以双硫酯为链转移剂的活性自由基聚合

LIVING FREE-RADICAL POLYMERIZATION IN THE PRESENCE OF DITHIOESTERS

合成并研究了两种双硫酯链转移剂的纯化方法 ,进行了多种单体以双硫酯为链转移剂的活性自由基聚合及嵌段共聚 .发现以PhC(S)SC(CH3) 2 Ph为链转移剂的效果比PhC(S)SCH(CH3)Ph好 ,聚合产物的多分散性系数较小 .引发剂与链转移剂的摩尔数比为 1∶3 5～ 1∶4 2时 ,得到多分散性系数小 ,实测分子量与理论分子量相近的聚合产物 .聚合物的分子量随时间和转化率的增加而增加 ,加入第二单体形成嵌段共聚物 ,具有活性聚合特征 .聚甲基丙烯酸酯大分子引发剂引发丙烯酸酯单体聚合时 ,聚合速度最快 .

A series of monomers (methacryle, acrylate and styrene) were polymerized by controlled/living radical polymerization in bulk using Reversible Addition-Fragmentation chain transfer (RAFT process). A detail purification process of chain transfer agent (CTA) dithioesters (2-phenylprop-2-yl dithiobenzoate and 1-phenylethyl dithiobenzoate) was described. Results of styrene (St), methyl methacrylate (MMA), ethyl methacrylate (EMA), butyl methacrylate (BMA), octyl methacrylate (OMA), methyl acrylate (MA), ethyl acrylate (EA) polymerization using the AIBN/CTA (mole ratio 1:4) initiating system at 70 similar to 100 degreesC confirmed the living polymerization characteristics. Diblock copolymers (PMMA-PEMA, PEMA-PMMA, PBMA-PMA, PBMA-PEA, PSt-PBA) with well defined structures as well as controlled and narrow molar mass distribution were obtained from; the lower-mass macroinitiator. The living character of the RAFT process is indicated by the narrow polydispersity product (1.1 similar to 1.3), a linear molecular weight-conversion profile,the predictability of the molecular weight from the ratio of monomer consumed to transfer agent and the ability to produce block copolymer by further monomer addition. In each reaction step, the effects of conversion and reaction time on the molar mass characteristics of the prepared block copolymers were investigated. The SEC curves shift toward lower elution volumes as the reaction time increases. While the polydispersity remained low and there was no detectable amount of unreacted starting macroinitiator block as analyzed by GPC. When high molecular weight starting macroinitiator ( M-n > 30000) was used, there was a substantial low molecular weight shoulder observed.