Controlling the environmentally induced rearrangements of perfluoropolyalkylethers at photopolymers surfaces

Perfluoropolyalkylethers (PFPAEs) show low polarizability, strong electronegativity, high C F bond energy, and exceptional mobility thanks to the oxygen bridges; they represent a special class of fluoropolymers with remarkable properties (low glass transition temperature, high thermal stability, excellent chemical inertness, low surface energy, tunable mechanical properties). They, are commercially available, mostly obtained from the photooxidation of perfluoroolefins. In this work, new functionalized oligomers containing a PFPAEs structure with end groups reactive in photopolymerization were synthesized by anionic polymerization of hexafluoropropoxide (HFPO), and used in very low concentration (≤2 wt.%) as efficient surface modifying agents of epoxy resins to obtain hydrophobic photocured copolymers. Thanks to the spontaneous surface segregation of the fluorinated comonomer, which migrate to the free surface due to its low surface energy, improved hydro- and oleophobicity can be imparted to the copolymer in a simple and effective way. However, due to their high chain mobility, the fluorinated chains can rapidly rearrange upon contact with different surrounding environments (e.g., water, oil, polluted air), leading to a substantial reduction in material performance. With the aim of controlling the fluorinated dangling chains reorganization at the copolymer surfaces, different approaches have been investigated. Specifically, to hinder the mobility of the fluorinated segments, the length of the fluorinated comonomer chain, the epoxy matrix stiffness, and the type of functional PFPAE end-group have been tuned. We thus demonstrate that applying one of these strategies, it is possible to reduce or even inhibit the environmentally induced reorganizations of PFPAE chains, retaining the advanced surface performances of the fluorinated photocured copolymers.