Cross-linking fluorene copolymers via thiol-ene click chemistry

Abstract

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.