Thin films of block copolymers are extremely attractive for nanofabrication because of their ability to form uniform and periodic nanoscale structures by microphase separation. One shortcoming of this approach is that to date the design of a desired equilibrium structure requires synthesis of a block copolymer de novo within the corresponding volume ratio of the blocks. In this work, solvent vapor annealing in supported thin films of poly(2-hydroxyethyl methacrylate)-block-poly(methyl methacrylate) [PHEMA-b-PMMA] by means of grazing incidence small angle X-ray scattering (GISAXS) is investigated. A spin-coated thin film of a lamellar block copolymer is solvent vapor annealed to induce microphase separation and improve the long-range order of the self-assembled pattern. Annealing in a mixture of solvent vapors using a controlled volume ratio of solvents, which are chosen to be preferential for each block, enables selective formation of ordered lamellae, gyroid, hexagonal, or spherical morphologies from a single-block copolymer with a fixed volume fraction. The selected microstructure is then kinetically trapped in the dry film by rapid drying. This paper describes what is thought to be the first reported case where in situ methods are used to study the transition of block copolymer films from one initial disordered morphology to four different ordered morphologies, covering much of the theoretical diblock copolymer phase diagram.