Self-healing hydroxypropyl guar gum/poly (acrylamide-co-3-acrylamidophenyl boronic acid) composite hydrogels with yield phenomenon based on dynamic PBA ester bonds and H-bond

In this report, the self-healable hydrogels containing hydroxypropyl guar gum (HPG), acrylamide (AM) and 3-acrylamidophenylboronic acid (AAPBA) were prepared through a facile strategy. The double bond in AAPBA could polymerize with AM to form copolymers. Moreover, the boronic acid groups of AAPBA can interact with cis-diol of HPG which make AAPBA act not only polymer but cross-linkers simultaneously connecting PAM and HPG chains. The mechanical strength of the hydrogels was systematically investigated as a function of AAPBA content, HPG content, AM content and pH. It was found the hydrogels exhibited higher stress, elongations and self-healing properties due to the synergistic interaction of H-bond and dynamic covalent phenylboronic (PBA)-diol ester bonds. Furthermore, the hydrogels showed yielding phenomenon depending on the content of AM and pH, which could play a vital influence on the crosslinking manners and density. The detailed discussions of the relationship between crosslinking manners and yielding phenomenon provide a better understanding on the appearance of yielding phenomenon and their correlation with hydrogel structure.