Hydroxyl group concentration

Consider the polyesterification of Eq. 2-58 under stoichiometric conditions, where k and k2 are the rate constants for the forward and back reactions. The initial carboxyl and hydroxyl group concentrations are [M]0. The values at any time are [M], which is given by (1 — p) [M]0. The concentrations of the products, [COO] and [H20], at any time are equal because of the stoichiometry and are given by p[M]0. The polymerization rate is the difference between the rates of the forward and back reactions... 

The effect of drying temperature on the available surface hydroxyl concentration of a silica is shown in Figure 8. A constant slurry concentration of 4% silica/toluene was used in these experiments. These results are comparable with other data (20, 62), and they indicate that the surface hydroxyl group concentration is reduced with increasing drying temperatures. The reaction of metal hydrocarbyl compounds with strained siloxane groups is illustrated in Reaction 4. 

Boehm et al.2 29 utilized this reaction to evaluate the hydroxyl group concentration at the surface of Aerosil. They found a maximal hydroxyl coverage of 3.1 OH/nm2 for a pretreatment temperature of 450 K. In the same period, also Uytterhoeven,30 Elmer31 and Folman14 have investigated the reaction of silica with SOCl2. 

Chemisorption of pyridine results in the disappearance of these groups and the formation of pyridinium ions. The concentration of pyridinium ions, and hence accessible Bronsted acid sites, follows a similar relationship to that of the hydroxyl group concentrations. Thus, the acid site concentration remains constant until about 16-18 calcium ions have been introduced. The acidity concentration then decreases rapidly as the calcium ions are exchanged for ammonium ions in accessible positions. At the same degree of exchange, the cation-pyridine band near 1444 cm" is observed first, confirming the appearance of calcium ions in accessible positions in the structure. 

Abstract Solid-state NMR studies on bone, bone mineral standards and collagen are reviewed. NMR spectroscopy was mostly applied to the bone mineral and confirmed that the structure resembles that of calcium carbonatoapatite of type B. Apatite in bone was found to be deficient in structural hydroxyl groups. Concentration and distribution of hydrogen-phosphate and carbonate ions, and of water in apatite crystals (interior vs surface and crystal defects vs structural positions) were closely investigated. The NMR characterization of the organic matrix still remains a challenge for future research. 

Although it is possible that several pathways for cumene dealkylation exist, complete rejection of a protonic mechanism 40,84) seems unjustified at this time. Very recently, Ward has, in fact, demonstrated correlations between Brohsted acidity, hydroxyl group concentration, and cumene dealkylation activity in HY 139a) and alkaline earth cation-exchange Y zeolites 139b). 

Figure 18 demonstrates the increased reactivity of the amine groups when in the presence of hydroxyls. It plots the change of primary to tertiary amines. Resins with high hydroxyl group concentrations are more reactive and show an immediate production of tertiary amine. 

Figure 4.8 The value of propagation constant Kp as function of hydroxyl groups concentrations in anionic polymerisation of EO and PO...

Equation 4.12 is the general equation of the anionic polymerisation of PO, representing a complex dependence on the hydroxyl group concentration. The value of Kp in the general equation 4.12 is a function of hydroxyl group concentration ... 

Equation (4.13) is a more general equation of the PO anionic polymerisation of PO, where the propagation constant is a function of the hydroxyl group concentration and of the dissociation constant of the alcoholate anion. 

If the hydroxyl group concentration [OH] is constant and a = 0, we obtain the well known equation (4.6) for the propagation reaction Rp in anionic PO polymerisation. 

In order to clarify the nature of hydroxylic cover and to determine the hydroxyl group concentration on silica... 

The role of antimony is to establish a favorable spatial configuration for the transition state. An earlier study, however, resulted in a conclusion that antimony s activity is inversely proportional to the hydroxyl group concentration ... 

Considering the absorption maximum of [OH] vibrations, presence of HAp and its thermal stability can be determined, as well as hydroxyl group concentration in the sample. 

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