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
Kinetics of Photocationically Curable Formulations Involving Glycerol Diglycidyl Ether and Phenyl Glycidyl Ether
Kinetic analysis of formulations based on glycerol diglycidyl ether and phenyl glycidyl ether were carried out in the presence of sulfonium salt as initiator at 35 mW cm−2using photo differential scanning calorimeter and the final conversion was found to increase with an increase in phenyl glycidyl ether content. The effects of formulation monomer ratios at three different temperatures were studied. The variations in the observed kinetic parameters can be related to increase in mobility of reactive species with temperature, distance of counter ion from the propagating cationic center, as well as extent of crosslinking reaction which controlled the course and duration of the reaction. The applicability of autocatalytic kinetic model was also evaluated and the system underwent early gelation and the activation energy decreased with an increase in phenyl glycidyl ether content. Analysis of stable photocured films containing glycerol diglycidyl ether and phenyl glycidyl ether showed better thermal stability than rigid films obtained with glycerol diglycidyl ether.
Polymerization of n-butyl vinylether initiated by polymeric peroxycarbamates and active polystyrenes
The free radical promoted cationic polymerization of n-butyl vinylether (BVE) was achieved by thermal decomposition of polymeric peroxycarbamates (PPC) or active polystyrene (APS), having fragments of PPC in the presence of diphenyliodonium hexafluorophosphate (Ph2I+ PF) or silver tetrafluoroborate (AgBF4). Polymerizations were accompanied by phase separation. Formation of block copolymers, mainly in the solid phase, was evidenced by NMR spectroscopy. Polymer samples obtained by this procedure contained only a very small fraction of block copolymer structure due to the phase separation and very effective chain transfer reactions predominating the cationic polymerization of BVE. 
 
 
 
Durch die thermische Zersetzung von polymeren Peroxycarbamaten (PPC) oder von mit Anteilen von PPC aktivierten Polystyrolen (APS) wurde in Gegenwart von Diphenyljodoniumhexafluorophosphat (Ph2I+ PF) oder von Silbertetrafluoroborat (AgBF4) die durch freie Radikale promovierte kationische Polymerisation von n-Butylvinylather (BVE) erreicht. Wahrend der Polymerisation wurde eine Phasenseparation beobachtet. Die im wesentlichen in der festen Phase gebildeten Blockcopolymeren wurden mittels NMR-Spektroskopie nachgewiesen. Die so gewonnenen Polymerproben enthielten infolge dieser Phasenseparation und der bei der kationischen Polymerisation des BVE dominierenden Kettentransferreaktion nur sehr kleine Anteile an Blockcopolymeren.