This work provides a new method to prepare poly(vinyl alcohol) (PVA) hydrogel. Compared with the traditional repeated freeze–thaw method, the physical cross-linking method was adopted to prepare a high-strength hydrogel in one step. The morphology, melting, and crystallization behavior and mechanical properties of the hydrogel were investigated. The hydrogel has a high water content and reswelling rate, as well as a high melting temperature and mechanical strength. It also has a stable cross-linked structure in the temperature range of 25–65 °C. The hydrogel fracture surface shows ductile and brittle fracture morphology. The protrusions in the hydrogel three-dimensional topography are more numerous and homogeneous when the solvent preparation ratio is 4–6. On the basis of the good plasticity of the hydrogels, tubular hydrogels with inner diameters of 1–6 mm are also prepared to widen their applications.

An efficient and general protocol for palladium-catalyzed chelation-assisted ortho-nitration of 2-arylbenzoxazoles has been developed. This nitration exhibits high regioselectivity for the substrates, and the reaction could tolerate many functional groups such as F, Cl, Br, CH3, CH3O, affording ortho-nitration products in moderate to good yields. Moreover, some 2-arylbenzoxazole heterocyclic analogues proceed well under this catalytic system. Further studies have been performed to obtain insight into the mechanism.This palladium-catalyzed ortho-nitration could tolerate many functional groups in the 2-arylbenzoxazole (e.g. F, Cl, Br, CH3 and CH3O), affording ortho-nitration products in moderate to good yields. Moreover, some 2-arylbenzoxazole heterocyclic analogues proceed well under this catalytic system.