Direct synthesis of controlled poly(styrene-co-acrylic acid)s of various compositions by nitroxide-mediated random copolymerization

Full Paper: Styrene and acrylic acid were copolymerized under controlled conditions, in 4-dioxane solution at 120degreesC and 2 bar, using an alkoxyamine initiator based on the N-tertbutyl-N-(1-diethylphoshono-2, 2-dimethylpropyl)nitroxide, SG1. A broad composition range from 90/10 to 10/90 was investigated. With slightly different initiator concentrations and a similar initial proportion of free SG1 (4.5 mol-% with respect to the initiator) the polmerizations exhibited very similar rates, irrespective of the proportion of acrylic acid in the comonomer mixture (80% conversion within 8 h). In all cases, the copolymers presented number average molar masses, (M) over bar (n) , that increased linearly with overall monomer conversion, and polydispersity indexes that ranged between 1.2 and 1.4. Moreover, (M) over bar (n) followed the calculated values, based on the initial concentrations of monomers and initiator. The variation in the initiator concentration allowed to target various molar masses, but some limitation appeared at low initiator concentrations owing to chain transfer to 1, 4-dioxane. From the kinetic data, the reactivity ratios were determined: r(A) = 0.27 +/- 0.07 for acrylic acid and r(S) = 0.72 +/- 0.04 for styrene. Depending on the initial comonomer composition, chains exhibited no or small composition drift, and hence a slightly pronounced gradient structure.