Miscibility and thermal and dynamic mechanical behaviour of semi-interpenetrating polymer networks based on polyurethane and poly(hydroxyethyl methacrylate)

The thermodynamic miscibility and thermal and dynamic mechanical behaviour of semi-interpenetrating polymer networks (semi-IPNs) of crosslinked polyurethane (PU) and linear poly(hydroxyethyl methacrylate) (PHEMA) have been investigated. The free energies of mixing of the semi-IPN components have been determined by the vapour sorption method and it was established that the parameters are positive and depend on the amount of PHEMA in the semi-IPN samples. Thermal analyses glass transition temperatures evidenced two in the semi-IPNs in accordance with the investigation of the thermodynamic miscibility of these systems. Dynamic mechanical analysis revealed a pronounced change in the viscoelastic properties of the PU-based semi-IPNs with different amounts of PHEMA in the samples. The semi-IPNs have two distinct tan delta maxima related to the relaxations of the two polymers in their glass temperature domains. The temperature position of PU relaxation maximum tan delta is invariable but its amplitude decreases in the semi-IPNs with increasing amount of PHEMA in the systems. The tan delta maximum of PHEMA is shifted to a lower temperature and its amplitude decreases with increasing amount of PU in the semi-IPNs. The segregation degree of components alpha was calculated using the viscoelastic properties of semi-IPNs. It was concluded that the studied semi-IPNs are two-phase systems with incomplete phase separation. The different levels of immiscibility lead to the different degree of phase separation in the semi-IPNs with compositions. (C) 2004 Society of Chemical Industry.