Polymerization of methyl methacrylate with the use of cetyl trimethyl ammonium bromide-benzoyl peroxide combination as the initiating system

Methyl methacrylate (MMA) was polymerized at 40 in the presence of dimethyl formamide (DMF), using cetyl trimethyl ammonium bromide with benzoyl peroxide (CTABBZ₂O₂) as the initiating system. At high dilutions the rate of polymerization was proportional to (initiator)^1–2. In near-bulk conditions using low [DMF], the rate was practically independent of [BZ₂O₂], while the kinetic order with respect to CTAB was about 0.16. The polymerization was inhibited by hydroquinone. A radical mechanism is suggested for the polymerization with primary radical termination significant in near-bulk systems and bimolecular termination significant for high dilution with DMF. Effects of various other solvents or additives on the polymerization were examined. DMF, acetonitrile and pyridine act as rate accelerating diluents; benzene, methanol, chloroform and acetone as inert diluents; formamide and acetamide cause pronounced retardation.     

Binuclear oxomolybdenum(V) chlorides: Molecular structure of Mo2O4Cl2(DMF)4 and Mo2O4Cl2(bipy)2 · DMF

Reduction of MoO₂Cl₂(DMF)₂ (DMF = dimethylformamide) with PPh₃ in mild conditions afforded the dinuclear species Mo₂O₃Cl₄(DMF)₄. Related compounds could be prepared by substitution of DMF with stronger bases. While attempting to grow crystals of these compounds new complexes with the syn-[Mo₂O₄]²⁺ core were obtained. The molecular structures of Mo₂O₄Cl₂(DMF)₄, and Mo₂O₄Cl₂(bipy)₂ (bipy = 2,2′-bipyridine) have been established by X-ray diffraction analysis.     

Effect of benzophenone on the H2O2-induced photopolymerization of methyl methacrylate

Benzophenone (BP) in low concentrations (<0.001 mol 1^?1) produces a rate enhancing effect in the H₂O₂-induced bulk photopolymerization of MMA. R_p is proportional to [H₂O₂]^0.4 and [BP]^0.4, and $\text{k}{}_{\mathrm{p}}{}^2\text{k}{}_1$ at 30° is 1.00 × 10^?2 1.mol^?1 sec^?1. In diluted systems, different solvents produce different kinetic effects, reaction order with respect to monomer being negative for IPA and THF as solvent, positive but <1.0 for benzene and chloroform, 1.2 for acetonitrile, CCl₄ and t-butanol and 1.8 for DMA. The variable solvent effect is attributed to modification of the initiation process by the various solvents to different extents. Kinetic analysis of data for bulk photopolymerization gives evidence for primary radical termination and degradative initiator transfer.     

Catalytic action of metallic salts in autoxidation and polymerization. IX. Polymerization of methyl methacrylate with sodium hexanitrocobaltate(III) in mixed solvent of acetone and water

Polymerization of methyl methacrylate with some cobalt (III) complexes was carried out in various solvents and in mixed solvents of acetone and water or alcohols. Sodium hexanitrocobaltate(III) was found to be an effective initiator in mixed solvent of water and acetone. The kinetic study on the polymerization of methyl methacrylate with Na₃[Co(NO₂)₆] in a water-acetone mixed solvent gave the following over-all rate equation: R_p = 8.04 × 10⁴ exp{ ?13,500/RT} [I]^1/2[M]² (mol/1.?sec). The effects of various additives on polymerization rate and the copolymerization curve with styrene suggest that polymerization proceeds via a radical mechanism. The dependence of the polymerization rate on the square of monomer concentration and the spectroscopic data were indicative of the formation of a complex between initiator and monomer.     

