ACM – Polyacrylic Rubber
Polyacrylic elastomers, also called alkyl acrylate copolymers or ACM rubbers, are synthetic rubbers. 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.
COMMERCIAL ACM Elastomers
Important manufacturers and suppliers of ACM rubbers are Zeon, and DuPont.
ACM elastomers are primarily used where combined resistance to heat and oils is required. They are often 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 and fuel. 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).