-46: 71, 1961
Chemical structure and glass transition temperatures of polyarimides
408
19. J. C. WATI~ERSON and H. G. ET.TAS,Makromolek. Chem. 157: 237, 1972 20. O. WOLF, A. SIUIERBERG, Z. PRIEL and M. N. LAYEC-RAPHLEN, Polymer 20: 281, 1979 21. L. KOSZTERSZITZ, W. K. R. RAVNIKOL and L. V. SCHULZ, Makromolek. Chem. 178: 1133, 1977 22. L. KOSZTERSZITZ and G. V. SCHULZ, Makromolek. Chem. 178: 2434, 1977 23. H. REIMI.INGER, lqaturwissenschaften 63: 574, 1976
Polymer Science U.S.S.R.Vol.23, No. 2, pp. 409-418,1981 Printed in Poland
0032-3950/81/020409-10507.50/O 1982Pergamonpress Ltd.
THE CHEMICAL STRUCTURE AND GLASS TRANSITION TEMPERATURES OF POLYARIMIDES* L. N. KORZHAVII~, S. V. BRONNIKOVand S. YA. FRENKEL' High Polymer Institute, U.S.S.R. Academy of Sciences
(Received 16 Nowmber 1979) Glass transition temperature have been calculated for 48 polyarimides, using the Askadskii--Slonimskii relation. A relationship has been found between glass transition temperatures, and the chain flexibility and number of imide rings providing for intermolecular interaction. I t was found that the critical chain rigidity value is 0.67. If the rigidity exceeds 0.67, the glass transition temperatures of the polymers are determined solely by forces of intermolecular interaction between adjacent chains.
INTERMOLECULARinteractions between adjacent macromolecules are one of t h e main factors determining the physical properties of polymers. Intermolecular forces act as pseudo network points inhibiting free rotation of individual chain segments and are responsible for major limitations in the number of chain conformations possible for maeromolecules in bulk. The introduction of bridge groups as loops between maeromolecules leads to increased kinetic and thermodynamic flexibility levels, a n d increased molecular mobility. The increased flexibility leads, in t u r n , to a r e d u c t i o n in the glass t r a n s i t i o n t e m p e r a t u r e o f t h e p o l y m e r s [1]. I n the p r e s e n t instance we t o o k as an example the following series of polyarimides, w i t h oligomerization coefficients n = 1-8 a n d i n v e s t i g a t e d intermoleeular i n t e r a c t i o n a n d chain flexibility in relation to the glass t r a n s i t i o n t e m p e r a t u r e of the polymers * Vysokomol. soyed. A23: 1~o. 2, 366-374, 1981.