Specialized catalysts are used to polymerize the monomers into controlled polymer structures. Since their introduction, ethylene-propylene elastomers have used a family of catalysts referred to as Zeigler-Natta named after their initial developers. Improvements in catalysts and processes have provided increased productivity while maintaining control of polymer structure. Most recently a new family of catalysts, referred to as metallocene catalysts, has been developed and are in commercial use.

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.

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.

The slurry (or suspension) process is a modification of bulk polymerization. The monomers and catalyst system are injected into the reactor filled with propylene. The polymerization takes place immediately, forming crumbs of polymer that are not soluble in the propylene. Slurry polymerization reduces the need for solvent and solvent handling equipment, and the low viscosity of the slurry helps to control temperature and handle the product. The process is not limited by solution viscosity, so high molecular weight polymer can be produced without a production penalty. Flashing off the propylene and ter-monomer completes the process before forming and packaging.

Gas-phase polymerization technology was recently developed for the manufacture of ethylene-propylene rubbers. The reactor consists of a vertical fluidized bed. Monomers and nitrogen in gas form along with catalyst are fed to the reactor and solid product is removed periodically. The heat of reaction is removed through the use of the circulating gas that also serves to fluidize the polymer bed. Solvents are not used eliminating the need for solvent stripping, washing, and drying. The process is also not limited by solution viscosity, so high molecular weight polymer can be produced without a productivity penalty.

Continuous injection of a substantial amount of carbon black used as a partitioning aid is necessary to prevent the polymer granules sticking to each other and to reactor walls. Products are made in a granular form to enable rapid mixing.