ACM – POLYACRYLIC RUBBER
Polyacrylic elastomers, also called ACM rubbers, are synthetic rubbers composed of acrylic monomers. These polymers are usually prepared by emulsion or suspension polymerization. The main repeat units are ethyl and butyl acrylate or a blend of both. Many other monomers can be included which allows for a wide variation of the thermophysical and mechanical properties. Very common is the addition of 5 percent 2-chloroethyl vinyl ether.
The combination of a saturated backbone with polar side groups results in a class of polymers with outstanding resistance to heat, oxidation and hydraulic oils. ACM’s also have good resistance to ozone, and weathering which is superior to nitrile rubber. However, water and moisture resistance is poor, as is resistance to acids and alkalis. Furthermore, low temperature applications are usually limited to approximately -10°C due to low cold temperature flexibility and compression set.
Various copolymer modifications have been developed to improve the properties of ACM’s. The modifications include other backbone monomers and the incorporation of reactive site groups (1-5 %) for subsequent crosslinking.
ACM elastomers are primarily used where combined resistance to heat and oils is required. They are often a good alternative to more expensive heat resistant elastomers such as fluorocarbon polymers (FKM), silicones (VMQ) and fluorosilicones (FVMQ) for elevated temperature applications (< 150 °C).
Typical applications include automotive transmission components like seals and hoses that have to be resistant to hot oil, fuel and many other common automotive lubricants and hydraulic fluids. ACM elastomer have also found use in vibration damping due to its excellent resilience. Other applications include textiles, adhesives, and coatings.
The typical continuous service temperature range is -10°C to 150°C (up to 175°C for limited periods of time).
Ethylene acrylate copolymers, also called AEM rubbers, are synthetic rubbers composed of both ethylene and acrylic monomers. The ethylene imparts good low temperature properties, while the acrylic portion improves the oil resistance. The combination of a saturated backbone with polar side groups also provides good resistance to heat, ozone (weathering), and many chemicals.
In general, AEM’s resistance to ozone and weathering is superior to (NBR) and its cold temperature performance is better than that of ACM. Besides excellent heat and ozone resistance, AEMs have outstanding vibration dampening and good dynamic and abrasion properties over a wide temperature range. However, water and moisture resistance is only fair, as is the resistance to dilute acids and alkalis. Furthermore, AEMs are much more expensive than most standard elastomers including NR, NBR, CR, EPDM, and SBR.
AEM elastomers are primarily used where combined resistance to ozone, heat and oils is required. They are sometimes a good alternative to more expensive heat resistant elastomers such as fluorocarbon polymers (FKM), silicones (VMQ) and fluorosilicones (FVMQ) for elevated temperature applications (< 150 °C). However, AEMs are not recommended for exposure to aromatic hydrocarbons, gasoline, brake fluids and phosphate esters.
Typical applications include automotive transmission / power steering seals and O-rings that have to be resistant to transmission fluids and many other common automotive lubricants and hydraulic fluids. Other applications include diaphragms, plumbing seals, boots, hoses, vibration mounts, pads, isolators and custom molded rubber goods and parts.
The typical continuous operating temperature range is -30°C to 150°C (up to 175°C for limited periods of time).