Catalytic polymerization of bicyclodimethylsiloxanes

K. A. ADRIAI~OVand Lo~A M. VoLxovx

1840 12. 13. 14. 15.

J. BOOR, J. Polymer Sci. 62: 45, 1962 E. B. MILOVSKAYA and P. I. DOLGOPOL'SKAYA, Vysokomol. soyed. 4: 1049, 1962 M. I. MOSEVITSKII, Uspekhi khimii 28: 465, 1959 E. VECCHI, R. ZANNETTI, L. LUCIAN and P. BARBE, Chemica e industria 43: 741, 1961

CATALYTIC POLYMERIZATION OF BICYCLODIMETHYLSILOXANES* K. A. ANDRIANOV and LORA M. VOLKOVA The M. V. Lomonosov Institute of Fine Chemical Technology, Moscow

(Received 12 November 1963)

TO STUDY the synthesis of polyorganodimethylsiloxanes of branched structure with regular distribution in the molecular chain of silsesquioxane groups

i

O

I

CH3--Si--O--

I I

O

the catalytic polymerization of bieyelic dimethylsiloxane compounds was carried out. To construct molecular chains in which the methylsilsesquioxane groups would be regularly distributed in the polymer molecule chain, bicyclic compounds of the dimethylsiloxane series of the following general formula were taken: (CH3)s Si

Si (CHa)s

o/ o (CHa)2 Si

o/\o Si--O--(SiO)n--Si

\o

\/

(CHs)s

CHaO '\

Si (CHa)s

\/

0/

Si (CH~)s

where n----2, 3, 4, 5, 13, 32, 66, 145, 170, 198, 224, 270. Oligomers with from 2 to 5 d i m e t h y l s i l o x a n e units were o b t a i n e d in the form o f individual c o m p o u n d s according to m e t h o d s p r e v i o u s l y described [1]. Oligomers with larger n u m b e r s of d i m e t h y l s i l o x a n e units were o b t a i n e d b y condensation of a, ¢o-dioxypolydimethylsiloxanes w i t h h e p t a m e t h y l c h l o r o e y c l o t e t r a siloxane: * Yysokomol. soyed. 6: No. 9, 1662-1667, 1964.

Catalytic polymerization of bicyclodimethylsiloxaaes

1841

CtI a CI-I2

\/

Si O

0

HO (SiO)nH+ 2Si ~

I

I

(CH3)~

C1 ~Si~

0

0

(CH.h ~ /

CH~

Si (CH3),~

(CH3) 2 Si

Si (CH3) 2

0

O

-->(CH3)~ Si ~

O

O

I o CH+

o

~Si--0--(Si0)n--Si~

o ~/ o

I CH+

I (CH,),,

~ S i (CH3)~+ 2HC1 ~/

(CH3) ~ Si

Si (CH3) ~

A study has been made of the conversion of oligomers into polymers of branched structure with regular distribution of methyl silsesquioxane groups in t h e m o l e c u l a r c h a i n CH 3

1

CH 3

CHa

I

I

CH 3

I

CHa--Si--0--Si--CH 3 CI-I3--Si--0--Si--CH 3

I

I

0

0

I

I

I

I

CH 3

0

0

I

I

I

K0H

)

CH3--Si--0--Si--0--(Si0 )+,--Si--0--Si--CH 3

I

I

CHa CH 3

CH3

I

CH3

I

CH3

CI-I 3

I

t

CI-Ia--Si--O--Si--CH

O

I

CHz

O

3 CH 3

OH

CH 3

CH 3

CH 3

CHa--Si--0--Si---0--(SiO)n--Si--0--Si--0--Si--O--Si--O-

I

CH a

I

CH+ CI-I 3

I

CH a CI-I 3

I

CH a CH~

I

CH+ CI-I 3

I

CH z CHa

i

I

r

I

]

I

I

i

l

L

CI-I 3--Si--O--Si--O--(SiO)n--Si--0--Si--CH

-+

O

O

I

I

cIH3

O

O

I

t

3

-+

Ctta--Si--0--Si--CH 3 CtI3--Si--0--Si--CI-I3

I

CH8

I

CH3

I

CH3

I

CH.:,

K. A. ADRIAN0V and LORA M. VOL:K0VA

1842 CH 8

CH3

C I - I a - - S i - - O - - S i - - C Ha -+

O

O

I

I

CH 3

OH

CH8

J

CH3

CH3

CHa

i

i

W

CI-Ia--S i - - O - - S i - - O - - ( S i 0 ) n - - ~ i - - O - - ~ i - - O - - S i - - O - - S i - - 0 - - S i - CH a

