Design of Graft Copolymer by Using Monomer-Initiator

自由基聚合是制备由多种聚合物链组成的嵌段或接枝共聚物的一种最有前途的方法。本研究合成了4，4 ′-偶氮双-4-氰基戊酸2-甲基丙烯酰氧基乙酯（HEMA-azo）、4，4 ′-偶氮双-4-氰基戊酸对异丙烯酯（<alph>-MeSt-azo）、1，1 ′-偶氮双-1-甲基丙烯酰氧基苯基乙烷、2，2 ′-偶氮双（甲基丙烯酰氧基甲基）丙腈和2，2 ′-偶氮双-2-甲基-N-（2-甲基丙烯酰氧基乙基）丙酰胺等单体引发剂，并与苯乙烯或甲基丙烯酸甲酯共聚制备聚合物引发剂。聚合物中引发剂单元的含量主要为0.5-5摩尔%。用1，3，5-三苯基维拉基清除法测定的聚合物-引发剂的引发速率似乎并不大于相应的低分子量引发剂，这是由于效率较低，虽然聚合物-引发剂的分解导致大自由基和低分子量片段，导致不可避免地形成对应于分支的均聚物，所有聚合物引发剂提供了包含50-70重量%接枝共聚物的混合物。由<alph>甲基丙烯酸2-羟乙酯和对羟基<alph>-甲基苯乙烯分别与偶氮氯化物反应制备的HEMA-偶氮和-MeSt-偶氮被认为是有用的单体引发剂，产生具有适当分解速率的聚合物引发剂。然而，含有<alph>-MeSt-偶氮单元的聚合物-引发剂优于含有HEMA-偶氮单元的聚合物-引发剂，因为后者倾向于形成交联产物。得到的接枝共聚物的结构控制，主链聚合物的链长，分支的nunbmer，和分支的链长，获得的自由基聚合的标准动力学的基础上。

For prepatation of block or graft copolymers consisting of varieties of polymer chains by radical polymerization, one of the most promising procedures is polymerization with a polymer-initiator. In this study, monomer-initiators, 2-methacryloyloxyethyl 4,4'-azobis-4-cyanopentanoate (HEMA-azo), p-isopropenyl 4,4'-azobis-4-cyanopentanoate (<alph>-MeSt-azo), 1,1'-azobis-1-methacryloyloxyphenyl-ethane, 2,2'-azobis(methacryloyloxymethyl)propionitrile, and 2,2'-azobis-2-methyl-N-(2-methacryloyloxyethyl)propionamide were synthesized as to prepare the polymer-initaitor by copolymerization with styrene or methyl methacrylate. The content of the initiator unit in the polymer was mainly 0.5-5 mol-%. Initiation rate of the polymer-initiator being determined by scavenging with 1,3,5-triphenylveradzyl seemed to be not greater than that of the corresponding low molecular weight initiator, owing to a lower efficiency.Although decomposition of the polymer-initiator results in a macroradical and a lower molecular weight fragment leading to unavoidable formation of the homopolymer corresponding to the branch, all the polymer-initiators afforded the mixtures involving 50-70 wt-% of the graft copolymers. HEMA-azo and <alph>-MeSt-azo which were prepared by the reactions of 2-hydroxyethyl methacrylate and p-hydroxy-<alph>-methylstyrene with the azo chloride, respectively, were noted as useful monomer-initiators yielding the polymer-initiator with appropriate decomposition rates. However, the polymer-initiator containing <alph>-MeSt-azo unit is preferable to that containing HEMA-azo unit, because the latter tends to form cross-linked product.These findings suggest that almost any combination of polymer chains is obtainable by this technique. Structual control of the resulting graft copolymer, chain length of the back bone polymer, nunbmer of the branch, and chain length of the branch, were attained on the basis of standard kinetics of radical polymerization.