ANIONIC POLYMERIZATION OF STYRENE EFFECT OF TETRAHYDROFURAN

1962 ◽  
Vol 40 (8) ◽  
pp. 1564-1570 ◽  
Author(s):  
S. Bywater ◽  
D. J. Worsfold
Keyword(s):  
Anionic Polymerization ◽  
Benzene Solution ◽  
Ion Pairs ◽  
High Reactivity ◽  
Small Concentration ◽  
Kinetic Order ◽  
Highly Active ◽  
Lower Reactivity ◽  
Free Ion ◽  
Complete Breakdown

The propagation step in the butyllithium­initiated polymerization of styrene in benzene solution is thought to be due to a small concentration of highly active free ion-pairs in equilibrium with unreactive dimeric ion­pairs. This work shows that these dimers may be broken down by the addition of tetrahydrofuran. Small quantities of tetrahydrofuran form, first, a low concentration of a monoetherate of the ion­pair with a high reactivity, and this augments the propagation reaction without changing the kinetic order with respect to the initiator. This, at higher tetrahydrofuran concentrations, is followed by the complete breakdown of the dimers to give a dietherate in much higher concentration and lower reactivity compared with the initial ion­pair and monoetherate. The kinetic order with respect to the initial initiator species changes from one half to one during this process, and a maximum appears in the rate as the ether concentration increases.

Isotope effects and activation parameters for the proton transfer reaction from 1-(4-nitrophenyl)-1-nitroethane to free anions and ion pairs of cesium n-propoxide in n-propanol solvent

1986 ◽  
Vol 64 (6) ◽  
pp. 1021-1025 ◽  
Author(s):  
Arnold Jarczewski ◽  
Grzegorz Schroeder ◽  
Przemyslaw Pruszynski ◽  
Kenneth T. Leffek
Keyword(s):  
Proton Transfer ◽  
Rate Constants ◽  
Isotope Effects ◽  
Ion Pairs ◽  
Activation Parameters ◽  
Solvation Shell ◽  
Ion Pair ◽  
Initial State ◽  
Free Ion ◽  
Deuteron Transfer

Rate constants for the proton and deuteron transfer from 1-(4-nitrophenyl)-1-nitroethane to cesium n-propoxide in n-propanol have been measured under pseudo-first-order conditions with an excess of base for four temperatures between 5 and 35 °C. Using literature values of the fraction of cesium n-propoxide ion pairs that are dissociated into free ions, separate second-order rate constants for the proton and deuteron transfer to the ion pair and to the free ion have been calculated. The cesium n-propoxide ion pair is about 2.8 times more reactive than the free n-propoxide ion. The primary kinetic isotope effects for the two reactions are the same (kH/kD = 6.1–6.3 at 25 °C) within experimental error. The enthalpy of activation is smaller for the ion-pair reaction and the entropy of activation more negative than for the free-ion reaction. For proton transfer, ΔH±ion pair = 8.3 ± 0.2 kcal mol−1, ΔH±ion = 9.6 ± 1.0 kcal mol−1, ΔS±ion pair = −12.3 ± 0.6 cal mol−1 deg−1, ΔS±ion = −10.1 ± 3.4 cal mol−1 deg−1. The greater reactivity of the ion pair relative to the free ion is interpreted in terms of the weaker solvation shell of the ion pair in the initial state.

ANIONIC POLYMERIZATION OF ISOPRENE

1964 ◽  
Vol 42 (12) ◽  
pp. 2884-2892 ◽  
Author(s):  
D. J. Worsfold ◽  
S. Bywater
Keyword(s):  
Light Scattering ◽  
Anionic Polymerization ◽  
Great Increase ◽  
Major Effect ◽  
Dilute Solution ◽  
Initiation Rate ◽  
Kinetic Order ◽  
Initiation Reaction

The polymerization of isoprene with butyllithium in cyclohexane has been studied. The initiation reaction was found to be complex; plots of conversion of butyllithium against time are sigmoidal. The order with respect to the initiator was found to be between one-half and one. The order of the isolated propagation reaction in polyisoprenyllithium was found to be one-quarter and was correlated with a fourfold association of active chain ends determined by dilute solution light-scattering measurements.The major effect of tetrahydrofuran on the reaction was the great increase of the initiation rate. The kinetic order changes slowly with the addition of small amounts of tetrahydrofuran, suggesting that the aggregates are broken down with difficulty. The microstructure of the polymer has been determined by n.m.r. measurements and shows a steady transition from a largely 1:4 to a largely 3:4 structure as the polarity of the solvent is increased by the addition of tetrahydrofuran.

