Process for making poly (urethane-urea)/addition polymer composite particles

摘要

A process for making poly(urethane-urea)/addition polymer composite particles which avoids the need to use a highly viscous solution of a prepolymer for the poly(urethane-urea). The process comprises dissolving diol and di-isocyanate in addition polymerisable monomers and allowing them to co-react but for only long enough to form a precursor for the prepolymer which is of a lower molecular weight than the prepolymer so that the precursor forms a solution of much lower viscosity. This lower viscosity solution is then dispersed in water to give droplets in which the co-reaction continues and completes the formation of the prepolymer whilst water diffuses into the droplets and causes chain extension to create the poly(urethane-urea) particles. The addition polymerisable monomers in the dispersed droplets spontaneously diffuse into the poly(urethane-urea) particles where they are subjected to a conventional free radical addition polymerisation process whereupon composite the poly(urethane-urea)/addition polymer particles are formed. The composite particles can be obtained as stable aqueous dispersions optionally containing less than 3 wt % organic solvent and over 40 wt % of the composite particles.