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In organic chemistry, the polydispersity index (PDI), is a measure of the distribution of molecular mass in a given polymer sample. The PDI calculated is the weight average molecular mass divided by the number average molecular mass. It indicates the distribution of individual molecular masss 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). The PDI from polymerization is often denoted as: