| Abstract: | 1,1,3,3-Tetramethyl-1,3-disilacyclobutane (I) was polymerized under the following conditions with H2PtCl6·6H2O as catalyst: (a) addition of I dropwise to a large excess of catalyst at room temperature, producing (CH3)3SiCH2(CH3)2Si]2O in 90% yield; (b) polymerization at room temperature in the presence of 10% water with 23 ppm Pt, yielding 9% conversion to low molecular weight polymer after 4 weeks; (c) polymerization in an open vessel (25°C., 7 ppm Pt, M?n = 1.2 × 105), a closed vessel (100°C., 28 ppm Pt, M?n = 1.7 × 105), in a closed tube after twice freezing and evacuating (25°C., 23 ppm Pt, M?n = 2.9 × 105); (d) polymerization in an oxygen atmosphere (25°C., 17 ppm Pt, M?n = 2.7 × 105). The molecular weight distributions of the polymers with M?n = 1.2 × 105 and 1.7 × 105 was studied by gel-permeation chromatography. Ratios of M?w/M?n are 3.1 and 2.7, respectively. In both cases a long tail of high molecular weight polymer is evident. Interpretation of the molecular weight distributions is qualitatively discussed on the basis of a postulated seven-step mechanism. Water is shown to be a source of chain termination. Evidence is presented for the existance of ?SiOSi? and ?SiOH in the silmethylene polymers. Negligible cyclization occurs. Orders of thermal stability measured by DTA and TGA for polydimethylsilmethylene (A), polydimethylsiloxane (B), and polysiobutylene (C) are: in He, A > B > C; in air, in air, B > C ? A. A fractionally precipitated polydimethylsilmethylene had a weight loss of less than 5% by 600°C. by TGA analysis at 10°C./min. in He. |
