- Email: [email protected]
Some problems involved in copolycondensation processes
SOME P R O B L E M S I N V O L V E D IN COPOLYCONDENSATION PROCESSES * E. TURSKA Lodzen Polytcchnical Institute
{Received 2 December 1971) ~N EARLY studies of copolymerization processes the aim of the authors was mainly to discover .conditions under which it would be possible for copolymers with particular compositions and properties to be prepared, and in addition there was the need to determine the relationship between the compositions and structures of these copolymers. In more recent investigations, including in particular the work reported in papers [1-5], a more complex problem is dealt with and it was found as a result of these investigations t h a t the properties of copolymers depend not only on their average molecular compositions, but also (to some considerable extent) on the structure of the individual maeromolecules. I t was found that copolymers which were identical in respect to their average molecular compositions and some other average physicochemical characteristics, differed in respect to their properties in those cases where dissimilarity in the degree of compositional inhomogeneity of these copolymers was observed. The results reported in papers [6-10] show t h a t the maeromolecular structure of copolymers prepared by polycondensation m a y vary according to the particular method adopted and the synthesis conditions. Block copolymers are obtainable by means of non-equilibrium polycondensation (interfacial or low-temperature processes of solution polycondensation) although macromolecules with alternating units are obtainable only by adopting specially selected reaction conditions. Compositional inhomogeneity occurs in statistical and in block copolycondensates: with the former one m a y assume, despite the completely statistical chaotic distribution of the differ ent monomer units in each macromolecule, t h a t the chemical composition of individual macromolecules m a y differ; in the latter case, though all the maeromolecules are made up of chain segments consisting of different units, individual macromolecules m ay differ as t o the length and number of these segments. In the literature regarding eopolycondensation processes authors have yet to throw light upon the problem of the compositional inhomogeneity of macromolecules. We have first to analyse the possible appearance of compositional inhomogeneity in relation to synthesis conditions, starting with known mechanisms of polycondensation processes. The methods most often used in the industry (though these are not the best methods) are equilibrium ones, namely those of high-temperature polycondensation in melts, and in high-boiling solvents. In consider ing copolymerization processes, let us begin with one of copolyesterification involving three starting materials, taking monomers with the same functional groups A and B in equimolar amounts, the total a m o u n t of these monomers being equimolar in respect to the a m o u n t of a third monomer with functional groups C. Let us assume t h a t the initial reactivity of both functional groups of each monomer is identicul, whether or not one of these groups m a y be substituted. W i t h simplifications of this nature Shtraikhman [11] and Tyuzyo [12], * Vysokomol. soyed, h i 5 : No. 2, 393-399, 1973. 448
S o m e p r o b l e m s i n v o l v e d m c o p o l y e o n d e n s a t i o n processes
449
s t a r t i n g w i t h t h e o r e t i c a l c o n s i d e r a t i o n s , d e r i v e d a n e q u a t i o n g i v i n g t h e c o m p o s i t i o n of t.he p r o d u c t of c o p o l y c o n d e n s a t i o n w h i c h in its final f o r m t a k e s t h e f o r m of
CA0
\C~o/
w h e r e ca0 a n d c~0 are t h e s t a r t i n g c o n c e n t r a t i o n s of e o m o n o m e r s w i t h i d e n t i c a l e n d g r o u p s ; cA a n d CB a r e t h e c o n c e n t r a t i o n s of t h e s a m e e n d g r o u p s a t a g i v e n degree of c o m p l e t e n e s s of t h e re,ration; r is t h e r e a c t i v i t y coefficient for t h e s t u d i e d c o m o n o m e r s ; r=k~/k.~, w h e r e k~ a n d ]c2 are r a t e c o n s t a n t s of t h e h o m o p o l y e o n d e n s a t i o n processes. O n a n a l y s i n g t h e a b o v e e q u a t i o n one m a y c v n c l u d e t h a t t h e c o m p o s i t i o n of t h e m a c r o m o l e c u l e s f o r m e d a t a g i v e n m o m e n t d e p e n d s o n t h e r e a c t i v i t y r a t i o of b o t h m o n o m e r s , ml(l c o n s e q u e n t l y o n t h e degree of c o m p l e t e n e s s of t h e r e a c t i o n . T h e r e s u l t s r e p o r t e d in p a p e r s [13 15] b y a u t h o r s i n v e s t i g a t i n g e o p o l y a m i d e s g e n e r a l l y b~ar o u t t h i s eonelusi0n. A f t e r a n a l y s i n g t h e r e a c t i o n kinetics, a n d also in v i e w of p u b l i s h e r i n f o r m a t i o n , it is r ~ a s o n a b l e ~o c o n c l u d e t h a t t h e r a t e a t w h i c h e a c h o f t h e t w o m o n o m e r s w i t h i d e n t i c a l e n d g r o u p s r e a c t s will differ a c c o r d i n g to t h e r e a c t i v i t y a n d t h e a m o u n t of t h e m o n o m e r in q u e s t i o n , a n d t h e r a t e s of r e a c t i o n o f t h e s e m o n o m e r s v a r y w i t h t i m e . I t is fair to a s s u m e th~tt t h e m a c r o m o l e c u l e s f o r m e d in t h e e a r l y stages of t h e r e a c t i o n will c o n t a i n c o n s i d e r a b l y m o r e m o n o m e r u n i t s b e l o n g i n g t o t h e m o r