Properties of waterborne polyurethane-fluorinated marine coatings: The effect of different types of diisocyanates and tetrafluorobutanediol chain extender content

Three series of waterborne polyurethane- (WBPU) fluorinated coatings were prepared with single aliphatic (4,4′-dicyclohexylmethane diisocyanate, H₁₂MDI), aromatic (4,4′-diphenylmethane, MDI) and a mixture of aliphatic and aromatic diisocyanates (1: 1). Different contents of 2,2,3,3-tetrafluoro1,4-butanediol (TFBD) as a chain extender were used in the WBPU coatings. The fluoro-enriched surface of the WBPU coatings was obtained with a combination of a high TFBD content (8.77 mol %) as well as the aliphatic or mixed diisocyanates. The tensile strength, Young's modulus, elongation at break (%) and adhesive strength were characterized with respect to the TFBD contents. The mechanical strength and adhesive strength increased with increasing TFBD content in the three series. In artificial salt water, the maximum adhesive strength of WBPU was observed for this coating, which was achieved by TFBD bonded H₁₂MDI of mixed diisocyanates with a higher TFBD content (8.77 mol %).