Study of the structure of phenol-formaldehyde novolac resins by NMR spectroscopy and gel-permeation chromatography

Abstract

C-13-NMR spectroscopy and gel-permeation chromatography studies were carried out on different samples of typical commercial phenol-formaldehyde novolac resins. Six random novolac resins (NLO 1-6), with decreasing ratios of phenol/formaldehyde from 1:0.75 to 1:0.85, were prepared in the presence of oxalic acid at two different concentratons. A high-ortho novolac resin (NL-OO') was synthesized in the pH range 4-6 using zinc acetate (Zn(OAc)(2)), as catalyst. An improved description of the chemical structure, in terms of composition, the number of free para- and ortho-positions, the isomeric distribution, the degree of polymerization, the number average molecular weight, the degree of branching and molecular weight distribution, was obtained.