Alraddadi Maher A, Chiaradia Viviane, Stubbs Connor J, Worch Joshua C, Dove Andrew P
School of Chemistry, University of Birmingham Edgbaston B15 2TT UK
Polym Chem. 2021 Sep 17;12(40):5796-5802. doi: 10.1039/d1py00754h. eCollection 2021 Oct 19.
The modern materials economy is inefficient since most products are principally derived from non-renewable feedstocks and largely single-use in nature. Conventional thermoset materials are often inherently unreprocessable due to their irreversible covalent crosslinks and hence are challenging to recycle and/or reprocess. Covalent adaptable networks (CAN)s, which incorporate reversible or dynamic covalent bonding, have emerged as an efficient means to afford reprocessable crosslinked materials and increasing the feedstock sustainability of CANs is a developing aim. In this study, the biomass-derived lipoic acid, which possesses a dynamic cyclic disulfide moiety, was transformed into a series of bifunctional monomers a one-step esterification or amidation reaction and reacted with a commercially available multi-valent thiol in the presence of an organobase catalyst to afford dynamically crosslinked networks. Large differences in material properties, such as storage modulus and glass transition temperature, were observed when the ratio of the lipoic acid-based monomer to thiol (from 1 : 1 to 16 : 1) and the composition of the monomer were changed to modify the network architecture. The thermomechanical properties of an optimised formulation were investigated more thoroughly to reveal a moderately strong rubber (ultimate tensile strength = 1.8 ± 0.4 MPa) possessing a large rubbery plateau (from 0 to 150 °C) which provides an adaptable material with a wide operational temperature range. Finally, the chemical recycling, or depolymerisation, of the optimised network was also demonstrated by simply solvating the material in the presence of an organobase catalyst.
现代材料经济效率低下，因为大多数产品主要源自不可再生原料，且本质上大多为一次性使用。传统热固性材料由于其不可逆的共价交联，通常本质上不可再加工，因此在回收和/或再加工方面具有挑战性。包含可逆或动态共价键的共价自适应网络（CANs）已成为提供可再加工交联材料的有效手段，提高CANs的原料可持续性是一个不断发展的目标。在本研究中，具有动态环状二硫键部分的生物质衍生硫辛酸通过一步酯化或酰胺化反应转化为一系列双功能单体，并在有机碱催化剂存在下与市售多价硫醇反应，以提供动态交联网络。当基于硫辛酸的单体与硫醇的比例（从1∶1到16∶1）以及单体组成发生变化以改变网络结构时，观察到材料性能如储能模量和玻璃化转变温度存在很大差异。对优化配方的热机械性能进行了更深入的研究，以揭示一种具有适度强度的橡胶（极限拉伸强度 = 1.8±0.4 MPa），其具有较大的橡胶平台区（从0到150°C），这为该材料提供了较宽的使用温度范围。最后，通过在有机碱催化剂存在下简单地使材料溶解，也证明了优化网络的化学回收或解聚。
