Polymer Chemistry Research Group, Centre of Macromolecular Chemistry (CMaC) and Laboratory of Organic Synthesis, Department of Organic and Macromolecular Chemistry, Faculty of Sciences, Ghent University, Krijgslaan 281-S4, Ghent, 9000, Belgium.
ACS Macro Lett. 2022 Jul 19;11(7):919-924. doi: 10.1021/acsmacrolett.2c00255. Epub 2022 Jul 6.
We present a simple method for increasing the reprocessability of vinylogous urethane (VU) vitrimers while decreasing the possibility of creep deformation at lower temperatures. In particular, varying amounts of triethylenetetramine were added as a comonomer to the curing VU formulation to ensure that all of the primary amines reacted to form enaminone cross-links, resulting in a network without reactive primary amine chain-ends. As a result, transamination was significantly slowed down because secondary amines are much less reactive to VU exchange. On the other hand, at higher temperatures, pendent primary amines can be released via a dynamic, endothermic exchange with a nearby less-reactive secondary amine, thereby (re)activating material flow. As a result, ambivalent viscoelastic behavior could be achieved without depolymerization by dynamically releasing pendent primary amines from vinylogous urethane polymer chains. Through careful comonomer selection, VU vitrimers with low viscosity at processing temperatures and at the same time high viscosity at service temperatures could be prepared without the use of catalysts or additives, leveraging the synergistic effects of mildly reactive functionalities through neighboring group participation.
我们提出了一种简单的方法来提高乙烯基尿烷（VU）类弹性体的可再处理性，同时降低在较低温度下发生蠕变变形的可能性。具体而言，将不同量的三亚乙基四胺作为共聚单体加入到固化 VU 配方中，以确保所有伯胺反应形成烯胺酮交联，从而形成没有反应性伯胺链末端的网络。结果，转氨反应明显减慢，因为仲胺对 VU 交换的反应性要低得多。另一方面，在较高温度下，通过与附近反应性较低的仲胺进行动态、吸热交换，可以释放出悬垂的伯胺，从而（重新）激活材料流动。因此，通过从乙烯基尿烷聚合物链上动态释放悬垂伯胺，可以实现具有双重粘弹性行为而不会发生解聚。通过仔细选择共聚单体，可以在不使用催化剂或添加剂的情况下制备在加工温度下具有低粘度且同时在使用温度下具有高粘度的 VU 类弹性体，利用相邻基团参与的轻度反应性功能的协同效应。
