polymerisationsgrad

Polymerisationsgrad, in English the degree of polymerization (DP), is the average number of repeating units contained in a polymer chain. It is often given as the number-average degree of polymerization (DPn) and the weight-average degree of polymerization (DPw), reflecting different weightings of the polymer population. The repeating unit molar mass M0 provides a link to molecular weight: Mn ≈ DPn × M0 and Mw ≈ DPw × M0, with Mw/Mn equal to the polydispersity index (PDI).

DP expresses the size of polymer chains and thus relates to many material properties. Higher DP generally leads to higher molecular weight, affecting viscosity, mechanical strength, thermal properties and processability. However, real polymers exhibit a distribution of chain lengths, so DP is an average value rather than a single fixed number.

Measuring DP can be done by several methods. End-group analysis uses NMR or titration to quantify chain ends when end groups are known. Spectroscopic and mass techniques can also determine end groups or average composition. More commonly, gel permeation chromatography (GPC, also called SEC) yields Mn and Mw, from which DPn = Mn/M0 and DPw = Mw/M0 can be calculated. For step-growth polymerizations, idealized relations such as DPn = 1/(1 − p) connect DP to the extent of reaction p (conversion). In chain-growth polymerization, DP is influenced by the ratio of monomer to initiator or chain-transfer events and can be controlled in living/controlled systems.

The concept is fundamental for understanding and predicting polymer properties, while recognizing that DP is a statistical average over a distribution of chain lengths.