Cationic polymerization of 2-vinylthiophene - the polymer structure formation

Summary The cationic polymerization of 2-vinylthiophene (VT) has been studied in solution and on the surface of silica particles. For this purpose different cationically active initiators have been used, e.g. SnCl₄, CF₃SO₃H, and CF₃COOH in homogeneous solution as well as (4-CH₃OC₆H₄)₂CH-Cl and (C₆H₅)₃CCl in conjunction with silica nanoparticles in a slurry. For all experiments a high conversion of VT to oligomers with M_n= 1500 −2000 g/mol (M_w/M_n= 1.4) (Tg = 109 °C) and oligoVT/silica hybrid particles, respectively, have been observed. The different head and endgroups have been ascertained by means of MALDI TOF spectroscopy. Different NMR spectra analyses of the oligomers show that both the vinyl double bond and the five position of the thiophene ring are involved in the propagation reaction. Received: 23 April 2001/Revised version: 25 July 2001/Accepted: 25 July 2001     

Photoelectron Spectroscopy of OH−-Anion–Water Clusters Generated by Ultrasonic Nebulizer

Investigating molecules in the gas phase is the only way to discover their intrinsic molecular properties; however, it is challenging to produce the gaseous phase of large-molecule chemicals. Thermal evaporation is typically used to convert molecules into gases, but it is still challenging to study ionic molecules in solutions in the gas phase. Electrospray ionization is one of the best methods to generate molecules in the gas phase, and it is uniquely capable of studying large biomolecules, including proteins. However, the molecular temperature required to study the spectroscopic properties of the molecules is very high. In this study, we developed a new, simple evaporation method using an ultrasonic nebulizer to obtain gas-phase molecules. Using this new equipment, we observed OH⁻ anions and their water clusters in the gas phase and obtained their photoelectron spectra. We observed that the vertical electron-detachment energy (VDE) of OH⁻ was 1.90 ± 0.05 eV and the VDEs of its water clusters and OH⁻ (H₂O)_n (n = 1–2) decreased to 1.50 ± 0.05 eV (n = 1) and 1.30 ± 0.05 eV (n = 2), respectively.     

Anionic living polymerization of macromonomers: Preparation of a particle-like purging reagent and characterization of poly(macromonomer)s

A cross-linked polystyrene particle (Merrifield resin, R-C₆H₅) was reacted with benzoyl chloride in nitrobenzene to produce R-C₆H₄-COC₆H₅ having a benzophenone group, and the R-C₆H₅-COC₆H₅ was reacted with a sodium mirror in THF under 10⁻⁵ mmHg to produce R-C₆H₅-CO⁻C₆H₅Na⁺ containing a benzophenone sodium as a particle-like purging reagent (PPBNa). (4-vinylbenzyl)Polystyrene macromonomers (PSM4: M_n=4.6₂×10³, M_w/M_n=1.0₃ and PSM7: M_n=7.1₀×10³, M_w/M_n=1.0₂) were dried under 10⁻⁶ mmHg for more than 72 h, purified by a special procedure using the PPBNa, and then were living anionically polymerized by sec-BuLi in benzene or n-BuLi in tetrahydrofuran to produce the corresponding poly(PSM)_n star polymers. The resultant star polymers were characterized by gel permeation chromatography equipped with low-angle laser light-scattering (GPC-LALLS), membrane osmometry (OSM), and light-scattering (LS). Anionic living polymerization of the PSM macromonomers was confirmed by the fact that the molecular weight of the poly(PSM)_n increased and by the fact that the initiation efficiency was constant despite an increase in the polymer yields. Some solution properties and specific dimensions characteristic to the poly(PSM)_n star polymers are discussed by comparing the GPC-LALLS, OSM, and LS results for those polymers with the results for linear polystyrenes.     

