Surface properties of fluorinated oxetane polyol modified polyurethane block copolymers

This article describes the surface properties of fluorinated oxetane polyol (F-Polyol) containing linear segmented polyurethane elastomers. A series of polyurethane elastomers derived from a soft segment based on 2300 g/mol polyhexamethylene carbonate, and a hard segment composed of 4,4′-methylene diphenyl diisocyanate chain extended with 1,4-butanediol were modified with a 3285 g/mol F-Polyol via either melt or solution reaction in dimethyl acetamide. X-ray photoelectron spectroscopy confirmed that the surfaces of the modified polyurethanes exhibit notable fluorine enrichment within the uppermost 5 nm, depending on the bulk composition and the polymerization method. Field emission scanning electron microscopy and tapping mode atomic force microscopy experiments demonstrated that relatively large micro-scale domain structures were exclusively found in the melt-polymerized polyurethanes. This was attributed to incompatibility of the F-Polyol with the other reactive constituents during the melt polymerization. Friction experiments revealed that the friction coefficient of the fluorinated polyurethanes decreased by about 2-fold as the surface fluorine concentration increased from 0 to about 20 at.%. Furthermore, the melt-polymerized polyurethanes underwent a stick-slip motion, whereas the more homogeneous solution-polymerized polyurethanes experienced a conventional stable sliding. These friction behaviors are discussed in terms of the surface topography and morphology.