A Study On Controlled Cationic Polymerization Of Isobutylene Initiated By Macroinitiator

A random copolymer of poly(styrene-co-isopropenyl acetate)(SIPA) with number-average molecular weight (Mn) of27200g/mol and relatively narrow molecular weight distribution (MWD, Mw/Mn=1.66) was prepared by free radical copolymerization of styrene with isopropenyl acetate using AIBN as initiator. The resulting copolymer was used for cationic copolymerization of isobutylene as macroinitiator in conjunction with coinitiator aluminium choride (AlCl3) or ethyl aluminum dichloride (AlEtCl2), sometimes in the absence of an external nucleophilic additive. The effects of charging sequence,[AlC13] or [AlEtCl2],[SIPA],[IB], the aging time on monomer conversion and copolymerization were investigated.Yielding graft copolymers were characterized by gel permeation chromatography (GPC) and’H-NMR. The experimental results show that:(1) Both SIPA and H2O in the polymerization system would complex with Lewis acid AlCl3or AlEtCl2to form the two different active centers, which initiated the cationic polymerization of isobutylene (IB) in competition and led to SIPA-g-PIB and homopolymer PIB, respectively.(2) The order of addition of the monomer charge, the initiator component and the Lewis acid is critical to the production.(3) The suitable charging sequence are charging the aging solvent of initiator and Lewis into the SIPA/IB/AlCl3/CH2Cl2reacting system and charging IB into the SIPA/IB/AlEtCl2/CH2Cl2reacting system at last.(4) The copolymerization product was dissolved by cyclohexane and precipitated by butanone to remove unreacted macroinitiator. Under suitable condition, graft copolymer with number-average molecular weight (Mn) of220000g/mol and relatively narrow molecular weight distribution (MWD, Mw/Mn=2.64) was obtained in the absence of AlCl3, and graft copolymer with number-average molecular weight (Mn) of214000g/mol and relatively narrow molecular weight distribution (MWD, Mw/Mn=2.68) was obtained in the absence of AlEtCl2.(5) The initiation efficiency of SIPA was around50%in the absence of AlCl3and can be increased up to70%in the absence of AlEtCl2under appropriate conditions without external nucleophilic additives.(6) 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.