Hydrodynamic and optical studies of fractions of methyl methacrylate-styrene graft copolymers

2364

T. KADYROV et al.

18. A. V. TOBOLSKY, P. M. NORLING, N. H. FRICK and H. IN, J. Amer. Chem. Soc. 86: 3925, 1964 19. V. N. KONDRATEV (Ed.), Energiya razryva khimicheskikh svyazei (Energy of Rupture of Chemical Bonds). Izv. Akad. Nauk SSSR, 1962 20. K. WASSERMEL, E. FISHER, K. GUTWEILER and H. D. CHERMAN, Ku~ststoffe 54: 410, 1964 21. A. B. BLYUMENFEL'D, M. B. NEIMAN and B. M. KOVARSKAYA, Vysokomol. soyed. 8: 1990, 1966 (Translated in Poly. Sci. U.S.S.R. 8: 11, 2199, 1966) 22. M. COHN and H. C. UREY, J. Amer. Chem. Soc. 60: 679, 1938 23. M. HALMANN and S. PINCHAEL, J. Chem. Soc., 1703, 1958 24. E. LIPPERT, D. SATUEL and E. FISHU, Ber. Bunsengesellschaft 69: 155, 1965

HYDRODYNAMIC AND OPTICAL STUDIES OF FRACTIONS OF METHYL METHACRYLATE-STYRENE GRAFT COPOLYMERS* T. KADYROV, A. i~. CHERKASOV, I. A. BARANOVSKAYA, V. YE. S. I. KLENIN, S. YA. MAGARIK and V. N. TSV~.TKOV

ESKIN,

Institute of Macromolecular Compounds, U.S.S.R. Academy of Sciences (Received 13 June 1966)

STUDIES of t h e h y d r o d y n a m i c a n d optical p r o p e r t i e s o f g r a f t e o p o l y m e r molecules h a v e b e e n r e p o r t e d in p r e v i o u s c o m m u n i c a t i o n s [1-3]. T h e results o f these studies showed t h a t t h e s t r u c t u r e of g r a f t c o p o l y m e r s is d e p e n d e n t on t h e molecu l a r p a r a m e t e r s o f t h e c o m p o n e n t h o m o p o l y m e r s . I t w a s t h e r e f o r e of interest t o s t u d y in detail g r a f t c o p o l y m e r s in w h i c h t h e c o m p o n e n t h o m o p o l y m e r s h a v e m a r k e d l y different characteristics.

f

,/,/ . / ' / r "

Y/////

////// i

o

J / / /~./ f .
I

05

7.0

FxG. 1. Double extrapolation graph of light scattering data for a solution of fraction 3 of graft copolymer I in methyl ethyl ketone. * Vysokomol. soyed. A9: No. I0, 2094-2099, 1967.

Methyl m e t h a c r y l a t e - s t y r e n e graft copolymers

2365

In this work we studied samples obtained by fractionation of two types of graft eopolymer in which polystyrene (PS) was grafted to a main chain of polymethyl methacrylate (PMMA), differing in molecular weight (M) and molecular weight distribution (MWD). The original and final products of synthesis and fraetionation were studied by means of various physical methods. Sedimentation and diffusion. Sedimentation measurements were made in a Russian UTSA-5 (SKB BFEM) ultracentrifuge provided with a polarizing interferometric optical system [4]. The coefficients of diffusion were determined in a Tsvetkov diffusiometer [5]. All measurements were made in b u t y l acetate. Light scattering. The intensity of light scattering b y the graft copolymer solutions was measured in a "Soflka" photoelectric nephelometer. The molecular weights (Mw) were found b y the m e t h o d of double extrapolation from measurement in a single solvent (butyl acetate or m e t h y l ethyl ketone) where the value of dn/dc is in the region of 0"2 and the error in determination of M w (even when there is substantial compositional in_homogeneity) does not exceed 10%. I n s t u d y of graft copolymers b y the light scattering method attention is drawn to the fact t h a t for all the studied samples the slope of the cH/Ip=f(e) curves (where c is the concentration of the solution, H the optical constant, which is dependent on the refractive index increment and I 0 the excess scattering intensity), beginning at concentrations of 0-02-0'01 g/100 em a and below becomes zero (see Fig. 1), regardless of the nature of the solvent. Consequently extrapolation to c = 0 from concentrations above t h e stated values can distort the value of M w. Flow birefringence. Flow birefringence was measured b y the s t a n d a r d m e t h o d [6] in an a p p a r a t u s with an internal rotor. The elliptical compensator h a d a p a t h difference of ~=0.041 × 5.4dX 10 -~ cm. The graft copolymers were prepared b y the method of reference [7]. I n this case it is possible to characterize the initial products of eopolymerization separately. Some character. istics of the orginal homopolymers are given in Table 1.

