Evaluation of isomeric composition of resol‐type phenol formaldehyde matrix resins for silica–phenolic composites and its effect on cure characteristics of the resin

The isomeric composition of several samples of resol‐type phenol formaldehyde resins used for silica–phenolic composites was evaluated by 1 H‐ and 13 C‐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 1 H‐NMR measurements. The samples were cured at 160°C 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. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2517–2524, 2003