Pluronic analogs based on block copolymers of poly(propylene oxide) and poly(ethyl ethylene phosphate) (PEEP-PPO-PEEP) were synthesized, and the thermoresponsive behavior, including aggregation at, low concentration and gelation at high concentration were studied. At lower concentrations up to 10 wt %, thermoinduced aggregation of PEEP-PPO-PEEP was demonstrated by UV-vis absorbance measurements using 1,6-diphenyl-1,3,5-hexatriene as a probe. Microthermal analyzes showed symmetrically endothermic and exothermic thermograms during the thermoinduced aggregation and de-association processes, which was also associated with the dehydration and rehydration of PPO blocks, as revealed by the variable temperature NMR measurements. Thermo-induced aggregation with the increased temperatures was also observed by dynamic light scattering. At higher concentration from 20 to 40 wt %, the aqueous solution of PEEP-PPO-PEEP underwent thermo-induced phase transitions from a clear solution to a turbid solution, then to opaque gel and syneresis phases, depending on the molecular weights of PEEP blocks. Such a thermoresponsive hydrogel was used for doxorubicin incorporation. Sustained release of drug was achieved from the gel, demonstrating the polyphosphoester-based Pluronic analogs' potential for biomedical applications. (C) 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6168-6179, 2009