Polyurethane–polyacrylate interpenetrating polymer networks. II

Two component topologically interpenetrating polymer networks of the SIN type (simultaneous interpenetrating networks) composed of a melamine-cured polyacrylate and three different polyether-based polyurethanes were prepared. The linear polymers and prepolymers were combined in solution, together with the necessary crosslinking agents and catalysts, films were cast and subsequently chain extended and crosslinked in situ. In all cases, maxima in tensile strength significantly higher than the tensile strengths of the component networks occurred at 50% polyurethane : 50% polyacrylate. This was explained by an increase in crosslink density resulting from interpenetration. One of the interpenetrating polymer networks showed only one glass transition temperature (T_g) (measured calorimetrically) intermediate in temperature to the T_g's of the components and as sharp as the component T_g's. This is indicative of phase mixing and indicates at least partial chain entanglement (interpenetration). Some enhancement of other physical properties was also noted.