An approach to develop high-Tg epoxy resins for halogen-free copper clad laminates

In this paper, by combining the structures of epoxy and benzoxazine, we report a method of preparing multifunctional epoxy resins without decreasing the overall number of functionality. Herein, a phosphorus-containing benzoxazine (1) with a hydroxyl linkage was designed. Based on (1), a series of advanced epoxy resins (2) with various phosphorus contents were prepared by the nucleophilic addition phenolic OH of (1) on the oxirane of CNE. In addition, the effect of reaction conditions on the preparation of (2) was monitored by EEW titration and NMR analysis. In our study, although the number of functionality of oxirane was reduced after the nucleophilic addition, the overall number of functionality of the resulting resins was not reduced because a curable benzoxazine linkage was also incorporated after the addition. In other words, the overall number of functionality was maintained after incorporating the phosphorus element. As a result, flame retardant thermosets with high Tg can be expected. After (2) curing with 4,4´-diaminediphenyl sulfone (DDS) or dicyanodiamine (DICY), the thermal properties, dimensional stability and flame retardancy of the resulting epoxy thermosets were evaluated. Based on these promising resins, manufacturing of flame-retardant copper clad laminates is in progress.