Some isomorphous copolyamides

Various copolyamides obtainable from heptamethylenediamine (7) and bis(3‐aminopropyl) ether (303) combined with adipic acid (6) and terephthalic acid (T) were prepared. They were characterized thoroughly as bulk polymer (visual appearance, viscosity number, polymer melt temperature, solubility), as melt‐pressed films (water absorption, glass transition temperature, crystallinity) and as melt‐spun, drawn monofils (tenacity, elongation, initial modulus, compliance ratio, tensile recovery, work recovery, orientation, crystallinity, fiber stick temperature, zero strength temperature, and crystalline melting point). The reality of isomorphism in polyamides was definitely established by the linear dependence on composition of all physical properties measured for the copolymer system 303‐6/7‐6. The copolymer systems 303‐T/7‐T, 303‐6/7‐T, and 7‐6/303‐T showed decreasing tendency toward ideal isomorphism, and the system 303‐6/303‐T showed deviation from perfect isomorphous behavior in all properties. It is concluded that in the aliphatic diamines used, and ether oxygen fits well as a substitute for a methylene group, but the benzene ring fits poorly as a substitute for the four‐carbon aliphatic chain of adipic acid.