e a c t i v e e o m o n o m e r , a n d t h a t o n l y w h e n a sufficient degree of d e p l e t i o n of t h i s m o n o m e r in t h e r e a c t i o n m i x t u r e h a s b e e n r e a c t e d will t h e n m u b,,r of m o n o m e r u n i t s b e l o n g i n g to t h e less a c t i v e m o n o m e r b e g i n to increase. I n eopolycond~,nsation processes g r o w t h of t h e m a c r o m o l e c u l e s t a k e s place e i t h e r t h r o u g h t h e a d d i t i o u of t h e m o n o m e r a n d o l i g o m e r molecules, or as a r e s u l t of r e a c t i o n s i n v o l v i n g t h e m a e r o m o l e eules t h a t h a v e a l r e a d y b e e n f o r m e d . T h e m o d e of g r o w t h o f m a c r o m o l e e u l e s is f a i r l y eompl~x, b u t t h e r e arc n o g r o u n d s for a s s u m i n g t h a t t h e s t a t i s t i c a l ehemicM c o m p o s i t i o n of all the, m a c r o m o l e c u l e s will be i n d e n t i c a l . A e c o r d i n g t o t h e s c h e m e of p r o p a g a t i o n o u t l i n e d a b o v e , t h e m a e r o m o l e c u l e s in t h e react i~n m i x t u r e will differ f r o m one a n o t h e r a c c o r d i n g to t h e degree of c o m p l e t e n e s s of t h e reaction. i.e. t h e n u m b e r of d i f f e r e n t m o n o m e r u n i t s in e a c h m a c r o m o l e c u l e will v a r y , a n d t h e c o m p o s i t i o n of c h a i n s e g m e n t s of w h i c h t h e s e m a c r o m o l e c u l e s consist m a y differ; f l l r t h e r m o r e t h e a m o u n t of difference in t h e c o m p o s i t i o n of t h e m a e r o m o l e e u l e s is u n r e l a t e d to t h e i r m o l e c u l a r weight. O n l y i n t e r - c h a i n e x c h a n g e r e a c t i o n s c o u l d lead to less d i s s i m i l a r i t y in t h e c o m p o s i t i o n of t h e m a e r o m o l e c u l e s . One w o u l d t h e r e f o r e e x p e c t t h a t t h e p r o d u c t s of eopolyc o n d e n s a t i o n processes c o n d u c t e d u n d e r c o n d i t i o n s c o n d u c t i v e to i n t e r - c h a i n e x c h a n g e r e a c t i o n s (e.g. p o l y e o n d e n s a t i o n in a m e l t ) w o u l d be c o m p o s i t i o n M l y m o r e h o m o g e n e o u s . M a r k e d c o m p o s i t i o n a l i n h o m o g e n e i t y , h o w e v e r , s h o u l d r e m a i n wit, h t h e p r o d u c t s of h i g h t e m p e r a t u r e s o l u t i o n c o p o l y e o n d e n s a t i o n , a n d t h e l a t t e r will p r o b a b l y also h a v e n o n - s t a t i s t i cal d i s t r i b u t i o n of m o n o m e r i e r a d i c a l s a l o n g t h e p o l y m e r c h a i n of i n d i v i d u a l m a e r o m o l e c u l e s . T h e r e are n o g r o u n d s a t all for a s s m n i n g t h a t s t a t i s t i c a l d i s t r i b u t i o n of m o n o m e r i e radie~fls a n d c o m p o s i t i o n a l h o m o g e n e i t y of e o p o l y m e r s will a p p e a r in t h e ease of p r o d u c t s (~f' n o n - e q u i l i b r i u m e o p o l y m e r i z a t i o n processes if t h e r e are differences in t h e r e a e t i v i t i c s ~)f th~ initial e o m o n o m e r s . I n t h e l i g h t o f t h e S a w a d a t h e o r y [16] one m a y p r e d i c t t h e m a e r o m o l e c u l a r s t r u c t u r e ~t" the: p r o d u c t s of e o p o l y c o n d e n s a t i o n processes f r o m p a r a m e t e r s s u c h as e n t h r o p y a n d ent t m l p y c h a n g e s , etc. T h i s i n t e r e s t i n g t h e o r y is m a i n l y c o n c e r n e d w i t h t h e t y p e of d i s t r i b u t i o n of th(, u n i t s , i.e. block, a l t e r n a t i n g or s t a t i s t i c a l d i s t r i b u t i o n , b u t it d~es n o t a p p l y to s t r u c t u ral a n d c o m p o s i t i o n a l h o m o g e n e i t y of m a e r o m o l e e u l e s . F r o m t h i s s h o r t r e v i e w of t h e p u b l i s h e d d a t a it a p p e a r s t h a t t h e p r o b l e m of c o m p o s i t i o n al i n h o m o g e n e i t y o f t h e p r o d u c t s of e o p o l y e o n d e n s a t i o n processes h a s y e t to be e l u c i d a t e d .
450
E. TURSKA
The papers that have appeared (whether of a theoretical or an experimental nature) concern the problem of the average composition of products of copolycondensation, or that of the average (general) mode of distribution of monomeric radicals. The possibility of compositional inhomogeneity becomes apparent in the light of a simple analysis of the mechanism underlying formation of the macrcmoleeules. I n regard to the significance of this inhomogcneity, one must assume in the light of an investigation of copolycondensation products that the physical and mechanical properties of the latter will be greatly influenced as a result of compositional inhomogeneity. To obtain preliminary experimental confirmation of the considerations discussed above we investigated the eopolymer --
r--0
--O--C
F
_c_
11 1-
]
CH3
_
-
which is an aromatic mixed polyester obtained b y reacting terephthalic acid chloride with a diane and 4,4'-dihydroxydinaphthyl-l,l'. The copolymer investigated by us was synthesized at the Faculty of Polymer Technology, Schlensk Polytech. Institute, where the investigation of the polymer properties also took place.
I L/mole cz-x i
I
500 ~,00 3gO 200 fO0 //~
~ i
O
i
)I
k i
260
L i
I
I
5-g0
Time,
I
1
I
I
750
rain
FIO. 1. Kinetic curves of the homopolycondensation of terephthalie acid chloride with the diane (1) and with 4,4'-dihydroxydinaphthyl-l,V (2) in a-chloronaphthalenc, the initial concentration of the reactants being 0.6 mole/1. 181 °.
