LOCAL MOLECULAR-MOTION IN POLYURETHANE POLY(METHYL METHACRYLATE) INTERPENETRATING POLYMER NETWORKS

Dynamic light scattering (photon correlation (PCS) and Brillouin spectroscopy (BS)) and dielectric relaxation (DS) techniques are employed to study local segmental motion in an interpenetrating polymer network (IPN) of poly(methyl methacrylate) (PMMA) with 50 wt % polyurethane (PUR) content and the constituent pure PMMA and PUR networks over the temperature (T) range from 140 to 410 K. For the PMMA network, the dielectric loss epsilon''(omega) shows a strong secondary (beta) relaxation, whereas dynamic light scattering arises from both beta and primary (alpha) relaxation with characteristics very similar to the linear PMMA. The PUR network displays a relatively broad alpha-relaxation process in the PCS and DS experiments. The IPN exhibits two well-separated primary relaxation processes assigned to local regions of mobility distinguished by different degrees of mixing. Beta-Relaxation becomes faster in the IPN, indicating a reduced packing density. At high temperatures the fast alpha-relaxation process dominates the Brillouin spectra, leading to significant hypersonic attenuation. The hypersonic velocity shows an additional temperature kink characteristic of the upper high glass transition temperature due to the hard PMMA phase. The use of complementary techniques allows the dynamic study of the present IPN over a broad temperature and time range.