IR - Polyisoprene

Clwyd reference IR
ASTM classification IR

The synthetic equivalent to Natural Rubber is polyisoprene (IR) which can be produced by polymerization of 2-methyl-1,3-butadiene with Ziegler-Natta catalyst.

Typical applications

In applications where consistency and good processability is required, synthetic polyisoprene is often the better choice. Since the polymerization of isoprene is carried out under narrowly controlled conditions, there is very little variation of composition, structure, and resulting properties, whereas natural rubber contains naturally occurring impurities and the molecular weight varies with the growth conditions of the rubber tree.

Both has a noticeable impact on the physical properties and processability of the rubber.


In general, synthetic rubber has superior resistance to aging and weathering and is easier to process due to its lower viscosity. It is also often more compatible with other rubbers such as SBR and EPDM.


Synthetic polyisoprene has lower strength than natural rubber but better low-temperature properties.

Available hardness range (Shore A) 30 - 95
Upper continuous service temp. 80°C
Min. temp. for sealing applications -50°C
Minimum non-brittle  temp.  -70°C
Tensile strength (up to) 23 MPa
Elongation at break (up to) 600%
Price Bracket Very low
ASTM 1 Oil None
ASTM 2 Oil None
ASTM 3 Oil None
Kerosene None
Liquid B None
Liquid 101 None
Phosphate ester Good
Ketone None
Toluene None
Iso-octane None
Methanol Excellent
Acid (weak) Average
Acid (strong) None
Base (weak) Good
Base (strong) None
Hydrogen sulphide None
Steam None
Ozone None
Radiation Average