Department of Chemical and Biological Engineering, Northwestern University, Evanston, IL, 60208, USA.
Department of Materials Science and Engineering, Northwestern University, Evanston, IL, 60208, USA.
Macromol Rapid Commun. 2024 Sep;45(18):e2400303. doi: 10.1002/marc.202400303. Epub 2024 Jul 11.
One method to improve the properties of covalent adaptable networks (CANs) is to reinforce them with a fraction of permanent cross-links without sacrificing their (re)processability. Here, a simple method to synthesize poly(n-hexyl methacrylate) (PHMA) and poly(n-lauryl methacrylate) (PLMA) networks containing static dialkyl disulfide cross-links (utilizing bis(2-methacryloyl)oxyethyl disulfide, or DSDMA, as a permanent cross-linker) and dynamic dialkylamino sulfur-sulfur cross-links (utilizing BiTEMPS methacrylate as a dissociative dynamic covalent cross-linker) is presented. The robustness and (re)processability of the CANs are demonstrated, including the full recovery of cross-link density after recycling. The authors also investigate the effect of static cross-link content on the stress relaxation responses of the CANs with and without percolated, static cross-links. As PHMA and PLMA have very different activation energies of their respective cooperative segmental mobilities, it is shown that the dissociative CANs without percolated, static cross-links have activation energies of stress relaxation that are dominated by the dissociation of BiTEMPS methacrylate cross-links rather than by the cooperative relaxations of backbone segments, i.e., the alpha relaxation. In CANs with percolated, static cross-links, the segmental relaxation of side chains, i.e., the beta relaxation, is critical in allowing for large-scale stress relaxation and governs their activation energies of stress relaxation.
一种提高共价适应性网络（CANs）性能的方法是在不牺牲其可加工性的情况下，用一定比例的永久交联剂对其进行增强。在这里，提出了一种简单的方法来合成含有静态二烷基二硫交联键（利用双（2-丙烯酰氧乙基）二硫代，或 DSDMA，作为永久交联剂）和动态二烷基氨基硫-硫交联键（利用 BiTEMPS 甲基丙烯酸酯作为离解动态共价交联剂）的聚（正己基甲基丙烯酸酯）（PHMA）和聚（正十二烷基甲基丙烯酸酯）（PLMA）网络。CANs 的坚固性和可加工性得到了证明，包括回收后完全恢复交联密度。作者还研究了静态交联含量对具有和不具有渗透静态交联的 CANs 的应力松弛响应的影响。由于 PHMA 和 PLMA 具有非常不同的协同链段迁移率的活化能，因此表明没有渗透静态交联的离解 CANs 的应力松弛活化能是由 BiTEMPS 甲基丙烯酸酯交联的离解而不是由主链段的协同松弛，即α松弛所控制。在具有渗透静态交联的 CANs 中，侧链的链段松弛，即β松弛，对于允许大规模的应力松弛至关重要，并控制其应力松弛的活化能。
