PREPARATION OF POLYMER WITH CONTROLLED MOLECULAR-WEIGHT UP TO HIGH CONVERSION USING METHYL 2-BROMOMETHYLACRYLATE AS A CHAIN TRANSFER AGENT IN RADICAL POLYMERIZATION

Radical polymerizations of methyl methacrylate (MMA) and styrene (St) in benzene up to high conversions were carried out in the presence of 2.5 and 2.0 mol% of methyl 2-bromomethylacrylate (MBMA) relative to the monomers, respectively. Number average molecular weight (M(n)BAR) of poly(MMA) was reduced by chain transfer with MBMA to ca. 3000, and polydispersity (M(w)BAR/M(n)BAR) remained at 1.55-1.71 throughout the polymerization. M(n)BAR and M(w)BAR/M(n)BAR of poly(MMA) obtained in the absence of MBMA were ca. 200000 and 1.74-2.16, respectively, depending on conversion. The 2-carbomethoxyallyl group formed by fragmentation of MBMA radical was quantitatively introduced at the omega-end of the polymer. Chain transfer which is much less affected by an increase in viscosity of the polymerization system than bimolecular termination of the polymer radical primarily limited M(n)BAR of the poly(MMA). While M(n)BAR of poly(St) was lowered by MBMA, increases in M(n)BAR and M(w)BAR/M(n)BAR with conversion were observed. Although the carbomethoxyallyl end-group was almost inactive toward poly(MMA) radical, addition of poly(St) radical to the allyl end group occurred to enhance M(n)BAR and M(w)BAR/M(n)BAR.