Ctt a

CH a

O--

CH3 C H a - - ]Si--CH8

i

O CH3-- ]Si--CH3 O

t

CHs--Si--CH a O-CH a

CHa

J

f

CH 3

f

- - ( S i O ) n - - S i - - O - - S i - - C Ha

I

I

CH a

i

O

O

I

i

C I - I a - - S i - - O - - S i - - C Ha

i

CI-Ia

]

CH a

In the study of the polymerization reaction of bicyclic oligomers it was established that in the presence of K 0 H t h e y are converted to polymers considerably more easily than octamethylcyclotetrasiloxane [2]. In ease of polymerization t h e y are similar to bicyclic compounds containing alkyl or arylsiloxy groups [3-6]. Irrespective of the distance between the rings, polymerization commences at room temperature, but takes place slowly at this temperature. Polymerization of bicyclic dimethylsiloxanes was effected in 0-5~ KOI-I at 70°C. The dilatometric method can only be used for polymerization of bicyclic polydimethylsiloxanes with n < 5, when contraction is 0.38 ~ (Fig. 1). 01igomers with large numbers of dimethylsiloxane units only contract in polymerization to a very small extent; therefore in these cases the dilatometric method is unsuitable.

•~

+ ~ +

o

~

÷ r

80

+ ~ +

~b

.+ d

~8o

rime, rn/n

FIG. 1. Polymerization kinetics of 1,9-(heptamethylcyclotetrasiloxy) decamethylpentasiloxane.

Catalytic polymerization of bieyclodimethylsiloxanes

1843

To study the polymerization kinetics of bicyclic compounds, a method based on determination of the gel fraction, was used. Figure 2 shows the dependence of conversion time of oligomers into insoluble polymers on the distance between

'-25o 0

10

I

J

i

I

1

4/7

7"[17"18 , h o u P 8

FIG. 2. Dependence of the conversion time of oligomers into insoluble polymer on the distance between rings: l - - n = 4, 2 - - n = 13, 3 - - n = 32, 4 - - n = 145, 5 - - n = 270. the rings. It is apparent from the figure t h a t the oligomers with polymerization coefficients of 3 and 5 are converted to an insoluble polymer to the extent of 99.4~ in 3 hours, and oligomers with polymerization coefficients of 13 and 32 become (,}8.8~o, and 98.6~ insoluble respectively. Oligomers with polymerization coefficients of 145 and 270 in 18 and 30 hours become 87 and 78~o insoluble respectively and further heating does not cause complete insolubility. Thus, the gel fraction content in oligomers with n----145 for 30 hours and with n--~270 for 40 hours, remained unchanged (87 and 78~). It can be seen from the experimental data that, with the increase of the number of dimethylsiloxane groups between the rings, not only is the reaction of oligomer conversion into insoluble product retarded but even prolonged polymerization does not produce completely cross-linked polymers, and the process reaches equilibrium. In addition, a considerable part of the soluble product is retained. Figure 3 shows the depend-

g0

~o

0

13

145

270n

FIG. 3. Dependence of insoluble polymer yield on the distance between rings (n) with a polymerization time of 4 hours.

1844

K. t . ADRIANOV a n d LORA M. VOLKOVA

ence of insoluble polymer yield on the distance between rings with a polymerization time of 4 hours. As can be seen from the curve, the rate of conversion of bicyclic oligomers of the dimethylsiloxane series into gel markedly decreases with increase of the distance between rings. After polymerization for 4 hours at 70°C the bicyclic oligomers with n = 13 is converted into an insoluble polymer to the extent of 98.8~o and the bicyclic oligomer with n = 2 7 0 is converted to gel to the extent of 17 ~o. All the polymers obtained are transparent products which swell satisfactorily in benzene and toluene. The polymers for which n = 12 and 66 are brittle gels and the polymers, for which n = 170 and more, are very elastic. On the basis of experimental data obtained an a t t e m p t was made to determine the reaction rate constant of catalytic polymerization o~ bicyclodimethylsiloxanes with 0.5 ~ KOH. I t can be seen from Fig. 4 t h a t the logarithmic dependence of gel concentration on the distance between rings is linear. Consequently, the amount of insoluble

