Cyclopolymerization. I. Structure of polyacrylic anhydride

Abstract

AbstractThe structure of the cyclopolymers of acrylic anhydride has been examined by infrared spectrometry (cyclized units) and by chemical analysis (bromometry for vinyl unsaturation). The infrared analysis was based on the study of the two carbonyl absorption bands at about 1750 and 1810 cm.−1; two types of cyclized hexaatomic anhydrides, different in their stereochemical structure, have been shown to be present. By comparison with the meso and racemic varieties of α,α′‐dimethyl glutaric anhydride, the syndiotactic structure (racemic) has been assigned to the polyanhydride obtained at 35°C. in cyclohexanone. By heating, or in the presence of traces of acid this variety isomerizes into the isotactic form (meso). Pentaatomic cyclized units are formed only by polymerization at high temperatures, e.g., 115°C. (bands at 1780 and 1860 cm.−1). On the other hand, residual unsaturation has always been found on the basis of the vinyl absorption band at 1625 cm.−1; its intensity increases with an increase of monomer concentration during polymerization. The chemical analysis of the cyclopolymers by bromometry makes it possible to evaluate quantitatively the ratio ke/kp of the rate constant of vinyl propagation to that of cyclization; at 35°C. this ratio is equal to 0.17. By analysis of the polymers obtained at 25, 45, and 70°C. it has been demonstrated that the cyclization reaction is enhanced by an increase of temperature; the difference between the activation energies of propagation and cyclization is equal to 2.4 kcal.