Structure-property relationships of aromatic polyamides and polythioamides: comparative consideration with those of analogous polyesters, polythioesters and polydithioesters

Conformational characteristics and configurational properties of aromatic polyamides and polythioamides, analogues of common aromatic polyesters such as poly(ethylene terephthalate) and poly(trimethylene terephthalate), have been investigated via NMR experiments and molecular orbital calculations on model compounds, and the refined rotational isomeric state calculations for the polymers. The polyamides and polythioamides were actually synthesized and characterized in terms of solubility, molecular weight, crystallinity, thermal transition, and thermal stability. Herein, the experimental results are discussed mainly from the viewpoint of the conformational characteristics and compared with those obtained from analogous aromatic polyesters, polythioesters, and polydithioesters to reveal the effects of the heteroatoms O, S, and NH included in the backbone on the polymer structures and properties.