The interaction of polystyryl radical with Cu(DMF)2Cl2

Kinetics of 2,2′-azobisisobutyronitrile initiated polymerization of styrene in N,N-dimethylformamide (DMF) were investigated in the presence of dichloro bis(N,N-dimethylformamide)copper(II) complex. The complex was prepared in situ by mixing tetrakis(N,N-dimethylformamide)copper(II) perchlorate with LiCl in the molar ratio of 1:2. The equilibrium constant for

was calculated by the limiting logarithmic method as 1.07 × 10¹⁰ l² mol^?2. The velocity constant at 60 for the interaction of polystyryl radical with Cu(DMF)₂Cl₂ is 2.16 × 10⁴ l. mol^?1 sec^?1.     

Polymerization behavior of propene with [t-BuNSiMe2Flu]TiMe2: effects of solvents and cocatalysts

The titanum complex [η¹:η³tert-butyldimethylfluorenylsilyl]-amido)dimethyltitanum ([t-BuNSiMe₂Flu]TiMe₂, Cat.A) was synthesized by an alternatively quicker one pot procedure. Polymerization of propene in the presence of [t-BuNSiMe₂Flu]TiMe₂/dried pure methylaluminoxane (d-PMAO) system at 0 °C was investigated in toluene and heptane. A strong enhancement of productivity was observed in toluene compared to heptane. Polymerization of propene was also investigated with Cat.A in heptane, with different cocatalysts, d-PMAO and dried pure modified methylaluminoxane (d-MMAO), which was prepared from the mixture of trimethylaluminum (TMA) and triisobutylaluminum (TIBA). A 10-fold higher number average molecular weight (M_n) and broad molecular weight distribution (MWD) was obtained with d-PMAO in heptane, even though kinetic features and other parameters signified the living nature of the polymerization process. However, the broadening of MWD was attributed to the poor insolubility of d-PMAO in heptane.     

Dinuclear oxomolybdenum(VI) acetylacetonates: Crystal and molecular structure of Mo2O5(acac)2L2 (L = D2O,DMF)

The behavior of MoO₂(acac)₂ (acac = acetylacetonate) towards representative amines, amides, sulfoxides and phosphine oxides in common solvents has been examined. Compounds of the composition Mo₂O₅(acac)₂L₂ [L = H₂O, D₂O, dimethylformamide (DMF), dimethylacetamide (DMA), dimethylbenzamide (DMBA), tetramethylurea (TMU), dimethylsulfoxide (DMSO), dibutylsulfoxide (Bu₂SO), p-tolylsulfoxide (p-Tol₂SO), tributylphosphine oxide (OPBu₃), triphenylphosphine oxide (OPPh₃), hexamethylphosphoramide (HMPA)], derived from partial hydrolysis of MoO₂(acac)₂ followed by condensation and coordination of L, can readily be isolated. The crystal and molecular structures of Mo₂O₅(acac)₂L₂ (L = D₂O, DMF) have been established by X-ray diffraction analysis.     

Synthesis,Crystal Structure and Electrochemistry of Two Complexes （YLn）3＋[PW12O40]3-（L=Me2SO,Me2NCHO）

The reaction of α-H3[PW12O40] with Y（NO3）3 in the presence of DMF or DMSO leads to two complexes with the formulae {Y（DMSO）7}·PW12O40（1） and {[Y（DMF）7]2PW12O40}·PW12O40（2）. The crystal structures indicate that complex 1 consists of discrete [YLn]3＋ cations and α-Keggin heteropolyanions [PW12O40]3-, whereas, in complex 2, donor-acceptor interaction results in a cation-anion-cation triplet. In addition, the electrochemical behavior of the two complexes indicates the usual successive reduction processes of the W atoms in the anions.     

An electrochemical study of (η-C5H5)2Ti(NCS)2

The reduction of titanocene dithiocyanate in various solvents has been examined using the techniques of polarography, voltammetry, controlled potential electrolysis and cyclic voltammetry. In THF and CH₂Cl₂, Cp₂Ti(NCS)₂ undergoes successive one-electron transfer reactions, and by using a combination of electrochemical and EPR techniques it has been possible to confirm the stability of [Cp₂Ti(NCS)₂]^? in these solvents. In DMF, however, an irreversible dimerization follows the first electron transfer.     

