Novel solvent-free synthesis and modification of polyaspartic acid hydrogel

Abstract

Polyaspartic acid (PASP) hydrogel, a hydrolysis derivative of polysuccinimide (PSI), has been previously synthesized by using organic solvents such as dimethyl formamide (DMF) or dimethyl sulfoxide (DMSO), making the process environmentally and economically unattractive. The present paper presents a “green” synthesis, without using organic solvents. It demonstrates that hydrolysis and modification can be combined with in situ cross-linking. Introducing an aqueous soluble cross-linker, experimental results would broaden the application area of PASP at significantly reduced preparation cost, whilst moreover improving the required properties. The PASP hydrogel obtained by this method has a 600 g g⁻¹ water-swelling ratio against 420 g g⁻¹ as obtained by the conventional method using DMF. To reduce the ionic strength sensitivity of the hydrogel, sulfo-groups from, e.g. taurine, can be grafted onto the main chain of PASP and produce a modified PASP hydrogel with a 300 g g⁻¹ water-swelling ratio in a 0.9% sodium chloride solution, against only 80 g g⁻¹ for the non-grafted PASP hydrogel.