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     

The role of solvent‐ligated metal(II) complexes incorporating (fluoroalkoxy)aluminates as weakly coordinating anions in isobutylene polymerization

Nitrile‐ligated copper(II) and zinc(II) complexes comprising (fluoroalkoxy)aluminates as weakly coordinating anions (WCAs) have been synthesized and applied for the polymerization of isobutylene at room temperature (30°C). The polymers obtained are in the low and moderate molecular weight range and show characteristics of the highly reactive polyisobutylene. Results indicate that the fluoroalkoxy aluminate WCAs have even a higher tolerance toward water in IB polymerization than the earlier tested perfluoroborate WCAs. Studies showed that water plays an important role in the polymerization process, which indicates a polymerization mechanism similar to a proton‐initiated carbocation polymerization. The role of the WCAs and their importance for the room‐temperature polymerization process was re‐examined, and the effect of the addition of proton and electron donors including proton traps (2,6‐di‐tert‐butyl‐4‐methylpyridine or DTBP) was studied in detail. The polymerization reaction seems to be dominated by transfer reactions that lead to the high content of exo double bonds while propagation proceeds via conventional cationic polymerization. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Dual photo‐ and thermally initiated cationic polymerization of epoxy monomers

Selective inhibition of the photoinitiated cationic ring‐opening polymerization of epoxides by dialkyl sulfides has provided dual systems that can be “activated” by UV irradiation and then subsequently be polymerized by the application of heat. It is proposed that dialkyl sulfides terminate the initial or growing polyether chains at an early stage to form stable trialkylsulfonium salts. These systems are dormant at room temperature but on thermolysis, the sulfonium salts are capable of reinitiating ring‐opening polymerization. These dual photo‐ and thermal cure systems have potential applications in adhesives, potting resins, and composites. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6750–6764, 2006     

Novel panchromatic photopolymerizable matrices: N,N'‐dibutylquinacridone as an efficient and versatile photoinitiator

N,N'‐dibutylquinacridone (DBQA) is utilized here for the first time as a high‐performance panchromatic photoinitiator for the cationic polymerization (CP) of epoxides, the free radical polymerization (FRP) of acrylates, the thiol‐ene polymerization and the synthesis of interpenetrated polymer networks (epoxide/acrylate) under violet, blue, green and yellow lights (emitted from LED at 405 nm, 470 nm, 520 nm, or 594 nm, or laser diode at 532 nm). It confers a panchromatic character to the photopolymerizable matrices. Remarkably, the proposed DBQA based photoinitiating systems exhibit quite excellent efficiency (the final monomer conversion for multifunctional monomers at room temperature can reach 62% and 50% in CP and FRP, respectively) and appear as much more powerful than the camphorquinone or Eosin‐Y containing reference systems for visible light. For green light, DBQA is much more reactive than the literature reference (Eosin‐Y) and for blue light, a good reactivity is found compared with camphorquinone. The photochemical mechanisms are studied by molecular orbital calculations, steady state photolysis, fluorescence, cyclic voltammetry, laser flash photolysis, and electron spin resonance spin trapping techniques. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1719–1727     

Functional benzoxazines containing ammonium salt of carboxylic acid: Synthesis and highly activated thermally induced ring‐opening polymerization

1,3‐Benzoxazine monomers having ammonium salt of carboxylic acid have been developed. These 1,3‐benzoxazines 1a and 1b were easily synthesized from the corresponding tetrabutylammonium salts of glycine and β‐alanine, respectively. The glycine‐derived benzoxazine 1a exhibited remarkably high reactivity, which allowed its thermally induced ring‐opening polymerization in bulk at 100 °C, at which N‐methyl‐1,3‐benzoxazine 1d did not undergo the polymerization at all. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Controlled synthesis of polyepichlorohydrin with pendant cyclic carbonate functions for isocyanate‐free polyurethane networks

Poly(allyl glycidyl ether) and poly(allyl glycidyl ether‐co‐epichlorohydrin) were prepared by monomer‐activated anionic polymerization. Quantitative and controlled polymerization of allyl glycidyl ether (AGE) giving high molar mass polyether was achieved in a few hours at room temperature in toluene using tetraoctylammonium salt as initiator in presence of an excess of triisobutylaluminum ([i‐Bu₃Al]/[NOct₄Br] = 2?4). Following the same polymerization route, the copolymerization of AGE and epichlorohydrin yields in a living‐like manner gradient‐type copolymers with controlled molar masses. Chemical modification of the pendant allyl group into cyclic carbonate was then investigated and the corresponding polymers were used as precursors for the isocyanate‐free synthesis of polyurethane networks in presence of a diamine. Formation of crosslinked materials was followed and characterized by infrared and differential scanning calorimetry. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Application of S‐alkylsulfonium salts of aromatic sulfides as new thermal latent cationic initiators

