Photoinitiated cationic polymerization by dialkylphenacylsulfonium salts

Dialkylphenacylsulfonium salts in which the anions are of the general type BF, AsF, PF, and SbF are a new class of useful photoinitiators for cationic polymerization. On irradiation these salts underwent reversible ylid formation with the simultaneous generation of strong Br?nsted acids. The photoinitiated cationic polymerization of a number of monomers with dialkylphenacylsulfonium salts demonstrated the utility of these new photoinitiators.     

Photoinitiated cationic polymerization by triarylselenonium salts

Triarylselenonium salts with complex metal halide anions such as BF, AsF, and SbF have been prepared and have been shown to be efficient photoinitiators of cationic polymerization. The photolysis rates of these compounds were studied and their quantum yields of photolysis were reported. Use of specific triarylselenonium salts in the polymerizations of cyclohexene oxide, epichlorohydrin, and 2-chloroethyl vinyl ether are described.     

Photoinitiated cationic polymerization with triarylsulfonium salts

Triarylsulfonium salts Ar₃S⁺MX with complex metal halide anions such as BF, AsF, PF, and SbF are a new class of highly efficient photoinitiators for cationic polymerization. In this article we describe several synthetic routes to the preparation of these compounds along with their physical and spectroscopic properties. Mechanistic studies have shown that when these compounds are irradiated at wavelengths of 190–365 nm carbon–sulfur bond cleavage occurs to form radical fragments. At the same time the strong Br??nsted acid HMX_n, which is the active initiator of cationic polymerization that takes place in subsequent “dark” steps, is also produced. A study of the parameters that affect the photolysis of triarylsulfonium salts is reported with a measurement of the absolute quantum yields. The cationic polymerizations of four typical monomers—styrene oxide, cyclohexene oxide, tetrahydrofuran, and 2-chloroethyl vinyl ether—with triarylsulfonium salt photoinitiators are described.     

Photoinitiated cationic polymerization with triarylsulfonium salts

Triarylsulfonium salts Ar₃S⁺MX_n⁻ with complex metal halide anions such as BF₄⁻, AsF₆⁻, PF₆⁻, and SbF₆⁻ are a new class of highly efficient photoinitiators for cationic polymerization. In this article we describe several synthetic routes to the preparation of these compounds along with their physical and spectroscopic properties. Mechanistic studies have shown that when these compounds are irradiated at wavelengths of 190–365 nm carbon-sulfur bond cleavage occurs to form radical fragments. At the same time the strong Brϕnsted acid HMX_n, which is the active initiator of cationic polymerization that takes place in subsequent “dark” steps, is also produced. A study of the parameters that affect the photolysis of triarylsulfonium salts is reported with a measurement of the absolute quantum yields. The cationic polymerizations of four typical monomers—styrene oxide, cyclohexene oxide, tetrahydrofuran, and 2-chloroethyl vinyl ether—with triarylsulfonium salt photoinitiators are described.     

Photoinitiated cationic polymerization of monofunctional benzoxazine

The photoinitiated ring‐opening cationic polymerization of a monofunctional benzoxazine, 3‐phenyl‐3,4‐dihydro‐2H‐1,3‐benzoxazine, with onium salts such as diphenyliodonium hexafluorophosphate and triphenylsulfonium hexafluorophosphate as initiators was examined. The structures of the polymers thus formed were complex and related to the ring‐opening process of the protonated monomer either at the oxygen or nitrogen atoms. The phenolic mechanism also contributed, but its influence decreased with decreasing monomer concentration. Thermal properties of the polymers were also investigated by differential scanning calorimetry and thermogravimetric analysis. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3320–3328, 2003     

Photoinitiated cationic polymerization of epoxy alcohol monomers

A series of epoxy alcohols were prepared by simple, straightforward methods. These compounds were very reactive monomers that polymerized rapidly on UV irradiation in the presence of cationic photoinitiators. The kinetics of the cationic photopolymerization of these monomers were studied with diaryliodonium salt photoinitiators and real‐time IR spectroscopy. The rate of epoxide ring‐opening polymerization was enhanced markedly by the presence of the hydroxy group. Using model compounds, the monomers were shown to polymerize via an activated monomer mechanism. Simple epoxy alcohols polymerized to give polymers with a hyperbranched structure. The novel monomers also were observed to accelerate the rate of the photopolymerization of mono‐ and multifunctional epoxides. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 389–401, 2000     

