Curing agents for epoxy resins play a significant role in initiating crosslinking reactions resulting in the hardened and durable material with enhanced properties as per end-user applications. The industrial world still lacks efficient, environmentally friendly, and cheap curing agents for epoxy resins. Here, we report the development of deep eutectic solvents (DESs) based on N, N’-Bis(2-aminoethyl)ethane-1,2-diamine (commonly known as triethylenetetramine, TETA) as hydrogen bond donor (HBD), and salicylic acid (SA) and choline chloride (CC) as hydrogen bond acceptor (HBA). The formulated DESs are suggested to be relatively safe, affordable, and eco-friendly and the active groups in the DESs are capable of initiating crosslinking reactions. The physical stability of the formulated deep eutectic solvents was examined by polarizing optical microscopic (POM) analysis, which confirmed the absence of any crystals or residues. The purity was ensured by C nmr spectroscopy. Additionally, supportive evidence for the hydrogen bond formation between the constituents was gained from the outcomes of FTIR, H nmr, and mass spectrometry. Deep depression in melting points was confirmed from DSC studies, and TGA suggested better thermal stability for DESs than its constituents. Density functional theory (DFT) at B3LYP6-31G* of Gaussian computational framework was applied to energetically optimize the isolated structure and determine the bond lengths in angstroms. The structural characteristics and nonbonding interactions of DESs were investigated by the same. In addition, the density and rheological characteristics were assessed for the ideal utilization of the formulated DESs as epoxy resin curing agents. The detailed comparative studies demonstrated the advantages of deep eutectic solvents over conventional curing agents. The efficacy of the formulations as a curing agent was primarily confirmed from FTIR analysis and the curing behavior was investigated by DSC studies.

中文翻译：

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非常规前驱体材料低共熔溶剂（DES）的制备、理化分析及比较评价研究，用作环氧树脂催化固化剂


环氧树脂固化剂在引发交联反应方面发挥着重要作用，从而产生硬化且耐用的材料，并根据最终用户的应用具有增强的性能。工业界仍然缺乏高效、环保、廉价的环氧树脂固化剂。在这里，我们报告了基于N,N'-双(2-氨基乙基)乙烷-1,2-二胺（俗称三乙烯四胺，TETA）作为氢键供体（HBD）的低共熔溶剂（DES）的开发，以及水杨酸（SA）和氯化胆碱（CC）作为氢键受体（HBA）。所配制的 DES 相对安全、经济且环保，并且 DES 中的活性基团能够引发交联反应。通过偏光光学显微镜 (POM) 分析检查了配制的低共熔溶剂的物理稳定性，结果证实不存在任何晶体或残留物。通过13C核磁共振光谱确保纯度。此外，从 FTIR、1H 核磁共振和质谱的结果中获得了成分之间氢键形成的支持证据。 DSC 研究证实了熔点深度降低，TGA 表明 DES 的热稳定性比其成分更好。应用高斯计算框架 B3LYP6-31G* 的密度泛函理论 (DFT) 大力优化孤立结构并确定以埃为单位的键长。通过同样的方法研究了 DES 的结构特征和非键相互作用。此外，还评估了密度和流变特性，以确保配制的 DES 作为环氧树脂固化剂的理想用途。 详细的比较研究证明了低共熔溶剂相对于传统固化剂的优势。该配方作为固化剂的功效主要通过 FTIR 分析得到证实，并通过 DSC 研究研究固化行为。