Visible Light-Induced Cationic Polymerization Using Fullerenes

A novel visible light sensitive photoinitiator system for the cationic polymerization of typical monomers, for example, of oxiranes, such as cyclohexene oxide, vinyl ethers, such as iso-butyl vinyl ether, and other vinyl monomers, such as <i>N</i>-vinylcarbazole, using fullerene derivatives is described. The cationic polymerization of these monomers was initiated at room temperature upon irradiation in the visible region (λ_inc > 400 nm) in bulk or chlorobenzene solutions with polystyrene-C₆₀ (PS-C₆₀) adduct or bare C₆₀, respectively, in the presence of oxidizing salts such as silver hexafluorophosphate (AgPF₆) and diphenyliodonium hexafluorophosphate (Ph₂I⁺PF₆^–). A feasible mechanism, as correlated with optical absorption measurements, free energy changes (Δ<i>G</i>), and proton scavenging studies, involves formation of exciplex by the absorption of light in the first step. Subsequent electron transfer from excited C₆₀ or PS-C₆₀ to oxidizing salt yields radical cations of the fullerene derivatives. Both radical cations and a strong Brønsted acid derived by hydrogen abstraction initiate the cationic polymerization of a variety of monomers

Highly Fluorescent Pyrene-Functional Polystyrene Copolymer Nanofibers for Enhanced Sensing Performance of TNT

A pyrene-functional polystyrene copolymer was prepared via 1,3-dipolar cycloaddition reaction (Sharpless-type click recation) between azide-functional styrene copolymer and 1-ethynylpyrene. Subsequently, nanofibers of pyrene-functional polystyrene copolymer were obtained by using electrospinning technique. The nanofibers thus obtained, found to preserve their parent fluorescence nature, confirmed the avoidance of aggregation during fiber formation. The trace detection of trinitrotoluene (TNT) in water with a detection limit of 5 nM was demonstrated, which is much lower than the maximum allowable limit set by the U.S. Environmental Protection Agency. Interestingly, the sensing performance was found to be selective toward TNT in water, even in the presence of higher concentrations of toxic metal pollutants such as Cd²⁺, Co²⁺, Cu²⁺, and Hg²⁺. The enhanced sensing performance was found to be due to the enlarged contact area and intrinsic nanoporous fiber morphology. Effortlessly, the visual colorimetric sensing performance can be seen by naked eye with a color change in a response time of few seconds. Furthermore, vapor-phase detection of TNT was studied, and the results are discussed herein. In terms of practical application, electrospun nanofibrous web of pyrene-functional polystyrene copolymer has various salient features including flexibility, reproducibility, and ease of use, and visual outputs increase their value and add to their advantage