A high resolution NMR investigation into the microstructure of HEMA and EEMA copolymers

13C NMR spectra (125 MHz) of 2-hydroxyethyl methacrylate (HEMA) and 2-ethoxyethyl methacrylate (EEMA) copolymers, prepared by bulk free radical copolymerisation, were analysed in terms of the comonomer composition and relative stereochemical configuration. The monomer reactivity ratios were evaluated using a nonlinear least squares analysis, considering both the terminal and penultimate models. Although both models adequately describe the experimentally determined copolymer compositions at a 99.5% confidence level or better, the statistical F-test showed that there is no significant improvement in the fit of the data for the penultimate model over that for the terminal model. The best estimates for the terminal model reactivity ratios are rH = 1.202 and rE = 0.724. The copolymers were found to be mainly syndiotactic. Using the Bernoullian distribution of stereoregularity, the coisotacticity parameters ΘHH = 0.25, ΘEE = 0.23 and Θ* = ΘHE = ΘEH = 0.21 were determined. Predictions for stereochemical and comonomer distributions in a copolymer prepared to high conversions are presented