For the application of low-temperature curing on automotive clearcoats, isocyanate cross-linkers blocked with imidazole derivatives were newly synthesized. The effect of the alkyl groups in the imidazole derivatives on the deblocking behavior and curing kinetics was investigated. The free isocyanate groups exposed by the deblocking of imidazole-based blocking agents were monitored by real-time Fourier-transform infrared spectroscopy. The bond dissociation energy, activation energy of deblocking, and H–N distance were interpreted through density functional theory simulation of various imidazole-based blocked isocyanates. To evaluate their applicability to automotive clearcoats, the synthesized imidazole-based blocked isocyanates were mixed with a polyol binder containing hydroxyl groups, and the clearcoat samples were cured at relatively low curing temperatures (100, 110, and 120 °C). The real-time storage modulus was measured using a rotational rheometer to elucidate the thermal curing dynamics by the blocking agents. In addition, the surface hardness of the cured clearcoat layers, which is affected by the chemical structure of the imidazole derivatives, was evaluated by nanoindentation test. In-depth analyses of the deblocking behaviors and thermal curing properties of clearcoats using imidazole-based blocked isocyanates demonstrated that the newly developed coating system could be suitably applied for the development of low-temperature curing technology.

中文翻译：

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异氰酸酯交联剂与咪唑基封闭剂的反应性和固化效率，用于汽车清漆的低温固化

为了在汽车透明涂料中进行低温固化，新合成了由咪唑衍生物封端的异氰酸酯交联剂。研究了咪唑衍生物中烷基对去嵌段行为和固化动力学的影响。通过实时傅立叶变换红外光谱法监测通过咪唑基封闭剂解封闭而暴露的游离异氰酸酯基。通过各种基于咪唑的封端异氰酸酯的密度泛函理论模拟，解释了键解离能，解封活化能和H–N距离。为了评估其在汽车清漆中的适用性，将合成的基于咪唑的嵌段异氰酸酯与含有羟基的多元醇粘合剂混合，透明涂料样品在相对较低的固化温度（100、110和120℃）下固化。使用旋转流变仪测量实时储能模量，以阐明封闭剂的热固化动力学。另外，通过纳米压痕试验评价固化的透明涂层的表面硬度，其受咪唑衍生物的化学结构的影响。对使用咪唑基封端异氰酸酯的清漆的脱粘行为和热固化性能的深入分析表明，新开发的涂料体系可适用于低温固化技术的发展。另外，通过纳米压痕试验评价固化的透明涂层的表面硬度，其受咪唑衍生物的化学结构的影响。对使用咪唑基封端异氰酸酯的清漆的脱粘行为和热固化性能的深入分析表明，新开发的涂料体系可适用于低温固化技术的发展。另外，通过纳米压痕试验评价固化的透明涂层的表面硬度，其受咪唑衍生物的化学结构的影响。对使用咪唑基封端异氰酸酯的清漆的脱粘行为和热固化性能的深入分析表明，新开发的涂料体系可适用于低温固化技术的发展。