Free-radical copolymerization of styrene and itaconic acid studied by¹H NMR kinetic experiments

The free-radical copolymerization of itaconic acid (IA) and styrène in solutions of dimethylformamide and d₆-dimethyl sulfoxide (50 wt %) has been studied by ¹H NMR kinetic experiments. Monomer conversion versus time data were used to estimate the ratio k_p · k_t^-0.5 for various comonomer mixture compositions. The ratio k_p · k_t^-0.5 varies from 5.2 ·10^-2 for pure styrene to 2.0 · 10^-2 mol^-0.5 L^-0.5 s^-0.5 for pure IA, indicating a significant decrease in the rate of polymerization. Individual monomer conversion versus time traces were used to map out the comonomer mixture-composition drift up to overall monomer conversions of 60%. Within this conversion range, a slight but significant depletion of styrène in the monomer feed can be observed. This depletion becomes more pronounced at higher levels of IA in the initial comonomer mixture. The kinetic information is supplemented by molecular weight data for IA/ styrène copolymers obtained by variation of the comonomer mixture composition. A significant decrease in molecular weight of a factor of 2 can be observed when increasing the mole fraction of IA in the initial reaction mixture from 0 to 0.5.