Konstitutionsisomerie in Polykondensaten. Teil VI. Synthese und Eigenschaften von völlig geordneten und ungeordneten Bipolyamiden aus cis‐2,6‐Dimethylpiperazin und 1,2,5‐Thiadiazol‐3,4‐dicarbonyl‐dichlorid

Constitutional Isomerism in Polycondensates. Synthesis and Properties of Perfectly Regular and Random Bipolyamides from cis‐2,6‐Dimethylpiperazine and 1,2,5‐Thiadiazole‐3,4‐dicarbonyl Dichloride The synthesis of constitutionally perfectly regular and random alternating copolyamides from the ‘symmetric’ monomer 1,2,5‐thiadiazol‐3,4‐dicarbonyl dichloride (4) and the ‘non‐symmetric’ monomer cis‐2,6‐dimethylpiper‐azine (7) by solution and interfacial polycondensation methods is described. Their constitutional regularities (s values) were determined by high‐resolution 13C‐NMR spectroscopy in CDCl3 solutions. Ordered and random copolyamides were amorphous with Tg values of ca. 200°. However, the regular head/tail and the random copolyamides with low molecular weights could be partially crystallized by annealing and showed large differences in their melting points (54°). Beside other physical properties, the membrane properties of the copolyamides were carefully investigated. In H2O desalination by reverse osmosis, no differences in salt rejections and permeabilities between constitutionally regular and random copolyamides were found (within experimental errors). In contrast, the regular head/head/tail/tail‐ and head/tail‐type copolyamides showed considerably larger separation factors in the gas separation (methane/hydrogen) than the random ones.