What are saturated & unsaturated polymers?

Polymer chains can be differentiated according to the presence of double bonds in the main chain. Saturated polymers consist exclusively of single bonds between the carbon atoms, which cannot form any further bonds. The carbon atoms are therefore „saturated“. Unsaturated polymers, on the other hand, contain double bonds, which are reactive points of attack and enable both chemical reactions and cross-linking.

 

Unsaturated polymers

Unsaturated polymers contain double bonds in the main chain, which make the material more reactive. On the one hand, this enables the Sulphur crosslinking, on the other hand, they increase the sensitivity to ozone, oxygen and UV radiation, which means that the Resistance to ageing is reduced. Examples of unsaturated polymers are natural rubber (NR), NBR, SBR etc. NBR and SBR are each Copolymers, where the butadiene portion has the double bond.

 

Unsaturated polymers have the following properties:

  • Very good elasticity and mechanical strength
  • Good workability and Sulphur crosslinkability
  • Susceptible to ozone and UV-induced cracking without Anti-ageing agent
  • Partially lower weather resistance compared to saturated types
  • Labelling according to the nomenclature for rubber materials as R polymers (NR, NBR, SBR...)

 

Saturated polymers

Saturated polymers only have single bonds between the carbon atoms in their main chain. They are therefore chemically more stable, less reactive to oxygen, ozone or UV radiation and offer a higher level of stability. Ageing- and weather resistance. Due to their improved stability, these polymers can generally only be cross-linked using more reactive substances such as peroxides. One exception is EPDM which, due to an unspecified -diene with a double bond in the side chain sulphur-crosslinkable is. Examples of saturated polymers are EPDM, FKM etc. The majority of thermoplastic elastomers are also saturated.

 

Saturated polymers have the following properties:

  • Very good ozone and UV resistance
  • Good chemical resistance
  • Lower tendency to thermal ageing
  • Cannot be readily cross-linked via sulphur, often require Peroxide crosslinking or other systems
  • Labelling according to the nomenclature for rubber materials as M-polymers (EPDM, FKM, FFKM ...)

 

Application of saturated & unsaturated polymers

The choice between saturated and unsaturated polymers depends heavily on the application conditions. For outdoor applications with high ozone or UV exposure, saturated grades such as EPDM are used. For dynamically highly stressed parts with high demands on elasticity and adhesion, unsaturated grades such as NR or SBR often superior.