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Solvent Effects in Semibatch Free Radical Copolymerization of 2-Hydroxyethyl methacrylate and Styrene at High Temperatures



High temperature semibatch free radical copolymerizations of 2-hydroxyethyl methacrylate (HEMA) and styrene (ST) were carried out in xylene and DMF solution. Experimental free monomer and polymer molecular weight (MW) profiles at different temperatures and solvent concentrations are compared to those for ST polymerized with butyl methacrylate (BMA). Solvent choice, through its influence on hydrogen bonding of HEMA monomer, has a significant impact on the polymerization that is not seen for the corresponding ST/BMA reactions. The weight-average polymer MWs of ST/HEMA are unusually high (>40 kg/mol), a result of branching reactions involving dimethacrylate impurity contained in HEMA monomer. The importance of these branching reactions is also influenced by solvent choice.