Tetrabutylammonium Salts of 2-Nitropropane, Cyclopentadiene and 9-Ethylfluorene: Crystal Structures and Use in Anionic Polymerization

1995 ◽  
Vol 50 (3) ◽  
pp. 415-422 ◽  
Author(s):  
Manfred T. Reetz ◽  
Stephan Hütte ◽  
Richard Goddard
Keyword(s):  
Anionic Polymerization ◽  
Room Temperature ◽  
Ion Pairs ◽  
Three Dimensional ◽  
Star Polymers ◽  
X Ray ◽  
Dimensional Network ◽  
Acidic Compounds ◽  
Cyclopentadienyl Anion ◽  
Special Case

Reaction of the CH-acidic compounds 2-nitropropane, cyclopentadiene and 9-ethylfluorene with HON (nBu)4 affords the corresponding tetrabutylammonium salts in crystalline form, which have been characterized by X -ray structure analysis. The nitrostabilized salt is not a “naked ” anion (real carbanion). Rather, the α-methylene entities of the N+(nBu)4 cations form relatively strong hydrogen bonds with the O -atom s of the nitronateanion, forming dimers in a three-dimensional network. In solution dimers in the form of supramolecular ion pairs exist. In contrast, the cyclopentadienyl anion appears to be a real carbanion, since anion and cation do not interact with one another via H -bonding. The structure of the N+(nBu)4 salt of the 9-ethylfluorenyl anion is a special case in that closer contacts between cation and anion occur, which may be indicative of unusual [CH ··· C]- bonding. All three salts function as initiators in the metal-free anionic polymerization of acrylates and methacrylates at room temperature. In the case of tetrabutylammoniumcyclopentadienide, star polymers are formed.

Ionization of Liquid Tetramethyl Germanium by 60Co-γ-Radiation

1990 ◽  
Vol 45 (6) ◽  
pp. 832-834 ◽  
Author(s):  
I. Lopes ◽  
W. F. Schmidt
Keyword(s):  
Field Strength ◽  
Electric Field ◽  
Applied Electric Field ◽  
Ionization Chamber ◽  
Parallel Plate ◽  
Ion Pairs ◽  
Guard Ring ◽  
Applied Electric Field Strength ◽  
Γ Radiation ◽  
Free Ion

AbstractThe ionization current produced in liquid tetramethyl germanium by 60Co-γ-radiation was measured with a guard ring type, parallel plate ionization chamber. The yield of ion pairs as a function of the applied electric field strength was determined and the free ion yield without applied electric field was obtained to be Gfi (0) = 0.68 ±0.10.

Monomer Solvation of Ion Pairs in Anionic Polymerization

Nature ◽  
1967 ◽  
Vol 215 (5098) ◽  
pp. 273-274
Author(s):  
G. C. EAST ◽  
M. A. HARRISON
Keyword(s):  
Anionic Polymerization ◽  
Ion Pairs

scholarly journals Preparation of photocatalyst with high reactivity from cellulose-based graphitic carbon

BioResources ◽  
2019 ◽  
Vol 14 (3) ◽  
pp. 7213-7228
Author(s):  
Chao Chen ◽  
Kang Sun ◽  
Ao Wang ◽  
Hao Sun ◽  
Xincheng Lu ◽  
...  
Keyword(s):  
Graphene Oxide ◽  
Catalyst System ◽  
Reaction Rates ◽  
High Reactivity ◽  
Walnut Shell ◽  
Carbon Substrate ◽  
In Situ Deposition ◽  
Lower Reactivity ◽  
Excellent Photocatalytic Activity ◽  
Heating Treatment

