Abstract <p>This study was aimed at modifying the surface of aromatic phthalide-containing polymers, promising for use in membrane technologies, with aliphatic polymer brushes of varying polarity. Mono- and polyfunctional vinyl monomers with various side groups, including reactive ones, were used: hydroxyl, ether, ester, acid, epoxy, and nitrile. The possibility of graft copolymerization of acrylates and methacrylates, as well as some other vinyl monomers, on the surface of brominated polydiphenylenephthalide (PDP-Br) was investigated. The influence of the degree of halogenation of PDP-Br and irradiation dose and duration on the degree of grafting was studied. It has been shown that brominated PDP is a polymeric photoinitiator for a wide range of vinyl monomers, the use of which in graft copolymerization processes allows the production of grafted aromatic–aliphatic copolymers of various chemical structures with different hydrophilic/hydrophobic ratios.</p>