Crosslinking of waterborne polyurethane using dibromide as a crosslinker and 1,1,3,3-tetramethylguanidine (TMG) as an esterification promotor

Pursuing high performance and solving the dilemma of existing materials are the driving force of material research. Waterborne polyurethane (WPU) is an environmentally benign material with excellent performance and wide use. However, due to its inherent hydrophilic groups, such as carboxyl, the waterproof and mechanical properties of its corresponding films have been seriously affected. To address this dilemma, herein we proposed a new crosslinking method by using commercialized dibromide as a crosslinker and 1,1,3,3-tetramethylguanidine (TMG) as an esterification promoter, to make the carboxyl groups of waterborne polyurethane and dibromide undergo esterification crosslinking reaction, which reduces the content of carboxyl groups while realizing the crosslinking of WPU films. The results show that the water absorption of WPU films crosslinked by this method is greatly reduced, the hydrophobic property (contact angle) is significantly improved, and the mechanical properties are greatly enhanced. Meanwhile, to facilitate construction and commercial application, we designed a two-component WPU coating, and their corresponding films also show great hydrophobic and mechanical properties. In a word, the crosslinking method has the advantages of low cost, simple operation, high crosslinking efficiency and mild reaction conditions.