Anionic and Cationic Ring-Opening Polymerization of 2,2,4,4,6,6-Hexamethyl-8,8-divinylcyclotetrasiloxane

Abstract

Ring-opening polymerization (ROP) of 2,2,4,4,6,6-hexamethyl-8,8-divinylcyclotetrasiloxane (I) initiated by both 1-tert-butyl-4,4,4-tris(dimethylamino)-2,2-bis[tris(dimethylamino)phosphoranylidenamino]-2λ5,4λ5-catenadi(phosphazene) (C22H63N13P4, P4-t-Bu superbase) and trifluoromethanesulfonic acid (CF3SO3H, triflic acid) has been studied. Both reactions lead to mixtures of linear copolymer, low molecular weight co-oligomers and monomeric cyclosiloxanes. The composition, molecular weight distribution, microstructure, and thermal properties of the copolymers have been determined. The copolymer microstructure has been determined by 29Si NMR spectroscopy. Monomeric cyclosiloxanes have been identified by GC/MS. Both copolymer microstructure and cyclosiloxanes formed depend on the particular catalyst system utilized. P4-t-Bu superbase-initiated anionic ROP of I leads to a copolymer with a random microstructure and to a series of monomeric cyclotetra-, cyclopenta-, and cyclohexasiloxanes formed by random combination of dimethylsiloxane (D) and divinylsiloxane (V) units. On the other hand, triflic acid-initiated ROP of I occurs in a chemoselective manner. This leads to a copolymer with a more ordered microstructure. In this case, I is the only monomeric cyclosiloxane found.