Zhang Xinpeng, Huang Sijia, Podgórski Maciej, Han Xun, Claudino Mauro, Bowman Christopher N
Department of Chemical and Biological Engineering, University of Colorado Boulder, 596 UCB, Boulder, CO 80309-0596, United States.
Faculty of Chemistry, Department of Polymer Chemistry, Maria Curie-Sklodowska University, pl. Marii Curie-Sklodowskiej 5, 20-031 Lublin, Poland.
Polym Chem. 2018 Aug 28;9(32):4294-4302. doi: 10.1039/C8PY00662H. Epub 2018 Jul 14.
We present a thermally initiated thiol-Michael reaction based on initiation via the temperature-dependent thiol-TEMPO oxidation-reduction reaction. In the presence of a thiol, 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO, p = 5.5) is reduced to produce a much stronger base, i.e., tetramethylpiperidine (TMP, p = 11.4) in a temperature dependent process. This oxidation-reduction process is dramatically accelerated at elevated temperature, which allows for thermally controlled initiation of the base-catalyzed thiol-Michael addition reaction and potentially other base-catalyzed reaction systems. Several critical factors that affect base generation from TEMPO reduction were investigated systematic variation of reaction conditions including the solvent, temperature, and the thiol type and concentration. The highly temperature-dependent attributes of this redox reaction were demonstrated in various thiol-TEMPO based systems and were further utilized to thermally control thiol-Michael polymerizations under different heating conditions. The strong amine species, TMP, formed at elevated temperatures from the TEMPO-thiol interaction combined with high temperature, enables rapid formation of thiol-Michael-based polymer networks and large scale material preparation without any detrimental effects often associated with highly exothermic polymerizations. This novel approach to develop thermally-initiated thiol-Michael polymer networks is unique, versatile and robust, resulting in wide utility in applications such as facile handling of highly reactive resins, bulk material preparation, pH sensitive materials construction, and composite/macro-particle synthesis.
我们提出了一种基于温度依赖性硫醇 - TEMPO氧化还原反应引发的热引发硫醇 - 迈克尔反应。在硫醇存在下，2,2,6,6 - 四甲基哌啶 - 1 - 氧基（TEMPO，pKa = 5.5）被还原，在温度依赖性过程中生成碱性强得多的四甲基哌啶（TMP，pKa = 11.4）。这种氧化还原过程在升高的温度下会显著加速，从而实现对碱催化的硫醇 - 迈克尔加成反应以及其他潜在的碱催化反应体系的热控制引发。研究了影响由TEMPO还原产生碱的几个关键因素——包括溶剂、温度、硫醇类型和浓度在内的反应条件的系统变化。这种氧化还原反应的高度温度依赖性特性在各种基于硫醇 - TEMPO的体系中得到了证明，并进一步用于在不同加热条件下热控制硫醇 - 迈克尔聚合反应。在高温下由TEMPO - 硫醇相互作用形成的强胺类物质TMP与高温相结合，能够快速形成基于硫醇 - 迈克尔的聚合物网络并进行大规模材料制备，而不会产生通常与高度放热聚合反应相关的任何有害影响。这种开发热引发硫醇 - 迈克尔聚合物网络的新方法独特、通用且稳健，在诸如高反应性树脂的简便处理、块状材料制备、pH敏感材料构建以及复合材料/宏观颗粒合成等应用中具有广泛的用途。
