Branched methyl methacrylate copolymer particles prepared by RAFT dispersion polymerization

Reversible addition-fragmentation chain transfer (RAFT) dispersion copolymerization of methyl methacrylate (MMA) and tripropylene glycol diacrylate (TPGDA) was carried out in ethanol/water in the present work. S-1-Dodecyl-S'-(alpha,alpha-dimethyl-alpha aEuro(3)-aceticacid) trithiocarbonate (TTC) was used as a chain transfer agent to inhibit the occurrence of gelation. Branched poly(methyl methacrylate) (PMMA) particles with a very narrow size distribution was prepared by a two-stage method: the addition of a RAFT agent and a TPGDA agent to the system followed the nucleation stage. The particles had an average diameter within 1.9-2.7 mu m and size distribution of 1.12-1.24. Molecular weight, molecular weight distribution, compositions and structure of copolymer were investigated by GPC and 1H NMR characterization. The GPC curves showed a bimodal distribution, indicating that MMA homopolymer was synthesised during the nucleation stage. In addition, 1H-NMR proved that MMA and TPGDA branched copolymer was synthesised after the nucleation stage. TPGDA fraction in the copolymer was lower than that in the initial monomer. It was determined that the intrinsic viscosity of the copolymer decreased with conversion and the Mark-Houwink exponent alpha of copolymer was reduced from 0.643 to 0.548, which further confirmed the branched structure of the copolymer.