The polydispersity index, or PDI, is the ratio of the weight average molecular weight to the number average molecular weight. It indicates the distribution of individual molecular weights in a batch of polymers. In biological polymers, it can be very close or equal to 1, indicating only one length of polymer is present. In synthetic polymers, it can vary greatly due to reactant ratio, how close the polymerization went to completion, etc. 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. ... This page deals with mathematical distributions. ... 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 generic term used to describe a substantially long molecule. ... In chemistry, the reactants are the substances that exist at the start of a chemical reaction. ... Polymerization is a process of reacting monomer molecules together in a chemical reaction to form linear chains or a three-dimensional network of polymer chains [1]. There are many forms of polymerization and different systems exist to categorize them. ...