Preparation of polymer with controlled molecular weight up to high conversion using methyl 2-bromomethylacrylate as a chain transfer agent in radical polymerization

Summary

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 ($\bar Mn$) of poly(MMA) was reduced by chain transfer with MBMA to ca. 3000, and polydispersity ($\bar Mw/\bar Mn$) remained at 1.55–1.71 throughout the polymerization.$\bar Mn$ and$\bar Mw/\bar Mn$ 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 ω-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$\bar Mn$ of the poly(MMA). While$\bar Mn$ of poly(St) was lowered by MBMA, increases in$\bar Mn$ and$\bar Mw/\bar Mn$ 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$\bar Mn$ and$\bar Mw/\bar Mn$.