The cationic initiation activity of derivatives of S‐methylsulfonium salts of dibenzothiophene ( 3a ), diphenyl sulfide ( 4a ), thioanisole ( 4d ), and tetrahydrothiophene ( 5 ) was evaluated in the polymerization of glycidyl phenyl ether ( 1 ). These initiators were soluble in 1 and capable of initiating the cationic polymerization of 1 on heating, with the exception of methyltetrahydrothiophenium tetrafluoroborate ( 5 ; in the range of room temperature to 160 °C). Among them, methyldiphenylsulfonium tetrafluoroborate ( 4a ) showed a moderate thermal latency that brought about the polymerization of 1 efficiently at 160 °C but not below 80 °C. S‐Alkylsulfonium salts of aromatic sulfides such as phenoxathiin ( 6a ) and thianthrene ( 6b ) also were evaluated for their activity in the cationic polymerization of 1 , from which the thermal latent behavior of these salts also was confirmed (i.e., there was no reaction at 60 °C for 3 h, but there was a high enough conversion at 140 °C). Furthermore, the catalytic activity of S‐alkylsulfonium derivatives was controllable by both the property of the substituents on the aromatic rings and the character of the alkyl groups on the sulfur atom. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 18–27, 2000     

ATRP of MMA under 60Co γ‐irradiation at room temperature

In this work, atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) was successfully carried out at room temperature (25 °C) under ⁶⁰Co γ‐irradiation environment. The polymerization proceeded smoothly with high conversion (>90%) within 7 h. The polymerizations kept the features of controlled radical polymerization: first‐order kinetics, well‐predetermined number‐average molecular weights (M_n,GPC), and narrow molecular weight distributions (M_w/M_n < 1.25). ¹H NMR spectroscope and matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry confirmed that poly(methyl methacrylate) (PMMA) chain was end‐capped by the initiator moieties. The Cu(II) concentration could reduce to 20 ppm level while keeping good control over molecular weights. This is the first successful example for the ATRP of MMA under ⁶⁰Co γ‐irradiation at room temperature. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

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     

Metallocene‐mediated cationic ring‐opening polymerization of 2‐methyl‐ and 2‐phenyl‐oxazoline

The cationic ring‐opening polymerization of 2‐methyl‐2‐oxazoline and 2‐phenyl‐2‐oxazoline was efficiently used using bis(η⁵‐cyclopentadienyl)dimethyl zirconium, Cp₂ZrMe₂, or bis(η⁵‐tert‐butyl‐cyclopentadienyl)dimethyl hafnium in combination with either tris(pentafluorophenyl)borate or tetrakis(pentafluorophenyl)borate dimethylanilinum salt as initiation systems. The evolution of polymer yield, molecular weight, and molecular weight distribution with time was examined. In addition, the influence of the initiation system and the monomer on the control of the polymerization was studied. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 000: 000–000, 2011     

Silyl‐protected hydroxystyrenes: Living anionic polymerization at room temperature and selective desilylation

Both 4‐ and 3‐(tert‐butyldimethylsilyl)oxystyrene (MSOST) undergo living anionic polymerization at room temperature with sec‐butyllithium (sBuLi) in cyclohexane or methylcyclohexane upon injection of a small amount of tetrahydrofuran. Desilylation can be conveniently afforded with hydrogen chloride or tetra(alkyl)ammonium fluoride to provide poly(hydroxystyrene) (PHOST) with a narrow molecular weight distribution, which could be further transformed to other polystyrene derivatives. ¹³C NMR spectra of poly(tert‐butyldimethylsilyloxystyrene) (PMSOST) and PHOST prepared under different conditions (tetrahydrofuran vs. cyclohexane, −78 °C vs. 20 °C) have indicated that the room temperature living polymerization in the hydrocarbon‐rich solvent produces polymers with high syndiotacticity. Similarly, 4‐(tert‐butyldiphenylsilyl)oxystyrene (PhSOST), a new monomer, provides living anionic polymerization at room temperature. Desilylation of this polymer can be achieved using tetra(n‐butyl)ammonium or tetraethylammonium fluoride. Inertness of the phenylsilyl ether to HCl allows selective desilylation of the dimethylsilyl ether with HCl in the presence of the phenylsilyl ether group, providing a new route to interesting macromolecules. Application of the selective desilylation technique to the synthesis of a block copolymer of HOST and 4‐tert‐butoxycarbonyloxystyrene (BOCST) is described. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2415–2427, 2000     

Controlled radical polymerization of tert‐butyl acrylate at ambient temperature: Effect of initiator structure and synthesis of amphiphilic block copolymers

