Diphenyliodonium Salt Research Articles

Copolymerization of butyl vinyl ether and methyl methacrylate by combination of radical and radical promoted cationic mechanisms

Butyl vinyl ether (BVE) and methyl methacrylate (MMA) mixtures were polymerized by using free radical initiators in conjunction with a cationic initiator such as diphenyl iodonium salt. Polymerization mechanism involves free radical polymerization of MMA which is switched to cationic polymerization of BVE by addition of growing poly(MMA) radicals to BVE and subsequent oxidation of electron donating polymeric radicals to the corresponding cations by iodonium ions. Two representative bifunctional monomers, ethylene glycol divinyl ether (EGDVE) and ethylene glycol dimethacrylate (EGDMA) were also used together with MMA and BVE, respectively, in photo and thermal crosslinking polymerizations. Vinyl ether and methacrylate type monomers can successfully be copolymerized by this double-mode polymerization under photochemical conditions.

A mechanistic investigation of a three-component radical photoinitiator system comprising methylene blue,N-methyldiethanolamine, and diphenyliodonium chloride

Three-component systems, which contain a light-absorbing species (typically a dye), an electron donor (typically an amine), and a third component (usually an iodonium salt), have emerged as efficient, visible-light-sensitive photoinitiators. Although three-component systems have been consistently found to be faster and more efficient than their two-component counterparts, these systems are not well understood and a number of distinct mechanisms have been reported in the literature. In this contribution, photodifferential scanning calorimetry and in situ, time-resolved, laser-induced, steady-state fluorescence spectroscopy were used to study the initiation mechanism of the three-component system methylene blue, N-methyldiethanolamine and diphenyliodonium chloride. Kinetic studies based upon photodifferential scanning calorimetry reveal a significant increase in polymerization rate with increasing concentration of either the amine or the iodonium salt. However, the laser-induced fluorescence experiments show that while increasing the amine concentration dramatically increases the rate of dye fluorescence decay, increasing the DPI concentration actually slows consumption of the dye. We concluded that the primary photochemical reaction involves electron transfer from the amine to the dye. We suggest that the iodonium salt reacts with the resulting dye-based radical (which is active only for termination) to regenerate the original dye and simultaneously produce a phenyl radical (active in initiation) derived from the diphenyliodonium salt. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2057–2066, 2000

Sensitized Photolysis of Iodonium Salts Studied by CIDNP. Solvent Dependence and Influence of Lipophilic Substituents

The sensitized photoreactions of diphenyliodonium salt and four of its technically relevant derivatives bearing lipophilic substituents were investigated by pseudo-steady-state and time-resolved CIDNP experiments. Singlet (naphthalene, diphenylanthracene, dimethylanthracene) and triplet (xanthone, thioxanthone, Michler's ketone) sensitizers were used in a variety of solvents (acetonitrile, dimethyl sulfoxide, dimethylformamide, methanol, chloroform, tetrahydrofurane, diethylene glycol dimethyl ether, dioxane, toluene). Under all conditions, the primary step leading to CIDNP was found to be electron transfer from the excited sensitizer *Sens to the onium cation On+. All spin-polarization effects could be explained consistently within the framework of radical pair theory (S−T0-type CIDNP). Pair substitution, i.e., the transformation of the primary radical pairs RP 1 into secondary pairs RP 2 ( where Ph• is the phenyl or an aryl radical) plays a key role for the CIDNP effects and even leads to a field dependence of the polarization phases for the system diphenyliodonium cation/naphthalene in dioxane. Decreasing solvent polarity causes an increase of the rate RP 1 → RP 2. The introduction of a long lipophilic side chain into the onium salt has the same effect, presumably owing to self-solvation.

