EFFECTS OF LIQUID-CRYSTALLINE STRUCTURE FORMATION ON THE CURING KINETICS OF AN EPOXY-RESIN

The curing kinetics of a system containing 4,4'-diglycidyloxy-alpha-me thylstilbene (DOMS) and different functionality amines, N-ethylaniline (NEA), aniline, benzenesulfonamide (BSA), and sulfanilamide (SAA), ha ve been studied by differential scanning calorimetry (DSC) under isoth ermal conditions. The phase transformations during curing of the syste ms have been monitored by a crosspolarized optical microscope equipped with a hot-stage and photo detector. It has been found that the growt h of a nematic liquid crystal structure does not cause a discrepancy f rom the autocatalytic model for the reactions between aniline and epox y. There is no liquid crystalline structure formed for the systems con taining NEA or BSA, which follow the autocatalytic kinetic models with in the temperature range of 120-150 degrees C. For the curing reaction s between DOMS and SAA, there is a big deviation from the autocatalyti c model when the liquid crystals transfer from a nematic structure to a smectic structure. Unlike the usual decrease of reaction rate result ing from diffusion in a heterogeneous reaction, the reaction rate is e nhanced. A modified kinetic model has been constructed for this reacti on system by introducing a pseudoconcentration term caused from the li quid crystalline structure formation. (C) 1997 John Wiley & Sons, Inc.