Photoinitiated cationic oligomerization of terminal and internal epoxides

The iodonium salt‐catalyzed, photoinduced cationic oligomerization of terminal and internal monoepoxides from oleochemical as well as the petrochemical origin was studied. The ring‐opening of terminal epoxides (1,2‐octene oxide, phenyl glycidyl ether, 9,10‐epoxy decanoic acid methyl ester and 10,11‐epoxy undecanoic acid methyl ester) predominantly led to macrocyclic oligoethers (M_n = 650—1,100 g/mol) via backbiting in quantitative yields. Mixtures of cyclic and bishydroxy‐terminated oligoethers (M_n = 1,050—1,500 g/mol) were achieved by the conversion of internal epoxides (7,8‐tetradecene oxide and cis‐9,10‐epoxy octadecanoic acid methyl ester) in yields of 80—95%. Macrocyclization was completely suppressed by addition of 20 mol‐% water or ethylene glycol receiving diol‐oligoethers for potential application as soft segments for polyurethanes with molecular weights of approximately 1,300 g/mol.     

光引发阳离子聚合及其在环氧树脂固化研究中的进展

从光引发阳离子聚合的特点、常见阳离子型光敏引发剂及其引发聚合机理、光引发环氧树脂阳离子聚合体系及发展前景等几个方面进行了简要概述。     

Synthesis of novel sulfonium salts and cationic polymerization of epoxides and vinyl ether

Novel 1‐methoxycarbonylethylmethylphenylsulfonium salts with nonnucleophilic anions, namely, hexafluorophosphate, hexafluoroantimonate, and tetrafluoroborate, were synthesized by the reaction of 1‐methoxycarbonylethylphenylsulfide and dimethyl sulfate followed by anion exchange with potassium hexafluorophosphate, sodium hexafluoroantimonate, and sodium tetrafluoroborate, respectively. The cationic polymerization (photopolymerization and thermal polymerization) of epoxy and vinyl ether monomers was carried out to demonstrate the applicability of the newly synthesized sulfonium salts. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3157–3163, 2007     

Novel dibenzocycloheptenyl phosphonium salts as thermolatent initiator in cationic polymerization

In this study, novel thermolatent cationic initiators based on dibenzocycloheptenyl phosphonium salts ( 1a , 1b , 1c , 1d , 2a , and 3a ) were synthesized and their efficiency was examined in bulk polymerization of glycidyl phenyl ether (GPE). The polymerization of GPE was performed with 1 mol % of dibenzocycloheptenyl triphenylphosphonium salts ( 1a – 1d ) with different counter anions (SbF₆^?, PF₆^?, AsF₆^?, and BF₄^?) at 25–200°C for 1 h. The order of initiator activity was found as 1a > 1d > 1b > 1c . To examine the effect of phosphine moiety, the activity of 1a was compared with dibenzocycloheptenyl‐tri‐n‐butylphosphonium hexafluoroantimonate ( 2a ). The order of initiator activity was observed as 1a > 2a. The initiator activity of 1a was compared with that of 10,11‐dihydro‐dibenzocycloheptenyltriphenylphosphonium hexafluoroantimonate ( 3a ) to understand the effect of extended conjugation in dibenzocycloheptenyl ring. In general, with the increase in the polymerization temperature, conversion (%) also increases. The solubility of initiators in various solvents and epoxy monomers was also examined. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Carbazole‐bound ferrocenium salt as an efficient cationic photoinitiator for epoxy polymerization

The low absorption of cyclopentadienyl‐Fe‐cumene hexafluorophosphate (I‐261) above 300 nm limits its utilization of longer wavelength emission from light sources. We report here the synthesis and photoactivity of a carbazole‐bound ferrocenium salt, cyclopentadienyl‐Fe‐carbazole hexafluorophosphate ([Cp‐Fe‐carbazole]⁺PF₆^?), which efficiently absorbs radiation between 300 and 400 nm. Its photoactivity is higher than that of I‐261 as a cationic photoinitiator. When the photosensitizer benzoyl peroxide (BPO) is employed, [Cp‐Fe‐carbazole]⁺PF₆^? can obviously be sensitized. Two other ferrocenium salts with amine groups, cyclopentadienyl‐Fe‐aniline hexafluorophosphate ([Cp‐Fe‐aniline]⁺PF₆^?) and cyclopentadienyl‐Fe‐p‐methylaniline hexafluorophosphate ([Cp‐Fe‐p‐methylaniline]⁺PF₆^?) were also studied. As photoinitiators, they perform poorly and can not be sensitized by BPO. Copyright © 2005 Society of Chemical Industry     