TABLE 1. CHARACTERISTICS OF THE INITIAL PRODUCTS OF COPOLYM:ERIZATION AND O1~ FRACTIONATION eli' THE GRAFT COPOLYMERS Initial products PMMAI (main chain of graft copolymer I) PMMA v (main chain of graft copolymer V) PS chain of graft copolymer I PS chain of graft copolymer V ~raft eopolymer V before fractionation

[S] X 10

TM

D X 10'

M~n × 10 -8

M w x 10 -s

I0 X 10'

60

0'55

9"7 × lO s

7"2; 8-6; 9"8 1"2 0"8

2"7

8"9 11'5

220, 250, 290 25 11

25

1"5

2.1 x 10 3

m

1-9 X I0 a

Figure 2 shows sedimentation diagrams of the two PMMA samples forming the m a i n chains of graft copolymers I and V. The polymer forming the backbone of graft eopolymer

2366

T. KADYROV et al.

I c o r r e s p o n d s t o a n a r r o w f r a c t i o n (Fig. 2b), w h e r e a s t h e b a c k b o n e of g r a f t c o p o l y m e r V h a s a b r o a d M W D a n d c o n s i s t s o f i n d i v i d u a l c o m p o n e n t s (Fig. 2a). G r a f t e o p o l y m e r s I a n d V were f r a e t i o n a t e d b y p r e c i p i t a t i o n w i t h p e t r o l e u m e t h e r f r o m a 1 % s o l u t i o n in a b e n z e n e - c M o r o b e n z e n e (1 : 1) m i x t u r e , t h e l a t e r f r a c t i o n s b e i n g prec i p i t a t e d b y m e t h a n o l [8]. T h e r e s u l t s o f s t u d y o f t h e s e f r a c t i o n s are p r e s e n t e d i n T a b l e 2.

F r o . 2. S e d i m e n t a t i o n d i a g r a m s of s a m p l e s o f P M M A f o r m i n g t h e b a c k b o n e c h a i n s o f t h e g r a f t c o p o l y m e r s : a - - P M M A v , b - - P M M A I.

T h e c o m p o s i t i o n s o f t h e f r a c t i o n s (x d e n o t e s t h e P S c o n t e n t ) were c a l c u l a t e d f r o m t h e refractive index increments assuming additivity of the homopolymer increments. The i n c r e m e n t s were m e a s u r e d i n a n I R F - 2 3 r e f r a c t o m e t e r w i t h a d i f f e r e n t i a l cell. T h e c o m p o s i t i o n s o b t a i n e d i n t h i s w a y were c o m p a r e d w i t h t h e r e s u l t s of e l e m e n t a r y a n a l y s i s (for C a n d I-I) a n d i n s o m e cases s u b s t a n t i a l differences were f o u n d . I n o r d e r t o find t h e r e a s o n for t h e s e TABLE

2.

S U M M A R Y T A B L E OF T H E

R E S U L T S OF M E A S U R E M E N T S

x~ x x

V x=91~

I x=83~o

o

x

.~

x

24.7 0.84 3.2 0"075 2.7 25 1 0.295 25.7 0.93 2.9 0.480 1.12 2-3 0.204 24 25 1.18 2.1 0.072 0.182 19.6 1.2 1.8 13.6 2.4 0.6 0-055 1 0 x 10 -a I1-4 0"059 0.21 0.43 8 3O 0.25 3 0 - 6 0 0.48 5 - 1 2 0.15 3 0 - 4 0 0.57 5 - 7 0"39 8.7 25 x 10 -a

3~

89 91 91 91 92 2.1 92

-- L0( ll 73 32 75 18 81 -- LO(

710 83( 70( 78( 78( 78( 47( -llC 118C 2.1 x 10 a (1.2-3) x 10 a 354C (0.95-1.3) x 103 703G 350 240 260 210 170 150

43 490 430 60 36 460 460 60 39 -510 32 450 i 470 56 300 -460 56 3O0 3 0 0 ] 4 3 0 5O 150 -290 ,)20 170 110

140011220 1500]1160

Methyl methacrylate-styrene divergences the compositions

were also determined

that indicates the presence of impurities

2367

graft copolymers

by means of a polarizing diffusiometer,

and takes account

of the error thus introduced

into the increments of the copolymers [9]. It was found that the copolymer fractions contain low molecular weight impurities which distort the composition refractometer.

calculated

by means of the

Figure 3 shows interference diffraction curves of fraction 2 of graft copolymer

FIG. 3. Interference

(6) curves obtained

during diffusion of fraction

copolymer

2 of graft

V.

V in bromoform.

