Thermo-responsive block copolymers based on linear-type poly(ethylene glycol): Tunable LCST within the physiological range

Thermo-responsive block copolymers poly(ethylene glycol)-block-poly(N-acryloyl-2,2-dimethyl-1,3-oxazolidine), PEG-b-PADMO, based on linear PEG were prepared via a versatile reversible addition-fragmentation chain transfer (RAFT) polymerization. PEG22 (Mw = 1000) was used as the hydrophilic component, whose dehydration was the main driving force for the phase transition of these copolymers, as demonstrated by the 1H-NMR spectra. Their lower critical solution temperatures (LCSTs) could be tuned in the range of 20°C to 35°C, by adjusting the degree of polymerization (DP) of PADMO between 14–27. Furthermore, a sharp phase transition at ca. 33°C, close to the physiological temperature with minimal hysteresis, was observed for the PEG22-b-PADMO14 copolymer. Moreover, excellent reversibility and reproducibility were displayed for the same copolymer over 10 cycles of repeated temperature change between 25°C (below the LCST) and 40°C (above the LCST).