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Bisphenol‐A‐based benzoxazine was copolymerized with epoxy and chain‐extended epoxies in order to study the effect of molecular weight on cured resin properties. Cure behaviour of the copolymers was studied using differential scanning calorimetry, which indicated a single exothermic curing peak at 248 °C. Dynamic mechanical thermal analysis was used to study the viscoelastic properties of the cured resins. A decrease in tan δ peak position and an increase in storage modulus and tan δ peak height were observed due to chain extension. Higher char yield was observed for the copolymer chain extended with tetrabromobisphenol‐A. Copyright © 2005 Society of Chemical Industry

Phenalkamine, the Mannich reaction products from cardanol, formaldehyde, and polyamines were prepared using ethylene diamine, diethylene triamine and triethlene tetraamine. These products were characterized by high-pressure liquid chromatography (HPLC), infrared spectroscopy, and nuclear magnetic resonance spectroscopy (1H NMR). Clearly resolved peaks due to presence of triene, diene, monoene, and saturated side chain containing species of cardanol were observed in HPLC. The presence of characteristic methylene linkages of Mannich bases at d 3.5-4.0 ppm was observed by 1H NMR. These curing agents were reacted with diglycidyl ether of bisphenol-A at room temperature and the curing times were optimized. The cured resins showed good adhesion with different metal surfaces particularly higher values were observed with copper due to its high surface energy. The viscoelastic properties of the cured samples were determined by dynamic mechanical thermal analysis. The storage modulus (E 0 ) was found to be in the order of 10 9 Pa and tan d values are around 908C. A reduction in storage modulus (E 0 ) and an increase in tan d values on postcuring were observed. Thermogravimetry analysis showed two-stage degradation above 2508C for the cured samples.

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 ␦ 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°C increased with increasing EB percentage in the networks.

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