Oxime-Based and Catalyst-Free Dynamic Covalent Polyurethanes,Journal of the American Chemical Society

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Oxime-Based and Catalyst-Free Dynamic Covalent Polyurethanes
Journal of the American Chemical Society ( IF 14.4 ) Pub Date : 2017-06-13 , DOI: 10.1021/jacs.7b03967
Wen-Xing Liu _{1,

2} , Chi Zhang ₃ , Huan Zhang _{1,

2} , Ning Zhao ₁ , Zhi-Xiang Yu ₃ , Jian Xu _{1,

2}

Affiliation

Polyurethanes (PUs) have many applications resulting from their preeminent properties, but being commonly used toxic catalysts, and the lack of processability for PU thermosets cause limitations. Herein, we report a new class of the PU-like dynamic covalent polymers, poly(oxime-urethanes) (POUs), which are prepared from the uncatalyzed polyaddition of multifunctional oximes and hexamethylene diisocyanate (HDI) at ambient temperature. Kinetics studies reveal that almost complete polymerization (∼99% conversion) can be achieved in 3 h at 30 °C in dichloromethane (DCM), the most effective among the solvents evaluated, producing linear POUs with comparable molecular weights to the catalyzed PUs. We find that the oxime-carbamate structures are reversible at about 100 °C through oxime-enabled transcarbamoylation via a thermally dissociative mechanism. The cross-linked POUs based on oxime-carbamate bonds show efficient catalyst-free healable/recyclable properties. Density functional theory (DFT) calculations suggest that the fast oxime-urethanation and the mild thermoreversible nature are mediated by the characteristic nitrone tautomer of the oxime. Given widespread urethane-containing materials, POUs are of promising potential in applications because of the excellent mechanical performances, facile preparation, and dynamic property without using catalysts.

中文翻译：

基于肟和无催化剂的动态共价聚氨酯

聚氨酯 (PU) 因其卓越的性能而具有许多应用，但它是常用的有毒催化剂，并且 PU 热固性塑料缺乏可加工性，因此存在局限性。在此，我们报告了一类新的类 PU 动态共价聚合物，聚（肟-氨基甲酸乙酯）（POU），它是在环境温度下由多功能肟和六亚甲基二异氰酸酯（HDI）的未催化加聚反应制备的。动力学研究表明，在 30 °C 的二氯甲烷 (DCM) 中，3 小时内可以实现几乎完全聚合（约 99% 的转化率），这是所评估的溶剂中最有效的，产生的线性 POU 的分子量与催化的 PU 相当。我们发现肟-氨基甲酸酯结构在大约 100°C 时通过热解离机制通过肟启用的氨基甲酰化反应是可逆的。基于肟-氨基甲酸酯键的交联 POU 显示出有效的无催化剂可修复/可回收特性。密度泛函理论 (DFT) 计算表明，快速肟-氨基甲酸酯化和温和的热可逆性质是由肟的特征硝酮互变异构体介导的。鉴于含氨基甲酸酯材料的广泛应用，POU 具有优异的机械性能、易于制备和不使用催化剂的动态性能，因此在应用中具有广阔的前景。

更新日期：2017-06-13

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