The isomeric composition of several samples of resol-type phenol formaldehyde resins used for silica-phenolic composites was evaluated by H-1- and C-13-NMR spectroscopy and reverse-phase HPLC techniques. The variations in the isomeric compositions were attributed to inadvertent variations in the process parameters. A mathematical relation was determined for calculation of free phenol from H-1-NMR measurements. The samples were cured at 160degreesC for 8 h in an inert atmosphere of N-2. The extent of cure in the hardened samples was measured by FTIR analysis. The effect of isomeric composition on the extent of cure was studied. Free phenol and p-hydroxymethyl phenol, exhibiting a linear correlation, were found to have a pronounced effect on the extent of cure. The cure kinetics were derived by dynamic DSC measurements. Activation energy (E) for curing exhibited a near linear correlation independently with free phenol content and the extent of cure. (C) 2003 Wiley Periodicals, Inc.