Cure study of addition-cure-type and condensation–addition-type phenolic resins

By the incorporation of propargyl and methylol groups on to novolac backbone, a series of addition-curable phenolic resins and condensation–addition dual-cure type phenolic resins (novolac modified by propargyl groups referred as PN, and novolac modified by propargyl and methylol groups simultaneously referred as MPN) were synthesized. The processing characteristics, thermal cure and catalytic cure behavior for both resins were investigated mainly by means of viscosity measurement and non-isothermal differential scanning calorimetry (DSC) techniques. The effect of propargyl and methylol content of PN and MPN, the molecular weight and the configuration of the parent novolac, on the processing and cure behavior was studied in details. Processing parameters and curing kinetic parameters were obtained. Both resins exhibit excellent processing properties. Thermal cure of PN resins possessed one cure mechanism and that of MPN resins possessed two cure mechanisms according to DSC analysis. The dual-cure-type mechanism made MPN resins superior to PN resins in terms of a mild and controllable cure process. Compared with thermal cure, catalytic cure of PN resins showed lower initiation temperature and cure temperature by about 60 °C. These novel resins have a bright prospect of application as matrix for thermal–structural composite materials.