Structure effect on mechanical and thermal properties in aromatic copolyamides with phenyl substituents

Six aromatic copolyamides contanining phenyl groups were synthesized and characterized. The concentrations of the para -linked phenyl groups and meta -linked phenyl groups were varied systematically on the copolymers general structure to obtain a set of random copolyamides. Effect of copolymerization on glass transition temperature ( T g ), tensile modulus ( E ), Tensile strength (σ) were measured. Changes in density were determined to estimate the effect on Fractional Free Volume ( FFV ). Results indicate that the substitution of para -linked phenyl group by meta -linked phenyl group causes an increase in tensile modulus E and tensile strength a decrease in T g . The observed results are attributed to the asymmetric position of the linkages in the TERE and ISO isomers, because symmetric linkages, such as TERE, induces a higher packing of the polyamide chains while the asymmetry of ISO isomer inhibits packing causing an expansion in the FFV.