Three diblock copolymers of polystyrene‐b‐poly(N‐isopropylacrylamide) (PS‐b‐PNIPAM) were prepared by reversible addition‐fragmentation chain transfer technique (RAFT) with compositions f_PS = 0.84, f_PS = 0.29, and f_PS = 0.33. Block copolymers rich in PNIPAM were blended with polystyrene and its morphological effects were studied. The morphology of thin films was induced by acetone vapor and determined in the dried state by means of TEM. Copolymers with f_PS = 0.84 and f_PS = 0.29 form hexagonally packed cylinder (HPC) morphologies while that with f_PS = 0.33 corresponds to a lamellar structure. In almost all cases where PNIPAM constitutes the continuous phase, a contraction of the PNIPAM blocks with respect to their average unperturbed dimension was observed, contrary to what one expects from the physics of self‐assembly of block copolymers. In contrast, for HPC morphology where PNIPAM is confined in a PS matrix, both blocks are highly extended. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 1368–1376