聚醋酸乙烯酯和共聚物大分子引发剂引发异丁烯正离子接枝共聚合反应

以AIBN为引发剂,通过自由基聚合方法先合成一定分子量(Mn=1.9×104g mol)和分子量分布(MWD,Mw Mn<2.5)的聚醋酸乙烯酯(PVAc)和醋酸乙烯酯(VAc)与醋酸异丙烯酯(IPAc)的无规共聚物聚(PVIPA).再以PVAc或PVIPA作为大分子引发剂,与共引发剂TiCl4配合,引发异丁烯进行正离子接枝共聚反应,并分别考察大分子引发剂用量、TiCl4浓度以及添加剂2,6二叔丁基吡啶(DtBP)或2甲基吡啶(MPY)对异丁烯聚合转化率和PVIPA或PVAc引发效率的影响,并进一步表征接枝共聚物的微观结构与组成含量.实验结果表明,PVIPA和PVAc可引发异丁烯进行正离子接枝共聚反应,前者的引发效率高于后者.加入适量DtBP或MPY时,可不同程度地提高引发效率.DtBP对减少聚合体系中微量水的引发和提高PVAc引发效率的作用更为明显,引发效率可达90%以上,加入适量添加剂MPY时,PVIPA引发效率可达60%左右.适当增加大分子引发剂用量和TiCl4浓度,也可提高PVIPA的引发效率至接近70%.在合适的实验条件下,可以得到极性主链为PVIPA与非极性支链为聚异丁烯(35.2%mol)的接枝共聚物PVIPA g PIB,该接枝共聚物的Mn为3.7×104g mol,分布指数MWD为2.52,且PIB支链平均分子量约为5.4×103g mol.

THE CATIONIC POLYMERIZATION OF ISOBUTYLENE BY GRAFTING FROM PVAc AND ITS COPOLYMER

Polyvinylacetate (PVAc) and a random copolymer of poly(vinyl acetate-co-isopropenyl acetate) (PVIPA) with number-average molecular weight (M_n) around 2×104?g/mol and molecular weight distribution(MWD,M_w/M_n<2.5) were prepared by radical polymerization using AIBN as initiator.Then,the cationic polymerizations of isobutylene were carried out by using the above PVAc or copolymer PVIPA as macroinitiator in conjunction with coinitiator TiCl_4 at -60℃ in the presence of a small amount of additives.The effects of macroinitiator,[TiCl_4],the concentration of additives,such as 2,6-di-tert-butylpyridine (DtBP) and 2-methylpyridine (MPY) on monomer conversion and initiation efficiency of PVAc or copolymer PVIPA were investigated.The copolymerization product was extracted by methanol and petroleum ether to remove unreacted macroinitiator and polyisobutylene, respectively, and thus the graft copolymer was obtained.The microstructure and composition of the graft copolymers were characterized by GPC and 1H-NMR spectrum.The initiation efficiency of PVIPA was higher than that of PVAc.The initiation efficiency of PVAc or PVIPA was increased to more than 90% by introduction of a small amount of DtBP and to around 60% by addition of an enough amount of MPY.The initiation efficiency increased to near 70% with increasing the concentration of macroinitiator and TiCl_4, respectively.The graft copolymer PVIPA-g-PIB,consisting of PVIPA backbone and PIB side chains of 35.2 mol%,with M_n of 3.7×104 g/mol and MWD of 2.52 could be obtained under proper reaction conditions.The average molecular weight of PIB side chains in PVIPA-g-PIB was further calculated to be around 5.4×103g/mol.