DETERMINATION OF MOLECULAR-WEIGHT DISTRIBUTIONS OF NOVOLAC RESINS BY GEL-PERMEATION CHROMATOGRAPHY

The number- and weight-average molecular weights of several statistica l and high ortho novolac resins were determined using gel permeation c hromatography (GPC). The standards used were pure compounds having bet ween 2 and 12 phenol units bridged via methylene linkages. Three serie s of compounds were studied: (i) those with methylene linkages substit uted in only the ortho positions relative to the phenolic hydroxyl gro up; (ii) those in which all para positions, together with sufficient o rtho positions, were used to synthesize the compounds; and (iii) those in which the methylene linkages were substituted at a mixture of orth o and para positions. Such compounds, having known molecular architect ure and units similar to the segments of industrial novolac resins, pr ovide for a more exact measurement of the molecular weight than do the commonly used poly(styrene) standards. Using these new standards the number average molecular weights of the resins determined by GPC were in good agreement with the average molecular weight obtained by H-1-NM R spectra of the resins, particularly for low molecular weight resins. GPC analysis of higher molecular weight resins tends to underestimate the molecular weights because of complications introduced by hydrogen bonding. (C) 1997 John Wiley & Sons, Inc.