Photoinitiated polymerization of aryl cyclic sulfonium salts

Polymers are produced by direct photolysis of substituted aryl cyclic sulfonium Zwitterionic salts in solution or film. Analysis of zwitterionic monomers via ¹³C NMR, UV, and IR spectroscopy as well as X‐ray diffraction clearly identifies the structures taking part in the photoinduced polymerization in the solid crystalline films. The protonated form of the zwitterionic monomers, however, fails to produce detectable amounts of polymer upon photolysis under any conditions. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 571–584, 2001     

Photoinitiated cationic polymerization of oxetane formulated with oxirane

Photoinitiated cationic polymerization of oxetane, oxirane (epoxide), and a formulation of both was carried out and their reactivity compared. To investigate a formulated system of oxetane and oxirane in photoinitiated cationic polymerization, computational and experimental methods were used. In the computational study, we employed a semiempirical molecular orbital method (AM1). On the other hand, the reactivities of each system were evaluated and compared experimentally by a real-time FT-IR method. The computational study reveals that oxetane seems to polymerize in S_N2 mechanism, but two possibilities, of S_N1 mechanism through the α-cleavage and of S_N2 mechanism through β-cleavage, are implied for oxirane. Using the real-time FT-IR method, the formulation of oxetane and oxirane was proved to possess rather high reactivities of oxetane toward photoinitiated cationic polymerization. The formulated system exhibited slightly lower number-average molecular weight than oxetane but higher than oxirane. These experimental observations are well explained in terms of the calculated reaction paths. © 1995 John Wiley & Sons, Inc.     

Photoinitiated cationic polymerization using o-phthaldehyde and pyridinium salt

The cationic polymerization of cyclohexene oxide (CHO), n-butyl vinylether (BVE), N-vinylcarbazole (NVC), and 4-vinyl cyclohexenedioxide (4-VCHD) is initiated upon UV irradiation (Λ_inc. = 350 nm) of dichloromethane solution containing N-ethoxy-2-methyl-pyridinium hexafluorophosphate (EMP⁺PF₆) and o-phthaldehyde. A feasible initiation mechanism involves formation of biradical by intramolecular hydrogen abstraction of triplet o-phthaldehyde. Oxidation of these radicals by EMP⁺ ions yields protons capable of initiating the cationic polymerization. © 1995 John Wiley & Sons, Inc.     

Diaryliodonium salts as thermal initiators of cationic polymerization

Diaryliodonium salts (I) undergo efficient thermal decomposition in the presence of copper (II) compounds. Such systems can be employed as a novel class of latent thermal initiators for cationic polymerization. An investigation of the mechanism of the reaction demonstrated that the copper (II) compound is first reduced to the corresponding copper (I) compound, which subsequently reduces the diaryliodonium salt. The cationic polymerization of some typical monomers using these new initiators was carried out to demonstrate the scope of their utility.     

Chlorothioxanthone-Onium salts: Efficient photoinitiators of cationic polymerization

The interaction of iodonium, sulphonium, phosphonium, arsonium, selenonium, and heterocyclic nitrogen salts with the excited triplet state of 2-chlorothioxanthone (CTX) has been studied through time-resolved laser spectroscopy. Bimolecular quenching rate constants (k_e) have been measured for the first time. Measuring of the rate constants (k_q) of the quenching reaction by monomers permits the calculation of charge transfer (ø_CT) quantum yields. © 1992 John Wiley & Sons, Inc.     

