Visible light induced free radical promoted cationic polymerization using thioxanthone derivatives

The free radical promoted cationic polymerization cyclohexene oxide (CHO), was achieved by visible light irradiation (λ_inc = 430–490 nm) of methylene chloride solutions containing thioxanthone‐fluorene carboxylic acid (TX‐FLCOOH) or thioxanthone‐carbazole (TX‐C) and cationic salts, such as diphenyliodonium hexafluorophosphate (Ph₂I⁺PF) or silver hexafluorophosphate (Ag⁺PF) in the presence of hydrogen donors. A feasible initiation mechanism involves the photogeneration of ketyl radicals by hydrogen abstraction in the first step. Subsequent oxidation of ketyl radicals by the oxidizing salts yields Bronsted acids capable of initiating the polymerization of CHO. In agreement with the proposed mechanism, the polymerization was completely inhibited by 2,2,6,6‐tetramethylpiperidinyl‐1‐oxy and di‐2,6‐di‐tert‐butylpyridine as radical and acid scavengers, respectively. Additionally polymerization efficiency was directly related to the reduction potential of the cationic salts, that is, Ag⁺PF (E = +0.8 V) was found to be more efficient than Ph₂I⁺PF (E = ?0.2 V). In addition to CHO, vinyl monomers such as isobutyl vinyl ether and N‐vinyl carbazole, and a bisepoxide such as 3,4‐epoxycyclohexyl‐3′,4′‐epoxycyclohexene carboxylate, were polymerized in the presence of TX‐FLCOOH or TX‐C and iodonium salt with high efficiency. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Über Tris[(trialkylphosphan)gold(I)]oxonium-tetrafluoroborate und Tris[(triphenylphosphan)gold(I)]sulfonium-tetrafluoroborat

On Tris[(trialkylphosphine)gold(I)]oxonium Tetrafluoroborates and Tris[(triphenylphosphine)gold(I)]sulfonium Tetrafluoroborate [Et₃PAu]⁺BF, obtained from Et₃PAuCl and AgBF₄ in tetrahydrofuran, reacts with KOH (molar ratio 3:1) to give the oxonium salt [(Et₃P)Au]₃O⁺BF ( 1 ). The homologous [^t(Bu₃P)Au]₃O⁺BF ( 2 ) is generated similarly from ^tBu₃PAuCl and Ag₂O in the presence of NaBF₄ in THF. The composition and identity of these two first tris[(tri alkyl phosphine)gold(I)]oxonium salts have been confirmed by analytical and spectroscopic data. The compounds are useful aurating agents. From the corresponding triphenylphosphine complex and (Me₃Si)₂S quantitative yields of the sulfonium salt [(Ph₃P)Au]₃S⁺BF ( 3 ) are obtained. Its crystal structure features monomeric cations, and in these small Au? S? Au angles indicate significant metal-metal bonding.     

Anionic Polymerization Behavior of α-Methylene-N-methylpyrrolidone

Anionic polymerization of α-methylene-N-methylpyrrolidone ( MMP ) was carried out in THF at −78∼0 °C with diphenylmethylpotassium (Ph₂CHK) and with diphenylmethyllithium (Ph₂CHLi) in the presence of Lewis acidic diethylzinc (Et₂Zn). Poly( MMP )s possessing predicted molecular weights based on the molar ratios between monomer and initiators and narrow molecular weight distributions (M_w/M_n < 1.1) were obtained in quantitative yields. It was demonstrated that the propagating chain end of poly( MMP ) was stable at −30 °C to form the polymers with well-defined chain structures. From the polymerizations at the various temperatures ranging from −50 to −30 °C, the apparent rate constant and the activation energy of the polymerization were estimated as follows: ln k = −6.93 × 10³/T + 25.7 and 57 ± 5 kJ mol⁻¹, respectively.     

