Partially fluorinated isocyanates were synthesized from hexamethylene diisocyanate (HDI) and an HDI trimer (Desmodur N3300). The perfluoroalkyl group (Rf) was C6F13 or C8F17, and the ratio between Rf and the isocyanate group (NCO) was 1/99 in the case of HDI or 1/49 in the case of N3300. Polymeric films with surface energies as low as 10 mN/m were obtained from mixtures of these partially fluorinated isocyanates and a previously reported hydroxyl-end-capped solventless liquid oligoester. Contact angles of water and hexadecane reached 120° and 80°, respectively, when less than 1 wt % of fluorine was present in the films. The surface enrichment of fluorine-containing species was confirmed by X-ray photoelectron spectroscopy (XPS) investigations. At a fluorine concentration of 0.5−1.0 wt %, the surface F/C atomic ratio (at a 15° takeoff angle) was greater than 1; the surface enrichment factor of fluorine was up to 600. The topological structures of the polymeric films were recorded by an atomic force microscope under tapping mode. While the height images indicated that the surface was smooth at the nanometer scale in a 1 μm × 1 μm area, the phase images revealed that fluorine-enriched domains were present at the surface. As the fluorine concentration increased, the fluorine-enriched domains grew from tiny spots (2−3 nm) to larger round domains (15−25 nm in diameter). The low surface energies of the films could be ascribed to the strong surface segregation of fluorinated species.

Polymeric films with surface energies as low as 10 mN/m were prepared from a mixture of a hydroxyl-end-capped solventless liquid oligoester (SLO), a blocked polyisocyanate, and a novel fluorinated blocked isocyanate (F nB-NCO; the ratio of the fluorinated tail and the caprolactam blocking group: 1:1), with less than 4 wt % of fluorine in the films. The curing temperature demonstrated a significant effect on the reaction rate and the film wettability: a higher curing temperature led to a less significant surface enrichment of fluorine, especially at a low F content (<2 wt %), due to the fast immobilization of the cross-linked networks. The mixtures had excellent stability below the deblocking temperature (∼ 140°C ) of the blocked isocyanates, which allowed the determination of the diffusion coefficients of fluorinated species in the reaction mixtures by pulsed field gradient (PFG) NMR. The well-defined F nB-NCOs enabled an easy and accurate adjustment of the fluorine concentration, making this approach practically attractive and efficient to prepare low surface energy films by using small amounts of fluorinated species.