Copolymerization of acrylamide and a hydrophobic monomer in an aqueous micellar medium: Effect of the surfactant on the copolymer microstructure

The effects of surfactant on the radical copolymerization of acrylamide with small amounts of a hydrophobic comonomer, in an aqueous micellar medium, have been investigated. At all the surfactant and hydrophobe concentrations used here, monomers conversion-time data can be fitted by a theoretical curve calculated for the homopolymerization of acrylamide in pure water solution. Classical light scattering measurements have led to copolymer molecular weights, as a function of monomer conversion, which are in the range 1.5 × 10⁶-3 × 10⁶. The molecular weight is seen to depend on both the surfactant and the hydrophobe concentrations. The copolymer compositions, also as a function of conversion, have been determined by UV spectrophotometry. Comparison with a copolymerization performed in a homogeneous water/formamide mixture has shown clearly that the presence of micelles in the reaction medium increases the initial rate of hydrophobic monomer incorporation into the copolymers. As a result, the average hydrophobe incorporation in the copolymers was seen to decrease toward the feed composition as a function of conversion, the larger the decrease the higher the hydrophobe to surfactant ratio. Analysis of all the above data has led to the proposal of a mechanism of copolymerization in an aqueous micellar medium.