EPDM (EPDM), a terpolymer of ethylene, propylene, and a small amount of non-conjugated diene, has a main chain composed of chemically stable saturated hydrocarbons, with unsaturated double bonds only in the side chains. This unique molecular structure gives it significantly superior aging resistance to other general-purpose rubbers, making it a key material for automotive seals, building waterproofing, and wire and cable sheathing. The influence of its main chain saturation on aging resistance is primarily reflected in five aspects: oxidation resistance, ozone resistance, UV resistance, thermal stability, and chemical stability.
This main chain saturation imparts EPDM with excellent oxidation resistance. During rubber aging, free radical attack on double bonds is the core mechanism that triggers oxidative degradation. Because the EPDM main chain lacks double bonds, free radicals are less likely to attack main chain carbon atoms, effectively blocking the initiation of the oxidative chain reaction. In contrast, rubbers with double bonds in their main chains, such as natural rubber and styrene-butadiene rubber, are susceptible to free radical generation under the influence of heat, light, or mechanical stress, leading to molecular chain breakage and destruction of the crosslinking structure. EPDM's saturated backbone acts as a "chemical barrier," preventing direct oxygen attack. Only a small number of double bonds in the side chains may participate in localized oxidation reactions, but the overall molecular structure remains stable, significantly extending the material's service life.
Ozone resistance is another major advantage of EPDM. Ozone molecules are highly oxidizing and can undergo cycloaddition reactions with double bonds in rubber, leading to molecular chain breakage and surface cracking. EPDM's backbone lacks double bonds, preventing direct ozone attack. Only the side chain double bonds can become reactive sites. However, the low content and dispersed distribution of side chain double bonds significantly reduce the likelihood of ozone attack. Experiments have shown that in environments with high ozone concentrations, EPDM products maintain their surface integrity for long periods of time, while rubbers containing double bonds will rapidly crack under the same conditions. This property makes it an ideal material for outdoor seals, automotive door and window seals, and other applications subject to long-term ozone exposure.
Ultraviolet light is a significant environmental factor in rubber aging. Its energy can excite double bonds in rubber molecules, generating free radicals and initiating a chain-like degradation reaction. EPDM's saturated backbone provides a natural shield against UV rays. Ultraviolet energy is insufficient to break the carbon-carbon single bonds in the main chain and can only affect the double bonds in the side chains. Due to the low content of double bonds in the side chains, UV-induced degradation reactions are limited, maintaining the overall material performance. In contrast, rubber containing double bonds can quickly harden, become brittle, and even powderize under UV exposure. EPDM's UV resistance makes it an outstanding material for applications such as building waterproofing membranes and solar cell seals.
In terms of thermal stability, EPDM's saturated main chain structure provides excellent heat resistance. At high temperatures, rubber molecular chains may break or crosslink due to increased thermal motion, resulting in performance degradation. EPDM, with its saturated hydrocarbon main chain, offers high bond energy and flexible molecular chains, maintaining stability over a wide temperature range. Even under prolonged exposure to 120°C or short-term exposure to temperatures of 150-200°C, its molecular structure maintains its integrity, with only minor thermal degradation of the side chain double bonds. This property makes it a preferred material for high-temperature applications such as heat-resistant hoses and engine seals.
In terms of chemical stability, EPDM's backbone lacks double bonds, offering excellent resistance to polar chemicals such as acids, alkalis, alcohols, and oxidants. Polar chemicals typically destroy the rubber structure by reacting with double bonds, but the EPDM backbone lacks reactive sites, leaving only side chain double bonds potentially involved in localized reactions. This characteristic makes it outstanding in applications such as chemical pipeline sealing and anti-corrosion coatings, allowing it to withstand long-term exposure to various chemical media without performance degradation.
EPDM's saturated backbone structure eliminates double bonds, blocking degradation reactions induced by oxidation, ozone, UV radiation, and heat at the molecular level while also imparting excellent chemical stability. This structural characteristic makes it one of the most resistant rubber materials to aging, making it widely used in industrial applications requiring stringent reliability.
