The synthesis and aqueous gelation behavior of ABA triblock copolymers, in which the hydrophobic character of the A block is systematically varied were investigated. Three types pf ABA triblock copolymers of approximately the same overall composition were prepared in which the A block is either poly(methyl methacrylate) or poly(2-hydroxyethyl methacrylate). Each of these copolymers was synthesized by ATRP in methanol using sequential monomer addition. The results showed that the viscosity of a 10% w/v aqueous solution of the copolymers unexpectedly increased by almost 2 orders of magnitude on heating from 0°C to 30°C. The analogous PHEMA-based triblock copolymer is found to be too hydrophobic to undergo efficient gelation, while the PMMA-based triblock copolymers cannot be molecularly dissolved/dispersed in water under any conditions.