Influence of fluorinated acids bonding on surface properties of crosslinked epoxy-based polymers

Two series of crosslinked fluorinated epoxy-based materials containing variable fluorine contents (from 0 to 6 wt.% F) were prepared using formulations based on a fluorinated acid (FA), epoxy monomer and a diamine. The epoxy monomer was based on diglycidyl ether of bisphenol A (DGEBA) while the curing agent was propyleneoxide diamine (Jeffamine D-230). The selected FA were: 2,2,3,3,4,4,5,5,6,6,7,7-dodecafluoroheptanoic acid (FA1), perfluoro-heptanoic acid (FA2), and perfluoro-nonanoic acid (FA3). One of the series synthesized, FA-DGEBA/Jeffamine, is characterized by covalent attachment of the FA to the polymer by an ester bond. The other series, FA-Jeffamine/DGEBA, is characterized by ionic interaction between FA and polymer chains. The influence on thermal and surface properties of the architecture and chain-length of FA, and the nature of the linkage between FA and network precursors, was analyzed and discussed. It was found that both series showed high oleophobicity, but depending on the linkage between the fluorinated acid and the network, it was possible to develop hydrophobic or hydrophilic materials. The fluorine enrichment with the perfluoroalkyl substitutions was proved by XPS. By this technique it was possible also to analyze the concentration of ammonium groups at the surface.