Thermal behavior and morphology of rubber‐modified epoxies

Rubber‐modified epoxies of tetraglycidyl‐4,4′‐diaminodiphenyl methane and a carboxylterminated copolymer of butadiene–acrylonitrile (CTBN) have been investigated by differential scanning calorimetry, scanning electron microscopy, and micrograph image analysis. Bisphenol‐A (BPA) was used to produce chain‐extended resins by reaction with the epoxy‐terminated rubber. Diaminodiphenyl sulfone was used as a hardener. Partially cured resins were prepared with different amounts of added CTBN and cured in an oven for different cure times at 448 K. From the measured heat of reaction of the samples, a fast curing reaction was observed when BPA was present in the resin formulation. In the study of the morphology, the average size of the domains was seen to increase with the CTBN content. These CTBN‐rich domains appear to include substantial amounts of epoxy material, as indicated by the measured glass transition temperature of the CTBN‐rich phase. The size of domains was observed to range mostly from 0.1 to 5 μm in diameter and to show a slightly bimodal distribution, with modes around 1 μm and 3–4 μm when 15 and 20 phr CTBN was added. © 1993 John Wiley & Sons, Inc.