SYNTHESIS AND STRUCTURE OF A HIGHLY BRANCHED POLYCARBOSILANE DERIVED FROM (CHLOROMETHYL)TRICHLOROSILANE

A highly branched hydridopolycarbosilane has been prepared by Grignard coupling of (chloromethyl)trichlorosilane, followed by reduction with lithium aluminum hydride. Trapping studies show that the initial step in the polymerization is a nearly quantitative formation of the Grignard compound Cl3-SiCH2MgCl. This Grignard compound undergoes head-to-tail (Si-C) coupling almost exclusively, and due to its trifunctional SiCl3 ''tail'', a complicated, branched, polycarbosilane polymer results, which contains the following structural units: SiCl3CH2-, -SiCl2CH2-, > SiClCH2-, and -> SiCH2-. The chloropolycarbosilane undergoes side reactions with ether, leading to incorporation of small amounts of ethyl and ethoxy functionality. During the reduction step the ethoxy groups are eliminated, yielding a polymer with the approximate formula [SiH1.85Et0.15CH2]n, which has been characterized by H-1, C-13, and Si-29 NMR, IR, GPC, and elemental analysis. This polymer is of interest as a precursor to near-stoichiometric silicon carbide.