Synthesis and cationic photopolymerization of monomers based on nopol

Starting with nopol [(R)‐(−)‐2‐(2′‐hydroxyethyl)‐6,6‐dimethyl‐8‐oxatricyclo[3.1.1.1^2,3]octane, I] as a substrate, two new, interesting monomers, allyl nopol ether epoxide III and nopol 1‐propenyl ether epoxide IV, were prepared. The photoinitiated cationic polymerizations of these two monomers as well as several other model compounds were studied using real‐time infrared spectroscopy. Surprisingly, the rates of epoxide ring‐opening polymerization of both monomers were enhanced as compared to those of the model compounds. Two different mechanisms which involve the free radical induced decomposition of the diaryliodonium salt photoinitiator were proposed to explain the rate acceleration effects. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1199–1209, 1999     

Interaction of epoxy and vinyl ethers during photoinitiated cationic polymerization

A kinetic study of the independent and simultaneous photoinitiated cationic polymerization of a number of epoxide and vinyl (enol) ether monomer pairs was conducted. The results show that, although no appreciable copolymerization takes place, these monomers undergo complex interactions with one another. These interactions are highly dependent on the epoxide monomer employed. In all cases, the rate of epoxide ring-opening polymerization is accelerated, whereas that of the vinyl ether is depressed. When highly reactive cycloaliphatic epoxides are subjected to photoinitiated cationic polymerization in the presence of vinyl ethers, the two polymerizations proceed in a sequential fashion, with the vinyl ether polymerization taking place after the epoxide polymerization is essentially complete. A mechanism involving an equilibration between alkoxy-carbenium and oxonium ions has been proposed to explain the results. In addition, the free-radical-induced decomposition of the diaryliodonium salt photoinitiator also takes place, leading to a decrease in the induction period. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 4007–4018, 1999     

The synthesis and cationic photopolymerization of monomers based on dicyclopentadiene

Several new epoxide monomers based on dicyclopentadiene (DCPD) were prepared using straightforward reaction chemistry. Those monomer-bearing groups in addition to the epoxy moiety, which can stabilize free radicals, display a pronounced acceleration of the rate of cationic ring-opening polymerization in the presence of diaryliodonium salt photoinitiators. Mechanistic studies conducted with the aid of model compounds have shown that the apparent rate acceleration is due to the free radical chain-induced decomposition of the photoinitiator. One of the chain carriers in this reaction involves a monomer-derived free radical. Also prepared was dicyclopentadiene monomer (V) bearing polymerizable epoxide and 1-propenyl ether groups in the same molecule. The functional groups in V appear to undergo independent vinyl and epoxide ring-opening polymerization. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3427–3440, 1999     

Redox initiated cationic polymerization

A novel catalytic method for carrying out the cationic polymerizations has been developed based on a redox initiator system in which the reducing component is delivered to the reaction mixture in the vapor state. The redox couple consists of a diaryliodonium salt that is dissolved in the monomer and a noble metal catalyst is added. The silane reducing agent is introduced to the reaction mixture in the vapor state using air as the carrier gas. Reduction of the diaryliodonium salt by the silane results in the liberation of a Brønsted superacid that initiates cationic polymerizations. A study of the effects of variations in the structures of the diaryliodonium salt, the silane, and the type of noble metal catalyst was carried out. In principle, the initiator system is applicable to all types of cationically polymerizable monomers and oligomers including: the ring‐opening polymerizations of such heterocyclic monomers as epoxides and oxetanes and, in addition, the polymerization of vinyl ether monomers such as vinyl ethers. The use of this initiator system for carrying out commercially attractive cross‐linking polymerizations for coatings, composites, and encapsulations is discussed. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1825–1835, 2009     

Synergistic interaction of epoxides and N‐vinylcarbazole during photoinitiated cationic polymerization

A kinetic study was conducted of the independent photoinitiated cationic polymerization of a number of epoxide monomers and mixtures of these monomers with N‐vinylcarbazole. The results show that these two different classes of monomers undergo complex synergistic interactions with one another during polymerization. It was demonstrated that N‐vinylcarbazole as well as other carbazoles are efficient photosensitizers for the photolysis of both diaryliodonium and triarylsulfonium salt photoinitiators. In the presence of large amounts of N‐vinylcarbazole, the rates of the cationic ring‐opening photopolymerization of epoxides are markedly accelerated. This effect has been ascribed to a photoinitiated free‐radical chain reaction that results in the oxidation of monomeric and polymeric N‐vinylcarbazole radicals by the onium salt photoinitiators to generate cations. These cations can initiate the ring‐opening polymerization of the epoxides, leading to the production of copolymers. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3697–3709, 2000     

Dye-sensitized photoinitiated cationic polymerization

Several dyes have been discovered which sensitize the photolysis of diaryliodonium salts at visible wavelengths. By using the combination of a dye and a diaryliodonium salt, visible light can be used to photoinitiate cationic polymerization. In this article, the dye-sensitized photopolymerizations of cyclohexene oxide, epichlorohydrin, and 2-chloroethyl vinyl ether are described.     