The aim of the resulting experiments was to verify the compositional inhomogeneity of the copolyester, a n d the extent to which its composition might be affected by the synthesis conditions adopted. The products of the high- and low-temperature polyeondensation processes were investigated, respectively, in a-chloronaphthalene and in methylene chloride (in a heterogeneous system) in presence of triethylamine. According to the literature data, the reaction between bisphenols a n d diearboxylic acid dichlorides under conditions of high-temperature polycondensation proceeds by a mechanism of nucleophilie substitution, a n d there is every reason to suppose that the diane OH groups reactivity m a y differ from t h a t of the OH groups of 4,4'-dihydroxydinaphthyl-l,l'. To verify this assumption we undertook a kinetic analysis of the homopolycondensation processes of
451
Some problems involved in copolycondensation processes
each bisphenol with terephthalie acid chloride. Under the 0onditions investigated (with qchloronaphthalene as solvent, 181 °) the reactivity of the diane is practically twice t h a t of the 4 , 4 ' - d i h y d r o x y d i n a p h t h y l - l , l ' (Fig. 1). I t must also be remembered t h a t bisnaphthol will
b
-0.5~ I I I I i
C/
I
I
I
I
I
/0'3
I
I
|
I
O'3
/ -I'0
0"5
/
-I'5
4_I. 0
-2"0
-1"5 d 1
-0"5
J
8
5
I
-0"5
-I.0
-1"0
.-1"5
FIG. 2. Tonge relationships plotted for mixed polyarylates with [~]~0.400 (1); 0.530 (2); 1.290 (3, 5-7) and 1.020, (4, 8-10) prepared b y high- (a, b) and low-temperature (c, d) solution polyeondensation and fraetionated in the systems: c h l o r o f o r m - - e t h a n o l : e t h y l e n e glycol (5 : 1) (a, c) and tetrachloroetlmne : phenol (3 : 1)--n-heptane (b, d) at 25 °.
452
E. TU~SKA
dissolve completely in ~-ehloronaphthalene only at 150 °, i.e. when the diane (that is completely soluble at room temperature) will already be reacting quite rapidly with terephthalic acid chloride. I n view of this on~ would expect t h a t oligomer molecules and polymer macromolecules containing preferentially the more active comonomer, i.e. the diane, will be formed in the early stages of the copolycondensation reaction. Accordingly the reaction will result in oligomer molecules and polymer macromolecules containing mainly the bisphenol, and subsequently, after the macromolecules have a l r e a d y grown to some considerable size, there will be the addition of chain segments of a different composition, containing mainly the bisnaphthol.
l(x) i(x); dI(x)
dI(x) dx
3.0
b
2.5 f'52.0 /'2 /.5 4
3
f.O 0.5 0
0"4
0.8
0"5
/'2 x=
['7]
1"0
1"5 x=[,2]
dI(x) dx 1.5
1.0
0.5
~6
l'O
1"5
2"g
2"5
3"0 x=[9]
FIe. 3. Integral (1, 3) and differential (2, 4-8) curves of distribution b y molecular weight for mixed polyarylates with [~/]=0.400 (1, 2); 0.530 (3, 4) 1-290 (5, 7) and 1.020 (6, 8) prepared b y high- (a, b) and low-temperature solution polyeondensation (c) and fractionated in the systems: chloroform--ethanol : ethylene glycol (5 : 1) (1, 2, 5, 6) and tetrachloroethane : phenol (3 : 1)--n-heptane (3, 4, 7, 8) at 25 °. '~herefore, unless there ale inter-chain exchange reactions taking place at a considerable rate, the resulting product must be compositionally inhomogeneous, as m a y be confirmed without much difficulty by experiments.
Some p r o b l e m s i n v o l v e d in c o p o l y e o n d e n s a t i o n processes
453
Moreover, i n d i v i d u a l maeromolecules will n o t h a v e a c o m p l e t e l y chaotic statistical distri bution of m o n o m e r units along the chain, b u t will r a t h e r be fairly specific block c o p o l y m e r s . This a s s u m p t i o n is v e r y difficult to confirm e x p e r i m e n t a l l y . To throw, light on t h e compositional i n h o m o g e n e i t y of the studied m i x e d p o l y a r y l a t e , the latter u n d e r w e n t f r a c t i o n a t i o n in two different systems t h a t had been especially selected, the first being d s y s t e m consisting of chloroform (solvent) and a m i x t u r e of ethanol and ethylone glycol ( p r e c i p i t a n t ) ( 5 : 1 wt. ~o). I n this s y s t e m the f r a c t i o n a t i o n of the c o p o l y m e r t o o k place m a i n l y according to molecular weight. The other system was a m i x t u r e of t e t r a c h l o r o e t h a n e and phenol (solvent) (3 : 1 wt. ~o), with n - h e p t a n e as the precipitant. The fractionation results o b t a i n e d w i t h this s y s t e m are greatly influenced by the chemical composition of the copolymer. Tile systems were selected by test f r a c t i o n a t i o n as the Elias m e t h o d [I7] was inapplicable ~)wing to the insolubility of one of the homopolyiners. The f r a c t i o n a t i o n results showed t h a t the d a t a o b t a i n e d in the first system, using t h e T o n g e m e t h o d of calculation, plot into the straight line seen in Fig. 2a, while the differential curves of distribution according to molecular weight look like characteristic distribuion curves for p o l y c o n d e n s a t i o n p r o d u c t s (Fig. 3a). The results of I R - a n a l y s i s a n d e l e m e n t a r y analysis of the fractions o b t a i n e d in t h e first syst.enl showed t h a t there is no nlarked difference in the chemical composition of these fract ions, and were it n o t for the fractionation results o b t a i n e d with the second system, one m i g h t err(mt~ously conclude, in v i e w of the results n o t e d above, t h a t the studied c o p o l