Influence of Synthesis Method on the Properties of Carbon Fiber Precursors Based on Acrylonitrile and Acrylic Acid Copolymers

Abstract A comparative study of the thermal behavior of acrylonitrile-acrylic acid copolymers synthesized by conventional radical polymerization and reversible addition-fragmentation chain transfer polymerization to deep conversions with different modes of introducing acrylic acid into the reaction is carried out. It is shown that, at similar average compositions of conventional copolymers, the difference in their compositional heterogeneity leads to an unpredictable change in the activation energy of cyclization, the degree of stabilization, and the thermal stability of the copolymers. In contrast, for copolymers of the same average composition obtained under reversible chain transfer conditions, a change in the chain microstructure, that is, the distribution of acrylic acid units along the chain, makes it possible to control the rate of cyclization while maintaining a high thermal stability of the copolymers.