Photoinitiated ring opening

The photoinitiated ring-opening polymerization of 2-methylene-l,3-dioxe-pane has been demonstrated to occur very efficiently through the mechanism shown in Scheme 6. The products are supposedly very useful industrial photoresists. 

Photoinitiated Ring-Opening Polymerization of Epoxidized Polyisoprene... 

Cationic guar gum, 4 724t Cationic hydroxyethylcellulose, 5 455-456 Cationic initiators, 14 265-273 controlled initiation and, 14 268-269 direct initiation and, 14 270 initiating systems for, 14 266-268 photoinitiation and, 14 270 ring-opening polymerization and,... 

Cafionic photoinitiation is based on the ring opening of the oxirane group. The photoinitiators of practical importance belong to three main classes of compounds diazonium salts, onium (e.g., iodonium and sulfonium) salts, and organometallic complexes, which upon irradiation by UV light decompose and yield an acid catalyst. 

This discovery was employed for the photoinitiated cross-linking of poly(methacrylate) by ring-opening polymerization of a tethered SCB moiety <1999CM3687>. 

Aromatic onium ions are a unique class of onium ions which are photoactive and decompose in the presence of light to generate radical-cations [58]. These radical-cations react with solvent or residual moisture to release protons that initiate cationic polymerization [Eq. (43)]. Thus, aromatic onium ions are used as cationic photoinitiators in both carbocati-onic olefin and ring-opening polymerizations, especially in photocuring and photolithographic processes. 

Photoinitiated epoxy crosslinking is generally based (with one exception on cationic ring-opening polymerization of the oxirane group, yielding polyether structures. 

On the other hand, it has been reported that triarylsulfonium salts are very reactive photoinitiators for the ring opening of epoxy monomers 7J. It was also reported (49) that a coating composed of 4% by weight of triphenylsulfonium hexafluorophosphate in 3,4-epoxy cyclohexyl methyl-3,4-epoxy cyclohexane carboxylate cured in 20 seconds exposure. 

A number of reviews have appeared on the function of different types of photoinitiators and their future development and applications. A number of articles have targeted interest in photosensitive polyelectrolyte diazo systems," pressure sensitive adhesives and coatings, bonding of epoxy resins, electrodeposition materials, heat transfer in thick films, ring opening metathesis and curing for microelectronics. ... 

Photoinitiated cationic polymerization has been the subject of numerous reviews. Cationic polymerization initiated by photolysis of diaryliodonium and triarylsulfonium salts was reviewed by Crivello [25] in 1984. The same author also reviewed cationic photopolymerization, including mechanisms, in 1984 [115]. Lohse et al. [116], reviewed the use of aryldiazonium, diphenyliodonium, and triarylsufonium salts as well as iron arene complexes as photoinitiators for cationic ring opening polymerization of epoxides. Yagci and Schnabel [117] reviewed mechanistic studies of the photoinitiation of cationic polymerization by diaryliodonium and triarylsulfonium salts in 1988. Use of diaryliodonium and sulfonium salts as the photoinitiators of cationic polymerization and depolymerization was again reviewed by Crivello [118] in 1989 and by Timpe [10b] in 1990. 

Photoinitiated Cationic Polymerization of Unusual Monomers Recently, novel monomers and macromonomers (Chart 11.12), namely, benzoxazines, monothiocarbonates, thiophene, and epoxy and vinyl ether functional polymers were reported to undergo photoinitiated cationic polymerization [2,118], Among them, benzoxazine monomers deserves a special attention as they yield thermosets with several excellent characteristics including heat resistance good flame retardance stable dielectric constants low water absorption and perfect dimensional stability. This type of thermosets is also obtained by thermally activated ring-opening polymerization at elevated temperatures without catalysts [19]. 

Photoinitiated cationic ring-opening polymerization of epoxy monomers initiated by onium salts are obviously accelerated by addition of benzyl alcohols [108], The best way to understand how benzyl alcohols are effective in the polymerization is determination of acceleration factor (AF). AF is the ratio of the rate of ring-opening polymerization epoxy in the presence of the benzyl alcohol (Rpa) to the rate of that in the absence of the alcohol (Rp). Notably, [M0]a is the initial concentration of the monomer in the presence of the alcohol, and [Mo]a is in the absence [108],... 

J.H. Ge, M. Trujillo-Lemon, and J.W. Stansbury, A mechanistic and kinetic study of the photoinitiated cationic double ring-opening polymerization of 2-methylene-7-phenyl-l,4,6,9-tetraoxa-spiro[4.4]nonane. Macromolecules 2006, 39(26), 8968-8976. 

Recent review articles on the following topics were published the controversy concerning the cationic ring-opening polymerization of cyclic acetals (213), photoinitiators for cationic polymerization (21A), living polymerization and selective dimerization (215). raacroraonomers (216), and functional polymers and sequential copolymers by carbocationic polymerization (217). 

The ring-opening polymerization of the EPI epoxy groups was followed by IR spectroscopy and shown to proceed rapidly upon UV exposure. The photoinitiated chain reaction can be formally written as follows hv... 

---