Heterogeneity of glass transition dynamics in polyurethane-poly(2-hydroxyethyl methacrylate) semi-interpenetrating polymer networks

The peculiarities of segmental dynamics over the temperature range of -140 to 180 degrees C were studied in polyurethane-poly(2-hydroxyethyl methacrylate) semi-interpenetrating polymer networks (PU-PHEMA semi-IPNs) with two-phase, nanoheterogeneous structure. The networks were synthesized by the sequential method when the PU network was obtained from poly(oxypropylene glycol) (PPG) and adduct of trimethylolpropane (TMP) and toluylene diisocyanate (TDI), and then swollen with 2-hydroxyethyl methacrylate monomer with its subsequent photopolymerization. PHEMA content in the semi-IPNs varied from 10 to 57 wt %. Laser-interferometric creep rate spectroscopy (CRS), supplemented with differential scanning calorimetry (DSC), was used for discrete dynamic analysis of these IPNs. The effects of anomalous, large broadening of the PHEMA glass transition to higher temperatures in comparison with that of neat PHEMA, despite much lower T, of the PU constituent, and the pronounced heterogeneity of glass transition dynamics were found in these networks. Up to 3 or 4 overlapping creep rate peaks, characterizing different segmental dynamics modes, have been registered within both PU and PHEMA glass transitions in these semi-IPNs. On the whole, the united semi-IPN glass transition ranged virtually from -60 to 160 degrees C. As proved by IR spectra, some hybridization of the semi-IPN constituents took place, and therefore the effects observed could be properly interpreted in the framework of the notion of "constrained dynamics." The peculiar segmental dynamics in the semi-IPNs studied may help in developing advanced biomedical, damping, and membrane materials based thereon. (c) 2007 Wiley Periodicals, Inc.