Diphenyliodonium Hexafluorophosphate Research Articles

Transmission Holographic Gratings Using Siloxane-containing Liquid Crystalline Compounds. Importance of Chemical Structure of Polymer Matrix Components

Siloxane-containing liquid crystalline compounds were found effective to induce distinct phase separation, when combined with multi-functional acrylates, over a wide concentration range from 6 wt % to 20 wt % in the formation of holographic gratings. Use of ring-opening polymerizable bi-functional epoxides as one of the reactive cross-linking matrix component together with penta- or tetra acrylate initiated by 3,3′-carbonylbis(7-diethylaminocoumarin)-diphenyliodonium hexafluorophosphate greatly improved the diffraction efficiency and angular selectivity of the formed grating. Fine gratings with 70% and 78% diffraction efficiency and angular selectivity of about 5° were formed with 10 wt % 4-cyano-4′-{(5-heptamethyltrisiloxan-1-yl)pentyloxy} biphenyl and 4-cyanophenyl 4-{(5-heptamethyltrisiloxan-1-yl)pentyloxy}benzoate using pentaerythrytol pentaacrylate-neopentylglycol diglycidyl ether-tripropylene glycol diacrylate (4:5:1) as the polymer matrix component.

ELECTRON-BEAM CURING CHARACTERIZATION OF EPOXY RESIN SYSTEMS CONTAINING CO-INITIATOR

Electron beam (EB) curing of polymer matrix composites offers many particular advantages compared to conventional thermal curing.There has been a considerable development about the EB curing advanced composites for the use of aerospace and other industries in recent years.Most variety of epoxy resin has been confirmed to possess radiation reactivity and have already become chief resin matrices used in EB curable composites.The influences of initiator variety and concentration on the curing characterizations of epoxy resin system containing co-initiator benzophenone and isopropanol were analyzed.The variation regularities of temperature during the radiation,the gel fraction,damping factor and dynamic modulus of samples were studied.The experimental results indicate that under the same condition of epoxy resin content and absorbed dose,the addition of co-initiator can enhance the gel fraction of system,but the enhanced extent of gel fraction does not increase with the increase co-initiator content,there exists an optimal content of the co-initiator.With the increase of onium salt initiator,the enhanced extent of gel fraction induced by co-initiator will decrease.A temperature peak appears during the radiation,and the influences of co-initiator on the peak temperature and the glass transition temperature are the same as those on the gel fraction.The room temperature modulus and high temperature modulus of cured samples with low content of onium salt initiator have little change before and after the addition of co-initiator.When the diphenyliodonium hexafluorophosphate initiator content is high,the room temperature modulus of samples with co-initiator increases,while the high temperature modulus has little changes.

Design of high-performance holographic gratings using siloxane-containing mesogenic compounds

Abstract Fine holographic gratings were fabricated using siloxane- and mesogen-containing compounds. A grating with 40 % diffraction efficiency was formed with 10 wt % non-liquid-crystalline 4-methoxyphenyl 4-[4-(pentamethyldisiloxanyl)butoxy]benzoate and trimethylolpropane triacrylate. 4-Methoxyphenyl 4-[4-(1,1,3,3,5,5,5-heptamethyltrisiloxan-1-yl)butoxy]-benzoate gave 50 % diffraction efficiency and angular selectivity of 5°. Siloxane-containing liquid-crystalline compounds were also effective in fabricating fine gratings. These compounds induced distinct phase separation over a concentration range from 6 to 20 wt % in the formation of holographic gratings. The use of ring-opening polymerizable bifunctional epoxides as one of the reactive cross-linking matrix components, together with penta- or tetra-acrylate initiated by 3,3'-carbonylbis(7-diethylaminocoumarin)diphenyliodonium hexafluorophosphate, greatly improved the diffraction efficiency. Fine gratings with 70 and 78 % diffraction efficiency and angular selectivity of 5° were formed with 10 wt % 4-cyano-4'-[(5-heptamethyltrisiloxan-1-yl)pentyloxy]-biphenyl and 4-cyanophenyl 4-[(5-heptamethyltrisiloxan-1-yl)pentyloxy]benzoate using pentaerythritol pentaacrylate-neopentylglycol diglycidyl ether-tripropylene glycol diacrylate (4:5:1) as the polymer matrix component.

