Well-defined polycaprolactone precursors for low surface-energy polyurethane films

For the purpose of developing model coating systems, it is important to use well-defined coating precursors. In this work, polyester oligomers were synthesized by controlled ring-opening polymerization of ε-caprolactone and 4-tert-butyl-ε-caprolactone via an activated monomer mechanism. These well-defined oligomers, including 3-armed hydroxyl-functionalized polyesters and perfluoroalkyl-end-capped linear polyesters, have been obtained with controlled functionality and low-molecular weight polydispersity and without the formation of cyclic structures, as demonstrated by MALDI-ToF MS analyses. The polymer architecture and functionality can be tuned by using different initiating alcohols. These oligomers have been used as precursors to prepare model low surface-energy polyurethane coatings. Upon the addition of about 1 wt % of fluorine in the polyurethane films, the advancing contact angles for water and hexadecane have been increased to 105° and 78°, respectively; the surface enrichment of fluorinated species has been confirmed by X-ray photoelectron spectroscopy.