Equilibrated radical polymerization of acrylic propionic anhydride as a mono-ene counterpart of acrylic anhydride

Radical polymerization of acrylic propionic anhydride (APA) as a mono‐ene counterpart of acrylic anhydride (AA) was investigated in order to obtain supporting evidence for a previously proposed mechanism based on polymerization equilibrium for the cyclopolymerization of AA. The deviation from first‐order dependence of the rate of polymerization Rp on monomer concentration was enhanced by a decrease in monomer concentration. The Arrhenius plot of lnRp vs. 1/T was clearly curved in a highly dilute system. These results suggest increased significance of the depropagation reaction equilibrated with propagation under polymerization conditions favorable to five‐membered ring formation in cyclopolymerization of AA. Under these conditions, the disproportionation reaction of APA became important and the liberated AA was incorporated into the polymer chain through copolymerization with APA, resulting in poly(APA‐co‐AA) having five‐membered anhydride units.