Polyurethane-based simultaneous interpenetrating polymer networks of controlled microphase morphology and high damping characteristics
A number of simultaneous interpenetrating polymer networks (IPNs) were investigated with regard to morphology and energy absorbing ability. The materials were all based on polyurethane (PUR) with the second polymer components being polystyrene (PS) or poly(ethyl methacrylate) (PEMA). Also, three-component IPNs were synthesised. This was achieved by incorporating functionalised PS latex particles into a PUR/poly(butyl methacrylate) (PBMA) IPN. The morphology of the IPNs was determined with dynamic mechanical thermal analysis (DMTA), transmission (TEM) and scanning (SEM) electron microscopy and modulated-temperature differential scanning calorimetry (M-TDSC). The mechanical properties were investigated using tensile testing and hardness measurements. The PUR/PS IPNs were found to be grossly phase separated at every composition, even when crosslinked at very high levels. However, a structural modification of the materials was conducted by introducing inter-network grafting, compatibilisers and ionic interactions. All three structure modifications proved successful in achieving a finer morphology. By conducting a stirred synthesis, a very complicated morphology with a very high and broad transition was obtained. The PUR/PEMA IPNs were semimiscible and the 70:30 composition exhibited a very broad, almost rectangular, transition as evidenced by DMTA data. Phase domains between I - 500 run were found by TEM. The degree of mixing and, thus, the location and breadth of the transition could be adjusted by varying the composition and the crosslink densities in both networks. Also, variation of the chemical nature of the PUR soft and hard segments proved successful in obtaining a broad transition range. Materials with a controlled microheterogeneous morphology which exhibited excellent energy absorbing characteristics were developed. PUR/PEMA IPNs generally exhibited better damping properties as indicated by the area under the linear loss modulus (LA) and loss factor (TA) curves. Some of these materials exhibited values for the loss factor of >- 0.3 spanning a temperature range of more than 170°C. The study of IPN s containing latex' particles revealed promising results. Further concentrating on this approach might yield damping materials with even broader energy absorbing temperature/frequency ranges.