Utilization of LVO 2? species (L2? is a tridentate ONS donor) as an inorganic analogue of carboxylate group: A journey to a new domain of coordination chemistry

The anionic cis-dioxovanadium (V) complex species LVO ₂ ^- of tridentate biprotic dithiocarbazate-based ligands H₂L (S-methyl-3-((5-R-2-hydroxyphenyl)methyl)dithiocabazate, R = H, L = L¹; and R = Br, L = L²) can bind alkali metal ions. The products [LVO₂M(H₂O)_n] (M = Na⁺, L = L¹,1; L = L², 2 and M = K⁺, L = L¹,3) have extended chain structures in the solid state, stabilized by strong hydrogen bonding and Coulombic interactions as revealed from X-ray crystallography. The LVO ₂ ^- moieties here behave like analogues of carboxylate groups and display interesting variations in their binding patterns. It appears thatl is a single stranded helicate with LVO ₂ ^- units forming the strands which surround the labile sodium ions occupying positions on the axis. The compounds are stable in water and methanol as solvents, while in aprotic solvents of higher donor strengths, viz. CH₃CN, DMF and DMSO, they undergo photo-induced reduction when exposed to visible light, yielding green solutions from their initial yellow colour. The putative product is a mixed-oxidation (μ-oxo)divanadium (IV/V) species as revealed from EPR, electronic spectroscopy, dynamic¹H NMR, and redox studies.     

Solvent effects on the redox potential of cis-tetracarbonyl-bis-(1,3 dimethylimidazolidin-2-ylidene) chromium(0)

Polarography and cyclic voltammetry have been performed on cis-tetracarbonyl-bis-(1,3 dimethylimidazolidin-2-ylidene) chromium(0) [cis(imidine)₂Cr(CO)₄] in dichloromethane, 1,2-dichloroethane, methanol, ethanol, nitromethane, 2,2′ thiodiethanol, acetonitrile, formamide, N-methylformamide, N,N-dimethylformamide, N,N-dimethylthioformamide, acetone, propylene carbonate, N-methylpyrrolidone(2), N-methylthiopyrrolidone(2), tetramethylene sulfone, butyrolactone, N,N,N′,N′-tetramethylurea, N,N-diethylacetamide, N,N-dimethylacetamide, trimethylphosphate, dimethylsulfoxide and hexamethylene phosphoric acid triamide.A reversible oxidation to the [cis(imidine)₂Cr(CO)₄]⁺ cation has been observed in the solvents mentioned. The half-wave and 1/2(E_pa+E_pc) potentials recorded vs. bisbiphenylchromium(I)/bisbiphenylchromium(0) as a reference redox system were found to shift to more positive values with increasing electron-pair donor properties of the solvents. The polarographic and voltammetric behaviour of ferrocene and bisbiphenylchromium tetraphenyloborate has been studied in N,N-diethylacetamide, N,N-dimethylacetamide, formamide, trimethylphosphate, N,N,N′,N′-tetramethylurea and hexamethylene phosphoric acid triamide.     

New electrolytes using Li2O or Li2O2 oxides and tris(pentafluorophenyl) borane as boron based anion receptor for lithium batteries

A new system of electrolytes has been developed and studied for lithium-ion batteries. This new system is based on the interactions between Li₂O or Li₂O₂ and tris(pentafluorophenyl) borane (TPFPB) in carbonate based organic solvents. This opens up a completely new approach in developing non-aqueous electrolytes. In general, the solubility of Li₂O or Li₂O₂ is very low in organic solvents and the ionic conductivities of these solutions are almost undetectable. By adding certain amount of tris(pentafluorophenyl) borane (TPFPB), one type of boron based anion receptors (BBARs), the solubility of Li₂O or Li₂O₂ in carbonate based solvents was significantly enhanced. In addition, the Li⁺ transference numbers of these new electrolytes measured were as high as 0.7, which are more than 100% higher than the values for the conventional electrolytes for lithium-ion batteries. The room-temperature conductivities are around 1 × 10⁻³ S/cm. These new electrolytes are compatible with LiMn₂O₄ cathode for lithium-ion batteries.     

