Epoxy-imide resins from 2,2-bis[4-(4-trimellitimidophenoxy)pheny1]propane: Adhesive and thermal properties

Epoxy-imide resins were obtained by curing the epoxy resin Araldite GY 250 (DGEBA; difunctional) and Araldite(R) EPN 1138 (Novolac epoxy; polyfunctional) with the diimide-diacid, 2,2-bis[4-(4-trimellitimidophenoxy)phenyl]propane. The adhesive lap shear strength of epoxy-imide resins at room temperature and at 100 and 150degreesC was determined on a stainless-steel substrate. The effect of solvent on the adhesive strength of epoxy-imide resins was studied, and tetrahydrofuran was found to give the best results for improving the wetting behavior of epoxy resins. It is observed that with the increase in imide content the adhesive strength at room temperature as well as at elevated temperature increases when tetrahydrofuran is used as a solvent in the adhesive formulation. The room temperature adhesive strength for GY 250-based systems is in the range of 20.8-23.5 MPa and 45-58% of this strength is retained at 150degreesC. For EPN 1138-based systems, the room temperature adhesive strength is in the range of 14.3-20.3 MPa, and in fact, an increase in adhesive strength by 1-26% is observed at 150degreesC. All these systems are stable up to 370degreesC, and char residues of GY 250- and EPN 1138-based systems at 800degreesC are in the range of 27-31 and 33-41%, respectively, in nitrogen atmosphere. The overall thermal stability and retention of room temperature adhesive strength at elevated temperature are higher for EPN 1138-based systems when compared to those of GY 250-based systems, and this observation has been attributed to the higher crosslinking possible for EPN-based systems when compared to GY 250-based systems. (C) 2003 Wiley Periodicals, Inc.