Facile synthesis and characterization of soluble aramid containing polar hydroxyl side group

Abstract

A series of aramids containing hydroxyl side group (NOM-OHc, where c is the molar fraction of hydroxyl substitution in the polymer, and c = 0, 10, 20, 40, 60, 80, 100) were synthesized by direct high-temperature polycondensation. The synthesis employed a facile process. The monomer, 4,4'-(terephthaloylbis(azanediyl))bis(2-hydroxybenzoic acid), was prepared simply via an esterification reaction. The chemical structures of the soluble aramids were confirmed by 1H NMR. And the molecular weight and mass dispersity of the aramids were obtained by size exclusion chromatography, instead of the traditional intrinsic viscosity method. The use of unsymmetrical monomers and the introduction of hydroxyl side group into the aramid structure decrease the conjugation of the polymer main chain, and thus the resulting aramid has excellent solubility in relatively polar solvents, such as N-methy-2-pyrrolidone, dimethylsulfoxide, N,N-dimethylacetamide, and N,N-dimethylformamide. As a result, the molding processability of the aramids and their composites is greatly improved. For example, films can be made by solution spinning and casting. The films have good mechanical strength, with tensile strength, tensile modulus, and elongation at break in the range of 68–95 MPa, 2.65–3.12 GPa, and 5–10%. The thermal resistance of the aramids is still quite good, with 5% weight loss temperatures in nitrogen and in air in the range of 360–430 °C.