Free-radical copolymerization propagation kinetics of styrene (ST) and 2- hydroxyethyl methacrylate (HEMA) have been investigated using pulsed laser polymerization (PLP) combined with size exclusion chromatography (SEC) and proton NMR. Monomer reactivity ratios for bulk ST/HEMA copolymerization are r HEMA = 0.49 and r ST = 0.27, with no significant variation with temperature found between 50 and 120 °C. The composition-averaged copolymerization propagation rate coefficient, k p,cop, is well represented by the implicit penultimate unit effect (IPUE) model. The copolymerization kinetics of HEMA with ST is quite similar to that of glycidyl methacrylate (GMA) with ST. A computational study based on quantum chemistry supports the finding that GMA and HEMA are more reactive toward ST radicals compared to alkyl methacrylates.

Solvent effects on free-radical copolymer composition and propagation kinetics of styrene (ST) with three methacrylates, 2-hydroxyethyl methacrylate (HEMA), glycidyl methacrylate (GMA), and n-butyl methacrylate (BMA), are investigated using pulsed-laser polymerization combined with size exclusion chromatography and proton NMR. Three representative solvents, n-butanol, toluene, and DMF ( N,N -dimethylformamide), are selected based on their polarity and structure. It was found that all three solvents have an effect on ST/HEMA copolymer composition compared to bulk copolymerization, with a systematic variation in monomer reactivity ratios observed with solvent polarity. Only butanol affects ST/BMA copolymer composition, and solvent choice has no effect on composition for the ST/GMA system. Butanol increases the composition-averaged copolymerization propagation rate coefficient, k p,cop, only for the ST/BMA system, while DMF causes a uniform decrease of k p,cop for all three systems and toluene has no observable effect on k p,cop. These rate effects are linked to corresponding solvent effects on homopropagation kinetics. It is difficult to reconcile the combined copolymer composition and k p,cop data for ST/HEMA systems and for ST/BMA in butanol using the implicit penultimate model of chain-growth, suggesting that H-bonding interactions need to be explicitly considered.

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Radical copolymerizations of 2-hydroxyethyl methacrylate (HEMA) with n-butyl methacrylate (BMA) and n-butyl acrylate (BA) were carried out in xylene, DMF, and n-butanol solutions. Solvent effects on copolymerization propagation kinetics were investigated using pulsed laser polymerization (PLP) combined with size exclusion chromatography (SEC) as well as proton NMR, while starved-feed higher temperature semibatch reactions were carried out in different solutions to simulate industrial production. Solvent choice, through its influence on hydrogen bonding of HEMA monomer, has a significant impact on the copolymer composition and propagation rate coefficient and thus influences the semibatch polymerization behavior of BMA/HEMA, as previously found for the styrene/HEMA system. The presence of HEMA leads to increased polymer molecular weight, a result attributed to branching reactions involving dimethacrylate impurity. Although H-bonding (and solvent choice) influences BA/HEMA kinetics, its relative effect is negligible on semibatch operation under the conditions studied.