极性/非极性接枝共聚物PVIPA-g-PIB的合成研究

通过自由基共聚合方法,以AIBN为引发剂引发醋酸乙烯酯(VAc)和醋酸异丙烯酯(IPA)共聚,得到两者的无规共聚物聚(PVIPA).再以PVIPA作为大分子引发剂,以四氯化钛(TiCl4)为共引发剂,引发异丁烯进行正离子接枝共聚反应,分别考察了PVIPA/TiCl4/IB体系中TiCl4浓度、大分子引发剂浓度、陈化温度、陈化时间以及外加含氮亲核试剂2,6-二甲基吡啶(DMP)对异丁烯聚合转化率和PVIPA引发效率的影响,并采用GPC表征方法研究了聚合体系中两种引发活性中心(A)和(B)的引发竞争.实验结果表明,在没有外加亲核试剂的情况下,PVIPA与微量水均可参与与TiCl4的络合竞争,分别形成活性中心(A)和(B),并产生竞争引发异丁烯正离子聚合,生成相应的接枝共聚物PVIPA-g-PIB和均聚物PIB.TiCl4和PVIPA用量以及两者的络合作用温度与时间对异丁烯正离子接枝共聚起着重要作用.合适的TiCl4浓度与PVIPA浓度、低的微量水浓度以及在较低温度下使PVIPA与TiCl4充分络合,都有利于提高大分子引发剂PVIPA的引发效率.引发效率可以达到90%左右,并可制备出极性主链与非极性支链的接枝共聚物PVIPA-g-PIB,其GPC谱图呈现单峰分布,分子量分布(Mw/Mn)可达到2.17.此外,在聚合体系中加入适量含氮亲核试剂DMP,一定程度上可以提高PVIPA的引发效率.

SYNTHESIS OF GRAFT COPOLYMER(PVIPA-g-PIB) via CATIONIC POLYMERIZATION OF ISOBUTYLENE WITH PVIPA MACROINITIATOR/TiCl4 INITIATING SYSTEM

A random copolymer of(poly(vinyl) acetate-co-isopropenyl acetate)(PVIPA) with number-average molecular weight(M_n) of 9600 and relatively narrow molecular weight distribution(MWD,M_w/M_n=2.03)was prepared by free radical copolymerization of vinyl acetate with isopropenyl acetate using AIBN as initiator.Then,the cationic polymerizations of isobutylene were carried out by using the above copolymer PVIPA as macroinitiator in conjunction with coinitiator TiCl_4 in the absence of an external nucleophilic additive.The effects of [TiCl_4],[PVIPA],the ageing temperature and time on monomer conversion and initiation efficiency of PVIPA,molecular weight and molecular weight distribution were investigated.Both PVIPA and H_2O in the polymerization system would complex with Lewis acid TiCl_4 to form the two different active centers(A) and(B).(A) and(B) initiated the cationic polymerization of isobutylene(IB) in competition and led to PVIPA-g-PIB and homopolymer PIB,respectively.The copolymerization product was extracted by methanol to remove unreacted macroinitiator.The initiation efficiency of PVIPA was dependent on [TiCl_4],,the ageing temperature and time.The polymerization could be started under the condition of enough concentration of TiCl_4 and the initiation efficiency of PVIPA increased with increases in [TiCl_4] and or a decrease in or at lower ageing temperature or for longer ageing time.However,the initiation from(B) increased when TiCl_4 was at high concentrationc.The initiation efficiency of PVIPA increased up to around 90% under the appropriate conditions.The graft copolymer PVIPA-g-PIB with M_n of 163700 and polydispersity of 2.17 could be obtained under proper reaction conditions.Furthermore,the initiation efficiency was also increased by introduction of small amount of 2,6-dimethyl pyridine(DMP).