Poly(epichlorohydrin) [poly(oxy-1-chloro-methylethylene)] (PECH) has been modified chemically by basic nucleophiles, such as phenolate, producing dehydrochlorination as side reaction. The comonomer composition of the resulting poly(oxy-1-chloromethylethylene-co-oxy-1-phenoxymethyl-ethylene-co-oxy-1-methyleneethylene) can be determined by quantitative C-13 nuclear magnetic resonance (n.m.r.) spectroscopy. Some polymeric models were synthesized in order to make accurate assignments, since most of the signals were not completely resolved. The various C-13 n.m.r. signals were assigned to comonomer sequences in the main chain, which were fitted to a Bernouillian statistical model.