N-Methacryloyloxy phthalimide (NMph) and N-methacryloyloxy tetrachlorophthalimide (NMTClph) monomers were prepared by the reaction of methacrylic acid with N-hydroxy phthalimide and N-hydroxy tetrachlorophthalimide in the presence of dicyclohexyl carbodimide (DCCI). The prepared monomers were polymerized or copolymerized with acrylonitrile (AN). The prepared homopolymers as well as the copolymers were characterized by a variety of analytical, spectral and thermal methods. The thermal behaviour in nitrogen of the homopolymers as well as the copolymers was investigated using differential thermal analysis (DTA) and thermogravimetric (TG) techniques. NMph and NMTClph were found to initiate the nitrile oligomerization in the copolymers upon heating. A mechanism for the degradation and initiation of the methacryloyloxy units in the nitrile copolymers is proposed; this was confirmed by interpreting the fragmentation patterns of the obtained mass spectra of the two monomers, as well as the IR spectra of the copolymers after heating.