The conventional curing methods pose a significant environmental threat due to the use of toxic vulcanizing agents, the release of irritating volatile organic compounds, and the difficulties in recycling end-of-life rubber products. This work demonstrates a catalyst-free, facile, and eco-friendly crosslinking strategy based on the reaction between epoxy-functionalized ethylene-propylene-diene monomer (EEPDM) and dicarboxylic acids. The EEPDM was synthesized via a reusable reaction-controlled phase-transfer catalyst. Then, EEPDM could be effectively crosslinked by dicarboxylic acids without additional additives. The increased acidity of dicarboxylic acids could be conducive to improving the crosslinking rate. Moreover, the curing mechanism and the nature of the crosslinks were investigated, which is crucial for the recyclability of rubbers. The dicarboxylic acid-cured EEPDM exhibited undesirable side reactions, the extent of which showed a positive correlation with the acidity of carboxylic groups. This phenomenon could be primarily attributed to acid-catalyzed self-polymerization via epoxide ring-opening mechanisms, which would be detrimental to the reprocessability. Due to the formation of thermally stable ether linkages, the crosslinked EEPDM exhibited enhanced thermal-oxidative aging behavior. Hence, we envision that this catalyst-free, high-efficiency crosslinking strategy may offer a promising bridge between sustainable modification and high-performance for epoxy-functionalized rubbers, holding potential application in eco-friendly, low-odor automotive sealing strips.
High-molecular-weight poly[(aminopropyl)methylsiloxane-co-dimethylsiloxane] (P2) and poly[(aminoethylaminopropyl)-methylsiloxane-co-dimethylsiloxane] (P3) were synthesized through base equilibration of 3-aminopropylheptamethylcyclo-tetrasiloxane or N-β-aminoethyl-γ-aminopropylheptamethylcyclotetrasiloxane with octamethylcyclotetrasiloxane. These materials were crosslinked with oligo[(acryloxypropyl)methylsiloxane-co-dimethylsiloxane] (AP-PDMS) via an aza-Michael reaction to produce novel silicone rubbers. Diaddition and triaddition reactions occurred between the aminopropyl groups of P2 and the aminoethylaminopropyl groups of P3 with the acyl groups of AP-PDMS. This led to the higher modulus of novel silicone rubbers prepared via “tension spring-type crosslinking” compared with that of the silicone rubber prepared from poly[(piperazinylpropyl)methylsiloxane-co-dimethylsiloxane] (P1) via monoaddition reaction. Crosslinking mechanism was proven by solid-state 13C NMR and Fourier transform infrared spectroscopy. Curing characteristics were measured through cure curves conducted on rheometry. The postcure conditions and the ratio of crosslinkers used were investigated in detail. Analysis of mechanical properties showed that tension spring-type crosslinking improved the modulus of silicone rubber based on P2 or P3.
危险品化学品经营许可证（带存储）