Supramolecular diaryliodonium salt‐crown ether complexes as cationic photoinitiators

Diaryliodonium salts spontaneously form crystalline 1:1 supramolecular complexes at room temperature in good to excellent yields with 18‐crown‐6 ether and its cyclohexano‐ and benzo‐substituted analogs. The complexes were characterized using IR, UV, MS, ¹H, and ¹³C‐NMR spectroscopy and by single crystal X‐ray crystallography. The analytical data obtained were consistent with a structure in which the positively charged iodine atom of diaryliodonium cation is positioned above and over the center of the crown ether ring with the positively charged iodine atom coordinated to the crown ether oxygen atoms. The diaryliodonium salt‐crown ether complexes are photosensitive and were used to carry out the photoinitiated cationic polymerizations of a number of mono‐ and difunctional monomers. During irradiation with UV light, the supramolecular complexes undergo photolysis with the generation of a Brønsted acid and with the concomitant release of the crown ether. When used as photoinitiators, the crown ether that is released markedly influences the kinetics of the subsequent cationic polymerization of the monomer. Further studies demonstrated that the photolysis of diaryliodonium salt‐crown ether supramolecular complexes can be photosensitized using typical‐electron transfer photosensitizers. Free radical‐promoted photosensitization using typical unimolecular free radical photoinitiators such as 2,2‐dimethoxy‐2‐phenylacetophenone also takes place readily. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

A new visible light sensitive photoinitiator system for the cationic polymerization of epoxides

This communication reports the development of an efficient three‐component visible light sensitive photoinitiator system for the cationic ring‐opening photopolymerization of epoxide monomers and epoxide functional oligomers. The photoinitiator system consists of camphorquinone in combination with a benzyl alcohol to generate free radicals by the absorption of visible light. Subsequently, the radicals participate in the free radical chain induced decomposition of a diaryliodonium salt. The resulting strong Brønsted acid derived from this process catalyzes the cationic ring‐opening polymerization of a variety of epoxide substrates. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 866–875, 2009     

Photoinitiated cationic polymerization of limonene 1,2‐oxide and α‐pinene oxide

Limonene 1,2‐oxide (LMO) and α‐pinene oxide (α‐PO) are two high reactivity biorenewable monomers that undergo facile photoinitiated cationic ring‐opening polymerizations using both diaryliodonium salt and triarylsufonium salt photoinitiators. Comparative studies showed that α‐PO is more reactive than LMO, and this is because it undergoes a simultaneous double ring‐opening reaction involving both the epoxide group and the cyclobutane ring. It was also observed that α‐PO also undergoes more undesirable side reactions than LMO. The greatest utility of these two monomers is projected to be as reactive diluents in crosslinking photocopolymerizations with multifunctional epoxide and oxetane monomers. Prototype copolymerization studies with several difunctional monomers showed that LMO and α‐PO were effective in increasing the reaction rates and shortening the induction periods of photopolymerizations of these monomers. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Synthesis and cationic photopolymerization of 1‐butenyl and 1‐pentenyl ethers

Several 1‐butenyl and 1‐pentenyl ether monomers were prepared by the ruthenium catalyzed multistage double bond isomerization of the corresponding 3‐butenyl and 4‐pentenyl ethers and characterized. Employing tris(triphenylphosphine)ruthenium(II) dichloride as a catalyst, the isomerization of octyl 4‐pentenyl ether to octyl 1‐pentenyl ether in 60% yield could be achieved in 110 min at 200–205°C. Under similar conditions, 3‐butenyl octyl ether was isomerized to 1‐butenyl octyl ether in greater than 99% yield. The reactivities of both types of monomers in photoinitiated cationic polymerization were determined using real‐time infrared spectroscopy and the monomers were found to polymerize at very nearly the same rate in the presence of a diaryliodonium salt photoinitiator. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 199–209, 1999     

