Semi-interpenetrating polymer networks based on polyurethane and poly(2-hydroxyethyl methacrylate): Dielectric study of relaxation behavior

International audienceThe study of molecular dynamics by broadband dielectric spectroscopy (BDS) is presented for polyurethane (PU), poly(2-hydroxyethyl methacrylate) (PHEMA) and for semi-IPNs based on PU and PHEMA synthesized by photopolymerization. The dielectric properties were performed in wide range of frequencies and temperatures with the goal to establish the relation between the relaxations and the structure. Five relaxation phenomena were finally detected for PHEMA : gamma-, beta sw-, beta-relaxations at low temperatures and a-relaxation at 150 degrees C at high frequencies plus ionic conductivity relaxation which starts at 0 degrees C. For semi-IPNs the overlapping of gamma- and beta sw-relaxations of PHEMA (-125/-75 degrees C) then with increasing the temperature alpha-relaxation in PU (-75/0 degrees C), next ionic conductivity relaxation which starts at 0 degrees C, and finally the alpha-relaxation of PHEMA (+125/+170 degrees C) were detected. The alpha-relaxation of PHEMA in semi-IPNs shifts to lower temperatures and became broader with increasing amount of PU due to incomplete phase separation in the system and formation of interphases. The dielectric relaxation phenomena were fitted with Havriliak-Negami equation. Activation energy, tau(o) and alpha parameters were calculated. For alpha-relaxations corresponding dielectric characteristics have been determined from Vogel-Fulcher-Tammann equation. The relaxation map for investigated PU, PHEMA and semi-IPNs was built

Phase separation in the polyurethane/poly(2-hydroxyethylmethacrylate) semi-interpenetrating polymer networks synthesized by different ways

International audienceThe thermal, dynamic mechanical analysis, morphology and mechanical properties of semi-interpenetrating polymer networks based on crosslinked polyurethane (PU) and poly(2-hydroxyethyl methacrylate) (PHEMA) synthesized by photopolymerization and by thermopolymerization have been investigated. The thermal analysis has evidenced the two glass temperature transitions in the semi-ΙPNs and this is confirmed by the thermodynamic miscibility investigation of the systems. The Dynamic Mechanical Analysis spectra have shown that the phase separation is more significant in the thermopolymerized semi-ΙPNs: the tan δ peaks of constituent polymers are more distinct and the minimum between the two peaks is deeper. The calculated segregation degree values of semi-IPN's components are significantly higher for thermopolymerized semi-IPNs, thereby the process of phase separation in the thermopolymerized semi-IPNs is more developed. The structures of two series of samples investigated by SEM are completely different. The mechanical properties reflect these changes in structure of semi-IPNs with increasing amount of PHEMA and with the changing of the method of synthesis. The results suggest that the studied semi-IPNs are two-phase systems with incomplete phase separation. The semi-IPN samples with early stage of phase separation demonstrate higher mechanical characteristics