Photoinitiated cationic polymerization of epoxides

Difunctional epoxy monomers have been polymerized cationically by UV irradiation in the presence of a triarylsulfonium photoinitiator. The curing process was followed quantitatively by monitoring the disappearance of the epoxy group by infrared spectroscopy and the insolubilization and hardening of the resin upon UV exposure. The addition of epoxidized soyabean oil (ESO) to an aromatic diepoxide was shown to accelerate the crosslinking reaction with formation of a tight polymer network. The photoinitiated copolymerization of ESO with a cycloaliphatic diepoxide proceeds extensively and leads within seconds to a fully cured insoluble material showing increased hardness, flexibility and scratch resistance. Interpenetrating polymer networks have been generated by a short UV‐irradiation of blends of acrylate and epoxy monomers. © 2001 Society of Chemical Industry     

Photoinitiated cationic polymerization of epoxide and vinyl monomers by p-trimethoxytrityl salts

Photoinitiated cationic polymerizations of cyclohexene oxide, tetrahydrofuran and N-vinylcarbazole were investigated in dichloromethane at 25°C, using stable, soluble and nonhygroscopic p-trimethoxytrityl salts having nonnucleophilic anions such as SbF₆ ⁻, AsF₆ ⁻, PF₆ ⁻, BF₄ ⁻, and SbCl₆ ⁻. The effects of anion, polymerization time, concentration of the salt and the intensity of light on the polymerization reaction are presented.     

Cure kinetics for the ultraviolet cationic polymerization of cycloliphatic and diglycidyl ether of bisphenol‐A (DGEBA) epoxy systems with sulfonium salt using an auto catalytic model

This paper investigates the cure kinetics for the ultraviolet (UV) cationic polymerization for both a cycloaliphatic and diglycidyl ether of bisphenol‐A (DGEBA) epoxy system, using the photoinitiator triarylsulfonium hexafluoroantimonate salt. Using an autocatalytic kinetic cure model, the reaction rate values for both cycloaliphatic and DGEBA epoxy systems were determined for different photoinitiator amount (wt %) added, and at different UV exposure temperatures. The value for the cycloaliphatic epoxy increased significantly with addition of the sulfonium salt, reaching a limiting maximum after 2%. The value for the DGEBA epoxy system also increased, to a limiting maximum after 3%. Addition of the sulfonium salt significantly lowered the activation energy for the cycloaliphatic epoxy at all levels of addition, with the reduction proportional to the amount of salt added. In contrast, the sulfonium salt did not have a major effect on the DEGBA until the addition of at least 3% of the salt. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1587–1591, 2002     

Photoinitiated cationic ring-opening polymerization of a cyclosiloxane

Hexamethylcyclotrisiloxane was found to undergo photoinitiated cationic ring-opening polymerization in solution and bulk, upon exposure to UV radiation, in the presence of either sulfonium or iodonium salts or an iminosulfonate derivative. Glass transition temperatures were below − 100 °C. Molecular weights, determined by size exclusion chromatography relative to polystyrene standards, increased with photolysis lamp intensity. Use of an iodonium photoinitiator afforded poly(dimethylsiloxane) with Mn = 172,000. Polymerization of hexamethylcyclotrisiloxane was accompanied by a small increase in volume (3 – 4%). Received: 12 September 1996/Revised: 29 October 1996/Accepted: 1 November 1996     

Visible light polymerization of epoxy monomers using an iodonium salt with camphorquinone/ethyl‐4‐dimethyl aminobenzoate