Deuterium kinetic isotopic study for hydrogenolysis of ethyl butyrate

The hydrogenation of ethyl butyrate, n-butyric acid, and n-butyraldehyde to their corresponding alcohol(s) has been studied over a γ-Al₂O₃-supported cobalt catalyst using a high-pressure fixed-bed reactor in the temperature range of 473–493 K. H₂–D₂–H₂ switching experiments show that ethyl butyrate and n-butyric acid follow an inverse kinetic isotope effect (KIE) (i.e. r^H/r^D = 0.50–0.54), whereas n-butyraldehyde did not display any KIE (i.e. r^H/r^D = 0.98). DRIFTS experiments were performed over the support and catalyst to monitor the surface species formed during the adsorption of ethyl butyrate and n-butyric acid at atmospheric pressure and the desired temperature. Butanoate and butanoyl species are the stable surface intermediates formed during hydrogenation of ethyl butyrate. Hydrogenation of butanoate to a partially hydrogenated intermediate is likely involved in the rate-determining step of ethyl butyrate and butyric acid hydrogenation.     

Kinetics of the Polymerization of Permethylcyclosiloxanes Initiated by Tetrakis(pentafluorophenyl)borate Protic Complex

The kinetics of ring opening polymerization of hexamethylcyclotrisiloxane, D₃, and octamethylcyclotetrasiloxane, D₄, in toluene initiated by protic borate complex H⁺ (H₂O)₃B(C₆F₅)₄ have been studied. The reaction is first order in monomer and first order in initiator. Rate constants and activation parameters were determined. The formation of cyclic oligomers was followed. The kinetics of the formation of decamethylcyclopentasiloxane, D₅, during the polymerization of D₄ was in agreement with a back-biting mechanism. D_3n cyclics (n = 2, 3,...) are exclusively formed during D₃ polymerization by intramolecular reactions between the chain ends. The amount of generated D₆ increases linearly with the monomer conversion in the range of the D₃ conversion between 0 and 60% and is almost independent of temperature. Kinetic results are interpreted in terms of a mechanism involving cyclic tertiary trisilyloxonium ion transitory intermediates.     

Structure and molecular weight of catenapoly [diphenoxy-λ5-phosphazene-co-bis(sulfophenoxy)-λ5-phosphazene] obtained from catenapoly (diphenoxy-λ5-phosphazene) in very strong acid medium

Acid polymers, ?[N=P(OC₆H₅)_2?x (OC₆H₄SO₃H) _x ] _n (II), having an entirely inorganic chain of fifth-group elements, with acid equivalent values between 2.90 and 5.19 mEq/g and molecular weights (M _w) of 10⁵?10⁶ (205≤n≤3582), have been obtained from ?[N=P(OC₆H₅)₂]? _n (I), 4325≤n ≤ 20,300, in very strong acid medium (SO₃/?P=N ?=1.15?3.10 mol/mol). Sulfonation of the pendant substituents occurs first in the meta position and successively at the para carbons, presumably due to reduced conformational mobility as the degree of substitution (x) in II increases.     

Coordination assemblies of CdII/ZnII/CoII with the 3-(pyridin-4-yl) benzoate tecton: Structural diversity and properties

Three novel coordination polymers{[CdL₂(HL)(H₂O)]·(H₂O)}_n (1), [Zn₂(OH)L₃]_n (2) and [CoL₂(H₂O)]_n (3) have been hydrothermally synthesized from M(NO₃)₂·nH₂O (M^II = Cd^II, Zn^II and Co^II) and an unsymmetrical tecton 3-(pyridin-4-yl) benzoic acid (HL). All complexes show interesting structural patterns, namely, unprecedented 1D double-stranded supramolecular clasp for 1, novel (3,5,6)-connected helical tubular double layer for 2, 2-fold interpenetrating cds network for 3. The fluorescent and thermal properties of complexes 1, 2 and/or 3 have also been investigated.     

