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• A macromolecular antioxidant PM containing thioether and aromatic secondary amine was synthesized. • PM reduces the negative effect of the coexisted of PETPM and MC (PETPM+MC) on rubber curing and improves the curing properties. • PM exhibits high anti-volatility and anti-migration properties due to its high molecular mass. • In PM, the aromatic secondary amine and thioether group have a synergistic effect that improves the anti-oxidation properties. A macromolecular antioxidant PM containing thioether and aromatic secondary amine was synthesized by the thiol-ene click reaction between the antioxidant N-(4-aminophenyl)maleimide (MC) and pentaerythritol tetra(3-mercapto propionate) (PETPM). Then, the curing properties and anti-oxidation properties of PM in EPDM were investigated. The results showed that PM reduced the negative effect of the coexisted of PETPM and MC (PETPM+MC) on rubber curing and improved the crosslinking density of the rubber. PM also exhibited high anti-volatility and anti-migration properties due to its high molecular mass. Moreover, the aromatic secondary amine group in PM was able to capture aging radicals and inhibit the occurrence of oxidation reactions, while the thioether group effectively decomposed hydroperoxides and inhibited the occurrence of autocatalytic oxidation reactions. The combination of these two groups improved the anti-oxidation properties of EPDM. As a result, PM/EPDM demonstrated the lowest crosslinking density change rate and carbonyl index, as well as the largest aging coefficient K when compared to the EPDM containing low molecular weight antioxidants (PETPM/EPDM, MC/EPDM, MC+PETPM/EPDM). [ABSTRACT FROM AUTHOR]

Abstract This study investigated the corrosion test of nitrile-butadiene rubber (NBR) in H 2 S. Butadiene rubber (BR) and hydrogenated nitrile-butadiene rubber (HNBR) were used to simulate the structural units of 1,4-polybutadiene and polyacrylonitrile in NBR. The characterizations of infrared spectra, CHNS elemental analysis, and XPS may indicate that when double bonds and nitrile groups coexist, NBR has the highest reactivity with H 2 S and crosslinks of monosulfur and disulfide appear inside the rubber. However, the reactivity of BR and HNBR was reduced and no crosslinking was produced when both were isolated. Therefore, double bonds and nitrile groups have a synergistic effect in the H 2 S environment. Highlights • Double bonds and nitrile groups of NBR decreased after the corrosion in H 2 S. • Synergy of double bonds and nitrile groups produce crosslinked structure. • Crosslinks contain of monosulfur and disulfide bonds. [ABSTRACT FROM AUTHOR]

• A high-molecular-weight antioxidant with crosslinking and antioxidation functions denoted as HVA-2@MB was synthesized. • HVA-2@MB reduces the inhibitory effect of antioxidant MB on rubber vulcanization and improves the crosslinking degree of rubber. • HVA-2@MB is chemically bonded to the rubber network, significantly reducing the migration of antioxidants. • HVA-2@MB endows the EPDM material with better thermal oxidation stability than the commercial antioxidant MB. A novel antioxidant denoted as HVA-2@MB was synthesized through the reaction of N,N'-1,3-phenylene bismaleimide (HVA-2) and 2-mercaptobenzimidazole (MB) catalyzed by triethylamine. This antioxidant had high molecular weight as well as crosslinking and antioxidation functions. Then, the effect of HVA-2@MB on the crosslinking and antioxidation behaviors of ethylene-propylene-diene rubber (EPDM) was investigated. HVA-2@MB greatly reduced the inhibitory effect of antioxidants on rubber vulcanization and improved the crosslinking density of rubber. In addition, due to the reactivity of HVA-2@MB, the antioxidant groups were chemically bonded to the rubber network, which significantly reduced the migration of antioxidants in the thermo-oxidative environment, thereby improving the thermo-oxidative stability of the rubber. Therefore, compared with MB/EPDM composites, HVA-2@MB/EPDM composites exhibited better mechanical properties and thermo-oxidative stability during thermo-oxidative aging. [ABSTRACT FROM AUTHOR]

