Effect of molecular weight and molecular weight distribution on cure reaction of novolac with hexamethylenetetramine and properties of related composites

The molecular weight Mw and molecular weight distribution MWD of phenolic novolacs play an important role in their production, processing and applications, yet their exact influences on the cure and properties are still less understood scientifically. Here we select two representative novolacs: PF-8062 with lower Mw and narrower MWD and PF-0193 with higher Mw and much broader MWD, and investigate their cure reaction with hexamethylenetetramine (HMTA) and the cured products with DSC and TG, respectively. PF-8062 exhibits the higher reactivity and reaction exotherm. The model-free kinetic analysis with the Vyazovkin methods shows the nonisothermal cure of PF-0193/HMTA has the higher activation energy, and moreover yields the reasonable prediction of the isothermal cure. Then the TG analysis reveals PF-0193 improves the char yield during the pyrolysis. Furthermore, the phenolic molding composites are prepared and the influences of Mw and MWD of the novolacs are highlighted from the rheological and mechanical analysis.