The curing reactions of ethynyl-functional benzoxazine

The model compounds 3-(3-ethynyl-phenyl)-6-methyl-3,4-dihydro-2H-benzoxazine (EPMB) and 6-methyl-3-phenyl-3,4-dihydro-2H-benzoxazine (PMB) were synthesized and the influence of ethynyl group on the thermal cure reaction of benzoxazine compound was investigated. The bond parameters of benzoxazine ring calculated at the level of B3LYP/6-31G(d) showed that the variations of benzoxazine structures due to the introduction of ethynyl were negligible. The cure reaction of EPMB and PMB was studied by DSC and kinetic parameters were determined by an autocatalytic model. The results revealed that the apparent activation energy for cure reaction of EPMB was 103.90 kJ/mol which was lower than that of PMB (124.14 kJ/mol). The kinetic parameters of cure reactions of PMB and EPMB obtained by the Kissinger and Ozawa methods agreed well with the results by the autocatalytic model. The structures of the cured EPMB were characterized by 1H NMR and solid-state 13C NMR. The results showed there are polyene structures and hydrogen bonds in the cured EPMB.