pH-responsive, dynamically restructuring hydrogels formed by reversible crosslinking of PVA with phenylboronic acid functionalised PPO-PEO-PPO spacers (Jeffamines®)

Dynamically restructuring ("self-healing") hydrogels were prepared by reversible formation of boronic-ester crosslinks between α,ω-phenylboronic acid terminated PPO-PEO-PPO spacers and poly(vinyl alcohol) (PVA). For this purpose two different bis-(phenylboronic acid) functionalised crosslinkers with Jeff-2AMPBA and Jeff-4AMPBA were synthesised via reductive coupling of 2- and 4-formylphenylboronic acid to Jeffamine® ED1900. Due to the different positions of the secondary amino group with respect to the boronic acid moiety ( ortho or para ) the p K a of the amino and boronic acid groups at the spacer endgroups differ significantly, thereby influencing the pH-dependency of boronic ester formation and gel properties. Upon mixing the boronic acid spacers with PVA (72-195 kDa) in the pH range 3-9 hydrogels were immediately formed. The gel strength and relaxation time of Jeff-2AMPBA gels increase with increasing acidity of the solution whereas those of Jeff-4AMPBA increase with increasing basicity. The pH-tunable properties could be explained in terms of pH effects on intra -molecular and inter -molecular B-N interactions in the Jeff-2AMPBA gels and Jeff-4AMPBA gels, respectively. o - or p -Aminomethylphenylboronic acid terminated PPO-PEO-PPO spacers form pH-tunable dynamically restructuring hydrogels with poly(vinyl alcohol).