Preparation and structure–property relationship of flexible aramid films with enhanced strength by introducing asymmetric and symmetric aromatic ether bond structures

Abstract

As the primary processing material for firefighter uniforms, the high rigidity of meta-aramid cannot be ignored. In order to improve the softness of meta-aramid, 1,3-bis(4-aminophenoxyl)benzene (MAPB) and 1,4-bis(4-aminophenoxyl)benzene (PAPB), with asymmetric and symmetric aromatic ether bond structures, were incorporated into the molecular chains, respectively, and two types of flexible polymers were obtained. By investigating the properties of copolymer films with different ratios of MAPB and PAPB, it was found that a combined improvement in softness and tensile strength of the films could be achieved when their addition was 10%, while maintaining thermal stability. Atomic force microscopy (AFM) confirmed the improvement of the flexibility and elasticity of the molecular chains at the microscopic level, which was consistent with the observed decrease in the glass transition temperature of the modified aramid copolymer in DSC and DMA. Molecular dynamics simulations indicated that the ether bond structures of MAPB and PAPB can increase chain spacing, weaken strong intermolecular forces, and thus reduce polymer rigidity. However, under weak external forces, the outstanding chain migration ability can lead molecular chains to form a mild H-bonding effect, which does not increase the rigidity of the molecular chain, but can improve the tensile strength of the polymer.