Effects of itaconic acid and ammonium itaconic acid on cyclization and thermal stabilization of narrow polydispersity polyacrylonitrile terpolymers synthesized in continuous flow

Abstract

In this work, polyacrylonitrile (PAN) homopolymer, poly(acrylonitrile-methyl acrylate)[P(AN-MA)], poly(acrylonitrile-methyl acrylate-itaconic acid)[P(AN-MA-IA)] and poly(acrylonitrile-methyl acrylate-ammonium itaconic acid)[P(AN-MA-AIA)] with narrow polydispersity were successfully produced in continuous flow. The compositions, molecular weights, molecular weight distributions and crystalline structures of these PAN polymers were measured and the influence of IA and AIA on cyclization reactions, structural transformation and thermal stability during the stabilization process was also explored. The incorporation of IA and AIA into polymer chains reduces the initial temperatures of cyclization reactions, broadens the exothermic peaks, eases the concentrated heat through an ionic mechanism and exhibits better stabilization at lower temperatures. Furthermore, AIA effectively promotes dehydrogenation reaction. Among these four PAN polymers, P(AN-MA-AIA) terpolymer presents the best stabilization since COO⁻NH₄⁺ has the strongest nucleophilicity towards nitrile groups that are close to carbon atoms.