Molecular weight distribution and thermal characterization of polydimethylsilmethylene

Abstract 1,1,3,3‐Tetramethyl‐1,3‐disilacyclobutane (I) was polymerized under the following conditions with H 2 PtCl 6 ·6H 2 O as catalyst: ( a ) addition of I dropwise to a large excess of catalyst at room temperature, producing [(CH 3 ) 3 SiCH 2 (CH 3 ) 2 Si] 2 O 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, M̄ n = 1.2 × 10 5 ), a closed vessel (100°C., 28 ppm Pt, M̄ n = 1.7 × 10 5 ), in a closed tube after twice freezing and evacuating (25°C., 23 ppm Pt, M̄ n = 2.9 × 10 5 ); ( d ) polymerization in an oxygen atmosphere (25°C., 17 ppm Pt, M̄ n = 2.7 × 10 5 ). The molecular weight distributions of the polymers with M̄ n = 1.2 × 10 5 and 1.7 × 10 5 was studied by gel‐permeation chromatography. Ratios of M̄ w /M̄ 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.