Thermoresponsive behaviour of terpolymers containing poly(ethylene oxide), poly(2-ethyl-2-oxazoline) and poly(ε-caprolactone) blocks in aqueous solutions: an NMR study

1H NMR spectroscopy was used for the first time to investigate temperature behaviour of aqueous solutions of nanoparticles (NPs) prepared from linear and Y-shape terpolymers containing blocks of poly(ethylene oxide) (PEO), poly(2-ethyl-2-oxazoline) (PEtOx) and one linear or two star poly(ε-caprolactone) (PCL) blocks with different length. Structural changes were characterized separately for all blocks in a temperature range 295–360 K, and a broad transition was observed at temperatures above ~320 K. The temperature behaviour of NPs solutions depends on polymer concentration and especially on terpolymer architecture. At the same time, NMR measurements revealed important role of PCL blocks in this behaviour. The spin-spin relaxation times T2 of water (HDO) give information on the behaviour of water and on polymer-water interactions within the aforementioned temperature range. In NPs solutions of the linear copolymer, two types of water were detected at higher temperatures: “free” and “bound” water molecules with long and very short T2 values, respectively. For NPs solution of non-linear terpolymer, two types of water were observed only for the highest used (1.5 wt%) polymer concentration.