++="~'++~4 0

I

I

1

2

I

31ogn

FIG. 4. Logarithmic dependence of yield C of the insoluble polymer on the distance between rings (n) with varying polymerization times. Time, hours: 1-- 3, 2-- 4, 3-- 7, 4--10.

product formed can be approximately expressed by the formula C = K . n -~, where C is the amount of insoluble polymer formed, n is the distance between rings, K is a constant which is numerically equal to the section cut off on the ordinate axis (Fig. 4), ~ is the reaction rate constant which is numerically equal to the tangent of slope of the straight line. With polymerization times of 3, 4 and 7 hours (straight lines 1, 2 and 3) these straight lines are parallel and the tangent of slope is 0.52. In particular, with a polymerization time of 4 hours, K = 1 8 2 and the equation takes the form C = 1 8 2 . n -°'52. With polymerization times of 10 hours and higher (straight line 4) the reaction rate constant does not conform to the previous value. For ~xample with a polymerization time of 10 hours, it is 0-7. This reduction of the constant with the increase of the distance between rings is probably explained by reduction of the number of collisions between the active centres of the molecules.

Catalytic polymerization of bicyclodimethylsiloxanes

1845

The s t u d y of t h e r m o m e e h a n i c a l properties of the p o l y m e r s o b t a i n e d showed t h a t t h e y differ c o n s i d e r a b l y f r o m l i n e a r p o l y d i m e t h y l s i l o x a n e s ; t h e glass t e m p e r a t u r e s Tg o f t h e p o l y m e r s o b t a i n e d h a v e b e e n d i s p l a c e d f r o m - - 5 8 ° t o - - 9 0 ° a n d lower. S u c h T~ v a l u e s a r e c o n s i d e r a b l y l o w e r t h a n Tg o f p o l y d i m e t h y l m e t h y l p h e n y l s i l o x a n e r u b b e r w i t h a r a t i o o f d i m e t h y l a n d m e t h y l p h e n y l u n i t s o f 24 : 1 for w h i c h Tg is i n t h e r e g i o n of - - 7 0 ° as c a n b e s e e n f r o m Fig. 5.

£

c

.--3

1

2

1"7

I:

/

/ ....

-lO0

-70

i

/

i

...... -50

/

.' 0

""

i

....-'" ~

250

300

/

Temperature, °C

FIG. 5. Thermomechanical curves of polymers obtained by catalytic polymerization of oligomers with varying polymerization coefficients : 1 -- n = 13, 2 -- n = 66, 3 -- n = 145, 4-- n =198, 5 - - n = 2 2 4 , 6 - - S K T , 7--polydimethylsiloxane, modified with 5% methylphenylsiloxane units. There are n o t sufficient d a t a a v a i l a b l e a t p r e s e n t to elucidate the causes w h i c h l e a d t o s u c h m a r k e d v a r i a t i o n s of p o l y m e r p r o p e r t i e s . W o r k c o n t i n u e s i n t h i s d i r e c t i o n a n d we shall d i s c u s s i n f o r m a t i o n a s i t b e c o m e s a v a i l a b l e .

EXPERIMENTAL ~, o~-Dioxydimethylsiloxanes were synthesized by known methods [7, 8]. t I e p t a m e t h y l chlorocyclotetrasiloxane was synthesized by the methods earlier proposed by the authors [9] 1,13-(Heptamethylcyclotetrasiloxy)sicosaheptamethyl tridecasiloxane. 19.6 g 1,13-dioxysicosaheptamethyltridecasiloxane and 7 g heptamethylchlorocyclotetrasiloxano were placed in a three-necked flask equipped with a stirrer with an oil seal, reflux condenser with a calcium chloride tube and a headpiece for introducing nitrogen. The reaction mixture was heated while stirring constantly for 30 hours, gradually raising the temperature from 20 to 120°C. The reaction product was heated in vacuo at 180°C, while 0.4 g of the cyclic product was distilled off. 30 ml benzene was added to the oligomer obtained and the solution washed with distilled water until it was neutral to Congo red. The water was separated in a funnel and benzene distilled off. 23 g 1,13-(heptamethylcyclotetrasiloxy)sicosaheptamethyltridccasiloxane was obtained. Bicyclic oligomers with 13, 66, 145, 170, 198, 224 and 270 of dimethylsiloxane units in the linear chain were obtained by the above methods. Polymerization of 1,3-bis-(heptamethylcyclotetrasiloxy)-hexamethyltrisiloxane and 1,5-bis(heptamethylcyclotetrasiloxy)-decamethylpentasiloxane was studied by a dilatometric method. Accurately measured amounts of 1,3-bis-(heptamethylcyclotetrasiloxy)hexamethyltrisilo-

