Synthesis And Characterization Of Polarity/Nopolarity Graft-Copolyner

The polar/nanpolar graft copolymer was synthesized via the combination of free radical polymerization and cationic polymerization. Random copolymers of poly(vinyl acetate-co-isopropenyl acetate)(PVIPA) with different composition and low number-average molecular weight (Mn=9600～13400g/mol) and relatively narrow molecular weight distribution (MWD, Mw/Mn=1.53～2.03) were 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 copolymers (PVIPA) as macroinitiator in conjunction with coinitiator TiCl4. The effects of [TiCl4],[PVIPA],[IB] and the ageing temperature and time on monomer conversion, initiation efficiency of PVIPA, molecular weight and molecular weight distribution were investigated. The copolymerization product was extracted by methanol to remove unreacted macroinitiator. The experimental results show that:(1) Both PVIPA and H2O in polymerization system would complex with Lewis acid TiCl4to 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 initiation efficiency of PVIPA was dependent on [TiCl4],[PVIPA], the ageing temperature and time. The polymerization could be started under the condition of enough concentration of TiCl4and the initiation efficiency of PVIPA increased with increases in [TiCl4] and [PVIPA] or a decrease in [H2O] or at lower ageing temperature or for longer ageing time. However, the initiation from (B) increased when TiCl4was at high concentration.(2) The initiation efficiency of PVIPA increased to more than90%under the appropriate conditions. The graft copolymer PVIPA-g-PIB with Mn of163700g/mol and polydispersity of2.17could be obtained under proper reaction conditions.(3) Poly (styrene-co-isopropenyl acetate) was used as macroinitiator instead of PVIPA in the graft copolymerizaion of isobutylene. It further indicates that isopropenyl acetate units in the backbone was the initiating site.(4) A concentrated emulsion system formed if graft copolymer was dissolved in n-hexane. The tiny polymer particles with1～3μm in diameter dispersed homogeneously in the nonpolar medium.