y m e r was compositionally homogeneous. H o w e v e r , t h e fractions o b t a i n e d as a result of f r a c t i o n a t i o n in the second s y s t e m differed considerably in their chemical compositions, as was s h o w n b y the results of I g spectroscopy and e l e m e n t a r y analysis. One has to t a k e into account, of course, t h a t t h e intrinsic viscosity, which was used as a measure of molecular weight, is likewise d e t e r m i n e d by the composition of the fractions. Therefore the distribution curves based on the results of ti'actionation in the second system, where the p a r a m e t e r x was t h e intrinsic viscosity, d e p e n d i n g on the composition of the fractions, m a y be used only for c o m p a r i s o n w i t h the distribution curves o b t a i n e d for f r a c t i o n a t i o n in the first system. i t was t h u s found t h a t three s t r a i g h t lines (Fig. 2b) were o b t a i n e d for f r a c t i o n a t i o n in the second system, using the Tonge m e t h o d of calculating the fractionation data, b u t the shape of the differential distribution curves was um~sual (Fig. 3b). A l t h o u g h tile e x p e r i m e n t a l results c a n n o t be a c c u r a t e l y e v a l u a t e d m a t h e m a t i c a l l y , t h e y nevertheless bear ou~ assumpti(ms regarding the compositional i n h o m o g e n e i t y of p r o d u c t s of h i g h - t e m p e r a t u r e solution polycondensation. The l o w - t e m p e r a t u r e p o l y c o n d e n s a t i o n in t h e presence of t e r t i a r y amines takes place by a different mechanism. I n view, of the literature d a t a it would appear t h a t the reaction m~y proceed through two c o m p e t i n g mechanisms, i.e. t h r o u g h r e a c t i v e complex compounds, formed b e t w e e n ttxe amines a n d bisphenols, and likewise between amines and diearboxylic acid chlorides. A p a r t from differences in the r e a c t i v i t y of functional groups of the co,nonomers there is p r o b a b l y a n o t h e r p a r a m e t e r t h a t m a y influence the compositional i n h o m o g e n e i t y of p r o d u c t s ef l o w - t e m p e r a t u r e polyeondensation, i.e. differences in the solubility of t h e m o n o m e r s , p a r t i c u l a r l y in a heterogeneous system, h i the v i e w of some authors, and also on tile basis of simple analysis of the chain p r o p a g a t i o n mechanism, one would e x p e c t t h e f o r m a t i o n of block p o l y m e r s in the ease in question. I t was i m p o r t a n t to o b t a i n confirmation the a s s u m p t i o n t h a t compositional inhomogcneity w o u l d likewise be f o u n d in the l a t t e r case also. To do so the p r o d u c t was f r a c t i o n a t e d in the two systems referred to above: the results o b t a i n e d were in some respects similar to th~ f r a e t i o n a t i o n results for the c o p o l y m c r synthesized by h i g h - t e m p e r a t u r e solution polycondensation.
454
E. TURSKA
The Tonge relationship, calculated from the fractionation results obtained using the first system, took the form of a single straigbt line (Fig. 2c) a n d the differential distribution curve had a single m a x i m u m (Fig. 3c). I n the second system, where the fractions differed in composition, the Tonge relationship took the form of three straight lines, (Fig. 2d) and the n u m b e r of peaks was larger (Fig. 3c). While the experimental data obtained by the author are as yet insufficient to provide a means of quantitative determination of the compositional inhomogeneity of the studied copolymer, they do undoubtedly confirm our assumption that compositional inhomogeneity was involved in the present case and was definitely related to the synthesis conditions.
CONCLUSIONS ( 1) I t is shown that the chemical inhomogeneity and the components distribution of tile macromoleeular chains of copolycondensates greatly influence the properties of the latter. (2) The possible effect of the method of synthesis on the composition of the copolycondensation products and on the components distribution in the macromoleeular chains is confirmed by the experimental data obtained.
Translated by R. J. A. HENDRY REFERENCES 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17.
G. E. HAMM, Copolymerization, p. 591, 1964 8. Ya. FRENKEL, Dokl. AN SSSR 186: 63I, 1969 S. Ya. FRENKEL, Europ. Polymer J., 64, 1970 A. D. LITMANOVICH and V. Ira. STERN, J. Polymer Sci. C16: 1375, 1967 M. J. R. CANTOW and O. FUCHS, Makromolek. Chem. 83: 244, 1965 P. W. MORGAN, J. Polymer Sci. A2: 437, ]964 T. M. FRUNZE, V. V. KORSHAK and V. A. MAKARKIN, Vysokomol. soyed. 1: 500, 1959 (Not translated in Polymer Sci. U.S.S.R.) V. V. KORSHAK, S. V. VINOGRADOVA and P. M. VALETSKII, Vysokomol. soyed. 4: 987, 1962 (Not translated in Polymer Sci. U.S.S.R.) V. V. KORSHAK, S. V. VINOGRADOVA and A. S. LEBEDEVA, Vysokomol. soyed. 5: 674, 1963 (Translated in Polymer Sci. U.S.S.R. 4: 6, 1375, 1963) V. V. KORSHAK, S. V. VINOGRADOVA and U. BAN-YUAN, Izv. AN SSSR, Cbem. series, 1288, 1963 G. A. SHTRAIKHMAN, Zh. prikl, khimii 32: 573, 1959 K. TYUZYO, J. Polymer Sci. A3: 3654, 1965 V. V. KORSHAK, T. M. FRUNZE and P. V. K0ZLOV, lzv. AN SSSR, Chem. sect., 2062, 1962 V. V. KORSHAK, T. M. FRUNZE and P. V. KOZLOV, Izv. AN SSSR, Chem. sect., 2226, 1962 L. B. SOKOLOV and T. L. KRUGLOVA, Vysokomol. soyed. 2: 704, 1960 (Not translated in Polymer Sei. U.S.S.R.) H. SAWADA, J. Polymer Sei. BI: 659, 1963; B2: 507, 1964 H. G. ELIAS and U. GRUBER, Makromolek. Chem. 78: 72, 1964