Comparative Evaluation of Tri-n-butyl Phosphate (TBP) and Tris(2-ethylhexyl) Phosphate (TEHP) for the Recovery of Uranium from Monazite Leach Solution

Separation of U(VI) from Th(IV) and rare earth elements (REEs) present in monazite leach solution (nitric acid medium) has been studied using tris(2-ethylhexyl) phosphate (TEHP) and tri-n-butyl phosphate (TBP) dissolved in n-paraffin as solvents under varying experimental conditions such as nitric acid, extractant and metal ion concentrations etc. There is an increase in distribution ratio of U(VI) (D _U ) with increase in aqueous phase acidity up to 5 M HNO₃ beyond which a decrease is observed. Typically for 1 × 10^?3 M U(VI), the D_U values increase from 8 (0.5 M HNO₃) to 80 (5 M HNO₃) for 1.1 M TEHP, and from 2 (0.5 M HNO₃) to 43 (5 M HNO₃) for 1.1 M TBP in n-paraffin. The separation factors of U(VI) (β: D_U/D_M) over metal ions (M) such as Th(IV) and Y(III) (chosen as a representative of heavy REEs) are better for TEHP than TBP at all nitric acid concentrations. Batch solvent extraction data have been used to construct the McCabe-Thiele diagrams for the recovery of U(VI) employing TEHP as the extractant. A process flow sheet has been proposed with 0.2 M TEHP in n-paraffin as solvent for the recovery of U(VI) from simulated monazite leach solution in HNO₃ medium.     

Preparation and properties of sol–gel synthesized Mg-substituted Ni2Y hexagonal ferrites

A series of single phased Y-type hexagonal ferrites Sr₂Ni_2?xMg_xFe₁₂O₂₂ (x=0.0, 0.1, 0.2, 0.3, 0.4, 0.5) were synthesized by the sol–gel auto combustion method. The effects on structural, magnetic and electrical properties have been investigated by substituting Mg²⁺ at Ni²⁺ sites. The X-ray diffraction (XRD) patterns confirm single phase Y-type hexaferrite and various parameters such as lattice constants, cell volume, X-ray density, bulk density and porosity have been calculated from XRD data. The Fourier transform infrared (FTIR) spectra show the characteristics absorption ferrite peaks of the sintered sample. The microstructure was studied by scanning electron microscopy (SEM). All the ferrites show a hexagonal platelet-like shape which is a most suitable shape for microwave absorption. The dielectric constant followed the Maxwell–Wagner interfacial polarization and relaxation peaks were observed in the dielectric loss properties. The room temperature dc electrical resistivity and activation energy were found to decrease for samples x=0.1, 0.2 and increase for the rest of samples hence making these materials suitable for multilayer chip inductors (MLCIs). A soft magnetic behavior was revealed by M–H loops. Saturation magnetization (M_s), retentivity (M_r), coercivity (H_c) and magnetic moment (n_B) were found to decrease as the Mg²⁺ contents increased.     

Differences in the molecular weight and the temperature dependences of self-diffusion and zero shear viscosity in linear polyethylene and hydrogenated polybutadiene

Within the context of a generalized coupling model we can support the hypothesis that, while the mode of relaxation for self diffusion (D) and shear flow (η) are the same, the entanglement interactions are different. We assume that there are two distinct coupling parameters n_D and n_η for self diffusion and shear flow respectively. The model predicts the molecular weight and temperature dependences to be scaled by the relevant coupling parameters as:

for melts with Arrhenius temperature dependences. We have found that n_n=0.43 and 0.42 for polyethylene (PE) and hydrogenated polybutadiene (HPB) which scale η as M^3.5 and M^3.4. Also the apparent flow activation energies $\text{E1}{}_{\mathrm{a}}$ of 6.35 kcal mole^?1 for PE and 7.2 kcal mol^?1 for HPB scale to primitive activation energies E_a of 3.6 and 4.2 kcal mole^?1 for PE and HPB respectively. On the other hand the M^?2 dependence of D results in n_D=1/3. Then the reported activation energies for self-diffusion in PE and HPB of 5.49 and 6.2 kcal mole^?1 scale to primitive activation energies of 3.7 and 4.1 kcal mole^?1, respectively.     

