Thermal and viscoelastic properties of sequentially polymerized networks composed of benzoxazine, epoxy, and phenalkamine curing agents

By using different ratios of phenalkamine/epoxy (EP) and benzoxazine/epoxy (EB), copolymer networks have been prepared sequentially by partially Curing at low temperature followed by a final cure at high temperature. A single exothermic peak was observed in the differential scanning calorimetry (DSC) for the high-temperature curing. Dynamic mechanical thermal analysis showed a single tan delta peak, indicating no phase separation. The copolymer networks showed T-g values lower than the parent EB polymer network. Incorporation of EP in small percentage in the copolymer networks has improved the storage modulus and crosslink densities and the maximum value was observed for a sample containing 80% EB with respect to EP content. The thermal stability of the copolymer networks is better than that of the individual networks. The char yield value at 600 degrees C increased with increasing EB percentage in the networks. (c) 2006 Wiley Periodicals, Inc.