Yang Hongkun, Wang Dong
State Key Laboratory of Organic-Inorganic Composites & Beijing Key Laboratory of Advanced Functional Polymer Composites, Beijing University of Chemical Technology, Beijing 100029, China.
ACS Appl Mater Interfaces. 2024 Mar 27;16(12):15479-15486. doi: 10.1021/acsami.3c17460. Epub 2024 Mar 12.
We used atomic force microscopy-based infrared spectroscopy (AFM-IR) and nanomechanical mapping (AFM-NM) to image the surface of a vitrimer, specifically dicarboxylic acid-cured diglycidyl ether of bisphenol A (DGEBA), to assess the curing process of a surface layer and compared this to the process in the bulk. We identified the β-hydroxy esters with various functionalities that are the key to form the cross-links for a system, including difunctional DGEBA and carboxylic acids. The IR peaks of the carbonyl group in generated ester groups are distinguished clearly from those in acids, allowing us to quantitatively assess the curing process at the surface and in the bulk. The initial curing at the surface exhibits a gradual cross-linking and is found to be lower than a rapid cross-linking in the bulk due to a relatively lower concentration of the β-hydroxy esters with high functionalities. This curing process leads to a smaller chemically and mechanically heterogeneous nanostructure at the surface relative to the bulk. After multiple reprocessings, a substantial number of esters lacking dynamic exchange capability form in the bulk, which decrease the flowability and reprocessability of the vitrimers and therefore the mechanical properties.
我们使用基于原子力显微镜的红外光谱（AFM-IR）和纳米力学映射（AFM-NM）对一种热致液晶聚合物（vitrimer）的表面进行成像，具体为二羧酸固化的双酚A二缩水甘油醚（DGEBA），以评估表面层的固化过程，并将其与本体中的过程进行比较。我们确定了具有各种官能团的β-羟基酯，它们是形成体系交联的关键，包括双官能的DGEBA和羧酸。生成的酯基中羰基的红外峰与酸中的红外峰明显不同，这使我们能够定量评估表面和本体中的固化过程。表面的初始固化表现出逐渐交联，并且由于具有高官能度的β-羟基酯浓度相对较低，发现其低于本体中的快速交联。这种固化过程导致表面相对于本体具有更小的化学和机械异质纳米结构。经过多次再加工后，本体中形成了大量缺乏动态交换能力的酯，这降低了热致液晶聚合物的流动性和再加工性，进而降低了其机械性能。