Tetraammin-Lithium-Kationen zur Stabilisierung phenylsubstituierter Zintl-Anionen: Die Verbindung [Li(NH3)4]2[Sn2Ph4]

Tetraammine Lithium Cations Stabilizing Phenylsubstituted Zintl-Anions: The Compound [Li(NH₃)₄]₂[Sn₂Ph₄] Ruby-red, brittle single crystals of [Li(NH₃)₄]₂[Sn₂Ph₄] were synthesized by the reaction of diphenyltin dichloride and metallic lithium in liquid ammonia at ?35°C. The structure was determined from X-ray singlecrystal diffractometer data: Space group, P1 , Z = 1, a = 9.462(2) Å, b = 9.727(2) Å, c = 11.232(2) Å, α = 66.22(3)°, β = 85.78(3)°, γ = 61.83(3)°, R₁ (F ? 4σF) = 5.13%, wR₂ (F₀² ? 4σF) = 10.5%, N(F ? 4σF) = 779, N(Var.) = 163. The compound contains to Sb₂Ph₄ isosteric centres [Sn₂Ph₄]^2? as anions which are connected to rods by lithium cations in distorted tetrahedral coordination by ammonia. These rods are arranged parallel to one another in the b,c-plane, but stacked along [100].     

Polymerization and reaction of tetraoxane with various olefins catalyzed by BF3O·(C2H5)2

The copolymerization of tetraoxane with various olefins by BF₃·O(C₂H₅)₂ in ethylene dichloride at 30°C has been studied. The gas chromatographic technique was employed for the determination of concentration of each compound. The rate of tetraoxane consumption was decreased by the addition of olefins in the order of; no addition > trans-stilbene > styrene > 1,1-diphenylethylene > 2-chloroethyl vinyl ether > cyclohexene ≥ indene ≥ α-methylstyrene. The formation of the methanol-insoluble copolymer of tetraoxane and olefin was not confirmed. However, 4-methyl-4-phenyl-1,3-dioxane and 4,4-diphenyl-1,3-dioxane were formed in the reaction of tetraoxane with α-methylstyrene and 1,1-diphenylethylene, respectively. 4,4-Diphenyl-1,3-dioxane was identified on the basis of the molecular weight measurement, elemental analysis and NMR and infrared spectroscopy. On the other hand, 1,3-dioxane derivatives were not formed in the reaction of tetraoxane with α,β-disubstituted olefins. Monomer composition dependence of the copolymerization of tetraoxane with 1,1-diphenylethylene or α-methylstyrene has been studied. The amount of 4,4-diphenyl-1,3-dioxane formed reached a maximum at a monomer composition of 1:1 in the reaction of tetraoxane with 1,1-diphenylethylene. The formation of cyclic dimer of α-methylstyrene was suppressed by tetraoxane.     

[(α‐Imino)enamino]phosphonium salts from propyne iminium salts and a phosphorane imine

Propyne iminium triflates R¹C(N⁺R³R⁴)CCR² CF₃SO readily react with Ph₃PNPh to form 1:1 adducts which formally result from a metathetical addition of the phosphorane imine across the triple bond of the alkyne. These adducts are best described as enamino‐phosphonium salts or iminio‐substituted phosphorus ylides. The configuration of these salts has been determined from NMR data and an X‐ray crystal structure analysis of salt 3h . The base‐induced elimination of the PPh₃ substituent from enamino‐phosphonium salt 3a was studied. © 2005 Wiley Periodicals, Inc. Heteroatom Chem 16:437–446, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20131     

Depolymerization kinetics of di(4‐tert‐butyl cyclohexyl) itaconate and Mark‐Houwink‐Kuhn‐Sakurada parameters of di(4‐tert‐butyl cyclohexyl) itaconate and di‐n‐butyl itaconate

