Altuna Facundo Ignacio, Hoppe Cristina Elena, Williams Roberto Juan José
Institute of Materials Science and Technology (INTEMA), University of Mar del Plata and National Research Council (CONICET), Av. J. B. Justo 4302, 7600 Mar del Plata, Argentina.
Polymers (Basel). 2018 Jan 3;10(1):43. doi: 10.3390/polym10010043.
Vitrimers are covalently crosslinked polymers that behave as conventional thermosets below the glass transition temperature (T) but can flow above a particular temperature, T > T, by bond exchange reactions. In epoxy vitrimers, transesterification reactions are responsible for their behavior at T > T that enables flow, thermoforming, recycling, self-healing and stress relaxation. A statistical analysis based on the fragment approach was performed to analyze the evolution of the network structure of epoxy vitrimers during transesterification reactions. An analytical solution was obtained for a formulation based on a diepoxide and a dicarboxylic acid. A numerical solution was derived for the reaction of a diepoxide with a tricarboxylic acid, as an example of the way to apply the model to polyfunctional monomers. As transesterification acts as a disproportionation reaction that converts two linear fragments (monoesters) into a terminal fragment (glycol) and a branching fragment (diester), its effect on network structure is to increase the concentration of crosslinks and pendant chains while leaving a sol fraction. Changes in the network structure of the epoxy vitrimer can take place after their synthesis, during their use at high temperatures, a fact that has to be considered in their technological applications.
玻璃转化弹性体是一种共价交联聚合物，在玻璃化转变温度（Tg）以下表现为传统热固性材料，但在特定温度（T>Tg）以上，可通过键交换反应流动。在环氧玻璃转化弹性体中，酯交换反应决定了其在T>Tg时的性能，实现流动、热成型、回收利用、自我修复和应力松弛。基于片段法进行了统计分析，以研究环氧玻璃转化弹性体在酯交换反应过程中网络结构的演变。得到了基于二环氧化物和二羧酸配方的解析解。以二环氧化物与三羧酸的反应为例，推导了数值解，以说明将该模型应用于多官能团单体的方法。由于酯交换反应是一种歧化反应，将两个线性片段（单酯）转化为一个末端片段（二醇）和一个支化片段（二酯），其对网络结构的影响是增加交联点和侧链的浓度，同时留下一个溶胶部分。环氧玻璃转化弹性体的网络结构在合成后、高温使用过程中可能发生变化，这一事实在其技术应用中必须予以考虑。
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