RAFT分散聚合方法制备支化聚甲基丙烯酸甲酯

SYNTHESIS OF BRANCHED POLYMETHYL METHACRYLATE VIA REVERSIBLE ADDITION-FRAGMENTATION CHAIN TRANSFER DISPERSION POLYMERIZATION

以甲基丙烯酸甲酯(MMA)与三缩丙二醇双丙烯酸酯(TPGDA)为单体,S-1-十二烷基-S′-(α,α′-二甲基-α″-乙酸)三硫代碳酸酯作为RAFT试剂防止反应体系交联,进行RAFT分散共聚合.通过在成核以后加入RAFT试剂和多官能度单体(TPGDA)的两步法分散聚合反应得到了粒径接近单分散的球形聚合物粒子,其粒径大小在1.9～2.7μm范围,粒径分布为1.12～1.24.采用凝胶色谱法(GPC)、核磁共振(1H-NMR)对所得共聚物的分子量、分子量分布(MWD)、共聚物组成、共聚物结构进行了表征.GPC结果表明所得聚合物的分子量分布曲线呈双峰分布,说明在成核期形成了线形的MMA均聚物,而在成核后由MMA与TPGDA共聚生成了支化的共聚物.1H-NMR结果显示所得共聚物具有支化的结构,共聚物中TPGDA的比例低于其在初始原料中的比例.此外,所得共聚物的特性黏度随转化率升高而降低,形状因子α从0.643降低到0.548,进一步证明了聚合物具有支化结构.

RAFT dispersion copolymerization was carried out using methyl methacrylate （MMA） and tripropylene glycol diacrylate （TPGDA） as comonomers and ethanol/water as a mixed solvent and S-l-dodecyl-S＇-（ α, α- dimethyl-α＂-acetieacid）trithiocarbonate as a chain transfer agent to inhibit the occurrence of gelation. The long nucleation period and gelation were observed in one-step, batch dispersion polymerizations. These problems can be overcomed by a two-stage method -- half of MMA, solvent and all RAFT agent and TPGDA were added to the system after the end of the nucleation stage. In this way, coagulum was avoided and the particle size was controlled. The morphology of PMMA particles was observed by optical microscope. Branched poly （methyl methacrylate）（MMA） particles with an average diameter within 1.9- 2.7 μm and size distribution of 1.12- 1.24 were prepared. Molecular weight, molecular weight distribution, compositions and structure of copolymers were investigated by GPC and ^1H-NMR characterization. The GPC curves showed a bimodal distribution, indicating that MMA homopolymer was formed during the nucleation stage and MMA and TPGDA branched copolymer was formed after the nucleation stage as proved by ^1H-NMR. TPGDA fraction in the copolymer was determined to be lower than that in the initial monomer system. In addition, the intrinsic viscosity of the copolymer decreased with conversion, and the Mark-Houwink exponent a of copolymer reduced from 0. 643 to 0. 548, which further confirmed the branched structure of the eopolymer.