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Depolymerization

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Depolymerization

Depolymerization (or depolymerisation) is the process of converting a polymer into a monomer or a mixture of monomers.[1] All polymers depolymerize at high temperatures, a process driven by an increase in entropy.

Ceiling temperature

The tendency of polymers to depolymerize is indicated by their ceiling temperature. At this temperature, the enthalpy of polymerization matches the entropy gained by converting a large molecule into monomers. Above the ceiling temperature, the rate of depolymerization is greater than the rate of polymerization, which inhibits the formation of the given polymer.[2]

Ceiling Temperatures of Common Organic Polymers
Polymer Ceiling Temperature (°C)[3] Monomer
polyethylene 610 CH2=CH2
polyisobutylene 175 CH2=CMe2
polyisoprene (natural rubber) 466 CH2=C(Me)CH=CH2
polymethylmethacrylate 198 CH2=C(Me)CO2Me
polystyrene 395 PhCH=CH2
Polytetrafluoroethylene 1100 CF2=CF2

Applications

Depolymerization is a very common process. Digestion of food involves depolymerization of macromolecules, such as proteins. It is relevant to polymer recycling. Sometimes the depolymerization is well behaved, and clean monomers can be reclaimed. In other cases, such as polyethylene, depolymerization gives a mixture of products.

Depolymerization is also related to production of chemicals and fuels from biomass. In this case, reagents are typically required. A simple case is the hydrolysis of celluloses to glucose by the action of water. Generally this process requires an acid catalyst:

(C6H10O5]n + n H2O → n C6H12O6

See also

References

  1. ^ Depolymerization, IUPAC Goldbook
  2. ^ Carraher Jr; Charles E (2010). "7". Introduction of Polymer Chemistry (2nd ed.). New York: CRC Press, Taylor and Francis. p. 224.  
  3. ^ Stevens, Malcolm P. (1999). "6". Polymer Chemistry an Introduction (3rd ed.). New York: Oxford University Press. pp. 193–194.  

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