Differences in curing behavior of cocured and IPN materials

This study addressed the blending and cocuring of resole and epoxy, using N aOH and 4,4'-diaminodiphenylmethane as curing agents. IR band shifts regard ing the molecular interactions were investigated with FTIR. Exothermic peak shifts during cocuring reactions were studied with dynamic DSC. Viscosity increases were measured with a Brookfield LVT viscometer at 100 degreesC. T he dynamic mechanical properties of the cocured samples were investigated u sing rheometric dynamic spectroscopy (RDS). Experimental results revealed t hat the molecular interactions between resole and epoxy resulted in good co mpatibility as shown by the single damping peak in the RDS curve and the si ngle glass transition for each cocured sample. Also apparent were accelerat ed curing rates, leading to shifts of the exothermic peaks to lower tempera ture and faster viscosity increases. Nevertheless, enhanced gel fractions a nd increased glass-transition temperatures (T-g) of the samples were genera lly observed for this cocured system. The average molecular weight between crosslinked points calculated for the cocured materials also showed much le ss than the two components. These curing behaviors were quite different fro m those of the Interpenetrating Polymer Network (IPN) materials, which usua lly indicated lowered gel fractions, decreased T-g, and higher average mole cular weight between crosslinkings than for components. (C) 2001 John Wiley & Sons, Inc.