Synthesis Of Polar/Nonpolar Graft Copolymers PVIPA-g-PIB

Graft copolymer is a kind of functional polymer with specific properties based on the chemical structure on the main chain and the branch. In this paper, a polar/nonpolar graft copolymer PVIPA)-g-PIB was prepared by the combination of radical polymerization and cationic polymerization. Polyvinylacetate (PVAc) and a random copolymer of poly(vinyl acetate-co-isopropenyl acetate) (PVIPA) with different number-average molecular weight (M_n) and relatively narrow 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 its copolymer PVIPA as macroinitiator in conjunction with coinitiator TiCl₄ at -60 ℃ in the presence of small amount of additives. The effects of macroinitiator, [TiCl₄], the concentration of additives, such as 2-methylpyridine (MPY) and 2,6-di-methylpyridine (DMP), ageing temperature, ageing time, IB concentration, polymerization time on monomer conversion and initiationefficiency of PVAc or its copolymer PVIPA were investigated in detail. The copolymerization product was extracted by methanol and petroleum ether to remove unreacted macroinitiator and polyisobutylene respectively and thus the graft copolymer was obtained. Monomer conversion and the initiation efficiency of macrioinitiator were determined gravimetrically. The molecular weight and molecular weight distribution of the graft copolymers were determined by GPC. The microstructure and morphology of the polymer were characterized by H-NMR spectrum and phase contrast microscope. The experimental results indicate that as follows. The macroinitiator PVIPA or PVAc was available for cationic polymerization of isobutylene (IB). The graft copolymer PVIPA-g-PIB. consisting of PVIPA backbone and PIB side chains could be obtained under proper reaction conditions. The initiation efficiency of PVIPA is higher than that of PVAc. Excess macroinitiator is disadvantageous to its initiation efficiency.The initiation efficiency of PVIPA or PVAc increased in the presence of appropriate content of MPY or DMP. DMP is more helpful for suppressing the initiation from protic impurity H2O and thus increasing the initiation efficiency of Polyvinylacetate. The initiation efficiency of macroinitiator increased to 70% with increasing the concentration of TiCl4. The initiation efficiency of macroinitiator could increase to more than 80% when initiating system was aged at -40^-70°C.