The electron beam-induced cationic polymerization of epoxy resins

The rapid, efficient electron beam-induced cationic polymerization of multifunctional epoxy monomers has been carried out in the presence of diaryliodonium and triarylsulfonium salts. These polymerizations take place at low doses (1–3 Mrad), which make them attractive for commercial applications. The factors that contribute to the high reactivity of these monomers are discussed.     

Study of the cationic photopolymerization kinetics of cyclic acetals

Summary Photocationic polymerization for three cyclic acetals, namely 1,3-dioxolane, 1,3-dioxepane and 1,3,6-trioxocane, respectively, has been studied. Several cationic photo-initiators (diaryliodonium or triarylsulfonium salts, and one arene-metal complex) have been used. Differential scanning photo-calorimetry (DPC) has been employed to record the dependence conversion versus time. DPC thermogrames, in turn, have been utilized to calculate the propagation reaction constants as well as the corresponding activation energies. The values for the propagation constants at 30°C are 1.6·10² L/mol·s for 1,3-dioxolane, using a diaryliodonium salt as photoinitiator, 1.6·10³ L/mol·s for 1,3-dioxepane and 6.1·10³ L/mol·s for 1,3,6-trioxocane, respectively, in the presence of a triarylsulfonium salt as photoinitiator. The activation energies are in the range of 9.6÷19.6 kcal/mole. Received: 19 July 2000/Revised version: 8 November 2001/ Accepted: 8 November 2001     

A study of epoxy resin–acrylated polyurethane semi-interpenetrating polymer networks

Epoxy resin–acrylated polyurethane semi-interpenetrating polymer networks (semi-IPNs) were synthesized containing various ratios of the diglycidyl ether of bisphenol-A (DGEBA)-based epoxy resin and an acrylated aliphatic urethane oligomer. The synthesis was carried out in the presence of a mixture of triarylsulfonium hexafluoroantimonate salts as a dual photoinitiator that initiates both the cationic polymerization of the epoxy resin and the free-radical polymerization of the acrylated urethane oligomer simultaneously, upon irradiation with ultraviolet light. The simultaneous photopolymerization, followed by isothermal differential scanning calorimetry measurements, gave rise to simultaneous semi-interpenetrating polymer networks (semi-SINs). During polymerization, partial inhibition of the cationic polymerization was noticed. This was investigated by determination of the gel content and the infrared spectroscopy of the soluble fraction, after extraction of the synthesized polymer films in a Soxhlet apparatus, and by determination of the network density of investigated systems with thermal mechanical analysis. The compatibility of the components in the semi-IPNs was investigated by dynamic mechanical thermal analysis. It was found that glass transition temperatures are shifted inwardly, which indicated that the epoxy resin–acrylated polyurethane semi-IPNs were compatible. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68:111–119, 1998     

鎓盐类阳离子聚合光引发剂的研究进展

碘鎓盐和硫鎓盐是最重要的和应用最广泛的阳离子聚合光引发剂。本文介绍了几种典型的碘鎓盐和硫鎓盐及其引发机理,并就碘鎓盐和硫鎓盐在增加光引发剂的光敏性、增加光引发剂在光引发阳离子聚合体系中的组分相容性以及在阳离子光引发剂中引入自由基等方面的发展状况进行了综述。     

Synthesis of 1-propenyl ethers and their using as modifiers of UV-cured coatings in radical and cationic polymerization

The 1-propenyl ethers of diols and polyols have recently attracted increasing attention as monomers and comonomers because these compounds undergo UV-photoinitiated polymerization. The synthesis of 1-propenyl ethers via the isomerization of corresponding, readily available allyl ethers catalysed by homogenized transition metal complexes with recycling of catalyst has been described. The properties of UV-cured coatings have been investigated for various compositions containing: the model ether (i.e. 1,4-di(1-propenyloxy)-butane), the unsaturated polyester resin [Estromal 103] or epoxy resin [Epidian 6] and radical (i.e. Irgacure 184) or cationic (i.e. triarylsulfonium salts with metal halide anions: PF₆⁻, SbF₆⁻) initiators. The purified or unrefined (i.e. including 0.05 mol% homogenized ruthenium(II) complex [RuClH(CO)(PPh₃)₃]) 1,4-di(1-propenyloxy)butane were applied as modifiers. The effect of presence of homogenized [RuClH(CO)(PPh₃)₃] in the composition has been discussed.     