Photoinduced Polymerization of Thiophene Using Iodonium Salt

AbstractSummary: Thiophene was polymerized by means of UV irradiation using diphenyliodonium hexafluorophosphate as a photoinitiator. An initiation mechanism involving electron transfer from photochemically generated onium radical cations to thiophene was proposed. N‐Ethoxy‐2‐methylpyridinium hexafluorophosphate and triphenylsulfonium hexafluorophosphate were also found to be effective in facilitating the polymerization of thiophene. Polymerization is accompanied with the film formation on the surface of the reaction tube. The photochemically obtained polymers were characterized by FT‐IR, DSC, and SEM analyses and compared with those obtained by oxidative and electrochemical means. Electrical conductivities of the samples were measured by four‐probe technique.Photograph of the polymerization mixture containing thiophene and iodonium salt in CH2Cl2 before (a), after 5 min of irradiation (b), and dried film (c).magnified imagePhotograph of the polymerization mixture containing thiophene and iodonium salt in CH2Cl2 before (a), after 5 min of irradiation (b), and dried film (c).

Photobleaching process of xanthene dyes initiated by N-phenylglycine in the polyvinylalcohol film

The parameters such as quantum yield and molar absorption coefficients of the photoinitiator that are responsible for holographic sensitivity in photopolymer material are investigated with a single beam exposure experiment. The influence of exposure intensity, the concentrations of N-phenylglycine and dye on the photobleaching process of xanthenes dyes are presented. In addition, the effect of diphenyliodonium hexafluorophosphate salt on the quantum yield and molar absorption of xanthene dyes is studied.

Use of N,N‐dimethylaniline end‐functional polymers in photoinduced block copolymerization

AbstractN,N‐Dimethylaniline functional polystyrenes with well‐defined structures and low polydispersities were synthesized by atom transfer radical polymerization of styrene in bulk at 110°C using 4‐(dimethylamino)benzyl 4‐(bromomethyl) benzoate as initiator in conjunction with a cuprous complex [Cu(I)Br/bipyridine]. These polymers were further used in block copolymerization with methyl methacrylate and cyclohexene oxide (CHO) by photoinduced radical and radical‐promoted cationic polymerization routes, respectively. In the former case, macroradical generation was achieved with benzophenone sensitizer by photoexcitation followed by hydrogen abstraction from amino end groups. A visible light initiating system was used in the radical‐promoted cationic polymerization of CHO. The system involves a xanthene dye (erythrosin B) as the sensitizer, an aromatic N,N‐dimethyl amino group and diphenyl iodonium hexafluorophosphate as the radical source and radical oxidizer, respectively. Whereas pure block copolymers were obtained in the free‐radical route, the free‐radical–promoted cationic polymerization yielded both block and homopolymers. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 387–394, 2004

Free radical promoted cationic polymerization by using bisacylphosphine oxide photoinitiators: substituent effect on the reactivity of phosphinoyl radicals

The cationic polymerization of cyclohexene oxide (CHO) was achieved upon UV irradiation (λ=380 nm) of methylene chloride solutions containing a series of bisacylphosphine oxides and onium salts, such as diphenyliodonium hexafluorophosphate (Ph 2I +PF 6 −) or N-ethoxy-2-methylpyridinium hexafluorophosphate (EMP +PF 6 −). A feasible initiation mechanism involves the photogeneration of phosphinoyl radicals and benzoyl radicals in the first step. Subsequent oxidation of phosphinoyl radicals by onium salts yields phosphonium ions capable of initiating the polymerization of CHO. In agreement with the proposed mechanism, the polymerization efficiency was directly related to the reduction potential of the onium salts, i.e. Ph 2I +PF 6 − (E 1/2 red=−0.2 V) was found to be more efficient than EMP +PF 6 − (E 1/2 red=−0.7 V). The variation in reactivity of the different phosphorous radicals was correlated with p-character of the phosphinoyl radical as reflected by the 31P hyperfine coupling constant. The results were compared to a monoacylphosphine oxide, (2,4,6-trimethylbenzoyl) diphenylphosphine oxide, which showed only a low efficiency in promoting cationic polymerization. In addition to CHO monomer, butyl vinyl ether and N-vinyl carbazole were polymerized in the presence of bisacylphosphine oxides and onium salts with high efficiency.

