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Why does EPDM resist ozone damage better than natural rubber?

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EPDM (ethylene-propylene-diene monomer) resists ozone damage more effectively than natural rubber because of the specific placement of its carbon-carbon double bonds.

In natural rubber and other typical diene polymers, carbon-carbon double bonds are located directly within the main polymer chain. When ozone reacts with these bonds, the main chain is broken, leading to molecular degradation and the formation of surface cracks.1

In contrast, the chemical structure of EPDM places these reactive double bonds in side groups attached to the polymer chain rather than within the chain itself. Consequently, while ozone can still react with these side groups, such reactions do not cause the main polymer chain to break. This structural difference makes EPDM significantly more resistant to degradation from weathering, sunlight, and ozone exposure compared to elastomers that possess double bonds in their main backbone.1