Synthesis of Polyglycidol-Based Analogues to Pluronic L121−F127 Copolymers. Self-Assembly, Thermodynamics, Turbidimetric, and Rheological Studies

Abstract

The fifth paper of a series, which is focused on polyglycidol-based analogues to Pluronic copolymers, describes the synthesis of another group of eight well-defined polyglycidol−poly(propylene oxide)−polyglycidol (PG−PPO−PG) block copolymers with PG contents varying from 10 to 80 wt % and fixed molecular weight of the middle PPO block of 4000. In composition these copolymers are closest to the Pluronic copolymers of the highest molecular weight of PPO, L121−F127. The copolymers were prepared by means of anionic polymerization of ethoxyethyl glycidyl ether (protected glycidol) followed by cleavage of the protective groups. In aqueous solutions the copolymers were found to self-associate above a certain critical concentration (CMC). The CMC variations with temperature and PG content as well as the thermodynamic parameters of the self-assembly were compared to those of the corresponding Pluronic copolymers and related PG-based copolymers studied earlier. The turbidity measurements carried out in the temperature range from −10 to 60 °C revealed four types of transmittance vs temperature curve patterns depending on PG content. Formation of qualitatively different self-assembled structures was suggested to explain the different curve patterns. Dilute and concentrated aqueous solutions were investigated by means of rheology. Shear thinning was observed for all copolymers even in the dilute (0.5−2.0 wt %) limit which imparts high magnitudes of the zero shear viscosity. The mechanical properties of the high concentrated solutions (33 wt %) were studied by frequency-dependent oscillatory experiments. The solutions of all copolymers invariably behaved as fluids and elastic gels at low (15 °C) and elevated (60 °C) temperatures, respectively.