A series of sorbents differing substantially in the content of phenyl groups were prepared by a base-catalysed reaction of poly(glycidyl methacrylate-co-ethylene dimethacrylate) with phenol. Methods are described for quantitative determination of the degree of substitution of epoxide groups by phenol, based on ¹³C nuclear magnetic resonance and infra-red spectroscopy and on elemental analysis (C, H); the last method was found to be inappropriate, however, owing to the large error involved. Infra-red spectroscopy is the method of choice for determining the degree of substitution. By studying the local properties of the regression surface, a polynomial equation was derived for the dependence of the degree of substitution of epoxide groups by phenol on the mole ratios phenol/epoxide and sodium hydroxide/phenol. The time dependence of the extent of reaction was also studied. The maximum degree of substitution attained was 0.65.