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:

H(C₆H₁₀O₅)_nOH + (n - 1) H₂O → n C₆H₁₂O₆

See also

• Polymer degradation
• Polymerisation
• Ceiling temperature

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. ISBN 978-1-4398-0953-2.
3. Stevens, Malcolm P. (1999). "6". Polymer Chemistry an Introduction (3rd ed.). New York: Oxford University Press. pp. 193–194. ISBN 978-0-19-512444-6.

External links