Controlled and very rapid ambient temperature polymerization of tert‐butyl acrylate (tBA) via atom transfer radical polymerization (ATRP) and single electron transfer living radical polymerization (SET‐LRP) conditions is reported. Two initiators, one that would generate a secondary radical and another that would generate a primary radical, upon activation, are used. A very active catalyst CuBr/Me₆TREN was found to initiate rapid polymerization whether it was the primary or the secondary initiator. The polymerization was well controlled and very rapid. The initiator that produces secondary initiating site is found to result in more rapid polymerization than the one that produces primary initiating site. To explore the possibility of rapid ambient temperature polymerization through the SET‐LRP mechanism, the polymerization was also carried out in the presence of DMSO. It was found that the polymerization was much faster compared to the bulk ATRP, without loss of control. Styrene was block copolymerized from PtBA macroinitiators and vice versa. In both the cases, block copolymers with controlled molecular weights were obtained. The tBA block of the polymer was selectively hydrolyzed to get amphiphilic block copolymers. This amphiphilic block copolymer was found to be useful in preparing stable cadmium sulfide (CdS) nanoparticulate dispersion. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Cationic addition polymerization of 1,4‐dioxene using gacl3 as lewis acid catalyst: Long‐lived species‐mediated polymerization

Effective cationic addition polymerization of 1,4‐dioxene, a six‐membered cyclic olefin with two oxygen atoms adjacent to the double bond, was performed using a simple metal halide catalyst system in dichloromethane. The polymerization was controlled when the reaction was conducted using GaCl₃ in conjunction with an isobutyl vinyl ether–HCl adduct as a cationogen at –78°C to give polymers with predetermined molecular weights and relatively narrow molecular weight distributions. The long‐lived properties of the propagating species were further confirmed by a monomer addition experiment and the analyses of the product polymers by ¹H NMR and MALDI–TOF–MS. Although highly clean propagation proceeded, the apparent rate constant changed during the controlled cationic polymerization of 1,4‐dioxene. The reason for the change was discussed based on polymerization results under various conditions. The obtained poly(1,4‐dioxene) exhibited a very high glass transition temperature (T_g) of 217°C and unique solubility. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Cationic polymerization of isobutylene at room temperature

This review highlights recent approaches toward polyisobutylene (PIB) by an energy efficient room temperature cationic polymerization. Special focus is laid on our own work using modified Lewis acids and nitrile‐ligated metal complexes associated with weakly coordinating anions. In both cases, suitable conditions have been found for efficient production of PIB characterized by medium to low molar masses and a high content of exo double bonds as end groups—the typical features of highly reactive PIB, an important commercial intermediate toward oil and gasoline additives. These and other approaches demonstrate that the cationic polymerization of isobutylene is still not fully explored, and new innovative catalyst systems can lead to surprising results of high commercial interest. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Unequal siblings: Adverse characteristics of naphtalene‐based hoveyda‐type second generation initiators in ring opening metathesis polymerization

A family of four different Hoveyda‐type initiators bearing a π‐extended carbene ligand was characterized regarding the activity in ring opening metathesis polymerization. One of the initiators shows high activity at ambient temperature, similar to the second generation Hoveyda–Grubbs catalyst and is even suited for the controlled polymerization of certain norbornene derivatives. The other family members exhibit a pronounced latency at room temperature, and polymerization can be triggered by heat. The scope of these initiators in the thermally triggered polymerizations of norbornene derivatives in general and dicyclopentadiene in particular was disclosed. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011.     

Redox initiated cationic polymerization: Silane‐N‐aryl heteroaromatic onium salt redox couples

In this article, a new route for the synthesis of N‐aryl heteroaromatic onium salts by the direct copper catalyzed arylation of pyridine, substituted pyridines, isoquinoline, and acridine with diaryliodonium salts is described. It was demonstrated that these N‐aryl heteroaromatic onium salts undergo facile platinum or rhodium‐catalyzed reduction by silanes bearing Si? H groups. The reduction of N‐aryl heteroaromatic onium salts generates Brønsted acids. When this redox reaction was carried out in situ in the presence of an appropriate monomer, cationic polymerization was observed. Using this approach, the cationic polymerizations of epoxides, oxetanes, 1,3,5‐trioxane, styrene, and vinyl ethers were carried out. The use of optical pyrometry to monitor the redox initiated cationic polymerizations of some representative multifunctional monomers is described. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Substituent effect on the cationic ring‐opening polymerization of acyloxymethyl five‐member cyclic dithiocarbonates