Photoinitiated cationic polymerization of monofunctional benzoxazine

AbstractThe 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

Photoinduced living cationic polymerization of tetrahydrofuran(IV): Syringe method

AbstractThe living nature of cationic poly(tetrahydrofuran), which is generated by the addition of the photolytic products of diphenyliodonium hexafluorophosphate (initiator) via syringe, was investigated in connection with the direct polymerization method in which polymerization of tetrahydrofuran is carried out in the presence of the initiator. Although the living nature of the polymerization (i.e., the linear relationship between the percentage of conversion and the molecular weight of the resulting polymer) is observed in the syringe method because of the absence of chain transfer or termination, unexceptionally, a lower rate of polymerization and higher molecular weights of the resulting polymers were observed in the syringe method when compared with those of the corresponding direct polymerization method. This leads us to the conclusion that the living nature is ascribed to the stabilization of the propagating cationic species due to ion pair formation with the less‐nucleophilic complex metal halide anion (PF), and the decreased rate of polymerization and higher molecular weight in the syringe method is attributed to the partial loss of the activity of the cationic species because of the nucleophilic attack of basic impurities, such as water, introduced to the system in the syringe manipulation. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2082–2087, 2002

Optical microstructures fabricated by femtosecond laser two-photon polymerization

We investigated the feasibility of two-photon absorption (TPA) photopolymerization of methyl methacrylate initiated by a bimolecular system composed of 7-diethylamino-3-(2'-benzimidazolyl) coumarin and diphenyliodonium hexafluorophosphate under the irradiation of a Ti:sapphire femtosecond laser. The TPA cross section of the photosensitizer proved to be about 30×10-50 cm4 s/photon for a laser wavelength of 800 nm and the sensitizer/coinitiator system had a 1.4×105 mJ cm-2 threshold for the photopolymerization of methyl methacrylate. Furthermore, this photopolymer system was demonstrated to fabricate several micro-optical components, such as a half-ellipsoid voxel, a waveguide, a coupler and a grating.

Initial step of anthracene‐sensitized photoacid generation from diphenyliodonium hexafluorophosphate in an epoxy matrix studied by steady‐state and laser‐flash photolyses

AbstractThe anthracene‐sensitized photodecomposition of diphenyliodonium hexafluorophosphate was studied in an epoxy matrix. From steady‐state photolysis, the generation of protons, which are considered to be the actual initiators of the polymerization of epoxides, was confirmed. In addition, 9‐phenylanthracene was detected as a main product from anthracene. From time‐resolved laser‐flash photolysis, a broad absorption band with a peak at about 500 nm was observed that was thought to be due to the precursor of 9‐phenylanthracene. On the basis of these results, we propose electron transfer from anthracene in the excited singlet state to the diphenyliodonium cation as the initial step of photoacid generation. This process is followed by fast chemical reactions, which generate 9‐phenylanthracene and protons, and back electron transfer from the diphenyliodine radical to the anthracene cation radical. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2937–2946, 2001

Two-photon microstructure-polymerization initiated by a coumarin derivative/iodonium salt system

Two-photon polymerization initiated by a bimolecular initiating system composed of 7-diethylamino-3-(2 ′-benzimidazolyl)coumarin and diphenyliodonium hexafluorophosphate was investigated. The photosensitizer has been proven to possess large two-photon absorption cross-section for 800 nm femtosecond laser. The sensitizer/coinitiator system has high photosensitivity for the photopolymerization of methyl methacrylate. This photopolymer system has been demonstrated for fabricating three-dimensional microstructure.

