Photoelasticity of polymethacrylic esters of alcohols containing fluorine

~380

A. YE. GRISHCHENKOe~ al.

4. Yu. S. LIPATOV and V. P. PRIVALKO, J. Macromolec. Sei. B7: 431, 1973 5. Yu. S. LIPATOV, Fiziko-khimiya napolnennykh polimerov (Physico-Chemistry of Filled Polymers). Izd. "Naukova dumka", 1967 6. G. KRAUSS and J. GRUVER, J. Polymer Sci. 8, A-S: 571, 1970 7. Yu. S. LIPATOV, V. F. ROSOVITSKII and V. F. BABICH, Dokl. AN SSSR 220: 1368, 1975 8. Yu. S. LIPATOV, V. F. ROSOVITSKII and V. F. BABICH, Sbornik. l~ovye metody issledovaniya polimerov (Polymer Research: New Methods). Izd. "l~aukova dumka", p. 106, 1975 9. K. NINOMIYA and J. FERRY, J. Colloid Sei. 14: 36, 1959 10. Yu. S. LIPATOV, Vysokomol. soyed. AI0: 2737, 1968 (Translated in Polymer Sci. U.S.S.R. 10: 12, 3174, 1968) 11. Yu. S. LIPATOV and L. M. SERGEYEVA, Adsorbtsiya polimerov (The Adsorption of Polymers). Izd. "l~aukova dumka", 1972

PHOTOELASTICITY OF POLYMETHACRYLIC ESTERS OF ALCOHOLS CONTAINING FLUORINE* A. YE. GRISHCHENKO, L. D. BUDOVSKAYA, YE. N. ROSTOVSKII and V. N. IVANOVA '50th Anniversary of the U.S.S.R.' Syktyvkar State University Institute of High Molecular Weight Compounds, U.S.S.R. Academy of Sciences

(Received 23 January 1976) A study was made of the photoelasticity of two polymethacrylic esters of alcohols containing fluorine in bulk and in gel. A study of relaxation of birefringence near T ~ T8 showed that optical properties of these polymers are characterized by a wide spectrum of relaxation times. From a comparison of differences of main polarizabilities of the polymers studied, determined from the Kuhn formula and natural anisotropy ~f PMMA the anisotropy of the C--I~ bond was evaluated Aac-F~ 10.2 × 10 -16 cm s. On investigating gels of these esters an inversion was observed in the sign of optical anisotropy with a variation of polymer concentration in gel. ORGANIC g r o u p s on t h e p o l y m e r chains r e d u c e m o l e c u l a r i n t e r a c t i o n a n d t h u s lower t h e glass t e m p e r a t u r e . This, h o w e v e r , i n v o l v e s a r e d u c t i o n in t h e r m a l s t a b i l i t y due to o x i d a t i o n a n d b r e a k d o w n o f l a t e r a l groups. One m e t h o d o f o b t a i n i n g p o l y m e r s c o m b i n i n g a fair t h e r m a l r e s i s t a n c e w i t h low m o l e c u l a r i n t e r a c t i o n is b y s y n t h e s i s o f m a c r o m o l e c u l e s w i t h lateral perfluoro-groups. R e s u l t s are g i v e n in t h i s p a p e r o f a n i n v e s t i g a t i o n o f t h e p h o t o e l a s t i c i t y o f t w o p o l y m e t h a c r y l a t e esters, in b u l k a n d in gel, o f alcohols c o n t a i n i n g fluorine. * Vysokomol. soy~l. AI8: tqo. 9, 2081-2085, 1976.

Photoolasticity of polymethacrylic esters of alcohols

2381

A stddy was made at different temperatures of the dependence of birofringenco An on the tensile stress q of two fluorinated polymethacrylate (PFMA) films: polyoctafluoramyl methacrylate (PFMA-2, n = 2 ) a n d polydodecafluoroheptyt methacrylato (PFMA-3, n = 3 ) . The samples were prepared b y polymerization of monomers in polyethylene cells in a layer 0.8 m m thick. Polymerization was carried out at 70 ° with a benzoyl peroxide initiator (0.2%). ~ " I0 fz cmZ/dgne

oL¢

qg

o~

S oo

¢

0

ZO ol ,,2

x3 cq .5 t

6g

1

18g

T ° "~

FIG. 1. Temperature relation of e of PFMA-2 with EGDM contents of 0.5 (1), 2.0 (2); 4.0 (3); 6.0 (4) a n d 8.0% (5).

