Molar mass exchange

Reaction that results in an exchange of atoms or groups between a polymer and low-molar-mass molecules, between polymer molecules, or between sites within the same macromolecule. 

The separation of macromolecules on the insoluble, crosslinked porous media was attempted by several researchers just after the World War II. However, the first successful separation of proteins on the crosslinked dextran in aqueous eluents was reported by Porath and Flodin [89] as late as in 1959. Independently, Moore [90] separated the dissolved polystyrenes according to their molar masses on the porous crosslinked polystyrene beads, the raw material for the ion exchangers, in 1964. Above researchers are considered the founders of SEC. 

Equivalent The amount of a substance that will react with one mole of H+ or OH-. The related term equivalent mass ( weight ) refers to a molar mass of a substance divided by the absolute value of its valence state. For anion exchange capacity and cation exchange capacity measurements, the results are usually reported in milliequivalents (1/1000 of an equivalent) per 100 g of material. 

The thermal conductivity of solvents, X, is an important property of solvents with respect to the removal of heat generated in exothermal reactions and in their uses as heat exchange fluids. When convection is the mechanism of thermal conductance, it depends on the mobility of the molecules of the solvent and therefore increases the smaller these molecules are. For globular molecules in the gaseous phase the thermal conductivity is proportional to the viscosity X/r = (5/2 )R/M, where Mis the molar mass, but this relationship does not hold in liquids. For the latter, the potential energy is also involved, and the expression that fits the data for over 270 solvents is (Marcus 1998) ... 

So long as there are no or limited interspin exchange interactions in a system, M increases with H until all spins are aligned with the external field to the maximum extent allowed by thermal motion. Thus, at higher fields, M plateaus and is said to be saturated (Msat). The value of Msat can be used to determine S, so long as one knows molar mass of the individual spin units to get Msat in emu/ mol by the following equation ... 

The porous nature of the fibers allows for exchange of nutrients and metabolites. Low-molar-mass molecules, such as glucose and ammonia, can move freely through the pores of the fibers, at a rate that is controlled just by the pressure gradients generated by the medium recirculation pump. High-molar-mass proteins, which can be produced by the cells or added as nutritional supplements to the extracapillary space, are not able to permeate the membrane fibers and are retained in the cell bed in the ECS. 

Desalting or buffer exchanges are often required between purification steps. At the laboratory scale, the protein solution is placed in a tube of a semipermeable polymer membrane immersed in the desired buffer. The membrane pore size determines the minimum molar mass of the compounds that are retained. Small molecules with a molar mass below the membrane cut-off will flow freely across the membrane until the osmotic pressure equilibrium is reached. Complete buffer exchange requires several changes of the dialysis liquid. The process should be carried out at a temperature around 4°C, to avoid loss of activity. 

The addition of ZnEt2 to the catalyst system NdV/DIBAH/EASC had the same effect on the decrease of molar mass as aluminum alkyls. Therefore, a reversible exchange of polybutadienyl chains between Nd and Zn was also assumed to apply for molar mass control by ZnEt2 (Schemes 34 and 35) [180]. 

Scheme 34 Molar mass control by ZnEt2 in the system NdV/DIBAH/EASC. Reversible exchange of poly(butadien)yl chains from Nd to Zn by poly(butadien)yl-ethyl interchange (charge and ligands of Nd are omitted for clarity), reproduced by permission of Taylor Francis Group, LLC., http //www.taylorandfrancis.com...

The controlled free-radical miniemulsion polymerization of styrene was performed by Lansalot et al. and Butte et al. in aqueous dispersions using a degenerative transfer process with iodine exchange [91, 92]. An efficiency of 100% was reached. It has also been demonstrated that the synthesis of block copolymers consisting of polystyrene and poly(butyl acrylate) can be easily performed [93]. This allows the synthesis of well-defined polymers with predictable molar mass, narrow molar mass distribution, and complex architecture. 

Electrochemical equivalent — Amount of a chemical substance deposited, dissolved, or transformed in an electrochemical redox reaction with exchange of one unit of electric charge. In the SI unit system the electrochemical-equivalent unit is in kgC-1, or alternatively, in molC-1. It means that in a n-electron redox reaction (Ox + ne Red) the electrochemical equivalent is equal to the molar mass M of the reacting compound divided by n times the - Faraday constant (M/nF). In some sources the electrochemical equivalent is defined as the mass of the substance transformed by electric charge corresponding to the Faraday constant. 

It is important to note that this separation, or even the comparison of quantities, must be expressed in mole or in equivalents. It is usual in the literature that the mass of the adsorbed, exchanged, or dissolved substances are expressed in grams (e.g., Bhattacharyya and Gupta 2008 Stuckey et al. 2008 Green-Ruiz 2009). Since the molar mass of ions is different, the quantities in the mass are not suitable for the comparison of quantities. 

Total exchange capacity = 5% of this = 0.64 peq Molar mass of NaCl 0.64 mmol of NaCl =... 

---