Photo-induced living cationic polymerization of tetrahydrofuran. III. Synthesis of poly(THF-co-3-MTHF)

Poly(3-methyltetrahydrofuran)(3-MTHF) and poly(tetrahydrofuran-co-3-MTHF), having very narrow molecular weight distribution were successfully synthesized via photo-induced living cationic polymerization in the presence of diphenyliodonium hexafluorophosphate. Linear relationship between % conversion and number average molecular weight of resulting poly(3-MTHF) in the polymerization of 3-MTHF, carried out at −22°C, indicates that the 5-membered cyclic oxonium ion, being responsible for the cationic propagation is stabilized by ion pair formation with hexafluorophosphate anion, supplied from the salt. The linear relationship between two parameters, mentioned above was also observed in the copolymerization of 3-MTHF with THF, carried out at 0 and −22°C. The molecular structures including the copolymer composition and average molecular weight and its distribution is determined by reaction parameters such as monomer feed ratio and reaction temperature.

The Near Ultraviolet and Infrared Light Dye-Sensitized Systems and Application to The Photoimaging.

Diphenyliodonium hexafluorophosphate can be sensitized efficiently by the dyes Michael Ketone and NK-2204 and produced H+ which can catalyzed the crossing reaction of the HMMA resin and the m-cresol resin. Therefore, the system composed of Diphenyl iodonium, sensitizer, Michael Ketone or NK-2204, and the HMMA resin and the m-cresol resin can be used in the photoimaging study. The effects of the molar ration of the HMMA resin and the m-cresol resin, the heated temperature and times on the resolution and the halftone dot repetition of the printing plate were carried out.

Photoinduced living cationic polymerization of tetrahydrofuran. II: Synthesis of four-armed star-shaped poly(tetrahydrofuran)

A four-armed star-shaped poly(tetrahydrofuran) (THF) having a pentaerythritol unit at the center of the molecule was synthesized from photoinduced cationic copolymerization of THF and pentaeryithritol tetrakis(3,4-epoxybutanoate) (PETE) in the presence of diphenyliodonium hexafluorophosphate. It was found that the molecular weight of the resulting polymer increases with increasing percent conversion and the rate of cationic polymerization of THF is remarkably increased by the addition of PETE when the concentration of PETE is kept much lower than that of THF. A similar enhancement effect was also observed in the photoinduced cationic polymerization of THF in the presence of epichlorohydrin (ECH). The enhancement effect of ECH and PETE was ascribed to the increased concentration of the cationic propagating species due to a rapid protonation process. The living nature was explained in terms of the stabilization of the cationic growing chain end by ion pair formation. Accordingly, the arm length of the polymer was determined by the molar ratio of THF and PETE. However, the polymer of well-defined structure was only obtainable in the early stage of the reaction because chain transfer to the polymer process plays an important role when the concentration of the polymer becomes high. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2637–2644, 1999

Synthesis of block copolymers by transformation of photosensitized cationic polymerization to stable free radical polymerization

Anthracene-photosensitized cationic polymerization of cyclohexene oxide at λ=350 nm in conjuction with onium salts, namely N-ethoxy-2-methyl pyridinium hexafluorophosphate (EMP +PF 6 −) or diphenyliodonium hexafluorophosphate (Ph 2I +PF 6 −), in the presence of a stable radical, 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO), yielded polymers with alkoxyamine terminal groups. These polymers were found to be efficient initiators for stable free radical polymerization (SFRP) of styrene. IR, 1H-NMR spectral analysis and GPC studies of the obtained polymers show that block copolymers are readily formed as a result of combination of photosensitized cationic and stable free radical polymerization mechanisms.

Photoinduced living cationic polymerization of tetrahydrofuran. I. Living nature of the system and its application to the diblock copolymer synthesis

The living nature of cationic polytetrahydrofuran (THF), photoinduced in the presence of diphenyliodonium hexafluorophosphate (initiator), was investigated. In the bulk polymerization of THF, the linear relationship between percent conversion and the number-average molecular weight of the resulting polymer strongly suggests the living nature of this polymer and this was confirmed by the monomer addition technique, that is, cationic poly(THF) is capable of initiating a newly added monomer. The loss of the living nature of the cationic poly(THF) in a polar solvent, dichloromethane, is explained in terms of the stabilization of the five-membered cyclic oxonium ion, a propagating species of cationic polymerization of THF, by ion-pair formation with a less nucleophilic counterion, hexafluorophosphate. Based on the living nature of cationic poly(THF), a diblock copolymer, composed of THF and N-2-(hydroxyethyl)ethyleneÍimine (HEEI) was synthesized by subsequent monomer addition method; however, it was found that the HEEI block of the compolymer has a nonlinear structure. The factors affecting the structure of the HEEI block are also discussed. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 611–618, 1998