Oxygen nonstoichiometry (δ) of TiO2−δ-revisited

Oxygen nonstoichiometry (δ) of “undoped” polycrystalline TiO_2−δ has been measured as a function of oxygen partial pressure in the widest ever examined range of 10^-18?P_O2/atm?10^-1 at elevated temperatures (1073?T/K?1473) by thermogravimetry and coulometric titrometry combined and compared with all the reported values. Isothermal variation of nonstoichiometry against P_O2 is explained with a defect model involving quadruply ionized titanium interstitials, electrons, holes, and unidentified acceptors which may be background impurity acceptors or cation vacancies. The equilibrium constants for intrinsic electronic excitation reaction and redox reaction are determined from the nonstoichiometry measured and compared exhaustively with all the reported values. The relative partial molar enthalpy and entropy of oxygen are evaluated as functions of nonstoichiometry and the inner workings of their variations discussed.     

Synthesis, crystal structure and characterization of a 2-D network organic-inorganic hybrid polymer with [α-BW12O40]5? as building blocks

A two-dimensional network compound [Ce(DMF)₄(H₂O)][α-BW₁₂O₄₀]·H₂O·(HDMA)₂ (HDMA = protoned dimethylamine, DMF = N,N-dimethylformamide) was synthesized from α-H₅BW₁₂O₄₀·nH₂O, Ce(NO₃)₃·6H₂O and DMF and characterized by IR, UV spectra and TG-DTA. The result of the X-ray single crystal diffraction indicates that the crystal is monoclinic, space group P2₁/n, with unit cell dimensional: a = 1.1983(3), b = 2.4216(5), c = 1.9517(4) nm, β = 92.91(3)°, Z = 4, R ₁ = 0.07710, wR ₂ = 0.1416. Structural analysis indicates that every [Ce(DMF)₄(H₂O)]³⁺ building block is surrounded by three adjacent [α-BW₁₂O₄₀]⁵⁻ polyanions, meanwhile, every [α-BW₁₂O₄₀]⁵⁻ polyanion interconnects with three neighboring [Ce(DMF)₄(H₂O)]³⁺ subunits, by making use of which two-dimensional network structure can be constructed. The result of thermogravimetric analysis manifests that the title compound has two-stage weight loss and the decomposition temperature of the title polyanionic framework is 560°C. The electrochemical analysis shows the title polyanion has three-step redox processes in the pH = 4–7 media.     

A new lead Mo(IV) phosphate with a tunnel structure: Pb2Mo2O(PO4)2P2O7

A molybdenum (IV) phosphate containing lead, Pb₂Mo₂(PO₄)2P₂O₇, has been synthesized for the first time. It crystallizes in the space group C2/c with a=14.098(1) Å, b=14.187(2) Å, c=6.5592(4) Å and β=102.08(1)°. Its original tunnel structure, built up of Mo₂O₁₁ bioctahedra, P₂O₇ and PO₄ phosphate groups can be described from the assemblage of [Mo₄P₄O₂₄]_∞ ribbons interconnected through monophosphate groups. The stereoactivity of the 6s² lone pair of Pb²⁺, which is surrounded by nine oxygen atoms, is discussed.     

