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Four-arm star-shaped poly(2-isopropyl-2-oxazoline) (PiPrOx4-S) with short arms was studied by turbidimetry and light scattering in aqueous solutions at concentrations ranging from 0.00024 to 0.0326 g cm−3. The molar mass M of the sample investigated was 5700 g mol−1. In order to reveal the influence of arm length on solution properties, the results obtained for PiPrOx4-S were compared with the characteristics of four-arm star PiPrOx4-L with long arms and M = 13,000 g mol−1. Arm shortening leads to appearance of the new type of particles and growth of the aggregation number. Stronger concentration dependences of phase transition temperatures and double widening of this interval are observed for PiPrOx4-S as compared to long-arm star. It is shown that arm lengthening causes more remarkable changes in solution behavior than the variation of arm number.

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.