REACTION-INDUCED PHASE-SEPARATION IN POLY(BUTYLENE TEREPHTHALATE)-EPOXY SYSTEMS .2. MORPHOLOGIES GENERATED AND RESULTING PROPERTIES

Poly(butylene terephthalate) (PET) was used as a semicrystalline modif ier of epoxy-aromatic diamine formulations in concentrations ranging f rom about 3 wt% to 8 wt%. The epoxy monomer was based on diglycidyleth er of bisphenol A (DGEBA) and the diamines were either 4,4'-methyleneb is [3-chloro 2,6-diethylaniline] (MCDEA) and 4,4'-diaminodiphenylsulfo ne (DDS). Using conversion-temperature transformation diagrams develop ed in part 1, thermal cycles were selected to generate different morph ologies. In the case of PBT-DGEBA-DDS systems, phase separation in the course of reaction led to a random dispersion of spherical particles (sizes in the range of 1 mu m), rich in PET. Small and wide angle X-ra y scattering, carried out in situ, during cure, revealed that the disp ersion of spherical particles was produced by a nucleation-growth mech anism and that crystallization took place after phase separation. A co mpletely different morphology, characterized by a distribution elf lar ge and irregular semicrystalline particles, was produced by crystalliz ation before reaction. However, both types of morphologies introduced a small increase in the critical stress intensity factor. The main tou ghening mechanism was crack bridging produced by highly drawn thermopl astic particles. On the other hand, PBT-DGEBA-MCDEA formulations were cured at temperatures high enough to avoid crystallization of PET duri ng reaction. In this case, the PET remaining dissolved in the matrix d id not introduce any toughening effect. Copyright (C) 1996 Elsevier Sc ience Ltd.