Effects of Molecular Weight on Thermal Properties and Rheological Behavior of Narrow Polydispersity Polyacrylonitrile Terpolymers Synthesized in Continuous Flow

This study successfully synthesized narrow‐distribution poly(acrylonitrile‐methacrylic acid‐itaconic acid) (P[AN‐IA‐MA]) terpolymers with weight‐average molecular weights ranging from 63.6 to 338.9 kg/mol using a microchannel reactor. The effects of polymerization temperature and residence time on molecular weight and composition were analyzed. The influence of molecular weight on the pre‐oxidation behavior of P(AN‐IA‐MA) was investigated, and kinetic parameters for the cyclization reaction were calculated. Steady‐state rheological tests were conducted to examine the effects of solid content, molecular weight, and molecular weight distribution on the viscous flow behavior of P(AN‐IA‐MA)/DMSO spinning solutions. Gelation behavior was studied based on dynamic rheological measurements. The results indicate that high‐molecular‐weight P(AN‐IA‐MA) copolymers exhibit inferior pre‐oxidation performance, with concentrated cyclization exotherms leading to lower stabilization degrees. Spinning solutions of high‐molecular‐weight copolymers show a stronger tendency toward gelation due to more intense chain entanglement networks. Low‐molecular‐weight, narrow‐distribution P(AN‐IA‐MA) demonstrates better spinnability.