A visible light initiator system for the photoinduced cationic polymerization of epoxy monomers is reported. The system consists of camphorquinone (CQ) in combination with ethyl‐4‐dimethyl aminobenzoate (EDMAB) and a diaryliodonium salt (Ph₂ISbF₆.) The three‐component system efficiently photoinitiates the polymerization of monomers containing an epoxycyclohexane group, 3,4‐epoxycyclohexylmethyl 3',4'‐epoxycyclohexane carboxylate (UVR) and 1,3‐bis(3,4‐epoxycyclohexyl‐2‐ethyl),1,1,3,3‐tetramethyldisiloxane (SIB), under irradiation with blue light (λ = 467 nm). Very rapid photopolymerization resulted from irradiation of SIB containing Ph₂ISbF₆ in combination with CQ and better results were obtained in the presence of EDMAB. On the other hand, no polymerization was detected after irradiation of UVR photoactivated with Ph₂ISbF₆ and CQ. However, this monomer polymerized readily and to high conversion when EDMAB was present. Moreover, almost complete conversion of UVR occurs in the absence of external heating. The polymer resulting from UVR displayed higher values of compressive and flexural properties than the polymer prepared from SIB. This is explained in terms of a higher density of crosslinking points in UVR which is accompanied by a lower content of non‐reacted monomer; this has a plasticizing effect on the hardened material. © 2013 Society of Chemical Industry     

Living cationic polymerization of isobutyl vinyl ether (II): Photoinduced living cationic polymerization in a mixed solvent of toluene and diethyl ether

A new method of preparation of living cationic polymer of isobutyl vinyl ether via photoinduced polymerization in the presence of diphenyliodonium iodide (DPII, initiator) and zinc iodide in a mixed solvent of toluene/diethyl ether, which was irradiated at ?78°C for short period, was completed within 15 min. The reaction was allowed for further reaction in the dark until monomer was fully consumed. It was found that increase in the conversion of monomer to polymer during the irradiation is very limited. Confirmation of the linear dependence of number‐average molar mass of resulting polymer on % conversion together with the fact that polymerization proceeds until monomer consumption, and controllability of number‐average molar mass of resulting polymer, depending on the molar ratio of monomer and initiator, strongly suggests the living nature of this polymerization, unless reaction temperature becomes higher than 0°C, i.e., the absence of chain breaking process. The narrow molar mass distribution, whose polydispersity index values are less than 1.2, reveals that the rate of initiation where irradiation is usually completed within 15 min is much faster than that of propagation in cationic nature in this system. Effect of some major factors, such as solvent polarity and temperature, on the living nature of the polymerization was also investigated. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3581–3586, 2006     

Generation of orthorhombic polyoxymethylene in a cationic polymerization system of trioxane

Orthorhombic polyoxymethylene, which was originally found two decades ago in Italy in a polymerization system of aqueous formaldehyde, has been rediscovered in a cationic polymerization system of trioxane designed to grow needle-like polyoxymethylene single crystals. Besides the single crystals obtained in the liquid phase, it has been known that a thin film bearing a number of particles, up to ～ 1 mm diameter, is formed as a by-product on the inner wall in contact with the gaseous phase. X-ray analysis has now revealed that the particles consist essentially of the orthorhombic crystalline form. The morphology has been investigated and the growth mechanism briefly discussed.     

Synthesis of polyvinyl alcohol stereoblock copolymer via the combination of living cationic polymerization and RAFT/MADIX polymerization using xanthate with vinyl ether moiety

