Hydrodynamic and thermodynamic properties of dissolved multiblock copolymers

Polymer Science U.S.S.R. Vol. 27, No. 4, pp. 875-882, 1985 Printed in Poland

0032-3950/85 $10.00+ .00 © 1986 Pergamon Press Ltd.

H Y D R O D Y N A M I C AND T H E R M O D Y N A M I C PROPERTIES OF DISSOLVED MULTIBLOCK COPOLYMERS* L. V. DUBROV]NA,S.-S. A. PAVLOVAand M. A. PONOMAREVA A. N. Nesmeyanov Institute of Element-Organic Compounds, U.S.S.R. Academy of Sciences (Received 16 August 1983) Properties of solutions of multiblock polyarylate-polyarylenesulphone copolymers having a similar composition have been investigated. The molecular weight dependence of intrinsic viscosity in good solvents does not follow the additivity rule. 0-conditions have been found. One of the investigated copolymers shows two 0-temperatures (upper and lower)lying close to those of the corresponding homopolymers. Conformational parameters of the studied copolymers are very similar. The specific behaviour of copolymer solutions can be explained by thermodynamic arguments. IN contrast to homopolymers, copolymers show a specific behaviour in solution, owing to interactions between components of different chemical nature. It has been shown in a number of papers [1-3] that the behaviour of A - B and A - B - A block copolymers differs from that of random copolymers. This gives evidence that the length of blocks (the number of consecutive links of one type) in the copolymer chain can affect substantially the properties of dilute solutions. The authors [4] maintain that in order to understand the specific features of copolymer solutions it is necessary to use "regular" copolymers, homogeneous with respect to both the composition and length of blocks, i.e., copolymers of the type ( A , - B m ) p. Dems [5], who investigated such copolymers, .came to the conclusion that the mean composition and the length of blocks do affect the solution properties. The present study has been undertaken with the aim to elucidate the effect of interaction between unlike parts in macromolecules of multiblock copolymers on their conformational parameters. Multiblock copolymers polyarylate-polyarylenesulphone prepared by polycondensation have been studied. The samples were prepared in three different ways described in detail elsewhere [6, 7]. The composition of all copolymers was close to the ratio 0.5 : 0.5. The copolymers were fractionated using the method described in [8] for homopolymers. For each sample 13 to 15 fractions were isolated. Solvents used in the measurements of intrinsic viscosity [rt] and molecular weight M were purified by distillation, the solutions were filtered or centrifuged; [r/] was measured with an Ubbelohde-type viscometer. The intensity of scattered light was measured 'with a photogoniometer Fica (France) at 2=546 nm between 285 and 318 K. The refractive index * Vysokomol. soyed. A27: No. 4, 780-785, 1985. 875

876

L.V. Dum~oviN^ et al. .

increments were determined with a Pulfrich refractometer in a differential cell. Temperature was. measured with the precision of + 0.05 °C. The 0-conditions were determined, similarly as in the case of homopolymers, by extrapolating. the temperature dependence of the second virial coefficient Az to zero. It has been established previously [9] that dioxan is a poor solvent both for polyarylates and polyarylenesulphones. The results. of extrapolation to zero value of A2 are shown in Fig. 1 in the temperature range 285 to 318 K..

A2~10q a

6 2 -2

_

sos

FIo. 1. Temperature dependence of the second virial coefficient in dioxan: polyarylate (1) and polyarylenesulphone (2) (a); copolymer I (1), 2 (2), and 3 (3) (b). The data plotted in Fig. 2 as log [r/] vs. log M for the investigated multiblock co-polymers reveal some specific features. Firstly, in contrast to published data, the d e pendence of It/] on Mw for the copolymers is in our case not additive with respect to. the corresponding plots for homopolymers. The straight line A which describes the molecular weight dependence of [t/] for the h o m o p o l y m e r - p o l y a r y l a t e - i n t e r s e c t s in the i n stigated range of molecular weight the straight lines corresponding to the respective copolymers 1 to 3. A similar pattern has been observed in [10], where the authors, using their own results and also data taken f r o m [11], were able to show that the intrinsic viscosity o f copolymers can be lower in the region of small M than the [r/]-values o f the respective homopolymers and vice versa; this observation has been explained by a strong long-range interaction between the unlike blocks. The reasons why [!/] is n o t additive were sought [12] in the effect of composition for r a n d o m copolymers and i n the length of blocks for block copolymers. Secondly, although the mean composition of the block copolymers e m p l o y e d in the present study was relatively similar, each sample was characterized by its o w n dependence of [r/] on Mw. At the same value of Mw the intrinsic viscosities measuredi

