Polymersomes are of interest as nanocarriers due to their physical and chemical robustness, which arises from the macromolecular nature of their block copolymer components. However, the physical robustness of polymersomes impairs transmembrane diffusion and responsiveness to mechanical forces. Polymer nanocarriers that can reversibly deform under stress while maintaining structural integrity and transmembrane diffusivity are desired for development of gas transport vehicles. Here, we report polymersomes composed of amphiphilic block copolymers containing polydimethylsiloxane with side-chain pendant vinyl groups. A reversibly deformable polymersome compartmentalizing membrane was obtained by cross-linkage of PEG-b-poly(dimethyl-r-methylvinyl)silane in a self-assembled bilayer via photoradical generation in aqueous media. The covalently cross-linked polymersomes exhibited superior physical robustness compared to unlinked polymersomes while maintaining deformability under stress. Transmembrane oxygen diffusion was confirmed when lumen-encapsulated Zn-porphyrin generated singlet O-2 under irradiation, and the anthracene-9,10-dipropionic acid O-2 quencher was consumed. Polymersome-encapsulated hemoglobin bound oxygen reversibly, indicating the polymersomes could be used as O-2 carriers that reversibly deform without sacrificing structural integrity or oxygen transportability.