Rheological, mechanical, and morphological studies of Epoxy/Poly(methyl methacrylate) semi-interpenetrating polymer networks

Semi-interpenetrating polymer networks (semi-IPNs) of epoxy resin and poly(methyl methacrylate) (PMMA) were synthesized. Methyl methacrylate (MMA) was polymerized by free radical mechanism with azo-bis-isobutyronitrile in the presence of oligomeric epoxy resin (DGEBA), and hexahydrophthalic anhydride as crosslinking agent. The gelation and vitrification transitions during cure /polymerization processes have been examined using parallel-plates rheological technique. From differential scanning calorimetry and rheological techniques, it was suggested that both curing and polymerization processes occur simultaneously. However, the gelation time was longer for the semi-IPN than those observed for the cure of pure DGEBA or polymerization of MMA. The gelation time increased significantly when 5% of MMA was employed, suggesting a diluent effect of the monomer. Higher amount of MMA resulted in a decrease of gel time, probably because of the simultaneous polymerization of MMA during the curing process. Structural examination of the semi-IPNs, using scanning electron microscopy, revealed phase separation in nanoscale size for semi-IPNs containing PMMA at concentrations up to 15%.