Single-chain folding and self-assembling of amphiphilic polyethyleneglycol-modified fluorinated styrene homopolymers in water solution

Amphiphilic tetrafluorostyrene monomers (EFSn) carrying in the para position a polyethyleneglycol (PEG) chain with varied lengths (n = 3-13) were synthesized and polymerized by ARGET-ATRP to obtain the corresponding amphiphilic homopolymers pEFSn-x with controlled and tailored polymerization degrees (x = 8-135). All polymers presented a reversible thermoresponsive LCST-type behavior, in water/methanol mixture when n <= 4 or in pure water when n >= 8, with a cloud point (C-p) temperature in the range 30-40 degrees C strictly dependent on the length of the PEG side chain. Combined small angle X-scattering (SAXS) and dynamic light scattering (DLS) measurements were used to study the self-assembly behavior in water of the water-soluble amphiphilic homopolymers. SAXS confirmed the formation of compact-sized and spherical single-chain self-folded nanostructures below C-p, that generally presented small hydrodynamic diameters (D-h <= 11 nm) as proven by DLS analysis. Above C-p, much larger multi-chain aggregates were formed (D-h >= 800 nm), that reversibly turned back to collapsed nanostructures on cooling below the C-p temperature. By contrast, the polymers were not able to self-assemble in THE or DMF solutions, in which they adopted conventional random coil conformations.