High resolution NMR investigation into the microstructure of HEMA and EEMA copolymers

C NMR spectra (125 MHz) of 2-hydroxyethly methacrylate (HEMA) and 2-ethoxyethyl methacrylate (EEMA) copolymers, prepared by bulk free radical copolymerization, 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 estimate for the terminal model reactivity ratios are r=1.202 and r=0.724. The copolymers were found to be mainly syndiotactic. Using the BBemoullian distribution of stereoregularity, the coisotacticity parameters Θ=0.25, Θ=0.23 and Θ= Θ = Θ = 0.21 were determined. The number average sequence length of the syndiotactic and isotactic blocks in all copolymers prepared were calculated to be 4.5 and 1.2 respectively