Cross-link heterogeneity and topological defects have been shown to affect the moduli of polymer networks in the low-strain regime. Probing their role in the high-strain regime, however, has been difficult because of premature network fracture. Here, we address this problem by using a double-network approach to investigate the high-strain behavior of both randomly and regularly cross-linked networks with the same backbone chemistry. Randomly cross-linked poly(n-butyl acrylate) networks with target molecular weights between cross-links of 5–30 kg/mol were synthesized via free-radical polymerization, while regularly cross-linked poly(n-butyl acrylate) networks with molecular weights between cross-links of 7–38 kg/mol were synthesized via cross-linking of tetrafunctional star polymers. Both types of networks were then swollen in a monomer/cross-linker mixture, polymerized to form double networks, and characterized via uniaxial tensile testing. The onset of strain stiffening was found to occur later in regular networks than in random networks with the same modulus but was well-predicted by the target molecular weight between cross-links of each sample. These results indicate that the low- and high-strain behavior of polymer networks result from different molecular-scale features of the material and suggest that controlling network architecture offers new opportunities to both further fundamental understanding of architecture–property relationships and design materials with independently controlled moduli and strain stiffening responses.

中文翻译：

---

交联均匀性对弹性聚合物网络高应变行为的影响


交联异质性和拓扑缺陷已被证明会影响低应变状态下聚合物网络的模量。然而，由于网络过早断裂，探究它们在高应变状态中的作用一直很困难。在这里，我们通过使用双网络方法来研究具有相同主链化学的随机和规则交联网络的高应变行为来解决这个问题。通过自由基聚合合成了目标分子量在 5-30 kg/mol 之间的随机交联聚（丙烯酸正丁酯）网络，而规则交联的聚（丙烯酸正丁酯）网络则具有分子通过四官能星形聚合物的交联合成了 7-38 kg/mol 的交联重量。然后两种类型的网络在单体/交联剂混合物中溶胀，聚合形成双网络，并通过单轴拉伸测试进行表征。发现应变硬化的发生在规则网络中比在具有相同模量的随机网络中晚，但可以通过每个样品的交联之间的目标分子量来很好地预测。这些结果表明，聚合物网络的低应变和高应变行为是由材料的不同分子尺度特征引起的，并表明控制网络结构为进一步基本了解结构-性能关系和设计具有独立控制的材料提供了新的机会。模量和应变硬化响应。