The polymerization of N-phenylmaleimide was carried out with the binary rare-earth coordination catalyst lanthanum phosphonate [La(P-507)]-trisobutyl aluminum [AI(i-BU)(3)] in toluene at 60 degrees C. The dependence of the polymerization on the polymerization time, the molar ratio of AI(i-BU)(3) to La(P-507), and the concentration of the catalyst were studied. The structures of the resultant polymer were characterized with H-1-NMR, C-13-NMR, and Fourier transform infrared spectrophotometry, and the thermal properties of the polymer were measured with thermogravimetric analysis. (c) 2005 Wiley Periodicals, Inc.