Imidazolium-based ionic thermoplastic polyurethane with low surface energy and antibacterial activities

A series of novel thermoplastic polyurethane elastomers with both low surface energy and antibacterial activity were synthesized in this paper. Firstly, four imidazole salt diols with different alkyl chain lengths at the N-position of imidazolium cation ([CnIm⁺][Cl⁻]) were prepared. Then, imidazolium-based ionic thermoplastic polyurethane elastomers (Si-ITPUs) were formulated by incorporating polydimethylsiloxane and polytetramethylene glycol as a mixed soft segment, 1,4-butanediol and [CnIm⁺][Cl⁻] as a chain extender, and 4,4′-dicyclohexylmethane diisocyanate. The structure, thermal stability, mechanical properties, physical crosslinking density, and the anti-graffiti properties of Si-ITPUs were evaluated. The surface energy and water absorption were evaluated through static contact angle and water resistance tests, respectively. Furthermore, the antibacterial activities against both Staphylococcus.aureus and Escherichia coli were characterized by the plate colony counting method. The results demonstrated that Si-ITPUs possessed surface energy of approximately 23 mN/m, which conferred excellent anti-graffiti and self-cleaning performance. Furthermore, the increase of the alkyl chain length of substitutions resulted in a decrease in the tensile strength but an increase in the elongation at break. Si-ITPU-C₄ exhibited optimized antibacterial activities with an antibacterial rate of more than 99.9% against both S. aureus and E. coli. This novel polyurethane is anticipated to find applications in the medical device industry and food processing sector.