Wang Yajian, Liu Huifang, Li Pengpeng, Wang Linbing
National Center for Materials Service Safety, University of Science and Technology Beijing (USTB), Beijing 100083, China.
Joint USTB Virginia Tech Lab on Multifunctional Materials, University of Science and Technology Beijing (USTB), Beijing 100083, China.
Polymers (Basel). 2022 Mar 24;14(7):1308. doi: 10.3390/polym14071308.
The cross-linking structure of the Ethylene-propylene-diene monomer (EPDM) is made up of a number of cross-linking types, including carbon atoms from the main chain or monomer and ether crosslinks formed during degradation. Through molecular dynamic simulations, the contribution of each type of cross-linked structure to the dynamics and mechanical properties of EPDM, the study's focus, were investigated. Cross-linking between the tertiary carbons of two main chains, cross-linking at the monomer's unsaturated position, ether cross-linking after oxidation, and other combinations of target cross-linked carbon atoms from different positions, totaling eight types of cross-linked types, were mixed with EPDM free chains in a 1:1 ratio to form eight types of cross-linked EPDMs. These varieties of cross-linked EPDMs were then compared to an uncross-linked EPDM in terms of density, radius of gyration, free volume, mean square displacement, and uniaxial tensile stress-strain curves. It was found that the cross-linking was always proven to have a favorable influence on mechanical characteristics; however, the relaxation inhibition effect varied. The cross-linking between the diene monomer at the C9 position resulted in a more flexible molecular shape and was more than double the free volume of the uncross-linked EPDM, resulting in an improved diffusion ability. The ether cross-linking produced by the oxidation of the side chain cross-linking improved the positive contribution to stiffness and enhanced the inhibitory impact on diffusion properties, whereas the main chain cross-linking had the opposite effect. The research presented in this study leads to a better knowledge of the microscopic aspects underlying EPDM performance.
三元乙丙橡胶（EPDM）的交联结构由多种交联类型组成，包括主链或单体中的碳原子以及降解过程中形成的醚交联。通过分子动力学模拟，研究了每种交联结构对EPDM动力学和力学性能的贡献，这是该研究的重点。两条主链的叔碳之间的交联、单体不饱和位置的交联、氧化后的醚交联以及来自不同位置的目标交联碳原子的其他组合，总共八种交联类型，与EPDM自由链以1:1的比例混合，形成八种交联EPDM。然后将这些不同类型的交联EPDM与未交联的EPDM在密度、回转半径、自由体积、均方位移和单轴拉伸应力-应变曲线方面进行比较。结果发现，交联总是被证明对力学性能有有利影响；然而，松弛抑制效果各不相同。C9位置的二烯单体之间的交联导致分子形状更灵活，自由体积是未交联EPDM的两倍多，从而提高了扩散能力。侧链交联氧化产生的醚交联改善了对刚度的正向贡献，并增强了对扩散性能的抑制作用，而主链交联则产生相反的效果。本研究中的研究有助于更好地理解EPDM性能背后的微观方面。
