Cross-linking fluorene copolymers via thiol-ene click chemistry

A series of 9,9-bis(allyl)fluorene copolymers (PFAF) with allyl groups on the side chain were synthesized by Suzuki coupling reaction. The cross-linked fluorene copolymers were realized via thiol-ene click reaction between allyl groups and thiol groups from crosslinker under ultraviolet light. Fourier transform infrared spectroscopy (FTIR), cyclic voltammetry (CV), UV-Vis absorption spectroscopy and photoluminescence spectroscopy (PL) were used to investigate the crosslinking efficiency of the thiol-ene click reaction and the impacts of crosslinking on the performances of fluorene copolymers. The results showed that allyl fluorene copolymers with high molecular weight and different content of 9,9-bis(allyl) fluorene units were successfully synthesized. Fluorene copolymers containing allyl fluorene structural units can be effectively crosslinked by the thiol-ene click reaction. The crosslinking conditions and the factors which influence the crosslinking were investigated in detail. The fluorene copolymer films which were composed of a fluorene copolymer with 10 mol% allyl fluorene structural units (PF10AF) and 39 wt% pentaerythritol tetra(3-mercaptopropionate) (PETMP) can be crosslinked to 85% crosslinking degree under irradiation of 1.8 mW/cm2 LED UV light at 390 nm for 50 s in air. It was found that the thiol-ene click cross-linking had little effects on the photoluminescence spectra of the fluorene copolymers. The thiol-ene click crosslinking showed a much faster crosslinking rate and higher crosslinking efficiency for fluorene copolymers than those of conventional free radical polymerization crosslinking. The results of this study provide a feasible method for cross-linking conjugated polymers in various applications.