Multipulse pulsed laser polymerization coupled with size exclusion chromatography (MP‐PLP‐SEC) has been employed to study the depropagation kinetics of the sterically demanding 1,1‐disubstituted monomer di(4‐tert‐butylcyclohexyl) itaconate (DBCHI). The effective rate coefficient of propagation, k, was determined for a solution of monomer in anisole at concentrations, c, 0.72 and 0.88 mol L^?1 in the temperature range 0 ≤ T ≤ 70 °C. The resulting Arrhenius plot (i.e., ln k vs. 1/RT) displayed a subtle curvature in the higher temperature regime and was analyzed in the linear part to yield the activation parameters of the forward reaction. In the temperature region where no depropagation was observed (0 ≤ T ≤ 50 °C), the following Arrhenius parameters for k_p were obtained (DBCHI, E_p = 35.5 ± 1.2 kJ mol^?1, ln A_p = 14.8 ± 0.5 L mol^?1 s^?1). In addition, the k data was analyzed in the depropagatation regime for DBCHI, resulting in estimates for the associated entropy (?ΔS = 150 J mol^?1 K^?1) of polymerization. With decreasing monomer concentration and increasing temperature, it is increasingly more difficult to obtain well structured molecular weight distributions. The Mark Houwink Kuhn Sakurada (MHKS) parameters for di‐n‐butyl itaconate (DBI) and DBCHI were determined using a triple detection GPC system incorporating online viscometry and multi‐angle laser light scattering in THF at 40 °C. The MHKS for poly‐DBI and poly‐DBCHI in the molecular weight range 35–256 kDa and 36.5–250 kDa, respectively, were determined to be K_DBI = 24.9 (10³ mL g^?1), α_DBI = 0.58, K_DBCHI = 12.8 (10³ mL g^?1), and α_DBCHI = 0.63. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1931–1943, 2007     

Stereoregularity of poly(methyl α-chloroacrylate)

Triad and tetrad tacticities of poly(methyl α-chloroacrylate) and poly(methyl α-chloroacrylate-β-d₁) were determined by nuclear magnetic resonance (NMR) spectroscopy. Methyl α-chloroacrylate-β-d₁ and its polymer were first synthesized. Isotactic poly(methyl α-chloroacrylate) was prepared with ethylmagnesium chloride-benzal-acetophenone in combination as catalyst. The syndiotacticity of radically polymerized polymers increased with decreasing polymerization temperature. For radical polymerization, enthalpy and entropy differences between isotactic and syndiotactic additions were calculated to give ΔH ? ΔH = 850 cal/mole and ΔS ? ΔS = 0.93 eu. The stereoregularity of the polymer prepared with phenylmagnesium bromide catalyst was analyzed in fairly good agreement with first-order Markov statistics, while polymerization with fluorenyllithium seems predominantly to proceed by a mechanism similar to free-radical mechanism. Stereoregularity-controlling power for individual substituents is briefly discussed.     

Cationic grafting from carbon black. II. Polymerization of styrene initiated by CO+ClO group on the surface of carbon black

The cationic grafting of polystyrene initiated by carbon black containing the CO⁺ClO group was investigated. The introduction of CO⁺ClO groups onto a carbon black surface was achieved by the reaction of AgClO₄ with carbon black that contained a COCI group. The latter was introduced by the reaction of carboxyl groups with SOCl₂. It was found that polystyrene chains could be grown from CO⁺ClO groups on the surface of carbon black. Moreover, polystyrene was effectively grafted from carbon black: the grafting ratio at 20°C increased to 58% as conversion increased. Furthermore, the grafting ratio and molecular weight of ungrafted polystyrene decreased with an increase in polymerization temperature. These results were explained by the fact that the increasing temperature of the polymerization caused an increase in the rate of chain transfer reaction of the growing polymer chain to the monomer. The carbon black obtained from the reaction produced a stable colloidal dispersion in a good solvent for polystyrene.     

Peroxo salts as initiators of vinyl polymerization. IV. Polymerization of methacrylamide initiated by peroxodisulfate ion and metal ion catalysis

The polymerization kinetics of methacrylamide (M) initiated by S₂O ion in the presence and absence of the metal ions Ag⁺ and Cu²⁺ has been studied. The rate laws have been established and are compared with those of acrylamide. The results indicate that steric hindrance from the α-methyl group affects the initiation reaction. Cu²⁺ ions are found to reduce the rate of polymerization.     

Photoinitiated cationic polymerization with triarylsulfonium salts

Triarylsulfonium salts Ar₃S⁺MX with complex metal halide anions such as BF, AsF, PF, and SbF are a new class of highly efficient photoinitiators for cationic polymerization. In this article we describe several synthetic routes to the preparation of these compounds along with their physical and spectroscopic properties. Mechanistic studies have shown that when these compounds are irradiated at wavelengths of 190–365 nm carbon–sulfur bond cleavage occurs to form radical fragments. At the same time the strong Br??nsted acid HMX_n, which is the active initiator of cationic polymerization that takes place in subsequent “dark” steps, is also produced. A study of the parameters that affect the photolysis of triarylsulfonium salts is reported with a measurement of the absolute quantum yields. The cationic polymerizations of four typical monomers—styrene oxide, cyclohexene oxide, tetrahydrofuran, and 2-chloroethyl vinyl ether—with triarylsulfonium salt photoinitiators are described.     

