Biodegradable polyurethanes: novel effects of the fluorine-containing chain extender on the thermal, physical and water vapor permeation properties

This study synthesized a novel fluoro chain extender, namely 2,2,3,3,4,4,4-heptafluoro-butynic acid 2,2-bis-hydroxymethyl-butyl ester (HFBA), by using 2,2,3,3,4,4,4-heptafluorobutanoyl chloride and trimethylolpropane. Novel polyurethanes (PUs), namely HFBA/PUs, were subsequently synthesized by adopting a hard segment (4,4′-diphenylmethane diisocyanate, MDI), a soft segment (polycaprolactone diol, PCL), and the synthesized chain extender (HFBA). The results of proton nuclear magnetic resonance spectroscopy, fluorine-19 nuclear magnetic resonance, and Fourier transform infrared spectroscopy (FT-IR) demonstrated the successful synthesis of the HFBA chain extender. Gel permeation chromatography revealed that the molecular weight of the HFBA/PUs increased with the HFBA content. Through FR-IR and X-ray photoelectron spectroscopy, we observed a strong hydrogen bond interaction between the NH groups and CF₂ or CF₃ groups in the HFBA/PUs. This interaction increased with the HFBA content. Additionally, increasing the HFBA content increased the initial decomposition temperature, glass transition temperature, dynamic Tg (Tgd), tensile strength, and Young’s modulus of the HFBA/PUs. These results were because HFBA was a hard segment, which stimulated a stronger interaction between the NH groups and CF₂ or CF₃ groups in the PUs. By contrast, the HFBA/PUs had low elongation-at-break values. Atomic force microscopy revealed a higher number of bump-like protrusions and higher surface roughness levels among HFBA/PUs with higher HFBA content ratios. Finally, we coated the HFBA/PUs onto polyethylene terephthalate fabrics and discovered that the coated fabrics demonstrated high waterproofing and water vapor permeability levels.