Time-Dependent Polymerization Kinetic Study and the Properties of Hybrid Polymers with Functional Silsesquioxanes

Methacrylate-functionalized cubic silsesquioxane homopolymers [p(MA-CSSQ)] were synthesized by reversible addition-fragmentation chain transfer (RAFT)-mediated living radical polymerization in the presence of dodecyl(dimethylacetic acid)trithiocarbonate (DDTA) chain transfer agent, and their polymerization kinetics were studied. The DDTA-terminated p(MA-CSSQ) was then employed as a macro-RAFT agent in the polymerization of methylmethacrylate (MMA) for the synthesis of a brushlike p(MA-CSSQ)-b-PMMA block copolymer. The kinetics study of p(MA-CSSQ) showed that the monomer to polymer conversion, evaluated by (1)H NMR, was found to be similar to 80% with the maximum number average molecular weight (M(n)) of 24000 and 32300 Da, for the [MA-CSSQ]/[DDTA] ratios of 100 and 200, respectively, as determined by gel permeation chromatography (GPC). The broadening of molecular weight distributions in p(MA-CSSQ) homopolymer GPC traces was observed, presumably due to the presence of the radical- radical termination products. The resultant homopolymer and block copolymer exhibited excellent thermal stability as evidenced by thermogravimetric and differential scanning calorimetric analyses. The surface properties of p(MA-CSSQ) homopolymer and p(MA-CSSQ)-b-PMMA block copolymer, determined by water contact angle and atomic force microscopy (AFM) measurements, strongly indicated the surface enrichment of the hydrophobic silsesquioxane groups. The AFM images showed the microsized granular domains of p(MA-CSSQ) homopolymer, whereas the islandlike phase-separated domains were observed in p(MA-CSSQ)-b-PMMA block copolymer.