{Received 2 December 1971) ~N EARLY studies of copolymerization processes the aim of the authors was mainly to discover .conditions under which it would be possible for copolymers with particular compositions and properties to be prepared, and in addition there was the need to determine the relationship between the compositions and structures of these copolymers. In more recent investigations, including in particular the work reported in papers [1-5], a more complex problem is dealt with and it was found as a result of these investigations t h a t the properties of copolymers depend not only on their average molecular compositions, but also (to some considerable extent) on the structure of the individual maeromolecules. I t was found that copolymers which were identical in respect to their average molecular compositions and some other average physicochemical characteristics, differed in respect to their properties in those cases where dissimilarity in the degree of compositional inhomogeneity of these copolymers was observed. The results reported in papers [6-10] show t h a t the maeromolecular structure of copolymers prepared by polycondensation m a y vary according to the particular method adopted and the synthesis conditions. Block copolymers are obtainable by means of non-equilibrium polycondensation (interfacial or low-temperature processes of solution polycondensation) although macromolecules with alternating units are obtainable only by adopting specially selected reaction conditions. Compositional inhomogeneity occurs in statistical and in block copolycondensates: with the former one m a y assume, despite the completely statistical chaotic distribution of the differ ent monomer units in each macromolecule, t h a t the chemical composition of individual macromolecules m a y differ; in the latter case, though all the maeromolecules are made up of chain segments consisting of different units, individual macromolecules m ay differ as t o the length and number of these segments. In the literature regarding eopolycondensation processes authors have yet to throw light upon the problem of the compositional inhomogeneity of macromolecules. We have first to analyse the possible appearance of compositional inhomogeneity in relation to synthesis conditions, starting with known mechanisms of polycondensation processes. The methods most often used in the industry (though these are not the best methods) are equilibrium ones, namely those of high-temperature polycondensation in melts, and in high-boiling solvents. In consider ing copolymerization processes, let us begin with one of copolyesterification involving three starting materials, taking monomers with the same functional groups A and B in equimolar amounts, the total a m o u n t of these monomers being equimolar in respect to the a m o u n t of a third monomer with functional groups C. Let us assume t h a t the initial reactivity of both functional groups of each monomer is identicul, whether or not one of these groups m a y be substituted. W i t h simplifications of this nature Shtraikhman [11] and Tyuzyo [12], * Vysokomol. soyed, h i 5 : No. 2, 393-399, 1973. 448
S o m e p r o b l e m s i n v o l v e d m c o p o l y e o n d e n s a t i o n processes
449
s t a r t i n g w i t h t h e o r e t i c a l c o n s i d e r a t i o n s , d e r i v e d a n e q u a t i o n g i v i n g t h e c o m p o s i t i o n of t.he p r o d u c t of c o p o l y c o n d e n s a t i o n w h i c h in its final f o r m t a k e s t h e f o r m of
CA0
\C~o/
w h e r e ca0 a n d c~0 are t h e s t a r t i n g c o n c e n t r a t i o n s of e o m o n o m e r s w i t h i d e n t i c a l e n d g r o u p s ; cA a n d CB a r e t h e c o n c e n t r a t i o n s of t h e s a m e e n d g r o u p s a t a g i v e n degree of c o m p l e t e n e s s of t h e re,ration; r is t h e r e a c t i v i t y coefficient for t h e s t u d i e d c o m o n o m e r s ; r=k~/k.~, w h e r e k~ a n d ]c2 are r a t e c o n s t a n t s of t h e h o m o p o l y e o n d e n s a t i o n processes. O n a n a l y s i n g t h e a b o v e e q u a t i o n one m a y c v n c l u d e t h a t t h e c o m p o s i t i o n of t h e m a c r o m o l e c u l e s f o r m e d a t a g i v e n m o m e n t d e p e n d s o n t h e r e a c t i v i t y r a t i o of b o t h m o n o m e r s , ml(l c o n s e q u e n t l y o n t h e degree of c o m p l e t e n e s s of t h e r e a c t i o n . T h e r e s u l t s r e p o r t e d in p a p e r s [13 15] b y a u t h o r s i n v e s t i g a t i n g e o p o l y a m i d e s g e n e r a l l y b~ar o u t t h i s eonelusi0n. A f t e r a n a l y s i n g t h e r e a c t i o n kinetics, a n d also in v i e w of p u b l i s h e r i n f o r m a t i o n , it is r ~ a s o n a b l e ~o c o n c l u d e t h a t t h e r a t e a t w h i c h e a c h o f t h e t w o m o n o m e r s w i t h i d e n t i c a l e n d g r o u p s r e a c t s will differ a c c o r d i n g to t h e r e a c t i v i t y a n d t h e a m o u n t of t h e m o n o m e r in q u e s t i o n , a n d t h e r a t e s of r e a c t i o n o f t h e s e m o n o m e r s v a r y w i t h t i m e . I t is fair to a s s u m e th~tt t h e m a c r o m o l e c u l e s f o r m e d in t h e e a r l y stages of t h e r e a c t i o n will c o n t a i n c o n s i d e r a b l y m o r e m o n o m e r u n i t s b e l o n g i n g t o t h e m o r e a c t i v e e o m o n o m e r , a n d t h a t o n l y w h e n a sufficient