Photopolymerization of unsaturated cyclic ethers

2,3-Dihydro-4H-pyran, DHP, and 2,3-dihydrofuran, DHF, are photopolymerized at ambient temperature with the aid of diphenyl iodonium hexafluorophosphate, Ph 2I +PF 6 − or triphenyl sulfonium hexafluorophosphate, Ph 3S +PF 6 − at λ inc = 310 or 340 nm, respectively. DHP is photopolymerized in bulk with the aid of Ph 2I +PF 6 − and in CH 2Cl 2 solution with the aid of Ph 3S +PF 6 −. The average molar mass of the polymer is low and the propagation involves both C  C bonds and ring-opening. DHF is photopolymerized in CH 2Cl 2 solution using Ph 3S +PF 6 −. The average molar mass of the polymer increases with conversion (living polymerization) and can become high (4 × 10 5 g mol −1). The propagation exclusively involves C  C bonds. Dark polymerization of DHF occurs at ambient temperature upon the addition of Ph 2I +PF 6 −, but Ph 3S + PF 6 − is inert against DHF. DHP does not undergo dark reactions with the two salts.

Acid generation in the thermal decomposition of diaryliodonium salts

Diphenyliodonium tetrafluoroborate and diphenyliodonium hexafluorophosphate have been found to generate up to two equivalents of hydrogen fluoride per equivalent of the iodonium salt by pyrolysis at 239°C in the neat state and at 150°C in the presence of anisole or nitrobenzene. The formation of hydrogen fluoride is presumed to arise by dissociation of hydrogen tetrafluoroborate or hydrogen hexafluorophosphate initially formed, due to the high temperatures, thus giving rise also to the Lewis acids boron trifluoride and phosphorus pentafluoride, respectively. A detailed analysis of the volatile organic products of the decomposition of the diphenyliodonium salts was also carried out. Many products were identified in all of the cases studied. For example, the neat decomposition of diphenyliodonium tetrafluoroborate afforded benzene, fluorobenzene, iodobenzene, the three isomeric iodobiphenyls, biphenyl, three isomeric terphenyls, and one or more of the diiodobiphenyls, iodoterphenyls, and polyaromatics. Among the iodobiphenyls, the ortho and para isomers were found to predominate over the meta isomer. The terphenyl isomers did not exhibit this ortho, para selectivity. It was significant that decomposition of the diaryliodonium salts in anisole suspension did not afford methoxybiphenyls or iodomethoxybiphenyls. An interpretation of these results is presented. © 1996 John Wiley & Sons, Inc.

Cationic photopolymerization under visible laser light: polymerization of oxiranes with coumarin/onium salt initiator systems

The cationic bulk polymerization of oxiranes such as cyclohexene oxide and 4-vinyl cyclohexene dioxide can be induced by light in the visible wavelength range with the aid of an initiator system consisting of an onium salt and a coumarin (appropriate for applications of lasers emitting light between 400 and 500 nm). This was demonstrated by irradiating neat monomers containing either coumarin 153 (C-153) or coumarin 7 (C-7) and isoquinolinium hexafluorophosphate, diphenyliodonium hexafluorophosphate or triphenylsulfonium hexafluorophosphate with a continuous laser beam (λ inc = 488nm). The monomer conversion was limited to ca. 60% due to consumption of the coumarin and insolubility of the onium salt in the polymerizing medium at lower monomer content levels. Initiator fragments were not incorporated into the polymer. In the presence of onium salts, the photolysis of coumarins in the absence of O 2 results in proton formation: /gf(H +) = 1.3 × 10 −2 (C-7) and /gf(H +) = 2.3 × 10 −2 (C-153) and it is concluded that protons play a major role in the initiation of the polymerization.