Different types of novel xanthates containing a vinyl ether moiety, S-benzyl O-2-(vinyloxy)ethyl carbonodithioate (Xanthate 1) and S-1-(ethoxycarbonyl)ethyl O-2-(vinyloxy)ethyl carbonodithioate (Xanthate 2) were synthesized. In particular, the Xanthate 2 enabled to design polyvinyl alcohol (PVA) stereoblock copolymer via the combination of living cationic vinyl polymerization and RAFT/MADIX polymerization. For cationic polymerization of isobutyl vinyl ether (IBVE) and tert-butyl vinyl ether (TBVE), the polymerizations were conducted under Xanthate 1-HCl adduct/SnCl₄ and Xanthate 1 or 2-CF₃COOH adduct/EtAlCl₂ initiating system in the presence of ethyl acetate. Both systems proceeded in living polymerization fashion because the calculated M_n of both poly(IBVE) and poly(TBVE) matches with the M_n polymerized assuming that one polymer chain is formed per one molecule of the Xanthate 1 or 2. The resulting poly(TBVE) had a high number average α-end functionality as determined by MALDI-TOF-MS spectrometry. Xanthate 2 is more efficient for the following RAFT/MADIX polymerization of vinyl acetate (VAc). The RAFT/MADIX polymerization of vinyl acetate (VAc) using azobis(isobutyronitrile) (AIBN) at 60 °C was conducted using either poly(IBVE) or poly(TBVE) macro-CTA. The poly(TBVE) macro-CTAs synthesized from the Xanthate 2 were able to polymerize VAc smoothly via RAFT/MADIX polymerization, to prepare well-defined diblock copolymer, poly(TBVE)-b-poly(VAc). The resulting block copolymer was then hydrolyzed using KOH in methanol and followed by acid hydrolysis using HBr gas bubbling. The resulting polymer is inherently stereoblock like copolymer, isotactic rich PVA-b-atactic PVA (iPVA-b-aPVA). From the DSC measurement, the iPVA-b-aPVA has one glass transition at 69.5 °C and two melting points according to iPVA and aPVA at 237.9 and 198.1 °C, respectively. Thus, it can be suggested that the obtained PVA has two different geometries by the combination of living cationic polymerization and RAFT/MADIX polymerization.     

阳离子聚合物粘土稳定剂的合成及性能研究

以二甲胺、环氧氯丙烷为原料,通过缩合聚合反应,合成了阳离子有机聚合物粘土稳定剂。考察了原料配比、反应温度、反应时间对防膨率的影响。结果表明,最佳合成工艺条件为:环氧氯丙烷与二甲胺的摩尔配比为1∶1.2,反应时间5 h,反应温度60℃。粘土稳定剂用量2.0%时,防膨率为87.5%;与KCl或NH4Cl以1∶1复配,用量为4%时,防膨率分别为94.9%,93.2%。粘土稳定剂用量2.0%时,第1次和第2次岩屑回收率分别为82.16%,79.49%;2%聚合物+1%KCl+1%NH4Cl三元复配,第1次和第2次回收率分别为89.66%,86.41%。     

Synthesis of thermoresponsive block and graft copolymers via the combination of living cationic polymerization and RAFT polymerization using a vinyl ether-type RAFT agent

A novel vinyl ether-type RAFT agent, benzyl 2-(vinyloxy)ethyl carbonotrithioate (BVCT) was synthesized for various block copolymers via the combination of living cationic polymerization of vinyl ethers and reversible addition−fragmentation chain transfer (RAFT) polymerization. The novel BVCT–trifluoroacetic acid adduct play an important role to produce well-defined block copolymers, which is both as a cationogen under EtAlCl₂ initiation system in the presence of ethyl acetate for living cationic polymerization and a RAFT agent for blocks by RAFT polymerization. The resulting polymer, poly(vinyl ether)s, by living cationic polymerization had a high number average α-end functionality (≥0.9) as determined by both ¹H NMR and MALDI-TOF-MS spectrometry. In addition, this poly(vinyl ether)s worked well as a macromolecular chain transfer agent for RAFT polymerization. The RAFT polymerization of radically polymerizable monomers was conducted in toluene using 2,2′-azobis(isobutyronitrile) at 70 °C. For example, a double thermoresponsive block copolymer (MOVE₆₁-b-NIPAM₁₅₀) consisting of 2-methoxyethyl vinyl ether (MOVE) and N-isopropylacrylamide (NIPAM) was prepared via the combination of living cationic polymerization and RAFT polymerization. The block copolymer reversibly formed and deformed micellar assemblies above the phase separation temperature (T_ps) of poly(NIPAM) block in water. This BVCT is not only functioned as an initiator, but also acted as a monomer. When BVCT was copolymerized with MOVE by living cationic polymerization, followed by graft copolymerization with NIPAM via RAFT polymerization, well-defined graft copolymers (MOVE_n-co-BVCT_m)-g-NIPAM_x (n = 62–73, m = 1–9, x = 19–214) were successfully obtained. However, no micelle formed in water above T_ps of poly(NIPAM) graft chain unlike the case of block copolymers.     