1,1-Dithio-oxalat als Brückenligand in Zwei- und Dreikernkomplexen

1,1-Dithio-oxalate as Bridging Ligand in Bi- and Trinuclear Complexes 1,1-Dithio-oxalate (i-dto), a four-dentate chalcogenrich ligand, possesses the unique constitution of C? C coupled CO₂ and CS₂. Due to its ambident behaviour i-dto forms mononuclear complexes and defined homo- and heterobimetallic bi- and trinuclear complexes. Obviously as a combined result of the symmetry and the electron distribution the ligand acts preferably bridging. The formation of coordination polymers can be prevented using coordinatively halfside-saturated species ?(Ph₃P)₂M⁺”? (M = Cu, Ag). From EPR investigations of a trinuclear CuCu¹¹ complex we could get information about the coordination geometry and the electron distribution.     

Chain-length dependent termination in pulsed-laser polymerization, 5. The evaluation of the rate coefficient of bimolecular termination kt for the reference system styrene in bulk at 25°C

Following earlier suggestions the values for the rate coefficient of chain termination k_t in the bulk polymerization of styrene at 25°C were formally calculated (a) from the second moment of the chainlength distribution (CLD) and (b) from the rate equation for laser-initiated pseudostationary polymerization (both expressions originally derived for chain-length independent termination) by inserting the appropriate experimental data including the rate constant of chain propagation k_p. These values were treated as average values, k and k , respectively. They exhibited good mutual agreement, even the predicted gradation (k < k by about 20%) was recovered. The log-log plot of k_t vs. the number-average degree of polymerization of the chains at the moment of their termination yielded exponents b of 0.16–0.18 in the power-law k_t = A · P_n ^−b, A ranging from 2.3 × 10⁸ to 2.7 × 10⁸ L · mol⁻¹ · s⁻¹. These data are only slightly affected if termination is not assumed to occur by recombination only and a small contribution of disproportionation is allowed for.     

Syndiospecific polymerization of styrene. II. Monocyclopentadienyltributoxy titanium/methylaluminoxane catalyst

Syndiospecific polymerization of styrene was catalyzed by monocyclopentadienyltributoxy titanium/methylaluminoxane [CpTi (OBu)₃/MAO]. The atactic and syndiotactic polystyrenes were separated by extracting the former with refluxing 2-butanone. The activity and syndiospecificity of the catalyst were affected by changes in catalyst concentration and composition, polymerization temperature, and monomer concentration. Extremely high activity of 5 × 10⁷ g PS (mol Ti mol S h)^?1 with 99% yield of the syndiotactic product were achieved. The concentration of active species, [C^*], has been determined by radiolabeling. The amount of the syndiospecific and nonspecific catalytic species, [C] and [C] respectively, correspond to 79 and 13% of the CpTi(OBu)₃. The rate constants of propagation for C and C at 45°C are 10.8 and 2.0 (M s)^?1, respectively, the corresponding rate constants for chain transfer to MAO are 6.2 × 10^?4 and 4.3 × 10^?4s^?1. There was no deactivation of the catalytic species during a batch polymerization. The rate constant of chain transfer with monomer is 6.7 × 10^?2 (M s)^?1; the spontaneous β-hydride transfer rate constant is 4.7 × 10^?2 s^?1. The polymerization activity and stereospecificity of the catalyst are highest at 45°C, both decreasing with either higher or lower temperature. The stereoregular polymer have broad MW distributions, M?_w/M?_n = 2.8–5.7, and up to three crystalline modifications. The T_m of the s-PS polymerized at 0–90°C decreased from 261.8 to 241°C indicating thermally activated monomer insertion errors. The styrene polymerization behaviors were essentially insensitive to the dielectric constant of the medium.     

