Polyurethanes are one of the most versatile families of polymers and are one of the most widely used in thermosets. Due to their static cross-linked structure, they have limited capacity to be reprocessed, recycled or reshaped and therefore once these materials suffer any damage, they are typically discarded. One of the key features of polyurethanes is given by the dynamic behavior of the urethane group at high temperatures, especially in the presence of an appropriate catalyst. In this work a detailed study is performed to demonstrate the dynamic nature of aliphatic and aromatic polyurethanes in the presence of different catalysts. Our study shows that the dynamic behavior is highly dependent on the nature of the isocyanate, the urethane/free alcohol ratio and the nature of the catalyst that is used in the polymerization. We found that the stress relaxation of polyurethane thermosets in the absence of a catalyst is related to the degradation of the network and that the catalyst plays a pivotal role in enhancing the dynamic behavior prior to degradation, especially in aromatic polyurethanes. In fact, the organocatalyst p-toluensulfonic acid (PTSA) is shown to have the ability to enhance the dynamic behavior via hydroxyl mediated transcarbamoylation (associative mechanism) whereas dibutyltin dilaurate (DBTDL) catalyzes transcarbamoylation reactions via both associative and dissociative exchange mechanisms at temperatures as low as 120 °C. These results have been confirmed by model reactions performed with low molecular weight compounds. We believe that this work offers a significant insight into the influence of structural parameters and catalyst effects in the intrinsic dynamic behavior of polyurethanes, and moreover, provides new alternatives to selectively enhance the dynamic nature of polyurethanes.

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动态聚氨酯热固性塑料：通过选择催化剂来调节缔合/解离行为

聚氨酯是最通用的聚合物家族之一，也是热固性塑料中使用最广泛的家族之一。由于它们的静态交联结构，它们的再加工，再循环或重塑能力有限，因此一旦这些材料遭受任何损坏，通常将其丢弃。聚氨酯的关键特征之一是氨基甲酸酯基团在高温下的动力学行为，特别是在合适的催化剂存在下的动力学行为。在这项工作中进行了详细的研究，以证明在不同催化剂存在下脂肪族和芳香族聚氨酯的动力学性质。我们的研究表明，动力学行为高度依赖于异氰酸酯的性质，氨基甲酸酯/游离醇的比例以及用于聚合反应的催化剂的性质。我们发现，在没有催化剂的情况下，聚氨酯热固性材料的应力松弛与网络的降解有关，并且催化剂在增强降解前的动力学行为方面起着举足轻重的作用，尤其是在芳族聚氨酯中。实际上，有机催化剂对甲苯磺酸（PTSA）具有通过羟基介导的氨基甲酸酯化反应（缔合机制）增强动力学行为的能力，而二月桂酸二丁锡（DBTDL）通过低至120°C的缔合和解离交换机制催化氨基甲酸酯化反应。。这些结果已通过使用低分子量化合物进行的模型反应得到证实。我们认为，这项工作为结构参数和催化剂效应对聚氨酯固有动力学行为的影响提供了重要的见识，此外，它为选择性增强聚氨酯的动力学性质提供了新的选择。