The present application describes a new process for the preparation of polyisobutene derivatives, such polyisobutene derivatives, and their use. The process irradiates a reaction mixture containing an oxygen-containing gas in contact with polyisobutene, a photosensitizer and an optional solvent, with monochromatic light emitted from an electroluminescent lighting device, at least 90% of power of said monochromatic light and at most 100% of said power being emitted in the range from 350 nm to 680 nm.