Dimer-monomer method

Another technique used to measure activity in alloys with a single-cell KEMS is the dimer-monomer method that was developed by Berkowitz and Chupka [96]. This... 

An alternative method of fraction (see Fig. 2) has been developed which takes advantage of the observation that cleavage of the single disulfide bond induces the dimer - monomer transition of fraction IV (B6, S17, S19). If the fractionation procedure is carried out in the presence of a reducing agent, such as j8-mercapthoethanol, the reduced IV can be reoxidized into the dimer form by oxygen. The choice of the method... 

We investigated two systems by this method, namely, the living a-methylstyrene tetramer + monomer and the living a-methylstyrene dimer + monomer. Both the tetramer and dimer represent those oligomers which may grow, but not degrade. This means that the present tetramer is different from a tetramer obtained from the dimer. (Further discussion of this point is given below.)... 

The enthalpy of formation Is derived from the sublimation and vaporization data analyzed below. Numerous investigators have obtained total pressures by static methods or "apparent" pressures by effusion or transpiration. These pressures are converted to monomer pressures by use of functions [see K2Br2(g) table] which are consistent with the dimer-monomer equilibrium data of Hagemark et al. (6). 2nd and 3rd law analyses of the monomer pressures show remarkable consistency over temperatures from 637 to 1068 K. The selected value of A H (298 K) = -43.04 0.5 kcal mol" (-180.079 2.1 kJ mol" ) may be compared with -43.8 kcal mol" ... 

The enthalpy of formation, AjH (WClg, cr, 298.15 K) -122.6 kcal mol , is calculated from that of the gas less the heat of sublimation, Ag H (298.15 K) 24.0 kcal mol . The latter is calculated by the 3rd law method from partial pressures of WClg(g) derived from the total pressure data of Shchukarev et al. (1 ). Dimer pressures, calculated from the same authors dimer-monomer dissociation data, are subtracted from the total pressures in order to obtain the monomer pressures. Analyses of... 

Brown and Lin reported a quantitative method for methanol based on its effect on the visible spectrum of methylene blue. In the absence of methanol, the visible spectrum for methylene blue shows two prominent absorption bands centered at approximately 610 nm and 660 nm, corresponding to the monomer and dimer, respectively. In the presence of methanol, the intensity of the dimer s absorption band decreases, and that of the monomer increases. For concentrations of methanol between 0 and 30% v/v, the ratio of the absorbance at 663 nm, Asss, to that at 610 nm, Asio, is a linear function of the amount of methanol. Using the following standardization data, determine the %v/v methanol in a sample for which Agio is 0.75 and Ag63 is 1.07. 

Properties. Anhydrous aluminum chloride is a hygroscopic, white soHd that reacts with moisture ia air. Properties are shown ia Table 1. Commercial grades vary ia color from light yellow to light gray as a result of impurities. Crystal size is dependent upon method of manufacture. At atmospheric pressure, anhydrous aluminum chloride sublimes at 180°C as the dimer [13845-12-0] Al2Qg, which dissociates to the monomer beginning at... 

Currently, there is continuing work on an iadustry standard method for the direct determination of monomer, dimer, and trimer acids. Urea adduction (of the methyl esters) has been suggested as a means of determining monomer ia distilled dimer (74). The method is tedious and the nonadductiag branched-chain monomer is recovered with the polymeric fraction. A micro sublimation procedure was developed as an improvement on urea adduction for estimation of the polymer fraction. Incomplete removal of monomer esters or loss of dimer duriag distillation can lead to error (75). 

Thin-layer chromatography (76,77) has been used for the estimation of the amounts of dimer, trimer, and monomer ia methyl esters. Both this method and paper chromatography are characterized by lack of precision (78,79) (see Chromatography). 

Somewhat later, Travis and Busch reported that extraction of the residue from Eq. (6.8) with hot ethanol afforded the dimer of 10 in 25% yield . The latter, 1,4,8,11, 15,18,22,25-octathiooctacosane, was characterized by mass spectrometric analysis as well as the customary analytical methods. It was found that by dilution of reactants prior to mixing, the yield of [monomer] is greatly increased (50—60%) while the yield of [dimer] is lowered substantially . One might have expected the larger rather than the smaller ring to be more favored at higher dilution, but there is no further comment on this point. 

This peculiar form applies when a dimeric molecule dissociates to a reactive monomer that then undergoes a first-order or pseudo-first-order reaction. This scheme is considered in Section 4.3. Unless one can work at either of the limits, the form is such that a numerical solution or the method of initial rates will be needed, since the integrated equation has no solution for [A]r. 

Functional biaryl derivatives are important industrial chemicals. They are used as monomers for the production of high performance and other polymers, as well as dyes, pharmaceuticals and agrochemical intermediates. We have developed an improved method for the dehalogeno-dimerization of aryl bromides to yield biaryl derivatives under mild conditions (temperature < 100°C, atmospheric pressure) using a common base, a 5 % Pd/C catalyst (0.1 - 10 % w/w, based on the starting material) in an aqueous medium and formyl hydrazine as the reducing agent. Several examples of biaryl derivatives are discussed. 

NR, styrene-butadiene mbber (SBR), polybutadiene rubber, nitrile mbber, acrylic copolymer, ethylene-vinyl acetate (EVA) copolymer, and A-B-A type block copolymer with conjugated dienes have been used to prepare pressure-sensitive adhesives by EB radiation [116-126]. It is not necessary to heat up the sample to join the elastomeric joints. This has only been possible due to cross-linking procedure by EB irradiation [127]. Polyfunctional acrylates, tackifier resin, and other additives have also been used to improve adhesive properties. Sasaki et al. [128] have studied the EB radiation-curable pressure-sensitive adhesives from dimer acid-based polyester urethane diacrylate with various methacrylate monomers. Acrylamide has been polymerized in the intercalation space of montmorillonite using an EB. The polymerization condition has been studied using a statistical method. The product shows a good water adsorption and retention capacity [129]. 

The structures of two polymorphs of pleconaril, enantiotropically related with a transition temperature of 35.7°C, have been reported [36], Form I was described as consisting of a network of dimers, while Form III was described as a three-dimensional network of monomers. The two forms contradicted the density rule, and the solid solid transition could occur only through a destructive-reconstructive mechanism. A quantitative differential scanning calorimetry method was also described that enabled the quantitative determination of Form I in bulk Form III to be made at levels as low as 0.1%. 

---