• poly(pentafluorostyrene)
• multichain aggregation
• dynamic light scattering (DLS)
• amphiphilic homopolymer
• small angle X-ray scattering (SAXS)
• self-assembly

Amphiphilic tetrafluorostyrene monomers (EFSn) carrying in para position an oligoethylene glycol chain with different lengths (n = 3-13) were synthesized and used for the preparation of the corresponding amphiphilic homopolymers (pEFSn-x) having different degrees of polymerization (x = 8-135) by a controlled radical polymerization reaction, such as ARGET-ATRP. The self-assembly behavior of monomers and homopolymers in water and organic solvents was studied by dynamic light scattering (DLS) and small angle X-ray scattering (SAXS). In particular, DLS measurements on water solutions of the water-soluble homopolymers at room temperature evidenced the presence of nanoassemblies with hydrodynamic radius Rh = 2.5 - 6 nm, compatible with the formation of unimer micelles. These nanoassemblies were proven to be disrupted by the addition of THF to the water/polymer solution. SAXS measurements revealed that self-folded nanoassemblies were compact globular spheres, with radius of gyration Rg in the range 1.7 - 2 nm, corresponding to radii of a spherical particle in the range 2 - 3 nm. The Rg/Rh radius was <0.5, consistent with a core-shell nanostructure. On heating above a critical temperature, identified as a cloud point temperature by light transmittance measurements, multi-chain microassemblies were formed, which reverted to nanoassemblies on cooling below this critical temperature. This LCST-type thermoresponsive transition was fully and sharply reversible.
Differential scanning calorimetry (DSC) analysis revealed that the homopolymers with n <= 8 were amorphous, while those with n = 13 were semicrystalline, owing to the crystallization of the longer oxyethylenic side chains. In any case the glass transition temperatures (Tg) were lower than room temperature, indicating that the EFSn backbone featured a relatively high flexibility. Moreover, thermogravimetric analysis (TGA) showed that the polymer backbone possessed an increased thermal stability with respect to the corresponding oligoethylene glycol side chain.
Wettability and surface composition of the homopolymers were investigated by static contact angle and X-ray photoelectron spectroscopy (XPS) measurements. XPS measurements confirmed the presence of fluorine at the film surface, even though its concentration was lower than the theoretical amount, thus indicating a low effectiveness in surface migration of the fluorinated backbone. Consistently, homopolymer films exhibited moderate to low hydrophobicity as estimated by the measurements of water and n-hexadecane contact angles. However, the initial water contact angle and the film ability to respond to the wetting liquid were generally correlated to the hydrophilic/hydrophobic balance of the specific repeating unit of the polymer.