Thermoplastic elastomer hydrogel networks, based on swelling of nanostructured blends of amphiphilic, sphere-forming AB diblock and ABA triblock copolymers, provide direct access to thermally processable plastics that exhibit exceptional elastic recovery and fatigue resistance even after hydration. In such two-component systems, the ratio of ABA triblock copolymer to AB diblock copolymer is used to control the resultant swelling ratio, system modulus, and overall mechanical response. In this report, we introduce a simplified one-component alternative which exploits a single-component, photoreactive AB diblock copolymer precursor to controllably generate ABA triblock copolymer in situ during melt-processing. This was accomplished using efficient photoinduced [4 + 4] cycloaddition (lambda = 365 nm) between terminal anthracene units on a omega-anthracenylpolystyrene-b-poly(ethylene oxide) diblock copolymer precursor (SO-anth, f(PS) = 0.13, M-n = 70 100 g mol(1)) to produce the desired amount of polystyrene-b-poly(ethylene oxide)-b-polystyrene (SOS) triblock copolymer. The amount of SOS triblock copolymer formed was tunable (from 11.7 to 45 mol %) using UV exposure time (2 to 20 min, similar to 30 mW cm(2)), giving direct control over swelling and mechanical properties in the resultant hydrogels produced upon subsequent vitrification of the melt sample followed by addition of water. Hydrogels produced in this manner were found to exhibit dynamic shear moduli and shape preservation characteristics typical of preblended, two-component SO/SOS TPE hydrogels of similar SOS concentrations.