Copolymers of p-nitrobenzyl acrylate and diisopropyl fumarate with different feed ratios were synthesized under microwave and thermal heating conditions, and then characterized by IR, ¹H-, and ¹³C-NMR spectroscopy. Average molecular weights were analyzed by size exclusion chromatography (SEC). Monomer reactivity ratios were obtained from an extended Kelen–Tüdös method. Differential scanning calorimetry and thermogravimetry were used to evaluate the thermal behavior of all copolymers synthesized under microwave energy. Based on the products analyzed by SEC and gas chromatography–mass spectrometry, a possible mechanism of degradation is postulated.