Gomez-Lopez Alvaro, Grignard Bruno, Calvo Iñigo, Detrembleur Christophe, Sardon Haritz
POLYMAT and Department of Polymers and Advanced Materials: Physics, Chemistry and Technology, Faculty of Chemistry, University of the Basque Country UPV/EHU, Paseo Manuel de Lardizabal 3, 20018Donostia-San Sebastián, Spain.
Center for Education and Research on Macromolecules (CERM), CESAM Research Unit, University of Liège, allée du 6 août, Building B6A, Agora Square, 4000Liège, Belgium.
ACS Appl Polym Mater. 2022 Dec 9;4(12):8786-8794. doi: 10.1021/acsapm.2c01195. Epub 2022 Nov 16.
The polyaddition between dicyclic carbonates and diamines leading to poly(hydroxy urethane)s (PHUs) has emerged as the preferred method for the synthesis of green, non-isocyanate polyurethanes. However, when proposed for use as structural adhesives, the long times for completion of aminolysis of the 5-membered cyclic carbonates under ambient conditions force the use of complementary chemistries to accelerate the curing process. In this work, a system that combines an amino-terminated PHU (NH-PHU-NH), an epoxy resin, and a thiol compound was employed to develop high-shear strength PHU-epoxy hybrid adhesives able to cure at room temperature in short times. A NH-PHU-NH prepolymer synthesized by using a sub-stoichiometric quantity of dicyclic carbonates was mixed with a bisphenol A-based epoxy resin for the preparation of the structural adhesive. While this adhesive showed good lap-shear strength and shear resistance under static load and temperature, the curing process was slow. In order to speed up the curing process, a thiol (trimethylolpropane tris(3-mercapto propionate)) was added and its impact on the curing process as well as on the adhesive properties was evaluated. The trifunctional thiol additive allowed for faster curing in the presence of the 1,1,3,3-tetramethylguanidine basic catalyst. Moreover, a combination of NH-PHU-NH and the thiol as curing agents for the epoxy resin resulted in adhesives with superior toughness, without any deterioration of the ultimate lap-shear strength or shear resistance under load and temperature, making these adhesives suitable for high-demand applications in the automotive industry.
双环碳酸酯与二胺之间的聚加成反应生成聚（羟基聚氨酯）（PHU），已成为合成绿色非异氰酸酯聚氨酯的首选方法。然而，当提议将其用作结构胶粘剂时，在环境条件下五元环碳酸酯的氨解反应完成时间较长，这就迫使人们使用互补化学方法来加速固化过程。在这项工作中，采用了一种将端氨基PHU（NH-PHU-NH）、环氧树脂和硫醇化合物相结合的体系，来开发能够在室温下短时间内固化的高剪切强度PHU-环氧混合胶粘剂。使用亚化学计量的双环碳酸酯合成的NH-PHU-NH预聚物与双酚A基环氧树脂混合，用于制备结构胶粘剂。虽然这种胶粘剂在静态载荷和温度下表现出良好的搭接剪切强度和抗剪强度，但固化过程较慢。为了加快固化过程，添加了一种硫醇（三羟甲基丙烷三（3-巯基丙酸酯）），并评估了其对固化过程以及胶粘剂性能的影响。在1,1,3,3-四甲基胍碱性催化剂存在下，三官能硫醇添加剂能够实现更快的固化。此外，NH-PHU-NH和硫醇作为环氧树脂的固化剂组合，得到的胶粘剂具有优异的韧性，在载荷和温度下的极限搭接剪切强度或抗剪强度没有任何下降，使得这些胶粘剂适用于汽车行业的高要求应用。
