PMMA gradient materials and in situ nanocoating via self-assembly of semifluorinated hyperbranched amphiphiles

Nanostructured poly(methyl methacrylate) (PMMA) gradient materials with in situ nanocoating were obtained via self-assembly of semifluorinated hyperbranched polyglycerol amphiphiles (FPG) at the PMMA surface during free-radical MMA bulk polymerisation. The FPG was designed as novel nanoadditive and prepared by etherification of the hydrophilic hyperbranched polyglycerol core with allylether and subsequent quantitative addition of the hydro- and oleophobic 3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluoro-octane-1-thiol to the double bond end groups. As a result of the FPG self-assembly, a fluorine-containing nanocoating, with an average thickness of 150 to 200 nm at the PMMA surface, was detected by transmission electron microscopy (TEM) and Rutherford backscattering spectrometry (RBS) of an He-4(+) beam. The resulting nanocoating formation was driven by the interactions of the perfluorohexyl end groups and the in situ phase separation with increasing conversion of the MMA polymerisation. The FPG nanocoating consisted of a nanolayered substructure composed of alternating fluorine-containing and fluorine-free layers with an average thickness of 3-5 nm, which was evidenced by atomic force microscopy (AFM) and small angle X-ray scattering (SAXS). Very small amounts of the FPG amphiphile, typically less than 3 wt.-% added to PMMA, were found to be sufficient to achieve the in situ nanocoating formation at the PMMA surface. The surfaces of the PMMA/FPG surface gradient materials were water and oil repellent.