TRANSITION BROADENING AND WLF RELATIONSHIP IN POLYURETHANE POLY(METHYL METHACRYLATE) INTERPENETRATING POLYMER NETWORKS

A range of simultaneous fully interpenetrating polymer networks (IPNs) based on polyurethane (PU) and poly(methyl methacrylate) (PMMA) were prepared and evaluated using dynamic mechanical analysis. The tests were conducted at resonance frequencies over a wide temperature range. The IPNs produced broad glass transitions, with a unique tan delta peak of rectangular waveform occurring at approximately 70/30 by weight PU/PMMA composition. Tan delta broadening was explained in terms of the patterns of behaviour of the dynamic loss and real moduli during the transition. The type of tan delta broadening was not experienced in PU by crosslinking variation alone. Multiplexed dynamic mechanical runs for the time-temperature superposition were conducted at various frequencies. The Williams-Landel-Ferry (WLF) equation fitted the experimental shift factors over the wide transition regions. The resultant WLF coefficients indicated the presence of larger-than-expected free volumes in the PU-dominated IPN compositions, which, in turn, precipitated glass transitions.