Novel visible photoinitiators systems for free-radical/cationic hybrid photopolymerization

Free radical/cationic hybrid photopolymerization of acrylates and epoxides was induced using an initiator system comprised of the dye derivative 5,12-dihydroquinoxalino[2,3-b]quinoxaline or 5,12-dihydroquinoxalino[2,3-b]pyridopyrazine as the sensitizers and hexafluoroantimonate triarylsulfonium salt as the initiators. The curing experiments were carried out in the presence of air and the consumption of each monomer upon VIS-radiation was monitored in situ by real-time infrared spectroscopy. Hardness (H), elastic modulus (E) and the H/E ratio of the coatings obtained by visible-initiated acrylate/epoxide hybrid photopolymerization were determined using nanoindentation. DSC measurements show that the initiator system presented here may produce an interpenetrating polymer network. The pencil hardness of the obtained coatings indicates that the dye/hexafluoroantimonate triarylsulfonium salts systems studied here may have practical applications as visible-light hybrid initiators.     

Novel visible photoinitiators systems for free-radical/cationic hybrid photopolymerization

Free radical/cationic hybrid photopolymerization of acrylates and epoxides was induced using an initiator system comprised of the dye derivative 5,12-dihydroquinoxalino[2,3-b]quinoxaline or 5,12-dihydroquinoxalino[2,3-b]pyridopyrazine as the sensitizers and hexafluoroantimonate triarylsulfonium salt as the initiators. The curing experiments were carried out in the presence of air and the consumption of each monomer upon VIS-radiation was monitored in situ by real-time infrared spectroscopy. Hardness (H), elastic modulus (E) and the H/E ratio of the coatings obtained by visible-initiated acrylate/epoxide hybrid photopolymerization were determined using nanoindentation. DSC measurements show that the initiator system presented here may produce an interpenetrating polymer network. The pencil hardness of the obtained coatings indicates that the dye/hexafluoroantimonate triarylsulfonium salts systems studied here may have practical applications as visible-light hybrid initiators.     

分子内敏化鎓盐的合成及光敏性研究

二芳基碘鎓盐和三芳基硫鎓盐是阳离子聚合的光引发剂和光敏产酸物,但他们在300nm以上的光吸收很低,限制了对紫外光的利用效率。为解决此问题,本文合成了一些新的碘鎓盐和硫鎓盐,并用凝胶时间方法考察了它们的光引发效率。实验结果表明,2-苯硫基甲基,2′,4′-二甲基二苯碘鎓盐和9-蒽丙基,二苯基硫鎓盐具有特别高的光引发效率,这归之于光照时这些鎓盐发生了分子内电荷转移反应,即发生了分子内敏化。9-蒽丙基二苯硫鎓盐分子中的蒽基(An)是电子给体也是敏化基团,光照时可发生如下反应:     

Redox Initiated Cationic Polymerization: Reduction of Triarylsulfonium Salts by Silanes

A novel redox initiator system for carrying out the cationic polymerization of epoxide, oxetane and vinyl ether monomers has been developed. The redox couple is based on a triarylsulfonium salt as the oxidant with an organosilane as the reducing agent. The reaction between these two agents is markedly catalyzed by platinum and palladium complexes. Cationic polymerizations using this redox initiator system were carried out in a conventional manner with neat monomer or under solution conditions. This paper also describes the novel use of a two-component redox system in which the silane is delivered to the monomer sample in the vapor state. Optical pyrometry (infrared thermography) was employed as a convenient method with which to monitor the polymerizations. A study of the effects of variations in the structures of the triarylsulfonium salt, the silane and the type of noble metal catalyst were carried out. The use of this initiator system for carrying out commercially attractive cross-linking polymerizations for coatings, composites and electronic encapsulations is discussed.     

Design of network polymers by photopolymerization

The base and transition metal catalyzed isomerization of allyl and crotyl ethers affords a facile, high yield route to the preparation of a variety of mono-, di-, and multifunctional 1-propenyl and 1-butenyl ethers. Employing this novel method, monomers containing epoxide, ester, ether carbonate and urethane groups can be prepared from their readily available allyl and crotyl precursors. In general, these monomers display very high reactivity in cationic polymerizations. In our work, we have focused on photoinduced cationic polymerizations of these monomers using diaryliodonium and triarylsulfonium salt photoinitiators. To study these very fast photopolymerizations, extensive use of real-time infrared spectroscopy was made. Employing this technique, the effects of monomer and photoinitiator structure on the rates of polymerization were studied.     

Possibilities for photoimaging using onium salts

The recent discovery that the photolysis of certain onium salts produces strong Brønsted acids presents a unique opportunity to design novel photoimaging systems based on these materials. For example, when used as photoinitiators, they can induce the negative image wise cationic polymerization of multifunctional epoxides, vinyl ethers, and lactones. Alternatively, they may be used to catalyze the degradation of hydrolytically sensitive polymers to give positive photoresists. The ability of still other onium salts to generate radical species as well as strong acids has been exploited to develop photoimaging processes which have no parallel in present photoresist technology. The processes consist of simultaneous radical polymerization and acid-induced cationic polymerization. Finally, the recent observation that the onium salts can be dye-sensitized allows them to be responsive to both the ultraviolet and visible regions of the spectrum and to be used with many commercial optical imaging systems.     

