Bao Xianyang, Nian Guodong, Kutsovsky Yakov, Kim Junsoo, Jiao Quan, Suo Zhigang
John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138, USA.
Centre for Polymer from Renewable Resource, SFSE, South China University of Technology, Guangzhou 510640, China.
Soft Matter. 2023 Aug 9;19(31):5956-5966. doi: 10.1039/d3sm00687e.
Many polymer networks are prepared by crosslinking polymer chains. The polymer chains and crosslinkers are commonly mixed in internal mixers or roll mills. These intense processes break the polymer chains, lower viscosity, and ease mixing. The resulting polymer networks have short chains and a fatigue threshold of ∼100 J m. Here, we show that a low-intensity process, a combination of kneading and annealing, preserves long chains, leading to a network of polybutadiene to achieve a fatigue threshold of 440 J m. In a network, each chain has multiple crosslinks, which divides the chain into multiple strands. At the ends of the chain are two dangling strands that do not bear the load. The larger the number of crosslinks per chain, the lower the fraction of dangling strands. High fatigue threshold requires long strands, as well as a low fraction of dangling strands. Once intense mixing cuts chains short, each short chain can only have a few crosslinks; the strands are short and the fraction of dangling strands is high-both lower the fatigue threshold. By contrast, a low-intensity mixing process preserves long chains, which can have many crosslinks; the strands are long and the fraction of dangling strands is low-both increase the fatigue threshold. It is hoped that this work will aid the development of fatigue-resistant elastomers.
许多聚合物网络是通过交联聚合物链制备的。聚合物链和交联剂通常在内混机或辊磨机中混合。这些剧烈的过程会打断聚合物链，降低粘度并便于混合。所得的聚合物网络具有短链，疲劳阈值约为100 J/m。在此，我们表明一种低强度的过程，即捏合和退火相结合，可以保留长链，从而使聚丁二烯网络的疲劳阈值达到440 J/m。在一个网络中，每条链都有多个交联点，这将链分成多股链。链的末端是两条不承受负荷的悬垂链段。每条链的交联点数量越多，悬垂链段的比例就越低。高疲劳阈值需要长链段以及低比例的悬垂链段。一旦剧烈混合使链变短，每条短链只能有几个交联点；链段很短，悬垂链段的比例很高，这两者都会降低疲劳阈值。相比之下，低强度混合过程保留了长链，长链可以有许多交联点；链段很长，悬垂链段的比例很低，这两者都会提高疲劳阈值。希望这项工作将有助于抗疲劳弹性体的开发。
