Facile synthesis of hyperbranched and star-shaped polymers by RAFT polymerization based on a polymerizable trithiocarbonate

摘要

Facile synthesis of hyperbranched and star polymers on the basis of S-(4-vinyl)benzyl S′-propyltrithiocarbonate (VBPT) was described. RAFT copolymerization of VBPT with vinyl monomers such as methyl methacrylates (MMA), styrene (St), methyl acrylate (MA), and tert-butyl acrylate (tBA) afforded hyperbranched copolymers with variable branch length and degree of branching. Hyperbranched copolymers obtained at a low feed ratio of vinyl monomers to VBPT usually possessed repeat units per branch higher than the expected values due to the presence of VBPT unit with pendant trithiocarbonate group and side reactions resulting in partial loss of CTA functionality. RAFT copolymerization at various feed ratios afforded poly(VBPT-co-MA) branched copolymers with weight-average CTA functionality up to 107 or more, which were further used to generate star PSt and PtBA with adjustable molecular weight and variable polydispersity (1.12 < PDI < 1.88). The approach based on two successive RAFT processes is general and versatile to synthesize multiarm star polymers with controllable arm length. The resultant polymers were characterized by ~1H NMR, GPC-MALLS, DSC, and TGA. The intrinsic viscosities of branched and star-shaped polymers were lower than those of their linear analogues with the same molecular weights; both Mark-Houwink-Sakurada exponent and contractor factor of branched copolymers were observed to increase with decreasing degree of branching, thus confirming a branching nature. The single glass transition temperature in DSC traces indicated branched copolymers obtained at various feed ratios had good compatibility.