Synthesis and characterization of natural rubber-based telechelic oligomers via olefin metathesis

Metathesis degradation and functionalization of natural rubber (NR) were conducted with 1-hexene, 1-octene, 1-decene, 1-dodecene, trans-stilbene, and 4,4′-dibromo-trans-stilbene as chain transfer agents (CTAs) in presence of Grubbs 2nd generation catalyst to generate NR-based telechelic oligomers that had been a long-lasting challenge due to the structure and compositions of NR with various impurities. Orthogonal experiments were applied and the effects of the CTA type, CTA concentration, catalyst concentration, reaction time, and reaction temperature on the formation of telechelic oligomers were studied, indicating that the catalyst concentration was the major factor influencing the number average molecular weights (M_n) and polymer dispersity index (PDI) of telechelic oligomers. The structures of the oligomers were characterized using ¹H NMR, ¹³C NMR, and MALDI-TOF-MS, which confirmed the formation of the designed terminal groups. The results showed that well-defined telechelic oligomers with a M_n of a few thousand and a PDI around 1.6 were obtained, with potential applications in binder, lubricant and many other fields.     

Syntheses of AB2 3- and AB4 5-miktoarm star copolymers by combination of the anionic ring-opening polymerization of hexamethylcyclotrisiloxane and nitroxide-mediated radical polymerization of styrene

AB₂ 3- and AB₄ 5-miktoarm star copolymers were prepared by combination of the anionic ring-opening polymerization (AROP) of hexamethylcyclotrisiloxane (D₃) and the TEMPO-mediated radical polymerization of styrene (St). Initially, two kinds of dendritic multifunctional initiators were prepared. One has a 4-bromobutoxy group and two TEMPO-based alkoxyamines and the other has a 4-bromobutoxy group and four TEMPO-based alkoxyamines. Treatment of the multifunctional initiators with tert-butyllithium gave the corresponding lithiobutoxy derivatives, and AROP of D₃ by the lithiobutoxy derivatives gave poly(D₃) with M_w/M_n of 1.07-1.12. Nitroxide-mediated radical polymerization of St by the poly(D₃)s at 120 °C gave AB₂ 3- and AB₄ 5-miktoarm star copolymers with M_w/M_n of 1.15-1.28. Their structures were analyzed by means of ¹H NMR and SEC measurements.     

On the synthesis of acrylamide oligomers

The synthesis of low-molecular-weight poly(acrylamide)s (M?_n = 500 – 1 000) is described. Metal-activated and non-activated polymerization in aqueous solution was investigated employing hydrogen peroxide as initiator. Among four transition metal salts considered, Cu²⁺ cations proved to be the most efficient in decomposing H₂O₂ molecules and were used as activator. The experiments were run at three reaction temperatures (60, 80 and 95°C), at three H₂O₂ levels (4, 5 and 6 wt.-% on monomer), and at four Cu₂₊ levels (900, 600, 300 and 0 ppm by weight of metal on monomer). Thus, ist was possible to prepare acrylamide oligomers with monomer conversions exceeding 95%, and with M_n values covering the narrow range indicated above. Within these low limits a molecular weight control is impossible, even with inclusion of the differentiated levels of Cu²⁺cations. Intrinsic viscosities are very low, too ([η]) = 20 – 50 cm³/g, without any relations of the individual values to variations of the given process parameters. The work provides an industrial route to very-low-molecular-weight acrylamide oligomers.     

