Acrylonitrile was copolymerized with pentachlorophenyl methacrylate (PCPMA)in dimethyl formamide using azobisisobutyronitrile as initiator. The composition of the copolymers was determined by nitrogen analysis and the monomer reactivity ratios (r(1) and r(2)) were calculated. Both the homopolymer and the copolymers were characterized by a variety of spectral and thermal methods. Thermogravimetry and differential thermal analysis data showed that the comonomer (PCPMA) initiates the nitrile oligomerization reaction in the copolymer upon heating. A mechanism for the initiation of (PCPMA) units in the nitrile copolymers was also proposed. (C) 2003 Wiley Periodicals, Inc.