Photoinduced and thermally induced cationic polymerizations using S,S‐dialkyl‐S‐(3,5‐dimethylhydroxyphenyl)sulfonium salts

A study of the photoinitiated and thermally initiated cationic polymerizations of several monomer systems with S,S‐dialkyl‐S‐(3,5‐dimethylhydroxyphenyl)sulfonium salt (HPS) photoinitiators bearing different lengths of alkyl chains on the positively charged sulfur atom has been conducted. HPS photoinitiators are capable of photoinitiating the cationic polymerization of a wide variety of epoxy and vinyl ether monomers directly on irradiation with short‐wavelength UV light. Aryl ketone photosensitizers are effective in extending the spectral response of these photoinitiators into the long‐wavelength UV region. Kinetic studies with real‐time infrared spectroscopy show that HPS photoinitiators exhibit good efficiency in the polymerization of epoxide and vinyl ether monomers. Comparative studies also demonstrate that S,S‐dimethyl‐S‐(3,5‐dimethyl‐2‐hydroxyphenyl)sulfonium salts are more active photoinitiators than their isomeric S,S‐dimethyl‐S‐(3,5‐dimethyl‐4‐hydroxyphenyl)sulfonium salt counterparts. Both types of HPS photoinitiators display reversible photolysis as a result of facile termination reactions that take place between the growing chains ends with the photogenerated sulfur ylides. Preliminary studies have shown that HPS photoinitiators can also be employed as thermal initiators for the cationic ring‐opening polymerization of epoxides at moderate temperatures. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2570–2587, 2003     

Synthesis and Characterization of Bis(Isopropenylphenoxy)Alkanes and Bis(Vinylphenoxy)Alkanes: Two Classes of Highly Reactive,Photopolymerizable Monomers

Abstract

A novel and facile synthesis of difunctional, aromatic vinyl ether analogs is reported. These materials, which are conveniently prepared by the condensation of 4-acetoxystyrene or 4-isopropenylphenyl acetate with α, ω-dihaloalkanes in the presence of base, can be cationically polymerized using diaryliodonium or triarylsulfonium salts as photoinitiators to produce crosslinked polymers. Relative reactivities of the monomers toward cationic polymerization were studied using differential scanning photocalorimetry. The thermal stabilities of the polymers resulting from the photopolymerization of the difunctional, aromatic vinyl ether analogs were studied using thermogravimetric analysis.     

Synthesis of epoxy monomers that undergo synergistic photopolymerization by a radical‐induced cationic mechanism

A series of novel, cycloaliphatic, cationically photopolymerizable epoxide monomers bearing benzyl ether groups were prepared. These monomers display a considerable enhancement in the rate of their cationic ring‐opening polymerizations in comparison with monomers that do not contain such groups. In this article, a synergistic free‐radical mechanism is proposed that accounts for this effect, and supporting evidence is offered for its verification. During UV irradiation of an onium salt cationic photoinitiator, the aryl radicals that are generated abstract labile benzyl hydrogens present in such monomers to generate the corresponding carbon‐centered radicals. Subsequently, these radicals are oxidized to benzyl carbocations by the onium salt via a nonphotochemical chain process. The observed increase in the rate and extent of the cationic ring‐opening polymerization of the epoxide monomers is due to the aforementioned mechanism, which effectively increases the number of reactive cationic species present during polymerization. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3578–3592, 2001     

PHOTOINITIATED CATIONIC POLYMERIZATION OF EPOXY MONOMERS IN THE PRESENCE OF POLY(3,4-EPOXY-1-BUTENE)

ABSTRACT

Hydroxyl-terminated poly(3,4-epoxy-1-butene) (polyEPB) is an interesting and highly useful agent for the acceleration of the photoinitiated cationic ring-opening polymerization of epoxide monomers. Kinetic investigations using real-time infrared spectroscopy have shown that the observed acceleration of the polymerization is due to two independent mechanisms. Crosslinking polymerization of epoxide monomers is accelerated due to an activated monomer mechanism that results in facile chain transfer due to interaction of the terminal hydroxyl groups of polyEPB with the growing oxonium ion chain ends. A second mechanism involving participation of polyEPB in a free radical chain induced decomposition of the onium salt photoinitiator is mainly responsible for the observed acceleration in the rate of polymerization. A large number of polymer-bound carbocationic species are generated by this mechanism that are capable of initiating polymerization of the epoxide monomer.     

