PREPARATION AND THERMAL-PROPERTIES OF ASYMMETRICALLY SUBSTITUTED POLY(SILYLENEMETHYLENE)S

Poly(silylenemethylene)s of the types [SiMeRCH2](n) and [SiHRCH2](n) w ere prepared by the ring-opening polymerization (ROP) of 1,3-disilacyc lobutanes (DSCBs) containing n-alkyl substituents, such as C2H5, n-C3H 7, n-C4H9, n-C5H11, and n-C6H13, or a phenyl group on the Si. These ne w polymers include a monosilicon analog of poly(styrene), [SiHPhCH2](n ). Improved synthesis routes to the DSCB monomers were developed which proceed through Grignard ring closure reactions on alkoxy-substituted chlorocarbosilanes. All of these asymmetrically substituted polymers were obtained in high molecular weight form, except for [SiHPhCH2](n). The configurations of all of the polymers were found to be atactic. T he aryl-substituted polymers have higher glass transition temperatures (T(g)s) and thermal stability than those of the alkyl-substituted pol y(silylenemethylene)s. Unlike the polyolefins of the type [C(H)(R)CH2] (n), where T-g drops continuously from R = Me to n-Hex, the T(g)s of t he n-CnH2n+1 (n = 2-6)-substituted [SiMeRCH2](n) PSM's appear to reach a maximum (at -61 degrees C) for the R = n-Pr-substituted polymer. Mo reover, where it was possible to make direct comparisons among similar ly substituted atactic polymers, all of the poly(silylenemethylene)s w ere found to have lower T(g)s than their all-carbon analogs. (C) 1997 John Wiley & Sons, Inc.