Grating microstructures in photoactive polymers by laser interference patterns

The formation of grating microstructures in new photopolymer formulations are investigated by holographic recording. Holographic recording in cast polymer layers occurs in real-time and in-situ, meaning that no wet-chemical or post-thermal/photochemical processing are required. The hydrophilic photopolymers are based on acrylamide monomers, which are dissolved together with photoactive components, such as the sensitizing dye eosin and the new charge transfer agent diphenyl iodonium (DPI) salt with triethanolamine, in polyvinyl alcohol. The addition of DPI significantly increases the exposure sensitivity from about 35 to 12 mJ/cm 2, i.e. by a factor of about three, without affecting the maximum obtainable diffraction efficiency (DE). The influences on the storage mechanism by other additives, such as cross-linking agents and plasticizers are also investigated. The introduction of the cross-linking agent bisacrylamide stabilizes the formed structures against thermal and environmental relaxations. The introduction of plasticizers have a significant effect on the spatial modulation of the refractive index in the recorded grating patterns. Large enough refractive index modulations can be obtained, so as to yield very high DEs of about 90%. The angular-DE and thickness-DE responses closely follow the theoretical predictions, according to the coupled-wave theory. These photopolymer layers have potential in photonics applications, such as holographic optical elements and waveguide structures.

Efficiency and excited state processes in a three-component system, based on thioxanthene derived dye/amine/additive, usable in photopolymer plates

The excited state interactions occurring when a three-component system of thioxanthene derived dye TXD/amine/additive (diphenyliodonium salt, CBr4, benzoyl peroxide, cumene hydroperoxide) is subjected to sensitization processes in the visible range, were investigated through time-resolved absorption spectroscopy, spectrofluorometry, and photolysis. The rate constants of the various operative processes were measured together with the values of the fluorescence quantum yields (e.g. ϕ f = 0.75 ± 0.07 in methanol) and the lifetimes of the singlet excited state of the dye (e.g. 6 ns in methanol). Singlet state quenching by methyldiethanolamine (MDEA) occurs with a rate constant k = 109 M−1 s−1 in methanol. The reactivity of the triplet excited state of the dye is very low (k = 5.6 × 104 M−1s−1 for the TXD/MDEA interaction). The ketyl radicals that arise from the interaction of the singlet state of the dye with the amine, are quenched by such additives as CBr4 (k = 6.7 × 105M−1s−1), or the onium salts (k = 5.7 × 105M−1 s−1). The calculations of the yields of interaction of the singlet state of the dye with the two components of the system demonstrate that the process of quenching by the amine is the main one (ϕint = 0.5) compared to that by, e.g., an onium salt (ϕint = 0.07). Sensitivity of 0.3 mJ cm−2 obtained in a laser scanning system is also reported. © 1996 John Wiley & Sons, Inc.

Acridinium salt mediated photopolymerization of acrylates and methacrylates with dihydropyridine-iodonium salt combinations

In a photoassisted reaction, by exposure of 9-phenyl-10-methylacridinium salt to blue light ( λ = 405, 436 or 460 nm) in the presence of a 1,4-dihydropyridine derivative as electron donor and diphenyliodonium salt as electron acceptor, phenyl radicals are formed. The phenyl radicals initiate the polymerization of methyl methacrylate in acetonitrile solutions or of bulk multifunctional acrylate monomers usually used in industrial formulations. With bisphenol-A-diglycidylether diacrylate the utilization of the electron donor is not necessary, because this monomer can function as coinitiator in such formulations. The phenoxy molecular structure of the monomer gives rise to an electron transfer reaction responsible for the formation of initiating radicals. Other dyes can also be used as light-absorbing components in such ternary systems. Systems having tetrabromomethane instead of the iodonium salt as electron acceptors exhibit the same polymerization efficiency.

Long wavelength photoinitiated cationic polymerization using diphenyliodonium salt and catena-poly (phenyl-4-phenylphenylsilicon)

The photolysis of catena-poly (phenyl-4-phenylphenylsilicon) at λ inc = 365–400 nm leads to products (probably free radicals) which are oxidized by diphenyliodonium ions. The resulting ionic species is capable of readily initiating the cationic polymerization of tetrahydrofuran, n-butyl vinyl ether, cyclohexene oxide and N-vinylcarbazol.

