Ethylene Propylene Diene Monomer (M-Class) rubber or Ethylene-propylene rubbers & elastomers (also called EPDM and EPM) continue to be one of the most widely used and fastest growing synthetic rubbers having both specialty and general-purpose applications. The E refers to Ethylene, P to Propylene, D to diene and M refers to its classification in ASTM standard D-1418. The “M†class includes rubbers having a saturated chain of the polymethylene type. The diene(s) currently used in the manufacture of EPDM rubbers are DCPD (dicyclopentadiene), ENB (ethylidene norbornene) and VNB (vinyl norbornene). The ethylene content is around 45% to 75%. 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 polymers are also excellent in processing. This is very much influenced by their molecular structure. The dienes, typically comprising between 2.5 wt% up to 12 wt% of the composition serve as crosslinks when curing with sulphur and resin, with peroxide cures the diene (or third monomer) functions as a coagent, which provide resistance to unwanted tackiness, creep or flow during end use.Ethylene-propylene rubbers are valuable for their excellent resistance to heat, oxidation, ozone and weather aging due to their stable, saturated polymer backbone structure. Properly pigmented black and non-black compounds are color stable. Versatility in polymer design and performance has resulted in broad usage in automotive weather-stripping and seals, glass-run channel, radiator, garden and appliance hose, tubing, belts, electrical insulation, roofing membrane, rubber mechanical goods, plastic impact modification, thermoplastic vulcanizates and motor oil additive applications. The solution polymerization process is the most widely used and is highly versatile in making a wide range of polymers. Ethylene, propylene, and catalyst systems are polymerized in an excess of hydrocarbon solvent. Stabilizers and oils, if used, are added directly after polymerization. The solvent and unreacted monomers are then flashed off with hot water or steam, or with mechanical devolatilization. The polymer, which is in crumb form, is dried with dewatering in screens, mechanical presses or drying ovens. The crumb is formed into wrapped bales or extruded into pellets. The high viscosity, crystalline polymers are sold in loosely compacted, friable bales or as pellets. The amorphous polymers grades are typically in solid bales. Major producers and suppliers of EPDM and EPM are Bayer Polymers, Crompton Corp., Exxon-Mobil Chemical Co., DSM Elastomers, Dupont Dow Elastomers, Herdillia, JSR, Kumho Polychem, Mitsui Chemicals, Polimeri Europa, and Sumitomo Chemical Co. Wide ranges of grades are available worldwide to provide solutions to many product requirements. There are three major commercial processes, solution, slurry (suspension) and gas-phase, for manufacturing ethylene-propylene rubbers. The manufacturing systems vary with each of the several producers. There are differences in the product grade slates made by each producer and process, but all are capable of making a variety of EPDM and EPM polymers. The physical forms range from solid to friable bales, pellets and granular forms and oil blends. Ethylene-propylene elastomers are one of the most versatile, fastest growing and interesting synthetic rubber polymers with various end uses.