Internal field of polymer crystals: Polarizability tensor of the methylene group from the birefringence of paraffin crystal

Using the concept of a point dipole lattice, it is shown that the internal field of induced dipoles can be calculated for crystals comprised of simple chain molecules. The only structure which must be taken into account accurately is that of the chain molecule itself. From the calculations, reliable values of the polarizability tensor of the CH₂ unit are deduced from the birefringence of the paraffin crystal. In addition, it is shown that birefringence measurements provide a method for demonstrating the consistency of polarizability data so that no detailed structural information is needed. For the CH₂ unit, it is found by both methods that α^∥ ? α^? = ? 0.63 with respect to the chain direction [the units of polarizability α are 10^?24 cm³ (cgs)]. The most probable anisotropies for the bond polarizabilities are α ? α = 0.30, α ? α = ? 0.62.     

Exchange Equilibrium of Oxygen Isotopes between BrO,ClO, IO and Water

The liquid phase fractionation factors α_H = (¹⁸O/¹⁶O)_H2O/(¹⁸O/¹⁶O)xo and α_D = (¹⁸O/¹⁶O)_D2O/(¹⁸O/₁₆O)xo (X = Cl, Br, I) were calculated quantum mechanically between 0 and 100°. Experimental values were obtained in the case of BrO at 60° showing good agreement with the calculated results.     

Ethylene polymerization with homogeneous Ziegler-Natta catalysts: theoretical study on the role of ion pairs in the polymerization mechanism

The thermodynamics of the reaction of an ethylene molecule with the Cp₂TiCH₃Cl/Al(CH₃)₂Cl system (Cp = η₅-C₅H₅), as a model for olefin polymerization with homogeneous Ziegler-Natta catalysts, was investigated via quantum mechanical DFT calculations. The comparison of the calculated energies for three possible titanium-olefin coordinated intermediates, the ionic complex Cp₂TiCH₃(C₂H₄)⁺/Al(CH₃)₂Cl, the bimetallic complex Cp₂TiCH₃(C₂H₄)^δ+ · Al(CH₃)₂Cl and the olefin-separated ion pair Cp₂TiCH/C₂H₄/Al(CH₃)₂Cl, shows that the most feasible polymerization mechanism occurs via olefin-separated ion pair.     

Magnesium chloride supported high mileage catalysts for olefin (decene-l) polymerization XIV. Propagation and chain transfer

Decene-l was polymerized with the MgCl₂/ethylebenzoate/p-cresol/AIEt₃/TiCl₄-AlEt₃/methyl-p-toluate catalyst at 50° using an A/T ratio of 167 and a range of monomer concentration. The concentration of the two kinds of active sites are [Ti] = 12% and [Ti] = 4% of the total titanium. The rate constants of propagation are 24 M^?1 s^?1. Chain transfers to AIEt₃, monomer, and by β-hydride elimination have rate constant values of 1.7 × 10^?3 M^?1 s^?1, 1.34 × 10^?2 M^?1 s^?1, and 1.7 × 10^?2 s^?1, respectively. Poly(decene-l) have relatively narrow MW which are unchanged during the course of a polymerization. Therefore, the active site concentrations in the CW catalyst for propylene and decene polymerization are identical and their rate constant values agree within a factor of 2. However, the rate of decene polymerization depends on fractional order of monomer concentration and decreases with the increase of activator concentration. Furthermore, the formation of metal polymer bonds has a rate independent of these concentrations. These kinetic behaviors are a manifestation of absorption processes of these species which are not seen in propylene polymerizations.     

Über α-Dioximin-Komplexe der übergangsmetalle. XXIII) Kobalt(III)-nyoximin-Komplexe mit aromatischen Aminen

30 new binary salts of the heretofore unknown type [Co(NioxH)₂(Amin)₂]X were obtained by air oxidation of an alcoholic aqueous solution of Co^II acetate in the presence of 1,2-cyclohexanedione dioxime (nioxime) and an aromatic amine (aniline, o-and p-ethylaniline and m-xylidine). From the brown solutions of the resulting; Co(NioxH)₂(amine)₂; acetates the desired salts were separated by means of double decomposition reactions using X ? Br^?, NO, ClO, HSO, Pikart, [Cr(NH₃)₂(NCS)₄]^?, 1/3[Cr(NCS)₆]^3? and [Co(NioxH)₂(NO₂)₂]^?; NioxH ? C₆H₉N₂O₂. From spectroscopical investigations in the UV and IR regions some structural problems are resolved and discussed.