Copolymers with High PerFluoroPolyAlkylEthers (PFPAES) Content by Photo-Induced Cationic Polymerization

Perfluoropolyalkylethers (PFPAEs) show low polarizability, strong electronegativity, high C-F bond energy, and exceptional chain 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) (1–3). Commercially available PFPAEs are mostly obtained from the photooxidation of perfluoroolefins. In this work PFPAEs were synthesized by anionic polymerization of dodecafluorooctanedioyl difluoride, chain extended with different alkyl groups and functionalized with vinyl ether or epoxy end groups (Fig. 1a). A trivinyl ether resin (trimethylolpropane trivinyl ether) and a triepoxide resin (trimethylolpropane triglycidyl ether) were added (20 wt%) to the PFPAE vinyl ethers and to the PFPAE epoxides, respectively. The mixtures were photo-cured (Fig. 1b) and the non-fluorinated resins acted as crosslinking agent, improving the mechanical properties of the photocured networks. The UV-curing process of the copolymers with high PFPAE content was monitored by Photo-DSC and FT-IR-ATR spectroscopies; the crosslinked networks were characterized by DSC, TGA, refractive index, insoluble fraction and surface measurements. The copolymers showed an evident biphasicity (two Tgs: Tg1 < –60 °C, Tg2 > 20 °C), low refractive index (n ≈ 1.31), good chemical and thermal resistance, and low surface energy (Fig. 1b). Such properties can be usefully exploited in highly demanding applications such as photonic devices and fuel cell membranes.