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Abstract
The influence of introducing acrylic acid (AA) into the reaction mixture with acrylonitrile at the synthesis of copolymers by free-radical polymerization (FRP) and radical polymerization with reversible addition–fragmentation chain transfer (RAFT) on the rheological properties of their solutions in dimethyl sulfoxide, as well as on the capability to spin fibers by the mechanotropic method, is analyzed. The influence of AA dosing conditions on the rheological properties of the solutions in the concentration range above the crossover point was not revealed. In the case of RAFT synthesis, the rheological properties differ distinctively in the high concentration region that is expressed by unusual viscoelastic characteristics. Dilute solution viscometry revealed the influence of the comonomer loading order on the interaction intensity of the copolymer macromolecules with a solvent, which is more pronounced for samples synthesized by FRP and can be associated with the copolymers’ molecular structure. Fiber spinning from solutions of polyacrylonitrile and its copolymers (PAN) synthesized by the RAFT method was not able to achieve a high degree of orientation drawing, while for polymers with a wider molecular weight distribution synthesized by FRP, it was possible to realize large stretches, which led to high-quality fibers with strength values up to 640 MPa and elongation at a break of 20%.
Highlights
Polyacrylonitrile and its copolymers (PAN) are the most popular polymers for obtaining wool-like textile fibers, and high-strength and high-modulus carbon fibers [1]
Assuming a priori that the loading order predetermines the compositional heterogeneity of the macromolecules between themselves and along the chain (RAFT process), we demonstrated its manifestation for the second version of the synthetic procedure
The solutions of samples obtained by the reversible addition–fragmentation chain transfer (RAFT) method with equal molecular weight have a lower viscosity when compared with equi-concentrated solutions of samples prepared by free-radical polymerization (FRP), regardless of the nature of the distribution of the comonomer along the chain
Summary
Polyacrylonitrile and its copolymers (PAN) are the most popular polymers for obtaining wool-like textile fibers, and high-strength and high-modulus carbon fibers [1]. A rare exception are the following papers: [14] which presents data on the synthesis of PAN by the method of reversible addition–fragmentation chain transfer (RAFT), preparation of precursor fibers from its solutions and, further, CF; and [15], devoted to the synthesis of PAN in supercritical CO2 , with its dissolution in dimethylsulfoxide (DMSO) and the precursor fiber spinning process carried out by the wet method followed by carbonization The authors of these works emphasize the importance of a comprehensive review of the various stages of the process, stating that each of them has a significant impact on the subsequent, and on the structure and properties of the final product
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