Kong Sen, Wang Rui, Feng Shengyu, Wang Dengxu
National Engineering Research Center for Colloidal Materials and Key Laboratory of Special Functional Aggregated Materials, Ministry of Education, School of Chemistry and Chemical Engineering, Shandong University, Jinan, China.
Shandong Key Laboratory of Advanced Organosilicon Materials and Technologies and State Key Laboratory of Fluorinated Functional Membrane Materials, Zibo, China.
Front Chem. 2021 Oct 18;9:778896. doi: 10.3389/fchem.2021.778896. eCollection 2021.
The construction of silicone elastomers crosslinked by a natural crosslinker under a catalyst-free method is highly desirable. Herein we present catalyst-free silicone elastomers (SEs) by simply introducing tannic acid (TA) as a natural crosslinker when using poly (aminopropylmethylsiloxane--dimethylsiloxane) (PAPMS) as the base polymer. The crosslinked bonding of these SEs can be easily changed from hydrogen bonding to covalent bonding by altering the curing reaction from room temperature to heating condition. The formability and mechanical properties of the SEs can be tuned by altering various factors, including processing technique, the amount of TA and aminopropyl-terminated polydimethylsiloxane, the molecular weight and -NH content of PAPMS, and the amount of reinforcing filler. The hydrogen bonding was proved by the reversible crosslinking of the elastomers, which can be gradually dissolved in tetrahydrofuran and re-formed after removing the solvent. The covalent bonding was proved by a model reaction of catechol and -decylamine and occurred through a combination of hydroxylamine reaction and Michael addition reaction. These elastomers exhibit good thermal stability and excellent hydrophobic property and can bond iron sheets to hold the weight of 500 g, indicating their promising as adhesives. These results reveal that TA as a natural product is a suitable "green" crosslinker for the construction of catalyst-free silicone elastomers by a simple crosslinking strategy. Under this strategy, TA and more natural polyphenols could be certainly utilized as crosslinkers to fabricate more organic elastomers by selecting amine-containing polymers and further explore their extensive applications in adhesives, sealants, insulators, sensors, and so forth.
通过无催化剂方法由天然交联剂交联制备有机硅弹性体是非常理想的。在此，我们展示了一种无催化剂的有机硅弹性体（SEs），即在使用聚（氨丙基甲基硅氧烷 - 二甲基硅氧烷）（PAPMS）作为基础聚合物时，简单地引入单宁酸（TA）作为天然交联剂。通过将固化反应从室温改变为加热条件，这些SEs的交联键可以很容易地从氢键转变为共价键。SEs的可成型性和机械性能可以通过改变各种因素来调节，包括加工工艺、TA和氨丙基封端的聚二甲基硅氧烷的用量、PAPMS的分子量和 -NH含量以及增强填料的用量。弹性体的可逆交联证明了氢键的存在，其可逐渐溶解于四氢呋喃中，并在除去溶剂后重新形成。儿茶酚和癸胺的模型反应证明了共价键的存在，其通过羟胺反应和迈克尔加成反应的组合而发生。这些弹性体表现出良好的热稳定性和优异的疏水性，并且能够粘结铁片以承受500 g的重量，表明它们作为粘合剂具有广阔的应用前景。这些结果表明，TA作为一种天然产物，是通过简单的交联策略构建无催化剂有机硅弹性体的合适“绿色”交联剂。在这种策略下，通过选择含胺聚合物，TA和更多的天然多酚肯定可以用作交联剂来制备更多的有机弹性体，并进一步探索它们在粘合剂、密封剂、绝缘体、传感器等方面的广泛应用。
