Preparation Dendrimer Like Polymer by Radical Polymerization

一些α -（取代甲基）丙烯酸酯根据取代基的不同可以作为有效的加成-断裂链转移剂，这种类型的链转移可以在聚合物链端和转移剂的部分之间形成C-C键，从而使传统的双分子终止贡献最小。结果表明，乙烯基聚合在少量多功能加成-破碎链转移剂的存在下可以连接聚合物链。甲基α -（苄基硫甲基）丙烯酸甲酯(1)在甲基丙烯酸甲酯（MMA）聚合中作为有效的转移剂，降低了聚合产物的M_n，并且1的片段被定量地结合到聚合物端。在MMA聚合过程中，尽管不饱和端基仍在聚合物端，但在具有不饱和端基的聚（MMA）存在下，通过在端基上加入聚（St）自由基，得到支链共聚物或星形嵌段共聚物。当乙烯bis(α- (benzylthiomethyl)丙烯酸酯)(2)采用双官能加成断裂为MMA聚合链转移剂,两个保利(MMA)链连接通过2的一部分。值得注意的是，没有诱导凝胶化。聚St自由基的加入导致支链或星形共聚物具有更多的支链，并且未观察到交联凝胶化。在此基础上，合成了由α -（酰基氧甲基）丙烯酰和α -（苄基硫甲基）丙烯酰组成的可聚合加成-断裂链转移剂(3)，并加入到MMA的聚合中。由此产生的多边形（MMA）包含从3引入分支点的分支。进一步加入聚（St）自由基得到不形成凝胶的超支化嵌段共聚物。然而，St的过早均聚不能被抑制。

Some of alpha-(substituted methyl) acrylates function as effective addition-fragmentation chain transfer agent depending on the substituent, and this type of chain transfer could form C-C bond between the polymer chain end and the moiety form the transfer agent leading to a minimum contribution of conventional bimolecular termination. As a result, vinyl polymerization in the presence of a small amount of multifunctional addition-fragmentation chain transfer agent could link polymer chains. Methylalpha- (benzylthiomethyl) acrylate (1) functions as effective transfer agent in polymerization of methyl methacrylate (MMA) to decrease M_n of the resultant polymer, and the fragment from 1 was quantitatively bound to the polymer end. Although the unsaturated end group remained at the polymer end during the MMA polymerization, the stirene (St) polymerization in the presence of the poly-(MMA) with the unsaturated end group yielded branched or star block copolymer through addition of poly (St) radical to the end group. When ethylene bis [alpha-(benzylthiomethyl)-acrylate] (2) was employed as a bifunctional addition-fragmentation chain transfer agent for MMA polymerization, two poly (MMA) chains were connected through the moiety from 2. Noteworthy is that no gelation is induced. The addition of poly (St) radical lead to branched or star blook copolymer bearing more arms, and no gelation by crosslinking was observed. Furthermore, a polymerizable addition-fragmentation chain transfer agent (3) consisting of alpha-(acyloxymethyl) acryloyl and alpha-(benzylthiomethyl) acryloyl groups was synthesized and added to the polymerization of MMA.The resulting poly (MMA) contains the branches to which the branching points from 3 were introduced. Further addition of poly (St) radical proceeded to give hyperbranched block copolymer without gel formation. However, premature homopolymerization of St could not be suppressed.