The Softness Parameters of Ions. Prediction of the Occurrence of Miscibility Gaps in Molten Salt Mixtures

Softness parameters σ_M for cations and σ_X for anions, have been calculated as dimensionless quantities for approx. 90 cations and 18 anions. They are given by σ_M = [σ_A (M^m+) - σ_A(H⁺)]/σ_A(H⁺) and σ_X = [σ_B(X^a?) - σ_B(OH^?)]/σ_A(H⁺) where σ_A = [σI_i(M) + ΔH⁰_h(M^m+)]/m and σ_B = [-E_a(X) + ΔH⁰_h(X^a?)]/a are Ahrland's parameters. The new normalized and comparative (to the test ions H⁺ and OH^?) softness parameters are positive for soft ions and negative for hard ones. These parameters, obtained independently, are used with a four-coefficient equation to calculate coordinate bond energies for metal halides with acceptable accuracy. Considerations of the average coordination in reciprocal molten salt mixture lead to an expression for the metathesis energy change as proportional to the product of the differences in softness parameters of the two cations and the two anions. An empirical one-coefficient equation involving the softness parameters is proposed to deal with next-nearest-neighbor interactions in binary common-ion molten salt mixtures. These relationships are then used with Blander and Topol's equation to predict the occurrence of irascibility gaps in uni-univalent reciprocal salt mixtures. The gaps found in other systems are also discussed in terms of the softness of the constituent ions.     

Coupling of mutual diffusion to viscoelasticity in moderately concentrated polyisobutylene solutions

The normalized intensity autocorrelation function g⁽²⁾(t) were obtained by dynamic light scattering for moderately concentrated entangled solutions of polyisobutylene in n-heptane at 25.0 °C and in isoamyl isovalerate (IAIV) at 25.0 °C (Θ). The obtained data have been successfully analyzed by the ‘procedure X’ familiar for determination of mechanical relaxation spectra on the basis of the recent theory for g⁽²⁾(t). The results have shown that while the mutual diffusion coefficient D increases in the n-heptane solutions and decreases in the IAIV solutions with increasing polymer mass concentration c, the friction coefficient ζ for both solutions increases with c showing the same power-law behavior irrespective of the weight-average molecular weight M_w and solvent quality. It has been found that the instantaneous longitudinal modulus L₀ for n-heptane solutions increases in proportion to c², obeying the familiar relation for the plateau value (4/3)G_N of the longitudinal stress relaxation modulus, but L₀ for the IAIV solutions becomes progressively smaller than the values predicted from the relation with decreasing c. The terminal relaxation time τ_m has been found to follow the power-law τ_m∝M_w^3.4 established by rheological measurements.     

Three-dimensional network constructed with novel one-dimensional Z-shaped chains via intricate noncovalent interactions

Novel coordination polymers {[M(bpmb)(H₂O)₂(C₂H₅OH)₂]·(NO₃)₂}_n (M=Zn 1, Cd 2; bpmb= N,N^′-bis (3-pyridinylmethyl)-1,4-benzenedicarboxamide) have been synthesized by the reaction of bpmb with zinc(II) salt and cadmium(II) salt in ethanol–water solution, respectively. Elemental analysis, IR spectra and X-ray crystal structure analysis were carried out to determine the compositions and crystal structures of the two compounds, which reveal that bpmb bridges the metal centers to from a one-dimensional chain. These chains were linked through noncovalent interactions to form three-dimensional networks.     

Divalent cobalt,zinc, and copper coordination polymers based on a new bifunctional ligand: Syntheses,crystal structures,and properties

Three new coordination polymers, namely, [ML(H₂O)]_n (M = Co (1), Zn (2)) and [CuL(DMF)]_n (3), have been hydrothermally synthesized through the reaction of bifunctional ligand 5-((2-methyl-1H-imidazol-1-yl)methyl)benzene-1,3-dioic acid (H₂L) with divalent cobalt, zinc and copper salts, and structurally characterized by elemental analysis, IR and X-ray diffraction. Both complexes 1 and 2 are two-fold interpenetration 3D frameworks. Complex 3 exhibits (3,6)-connected framework with (4.6²)₂(4².6¹⁰.8³) topology. Furthermore, UV–vis absorption spectra and powder X-ray diffraction (PXRD) were investigated as well.     

