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 microscale 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. (C) 2002 Elsevier Science Ltd. All rights reserved.