Rheological Properties of Acrylonitrile Terpolymer Solutions Synthesized by Different Methods

Series of polyacrylonitrile terpolymers with molecular weights of (7–20) × 104 have been synthesized in dimethylsulfoxide using classical radical polymerization and reversible addition-fragmentation chain transfer (RAFT) polymerization. The effect of the synthesis method on the rheological behavior of dilute and concentrated solutions of the resulting copolymers has been analyzed. No differences have been found in the viscous properties and viscoelastic behavior of the concentrated solutions in the temperature range of 20–80°C. However, viscometry of the dilute solutions made it possible to detect a difference in the interaction between the solvent and macromolecules of the copolymers obtained by these methods. The copolymers differ in the values of the second virial coefficient, which indicates that the interaction of the solvent and polymer is specific to the synthesis method. This phenomenon seems to be caused by different branching of chains in the copolymer and/or its compositional heterogeneity. For dilute solutions, it was possible to construct a single generalized concentration dependence of reduced viscosity in the coordinates of the Martin equation. Transition to the region of concentrated solutions required an introduction of yet another parameter that describes the effective density of the mesh network, namely, the ratio of the current solution concentration to the crossover concentration. This approach made it possible to construct a generalized dependence of viscosity in the entire concentration range of solutions of polyacrylonitrile copolymers.