Polymer-Supported Lewis Acid Catalysts. II. Cationic Polymerization of α-Methylstyrene with Polystyrene-Gallium Trichloride Complex as Initiator

The polymerization of α-methylstyrene catalyzed by a polymer-supported Lewis acid catalyst, polystyrene-gallium trichloride complex, is described. The kinetic equation of the cationic polymerization is R_p = k˙C_ms˙C_cat , and the apparent activation energy is 20.9 kJ/mol. The effect of different solvents on the polymerization rate is quite pronounced; for example, the polymerization rate decreased in the following order in the three solvents: CH₂ ClCH₂ Cl < CH₂ Cl₂ < CCl₄. High molecular weight poly(α-methylstyrene) (T_g = 185°C) could be obtained at room temperature. The mechanism of the polymerization is also discussed.     

Reactivity Ratios of Diethyldiallylammonium Chloride with Acrylamide or Acrylic Acid

The compositions of copolymers of diethyldiallylammonium chloride (DEDAAC) with acrylamide (AM), acrylic acid (AA) or sodium acrylic acid (NaAA) at low conversion were determined by elemental analysis, and the reactivity ratios of monomers in copolymerization were obtained by Kelen-Tudos method. The results showed that the reactivity ratios rDE and rAM are 0.31 and 5.27 for DEDAAC with AM, rDE and rAA are 0.28 and 5.15 for DEDAAC with AA, and rDE and rNaAA are 0.40 and 3.97 for DEDAAC with NaAA, respectively. The copolymerizations for DEDAAC with AM, AA or NaAA are non-ideal copolymerization and the products are random copolymers.     

Polylactones. 13. Transesterification of Poly(L-Lactide) with Poly(Glycoude), Poly(β-Propio-Lactone), and Poly[ε -Caprolactone)

Homogeneous blends of poly(L-lactide) (M _n = 30 000 to 40 000) and poly(β-propiolactone) or poly(ε-caprolactone) were prepared in solution. The solvent-free blends were subjected to transesterification catalyzed by means of methyl triflate, triflic acid, boron trifluoride, or tributyltin methoxide at 100 or 150°C. At 100°C, transesterification was barely detectable even after 96 h. When poly(β-propiolactone) was used as the reactant at 150°C, degradation was faster than transesterification regardless of the catalyst. The same negative result was obtained for heterogeneous blends of poly(L-lactide) and poly(glycolide). In the case of poly(ε-caprolactone), copolyesters with slightly blocky sequences were obtained with tributyltin methoxide as catalyst, whereas the acidic catalysts caused rapid degradation. The copolyesters were characterized by means of ¹H-NMR spectroscopy with regard to their molar composition, by means of ¹³C-NMR spectroscopy with regard to their sequences, and by means of differential scanning calorimetry with regard to crystallinity.     

Immobilized Complexes of Copper(II) Chloride with Triethylenetetramine as Catalysts for the Reaction of C–Cl Bond Metathesis

The structure and activity of C–Cl bond metathesis catalysts containing CuCl₂and triethylenetetramine (TETA) supported on silica were studied. The catalysts were found to contain 40% Cu(II) as paramagnetic complexes of the composition Cu(TETA)₂Cl₂and diamagnetic binuclear or polynuclear copper complexes, which are undetectable by EPR spectroscopy. The catalytic activity of the test systems in the radical reaction of C–Cl bond metathesis in the CCl₄–C₁₀H₂₂system was maximum at a Cu(II) concentration of 0.5 wt % on the support. A kinetic scheme was proposed, which suggests that only mononuclear copper complexes participate at the stage of radical generation, whereas termination can also occur on binuclear or polynuclear complexes.     

Degradability of Poly(β-Hydroxybutyrate)s. Correlation with Chemical Microstructure

Abstract

Poly(β-hydroxybutyrate)s (PHB) of different microstructures were synthesized via anionic polymerization of β-butyrolactone initiated by two initiators: 1) supramolecular complexes of alkali metals with asymmetric induction agents, and 2) alkali metal alkoxides. The relationships between chemical microstructure and hydrolytic as well as thermal degradation properties of synthetic and natural PHB are discussed.     

Potentiometric Determination of the Stability Constants of Trimethyltin(IV) Chloride Complexes with Imino-bis(Methylphosphonic Acid) in Water and Dioxane–Water Mixtures

The interaction of trimethyltin(IV) (TMT) with imino-bis(methylphosphonic acid) (IDP), abbreviated as H₄L, was investigated at 25 °C and at ionic strength 0.1 mol⋅dm⁻³ (NaNO₃) using a potentiometric technique. The formation constants of the complexes formed in solution were calculated using the nonlinear least-squares program MINIQUAD-75. The stoichiometry and stability constants are reported for the complexes formed. The results show the formation of 110, 111, 112 and 11-1 complexes for the TMT–IDP system. The concentration distribution of the various complex species was evaluated. The effect of dioxane as a solvent, on both the protonation constants and the formation constants of trimethyltin(IV) complexes with IDP, is discussed. The thermodynamic parameters ΔH ^∘ and ΔS ^∘ calculated from the temperature dependence of the equilibrium constants were evaluated. The effect of ionic strength on the protonation constants of IDP is also discussed.     

