Three Yuan second grade third rubbers (EPDM) is the ethylene, the propylene and the few non-conjugate diolefin copolymer.

三元胶（EPDM）是烯、烯和少量非轭二烯烃聚物。

The diolefins and alkenyl aromatics are very unstable components which can give gums by polymerization.In giving olefins and alky aromatics the hydrogenation improves the product quality.

二烯烃和烯基芳烃是非常不稳定，可聚合产生凝胶。对于给定烯烃和烷基芳烃，氢化可以改善产品质量。