Studies on self-promoted cure behaviors of hydroxy-containing phthalonitrile model compounds

A series of hydroxy-containing phthalonitrile model compounds (HPNM) with 1:1 molar ratio of hydroxy group to phthalonitrile unit were successfully synthesized. The molecular structures were identified by FTIR and 1H NMR spectroscopic techniques. The model compounds can be thermally polymerized by duration at 225 °C for various times, even in the absence of curing additives. The thermal properties of the cured products were characterized by thermogravimetric analysis. Char yields (800 °C) of the final cured products were in the range 50–73%. The 5% and 10% weight loss ranged from 320 to 420 °C and 360–490 °C, respectively. Differential scanning calorimetry and FTIR were used to monitor the cure reaction. The results reveal that cure behaviors of the HPNM are closely correlated to their molecular structures, although each HPNM has a 1:1 molar ratio of hydroxy group to phthalonitrile unit. Therefore, the thermal properties of the final cured products depend mainly on the molecular structures of the corresponding HPNM, where differences in HPNM acidities should be considered and may contribute to their different cure behaviors.