Triplet state electron transfer pathway for tetrabenzoporphyrin-diphenyliodonium salt photoinitiator system

A triplet state electron transfer mechanism for the photoreaction between meso-diphenyl-tetrabenzoporphyrin (P 2TBP) metallo complexes, e.g. magnesium (1a, MgP 2TBP), zinc (1b, ZnP 2TBP) and cadmium (1c, CdP 2TBP), and diphenyliodonium (DPI) salt was confirmed by the detection of the cation radicals of P 2TBP using nanosecond laser flash photolysis equipment, as expected from the estimation of the free energy changes (ΔG T). Rate constants ( T k q) of the triplet state quenching of metallo P 2TBP complexes by DPI, determined from the slopes of Stern-Volmer plots, approximately obeyed a diffusion-controlled limit in accordance with fully exothermic ΔG T values. Since the fluorescence of the magnesium and zinc complexes was quenched by DPI at high concentrations (above 10 −3 M), as previously reported, both excited states were deactivated by the onium salt, depending on its concentration. However, it was presumed that a triplet state electron transfer pathway was preferred for the cadmium complex because of its short fluorescence lifetime.

Positive working resists sensitive to visible light, I: poly(tert‐butyl and 2‐phenylpropyl‐2 methacrylates) sensitized with diphenyliodonium salt — p‐aminobenzylidene dye system

AbstractVisible‐light‐sensitive positive type resists have been developed. The chemistry to form images is based on the cleavage of side chain ester bonds of poly(methacrylates) catalyzed by an acid which is generated on sensitized photodecomposition of a diphenyliodonium (DPI) salt. Homopolymers and copolymers of tert‐butyl methacrylate (BMA) and 2‐phenylpropyl‐2 methacrylate (PPMA) were used as acid labile polymers. Exposure of thin films of the poly(methacrylates) containing DPI salt and p‐dimethylaminobenzylidene derivatives to an Ar laser beam emitting 488 nm light and subsequent heat treatment resulted in solubility alteration of the polymers, which became soluble in a protic solvent system. Considerable reduction of film thickness was observed after heating an image‐wise exposed thin film of PPMA polymers. The minimum exposure energies of 488 nm light for the positive image formation were 60 mJ/cm2 and 40 mJ/cm2 for BMA and PPMA homopolymers, respectively.

Photoinitiation system for holographic recording material.

Some p-N, N- dimethylamine and diethylamine substituted benzal ketone derivatives (ABK) are used as a new class of sensitizer for laser light induced radical photopolymerization of N-vinyl carbazole (NVC) and methacrylic acid benzal ester (MABE) by combination with diphenyliodonium salt (DPIO). The relative efficiency of various ABK for polymerization of NVC and MABE to record holograms is in the order DEBP>DABA>ABA. An argon ion laser (488nm) is used for exposure. Trichromatic filters were made with the material.

Primary processes in the photosensitized polymerization of cationic monomers

AbstractA detailed time‐resolved laser spectroscopy investigation has been carried out on the electron transfer reactions of substituted thioxanthone derivatives with diphenyliodonium (Ph‐I+) salts having different metal halide counterions (MX−n). Quenching of thioxanthones' triplet state has been followed under various conditions, by changing the number and nature of substituents on the thioxanthone skeletone, using anion with different nucleophilicity and employing different solvents, namely methanol and acetonitrile. A Photosensitization mechanism is proposed involving an electron transfer from thioxanthone to diphenyliodonium salt. The absorption spectra of the thioxanthone's excited state and the formed new transient are recorded and the rate constants of the excited state processes are measured. The triplet state of thioxanthone derivatives has been quenched by cationically polymerizable monomers and the quantum yield of the major processes has been evaluated. Photolytic experiments have been performed to measure the extent of acid formation. Form photopolymerization experiments using different photoinitiating systems, the rate of polymerization and percentage of monomer conversion have been determined. Both the reactivity in the excited states and the nucleophilicity of the anions affect the efficiency of the photopolymerization reaction.