Hydrodynamic and thermodynamic properties of dissolved multiblock copolymers

877

in a good solvent (chloroform) decrease in the series [r/]l > [~/]2 > [r/]3. A considerable influence of the mean copolymer composition and length of blocks on the intrinsic viscosity was reported in [13], where the behaviour of r a n d o m and block copolymers was compared; the authors showed that [~/] increased when the length of blocks was increased and their number was simultaneously decreased so as to keep the molecular weight of the copolymer constant. Calculations of the extent of blocking, based on experimental values of M and orL the initial ratio of components in the condensation, show that only in sample 2 the blocks can be twice as long than in sample 1, and this should lead to lower values of [r/] for the former. Indeed, the intrinsic viscosities of sample 2 are smaller than ~hose of sample 1, but larger than those of sample 3. A different distribution inside blocks may be one of the reasons for the lower values of It/] for sample 3. We do not possess information on the distribution within the blocks (or, more precisely, how it can

1o!I~?/ijdl/g]

a

,%.3 --

_ ~ 7 _ _ ~•

- ,~,.?' /t

'?.:7

/

i "~" /

// ../o

,./ ~.~

]j/

i0~s ,,~

-L;.J

--

f

FIG. 2. Intrinsic viscosity plotted against molecular weight in logarithmic coordinates for polyarylate (A), polyarylenesulphone (B) and for copolymers 1 (1), 2 (2), 3 (3). Measured at 298 K in chloroform (a) and dioxan (b).

B ?B

L . V . D~B~OVtNA et aL

vary under the conditions of condensation), but we can state that in our copolyme,rs it apparently differs from sample to sample and affects their hydrodynamic properties. In contrast to the results obtained in the good solvent, a completely different picture with respect to the dependence of [,/] on M emerged in a poor solvent- dioxan at 298 K. Preliminary tests have shown that dioxan is a poor solvent not only for both homopolymers (polyarylate and polyarylenesulphone), but for the copolymers as well. The lines for samples 2 and 3 lie relatively close to each other, although the polymers differ in the length of blocks. On the other hand, the dependences for samples 1 and 3 are quite different, although the calculated length of blocks is the same. One may assume that the reason for the deviations lies neither in the copolymer composition nor in the length of blocks, but is connected with specific thermodynamic features of solutions in dioxan, which is a solvent poorer than the 0-solvent for both blocks at 298 K. It has been already shown [9] that just at this temperature there occurs an inversion in the distribution of outer and inner blocks, which is probably reflected in the behaviour described above. In view of these peculiarities we consider it important to study the hydrodynamic .behaviourunder 0-conditions in detail. Let us first turn attention to the homopolymers. Light scattering from homopolymer solutions in dioxan, measured between 285 and 318 K, and the resulting values of A2 show that the 0-temperatures of homopolymers lie within this interval, but are of principally different nature: the lower critical solution temperature (LCST) in the case of polyarylate and the upper critical solution temperature (UCST) in the case of polyarylenesulphone. The latter homopolymer fulfils at 300 K (when the second virial coefficient is zero) the second condition for the existence o f 0-temperature, namely that the Mark-Kuhn-Houwink exponent a is 0.5. Consequently, the molecules of polyarylenesulphone exist under these conditions as impermeable Gaussian coils. The segment length, calculated from experimental data, agrees reasonably well with the theory [14]. On the other hand, the exponent a is higher than ~)-5 for polyarylate under 0-conditions (see Table 1), and these macromolecules do not ,exist as Gaussian impermeable coils due to their partial permeability brought about by increased rigidity [15]. The concept of 0-temperature is not strictly defined for copolymers [16, 17]~ From the fact that 1(o depends on the nature of 0-solvent Dondos and Benoit [12] conclude that 0-conditions for copolymers do not exist. On the other hand, the criteria determining the 0-conditions have been shown to be the same for copolymers and homopolymers [17]. Kotaka [18] found for both random and block copolymers that at A2 =0 the macromolecules can possess a specific, non-Gaussian conformation. As a result of differences jn the thermodynamic quality of the solvent with repect to different parts of the macromolecule in a situation resembling the 0-conditions, the intermolecular interactions need not be exactly compensated (a#0.5) owing to attractive or repulsive forces between unlike links, although the intramolecular interactions do vanish (A2 =0). Temperatures corresponding to A2 = 0 have been determined also for the investigated block copolymers in the same temperature interval (285-315 K) and in the same solvent (dioxan). The character of the temperature dependence of A2 is identical for the samples

