Synthesis and properties of elastomer-modified epoxy-methacrylate sequential interpenetrating networks

The structure and properties of copolymerized sequential-interpenetrating n etworks (SeqIPNs) synthesized from amine-cured epoxies and free-radical pol ymerized dimethacrylates were examined. Materials were synthesized with and without the incorporation of an epoxy-terminated butadiene-nitrile reactiv e elastomer. Synthesis proceeded through full thermal cure of the epoxy-ami ne network, followed by polymerization of the methacrylate network. The met hacrylate reactions were free-radically induced using thermal (peroxide-ini tiated) or photochemical [electron-beam (e-beam)] techniques. Fourier trans form infrared spectroscopy was used to monitor epoxy-amine step-growth poly merization in situ and to measure final cure conversion of methacrylates. S tructural examination of the IPNs using atomic force microscopy and scannin g electron microscopy revealed microphase separation in the neat-SeqIPN mat erials and macroscopic phase separation of rubber-rich domains for elastome r-modified networks. Dynamic mechanical analysis of the SeqIPN determined t hat the properties of the network are strongly dependent on the cure condit ions. Furthermore, the viscoelastic behavior of the e-beam-cured SeqIPN cou ld be adequately described by the Williams-Landel-Ferry and Kohrausch-Willa ms-Watts equations, presumably because of a strong coupling between the epo xy-amine and methacrylate networks. (C) 2001 John Wiley & Sons, Inc.