Polymerization control

Ensuring flawless processing of unsaturated hydrocarbons

Background

In hydrocrackers, educts like styren, ethylen or propylen are treated at high temperature to form saturated carbons. To prohibit undesirable side reactions, inhibitors can be added to prevent the unsaturated carbons from forming a highly viscous sludge.

Polymerization is based on a mechanism of radical chain reaction. Stable radicals such as TEMPOL can stop the chain. The right proportion can be determined easily and fast by ESR spectroscopy (see diagram to the right). Too low concentrations cannot stop polymerization. Too high concentrations on the other hand support the polymerization process.

 

As a consequence, the monitoring of the content of free radicals which may have been added as in-process inhibitors could be a valuable control instrument. The most common stable free radicals used for this purpose are nitroxyl compounds having a very characteristic ESR spectrum entailing three lines when dissolved in a liquid (see diagram). ESRStudio automatically  records, saves and evaluates the measurement result. Predefined calibration curves for quantitative ESR make Polymerization control as simple as a microwave oven.

Application Example: Shell-core polymers

Polymer research also benefits from ESR. The interaction of the spin probe 16-DSA with amphiphilic core-shell polymers is studied by CW-EPR.

Results:

  • spin probe shows dynamic hydrophobic attachment

  • enables insights into temperature response, aggregation and binding properties of the polymer

  • physical features of core region is strongly influenced by length of hydrophobic chains (so-called shell)

  • wide variety of polymer properties can be adjusted with chain length and degree of polymerization

  • ESR results were confirmed by dynamic light scattering (DLS), transmission electron microscopy (TEM) and molecular dynamic simulations (MD)

References

  • Dariush Hinderberger , Jörg Reichenwallner, Anja Thomas, Lutz Nuhn, Tobias Johann, Annette Meister, Holger Frey (2016) Polymer Chemistry 7, 5783-5798