Using sequential RAFT polymerization, single monomer insertion, and click chemistry, a series of triblock copolymers, poly(ethylene oxide)-b-polystyrene-b-poly(ethylene oxide), PEO-b-PS-b-PEO, were synthesized, where one of the two junction points is a UV cleavable ortho-nitrobenzyl (ONB). Ordered patterns of PEO-b-PS-b-PEO were produced by solvent vapor annealing. Upon exposure to ultraviolet (UV) light, the PEO-b-PS-b-PEO was converted into a mixture of a PEO homopolymer and a PS-b-PEO diblock copolymer. It was found that the microdomain spacing could be tuned by adjusting the UV exposure time, due to the change in the copolymer architecture and the swelling of the PEO microdomain by the PEO homopolymer produced. By selective area exposure of the PEO-b-PS-b-PEO thin films, the domain spacing was changed over selected locations across the film, generating patterns of different microdomain sizes. (c) 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018, 56, 355-361.