Linear and Hyperbranched Polycarbosilanes with Si-CH2-Si Bridging Groups: A Synthetic Platform for the Construction of Novel Functional Polymeric Materials

Work carried in the authors’ laboratory on Si– CH2–Si bridged polycarbosilanes is reviewed. In pursuit of high-yield polymeric precursors to silicon carbide, convenient synthetic routes to both linear and hyperbranched polycarbosilanes having a ‘[SiH2CH2]n’ compositional formula have been developed. The linear [SiH2CH2]n polymer was prepared by ring-opening polymerization of a substituted disilacyclobutane, and was studied both as an analogue of polyethylene and as a high-yield precursor to SiC. Elaboration of the methods employed to prepare this polymer has yielded a wide range of new poly(silylenemethylene)s (PSMs) of the type [SiRR'CH2]n, where R and R' can be a wide range of different groups, including a series of symmetrically disubstituted polymers with R = R' = F, alkyl and alkoxy which form crystalline solid phases and various amorphous, atactic polymers having different R and R' groups. By using (Si)–Cl replacement reactions analogous to those developed previously for polydichlorophosphazene, as well as hydrosilation reactions similar to those used for [Si(H)(Me)O]n, a series of side-chain polymers having various groups attached to Si through Si–C or Si–O bonded linkages were obtained. Similar polymer modification reactions have recently been developed for the branched oligomer/polymer analogue of these linear polycarbosilanes, leading to hyperbranched species with functional substituents, including a di(ethyleneoxy) methyl ether-terminated derivative which readily dissolves lithium salts. The results of studies of these novel ‘inorganic/organic’ hybrid polycarbosilanes are described and their properties are compared with those of related carbon-backbone and siloxane polymers. # 1998 John Wiley & Sons, Ltd.