Structure‐property relationships of some RIM polyurethanes for potential sound damping applications

Abstract

Polyurethane elastomers are block copolymers made up of relatively short urethane hard block segments separating longer flexible polyether or polyester soft blocks. Polyurethanes often exhibit mechanical properties superior to conventional elastomers. They also frequently display considerable damping. When combined with other types of semi‐compatible or incompatible polymers in polymeric networks known as interpenetrating network polymers (IPN's), they have the potential for high damping over a broad range of temperatures and frequencies. In an effort to understand how chemical composition and physical morphology affect the damping of these materials, a series of experiments involving varying weight ratios of hard block to soft block segments, molecular weight of the soft block, different chain extenders, and catalyst were carried out. The reaction‐injection molded (RIM) urethanes were based upon poly(capro‐lactone) glycols, modified 4,4′‐diphenyl methane diisocyanate (MDI), 1,4 butane diol or trimethyl propanol, and dibutyl tin dilaurate. The dynamic Young's modulus was measured by a resonance technique for each group of samples over a range of temperatures and frequencies. The observed viscoelastic properties were correlated with thermomechanical transitions observed in differential scanning calorimetry analysis. The potential of these materials for use in IPN's in sound damping applications is discussed.