1846

K. A. ADRIANOVand LOI~AM. VOLKOVA

xane (4 g) and potassium hydroxide (0.02 g in 200/0 solution in ethanol) were placed in graduated ampoules. The ampoules were sealed and placed in a thermostat. Temperature was maintained at 70°±0.5°C. Polymerization took 3 hours. During polymerization, at certain time intervals, the ampoules were removed from the thermostat and the variation of the level in the graduated part of the ampoule at 20°C measured. Experimental data on the mean values of volume variation are shown in the curve in Fig. 1. Polymerization of 1,5-(heptamethylcyclotetrasiloxy)decamethylpentasiloxane was carried out b y similar methods. Experimental data showing mean volume variation are presented on a curve in Fig. 1 which agrees with the polymerization curve of 1,3-bis-(cyclotetrasiloxy)hexamethyltrisiloxane. Determination of the gel fraction. 1,2 g bicyclic oligomer and 0-006 g K O H in 25~o solution in ethanol, was placed in a porcelain crucible and polymerized in a thermostat at 70°C. At certain time intervals the crucibles were taken out, arranged in piles on glass fabric, weighed and placed in a Soxhlet device in which the monomer was extracted by benzene in 12-14 hours. Then the crucible were reheated in a thermostat to constant weight and weighed. The experimental gel fraction values for oligomers with varying polymerization coefficients are shown in Fig. 4. The thermomechanical curves were obtained with a Kargin balance with a load of 30 g/cm 2 according to the methods proposed by Slonimskii [10]. CONCLUSIONS (1) B i c y c l i e d i m e t h y l s i l o x a n e o l i g o m e r s w i t h n u m b e r s

of d i m e t h y l s i l o x a n e

u n i t s b e t w e e n t h e cycles o f 13, 32, 66, 145, 170, 224, 198 a n d 270 h a v e b e e n s y n thesized. (2) T h e r e a c t i o n o f c a t a l y t i c p o l y m e r i z a t i o n o f o l i g o m e r s o b t a i n e d h a s b e e n studied a n d it has been established t h a t they polymerize more easily t h a n octamethyicyclotetrasiloxane. (3) T h e p o l y m e r i z a t i o n k i n e t i c s o f t h e o l i g o m e r s s y n t h e s i z e d h a v e beeI1 i n v e s tigated.

Translated by E. SEMERE REFERENCES 1. K. A. ANDRIANOV, LORA M. VOLKOVA and M. S. OBUSHEVA, Izv. Akad. Nauk SSSR, Otd. khim. nauk, 1986, 1963 2. J. MARSDEN, U.S. Pat. 254003, 1951; Chem. Abstrs. 45: 5906, 1951 3. K. A. ANDRIANOV, S. I. DZHENCHEL'SKAYA and Yu. K. PETRASHKO, Zh. obsheh. khimii 28: 685, 1958 4. N. N. SOKOLOV, Metody sinteza poliorganosiloksanov. (Methods for the Synthesis of Polyorganosiloxanes.) Gosenergoizdat, Moscow, 1959 5. K. A. ANDRIANOV and S. E. YAKUSHKINA, Vysokomol. soyed. 3: 1554, 1901 6. K. A. ANDRIANOV, L. M. KHANANASHVILI and I. S. BELEN'KAYA, Vysokomol. soyed. 4: 592, 1962 7. J. F. HYDE, J. Amer. Chem. Soc. 75: 2160, 1953 8. K. A. ANDRIANOV, N. O. KURASHEVA, I. K. KUZNETSOVA and E. I. GERHARDT, Dokl. Akad. Nauk SSSR 140: 365, 1961 9. K. A. ANDRIANOV and LORA M. VOLKOVA, Izv. Akad. Nauk SSSR, Otd, khim. nauk, 264, 1962 10. G. L. SLONIMSKII, Zavodsk. lab. 22: 1247, 1956