A photocatalyst with high reactivity was prepared in liquid phase through the in situ deposition of TiO2 on cellulose-based graphitic material that had been oxidized via Hummers’ method that was followed by a heating treatment at 200 °C. The composite had excellent photocatalytic activity for degrading methyl orange (MO), and reducing hexavalent chromium (Cr(VI)) under ultraviolet irradiation as well as the reported graphene oxide/TiO2 composite. Under the optimal condition, the reaction rates for treating MO and Cr(VI) using the new catalyst system were 4.6 and 1.6 times higher, respectively, than that of commercial TiO2 (P25). In addition, the composite had good catalytic activity in acid solutions. Unlike the reported graphene oxide/TiO2 composite, TiO2 nanoparticles in the prepared composite aggregated to large particles of approximately 1 μm in size on the carbon substrate. When synthesized in the same procedure from other biomass materials, such as lignin, walnut shell, or fir sawdust, the composite had much lower reactivity, similar to that of neat TiO2; the lower graphitic degree of those materials might be the reason for the disparity in reactivity.

scholarly journals The Influencing Factors for Volume Stability of Ladle Slag

Processes ◽  
2022 ◽  
Vol 10 (1) ◽  
pp. 92
Author(s):  
Tung-Hsuan Lu ◽  
Ying-Liang Chen ◽  
Hong-Paul Wang ◽  
Juu-En Chang
Keyword(s):  
Cementitious Materials ◽  
Test Methods ◽  
Standard Test ◽  
High Reactivity ◽  
Cementitious Material ◽  
Ladle Slag ◽  
Volume Stability ◽  
Hydraulic Cement ◽  
Lower Reactivity ◽  
Higher Temperature

The purpose of this study was to investigate the mechanism causing the unsoundness of ladle slag. Calcination temperature may have an impact on the level of reactivity of f-CaO. When CaO was produced at a higher temperature, the reactivity of CaO was lower. For example, dead burnt CaO (DCaO) was produced at higher temperatures than light burnt CaO (LCaO); therefore, DCaO had less reactivity than LCaO. In a hydration test, DCaO (1500 °C) showed 62 times lower reactivity than LCaO (900 °C), which meant that DCaO would result in the delay of hydration of CaO easily. Additionally, DCaO would cause unsoundness more easily than LCaO when adding the same number of cementitious materials. For this reason, using ASTM C114-18 (Standard Test Methods for Chemical Analysis of Hydraulic Cement) to quantify DCaO content may underestimate DCaO content by up to 20%. Conversely, this method was more suitable for f-CaO since it had high reactivity. Moreover, this study demonstrated that ladle slag would cause unsoundness when added into the cementitious material because it was produced from a higher temperature process (over 1500 °C), which generates the DCaO. Therefore, when reusing ladle slag, the problem of low reactivity of DCaO should be considered.

Sternheimer Factors and Electric-Field-Gradient Hyperpolarisabilities for Ions in Crystals

1994 ◽  
Vol 49 (1-2) ◽  
pp. 125-128 ◽  
Author(s):  
P. W. Fowler ◽  
H. M. Kelly
Keyword(s):  
Electric Field ◽  
Electric Field Gradient ◽  
Field Gradient ◽  
Significant Variation ◽  
Ion Pairs ◽  
Lattice Parameter ◽  
Hartree Fock ◽  
Shielding Factor ◽  
Free Ion ◽  
Or Modelling

Abstract Analytic coupled Hartree-Fock calculations of the electric field gradient response properties y (the Sternheimer shielding factor) and e (the dipole-dipole-electric field gradient hyperpolarisability) have been carried out on anions in clusters that simulate that crystal environment. The systems studied are F- in LiF and NaF, Cl- in LiCl and NaCl, O2-in MgO, S2- in MgS, and H- in LiH. Both properties show large reductions from free-ion values and significant variation with lattice parameter, and the results indicate that damped values of anion Sternheimer factors will be necessary in accurate simulation of N Q R data or modelling of properties of ion-pairs.

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