Degree of polymerization

The number of repeating units in a polymer chain or molecule. It may describe a specific chain or an average across a polymer sample.

Number-average molecular weight: A polymer sample’s total molecular mass divided by its number of molecules. It relates directly to number-average degree of polymerization through the mass of each repeat unit.
Polymer: A substance composed of macromolecules built from repeated structural units. Degree of polymerization describes how many units make up its chains.
Size-exclusion chromatography: A chromatography method that separates molecules mainly by their size in solution. It estimates polymer molar-mass distributions from which average chain lengths can be derived.
Molecular weight: A molecule’s relative mass compared with a reference scale; the term is commonly used for polymer molar mass. Mass depends on both unit count and repeat-unit mass, so it is not itself a unit count.
Weight-average molecular weight: A molecular-weight average that weights each molecule in a sample by its mass fraction. Comparing it with number-average molecular weight reveals how chain lengths are distributed.
Molar mass: The mass of a substance per mole of its entities. Repeat-unit molar mass converts polymer molar mass into an estimated unit count.
Melt viscosity: A polymer melt’s resistance to flow under applied deformation. Longer chains often entangle more strongly, making chain length a key control on flow.
Copolymer composition: The proportions and arrangement of two or more kinds of repeat units in a copolymer. A chain’s degree of polymerization counts units regardless of their chemical identities.
Repeat unit: The smallest structural unit repeated along a polymer chain. Counting these units gives the degree of polymerization.
Molecular weight distribution: The spread of molecular masses among molecules in a polymer sample. A sample can contain chains with many different degrees of polymerization.

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