Title：Vitrimerization of Linear Polyurethane via Group Revival-Induced Crosslinking

Abstract: Vitrimers are generally constructed via crosslinking polymerization in which a crosslinker is reacted along with monomer(s). Herein, we report another strategy named group revival-induced crosslinking (GRIC) to prepare polyurethane vitrimer (PUV) directly from liner polyurethane (LPU) without using any crosslinker. Under the catalysis of K₂CO₃, the NH function in the urethane group is activated and it is able to attack another urethane group to form an allophanate crosslinker and, in the meantime, to release a free OH group. The allophanate is a dynamic covalent crosslinker in which reversible transesterification between free OH and allophanate groups allows the reprocessability for the obtained networks. The stress relaxation of the obtained networks prove the formation of the vitrimer. Both catalyst loading and vitrimerization temperature affect the gel fraction and further the mechanical properties of the obtained PUVs. Compared with LPU, the elongation at break of PUVs could be increased from 180 to 370%, while the tensile strength remains at the same level. Furthermore, the chemical structures and thermal and mechanical properties of the reprocessed PUVs remain the same as the pristine ones. This GRIC strategy is an efficient tool for enhancing the performance of thermoplastic polyurethanes (PUs) and, especially, for the value-added modification of recycled thermoplastic PUs as well as recycled polyamides.

DOI：10.1021/acsapm.3c00874