These clearly show the presence of an impurity with a negative refractive

index

(curve with the maximum

increment

which has a very small increment pointing upward.

pointing

in bromoform,

The refractive index of n=1.5

downward).

The copolymer

itself,

forms a small peak with the maximum calculated for the impurity

suggests that

the fractions contain some solvent that does not evaporate when they are dried to constant weight. A similar observation was made recently in reference [lo]. The compositions obtained by means of the polarizing diffusiometer are in agreement with the analytical results.

DISCUSSION

It is seen from Table 2 that the weight fraction of styrene in the fractions of copolymer V remains practically constant with decrease in the molecular weight of the fraction and consequently also in M for the main chain of these fractions. This indicates random grafting of the PS. This would be confirmed by identity of the MWD’s of the graft copolymer and its main chain. In fact sedimentation (Fig. 4~) and diffusion (see reference [ll]) determinations of the MWD ofthe fractions of sample V show that it consists of three components, in conformity with the polydispersity of the polymer forming the main chain (Fig. 2a), reduction in M for the fractions occurring as the fraction of the low molecular weight component increases (Table 3). In contrast to sample V the MWD of graft copolymer I differs considerably from the MWD of the backbone polymer, which is a narrow fraction (Fig. 2b). Sedimentation study of copolymer I (Fig. 4b) and of a number of similar samples obtained from high molecular weight backbone chains with narrow MWD’s showed that they all consist of a number of discrete components differing considerably in M, for some fractions Jl,, ([Xl constants) being even lower than the molecular weight of the backbone. This suggests that degradation of the main chain can occur during grafting on to backbone polymers of high molecular weight,. As a result of the high polydisper-

2368

T.

et

KADYROV

d.

TABLE~.CHARACTERISTICSOFTHEYOLECULARWEI~HTDISTRIBUTIONOBTRREE FRACTIONS

Fraction

2 4

6

1 Component*

OF GRAFT

1 gzt:

/

COPOLYMER

[S]XlO"

/

V

DX107

j MsnX

1O-6

I

0.6

27

0.9

3.4

II

0.4

22

1.2

2

I

0.3

30

0.8

4

II

0.5

27

1.2

2.3

III

0.2

21

2.2

1

I

0.2

27

0.8

3.4

II

0.5

24

I.4

2.1

III

0.3

15

2.5

0.7

sity of the fractions of copolymer

I the values of MS0 and ill, for fractions 2 and 3

differed considerably. MS0 and A!, were close only for fraction 1, which is unimodal. The difference in composition of the fractions of copolymer I shows that it is fractionated according to both the molecular weight of the backbone and

FIG

4. Typical sedimentation

diagrams

graft copolymer

of fractions of graft copolymers: a-fraction

V, b-fraction

2 of graft copolymer

4 of

I.

the styrene content, whereas fractionation of copolymer V is according to M of the backbone, as is shown by the small difference in the styrene content of the fractions. This is confirmed by the data on the optical anisotropy, (u~-cI~), of the statistical segment of the polymer molecule, which is a direct characteristic of the structure of macromolecules (Table 2). It was shown in reference [ 121 that under otherwise equal conditions the optical anisotropy of a graft copolymer molecule is practically independent of the length

Methyl methacrylate-styrene

2369

graft copolymers

of its main chain, just as (cur- Q) is independent of the molecular weight of linear homopolymers. Hence the agreement of the optical anisotropies of all the fractions of sample V (except fraction 7) indicates identity of the structures of their molecules with respect to frequency of grafting and the length of the grafted branches. In the case of fraction 7 the length of the main chain and the added branches have already become comensurable and the “comb” model is no longer applicable,

and this evidently

results in a marked decrease in optical anisotropy.

On the other hand for the fractions

of sample I it is the difference in compo-

sition (the value of z) that causes the large difference in the anisotropy

values.

The value of (c~~-c(.J for fraction 3, which contains the largest quantity of polystyrene, is very high and equal to the value for one of the copolymers (BI,) of reference [12]. In comparable copolymers the side branches are long (M x 25,000). The values of S (the number of monomer units in the statistical segment) given in Table 2 are obtained by using the method of estimation of the flexibility of the backbone chains of graft copolymers from their optical anisotropy, proposed in reference [12]. They indicate that polymer chains become considerably more rigid when they are combined in the macromolecule of a graft copolymer. It was shown in reference [13] that the dimensions of graft copolymers are always considerably smaller than the dimensions of homopolymer molecules of the same molecular weight. Table 2 includes dimensions of the macromolecules obtained from data on diffusion,