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     

Synthesis and Cationic Polymerization of Open-Chain and Cyclic Enol Ethers

Abstract

Several new open-chain and cyclic enol ether monomers were prepared using simple, straightforward procedures. The reactivities of these monomers were compared using both differential scanning photocalorimetry and Fourier transform real-time infrared spectroscopy. In general, these new monomers were found to possess excellent reactivity in photoinitiated cationic polymerization using a diaryliodonium salt photoinitiator.     

Curcumin: A naturally occurring long‐wavelength photosensitizer for diaryliodonium salts

Curcumin, a naturally occurring, intensely yellow dye extracted from the spice turmeric, is an efficient photosensitizer for diaryliodonium salt photoinitiators at wavelengths ranging from 340 to 535 nm. With curcumin as a photosensitizer, it is possible to carry out the cationic photopolymerization of a wide variety of epoxide, oxetane, and vinyl monomers with long‐wavelength UV and visible light. An example of the photopolymerization of an epoxide monomer with ambient solar irradiation is provided. Several other curcumin analogues were synthesized, and their use as photosensitizers is examined. With such photosensitizers, the range of spectral sensitivity can be extended well into the visible region of the electromagnetic spectrum. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5217–5231, 2005     

Redox initiated cationic polymerization of oxetanes

3,3‐Disubstituted oxetane monomers were found to undergo rapid, exothermic redox initiated cationic ring‐opening polymerization in the presence of a diaryliodonium or triarylsulfonium salt oxidizing agent and a hydrosilane reducing agent. The redox reaction requires a noble metal complex as a catalyst and several potential catalysts were evaluated. The palladium complex, Cl₂(COD)Pd^II, was observed to provide good shelf life stability while, at the same time, affording high reactivity in the presence of a variety of hydrosilane reducing agents. A range of structurally diverse oxetane monomers undergo polymerization under redox cationic conditions. When a small amount of an alkylated epoxide was added as a “kick‐start” accelerator to these same oxetanes, the redox initiated cationic polymerizations were extraordinarily rapid owing to the marked reduction in the induction period. A mechanistic interpretation of these results is offered. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1854–1861     

Novel photocurable monomers: The synthesis of difunctional vinyl ethers with a phosphonate group and difunctional 1‐propenyl ethers with a phosphonate group and their photoinitiated cationic polymerization

Phosphorus‐containing vinyl ether monomers and 1‐propenyl ether monomers were prepared by the regioselective addition reaction of glycidyl vinyl ether (GVE) or 1‐propenyl glycidyl ether with diaryl phosphonates with quaternary onium salts as catalysts. The reaction of GVE with bis(4‐chlorophenyl) phenylphosphonate gave bis[1‐(4‐chlorophenoxy methyl)‐2‐(vinyloxy)ethyl]phenylphosphonate in a 68% yield. The structures of the resulting phosphorus‐containing vinyl ether monomers and 1‐propenyl ether monomers were confirmed by IR and ¹H NMR spectra and elemental analysis. Photoinitiated cationic polymerizations of the resulting phosphorus‐containing vinyl ether monomers and 1‐propenyl ether monomers were investigated with photoacid generators. The polymerization of vinyl ether groups and 1‐propenyl ether groups of the obtained monomers proceeded very smoothly with a sulfonium‐type cationic photoinitiator, bis[4‐(diphenylsulfonio)phenyl]sulfide‐bis(hexafluorophosphate), upon UV irradiation. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3105–3115, 2005     

Dibenzophenazine derivatives as visible photosensitizers for diaryliodonium salts

The use of two dibenzo[a,c]phenazine derivatives, 10,13‐bis(2,3‐dihydrothieno[3,4‐b][1,4]dioxin‐5‐yl)dibenzo[a,c]phenazine and 10,13‐bis(4‐hexylthiophen‐2‐yl)dibenzo[a,c]phenazine are reported as photosensitizers for diaryliodonium salt photoinitiators. Novel dyes based on the dibenzo[a,c]phenazine skeleton are shown to be efficient in carrying out the cationic photopolymerizations. Representative examples of different types of monomers including epoxide, and vinyl monomers are polymerized in the presence of the photosensitizers and diphenyliodonium hexafluorophosphate (Ph₂I⁺PF). Polymerizations are initiated at room temperature using long wavelength UV and visible light, and monitored by optical pyrometry. The photopolymerization of an epoxide monomer via solar irradiation is also demonstrated. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011