CURING BEHAVIOR OF FULLY AND SEMIINTERPENETRATING POLYMER NETWORKS BASED ON EPOXY AND ACRYLICS

Fully interpenetrating polymer networks (IPNs) based on diglycidyl ether of bisphenol A (DGEBA) and ethylene dimethacrylate (EDMA) were prepared by using isophoronediamine and benzoyl peroxide as curing agents. Semi-IPNs based on DGEBA and 2-hydroxyethyl methacrylate (HEMA) were also prepared using the same curing agents. Intermolecular interactions were investigated by Fourier transform infra-red spectroscopy. Curing behaviours were studied by dynamic differential scanning calorimetry (d.s.c.) and a Brookfield viscometer. Experimental results revealed that H-bonding in DGEBA/EDMA and DGEBA/HEMA occurred, in shifting of carbonyl and epoxide absorptions to lower wavenumber. Results also revealed that during curing reactions the dynamic d.s.c. thermograms for the fully IPNs showed a shift of the exothermic peaks to a higher and broader temperature range, while in HEMA/DGEBA semi-IPNs, the exothermic peaks shifted to a lower temperature range. On the other hand, a retarded viscosity increase was observed for fully IPNs, and an accelerated viscosity increase was found for semi-IPNs. An effect of network interlock was proposed to interpret this retarded curing behaviour of fully IPNs, while a catalytic effect of the OH group was found to explain the accelerated curing behaviour of semi-IPNs. These findings were reasonably consistent with the lower gel fractions and lower glass transitions found for fully IPNs. The calculated average molecular weight of chain length ((M) over bar(c)) between crosslinkages also conforms to the experimental results.