The radical copolymerization of electron-deficient maleic anhydride (MA) and electron-rich norbornene (NB) derivatives with 2,2'-azobis(isobutyronitrile) (AIBN) in di-oxane-d(8) has been monitored in situ by H-1 NMR spectroscopy with free induction decays recorded every 30 min at 60, 70, or 84 degrees C. The ratios of the monomer pairs were varied in some cases. The NE derivatives employed in this study included bicyclo[2.2.1]hept-2-ene (NB), t-butyl 5-norbornene-2-carboxylate, methyl 5-norbornene-2-methyl-2-carboxylate, and ethyl tetracyclo[4.4.0.1(2.5).1(7.10)]dodec-3-ene-8-carboxylate. Decomposition of AIBN, consumption of the monomers, feed ratios, endo/exo ratios, copolymer compositions, and copolymer yields were studied as a function of polymerization time. Furthermore, a homopolymerizable third monomer (t-butyl methacrylate, methacrylic acid, t-butyl acrylate, or acrylic acid) was added to the NB/MA 1/1 system, revealing that the methacrylic monomer polymerizes rapidly in the early stage and that the ratio of MA to NE in the terpolymer strongly deviates from 1/1. In contrast, however, the acrylic monomers are more uniformly incorporated into the polymer. Nevertheless, these studies indicate that MA and NE do not always behave as a pair in radical polymerization and disproves the commonly believed charge-transfer mechanism. Electron-deficient fumaronitrile was also included in the kinetics study. To further understand the copolymerization mechanism, MA and NE were competitively reacted with a cyclohexyl radical generated by the treatment of cyclo-hexylmercuric chloride with sodium borohydride (mercury method). A gas chromatographic analysis of the reaction mixtures has revealed that a cyclohexyl radical reacts with MA almost exclusively in competition and that the cyclohexyl adduct of MA essentially accounts for all the products in a mass balance experiment, eliminating a possibility of the formation of an adduct involving the MA-NE charge-transfer complex. Thus, the participation of a charge-transfer complex in the copolymerization of MA and NE cannot be important.