Stability of New Zinc Complexes with β,βʹ-(Ethylenediamine)-N,N-dipropionic Acid

Russian Journal of General Chemistry - Stability constants of new zinc complexes with β,β?-(ethylenediamine)-N,N-dipropionic acid:...     

Complexes of tetracyanobiimidazole—V. Self-association of Ir(I) complex anions

The self-association of the planar anion [Ir(CO)₂Tcbiim]⁻ where H₂Tcbiim is 4,4′,5,5′-tetracyano-2,2′-biimidazole has been studied in acetontrile solution by analysis of the charge-transfer spectra. At low concentrations (∼ 10⁻⁵ M) monomer units prevail. At intermediate concentrations (∼ 10⁻³ M) dimerization is evident and a very strong (ε = 18 500 M⁻¹ cm⁻¹) new absorption appears at 475 nm. A novel procedure was used to obtain this value and to estimate the equilibrium constant for dimerization, 13.2 M⁻¹ at 24.4°C. From the temperature dependence of the spectra, ΔH is calculated to be −28 to −30 kJ M⁻¹. At higher concentrations (∼ 10⁻² M) spectral changes consistent with further oligomerization are observed.     

Spectrophotometric Studies of V(V) Complexes of N-Methylaminothioformyl-N′-phenylhydroxylamine

The violet-colored complexes of V(V) and N-methylaminothio-formyl-N′-phenylhydroxylamine are extractable into chloroform. The spectrophotometric studies have shown that 1:3 and 1:4 (metal:ligand) complexes predominate in the acidity range 6.5–9 N and 9.5–10.5 N HCl, respectively. The values of stability constants, stepwise and overall, have been calculated by following extended Leden and Yatsimirskii methods. The analytical suitability of the reagent for the microdetermination of vanadium has also been investigated.     

Surface Properties of Polyacid–Poly(N-Vinyl Pyrrolidone) Complexes

The effect of the complexation of polyacrylic (PAA) and polymethacrylic (PMAA) acids with poly(N-vinyl pyrrolidone) (PVP) on their surface properties was studied by measuring surface tension, conductivity, and the viscosity of aqueous mixed polymer solutions, as well as by the potentiometric titration at 293.15 K. The values of relaxation times and the surface activity of polycomplexes were calculated from kinetic data and the surface tension isotherms of the solutions. The complexation was found to increase the surface layer relaxation time, surface activity, and the ability of the macromolecules to reduce the surface tension of solvent. The values of adsorption free energy were calculated for PVP and polycomplexes. They were equal to –22.0, –23.0, and –24.8 kJ/base-mole (per one mole of PVP monomer unit) for PVP and PMAA–PVP and PAA–PVP polycomplexes, respectively.     

Syntheses and Crystal Structures of Co(Ⅱ)Complexes with 5-Tert-butyl Isophthalic Acid

<正>Two new Co(Ⅱ)coordination polymers {[Co(Htbip)_2(H_2O)_4]·(H_2O)}_n 1 and {[Co_2(tbip)_2(bpa)_(1.5)](H_2tbip)}_n 2(H_2tbip=5-tert-butyl isophthalic acid,bpa=1,2-dis(4-pyridyl) ethane)have been synthesized under hydrothermal conditions and characterized by elemental analysis,IR spectroscopy and X-ray diffraction.Compound 1 exhibits a water-bridged 1-D linear chain which is extended by hydrogen bonds into a 3D supramolecular network,while compound 2 has a dinuclear unit extended by bpa ligand to form a 2-D layer.     

Boron(III) Tribromide or Titanium(IV) Bromide and Lewis Base Promoted Baylis-Hillman Reaction

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Synthesis and Characterization of Pheox– and Phebox–Aluminum Complexes: Application as Tunable Lewis Acid Catalysts in Organic Reactions

Pheox– and Phebox–aluminum complexes were synthesized and subsequently characterized by spectroscopic analysis. These complexes acted as Lewis acid catalysts, and their catalytic activities were controlled by using the Pheox, Phebox, and heteroatom ligands. The Pheox–aluminum complex exhibited an opposite substrate selectivity to AlCl₃ in a competitive hetero-Diels–Alder reaction between electron-rich and electron-deficient aldehydes.     

Gas Chromatographic Determination of Poly(3‐hydroxybutyrate) with Alkaline Hydrolysis and Acid Esterification

Abstract

A new pretreatment method for the gas chromatographic determination of poly(3‐hydroxybutyrate) (PHB) was developed based on a combination of alkaline hydrolysis and acid esterification. The determination principle is as follows: PHB is hydrolyzed to its monomer 3‐hydroxybutyrate by alkaline solution, followed by the esterification with methanol to generate the methyl ester of 3‐hydroxybutyrate catalyzed by acid, which is detected by a gas chromatography. From the comparison of effects of alkali and acid on PHB hydrolysis and 3‐hydroxybutyrate esterification, alkali resulted in a better performance for the hydrolysis, while acid was better for the esterification. The pretreatment conditions for PHB were optimized and the determination performance was characterized.     

