AbstractThe microstructure of poly(α‐acetoxystyrene), prepared from α‐acetoxystyrene by bulk thermal polymerization, was studied by1H and13C NMR spectroscopy. Anomalies observed in the NMR spectra could be ascribed to fragmentations with formation of benzoxy and acetoxy radicals followed by re‐initiation. The thermal degradation of the polymer, resulting in the formation of polyphenylacetylene, rules out certain types of transfer. α‐Acetoxystyrene was copolymerized with styrene or substituted styrenes and the NMR study (1H and13C) was limited to α‐acetoxystyrene. The composition of the copolymer could be ascertained by means of the resonances of the quaternary carbons of the aromatic cycle. The copolymers were characterized by viscometry, GPC, and thermal degradation. Their compositions, except that of poly(α‐acetoxystyrene‐co‐styrene) were determined b