Corrosion of stepwise dissolving metals; corrosion mechanism of indium

The corrosion of a metal dissolving stepwise with formation of low-valency intermediates and Mⁿ⁺ ion as the final corrosion product proceeds by a complex electrochemical-chemical mechanism comprising following steps: M → M⁺ + e; M⁺ → Mⁿ⁺ + (n ? 1)O_x → Mⁿ + )n ? 1)O^?_x and O_x + e → O^?_x. A criterion of such a corrosion mechanism is the deviation of the experimental corrosion rate (i_c) from the reduction rate of oxidant O_x at the corrosion potential (i^extr._c) found by extrapolation. Cathodic polarization curves on indium have been measured and its corrosion rate has been determined by a radiotracer method in aqueous NaClO₄ + HClO₄ solutions of varying acidity. i_c is considerably higher than i^extr., the ratio i_c/i^extr._c approaching 3 with increasing acidity. In the same solutions containing O·M NaCl i_c = i^extr._c independent of acidity.     

Studies of cyclic and linear poly(dimethyl siloxanes): 13. Static dielectric measurements and dipole moments

The static dielectric permittivities, refractive indices and densities of undiluted oligomeric cyclic and linear dimethyl siloxanes and narrow fractions of cyclic and linear poly(dimethyl siloxanes) have been measured for number-average molar masses M?_n in the range $\text{160 <}\text{M}\text{?}{}_{\mathrm{n}}\text{< 7700}$ at temperatures from 298 to 313 K. Measured total dielectric polarizations have been resolved into their electronic, atomic and orientation components and dipole moments have been derived. The dipole moments of cyclic oligomers ((CH₃)₂SiO)_x (for example, with x = 4, 5) are markedly lower than the dipole moments of the corresponding linear oligomers containing the same number of siloxane bonds. However, for x ? 10, the dipole moments of cyclic dimethyl siloxanes are identical, within experimental error, to those of the corresponding linear dimethyl siloxanes. Measured static dielectric permittivities of the dimethyl siloxanes and poly(dimethyl siloxanes) in solution in cyclohexane are markedly different from the corresponding values for the undiluted siloxanes. These differences are interpreted as resulting from the specific solvent effects.     

31P NMR spectroscopic studies of the influence of the environment in the degradation process of the Graham's salt

The “Graham's salt” is a vitreous sodium polyphosphate with a general formula of Na_(n+2)P_nO_(3n+1). It is used in the ceramics industry as a deflocculant additive in a matrix of sodium silicate with different SiO₂:Na₂O ratios. The influence of the environment in which the Graham's salt is usually placed on its degradation into smaller particles has been studied by ³¹P NMR spectroscopy at several temperatures on solutions with 7% of Graham's salt in sodium silicate with Rw = 1.6, 2.0, 3.3, in sodium carbonate 0.15 M, in sodium hydroxide 0.10 M and 1.0 M and in water. The signals in the ³¹P NMR spectra of Graham's salt in D₂O, depending on their chemical shift δ (ppm) and multiplicity, have been assigned to the different phosphorous atoms of the skeleton of the several polyphosphates that are present in the solution. The integration of these signals at different temperatures has enabled the collection of kinetic and thermodynamic data: kinetic constants k (s^?1), activation energy E_a, ΔH³ and ΔS³. Results indicate that the environment is a factor which favours the degradation of polyphosphates, since with increasing basicity of deflocculating solutions the rate of degradation is faster. White gel obtained as a final product of the degradation process of Graham's salt has been analyzed with ³¹P NMR spectroscopic measurements identifying orthophosphate and pyrophosphate as the main final species of the degradation of Graham's salt.