Photoinitiated cationic polymerization of cycloaliphatic epoxide with siloxane or alkoxysilane functionalized polyol coatings

Polyols were reacted with tetraethyl orthosilicate (TEOS) or 3-isocyanatopropyltriethoxysilane (IPTES) to form siloxane functionalized polyols. The UV-reactivity of these siloxane functionalized polyols were investigated using real-time FT-IR spectroscopy. The reactivity of TEOS modified polyols was dependent on the relative humidity. However, for the IPTES functionalized polyols the effect of relative humidity was dependent on the degree of IPTES functionalization. When the polyols were only partially functionalized with IPTES, the effect of relative humidity was minimal. However, when polyols were fully functionalized with IPTES, the curing was dependent on relative humidity. The siloxane functionalized polyols were formulated with a cycloaliphatic epoxide and cationic photoinitiator. The photo-induced curing kinetics of these cycloaliphatic epoxide/siloxane functionalized polyol coatings were also investigated. Unlike the TEOS functionalized polyols, the addition of IPTES functionalized polyols into the formulation inhibited the curing speed. This inhibition was attributed to the basicity nitrogen of the urethane linkage. The effect of relative humidity on the UV-curing reaction of cycloaliphatic epoxide coatings was lowered by the incorporation of the TEOS functionalized polyols.     

Surface promoted redox cationic polymerization of epoxy monomers catalyzed by silver salts

The first example of a one‐component room temperature curing redox cationic polymerization for metal surfaces is described. A weak Lewis acid (Ag⁺) is used as a latent catalyst to likely generate a much stronger one (Fe²⁺/Fe³⁺ or Cu²⁺) at the bond line interface. Such a process has been demonstrated for 3,4‐epoxycyclohexylmethyl‐3,4‐epoxycyclohexane carboxylate using [Ag(1,5‐cyclooctadiene)₂]SbF₆ with the polymerization monitored most conveniently by fourier transform infrared spectroscopy (FTIR). This system, however, demonstrates a relatively low adhesive strength even following curing for 24 h. Higher bond strengths were achieved using mixtures with other cationically polymerizable monomers (vinyl ethers, tetrahydrofuran (THF), oxetanes). Factors considered for optimization of the rates and extent of reaction were the concentrations of a vinyl ether comonomer and [AgL_n]X, the nature of the counterion (X), and of the ligand (L). The performance of the Ag(I) system was compared to that of Cu(I) and various organic cations and the activity of the redox cationic polymerizations on a range of metallic (iron, copper, and aluminium) and nonmetallic (glass and various plastics) substrates was studied. A relatively high glass transition temperature was recorded for the optimized model system and the bonding strength at elevated temperature (150–200 °C) following a room temperature cure was found to be attractive compared to selected model anaerobic acrylate compositions. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Solvent effect in the cationic polymerization of ethylene oxide by trityl salts

The kinetics of the cationic polymerization of ethylene oxide by trityl salts have been studied in dichloromethane at 285 K and chlorobenzene at 298 K. As previously reported for the same polymerization in nitrobenzene [1] (J. Polym. Sci. Lett. Ed. 21, 885, 1983), the internal order is unity, the paired and unpaired ions having the same reactivity. The lack of dependency of k_p on ε is interpreted as due to solvation of the oxonium ions.     

Direct and sensitized photoinitiated cationic polymerization using pyridinium salts

Results of polymerization and laser flash photolysis studies concerning the direct and indirect photoinitiation of cationic polymerizations using N-alkoxy pyridinium and N-alkoxy quinolinium salts are presented. The indirect action can be based on (a) the generation of carbocations via the oxidation of photochemically produced free radicals and (b) the generation of radical cations via the reaction of electronically excited sensitizers with pyridinium or quinolinium ions. With respect to (a) substituted vinyl bromides were found be an effective source of oxidizable free radicals (vinyl radicals), and regarding (b) singlet or triplet excited states of thioxanthone, anthracene, perylene and phenothiazine, which, in the ground state, strongly absorb light in the 300 to 400 nm range, were found to react rapidly with pyridinium salts.     

Unconventional methods of initiating cationic polymerization using onium salts

Onium salts are latent sources of cationic species that can be released on demand to initiate cationic polymerizations by the application of various external physical and chemical stimuli. This paper will report on the use of several different types of stimuli to provide interesting and useful unconventional methods for initiating cationic polymerizations.     

Photoinitiated polymerization on metal surfaces

Irradiation of acrolein vapors in the presence of films of nickel and other metals results in the formation of thin films of polyacrolein on the metal surface. The polyarcrolein film protects the metal surface from abrasion and corrosion. Polymer growth is more rapid on oxidized vs. unoxidized metal surfaces indicating a role for surface oxide sites in the polymerization process. Several other monomers investigated fail to form adhesive polymer films on metal films, but can be copolymerized with acrolein.