(@)$,

light scattering

(@)i

and from the intrinsic orien-

tation angles (F):. Comparison of the dimensions of the molecules of the copolymer fractions with the dimensions of the molecules of linear homopolymers shows that the graft copolymer molecules have a high degree of compactness. For example the ratio M/v (v is the volume of the molecule) for fraction 3 of sample I exceeds the value for the main chain polymer of the same fraction by a factor of about forty. CONCLUSIONS (1) Fractions

of two graft copolymers

of polymethyl

methacrylate

(PMMA)

and polystyrene (PS) with backbone chains (PMMA) differing in molecular weight and molecular weight distribution have been studied by means of flow birefringence, sedimentation, diffusion and light scattering. (2) Fractionation of a graft copolymer based on PMMA with a narrow MWD and M= 1 x 10’ gave fractions consisting of a wide range of discrete components and differing in polystyrene content. (3) Fractionation of a graft copolymer based on PMMA with M=S x 106 and a fairly broad MWD gave fractions with the same MWD as the backbone polymer and with very similar styrene contents. Translated by E.

0. PHILLIPS

REFERENCES 1. V. N. TSVETKOV, S. Ya. MAGARIK, S. I. KLElNJN and V. Ye. ESKIN, soyed. 5: 3, 1963 (Translated in Poly. Sci. U.S.S.R. 4: 4, 601, 1963)

Vysokomol.

2370

P. M. GORBUNOVet al.

2. V. N. TSVETKOV, S. I. KLENIN and S. Ya. MAGARIK, Vysokomol. soyed. 6: 400, 1964 (Translated in Poly. Sci. U.S.S.R. 6: 3, 443, 1964) 3. I. A. BARANOVSKAYA, S. I. KLENIN, S. Ya. MAGARIK, V. N. TSVETKOV and V. Ye. ESKIN, Vysokomol. soyed. 7: 878, 884, 1965 (Translated in Poly. Sci. U.S.S.R. 7: 5, 968, 975, 1965) 4. V. N. TSVETKOV, V. S. SKAZKA, N. A. NIKITIN and I. B. STEPANENKO, Vysokomol. soyed. 6: 69, 1964 (Translated in Poly. Sci. U.S.S.R. 6: 1, 79, 1964) 5. V. N. TSVETKOV, Zh. eksp. i teor. fiz. 21: 701, 1951 6. V. N. TSVETKOV, V. Ye. ESKIN and S. Ya. FRENKEL’, Struktura macromolekul v rastvorakh (The Structure of Macromolecules in Solution). Izd. “Nauka”, 1964 7. S. P. MITSENGENDLER, G. A. ANDREYEVA, K. I. SOKOLOVA and A. A. KOROTKOV, Vysokomol. soyed. 4: 1366, 1962 (Translated in Poly. Sci. U.S.S.R. 4: 3, 436, 1963) 8. Y. GALLOT, P. REMPP and Y. PARROD, J. Polymer Sci. Bl: 326, 1963 9. S. I. KLENIN, V. N. TSVETKOV and A. N. CHERKASOV, Vysokomol. soyed. A9: 1435, 1967 (Translated in Poly. Sci. U.S.S.R. 9A: 7, 1604, 1967) 10. P. H. NORBERG and L. 0. SUDELOF, Makromol. Chem. 77: 77, 1964 11. A. N. CHERKASOV, S. I. KLENIN and Yu. Ye. EIZNER, Vysokomol. soyed. 7: 902, 1965 (Translated in Poly. Sci. U.S.S.R. 7: 5, 996, 1965) 12. V. N. TSVETKOV, S. I. KLENIN and S. Ya. MAGARIK, Vysokomol. soyed. 6: 400, 1964 (Translated in Poly. Sci. U.S.S.R. 6: 3, 443, 1964) 13. V. N. TSVETKOV, G. A. ANDREYEVA, I. A. BARANOVSKAYA, S. I. KLENIN, S. Ya. MAGARIK and V. Ye. ESKIN, J. Polymer Sci. C16: 239, 1967

THE MORPHOLOGY OF OPTICALLY OBSERVED STRUCTURES IN CHLOROPRENE RUBBER * P. M. GORBUNOV, G. M. BARTENEV and T. P. SYROVATKO Research Institute of the Rubber Industry V. I. Lenin Pedagogical Institute, Moscow (Received 9 July 1966) SOME optically

observable structural formations in crystalline rubbers are optically anisotropic and can therefore be studied in a polarizing microscope. It should be borne in mind that the total birefringence of such formations is made up of intrinsic and non-intrinsic birefringence [l]. Precise determination of the contribution of effects is a comparatively difficult task because the shapes of the elementary structures making up these formations and the internal stresses cannot be determined accurately. In addition great difficulty is introduced into experimental investigations by the fact that under the action of heat, light, radioactive radiations, accelerated charged particles, etc. the pure rubber can * Vysokomol.

soyed. A9: No. 10, 2106-2104,

1967.