New biodegradable multiblock amphiphilic and thermosensitive poly(ether ester urethane)s consisting of poly[(R)-3-hydroxybutyrate] (PHB), poly(ethylene glycol) (PEG), and poly(propylene glycol) (PPG) blocks were synthesized, and their aqueous solutions were found to undergo a reversible sol-gel transition upon temperature change at very low copolymer concentrations. The multiblock poly(ether es...