To extend the high elasticity range, the samples were crosslinked b y addition of ethylene glycol dimothacrylato (EGI)I~) to the reaction mixture which also enabled the concentration dependences of optical properties of polymers mentioned to be examined in the swollen state. PGMA-2 contained 0"5; 2; 4; 6 a n d 8% EGDM, respectively; PGMA-3 contained 0"3% EGDM (molar concentratiorQ. I n each case examined the relation of A n = f (a) was linear, which enabled optical properties of samples to be described using a photoelas~ic coefficient (PEC) e=An/a. ~¢Iethods of measuring PEC were described in a previous paper [1]. Figures 1 a n d 2 show temperature relations of PEC of P1WFA-2 a n d PFMA-3. Birefringence was relaxed in the glass transition range on applying and relieving load. As an example Fig. 3 shows typical time relations of birefringenco of PFMA-2 p o l y m e r films at 41 and 46 ° .

:2382

A. Y~.. GRXSHCHE~r~Oet

al.

Time relations of birefringence An on relieving load may be described by the formula An=Ano exp ( - - ~ )

(1)

An=An o(1--e -t/~)

(2)

and on applying load Here r is the relaxation time dn0--1im An t-~ao

Let us transform equation (2) to

(An)

Tt

In 1--~nn0. ---

(2a)

The experimental relation shown in coordinates In (1--An/Ano)=f(t) enables relaxation time v to be determined. Figure 4 shows relations of ]n (1--An/Ano) = / ( t ) for PFMA-2 at temperatures which are close to the glass temperature ~ 101z~cmZ/d,.,une o

3O

10 I

I

100

I

I

zoo 7"0

Fzo. 2. Temperature relation of 8 of PFMA-3 crosslinke4 with 0.3% EGDM. (Tg=45°). It can be seen that the average relaxation time of birefringence increases with a reduction of temperature (T~cot a). When TTg temperature relations of 8 are explained by

Photoelasticity of polymethacrylio esters of alcohols

2383

t h e t e m p e r a t u r e v a r i a t i o n s of the a n i s t r o p y of polarizability of t h e statistical s e g m e n t =~--a2, which m a y be calculated f r o m t h e K u h n f o r m u l a [2] e = 2 ~ ( 4 5 k T n ) -1 ( n 2 + 2 ) 2 (~1--~2)

(3)

F i g u r e 5 shows t h e relation of = x - - a 2 = f (t) w h e n T > T g for PFMA-2. A similar relation is also observed for PFMA-3.

-l,n (l- ,An

~ l O ~" cm

717

~/dyne ~

o o

IO

o ~ Reliez

2g

30

Time, min

5

1/7

Time, rain Fro. 4

Fro. 3

FIe. 3. Time relations of the photoolastic coefficient at 41 (1) and 46 ° (2). Fie. 4. Relation ofln

1 Ano]

(t) of PFMA-2 crosslinke4 with 2.0% EGDM at 31 (l)

41 (2), 46 (3), 50 (4), 55 (5) and 65° (6). Values of ~ e x t r a p o l a t e d to r o o m t e m p e r a t u r e are: e----2×10 -11 cm2/dyne for P F M A - 2 a n d E----1.8 × 10 -11 cm2/dyne for PFMA-3. Values of a1--~2= -{-4.8 × × 10 -35 cm a and a l - - a 2 = + 4 . 6 × 1 0 -25 cm a correspond to this for P F M A - 2 a n d PFMA-3, respectively. I t is significant t h a t optical anisotropies of P F M A - 2 a n d P F M A - 3 segments are similar a n d so are values o f al--a2 o f p o l y m e t h y l m e t h a c r y l a t e [3, 4] which has the same ridge s t r u c t u r e as P F M A - 2 a n d P F M A - 3 and differs f r o m t h e p o l y m e r s studied b y t h e absence of - - C F 2 - - C F 2 - - groups. These e x p e r i m e n t a l facts no d o u b t indicate t h a t t h e - - C F 2 - - C F 2 - chemical g r o u p is optically isotropic. This enables t h e a n i s o t r o p y of polarizability of the C - - F b o n d t o be evaluated. F r o m the s t r u c t u r e of t h e - - C F 2 - - C F ~ - group shown in Fig. 6 AaC'I~'= (3 cos 2 ~ - - 1) AaC-C+ 2 (3 cos 2 90 ° - 1) AaC-F~ 1.1Aa c - c - 2Aa c - r

m a y be derived.

