Polyvinylacetate(PVAc)and a random copolymer of poly(vinyl acetate-co-isopmpenyl acetate) (PVIPA)with number-average molecular weight(Mn)around 2×104 g／mol and molecular weight distribution (MWD

Mw／Mn4 at-60℃ in the presence of a small amount of additives．The effects of macroinitiator

[TiCl4]

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 and1H—NMR spectrum．The initiation efficiencv of PVIPA was higher than that of PVAc．The initiation efficiency of PVAc or PVIPA was increased t0 more than 90％ by introduction of a smail 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 TiCl4

respectively．The graft copolymer PVIPA—g—PIB

consisting of PVIPA backbone and PIB side chains of 35．2 mol％．with Mnof 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．