Hydrodynamic and thermodynamic properties of dissolved multiblock copolymers

879

TABLE 1. MARK-KUFIN-HOUWINKCONSTANTSOF HOMOPOLYMERSAND BLOCKCOPOLYMERS T,K Sample Polyarylate Potyarylenesulphone Copolymers 1

2 3

UCST -

LCST 295.0

300-0 296.5 30O'0 295-0

chloroform, 298 K 0"69 0"49 0"57 1.14

a0 I K0 x 103 dioxan, 0-temperature 0-66 6.87 0.50 1.54

0-58 0-54 0'51

0-53 0-50 0.50

a

296"0 -

1 Kx

10 3

1.68 2.53 3-06

2.43 2.36 2.19

a

t Kx 103 dioxan, 298 K

0.58 0.47 0-43

1.17 3.33 4.98

1 and 3. All samples are characterized by UCST. However, a second temperature for which A2 = 0 has been found for sample 2 - i n this case corresponding to LCST. These two points lie close to the 0-temperatures of the corresponding homopolymers. The M a r k - K u h n - H o u w i n k exponent a is equal to 0.5 for this sample (Table 1). Although the values of IT/] for the same fractions are slightly different at 296 and 300 K, it was possible, within the limits of experimental error, to plot a single straight line with a = 0 . 5 through the points. The existence of two distinct 0-temperatures can be explained as follows: the composition of copolymers corresponds to equal amounts of the two components A : B and the blocks are sufficiently long; consequently, when the system approaches the 0-temperature of one homopolymer, the effect of this constituent prevails (i.e., polyarylate near 296 and polyarylenesulphone near 300 K). Parameters of the M a r k - K u h n - H o u w i n k equation valid for the 0-conditions are summarized in Table 1. One may state that the criteria decisive for the existence of 0conditions are fully satisfied for copolymers 2 and 3, while some deviations of the exponent a are observed in the case of sample 1. The dual character of the thermodynamic quality of solvent with respect to different parts of the macromolecule is obviously the reason why the conformation deviates from that of a Gaussian coil. The F i x m a n Stockmayer equation [ 19]

Ko +0.15, o

(1)

can serve for separating the effects of short-range and long-range interactions in copolymers and h o m o p o l y m e r s . A graphical extrapolation according to this equation was linear within the whole interval of M for all pairs of polymer-solvent. The value of K o was found to depend on the solvent but was only very slightly different between samples 1-3 in the same solvent. As follows f r o m the results summarized in Table 2, which represent a comparison of K0-values determined under 0-conditions and, on the other hand, found by extrapolation according to equation (1) from the data in chloroform, the unperturbed dimensions of block copolymers are larger in chloroform than in dioxan at the 0-temperature; this can be explained by the specific effect of the solvent on the unperturbed conformation of block copolymers.