2384

A. YE. OmSHOHEZ~O et al.

Since it follows from the experiment that ztac~F*~ 0, Ja c-F ~ 10.2 × 10 -*s cm s. I f we consider, according to results in the literature [5], the anisotropy of bonds between e~rbon and elements of the second series, carbon and elements of the seventh period of the Mendel~eff Table, it appears that AaC-C~18 × 10-~5; z i a C - C ~ 1 2 . 3 X 10-~s; A a C - ~ - - 1 0 . 2 × 10-*~; AaC-Cl_--15.9× 10-25; z i a C - ~ r ~ 2 1 . 6 X × 10 - ~ .

250

°°

20

YS0

0 °

120

80

I

1,,,

160

zOO

7-,"C

FIG. 5

Fro. 6

Fro. 5. Relation of ~l--a~--~] (t) of PFMA-2, crosslinked with 0.5% EGDM. Fro. 6. Calculation of the anisotropy of polarizability of a (--CF~--CF2--) group.

3b

o

Z

-

3 o

0

~'~J

c, %

100

-y

-0

_/'

:FIG. 7. Concentration dependence of e of PFMA-2 crosslinked with 0.5% EGDM (a) and P~MA-3, crosslinked with 0-3% EGDM (b) in butylacetate (1) and DM:F (2).

Photoelasticity of polymethacrylic esters of alcohols

2385

I t can be seen t h a t the anisotropy of the C - - F bond of AaC-F= 10"2 × 10 -35 cm 3 corresponds to the expected value. Figure 7 shows the concentration relations of PEC of PFMA-2 and PFMA-3 gels in butyl acetate (BAC) and DMF. These relations were determined by step-by-step measurement of e as the solvent evaporated from gel. Relations of e = f (c) shown in Fig. 7 are concentration relations of the optical anisotropy of PFMA-2 and PFMA-3 with an accuracy of up to a constant factor (formula (3)). The proximity of refractive indices of PFMA-2 ( n = 1.396), PFMA-3 ( n = 1-380), BAC (n=1.396) and DMF (n=1.425) enables the form effect to be ignored. Consequently, relations of e = f (c) are concentration relations of the natural anisotropy of PFMA-2 and PFMA-3 under conditions of different molecular interactions. Extrapolation of relations e = f ( c ) to ~=100% gives values of PEC coinciding with similar values derived by the extrapolation of temperature relations to 20 ° . With a reduction of concentration the negative value of c increases; an increase of the negative anisotropy of polarizability of PFMA-2 and PFMA-3 segments corresponds to this value. With a reduction of molecular interaction, the sign of optical anisotropy is reversed. The increase of negative optical anisotropy and therefore, the photoelastie coefficient e with a reduction of concentration is typical of polymers with comb structure. Similar relations were observed for polyoctyl methacrylate gels [6]. This may be used to establish grafting of lateral chains to macromolecules. Translated by E. SEMERE REFERENCES 1. V. N. TSVETKOV, A. Ye. GRISHCHENKO and Ye. P. VOROB'YEVA, Sb. Karbotsepnye vysokomol, soyed. (Carbon-Chain High Molecular Weight Compounds). Izd AN SSSR, 1963 2. W. KUHN and F. GRI~N, Kolloid-Z. 101: 248, 1942 3. V. N. TSVETKOV, V. Ye. ESKIN and S. Ya. FRENKEL', Struktura makromolekul v rastvorakh (Structure of Macromolecules in Solutions) Nauka, 1964 4. A. Ye. GRISHCHENKO, M. G. VITOVSKAYA, V. N. TSVETKOV, Ye. P. VOROB'YEVA, N. N. SAPRYKINA and L. I. MEZENTSEVA, Vysokomol. soyed. A9: 1280, 1967 (Translated in Polymer Sci. U.S.S.R. 9: 6, 1430, 1967) 5. K. G. DENBIGH, Trails. F a r a d a y Soc. 36: 946, 1940 6. A. Ye. GRISHCHENKO, M. G. VITOVSKAYA, V. N. TSVETKOV and L. N. ANDREYEVA, Vysokomol. soyed. 8: 800, 1966 (Translated in Polymer Sci. U.S.S.R. 8: 5, 878, 1966)