Synthesis of multifunctional poly(1-pyrenemethyl methacrylate)-b-poly(N-isopropylacrylamide)-b-poly(N-methylolacrylamide)s and their electrospun nanofibers for metal ion sensory applications

We report the synthesis and characterization of multifunctional triblock copolymers, poly(1-pyrenemethylmethacrylate)-block-poly(N-isopropylacrylamide)-block-poly(N-methylolacrylamide) (PPy-b-PNIPAAm-b-PNMA), and their electrospun (ES) nanofibers for temperature or metal-ion sensing. The triblock copolymers are composed of fluorescent and metal-ion-sensitive PPy, thermoresponsive PNIPAAm, and chemically crosslinkable PNMA segments. Non-crosslinked ES nanofibers are initially prepared using the aforementioned PPy-b-PNIPAAm-b-PNMA triblock copolymers followed by thermal crosslinking. It is found that ES nanofibers prepared from PPy-b-PNIPAAm-b-PNMA can self-assemble to form nano-scale spherical aggregates with PNMA located at the core, PNIPAAm at the center layer, and PPy at the shell. This self-assembly characteristic therefore induces a strong excimer emission between the pyrenyl moieties. The crosslinking process between PNMA blocks is then implemented to stabilize the ES nanofibers since the non-crosslinked ones are metastable objects. The resulting crosslinked nanofibers exhibit a predominant wettability and dimension stability under aqueous states, and can perform a detectable photoluminescence transition at different temperatures or toward an Fe3+ ion. In contrast to their counterpart drop-cast film, ES nanofibers with a high surface/volume ratio have obviously higher sensing ability toward thermal stimuli and metal ions, and are expected to be applied as multifunctional sensory devices.