Kinetic of a thermoplastic-modified epoxy-aromatic diamine formulation: modeling and influence of a trifunctional epoxy prepolymer

The influence of a trifunctional epoxy prepolymer (triglycidylparaaminophenol, TGpAP) on kinetic reactions of a diepoxy prepolymer, diglycidylether of bisphenol A, DGEBA/diamine 4,4'-methylenebis[3-chloro 2,6-diethylaniline] MCDEA system was investigated as the influence of the addition of an initially miscible thermoplastic (polyetherimide, PEI or polyethersulfone, PES). The reaction mechanism between an amine and TGpAP is very complex so a phenomenological kinetic model is used. A reactive epoxy-amine system with TGpAP shows a faster reaction rate increase with temperature than a system containing only DGEBA because cyclization and etherification reactions are favoured with temperature in the case of TGpAP. A large discrepancy between theoretical value and experimental conversions at the gel point insoluble fraction was observed and can be explained by the fact that three epoxy groups of TGpAP have quite different reactivities due to different structures and substitution effects and also by the fact that other side reactions as cyclizations tend to result in gelation conversions higher than those expected from Flory's equation. After vitrification, the glass transition temperature of systems containing TGpAP goes on, increasing significantly because of intermolecular etherification reactions. Before any phase separation. a nonreactive thermoplastic (polyetherimide) was found to have no influence on reaction rate whereas polyethersulfone with terminal reactive phenoxy groups was found to accelerate the reaction rate. Similar behaviors were observed after phase separation. (C) 2000 Elsevier Science Ltd. All rights reserved.