Novel pH-sensitive gel-forming pentablock copolymers based on commercially available Pluronic (poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide), PEO-b-PPO-b-PEO) triblock copolymers and cationic diblock copolymers based on polyethylene glycol) methyl ether (PEGME) were synthesized by oxyanionic polymerization. Polymerization of the cationic moiety, poly((diethylamino)-ethyl methacrylate), PDEAEM, was initiated by a difunctional potassium alcoholate of the triblock Pluronic copolymer F127 (PEO106-PPO69-PEO106) or PEGME. The difunctionality of the initiation using the triblock macroinitiator, indicating formation of a pentablock copolymer rather than a tetrablock copolymer, was verified by functionalized termination of the living polymer chains. Critical micellization temperatures (cmt) of the synthesized polymers were obtained from differential scanning calorimetry for the pentablock materials. The pentablock copolymers retained the thermoreversible gel-forming properties of Pluronic F127 as well as similar cmt values. The polydispersity of both the diblock and pentablock copolymers was similar to the macroinitiators, indicating a very low polydispersity associated with the addition of the cationic PDEAEM blocks. Both of the materials show pH-sensitive release behavior, whereas the native polymers do not.