The copolymerization of tert-butyl methacrylate (1) was carried out with the N-alkyl methacrylamides, e.g., N-octyl methacrylamide (2), N-ethyl methacrylamide (3), N-cyclohexyl methacrylamide (4), N-benzyl methacrylamide (5), and methacrylamide (6). Thermal treatment of these copolymers leads to thermal syn elimination of isobutene and to elimination of water due to the spontaneous imidization reaction. Substituted poly(methacrylimides) were obtained having octyl (12), ethyl (13), cyclohexyl (14), benzyl (15), and hydrogen (16) as substituents. The products were obtained as foams. Thermal syn elimination of isobutene and elimination of water were investigated by thermogravimetry. The products contain units of imide, anhydride, amide, and traces of ester. By means of NMR spectroscopy, the content of imide in relation to unreacted amide was calculated. The imide content varies from 44% to 85%. The glass transition temperatures (T-g) of the imides were found to be in the region of 73-165 degreesC. The molecular weights of the copolymers and the poly(methacrylimides) were analyzed by gel permeation chromatography.