From Polyacrylonitrile, Its Solutions, and Filaments to Carbon Fibers: I. Phase State and Rheology of Basic Polymers and Their Solutions

The phase state and rheological properties of dimethyl sulfoxide (DMSO) solutions of a series of acrylonitrile‐based copolymers (PAN), which were obtained by suspension polymerization and synthesized in supercritical CO₂, have been studied. For PAN‐DMSO (plus water) solutions, a bimodal amorphous phase equilibrium takes place at ~78°C. Comparison of the rheological behavior of homo‐ and copolymer solutions has shown that the presence of carboxylate ion(s) in the macromolecular chain leads to supramolecular structure formation. Small additions of non‐solvent (water) enhance the viscoelasticity of the solution, whereas a large amount of water results in gel formation; beyond a certain threshold of water concentration, macroscopic phase separation takes place. Addition of carbon nanotubes into the solution does not change their phase state or rheological behavior. Application of mechanical forces to concentrated solutions may cause specific phase separation without the addition of a non‐solvent.