Photoinitiated polymerization of vinyl ether-based systems

The photoinitiated polymerization of vinyl ether (VE)-based coatings has been studied by real-time infrared (RTIR) spectroscopy. In the presence of diaryliodonium or triarylsulfonium photoinitiators, the cationic polymerization occurs rapidly upon UV-exposure and continues to proceed upon storage in the dark. Increasing the formulation viscosity by introduction of telechelic VE oligomers was found to have a strong slowing down effect on the UV-curing, because of the reduced mobility of the reactive species. VEs proved to be very effective monomers to achieve a fast and extensive curing of dicycloaliphatic epoxides. Similar polymerization profiles have been recorded by RTIR spectroscopy for the two monomers upon UV-exposure, which argues in favor of a copolymerization process between VEs and epoxides. When associated to electron acceptor monomers, like unsaturated esters or N-substituted maleimides, VEs undergo a radical-type copolymerization upon UV-exposure. For the maleate/VE combination, the two monomers were found to disappear at the same rate, whatever the monomer feed composition. The resulting alternating copolymer was shown to be formed by homopolymerization of a donor/acceptor complex. A similar conclusion was drawn from the kinetic data obtained for the maleimide/VE combination which polymerizes readily upon UV-exposure, even in the absence of any added photoinitiator.     

A new fluidized bed coating process via photo‐initiated cationic polymerization

An ultraviolet (UV) photo‐polymerization particle coating process was developed by coupling the photo‐initiated cationic polymerization with the fluidized bed coating techniques. Unlike the conventional air‐suspension coating in the fluidized bed, the new process employs a UV curable composition instead of a solvent/water‐borne system as a coating material, which has a rapid curing rate and virtually no inhibition to oxygen and moisture. A modified fluidized bed coater equipped with a quartz window allows UV light to penetrate and to initiate the curing of photo‐sensitive polymerizable chemicals coated on the particles. A UV‐curable liquid composed of cycloaliphatic epoxide, oxetane, and triarylsulfonium cationic photo‐initiator was specifically formulated for the fluidized bed particle coating process. A systematic experimental approach including photo‐Differential Scanning Calorimetry, Fourier Transform Infrared Spectroscopy, and tackiness measurements has been developed to characterize the curing mechanism of the cationic UV curable formulations and to optimize the chemical compositions. The effects of the UV curable chemicals, viscosity of coating liquid, and the fluidization operating conditions on the physical properties of coated particles have been thoroughly investigated. Under optimized conditions, this novel process is very efficient as follows: particles can be coated very rapidly with ultra‐thin films of the cured chemicals, with little, if any, formation of particulate agglomeration. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Synthesis and homopolymerization studies of vinylimidazolium salts

The preparations and characterizations of several monomeric vinylimidazolium salts are presented from the quaternizations of 1-vinylimidazole and 2-methyl-1-vinylimidazole with n-alkyl iodides and with dimethyl sulphate. Although vinylimidazolium salts have been reported in the patent literature, many of these salts were not isolated and characterized prior to their polymerization. From the reactions of 1-vinylimidazole with n-alkyl iodides, a homologous series of 3-n-alkyl-1-vinylimidazolium iodides were prepared in which the longer chain derivatives appeared to form micelles in aqueous solution. Dicationic crosslinking agents were also prepared through similar quaternization reactions. All the cationic vinyl monomers were homopolymerized in aqueous solution by free radical initiation. The solution behaviour of the resulting polyions indicated that the longer side-chain polyions had polysoap properties.     

The initiation process in the polymerization of N-vinylcarbazole and 3-1,9-N-vinylcarbazole by trityl salts

Summary The initiation mechanism in the cationic polymerization of N-vinylcarbazole and 3-I,9-N-vinylcarbazole by trityl salts in nitrobenzene, methylene chloride and chlorobenzene has been studied. Spectroscopic studies and molecular weight analysis show that the polymerization mechanism depend on the used solvent.     