degree of d e p l e t i o n of t h i s m o n o m e r in t h e r e a c t i o n m i x t u r e h a s b e e n r e a c t e d will t h e n m u b,,r of m o n o m e r u n i t s b e l o n g i n g to t h e less a c t i v e m o n o m e r b e g i n to increase. I n eopolycond~,nsation processes g r o w t h of t h e m a c r o m o l e c u l e s t a k e s place e i t h e r t h r o u g h t h e a d d i t i o u of t h e m o n o m e r a n d o l i g o m e r molecules, or as a r e s u l t of r e a c t i o n s i n v o l v i n g t h e m a e r o m o l e eules t h a t h a v e a l r e a d y b e e n f o r m e d . T h e m o d e of g r o w t h o f m a c r o m o l e e u l e s is f a i r l y eompl~x, b u t t h e r e arc n o g r o u n d s for a s s u m i n g t h a t t h e s t a t i s t i c a l ehemicM c o m p o s i t i o n of all the, m a c r o m o l e c u l e s will be i n d e n t i c a l . A e c o r d i n g t o t h e s c h e m e of p r o p a g a t i o n o u t l i n e d a b o v e , t h e m a e r o m o l e c u l e s in t h e react i~n m i x t u r e will differ f r o m one a n o t h e r a c c o r d i n g to t h e degree of c o m p l e t e n e s s of t h e reaction. i.e. t h e n u m b e r of d i f f e r e n t m o n o m e r u n i t s in e a c h m a c r o m o l e c u l e will v a r y , a n d t h e c o m p o s i t i o n of c h a i n s e g m e n t s of w h i c h t h e s e m a c r o m o l e c u l e s consist m a y differ; f l l r t h e r m o r e t h e a m o u n t of difference in t h e c o m p o s i t i o n of t h e m a e r o m o l e e u l e s is u n r e l a t e d to t h e i r m o l e c u l a r weight. O n l y i n t e r - c h a i n e x c h a n g e r e a c t i o n s c o u l d lead to less d i s s i m i l a r i t y in t h e c o m p o s i t i o n of t h e m a e r o m o l e c u l e s . One w o u l d t h e r e f o r e e x p e c t t h a t t h e p r o d u c t s of eopolyc o n d e n s a t i o n processes c o n d u c t e d u n d e r c o n d i t i o n s c o n d u c t i v e to i n t e r - c h a i n e x c h a n g e r e a c t i o n s (e.g. p o l y e o n d e n s a t i o n in a m e l t ) w o u l d be c o m p o s i t i o n M l y m o r e h o m o g e n e o u s . M a r k e d c o m p o s i t i o n a l i n h o m o g e n e i t y , h o w e v e r , s h o u l d r e m a i n wit, h t h e p r o d u c t s of h i g h t e m p e r a t u r e s o l u t i o n c o p o l y e o n d e n s a t i o n , a n d t h e l a t t e r will p r o b a b l y also h a v e n o n - s t a t i s t i cal d i s t r i b u t i o n of m o n o m e r i e r a d i c a l s a l o n g t h e p o l y m e r c h a i n of i n d i v i d u a l m a e r o m o l e c u l e s . T h e r e are n o g r o u n d s a t all for a s s m n i n g t h a t s t a t i s t i c a l d i s t r i b u t i o n of m o n o m e r i e radie~fls a n d c o m p o s i t i o n a l h o m o g e n e i t y of e o p o l y m e r s will a p p e a r in t h e ease of p r o d u c t s (~f' n o n - e q u i l i b r i u m e o p o l y m e r i z a t i o n processes if t h e r e are differences in t h e r e a e t i v i t i c s ~)f th~ initial e o m o n o m e r s . I n t h e l i g h t o f t h e S a w a d a t h e o r y [16] one m a y p r e d i c t t h e m a e r o m o l e c u l a r s t r u c t u r e ~t" the: p r o d u c t s of e o p o l y c o n d e n s a t i o n processes f r o m p a r a m e t e r s s u c h as e n t h r o p y a n d ent t m l p y c h a n g e s , etc. T h i s i n t e r e s t i n g t h e o r y is m a i n l y c o n c e r n e d w i t h t h e t y p e of d i s t r i b u t i o n of th(, u n i t s , i.e. block, a l t e r n a t i n g or s t a t i s t i c a l d i s t r i b u t i o n , b u t it d~es n o t a p p l y to s t r u c t u ral a n d c o m p o s i t i o n a l h o m o g e n e i t y of m a e r o m o l e e u l e s . F r o m t h i s s h o r t r e v i e w of t h e p u b l i s h e d d a t a it a p p e a r s t h a t t h e p r o b l e m of c o m p o s i t i o n al i n h o m o g e n e i t y o f t h e p r o d u c t s of e o p o l y e o n d e n s a t i o n processes h a s y e t to be e l u c i d a t e d .
450
E. TURSKA
The papers that have appeared (whether of a theoretical or an experimental nature) concern the problem of the average composition of products of copolycondensation, or that of the average (general) mode of distribution of monomeric radicals. The possibility of compositional inhomogeneity becomes apparent in the light of a simple analysis of the mechanism underlying formation of the macrcmoleeules. I n regard to the significance of this inhomogcneity, one must assume in the light of an investigation of copolycondensation products that the physical and mechanical properties of the latter will be greatly influenced as a result of compositional inhomogeneity. To obtain preliminary experimental confirmation of the considerations discussed above we investigated the eopolymer --
r--0
--O--C
F
_c_
11 1-
]
CH3
_
-
which is an aromatic mixed polyester obtained b y reacting terephthalic acid chloride with a diane and 4,4'-dihydroxydinaphthyl-l,l'. The copolymer investigated by us was synthesized at the Faculty of Polymer Technology, Schlensk Polytech. Institute, where the investigation of the polymer properties also took place.
I L/mole cz-x i
I
500 ~,00 3gO 200 fO0 //~
~ i
O
i
)I
k i
260
L i
I
I
5-g0
Time,
I
1
I
I
750
rain
FIO. 1. Kinetic curves of the homopolycondensation of terephthalie acid chloride with the diane (1) and with 4,4'-dihydroxydinaphthyl-l,V (2) in a-chloronaphthalenc, the initial concentration of the reactants being 0.6 mole/1. 181 °.
