Synthesis of cyclolinear poly(carbosilane)-g-poly(methyl methacrylate or styrene) random copolymers

The cyclolinear polycarbosilane, (poly(1-hexyl-1,3-ditolyl-1,3-disilacyclobutane)poly(HDTDSCB)), which has tolyl groups attached to the main chain Si atoms, was prepared by ADMET polymerization with the second-generation Grubbs catalyst, and 10%, 5%, and 2% of the tolyl groups were brominated by reactions with N-bromosuccinimide. A series of well-controlled poly(methyl methacrylate) (PMMA) anions of 2.5K, 5K, and 10K molecular weight were introduced via the "grafting onto" strategy at low temperature to the randomly 10%, 5%, and 2% brominated poly(HDTDSCB), respectively, without any lithiation or ring opening of the disilacyclobutane in the main chain. Because of side reactions initiated by the PS anion under similar conditions, a "grafting from" strategy by ATRP was employed to yield the corresponding poly(HDTDSCB)-g-PS random copolymers. The product poly(HDTDSCB)-g-(PMMA or PS) random copolymers were purified by using total adsorption-desorption interaction chromatography, which involves selective adsorption of the polycarbosilane on a C18 HPLC column from a CH2Cl2/CH3CN (50/50) eluent, while the excess PMMA or PS homopolymer eluted. This method was also successfully applied to the separation of larger quantities of the copolymers by using multiple injections onto the C18 column.