Reactive Difunctional Siloxane Oligomers - American Chemical Society

14 Reactive Difunctional Siloxane Oligomers Synthesis and Characterization 1

ISKENDER YILGÖR, JUDY S. RIFFLE , and JAMES E. McGRATH

Downloaded by STANFORD UNIV on February 18, 2015 | http://pubs.acs.org Publication Date: July 9, 1985 | doi: 10.1021/bk-1985-0282.ch014

Department of Chemistry, Polymer Materials and Interfaces Laboratory, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061

Synthesis and characterization of well-defined, α,ω-terminated difunctional siloxane oligomers are discussed. Detailed procedures on the preparation of primary amine- and hydroxy-terminated oligomers are given. Control of the average molecular weight (Mn) and also the possible variations in the backbone structure and composition are explained. The effect of these variations on the physical, thermal and chemical properties of the resulting materials are discussed. Characterization of these oligomers by FT-IR, NMR and UV spectroscopy, potentiometric titration and DSC are summarized. Organosiloxane based segmented elastomers have been described i n the l i t e r a t u r e over the past twenty five y e a r s ( r - 5 ) . The main interest i n these type of block or segmented copolymers arises mainly due to the unique properties of the organosiloxane segments, which are quite different than those of conventional rubbery hydrocarbon polymers. In general polyorganosiloxanes display very good low temperature f l e x i b i l i t y (Tg as low as -123°C), good thermaloxidative s t a b i l i t y , ozone and UV resistance, r e l a t i v e l y high gas permeabilities, good biocompatibility and excellent e l e c t r i c a l properties. Moreover, they are non-polar and have very low s o l u b i l i t y parameters ( 0~ X ] type species, which may also cleave the siloxane bonds. This generally results i n the loss of terminal functionality i n the oligomers produced, which i s of course not desirable. +

X

Synthesis of Aminopropyl Terminated Oligomers

Poly(dimethyl-diphenyl)siloxane

Acid and base catalyzed coequilibration reactions of D4 and D 4 " have been studied i n the l i t e r a t u r e by several workers (16-18). These studies were directed towards either the synthesis of very high molecular weight "modified" s i l i c o n e rubbers, or to the analysis of reaction kinetics (13, 16-19). There has been no systematic studies i n the open l i t e r a t u r e on the synthesis and characterization of functionally terminated, low molecular weight (dimethyl-diphenyl)siloxane oligomers which can be used i n the preparation of segmented block copolymers. It i s known that the incorporation of diphenylsiloxane units generally disrupts the low temperature c r y s t a l l i z a tion of polydimethylsiloxane resins and also increases their thermal and radiation s t a b i l i t y (12,13). Glass temperature (Tg) and s o l u b i l i t y parameter values of the resulting polymers are also raised accordingly, depending on the l e v e l of diphenylsiloxane incorporation.

In Reactive Oligomers; Harris, F., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.


REACTIVE

OLIGOMERS

CH CH •Si-0 - S i CH CH3 n/ ' \

3

3

3

2

J

kJJ 5

A

3

2 b ppm

1

0

t

Figure 2. "'"H-NMR spectrum of a,a)-Hydroxybutyl polydimethylsiloxane oligomer (Mn ^1000)

terminated



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In this study our aim was to systematically synthesize a,oj^aminopropyl terminated (dimethyl-diphenyl)siloxane oligomers having low molecular weights (1000-3000 g/mole) and to subsequently analyze the composition and thermal behavior of the copolymers. Some of these oligomers have later been used i n the synthesis of various segmented urea or imide type copolymers and i n the modification of epoxy networks, which have been discussed elsewhere (5,11) . Table II provides a summary of the results on the c h a r a c t e r i s t i c s of aminopropyl terminated poly(dimethyl-diphenyl)siloxane oligomers synthesized. These reactions were conducted i n bulk at 160°C with K0H as the i n i t i a t o r . As can be seen from Table II the stoichiometric number average molecular weights sought and obtained are i n very good agreement. The l e v e l of diphenylsiloxane incorporation was determined by UV spectroscopy. There i s no absorption of dimethylsiloxane backbone i n the spectral range of 240 to 280 nm. On the other hand, phenyl groups absorb very strongly over these wavelengths (Figure 3). For quantitative analysis we have used the absorption peak at 270 nm as the reference. Chloroform was used as the solvent for the UV measurements. Standard mixtures of and D^" were used for the c a l i b r a t i o n . It i s clear from Table II that the l e v e l of diphenylsiloxane charged and incorporated shows almost a one to one correspondence. The s l i g h t difference may be due to the residual diphenyl containing c y c l i c species, which are d i f f i c u l t to remove because of their very high boiling points (17).

Table II Characteristics of Aminopropyl Terminated Poly(Dimethyldiphenyl)siloxane Oligomers

Sample No. 1 2 3 4 5 6 7 8

Mn (g/mole) Stiochiometry 0btd.( > a

1900 2000 2000 1250 2000 2000 2000 2000

1770 1780 1660 1380 1950 1990 2150 2330

% Diphenylsiloxane Charged 0 5.0 10.0 16.0 20.0 40.0 56.0 73.0

Incorp.

