Development and optimization of fast quantitative C-13 NMR characterization methods of novolac resins

Abstract

An improved C-13 NMR quantification technique of random and high-ortho novolacs in THF-CDCl3 solutions is reported. Full quantitative spectra of phenol formaldehyde resins with high signal-to-noise ratios are obtained by using chromium acetylacetonate under optimized spectral conditions within a few hours of spectrometer time. Attached proton test (APT) spectra were acquired to enable proper peak assignments in the region with significant overlap. For several novolacs, prepared under different catalytic conditions, the degree of polymerization, degree of branching, number average molecular weight, isomeric distribution, and number of unreacted ortho and para phenol ring positions could accurately be determined. The improved quantification method and the use of the aromatic instead of the aliphatic region permitted to measure for the first time small differences in network parameters for comparable novolac samples.