The spontaneous copolymerization of N-phenylmaleimide (NPMI) (M-1) with ethyl alpha-phenylacrylate (EPA)(M-2) were carried out in dioxane at 85 degrees C. A high alternating tendency was observed. The monomer reactivity ratios were r(1) = 0.07 +/-0.01 and r(2) = 0.09 +/- 0.02. The maximum copolymerization rate and molecular weight occurs at 70-80 mol% (M-1) in feed ratio. The spontaneous alternating copolymerization is considered to be carried out via a contact-type charge transfer complex (CTC) formed between the monomers. Thermogravimetric analyses (TGA) indicate the resulting copolymers have high thermal stability.