A new electron transfer sensitized initiation system for visible light, induced photopolymerization: p-N, N-dimethylaminobenzal ketone/diphenyliodonium salt system.

Some p-N, N-dimethylamine substituted benzal ketone derivatives(ABK) are used as a new class of sensitizes for visible light induced radical photopolymerization of methylmethacrylate (MMA) by combination with diphenyliodonium salt (DPIO). The electron-transfer sensitized photolysis of DPIO- DABA system was studied by spectroscopy and rate of radical photogeneration was determined to be 94.59 (mol.l-1 s-1), The relative efficiency of various ABK for polymerization of MMA is in the order DABA>DABP>ABA. The polymerization rate was proportional to [DPIO]0.37 [DABA]0.16 and [MMA]1.0. Photopolymerization was retarded by oxygen indicating a radical mechanism. Effect of several additives on the polymerization revealed that some heterocyclic thiol compounds exhibit significant role of rate acceleration.

Synthesis and reactivity of some diaryliodonium salts for photoresist application.

Diaryliodonium and triarylsulfonium salts with non-nucleophilic metal halide anions are well known photoinitiators for cationic polymerization as well as photosensitive super acid generators, and play an important role in the chemical amplificated resists. Generally, photosensitizer is required to enhance the spectral response of resists or polymerization systems into the longer wavelength region, due to the low absorptivity of the simple diphenyliodonium salts at above 300nm. In order to circumvent the need for a second component, auxochromic or other groups were incorporated into the iodonium salt molecule which can increase or shift the absorptivity to longer wavelengths. Therefore, a number of new unsymmetrical iodonium salts of general structure(I) were prepared by us by modifying a method already reported. The photoactivity of these iodonium salts were investigated by gel time study. The results indicated that the iodonium salts incorporated with auxochromic groups exhibited higher photoactivity than that of diphenyliodonium salt. The 2-phenylsulfur methhyl 2′, 4′dimethyl diphenyliodonium salt showed the highest activity and an intramolecular electron transfer mechanism was proposed to explain the unexpectedly high activity.

Photosensitive resins containing p‐dimethylaminobenzylidene derivatives and diphenyliodonium salt as photoinitiators

AbstractA series of p‐dimethylaminobenzylidene derivatives was able to sensitize the photodecomposition of diphenyliodonium salt to afford highly photosensitive negative‐type resins. When a polymer‐bearing methacryloylated group in the side chain was sensitized with a combination of the p‐dimethylaminobenzylidene compounds and the iodonium salt, the polymer demonstrated high sensitivity even to 488 nm light emitted from an Argon laser. The same photoinitiator systems were applicable to insolubilize poly(glycidyl methacrylate) through cationic photopolymerization. The storage stability of these types of photoinitiators depends on the structure of the benzylidene compounds; decreasing the basicity of the amino group enhanced the thermal stability.

Synthesis, structure, and chemistry of ligating dichlorodiazomethane. The crystal and molecular structures of [WBr(dppe)2N2CCl2]+[PF6]–and [WBr(dppe)2{N2C(Cl)C(CN)2}]·CH2Cl2

A complex of dichlorodiazomethane, [WBr(dppe)2N2CCl2]+[PF6]–, which is formed by reaction of [WBr(dppe)2N2H2]+Br– with CXCl3(X = Br or H) in the presence of a diphenyl iodonium salt and aqueous base, undergoes rapid reaction with nucleophiles to give a range of novel organodinitrogen complexes; the molecular structures of the parent dichlorodiazomethane complex, and its reaction product with dicyanomethanide ion (a vinyl diazenido complex), were determined by single-crystal X-ray analysis.