ANIONIC BLOCK COPOLYMERIZATION OF CYCLOTETRASILOXANES INITIATED BY P-BIS(DIMETHYLLITHIIOXYSILYL)BENZENE

The triblock copolymers of poly (diphenyl-b-dimethyl-b-diphenyl)siloxa ne (PMP) and enyl-b-dimethyl-co-methylvinyl-b-diphenyl)siloxane (PMVP) have been synthesized by the dianionic polymerization procedure. The polymerization of the cyclotetrasiloxane monomers initiated by lithium -based initiator has been carried out so as to avoid equilibration rea ctions. The new initiator, p-bis(dimethyllithiioxysilyl)benzene, was u sed. Dimethyl formamide (DMF) was used as a promotor. The effects of i nitiator concentration, polymerization temperature, and polymerization time on the reaction were investigated. The block copolymers have bee n determined by H-1-NMR, infrared, ultraviolet, and differential scann ing calorimetry. Progressive precipitation separation has been used to study the molecular weight distribution, and the integral distributio n curves of the molecular weight have been given. (C) 1996 John Wiley & Sons, Inc.