CTBN rubber phase precipitation in model epoxy resins

This study investigated the precipitation of three types of end-functionali sed Liquid rubber (two CTBN and one ATBN) from two homologous series of ami ne-cured epoxy polymers with variable cross-link density. The CTBN carboxyl endgroups strongly enhanced the curing rate through the impurity catalysis mechanism, however, the amino-terminated ATBN only retarded the reaction, possibly by dilutional effects or owing to changes in the dielectric consta nt of the reacting medium. The glass transition temperature (T-g) of the ep oxy phase was depressed by CTBN rubber dissolved in the epoxy matrix and th e T-g of the CTBN rubber was also lowered. The height of the DMTA rubber pe ak was a linear function of the level of CTBN and suggested that ca. 3% of the rubber was dissolved in the cured epoxy matrix. The microstructure of t he rubber particles was studied by SEM and related to the kinetics and ther modynamics of phase separation. (C) 2000 Elsevier Science Ltd. All rights r eserved.