MICROSTRUCTURE IN THE RING-OPENING POLYMERIZATION OF CYCLOTETRASILANES

Cyclotetrasilanes with methyl and phenyl substituents Si(4)Me(n)Ph(8-n ) (n=3,4,5,6) have been prepared by dearylation of octaphenylcyclotetr asilane and subsequent nucleophilic displacement with methylmagnesium bromide. All monomers are sufficiently strained to be polymerized to h igh molecular weight linear polysilanes. Ring Opening Polymerization, ROP, of cyclotetrasilanes proceeds with considerable stereoselectivity and regioselectivity. Silylcuprates lead to two inversions of configu ration at both the attacked Si atom and at the newly developed active center. The assignment of Si-29 NMR signals for poly(methylphenylsilyl ene) to heterotactic (-38.5 ppm), syndiotactic (-39.0 ppm) and isotact ic (-41.0 ppm) triads has been determined based on the polymerization of various mixtures of stereoisomers