Five‐member cyclic dithiocarbonates were synthesized by the reactions of carbon disulfide with benzoic, p‐anisic, p‐chlorobenzoic, 1‐naphthalenecarboxylic, p‐nitrobenzoic, and p‐(tert‐butyl)benzoic glycidyl esters, and their cationic ring‐opening polymerizations were carried out with methyl trifluoromethane sulfonate and trifluoromethane sulfonic acid as initiators at room temperature to 80 °C. Polymers with number‐average molecular weights of 3400–24,900 were obtained in high yields, and their structures were estimated by NMR and IR spectroscopy. The monomers showed a clear difference in the polymerization rate according to the substituents. The rate of polymerization decreased in the order of p‐chlorobenzoic ≥ benzoic > 1‐naphthalenecarboxylic > p‐nitro‐benzoic > p‐tert‐butylbenzoic > p‐anisic. The data of the reaction kinetics, NMR studies, and molecular orbital calculations proved a plausible mechanism involving the participation of p‐substituted benzoyloxymethyl groups to stabilize the cationic propagating end. The polymers showed decomposition temperatures with 5% weight loss ranging from 200 to 260 °C. No glass‐transition temperatures for the polymers were observed below 200 °C by differential scanning calorimetry. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3967–3980, 2001     

Surface promoted redox cationic polymerization of epoxy monomers catalyzed by silver salts

The first example of a one‐component room temperature curing redox cationic polymerization for metal surfaces is described. A weak Lewis acid (Ag⁺) is used as a latent catalyst to likely generate a much stronger one (Fe²⁺/Fe³⁺ or Cu²⁺) at the bond line interface. Such a process has been demonstrated for 3,4‐epoxycyclohexylmethyl‐3,4‐epoxycyclohexane carboxylate using [Ag(1,5‐cyclooctadiene)₂]SbF₆ with the polymerization monitored most conveniently by fourier transform infrared spectroscopy (FTIR). This system, however, demonstrates a relatively low adhesive strength even following curing for 24 h. Higher bond strengths were achieved using mixtures with other cationically polymerizable monomers (vinyl ethers, tetrahydrofuran (THF), oxetanes). Factors considered for optimization of the rates and extent of reaction were the concentrations of a vinyl ether comonomer and [AgL_n]X, the nature of the counterion (X), and of the ligand (L). The performance of the Ag(I) system was compared to that of Cu(I) and various organic cations and the activity of the redox cationic polymerizations on a range of metallic (iron, copper, and aluminium) and nonmetallic (glass and various plastics) substrates was studied. A relatively high glass transition temperature was recorded for the optimized model system and the bonding strength at elevated temperature (150–200 °C) following a room temperature cure was found to be attractive compared to selected model anaerobic acrylate compositions. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Benzotriazole derivatives as long wavelength photosensitizers for diaryliodonium salt initiators

Two benzotriazole derivative dyes 4,7‐bis(2,3‐dihydrothieno[3,4‐b][1,4]dioxin‐5‐yl)‐2‐dodecyl‐2H‐benzo[1,2,3]triazole, and 2‐dodecyl‐4,7‐bis(4‐hexylthiophen‐2‐yl)‐2H‐benzo[d][1,2,3]triazole are shown to work as efficient photosensitizers for a diphenyliodonium salt initiator in cationic photopolymerization of epoxide and vinyl monomers. Substituted thienyl groups are attached to benzotriazole backbone to extend conjugation and enhance electron density of the molecules. Thereby, it was possible to initiate polymerizations at room temperature using long wavelength UV and visible light. The progress of photopolymerizations was monitored using optical pyrometry. The photopolymerization of an epoxide monomer using solar irradiation was also demonstrated. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Living cationic polymerization of amide‐functional vinyl ethers: Specific properties of SnCl4‐based initiating system

Living cationic copolymerization of amide‐functional vinyl ethers with isobutyl vinyl ether (IBVE) was achieved using SnCl₄ in the presence of ethyl acetate at 0 °C: the number–average molecular weight of the obtained polymers increased in direct proportion to the monomer conversion with relatively low polydispersity, and the amide‐functional monomer units were introduced almost quantitatively. To optimize the reaction conditions, cationic polymerization of IBVE in the presence of amide compounds, as a model reaction, was also examined using various Lewis acids in dichloromethane. The combination of SnCl₄ and ethyl acetate induced living cationic polymerization of IBVE at 0 °C when an amide compound, whose nitrogen is adjacent to a phenyl group, was used. The versatile performance of SnCl₄ especially for achieving living cationic polymerization of various polar functional monomers was demonstrated in this study as well as in our previous studies. Thus, the specific properties of the SnCl₄ initiating system are discussed by comparing with the Et_xAlCl_3?x systems from viewpoints of hard and soft acids and bases principle and computational chemistry. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6129–6141, 2008