The effect of arm number and solution concentration on phase separation of thermosensitive poly(2-isopropyl-2-oxazoline) stars in aqueous solutions

Four-arm star-shaped poly(2-isopropyl-2-oxazoline) (PiPrOx₄) with calix[4]arene core was studied by methods of turbidimetry and light scattering in aqueous solutions at concentrations ranging from 0.0002 to 0.0364 g cm⁻³. The role of arm number in thermosensitive behavior was determined by comparing the experimental data with the results for eight-arm PiPrOx₈ star. First of all, it is concerned with the growth of large aggregate fraction in PiPrOx₄ solution and the formation of middle mode particles even at low temperature which causes the decrease phase separation temperatures. At relatively high concentrations (c >0.01 g cm⁻³), the dilution of PiPrOx₄ solutions is accompanied by slow growth of phase transition temperatures, and the width ΔT = (1–2) °C of this interval does not depend on the concentration. In the dilute regime, ΔT rises and reaches 9 °C. It is shown that the changes of thermosensitive stars’ behavior with arm number reduction are caused by lower intramolecular density of PiPrOx₄ in comparison with that of PiPrOx₈.