The aim of the resulting experiments was to verify the compositional inhomogeneity of the copolyester, a n d the extent to which its composition might be affected by the synthesis conditions adopted. The products of the high- and low-temperature polyeondensation processes were investigated, respectively, in a-chloronaphthalene and in methylene chloride (in a heterogeneous system) in presence of triethylamine. According to the literature data, the reaction between bisphenols a n d diearboxylic acid dichlorides under conditions of high-temperature polycondensation proceeds by a mechanism of nucleophilie substitution, a n d there is every reason to suppose that the diane OH groups reactivity m a y differ from t h a t of the OH groups of 4,4'-dihydroxydinaphthyl-l,l'. To verify this assumption we undertook a kinetic analysis of the homopolycondensation processes of
451
Some problems involved in copolycondensation processes
each bisphenol with terephthalie acid chloride. Under the 0onditions investigated (with qchloronaphthalene as solvent, 181 °) the reactivity of the diane is practically twice t h a t of the 4 , 4 ' - d i h y d r o x y d i n a p h t h y l - l , l ' (Fig. 1). I t must also be remembered t h a t bisnaphthol will
b
-0.5~ I I I I i
C/
I
I
I
I
I
/0'3
I
I
|
I
O'3
/ -I'0
0"5
/
-I'5
4_I. 0
-2"0
-1"5 d 1
-0"5
J
8
5
I
-0"5
-I.0
-1"0
.-1"5
FIG. 2. Tonge relationships plotted for mixed polyarylates with [~]~0.400 (1); 0.530 (2); 1.290 (3, 5-7) and 1.020, (4, 8-10) prepared b y high- (a, b) and low-temperature (c, d) solution polyeondensation and fraetionated in the systems: c h l o r o f o r m - - e t h a n o l : e t h y l e n e glycol (5 : 1) (a, c) and tetrachloroetlmne : phenol (3 : 1)--n-heptane (b, d) at 25 °.
452
E. TU~SKA
dissolve completely in ~-ehloronaphthalene only at 150 °, i.e. when the diane (that is completely soluble at room temperature) will already be reacting quite rapidly with terephthalic acid chloride. I n view of this on~ would expect t h a t oligomer molecules and polymer macromolecules containing preferentially the more active comonomer, i.e. the diane, will be formed in the early stages of the copolycondensation reaction. Accordingly the reaction will result in oligomer molecules and polymer macromolecules containing mainly the bisphenol, and subsequently, after the macromolecules have a l r e a d y grown to some considerable size, there will be the addition of chain segments of a different composition, containing mainly the bisnaphthol.
l(x) i(x); dI(x)
dI(x) dx
3.0
b
2.5 f'52.0 /'2 /.5 4
3
f.O 0.5 0
0"4
0.8
0"5
/'2 x=
['7]
1"0
1"5 x=[,2]
dI(x) dx 1.5
1.0
0.5
~6
l'O
1"5
2"g
2"5
3"0 x=[9]
FIe. 3. Integral (1, 3) and differential (2, 4-8) curves of distribution b y molecular weight for mixed polyarylates with [~/]=0.400 (1, 2); 0.530 (3, 4) 1-290 (5, 7) and 1.020 (6, 8) prepared b y high- (a, b) and low-temperature solution polyeondensation (c) and fractionated in the systems: chloroform--ethanol : ethylene glycol (5 : 1) (1, 2, 5, 6) and tetrachloroethane : phenol (3 : 1)--n-heptane (3, 4, 7, 8) at 25 °. '~herefore, unless there ale inter-chain exchange reactions taking place at a considerable rate, the resulting product must be compositionally inhomogeneous, as m a y be confirmed without much difficulty by experiments.
Some p r o b l e m s i n v o l v e d in c o p o l y e o n d e n s a t i o n processes
453
Moreover, i n d i v i d u a l maeromolecules will n o t h a v e a c o m p l e t e l y chaotic statistical distri bution of m o n o m e r units along the chain, b u t will r a t h e r be fairly specific block c o p o l y m e r s . This a s s u m p t i o n is v e r y difficult to confirm e x p e r i m e n t a l l y . To throw, light on t h e compositional i n h o m o g e n e i t y of the studied m i x e d p o l y a r y l a t e , the latter u n d e r w e n t f r a c t i o n a t i o n in two different systems t h a t had been especially selected, the first being d s y s t e m consisting of chloroform (solvent) and a m i x t u r e of ethanol and ethylone glycol ( p r e c i p i t a n t ) ( 5 : 1 wt. ~o). I n this s y s t e m the f r a c t i o n a t i o n of the c o p o l y m e r t o o k place m a i n l y according to molecular weight. The other system was a m i x t u r e of t e t r a c h l o r o e t h a n e and phenol (solvent) (3 : 1 wt. ~o), with n - h e p t a n e as the precipitant. The fractionation results o b t a i n e d w i t h this s y s t e m are greatly influenced by the chemical composition of the copolymer. Tile systems were selected by test f r a c t i o n a t i o n as the Elias m e t h o d [I7] was inapplicable ~)wing to the insolubility of one of the homopolyiners. The f r a c t i o n a t i o n results showed t h a t the d a t a o b t a i n e d in the first system, using t h e T o n g e m e t h o d of calculation, plot into the straight line seen in Fig. 2a, while the differential curves of distribution according to molecular weight look like characteristic distribuion curves for p o l y c o n d e n s a t i o n p r o d u c t s (Fig. 3a). The results of I R - a n a l y s i s a n d e l e m e n t a r y analysis of the fractions o b t a i n e d in t h e first syst.enl showed t h a t there is no nlarked difference in the chemical composition of these fract ions, and were it n o t for the fractionation results o b t a i n e d with the second system, one m i g h t err(mt~ously conclude, in v i e w of the results n o t e d above, t h a t the studied c o p o l y m e r was