Novel piperidinium salts as latent initiators for cationic polymerization of epoxide and vinyl ether

Novel dibenzylpiperidinium salts with nonnucleophilic anions (DBPi‐SbF₆, DBPi‐PF₆) have been prepared as latent cationic initiators. Utility of these salts in the photo and thermal‐induced cationic polymerizations of epoxide and vinyl ether monomer systems has been studied. The new initiator, DBPi‐SbF₆ showed good solubility, high reactivity, and high thermal latency for polymerizations of epoxide and vinyl ether monomers with only 1 wt % of concentration. Cationic polymerization of vinyl ether monomer was significantly faster than epoxide monomer by the synthesized initiators. This article describes the synthesis, characterization, and activity of novel initiators. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Thermal cationic curing with benzylammonium salts

Novel cationic initiators, benzylanilinium salts, were synthesized from benzylchloride and N,N-dimethylaniline followed by exchange of counter anion with SbF₆⁻. Benzylanilinium salts showed thermal latency as initiator in the cationic polymerization of glycidyl phenyl ether. The electrophilic characteristic of the benzyl group of benzylanilinium salts were estimated by the reaction of D₂O using ¹H NMR. The electrophilic characteristics of the benzyl group in benzylanilinium salts depended on the p-substituents (benzyl position in benzylanilinium salts). Cationic curing systems, consisting of benzylanilinium salts and the polymer containing oxirane moieties, were proposed and some properties of films obtained by this systems were evaluated. It was found that cationic curing systems had some better properties, especially resistance to acid, than those of the melamine curing systems and that anilinium salts were more useful than benzylpyridinium salts as the initiators for cationic curing systems for coatings.     

The formation of triarylsulfonium salts through a photochemical route

Summary An original method of synthesizing triarylsulfonium salts through UV light excitation of diphenylsulfides in presence of diphenyliodonium salts is described.Visiting Scientist from the Institute of Photographic Chemistry, Academia Sinica, Beijing, China     

(η6‐N‐alkylcarbazole) (η5‐cyclopentadienyl) iron hexafluorophosphate salts in photoinitiated and thermal epoxy polymerization

(η6‐Carbazole)(η5‐cyclopentadienyl) iron hexafluorophosphate salts (CFS PF₆) are capable of photoinitiating cationic polymerization of epoxy monomers directly upon irradiation with long‐wavelength UV light. To improve the solubility of CFS ferrocenium salts in epoxides, two CFS photoinitiators have been prepared: [cyclopentadiene‐Fe‐N‐buylcarbazole] hexafluorophosphate (C4‐CFS PF₆) and [cyclopentadiene‐Fe‐N‐octylcarbazole] hexafluorophosphate (C8‐CFS PF₆), bearing C4 and C8 alkyl chains, respectively, on the nitrogen atom. Studies with real‐time infrared spectroscopy have shown that C4‐CFS and C8‐CFS photoinitiators exhibit high efficiency in polymerization of 3,4‐epoxycyclohexylmethyl‐3,4‐epoxycyclohexane carboxylate (ERL‐4221) epoxy monomer, but lower efficiency in polymerization of di(2,3‐epoxypropyl)‐3,4‐epoxy‐1,2‐cyclohexanedioate (TDE‐85) epoxy monomer. Benzoyl peroxide (BPO) sensitizer was very effective in improving the photoinitiating activities of CFS in polymerization of both ERL‐4221 and TDE‐85. DSC studies have shown that C4‐CFS and C8‐CFS photoinitiators can also be employed as thermal initiators for the cationic ring‐opening polymerization of epoxides at moderate temperatures. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Ionic graft copolymerization. IV. Polymerization of β-propiolactone by acetic acid,p-toluenesulfonic acid,and their sodium salts

Acetic acid, toluenesulfonic acid, and their salts are used as four representative ionic catalysts for polymerization of β-propiolactone (βPL). They are classified as follows: sodium acetate is an anionic catalyst, acetic acid is a neutral one having more covalent character, sodium toluene sulfonate is a neutral one having more ionic character, toluenesulfonic acid is a cationic one. The neutral catalyst having more covalent nature is hardly dissociated, and therefore the rate of polymerization is quite small; however, dissociated ions consist of a higher neucleophilic anion and a higher electrophilic cation. On the contrary, the neutral catalyst having an ionic bond dissociates more easily, but the formed ions consist of the less reactive anion and cation. Therefore, it is of interest whether β-propiolactone is polymerized by a cationic mechanism or an anionic mechanism by these catalysts. The mechanisms of polymerizations of βPL by these neutral catalysts were studied on the basis of the different behaviors of polymerizations by the four catalysts described above. In the cationic polymerization by toluenesulfonic acid, the rate of polymerization was high, but the conversion reaches a low, limited value. In the anionic polymerization by sodium acetate, the rate of polymerization was high and the degree of polymerization of polymer was the highest. Acetic acid has the lowest catalyst activity and the degree of polymerization is also very small. It was found that the polymerization by sodium p-toluenesulfonate was accelerated in the presence of acrylic acid produced from βPL by hydrogen-transfer reaction.