The comonomer unit sequence distributions and stereoregularity of copolymers of p-methoxystyrene (p-MST) with maleic anhydride (MA), prepared in CHCl3 at 50 +/- 0.1 degrees C, have been determined over a wide range of comonomer feed mole fractions using C-13 n.m.r. spectroscopy. The results were compared with those obtained from p-MST/MA copolymers prepared in methyl ethyl ketone (MEK) at 50 degrees C that have been studied previously. The effects of the solvent on the stereoregularity and alternating tendency of these copolymers, as well as on the extent of comonomer electron donor-acceptor (EDA) complex formation in each system, have been discussed with reference to the mechanism of alternating copolymerization. An explanation for the observed trends is proposed in terms of the role of the EDA complex in alternating copolymerization.