POLYMER-DISPERSED LIQUID-CRYSTALS BASED ON EPOXY NETWORKS .1. EFFECTSOF THE LIQUID-CRYSTAL ADDITION ON THE EPOXY-AMINE REACTION

The kinetics of the epoxy-amine (diglycidylether of bisphenol A (DGEBA ) and polypropylene oxide diamine D-400) reaction was studied with or without a liquid crystal additive (E7) using different concentrations. The neat system was found to obey the second-order kinetic model fair ly well with a reactivity ratio n, i.e. the ratio of the rate constant s for primary to secondary amines, equal to 1. The conversion at the g el point, x(gel), was found at the theoretical value 0.57 for such a s ystem (diepoxide-aliphatic diamine). In contrast, the rate of the epox y-amine reaction underwent a dramatic decrease upon addition of the li quid crystal. This retarding effect is not only due to the dilution ef fect. In addition, the gel point was always observed at a higher conve rsion than for the neat matrix (x(gel) greater than or equal to 0.60), implying that the reactivity ratio n is strongly decreased. We sugges t reasons accounting for such a retarding effect in view of the intera ctions of the liquid crystal with the epoxy-amine reaction mechanism o r intramolecular reactions. After curing in a homogeneous phase (100 d egrees C), the polymer-dispersed liquid crystal systems were cooled do wn, which induced the phase separation of the liquid crystal-rich phas e. Copyright (C) 1996 Elsevier Science Ltd.