In organic chemistry, the polydispersity index (PDI), is a measure of the distribution of molecular weights in a given polymer sample. The PDI calculated is the weight average molecular weight divided by the number average molecular weight. It indicates the distribution of individual molecular weights in a batch of polymers. The PDI has a value always greater than 1, but as the polymer chains approach uniform chain length, the PDI approaches unity (1). Organic chemistry is a specific discipline within the subject of chemistry. ... 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). ... Polymer is a term used to describe large molecules consisting of repeating structural units, or monomers, connected by covalent chemical bonds. ... The weight average molecular weight is a way of describing the molecular weight of a polymer. ... The number average molecular weight is a way of determining the molecular weight of a polymer. ... 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). ... Polymer is a term used to describe large molecules consisting of repeating structural units, or monomers, connected by covalent chemical bonds. ...

Effect of Polymerization Mechanism on PDI

Typical PDI's vary based on the mechanism of polymerization and can be affected by a variety of reaction conditions. In synthetic polymers, it can vary greatly due to reactant ratio, how close the polymerization went to completion, etc. For typical addition polymerization, values of the PDI can range around 10 to 20. For typical step polymerization, most probable values of the PDI are around 2 —Carother's equation limits PDI to values of 2 and below. Living polymerization, a special case of addition polymerization, leads to values very close to 1. Such is the case also in biological polymers, where the PDI can be very close or equal to 1, indicating only one length of polymer is present. A reactant or reagent is any substance initially present in a chemical reaction. ... This is the article about the process. ... This is the article about the process. ... In step-growth polymerization, Carothers equation gives the number-average degree of polymerization, Xn, for a given fractional monomer conversion, p. ... In polymer chemistry, living polymerization is a form of addition polymerization where the ability of a growing polymer chain to terminate has been removed . ...