Study on wholly aromatic polyamides containing methyl-substituted phenylene linkage

In order to study the influence of chemical modification on properties of polyamides, wholly aromatic polyamides have been synthesized from p-phenylenediamine, its 2,5-dimethyl and 2-methyl derivatives, m-phenylenediamine, its 2-methyl and 4-methyl derivatives, and terephthaloyl and isophthaloyl dichlorides by solution polycondensation at low temperature. The thermal stability and solubility of the methyl-substituted polyamides were compared with those of unsubstituted ones. The introduction of methyl groups in a polymeric chain led to a decrease in their thermal stability to different degrees depending on the positions of methyl groups, accompanied by an increase in their solubility. The unsymmetrical introduction of methyl groups in benzene rings had a greater effect on the increase in solubility of polyamide than did symmetrical methyl groups.