Mesophase state and shear-affected phase separation of poly(p-phenylene-benzimidazole-terephthalamide) solutions in N,N-dimethylacetamide

• Published in: Journal of polymer research 2022-08, Vol.29 (8), Article 326
• Main Authors: Ilyin, Sergey O., Kotomin, Sergey V.
• Format: Article
• Language: English
• Subjects: Characterization and Evaluation of Materials; Chemistry; Chemistry and Materials Science; Copolymers; Deformation effects; Dimethyl acetamide; Equilibrium flow; Heating rate; Industrial Chemistry/Chemical Engineering; Mesophase; Molecular chains; Molecular conformation; Nucleation; Original Paper; Phase equilibria; Phase separation; Phase transitions; Polymer Sciences; Shear stress; Solubility; Temperature; Temperature effects
• ISSN: 1022-9760; 1572-8935
• DOI: 10.1007/s10965-022-03189-x

The solubility of poly( p -phenylene-benzimidazole-terephthalamide) (PABI) and its copolymer poly( p -phenylene-benzimidazole-terephthalamide- co - p -phenylene-terephthalamide) (CPABI) in N , N -dimethylacetamide (DMA) has been studied by laser microinterferometry. The solubility of PABI and CPABI in DMA (containing 3% LiCl) is 28.4% and 4.8% respectively and seems to be independent of temperature due to the LCST for both polymers. Microheterogenic mesophase was detected in PABI solutions at a concentration of 10.7–28.4%. The effect of temperature change rate and intensity of dynamic or continuous shear on microphase separation point of PABI and CPABI solutions was determined by a minimum of stationary or complex viscosity. The higher heating rate shifts the position of phase transition towards higher temperatures due to kinetic reasons. The increase in shear stress also elevates the phase separation temperature due to the intense mixing of the system and preventing formation of nucleation centers of a new phase. Large-amplitude shear oscillations help better maintain the system in a homogeneous state compared to a steady state flow due to the smaller influence on the conformation of macromolecular chains and their entropy. When deforming solutions are heated at a low rate, the effect of the shear on the phase equilibrium increases, and the phase separation temperature can shift to lower temperatures. Possible strategies for directed use of microphase separation to obtain aramid fibers and membranes have been discussed.