The number average molecular weight is a way of determining the molecular weight of a polymer. Polymer molecules, even ones of the same type, come in different sizes (chain lengths, for linear polymers), so the average molecular weight will depend on the method of averaging. The number average molecular weight is the common, mean, average of the molecular weights of the individual polymers. It is determined by measuring the molecular weight of n polymer molecules, summing the weights, and dividing by n. The molecular mass of a substance (less accurately called molecular weight and abbreviated as MW) is the mass of one molecule of that substance, relative to the unified atomic mass unit u (equal to 1/12 the mass of one atom of carbon-12). ... A polymer is a substance composed of molecules with large molecular mass consisting of repeating structural units, or monomers, connected by covalent chemical bonds. ... In statistics, mean has two related meanings: Look up mean in Wiktionary, the free dictionary. ... In mathematics, an average or central tendency of a set (list) of data refers to a measure of the middle of the data set. ...

The number average molecular weight of a polymer can be determined by gel permeation chromatography, viscometry, light scattering, analytical ultracentrifugation, vapor pressure osmometry, end-group titration, and colligative properties. Gel permeation chromatography (GPC) also known as size exclusion chromatography (SEC) is a chromatographic method in which molecules are separated based on their size. ... In particle physics, scattering is a class of phenomena by which particles are deflected by collisions with other particles. ... The ultracentrifuge is a centrifuge optimized for spinning a rotor at very high speeds, capable of generating acceleration as high as 1,000,000 G (9,800 km/s²) There are two kinds of ultracentrifuges, the preparative and the analytical ultracentrifuge. ... Vapor pressure osmometry is a technique to measure the number average molecular weight of a polymer. ... An end-group in polymer chemistry is a constitutional unit that is an extremity of a macromolecule or oligomer molecule. ...

An alternative measure of the molecular weight of a polymer is the weight average molecular weight. The ratio of the weight average to the number average is called the polydispersity index. The weight average molecular weight is a way of describing the molecular weight of a polymer. ... In organic chemistry, the polydispersity index (PDI), is a measure of the distribution of molecular weights in a given polymer sample. ...

High Number-Average Molecular Weight Polymers may be obtained only with a high fractional monomer conversion in the case of step-growth polymerization, as per the Carothers' equation. Step-growth polymerization is a polymerization process that involves a chemical reaction between multifunctional monomer molecules. ... In step-growth polymerization, Carothers equation gives the number-average degree of polymerization, Xn, for a given fractional monomer conversion, p. ...