High conductive copolymers of polypyrrole-α,ω-diamine polydimethylsiloxane

Block copolymers of α,ω-diamine polydimethylsiloxane (DA · PDMS) and polypyrrole have been produced by the polymerization of pyrrole with the redox system of ceric salt/DA · PDMS. The properties of the copolymers may be regulated by the ratio of DA · PDMS/Pyrrole/Ce₄(NH₄)₂(NO₃)₆. The copolymers with lower conductivities are soluble in solvents such as DMF and acetone but higher conductive copolymers are insoluble. A block copolymer with unusually high conductivity (4000 S/cm) was produced under one specific polymerization condition. The chemical structure and the surface morphology of the copolymer particles seem to be important for high conductivity.     

The production of H(2S) atoms in the energy-transfer reaction of O2(1Δg) with HO2(X̃2A″)

The reaction of O₂(¹Δg) with HO₂(X?) was studied in an isothermal flow reactor in the pressure range 7?p? 10.7 mbar at temperatures between 299?T? 423 K. H-atom production was observed in the reaction O₂(¹Δg) + HO₂(òA′) - H(²S)+ 2O₂ (³Σ_g^?). The rate of this reaction (k₁) is estimated to be k₁ = (1 ± 0.5) × 10¹⁴ CM³ Mol^?1 s^?1. The implications of this reaction to recent determinations of the rate of the reaction H + O₂(¹Δg) are discussed.     

Variable-temperature and solvent NMR study of bis(μ2-methanethiolato)-bis(dinitrosyliron) and bis(μ2-methaneselenolato)-bis(dinitrosyliron)

The ¹H NMR spectrum of Fe₂(SMe)₂(NO)₄ has been measured in a total of 22 solvents, and the activation barrier ΔG^≠ for the C_2h?C_2v isomerisation in nine of these solvents. In aromatic solvents, the solvent-induced shifts are consistent with the formation of charge-transfer complexes, either 1:1 or 1:n; in non-aromatic, non-halogenated solvents of high dipolarity/polarizability the solvent-induced shifts follow the variation of the solvatochromic parameter, π*. The behaviour of Fe₂(SeMe)₂(NO)₄ in a limited range of solvents is similar. The activation barrier ΔG^≠ in Fe₂(SMe)₂(NO)₄ is ca 78 kJ mol^?1 in the majority of solvents, but that for Fe₂(SeMe)₂(NO)₄ is significantly higher.     

Coordination polymerization with the novel η-C20H17Ti(OPr)3 complex

Modified corannulene based transition metal complexes of titanium as a novel group of metallocene catalysts were synthesized and investigated in coordination polymerization reactions as catalysts in the syndiospecific bulk polymerization of styrene. In comparison to the zirconium complex exo-(η⁵-C₂₀H₁₇)(η⁵-C₅H₅)ZrCl₂, the titanium complex η⁵-C₂₀H₁₇Ti(OⁱPr)₃ shows a significantly increased polymerization activity, a considerably improved stereoregularity of the syndiotactic polymer chain, indicated by the increased melting temperature of 269 °C, as well as a higher weight average molecular weight and a narrower molecular weight distribution.     

Photopolymerization with the use of titanocene dichoride as sensitizer

Titanocene dichloride sensitized photopolymerization of vinyl ethers and styrene but did not polymerize methyl methacrylate and vinyl acetate. In the case of 2-chloroethyl vinyl ether, polymerization started rapidly some time after the color of the liquid had changed from orange to green. Polymerization was also achieved by heating the monomer at 60°C after stopping the irradiation at the end of the induction period. On the basis of the reactivity of the monomers and the effect of additives, polymerization is considered to proceed cationically. In case of the polymerization of styrene, conversion increased linearly with time. The k/k_t value of 6.3 × 10^?5l./mole-sec obtained for the polymerization of styrene agrees well with the value reported for radical polymerization. The agreement of the value and ineffective inhibition of polymerization in the presence of pyridine indicates the polymerization follows a radical mechanism. Copolymerization of styrene (M₁) and 2-chloroethyl vinyl ether (M₂) proceeded radically, and the reactivity ratios were r₁ = 2.5 and r₂ = 0.6.