Adjaoud Antoine, Marcolini Benoit, Dieden Reiner, Puchot Laura, Verge Pierre
Luxembourg Institute of Science and Technology, 5 Avenue des Hauts-Fourneaux, Esch-sur-Alzette L-4362, Luxembourg.
University of Luxembourg, 2 Avenue de Université, Esch-sur-Alzette L-4365, Luxembourg.
J Am Chem Soc. 2024 May 15;146(19):13367-13376. doi: 10.1021/jacs.4c02153. Epub 2024 May 2.
The use of internal catalysts has emerged as a pivotal design principle to facilitate dynamic exchanges within covalent adaptable networks (CANs). Polybenzoxazines, specifically, have shown considerable potential in generating vitrimers through thermally induced transesterification reactions catalyzed internally by tertiary amines. This study aims to investigate the chemical complexities of transesterification reactions within benzoxazine vitrimers. To achieve this, model molecules using various phenolic acids and amino-alcohol derivatives were synthesized as precursors. The structure of these model molecules was fully elucidated by using nuclear magnetic resonance (NMR). Differential scanning calorimetry (DSC) and rheology experiments evidenced the accelerated network formation of the precursors due to the presence of aliphatic -OH groups. Thermogravimetric analysis coupled with microcomputed gas chromatography (TGA-μGC) was used to provide evidence of transesterification reactions. The results showed that the spatial proximity between tertiary amine and hydroxyl groups significantly enhances the rate exchange, attributed to a neighboring group participation (NGP) effect. Interestingly, kinetic experiments using complementary NMR techniques revealed the thermal latency of the tertiary amine of benzoxazine toward transesterification reactions as its opening is needed to trigger the dynamic exchange. The study highlights the crucial role of steric hindrance and tertiary amine basicity in promoting the dynamic exchange in an internally catalyzed system.
内部催化剂的使用已成为促进共价自适应网络（CANs）内动态交换的关键设计原则。具体而言，聚苯并恶嗪在通过叔胺内部催化的热诱导酯交换反应生成热致互穿聚合物网络方面显示出巨大潜力。本研究旨在探究苯并恶嗪热致互穿聚合物网络内酯交换反应的化学复杂性。为此，合成了使用各种酚酸和氨基醇衍生物的模型分子作为前体。通过核磁共振（NMR）全面阐明了这些模型分子的结构。差示扫描量热法（DSC）和流变学实验证明，由于脂肪族-OH基团的存在，前体的网络形成加速。热重分析结合微计算机气相色谱法（TGA-μGC）用于提供酯交换反应的证据。结果表明，叔胺与羟基之间的空间接近性显著提高了交换速率，这归因于邻基参与（NGP）效应。有趣的是，使用互补NMR技术的动力学实验揭示了苯并恶嗪叔胺对酯交换反应的热潜伏期，因为其开环是触发动态交换所必需的。该研究突出了空间位阻和叔胺碱性在促进内部催化体系中动态交换方面的关键作用。
