Block copolymer vesicles, also termed polymersomes, have tremendous potential as nanoscale capsules for drug-delivery or as nanoreactors. In order to turn a polymersome into a nanoreactor, its membrane needs to be permeable for substrates and products. This can be achieved by a variety of means, including the insertion of membrane proteins or by using custom-made block copolymers. However, a general approach to render the membrane of polymersomes permeable independent of its chemical composition, specially designed functional groups or expensive proteins did not exist. We have developed a simple protocol to permeabilize polymersomes by reacting the nanostructures with a radical-forming photoreagent. Under UV-irradiation, the reagent attached to the polymers, rendering them slightly more hydrophilic and therefore making them permeable, e.g. for fluorescent dyes and substrates of enzymes. Such photo-permeabilized nanoreactors enabled the bioATRP polymerizations in polymersome nanoreactors described above and pave the way to novel applications of polymersome nanoreactors.