Cationic photopolymerization of tetrahydrofuran: A mechanistic study on the use of a sulfonium salt-phenothiazine initiation system

Abstract

The kinetics aspects of the photoinitiated polymerization of tetrahydrofuran with triphenylsulfonium hexafluoroarsenate and sensitized by phenothiazine was studied under visible‐light irradiation. A photosensitizer mechanism was proposed involving electron transfer from phenothiazine to the triphenylsulfonium salt, forming a cation radical, the true precursor of the polymerization. An initial complex in the ground state between the phenothiazine and the triphenylsulfonium was formed prior to the excitation, and this complex actually activated the photopolymerization rate. The polymerization conversion presented an S‐shaped curve, suggesting an induction period caused by the existence of two pathways responsible for the beginning of the polymerization. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 46–55, 2001

Selective Controlled/Living Photoradical Polymerization of Glycidyl Methacrylate, Using a Nitroxide Mediator in the Presence of a Photosensitive Triarylsulfonium Salt

“…It was demonstrated that MTEMPO controlled the propagating radical at the chain end as well as the MTEMPO-mediated thermal polymerization based on the fact that the resulting polymer had the MTEMPO moiety at the chain end [11]. The electron transfer from MTEMPO to the onium salt has not been directly proved, however, this mechanism is supported by many electron transfer reactions from the electron donors to the onium salts [27][28][29] and by the electrochemical potentials of TEMPO [30][31][32] and the onium salts [33][34][35].…”

A study of the elemental reactions involved in the initiation of the polymerization of tetrahydrofuran induced by the photosensitization of a triphenylsulphonium salt by perylene

“…16,17 The solution was thoroughly deoxygenated by bubbling oxygen-free nitrogen. The dilatometer was constructed by attaching two capillaries (internal diameter 0.18 cm) to a cylindrical reaction vessel (internal diameter 2.2 cm, volume 8 mL), which was placed in a constant temperature bath (30.00 ± 0.01 o C) in front of the irradiation source.…”

“…24 After the formation of the cation radical of perylene Pery +• only a fraction of the sensitizer is regenerated (the rest will be bound to the polymer, as proved by the presence of perylene groups in the UV spectrum of the polymer), whereas the sulphonium radicals that are not involved in the electron back-transfer are decomposed forming diphenylsulphide and phenyl radicals. 24,17 The presence of larger concentrations of sulphonium salt will result in the formation of additional initiating species due to the photolysis of both the ground state complex [Pery … S + ] o and the non-complexed sensitizer, therefore increasing the polymerization rate. …”

“…The factor r (= 2.57) represents the ratio between the static quenching rates by the monomer and the sulphonium salt, and accounts for the excited Pery singlets that effectively lead to the initiation of polymerization. 5,17 Its value is calculated from the experimental quenching rate constants shown in Table 1.…”

“…Similar mechanistic studies were already reported for the cationic photopolymerization of THF by sulphonium salts sensitized by thioxanthone 16 and phenothiazine. 17 …”