Thermal stability and structural changes of polyacrylonitrile/N,N-dimethylacetamide solutions during heat treatment

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This study elucidated the correlation mechanism between the chemical structure evolution and rheological behavior of polyacrylonitrile (PAN)/N,N-Dimethylacetamide (DMAc) solutions during thermal heat treatment. The experimental findings elucidate a two-stage reaction mechanism governing the thermal treatment of PAN/DMAc solutions: (1) Intramolecular cyclization is initiated by –COOH groups, leading to partial C≡N triple bond cleavage and the formation of –C = NH intermediates; (2) Accelerated cyclization and intermolecular crosslinking occur, driven by the reactivity of –C = NH intermediates with adjacent nitrile groups. This cross-linking process elucidates the observed viscosity increase, color darkening, and gelation trends of the solution. Rheological analysis confirms that the transition from viscous to elastic behavior is temperature-dependent, with 120 °C identified as the critical threshold for significant chemical transformations. The formation of conjugated C = C and C = N structures accounts for chromophore generation, while the consumption of –COOH groups and the emergence of new IR and NMR peaks provide direct evidence for the proposed cyclization and crosslinking mechanisms. These findings provide a theoretical basis for improving the stability of PAN/DMAc spinning solutions.