Chen Yu, Shen Zhong, Barriau Emilie, Kautz Holger, Frey Holger
Department of Chemistry, Tianjin University, 300072, Tianjin, People's Republic of China.
Biomacromolecules. 2006 Mar;7(3):919-26. doi: 10.1021/bm050784e.
Well-defined multiarm star block copolymers poly(glycerol)-b-poly(2-hydroxyethyl methacrylate) (PG-b-PHEMA) with an average of 56, 66, and 90 PHEMA arms, respectively, have been prepared by atom transfer radical polymerization (ATRP) of HEMA in methanol by a core-first strategy. The hyperbranched macroinitiators employed were prepared on the basis of well-defined hyperbranched polyglycerol by esterification with 2-bromoisobutyryl bromide. Polydispersites M(w)/M(n) of the new multiarm stars were in the range of 1.11-1.82. Unexpectedly, with the combination of CuCl/CuBr(2)/2,2'-bipyridyl as catalyst, the polymerization conversion can be driven to maximum values of 79%. The control of CuCl catalyst concentration is also very important to achieve high conversion and narrow polydispersity. The absolute M(n) values of the obtained multiarm star polymers were in good agreement with the calculated ones, and the highest M(n) values of the multiarm star copolymer is around 10(6) g/mol. Kinetic analysis shows that an induction period exists in the polymerization of HEMA. After this induction period, a linear dependence of ln (M/M()) on time was observed. Due to the star architecture, the viscosity of the obtained multiarm star PHEMA is much lower than that of linear PHEMA.
通过采用先核后臂策略，在甲醇中通过原子转移自由基聚合（ATRP）制备了分别平均具有56、66和90个聚甲基丙烯酸2-羟乙酯（PHEMA）臂的结构明确的多臂星形嵌段共聚物聚甘油-b-聚甲基丙烯酸2-羟乙酯（PG-b-PHEMA）。所使用的超支化大分子引发剂是基于结构明确的超支化聚甘油通过与2-溴异丁酰溴酯化制备的。新型多臂星形聚合物的多分散指数M(w)/M(n)在1.11 - 1.82范围内。出乎意料的是，以氯化亚铜/溴化铜(2)/2,2'-联吡啶作为催化剂，聚合转化率可被驱动至最大值79%。控制氯化亚铜催化剂的浓度对于实现高转化率和窄多分散性也非常重要。所获得的多臂星形聚合物的绝对M(n)值与计算值吻合良好，多臂星形共聚物的最高M(n)值约为10(6) g/mol。动力学分析表明，甲基丙烯酸2-羟乙酯（HEMA）聚合过程中存在诱导期。在这个诱导期之后，观察到ln (M/M())与时间呈线性关系。由于星形结构，所获得的多臂星形聚甲基丙烯酸2-羟乙酯（PHEMA）的粘度远低于线性聚甲基丙烯酸2-羟乙酯（PHEMA）。
