Long-Chain Polythioamides: Synthesis and Mechanical Evaluation of Their Hydrogen Bonding Properties

Although the difference in hydrogen bonding between thioamide and amide groups has been widely discussed, their mechanical comparison remains unexplored. We report a postpolymerization modification strategy involving main-chain atom insertion to prepare polyethylenes bearing in-chain thioamide groups (polyethylene-thioamides) and their amide analogs (polyethylene-amides) with identical molecular weights and incorporation ratios, enabling mechanical evaluation of the difference in hydrogen bonding. Starting from polyethylenes bearing in-chain carbonyl groups (polyethylene-ketones), oxime formation followed by a (diethylamino)sulfur trifluoride (DAST) promoted rearrangement enabled nitrogen atom insertion into the polymer main-chain, and subsequent one-pot nucleophilic substitution with sodium hydrogen sulfide (NaSH) afforded polyethylene-thioamides. Mechanical testing revealed that polyethylene-thioamide containing 0.8 mol % thioamide groups exhibited a tensile strength of 21.3 MPa, significantly lower than that of polyethylene-amide (41.9 MPa, 0.7 mol % amide). These results provide direct experimental insight into the weaker hydrogen bonding of thioamides compared with that of amides, representing the first macroscopic mechanical comparison between the two.