Depolymerization
Depolymerization is a sequence of chemical reactions in which a polymer is broken down into its monomers or suitable building blocks ( molar mass <molar mass of the polymer), whereby they can then be reassembled into macromolecules. Thus, the depolymerization is the reverse of the polymerization and can be used in combination with polymerizations as a method for recycling plastics ( chemical recycling ). It can be triggered by thermal stress (heat), ionizing radiation (e.g. light, UV radiation or γ radiation), catalysts or the addition of chemicals.
In contrast to this, chain splitting does not involve splitting off a single monomer, rather the polymer chain is broken at any point on the backbone with the formation of two - mostly still polymeric - fragments. In addition, the fragments obtained are often unsuitable for building new polymers.
Biopolymers
In the case of ( biopolymers ), depolymerization can also occur under the influence of enzymes and can often be classified as hydrolysis (reaction with water).
When cells move with the help of actin filaments , the consumption of energy-rich phosphates can lead to the cleavage of polymer compounds, which are then made available for other polymerization processes.
Other polymers
Here, bonds in the main chain must first be split homolytically in a start reaction; in almost all cases this takes place through a radical mechanism . The kinetics of the depolymerization depends, among other things, on the temperature and the molar mass distribution . Depolymerization is a mechanism for the degradation of plastics .
Polystyrene
When heated above 150 ° C, polystyrene depolymerizes ; above 200 ° C , predominantly monomeric styrene is recovered .
Individual evidence
- ↑ Entry on depolymerization . In: IUPAC Compendium of Chemical Terminology (the “Gold Book”) . doi : 10.1351 / goldbook.D01600 Version: 2.3.3.
- ↑ Otto-Albrecht Neumüller (Ed.): Römpps Chemie-Lexikon. Volume 2: Cm-G. 8th revised and expanded edition. Franckh'sche Verlagshandlung, Stuttgart 1981, ISBN 3-440-04512-9 , p. 891.
- ↑ Sebastian Koltzenburg, Michael Maskos, Oskar Nuyken: Polymers - Synthesis, Properties and Applications. Springer Spectrum, 2014, ISBN 978-3-642-34772-6 , pp. 440–441.
- ^ Brockhaus ABC chemistry. VEB FA Brockhaus Verlag, Leipzig 1965, p. 275.