Ethylene propylene rubber EPM and EPDM:
Composing:
EPM is a copolymer consisting of ethylene and propylene units as part of the main polymer chain. It can be cross-linked with peroxides or radiation but not sulfur. EPM is used as an ethylene based plastic impact modifier and as a viscosity index improver for lubricating oils.

When a non-conjugated diene is grafted on to the main polymer chain it becomes a terpolymer, Ethylene propylene diene (EPDM) and interchain sulfur cross-linking becomes possible.

Properties and Applications:
EPDM is largely unaffected by weather with very good resistance to ozone. Low temperature flexibility is very good and compares well with NR, and like NR and SBR, EPDM (with a lower polarity than NR) has very poor oil resistance.Also useful to the compounder is the ability of EPDM to accept large amounts of filler and oil-based compounding ingredients, which can be lower in cost than the raw gum elastomer. Resistance to a number a number of concentrated mineral acids and bases is significantly better than that of NR or SBR.

The use of EPDM is dominant in roof membrane linings and extruded channels for windows because of the above properties. EPDM has also been used as a blend with NR in tire sidewalls to improve resistance to cracking by ozone attack. The excellent electrical resistance of EPDM promotes its use in medium and high voltage cable covers. Its very good resistance to water absorption, combined with good mechanical properties and relatively low cost, make it a good choice for pond liners.