compositionally homogeneous. H o w e v e r , t h e fractions o b t a i n e d as a result of f r a c t i o n a t i o n in the second s y s t e m differed considerably in their chemical compositions, as was s h o w n b y the results of I g spectroscopy and e l e m e n t a r y analysis. One has to t a k e into account, of course, t h a t t h e intrinsic viscosity, which was used as a measure of molecular weight, is likewise d e t e r m i n e d by the composition of the fractions. Therefore the distribution curves based on the results of ti'actionation in the second system, where the p a r a m e t e r x was t h e intrinsic viscosity, d e p e n d i n g on the composition of the fractions, m a y be used only for c o m p a r i s o n w i t h the distribution curves o b t a i n e d for f r a c t i o n a t i o n in the first system. i t was t h u s found t h a t three s t r a i g h t lines (Fig. 2b) were o b t a i n e d for f r a c t i o n a t i o n in the second system, using the Tonge m e t h o d of calculating the fractionation data, b u t the shape of the differential distribution curves was um~sual (Fig. 3b). A l t h o u g h tile e x p e r i m e n t a l results c a n n o t be a c c u r a t e l y e v a l u a t e d m a t h e m a t i c a l l y , t h e y nevertheless bear ou~ assumpti(ms regarding the compositional i n h o m o g e n e i t y of p r o d u c t s of h i g h - t e m p e r a t u r e solution polycondensation. The l o w - t e m p e r a t u r e p o l y c o n d e n s a t i o n in t h e presence of t e r t i a r y amines takes place by a different mechanism. I n view, of the literature d a t a it would appear t h a t the reaction m~y proceed through two c o m p e t i n g mechanisms, i.e. t h r o u g h r e a c t i v e complex compounds, formed b e t w e e n ttxe amines a n d bisphenols, and likewise between amines and diearboxylic acid chlorides. A p a r t from differences in the r e a c t i v i t y of functional groups of the co,nonomers there is p r o b a b l y a n o t h e r p a r a m e t e r t h a t m a y influence the compositional i n h o m o g e n e i t y of p r o d u c t s ef l o w - t e m p e r a t u r e polyeondensation, i.e. differences in the solubility of t h e m o n o m e r s , p a r t i c u l a r l y in a heterogeneous system, h i the v i e w of some authors, and also on tile basis of simple analysis of the chain p r o p a g a t i o n mechanism, one would e x p e c t t h e f o r m a t i o n of block p o l y m e r s in the ease in question. I t was i m p o r t a n t to o b t a i n confirmation the a s s u m p t i o n t h a t compositional inhomogcneity w o u l d likewise be f o u n d in the l a t t e r case also. To do so the p r o d u c t was f r a c t i o n a t e d in the two systems referred to above: the results o b t a i n e d were in some respects similar to th~ f r a e t i o n a t i o n results for the c o p o l y m c r synthesized by h i g h - t e m p e r a t u r e solution polycondensation.
454
E. TURSKA
The Tonge relationship, calculated from the fractionation results obtained using the first system, took the form of a single straigbt line (Fig. 2c) a n d the differential distribution curve had a single m a x i m u m (Fig. 3c). I n the second system, where the fractions differed in composition, the Tonge relationship took the form of three straight lines, (Fig. 2d) and the n u m b e r of peaks was larger (Fig. 3c). While the experimental data obtained by the author are as yet insufficient to provide a means of quantitative determination of the compositional inhomogeneity of the studied copolymer, they do undoubtedly confirm our assumption that compositional inhomogeneity was involved in the present case and was definitely related to the synthesis conditions.
CONCLUSIONS ( 1) I t is shown that the chemical inhomogeneity and the components distribution of tile macromoleeular chains of copolycondensates greatly influence the properties of the latter. (2) The possible effect of the method of synthesis on the composition of the copolycondensation products and on the components distribution in the macromoleeular chains is confirmed by the experimental data obtained.
Translated by R. J. A. HENDRY REFERENCES 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17.
G. E. HAMM, Copolymerization, p. 591, 1964 8. Ya. FRENKEL, Dokl. AN SSSR 186: 63I, 1969 S. Ya. FRENKEL, Europ. Polymer J., 64, 1970 A. D. LITMANOVICH and V. Ira. STERN, J. Polymer Sci. C16: 1375, 1967 M. J. R. CANTOW and O. FUCHS, Makromolek. Chem. 83: 244, 1965 P. W. MORGAN, J. Polymer Sci. A2: 437, ]964 T. M. FRUNZE, V. V. KORSHAK and V. A. MAKARKIN, Vysokomol. soyed. 1: 500, 1959 (Not translated in Polymer Sci. U.S.S.R.) V. V. KORSHAK, S. V. VINOGRADOVA and P. M. VALETSKII, Vysokomol. soyed. 4: 987, 1962 (Not translated in Polymer Sci. U.S.S.R.) V. V. KORSHAK, S. V. VINOGRADOVA and A. S. LEBEDEVA, Vysokomol. soyed. 5: 674, 1963 (Translated in Polymer Sci. U.S.S.R. 4: 6, 1375, 1963) V. V. KORSHAK, S. V. VINOGRADOVA and U. BAN-YUAN, Izv. AN SSSR, Cbem. series, 1288, 1963 G. A. SHTRAIKHMAN, Zh. prikl, khimii 32: 573, 1959 K. TYUZYO, J. Polymer Sci. A3: 3654, 1965 V. V. KORSHAK, T. M. FRUNZE and P. V. K0ZLOV, lzv. AN SSSR, Chem. sect., 2062, 1962 V. V. KORSHAK, T. M. FRUNZE and P. V. KOZLOV, Izv. AN SSSR, Chem. sect., 2226, 1962 L. B. SOKOLOV and T. L. KRUGLOVA, Vysokomol. soyed. 2: 704, 1960 (Not translated in Polymer Sei. U.S.S.R.) H. SAWADA, J. Polymer Sei. BI: 659, 1963; B2: 507, 1964 H. G. ELIAS and U. GRUBER, Makromolek. Chem. 78: 72, 1964