Semi‐ and fully interpenetrating polymer networks based on polyurethane–polyacrylate systems. V. An isomerically related semi‐1‐interpenetrating polymer network system

A series of polyurethane–poly(vinyl acetate) semi-1-IPNs were synthesized, and certain physical properties investigated. Electron microscopy showed all the materials to be substantially phase-separated, but evidence from dynamic mechanical analysis indicated that some mixing occurred, because the polyurethane glass transition was shifted in both the tan σ− and the E″–temperature curves. The variation of modulus with composition was found to be reasonably close to the predictions of the Davies equation. When the exponent in that relation was changed to ⅙, a good fit was obtained. Synergism with respect to tensile strength was observed for two of the semi-1-IPNs. Stress–relaxation measurements, over a fairly narrow temperature range, were made on the semi-1-IPN containing 40% by weight of the polyurethane network. A master curve was constructed. It was noted that the WLF equation was not obeyed by this semi-1-IPN at temperatures above about 50°C.