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.

We have recently shown that low surface energy polymeric films can be readily obtained from partially fluorinated hydroxyl-end-capped solventless liquid oligoesters by thermal curing [1]. Photocurable liquid oligoesters can be prepared by further substituting the remaining hydroxyl end groups with acrylic double bonds. A conventional photoinitiator containing 2-hydroxy-2-methylpropiophenone was used to cure the liquid oligoesters. As the fluorine content increases from 0 to about 1.57 wt %, the surface energy decreases by about 14 mN/m. The fluorine level in the outer few nanometers is significantly greater than that in the bulk, as revealed by XPS studies. The driving force for the surface segregation of fluorinated species comes from the large difference in surface energy between the oligoesters and their fluorinated counterparts.