Tg (°C)

0 5.5 11.9 15.8 21.5 43.4 59.6 78.3

-123 -119 -115 -112 -105 - 79 - 49 - 35

(a)Titrated value Glass t r a n s i t i o n temperatures of the resulting oligomers increase with increasing levels of diphenylsiloxane present i n the system as expected. This i s e n t i r e l y consistent with the idea that dimethyl and diphenyl units are randomly distributed along the



172

REACTIVE OLIGOMERS

-J 240

I

I

I

260

I— 280

WAVELENGTH , nm ff

Figure 3. Typical UV absorption spectrum of D^ or D^"/D^ blend or a poly(dimethyl-diphenyl)siloxane oligomer (CHC1~ solution)


14.

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Reactive Difunctional Siloxane Oligomers

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oligomer backbone. This i s an expected behavior i n view of the long e q u i l i b r a t i o n times, since the simultaneous formation and scission of siloxane bonds throughout the reactions should tend to randomize the sequence d i s t r i b u t i o n . However i t i s known that D 4 " i s more reactive than D4 i n base catalyzed reactions due to the s t a b i l i z a t i o n considerations of siloxanolate anion by the phenyl substituents (12,13) . Therefore i t may be possible to obtain "block-like" distributions i n these oligomers i f the reaction conditions ( i . e . type and concentration of catalyst, reaction time and temperature) can be adjusted properly. Our future work i s proceeding i n this d i r e c t i o n . A l t e r n a t i v e l y , we have also investigated lower e q u i l i b r a t i o n temperatures where the diphenyl tetramer i s less soluble. "Blocky" sequences could also be achieved i n this s i t u a t i o n . Conclusions We have demonstrated the synthesis and characterization of reactive, a, oj-difunctional siloxane oligomers with hydroxyl or primary amine silicon-carbon linked end groups by using acid or base catalyzed e q u i l i b r a t i o n reactions. We have also shown the effect of backbone composition on the thermal behavior of resulting oligomers. I t i s clear that, the Tg of the dimethyl-diphenyl oligomers can be varied from -123°C to -35°C by increasing the l e v e l of incorporation of diphenylsiloxane units, while maintaining or changing the number average molecular weight. This i s a very effective tool for the design and the synthesis of a wide variety of siloxane oligomers suitable for s p e c i f i c needs. In addition we are also investigating the synthesis and characterization of reactive, difunctional ( t r i f l u o r o p r o p y l , methyl)siloxane containing oligomers. Also very recently, we have been able to fractionate various functionally terminated siloxane oligomers into very narrow fractions by using the s u p e r c r i t i c a l f l u i d extraction techniques (20). This i s a very important step i n the production of a, ardifunctional reactive siloxane oligomers with narrow molecular weight d i s t r i b u t i o n s . Literature Cited

1. A. Noshay and J. E. McGrath, "Block Copolymers: Overview and Critical Survey", Academic Press, New York (1977). 2. J. B. Plumb and J. H. Atherton, in "Block Copolymers", Ed. D. C. Allport and W. H. Janes, Halstead Press, New York (1972), Ch. 6. 3. M. Morton, A. Rembaum and E. E. Bostick, J. Appl. Polym. Sci., 8, 2707 (1964). 4. E. E. Bostick, in "Block Copolymers", Ed. S. W. Aggarwal, Plenum Press, New York (1972) p. 237. 5. J. E. McGrath, et al., Polym. Prepr., 24(2), 35, 39, 47, 78, 80 (1983). 6. J. C. Saam, D. J. Gordon and S. Lindsey, Macromolecules, 3, 1 (1970). 7. H. A. Vaughn, Jr., J. Polym. Sci., Part B, 7, 569 (1969).



174

REACTIVE OLIGOMERS

8. M. Matzner, A. Noshay, L. M. Robeson, C. N. Merriam, R. Barlay, Jr. and J. E. McGrath, Appl. Polym. Symp., 22, 143 (1973). 9. Y. Kawakami, Y. Miki, T. Tsuda, R. A. N. Murty and Y. Yamashita, Polym. J., 14(11), 913 (1982). 10. J. S. Riffle, Ph.D. Thesis, VPI & SU, Blacksburg, VA (1981). 11. J. S. Riffle, I. Yilgor, C. Tran, G. L. Wilkes, J. E. McGrath and A. K. Banthia in "Epoxy Resins II", Ed. R. S. Bauer, ACS Symp. Ser. No: 221, Ch. 2 (1983). 12. M. C. Voronkov, V. P. Mileshkevich and Yu A. Yuzhelevskii, "The Siloxane Bond", Consultants Bureau, New York, 1978. 13. W. Noll, "Chemistry and Technology of Silicones", Academic Press, New York, 1968. 14. C. Eaborn, "Organosilicon Compounds", Butterworths Publ. Lim., London, 1960. 15. "Analysis of Silicones", Ed. A. Lee Smith, John Wiley, New York (1974), p. 135. 16. K. A. Andrianov, B. G. Zavin and G. F. Sablina, Polym. Sci. USSR, 14, 1294 (1972). 17. Z. Laita and M. Jelinek, Polym. Sci. USSR, 6, 342 (1964). 18. R. L. Merker and M. J. Scott, J. Polym. Sci., 43, 297 (1960). 19. K. A. Andrianov et al., Polym. Sci. USSR, 12, 1436 (1970). 20. I. Yilgor, J. E. McGrath and V. Krukonis, Polym. Bull., 12(6), 499, (1984). 21. K. Kojima, C. R. Gore and C. S. Marvel, J. Polym. Sci., A-l, 4(9), 2325, (1966). RECEIVED

February 19, 1985


Reactive Difunctional Siloxane Oligomers - American Chemical Society

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