Photochemically initiated free radical promoted living cationic polymerization of isobutyl vinyl ether

A new photoinitiating system for living cationic polymerization of vinyl ethers such as isobutyl vinyl ether (IBVE) has been reported. The photoinitiating system comprises free radical photoinitiators such as 2,2-dimethoxy-2-phenyl acetophenone (DMPA), benzophenone or thioxanthone, together with an onium salt, such as diphenyliodonium chloride and zinc bromide. In the first step, photochemically generated free radicals are oxidized to the corresponding carbocations which subsequently react with vinyl ether monomer to yield an adduct. In the presence of zinc salt, this adduct initiates living cationic polymerization of IBVE.     

Photoinitiated dispersion polymerization using polyurethane based macrophotoinitiator as stabilizer and photoinitiator

Polyurethane based macrophotoinitiator (PU-PI) had been designed and synthesized, and applied to photoinitiated dispersion polymerization of methyl methacrylate as both photoinitiator and stabilizer, with ethanol/water mixture as reaction medium. Monomer conversion over 90% was achieved within 25 min of UV irradiation at room temperature, and monodisperse PMMA microspheres were obtained. The structure of the microspheres had been analyzed by XPS, showing that about 50% of surface of the microspheres were covered with the stabilizer. PU-PI effectively stabilized the polymeric particles in photoinitiated dispersion polymerization due to the unique stabilization process. The size and size distribution of the microspheres became insensitive to the reaction condition such as stabilizer/initiator concentration, initial monomer concentration and reaction medium. The size of the microspheres obtained changed in the range from 0.88 μm to 1.06 μm at different reaction condition, with polydispersity index as low as 1.011. The research may provide a quick and facile approach to prepare monodisperse microspheres with tailored functional surface.     

Camphorquinone-amines photoinitating systems for the initiation of free radical polymerization

Results of the camphorquinone/hindered piperidines, visible-light photoinduced polymerization of triethyleneglycol dimethacrylate are presented. The effectiveness of piperidines as a coinitiator is compared with a few aliphatic amines and aromatic amines. The main objective in this research was to study the mechanism of photoinitiation of polymerization. Reactive radicals that initiate the polymerization are formed by a mechanism of hydrogen atom abstraction by the triplet state of camphorquinone, mediated by photoinduced electron transfer. The different efficiencies of the aliphatic amines and of the aromatic amines affecting photopolymerization are explained on the basis of the different quenching reactivities of the excited states of camphorquinone.     

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

The 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     

Classical cationic polymerization of styrene in a spinning disc reactor using silica‐supported BF3 catalyst

The carbo‐cationic polymerization of styrene has been studied in a Spinning Disc Reactor (SDR) and the results were compared to those observed in a conventional Stirred Tank Reactor (STR). Addition of styrene to a slurry of silica‐supported boron trifluoride (BF₃/SiO₂) in 1,2‐dichloroethane led to uncontrollable reactions in the STR at monomer concentrations > 25%w/w and initial temperatures of 20–25°C. By comparison, monomer concentrations of 75% w/w were safely and controllably polymerized in the SDR at 40°C to yield polymers with molecular weights comparable to those reported in the literature for polymer prepared at ?60°C. Exceptional heat transfer rates achieved in the SDR are sufficient to deal with the heat evolved when styrene is polymerized at concentrations as high as 75% w/w, the reaction proceeding under essentially isothermal conditions. In the present study, the effects of monomer/solvent feed rates, monomer concentrations, disc size, and disc speed on monomer conversions, polymer molecular weights, and polydispersities achieved in the SDR are investigated. Speculative explanations of the observed results are presented in terms of enhanced mixing effects on the polymerization mechanisms in the SDR. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 8–19, 2006