Epoxy-imide resins from N-(4 -carboxyphenyl )trimellitimide : effect of imide and aromatic content on adhesive and thermal properties

The effect of imide and aromatic content on the adhesive and thermal properties of epoxy-imide resins obtained through the reaction of epoxy resins viz., Araldite GY 250 (DGEBA; difunctional), Araldite EPN 1138 (novolac; polyfunctional) and epoxidized hydroxyl-terminated polybutadiene (EHTPB) with an imide-diacid viz., N-(4-carboxyphenyl)trimellitimide (IDA-I) was studied for different carboxyl equivalent to epoxy equivalent ratios (C/E ratios). The glass transition temperature of epoxy-imides varies from 80 to 144 °C, 120 to 184 °C and 41 to 143 °C for GY 250-IDA-I, EPN 1138-IDA-I and EHTPB-IDA-I respectively with the variation in C/E ratio from 0.5 to 2. For C/E ratio up to 1, the overall thermal stability of epoxy-imides follow the trend, EPN 1138-IDA-I > GY 250-IDA-I > EHTPB-IDA-I and above this ratio considerable improvement in overall thermal stability is observed only for EHTPB-IDA-I. The optimum C/E ratio for obtaining maximum room temperature and elevated temperature adhesive strength was found to be 1.25. For the optimum ratio, GY 250, EPN 1138 and EHTPB-based systems give adhesive strength of 29, 23 and 18 MPa respectively at room temperature and retain 78.3, 56.2 and 44.4% of the room temperature adhesive strength at 150 °C. The influence of C/E ratio or in otherwords, imide or aromatic content on the adhesive strength, thermal stability and glass transition temperature was more pronounced for aliphatic epoxy, i.e., EHTPB-based system.