α-Amino-iso-Butyric Acid Foldamers Terminated with Rhodium(I) N-Heterocyclic Carbene Catalysts

To investigate how remotely induced changes in ligand folding might affect catalysis by organometallic complexes, dynamic α-amino-iso-butyric acid (Aib) peptide foldamers bearing rhodium(I) N-heterocyclic carbene (NHC) complexes have been synthesized and studied. X-ray crystallography of a foldamer with an N-terminal azide and a C-terminal Rh(NHC)(Cl)(diene) complex showed a racemate with a chiral axis in the Rh(NHC) complex and a distorted 3₁₀ helical body. Replacing the azide with either one or two chiral L-α-methylvaline (L-αMeVal) residues gave diastereoisomeric foldamers that each possessed point, helical and axial chirality. NMR spectroscopy revealed an unequal ratio of diastereoisomers for some foldamers, indicating that the chiral conformational preference of the N-terminal residue(s) was relayed down the 1 nm helical body to the axially chiral Rh(NHC) complex. Although the remote chiral residue(s) did not affect the stereoselectivity of hydrosilylation reactions catalysed by these foldamers, these studies suggest a potential pathway towards remote conformational control of organometallic catalysts.     

Determination of Lewis Acid Base Properties of Poly(??-n-alkyl) Methacrylates Adsorbed on Silica by Inverse GC

In this paper, the acid base properties in the Lewis terms of poly(??-n-alkyl) methacrylates and when they are adsorbed on silica, were determined. The acid base constants K _A and K _D of various polymers were calculated by testing the classical model and proposed a new model giving K _A and K _D and a third constant K reflecting the amphoteric character of our solid substrates and obtaining more precise and quantified results. When the length of alkyl group in side chain of poly(??-n-alkyl) methacrylates changes, the surface properties of such polymers also change and consequently affect all superficial characteristics and especially the acid base constants and the transition phenomena. It was also proved that the specific enthalpy was directly correlated to the acid base constants, the carbon atom number in the side chain of poly(??-n-alkyl) methacrylates and the acceptor AN and donor DN numbers of electrons of polar organic molecules, by the following relationship: ??H ^sp?=???H ^sp(AN, DN, K _D, K _A, n _SC).     

Dioxygen Affinities and Catalytic Oxidation Performance of Cobalt (II)Complexes with N-Aryl Hydroxamic Acid

It is well known that the study on biomimetic oxygen carriers not only has important theoretic significance to discover the mechanism of reversible bonding, activating oxygen as well as the oxidation reaction in organism, but also has potential application in separating oxygen from air and realizing the high efficiency and selectivity of catalytic oxidation reaction under a mild condition1. Metal- porphyrin and metal- phthalol- gaunine have been extensively used as biomimetic oxygen carriers u…     

Crystallizability of Poly(ε-caprolactone) Blends with Poly(vinylphenol) under Different Conditions

The intermolecular interaction between poly（vinylphenol） （PVPh） and polycaprolactone （PCL） and the crystallization behavior of PCL in PCL/PVPh blends with different compositions and under different conditions were investigated by Fourier transform infrared spectra （FTIR） and differential scanning calorimetry （DSC）. It has been shown that the PCL in the blends with different blend ratios all exists in crystalline state after solution casting, even though the crystallinity decreases with increasing PVPh content. For the melt crystallized samples, PCL in its 80/20 PCL/PVPh sample can still crystallize. The crystallinity is, however, lower than that of the solution cast sample. For blends containing 50% or 20% PCL, the as-cast samples are semicrystalline and can change to compatible amorphous state after heat treatment process. FTIR analysis shows the existence of hydrogen bonding between PCL and PVPh and the fraction of hydrogen bonds increases remarkably after heat treatment process.     

Crystal Structures of the Inclusion Complexes of β-Cyclodextrin with Aliphatic Monoacids Tridecanoic Acid and (Z)-Tetradec-7-enoic Acid. Formation of [3]Pseudorotaxanes

The structures of the inclusion complexes of beta cyclodextrin with the aliphatic mono-acids tridecanoic acid (1) and (Z)-tetradec-7-enoic acid (2) have been determined at room temperature. Both compounds crystallise in P1, a = 15.654(6) Å, b = 15.650(6) Å, c = 15.937(6) Å, = 101.58(1)°, = 101.59(1)°, = 103.58(1)°, Z = 1, for 1 and a = 15.6259(9) Å, b = 15.623(1) Å, c = 15.935(1) Å, = 101.547(2)°, = 101.555(2)°, = 103.642(2)°, Z = 1, for 2. One molecule of the monoacids threads through two cyclodextrin macrocycles arranged in dimers thus forming [3]pseudorotaxanes. The host dimers are aligned along a channel in order to create a hydrophobic environment for the terminal methyl group of the guest and isolate it from the aqueous environment that surrounds the cyclodextrin dimeric units. The guests exhibit disorder over two orientations resulting in hydrogen bonding between the carboxyl groups of adjacent guest molecules along the channel and formation of carboxylic dimers. This crystal packing differs from that of -CD complexes of homologous dicarboxylic acids.