Thermoresponsive Luminescent Electrospun Fibers Prepared From Poly(DMAEMA-co-SA-co-StFl) Multifunctional Random Copolymers

We report novel thermoresponsive electrospun (ES) fibers prepared from multifunctional random copolymers of poly((2-(dimethylamino)ethyl methacrylate)-co-(stearyl acrylate) -co-(9,9-dihexyl-2-(4-vinylpenyl)-9H-fluorene)) (poly(DMAEMA-co-SA-co-StFl)). The moieties of DMAEMA, SA, and StFl were designed to exhibit the thermoresponsive, physical cross-linking, and fluorescent functionality, respectively. The effects of the copolymer compositions on the morphology and photoluminescence of the prepared ES fibers were explored. The prepared P4 copolymer with the DMAEMA/SA/StFl mole ratio of 92/3/5 showed the lower critical solution temperature (LCST) of 32.5 °C. A significant temperature-dependent swelling and de-swelling behavior was found in the P4 ES fibers, which had the diameter of 753 ± 174 nm and 5-10 nm StFl aggregated domain. Accompanied with volume-changing on the P4 ES fibers, a reversible photoluminescence (PL) quenching was also observed during the heating and cooling cycle between 40 and 60 °C. Such reversible switching of the "on-off" PL intensity was probably due to the light absorption ability of the StFl moiety, resulted from the extended/compact structural transformation on the PDMAEMA moiety. Furthermore, the high surface/volume ratio of the ES fibers led a much better temperature response compared with the corresponding spin-coated film. The present study demonstrated that the ES fibers prepared from multifunctional copolymers exhibited the thermoreversible variation on both volume and photoluminescence intensity.