Molecular aggregation structure and water repellency of poly(fluoroalkyl methacrylate)s with carbamate-bridged perfluoroalkyl side chains

Poly(fluoroalkyl methacrylate)s with carbamate-bridged perfluoroalkyl side chains, poly{2[perfluorohexylethylcarbamate]ethyl}methacrylate (PFMAUr-C6) and poly{2-[perfluorooctylethylcarbamate] ethyl}methacrylate (PFMAUr-C8), were successfully synthesized via free radical polymerization. The molecular aggregation structures in the bulk and thin films were investigated using differential scanning calorimetry (DSC), polarized optical microscopy (POM), thermogravimetric analysis (TGA), temperature-controlled wideangle X-ray diffraction (WAXD), temperature-controlled Fourier transform infrared (FTIR) spectroscopy, grazing incidence WAXD, contact angle measurements, and X-ray photoelectron spectroscopy (XPS). The impact of the alpha-methyl group on the molecular aggregation structure and water repellency was verified by comparing their structure and properties with their analogs without the alpha-methyl group. PFMAUr-C6 and PFMAUr-C8 produced bilayer smectic A and loosely packed smectic B structures, respectively. Although both the PFMAUr-C6 and PFMAUr-C8 thin films exhibited a smectic arrangement of perfluoroalkyl groups at the outermost surface, surface rearrangement occurred immediately upon exposure to water. Thermal annealing suppressed surface rearrangement of the PFMAUr-C8 film. The alpha-methyl group hindered the ordering of smectic structure owing to its main chain rigidity caused by the steric hindrance of the bulky alpha-methyl group, and the deteriorated ordering of the smectic structure resulted in their rapid surface rearrangement and poor water repellency.