ethylene propylene diene monomer [EPDM]

In by Mark Goodman

A single-ply membrane consisting of synthetic rubber, usually in 45 or 60 mils. Application can be ballasted, fully adhered or mechanically attached.

ethylene propylene diene monomer (Wikipedia)
Idealized EPDM polymer, red = ethylene-derived, blue = propylene-derived, black = ethylidene norbornene-derived.

EPDM rubber (ethylene propylene diene monomer rubber), a type of synthetic rubber, is an elastomer characterized by a wide range of applications. This is an M-Class rubber where the 'M' in M-Class refers to its classification in ASTM standard D-1418; the M class includes rubbers having a saturated chain of the polyethylene type. Dienes used in the manufacture of EPDM rubbers are dicyclopentadiene (DCPD), ethylidene norbornene (ENB), and vinyl norbornene (VNB). EPDM rubber is closely related to ethylene propylene rubber: ethylene propylene rubber is a copolymer of ethylene and propylene, whereas EPDM rubber is a terpolymer of ethylene, propylene, and a diene-component.

A roll of EPDM flashing with fleece on the back, used for waterproofing roofs

The ethylene content is around 45% to 85%. The higher the ethylene content, the higher the loading possibilities of the polymer, better mixing, and extrusion. Peroxide curing these polymers gives a higher crosslink density compared with their amorphous counterpart. The amorphous polymer is also excellent in processing. Processability is very much influenced by their molecular structure. The dienes, typically comprising from 2.5% to 12% by weight of the composition, serve as sites of cross-links when curing with sulphur and resin; with peroxide cures, the diene (or third monomer) functions as a coagent, which provides resistance to unwanted tackiness, creep, or flow during end use.

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