Tetrafluoroethylene-propylene elastomer (TFE/P) and octavinyl-polyhedral oligomeric silsesquioxane (OVPOSS) composites were prepared by milling at room temperature and heat vulcanization at 170 °C. Subsequently, the composites were immersed and aged in a 10 wt% hydrochloric acid solution for 2, 4, and 6 days at 140 °C, and their aging behaviors were investigated. The results show that as the aging time increases, the tensile strength and crosslink density gradually decrease, while the mass- and volume-change rates accordingly increase. The aging samples along with the unexposed sample were characterized by means of wide-angle X-ray diffraction (WAXD), scanning electron microscopy (SEM), 29Si nuclear magnetic resonance (NMR) spectroscopy, and X-ray photoelectron spectroscopy (XPS) analyses. The results reveal that in an aging environment, the crystalline structure of the OVPOSS aggregates and the cage structure of the OVPOSS were partly damaged. Meanwhile, the crosslinks between the OVPOSS and TFE/P chains were also damaged and the OVPOSS cage transformed into smaller compounds containing Si–OH groups. [ABSTRACT FROM AUTHOR]

• The degradation degree of the sulfur curing system is lower than that of the peroxide curing system. • The molecular main chain of the peroxide-cured EPDM was broken in an acid solution. • The presence of TAIC delays the degradation time of the EPDM molecular backbone. • The peroxide-cured EPDM undergoes a crosslinking reaction in the later stage of aging. • The crosslinking reaction of the curing precursor occurs in sulfur-cured EPDM. The degradation of peroxide-cured EPDM and sulfur-cured EPDM in an acid solution (12.5 ppm H 2 SO 4 +1.8 ppm HF) was investigated, and it was found that the degradation of the two in an acid solution was different. The degradation degree of the sulfur curing system is lower than that of the peroxide curing system. During the aging process, the molecular main chain of the peroxide-cured EPDM was broken, resulting in a double bond and C=O structure. When there is a coagent TAIC in the peroxide curing system, the presence of TAIC delays the degradation time of the EPDM molecular backbone, and the hydrolysis reaction of the TAIC crosslinking point occurs preferentially, which makes the stability of EPDM improved. In addition, regardless of the presence or absence of TAIC, the peroxide-cured EPDM undergoes a crosslinking reaction in the later stage of aging, resulting in an ether-crosslinked structure, thereby improving the damaged crosslinking network. Unlike the degradation of the peroxide curing system, the breakage of the molecular backbone does not occur in the sulfur-cured EPDM, but only an internal crosslinking reaction of the curing precursor occurs, resulting in a crosslinked network dominated by polysulfide bonds, thereby increasing the crosslinking density of the EPDM during the aging process. [ABSTRACT FROM AUTHOR]

The research on the applicability of elastomeric sealing materials in geothermal environments has focused on changes in physical properties, and our understanding of the chemical changes remains lacking. This work investigates the thermal and thermo-oxidative aging behaviors of tetrafluoroethylene–propylene elastomer (FEPM) at temperatures above 300 °C. During thermal aging, the polypropylene (PP) molecular chain that is not adjacent to the polytetrafluoroethylene (PTFE) component breaks and thus causes the removal of partial saturated hydrocarbons. During thermo-oxidative aging, the appearance of O 2 promotes the oxidative scission of the PP component and the removal of the PTFE component, thereby generating new carbonyl-containing substances and double bonds. Therefore, the degrees of mechanical and thermal property damages caused by thermo-oxidative aging are much higher than those caused by thermal aging. In addition, the triallyl isocyanurate crosslinked structure degrades during thermal and thermo-oxidative aging, resulting in the destruction of the crosslinked network. The analysis of the degradation mechanism of FEPM allows chemical changes to be correlated with physical modifications and provides theoretical guidance for the future development of fluoroelastomers. • The PP component rather than PTFE component in FEPM was degraded during thermal aging. • The damage degree of thermo-oxidative aging was far greater than that of thermal aging. • The TAIC structure was degraded during thermo-oxidative aging and thermal aging. • Thermo-oxidative aging cause more mechanical properties damage than thermal aging. • Thermo-oxidative aging reduced the thermal stability of FEPM more than thermal aging. [ABSTRACT FROM AUTHOR]