Curing behaviour of fully and semi-interpenetrating polymer networks based on epoxy and acrylics

Abstract

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 c ) between crosslinkages also conforms to the experimental results.