Synthesis and characterization of poly(urethane-g-acrylic acid)s

The free-radical copolymerization of a completely hard-block unsaturated polyurethane, based on methylene bis(4-phenylisocyanate), erythrol and butane-1,4-diol, with acrylic acid in the presence of 2,2′-azobisisobutyronitrile at 60°C under various reaction conditions is described. Grafting of poly(acrylic acid) onto the unsaturated polyurethane with pendant alkene groups was shown to be successful. Some of the characteristics of the ungrafted and grafted polyurethane copolymers were studied using microanalysis, gel permeation chromatography (g.p.c.), nuclear magnetic resonance, infra-red spectroscopy and differential scanning calorimetry. The resultant poly(urethane-g-acrylic acid)s, poly(U-g-AA)s, and the original unsaturated polyurethane were also studied viscometrically in a mixture of tetrahydrofuran and dimethylformamide (DMF) over the temperature range 26–56°C. Different-sized particles, formed in a solution of graft copolymer in water or DMF, were confirmed by photocorrelation scattering. These measurements indicated that predominantly two types of particle were present in both solutions, and values of the hydrodynamic radii and diffusion coefficients were obtained. The number-average molecular weights M̄n and weight-average molecular weights M̄W of the polyurethanes and poly(U-g-AA)s were determined by g.p.c. relative to polystyrene as a standard. Equilibrium water sorption measurements of the ungrafted polyurethanes were also carried out at room temperature.