Self-associating copolymers of methacrylic acid (MAA) with poly (ethylene glycol) monomethacrylate (PEGMA) were prepared by free radical copolymerization of MAA with PEGMA using dispersion polymerization in D2O, or solution polymerization in a 50/50 ethanol–D2O mixture. These copolymers have been studied as components of reversible hydrogels1 and in medical applications.2 In order to understand the relationship between the copolymer structure and its performance, it is important to determine the sequence distribution of the copolymer. The copolymer architecture is determined by the reactivity ratios and integrated instantaneous feed compositions. The reactivity ratios were determined using the first-order Markov method3 by running a series of reactions at various initial monomer ratios and determining the monomer incorporation into the copolymer as a function of time, via 1H nuclear magnetic resonance. The reactivity ratios for dispersion copolymerizations of MAA with PEGMA in water were determined to be r1 = 1.03 and r2 = 1.02, whereas solution copolymerization in 50/50 EtOH–H2O gave reactivity ratios of r1 = 2.0 and r2 = 3.6. These results show that the reactivity ratios and copolymer architecture are influenced by the solvent system.
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Smith et al. (1998) studied this question.
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