Structural unit in the context of Copolymer

The degree of polymerization, or DP, is the number of monomeric units in a macromolecule or polymer or oligomer molecule.

For a homopolymer, there is only one type of monomeric unit and the number-average degree of polymerization is given by ${\displaystyle {\overline {DP}}_{n}\equiv {\overline {X}}_{n}={\frac {{\overline {M}}_{n}}{M_{0}}}}$,where ${\displaystyle {\overline {M}}_{n}}$ is the number-average molecular weight and ${\displaystyle M_{0}}$ is the molecular weight of the monomer unit. The overlines indicate arithmetic mean values. For most industrial purposes, degrees of polymerization in the thousands or tens of thousands are desired. This number does not reflect the variation in molecule size of the polymer that typically occurs, it only represents the mean number of monomeric units.