880

L. V. DUBROVINA e t a l . TABLE 2. COMPARISON OF VALUES OF K o AT 298 K

[

Copolymer

Ke x 10 ~,

Ko x 103, I- calculated, eqn. (1) (0, dioxan) 2"43 2"36

chloroform 3-81 3.40

Copolydioxan ! mer i 2'49 2"61

1(ox 103, (0, dioxan) 2"19

Ko x 103, calculated, eqn. (1) chloroform dioxan 3"29

2.72

Stockmayer [20] proposed a simple additive dependence

for the determination of unperturbed dimensions of a binary copolymer A-B; WA and WB are the weight fractions of the two components in the copolymer, (h2/Mw) A and (h2/Mw) B are the characteristic dimensions of the respective macromolecular coils having the same molecular weight as the copolymer. We have ascertained that for the investigated multiblock copolymers the values of h2/Mw, calculated from equation (2), differ from those determined under the assumption of additivity. Flory [21] calculated the mean-square distance (~2) for random copolymers, showed that (~2) < ( ~ + h~)/2 at x = 0 . 5 , and concluded that the coil dimensions are affected by the more flexible component to a higher degree. It is possible that the smaller dimensions observed in our case are also due to the more important role of polyarylenesulphone, the more flexible component of the two. On this basis it is more appropriate to seek the additivity in the flexibility parameter (h2/Mw)-1 than in the parameter (h2/Mw) characterizing the chain rigidity; i.e.,

Table 3 shows that in this case the experimenta 1 and additive values lie somewhat closer to each other. It then follows that under the 0-conditions reciprocal values of [t/]0 should be also additive, Ib

[~l]0 = {WA [~3o~/3+ ~B [~]£2/3}- ~/~

(4)

The results of this comparison are in Table 3. The situation is different with regard to the good solvent-chloroform; the experimental values [r/]o deviate from [~/]ad calculated from a formula analogous to equation (4) (and containing WA, WB, the weight fractions of the two components, [~/]a and [r/]B, the intrinsic viscosities of the two homopolymers having the same molecular weight as the copolymer) in such a manner that [r/]~< [t/], d. Additional interactions inside the coil can be in all probability considered either as repulsion between unlike parts of the coil leading to its swelling or as attraction; in the latter case the interpenetration of unlike blocks may take place when the respective homopolymers are corn-

Hydrodynamic and thermodynamic properties of dissolved rnultiblock copolymers

881

TABLE 3. COMPARISONOF It/] AND MACROMOLECULARDIMENSIONSOF BLOCKCOPOLYMERS (experimental data and values calculated from equation (4)) Copolymer

WA

1 2 3

0.508 0.528 0'532

[~/]o 0.80/0.77 0.76/0.78 0.70/0-78

[q]' chloroform 1.43/0.89 1.26/0.90 1.07/0.91

(hZ/M)

x

1016

0"883/0.883 0.875/0.894 0.837/0-896

ZAB, chloroform -0"156 --0.220 - 0.450

N ote. Experimental data are in the numerator, calculated values in the denominator.

patible. The t h e r m o d y n a m i c interactions between the consituents in a c o p o l y m e r are characterized by the p a r a m e t e r ZAB [20], which can be d e t e r m i n e d from the interaction p a r a m e t e r of the copolymer, Zcop: y

Zeop= WAZA + WBZB -- WA I~B ZAB F o r o u r copolymers ZAB was f o u n d to be negative, confirming the a b o v e a s s u m p t i o n of a m u t u a l a t t r a c t i o n between unlike segments in the rnacromolecule. Thus, the conclusions arrived at earlier [9] o n the c o m p a t i b i l i t y of polyarylate a n d p o l y a r y l e n e s u l p h o n e have been confirmed; the investigation o f h y d r o d y n a m i c s a n d t h e r m o d y n a m i c s o f m u l t i b l o c k copolymers proved that these properties are highly sensitive to the structure. Translated by M. KtralN

