Preparation Dendrimer Like Polymer by Radical Polymerization

一些α-（取代甲基）丙烯酸酯根据取代基起有效的加成-断裂链转移剂的作用，并且这种类型的链转移可以在聚合物链端和形成转移剂的部分之间形成C-C键，导致常规双分子终止的贡献最小。结果表明，在乙烯基聚合中加入少量的多官能团加成-断裂链转移剂可以使聚合物链发生连接。α-（苄硫基甲基）丙烯酸甲酯（1）在甲基丙烯酸甲酯（MMA）的聚合中起着有效的转移剂作用，使聚合物的Mn降低，并使1的片段定量地结合到聚合物的末端。虽然在MMA聚合过程中不饱和端基仍保留在聚合物末端，但在具有不饱和端基的聚MMA存在下的苯乙烯（St）聚合通过将聚（St）自由基加成到端基上而产生支化或星星嵌段共聚物。当乙烯双[α-（苄硫基甲基）-丙烯酸酯]（2）用作MMA聚合的双官能加成-断裂链转移剂时，两个聚（MMA）链通过来自2的部分连接。值得注意的是，没有诱导凝胶化。聚（St）自由基的加入使共聚物具有更多的支链或星星状的嵌段结构，没有观察到交联凝胶化现象。此外，合成了由α-（酰氧基甲基）丙烯酰基和α-（苄硫基甲基）丙烯酰基组成的可聚合的加成-断裂链转移剂（3），并将其加入到MMA的聚合中。进一步加入聚（St）自由基，得到超支化嵌段共聚物，而不形成凝胶。然而，不能抑制St的过早均聚。

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.