Epoxy-diamine thermoset/thermoplastic blends. 1. Rates of reactions beforeand after phase separation

Rates of epoxy-amine reactions in thermoset/thermoplastic blends with diffe rent thermoplastic concentrations were studied. The selected thermoset syst em was bisphenol A diglycidyl ether cured with 4,4'-methylenebis[3-chloro-2 ,6-diethylaniline] in the presence of various concentrations of polyetherim ide (PEI) (10-64 wt %). As the initial systems are homogeneous, the rate co nstants for the epoxy-amine neat system and the rate constants of the blend s are the same, the addition of PEI in the epoxy-amine system leads only to a dilution of reactive groups during this first step. But due to the epoxy -amine reaction, a liquid-liquid phase separation occurs at a given convers ion (in the range 0.2-0.4). At the same time and for PEI concentrations equ al or higher than 30 wt %, a sudden increase of the reaction rate is observ ed from experimental results. Comparison between blends based on PEI and po lystyrene (PS) shows that after phase separation the reaction rate of the P S blend was higher than the PEI blend due to a faster phase separation proc ess for the PS blend. Estimations of the new dilution ratio of the two phas es have been made through glass transition temperature measurements. Modeli ng of the kinetics of the epoxy-amine reaction in each phase of a 48 wt % P EI blend have been made. The increase of the reaction rate at phase separat ion can be explained by the formation of an epoxy-amine-rich phase with a f aster reaction rate. Modeling permits to predict that gelation in this phas e occurs at a conversion close to 0.6.