REFERENCES l. D. C. ALLPORT and W. H. JANES, Block-copolymers, p. 586, J. Wiley, N. York-Toronto, 1973 2. A. NOSHEY and J. MeGRATH, Blok-sopolimery (Block-copolymers). 463 pp, Mir, Moscow, 1980 3. A. DONDOS, P. REMPP and H. BENOIT, Makromol. Chem. 130: 233, 1969 4. H. TANZAWA, T. TANAKA and A. SODA, J. Polym. Sci. A-2, 7: 929, 1969 5. A. DEMS, G. REDZIKOWSKA, L. PIETRZAK and A. BODEK, Preprints, vol. I, Macro Mainz, 1979 6. P. M. VALETSKII and I. P. STOROZHUK, Usp. Khim. 48: 75, 1979 7. I. P. STOROZHUK, L. B. SHIROKOVA, P. M. VALETSKII, L. Z. ROGOVINA, G. G. NIKIFOROVA, S. V. VINOGRADOVA and V. V. KORSHAK, Vysokomol. soyed. A21: 152, 1979 (Translated in Polymer Sci. U.S.S.R. 21: 1, 168, 1979) 8. G. I. TIMOFEYEVA, L. V. DUBROVINA, V. V. KORSHAK and S. A. PAVLOVA, Vysokomol. soyed. 6: 2008, 1964 (Translated in Polymer Sci. U.S.S.R. 6: 11, 2221, 1964) 9. L. V. DUBROVINA, S. A. PAVLOVA and M. A. PONOMAREVA, Vysokomol. soyed. A251536, 1983 (Translated in Polymer Sci. U.S.S.R. 25: 7, 1778, 1983) 10. H. INAGAKI and R. MIYAMOTO, Makromol. Chem. 87: 166, 1965 I I. J. URWIN and J. STEARNE, Makromol. Chem. 78: 204, 1964 12. A. DONDOS, P. REMPP and H. BENOIT, Polymer 13: 97, 1972 13. S. SCHLICK and M. LEVY, J. Phys. Chem. 64: 883, 1960 14. G. ALLEN, J. McAINSH and C. STRAZIELLE, Eur. Polym. J. 5: 319, 1969

V. I. Z~G~.'MAN eta/. 15. V. V. KORSHAK, S.-S. A. PAVLOVA, L. V. DUBROVINA, N. Yu. KOBAK and E. A. GLADKOVA, Vysokomol. soyed. All: 1458, 1980 (Translated in Polymer Sei. U.S.S.R, 22: 7, 1598,

1980) T. KOTAKA, H. OHNUMA and H. INAGAKI, Polymer 10: 517, 1969 A. DONDOS and H. BENOIT, Makromol. Chem. 118: 165, 1968 T, KOTAKA, H. OHNUMA and Y. MURAKAMI, J. Phys. Chem. 70: 4099, 1966 W. STOCKMA'~ER and M. HXMAN, J. Polym. Sci. C, 1,137, 1963 W. STOCKMAYER, L. MOORE) M. HXMAN and B. EPSTEIN, J. Polym. Sci. 16: 517, 1955 21. P. FLORY, Statisticheskaya mekhanika tsepnykh molekul (Statistical Mechanics of Chain Molecules). 440 pp, Mir, Moscow, 1971 16. 17. 18. 19. 20.

Polymer Science U.S.S.R. Vol. 27, No. 4, pp, 882-890, 1985 Printed in Poland

0032-3950/85$10.00+.00 © 1986 PergamonPress Ltd.

EFFECT OF IMPURITIES IN VINYL CHLORIDE ON THE KINETICS OF ITS POLYMERIZATION AND O N DEGRADATION OF PVC * V. I. ZEGEL'MAN,V. A. TITOVA, V. YA. KOLESNIKOV, S. 1. MIROSHNICHENKOand V. A. PoPov

(Received 17 August 1983) The effect of acetylene, butadiene, chloroprene, 2-chloropropene-1, and acetaldehyde on the kinetics of vinyl chloride polymerization, on the structure of chain defects formed, and on the thermal stability of PVC was investigated. The studied additions differ in the mechanism of their action in radical polymerization of vinyl chloride. Chloroprene and 2-chloropropene-1 show the most significant effect in lowering the thermal stability of PVC. THE relatively low thermal stability of PVC is considered to be due to the existence in the polymer of low-molecular-weight fractions [1, 2], tertiary chlorine atoms C1r [3, 4], ]/-chloroallyl chlorine atoms CIa [2, 5], ketoallyl [6], and other structures. The efforts of most investigators are devoted to the identification of defect groups responsible for the low thermal stability of PVC. On the other hand, studies dealing with the reasons underlying their formation in the polymer are practically absent. It has been proposed [7] that the presence of impurities in the monomer might be one of the reasons for their formation. Vinyl chloride usually contains insignificant amounts of acetylene, butadiene, chloroprene, acetaldehyde, 2-chloropropene-1, hydrogen chloride, and other impurities. * Vysokomol. soyed. A27: No. 4, 786-792, 1985.