Wavelength tunability in photoinitiated cationic polymerization
Onium salts, widely used cationic photoinitiators, have absorption in the short wavelength of the UV spectrum. However, their spectral sensitivity can be tuned up to the visible region by using several methods. Photosensitization of onium salts, their charge transfer complex formation and their free radical promotion are some techniques that are used to provide wavelength flexibility. This chapter summarizes these methods. Upon irradiation photosensitizers such as anthracene, perylene and phenothiazine form exciplexes with onium salts generating reactive species via electron transfer. Furthermore, ground state charge transfer formation Correspondence/Reprint request: Dr. Y. Yagci, Istanbul Technical University, Department of Chemistry, Maslak, Istanbul 34469, Turkey. E-mail: yusuf@itu.edu.tr
Highly conjugated visible and near-infrared light photoinitiating systems for radical and cationic polymerizations
Abstract In this communication, we report highly conjugated thiophenes having [1,2,5]-thiadiazolo and [1,2,5]-selenadiazolo [3,4-f]-benzo [1,2,3] triazole in conjunction with diphenyliodonium hexafluorophosphate salt (DPI) as new visible and near-infrared light (NIR) photoinitiator systems for free radical (FRP) and cationic polymerizations (CP). The postulated mechanism is based on the electron transfer reactions between the excited conjugated molecule and DPI ions. The radicals and Bronsted acid formed this way initiate FRP and CP of appropriate monomers such as methylacrylate (MA), methyl methacrylate (MMA), triethylene glycol dimethacrylate (TEGDMA) and cyclohexene oxide (CHO), isobutyl vinylether (IBVE) respectively. The possibility of in situ hybrid polymerization is also demonstrated using bifunctional monomer glycidyl methacrylate (GMA).
Design of a novel optical sensor for determination of trace gadolinium.
In this work, a highly selective and sensitive gadolinium (Gd) optical sensor based on immobilization of bis(thiophenal) pyridine-2,6-diamine (BPD), on a triacetylcellulose membrane has been reported. This optode exhibits a linear range of the Gd(III) ion concentration of 2.5 x 10(-6)M with a detection limit of 0.93 x 10(-8) M. Response time of the newly designed optode was within 1-2 min, depending on the Gd(III) ion concentration. Response of the sensor is independent of solution pH in the range of 2.0-9.0. It manifests advantages of: low detection limit, fast response time, and most significantly, very good selectivity with respect to a number of lanthanide ions (La, Ce, Sm, Tm, Ho, and Eu ions). The sensor was successfully regenerated with thiourea solutions and its response was reversible and reproducible (R.S.D. less than 1.4%). This optode was applied to determine Gd(III) in synthetic and water samples, and validated with certified reference materials (CRMs).