Mass Molecular Weight

The observation of molecular size or polydispersity and the subsequent determination of relative molecular mass, (MJ or molecular mass (weight) distribution (MWD), is the most common analytical application of SEC. The goal of these types of experiments is to either observe the solvated size of one or more molecular species or to observe the distribution of sizes present in a mixture... 

A measure of the breadth of the molecular mass distribution is given by the ratios of molecular mass averages. The most commonly used ratio Mw/Mn — H, is called the polydispersity index. Wiegand and Kohler discuss the determination of molecular masses (weights) and their distributions in Chapter 6. 

Number average molecular weight Relative molecular mass Weight average molecular weight Meter... 

Number of hot streams, heat-exchanger networks Molecular mass (weight)... 

Equilibrium constant for an ideal mixture Thermal conductivity Thermal conductivity of a mixture Latent heat of vaporisation Latent heat at normal boiling point Molecular mass (weight)... 

Molecular weightjmass detectors include light scattering detectors and viscosity detectors. When SEC is used in the characterisation of polymer systems, its main aim will be the production of a molecular mass/weight distribution and where possible absolute molecular weights. Mass calibration is a complicated matter (section 9.3.5.1) in that calibration curves differ for different polymer types, and for many commercial polymers, direct molar mass calibration is not possible because of the lack of suitable, known molecular weight standards. 

Having calibrated the system, the calculation of the molecular mass/weight distribution curve and molecular weight averages requires a number of data treatment steps (Evans, 1973). 

Pi = initial pressure Pi = final pressure v = initial volume Mu, = molecular mass (weight) of gas. ... 

An average molecular mass (weight) of the polymer also needs to be defined, since components of various molecular masses (weights) M, are present in the polymer. The number of moles of species i in the polymer can be obtained from the typical formula ni = W] / Mi where W is the weight fraction of the component i", and M, is the molecular mass of species i . The masses of molecules or groups can be calculated using two different conventions. One convention considers the natural isotopic abundance of elements and takes their sum based on the compound chemical formula. For the masses of polymers, the first convention is typically used. The other convention considers only the masses of the most abundant isotope, which is useful for MS... 

For an ideal polymer with all molecules having the same molecular mass, Mn = Mw, and the polymer is known as a monodisperse system. In most synthetic polymers, M, > Mn, and the ratio Q = M / Mn is called polydispersity index. The molecular mass (weight) for small molecules is noted MW and does not represent an average. 

Molecular Mass (Weight) and Molecular Weight Distribution... 

Molecular mass weight of repeat grnol Ethylene 28... 

The molecular mass (weight) of the analyte is often (bnt not always) represented by the peak with the highest miz valne, i.e., the one fnrthest to the right on the x-axis. This peak corresponds to the molecular ion, [MJ, or a directly related species, snch as the protonated molecule, [M +... 

An average molecular mass (viscosity average) An average molecular mass (number average) Molecular dimensions and an average molecular mass (weight average) Molecular mass distribution... 

Number average molecular mass Weight average molecular mass z-average molecular mass Number of crystallizable elements Isotactic poly(4-methylpentene-1)... 

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