Self-assembly of star-shaped poly(2-isopropyl-2-oxazoline) in aqueous solutions

Eight-arm star-shaped poly(2-isopropyl-2-oxazoline) (PiPrOx) with calix[8]arene core (M ≈ 20,000 g mol⁻¹) was studied by turbidimetry and light scattering in aqueous solutions within concentration c ranging from 0.002 to 0.19 g cm⁻³. The lower critical solution temperature (LCST) for PiPrOx is about 10 °C lower than for the linear analog. PiPrOx forms two types of particles at room temperature. The specie responsible for the fast mode is single macromolecules or 2–3 ones joined in aggregate with a hydrodynamic radius of 4.9 nm, irrespective of concentration. On heating, at first, growth of a large aggregate fraction was observed without variation of their hydrodynamic radii R _h ^(s). Then, R _h ^(s) increased up to 800 nm at c = 0.002 g cm⁻³, while the fast mode disappeared. At all concentrations, the third middle mode with a size ranging from 9 to 40 nm was registered. It was observed in a very narrow temperature interval near the cloud point. The hydrodynamic radii of species and their fraction in solution were monitored as a function of time after the change in temperature.