The physical and chemical properties of polymers directly depend on molar mass distributions. Control over shape and width of these distributions would, therefore, be useful.

Andreas Spinnrock and Helmut Cölfen, University of Konstanz, Germany, have combined analytical ultracentrifugation (AUC) with polymer chemistry to obtain desired broad molar mass distributions. The analytical ultracentrifugation was used to adjust a macroinitiator’s concentration gradient to control the molar mass distribution after subsequent polymerization. Depending on the rotational speed, the macroinitiator forms the desired concentration gradient. It can be detected at any point by optical systems. After the centrifugation, a free-radical polymerization is initiated by light.

Depending on the ratio of initiator to monomer concentration at each position, polymer chains with different lengths are formed (pictured). The desired distributions can be simulated in advance and, thus, tailored distributions can be obtained. This approach can potentially be transferred to diffusion or any type of controlled mixing.

• Control of Molar Mass Distribution by Polymerization in the Analytical Ultracentrifuge,
  Andreas Spinnrock, Helmut Cölfen,
  Angew. Chem. Int. Ed. 2018.
  https://doi.org/10.1002/anie.201713149