Tough hydrogel based on covalent crosslinking and ionic coordination from ferric iron and negative carboxylic groups

Abstract

In this work, carboxylic groups were introduced to latex microspheres (LMs) to obtain poly(styrene-butyl acrylate) (P(St-BA)-COOH) LMs with negative charges by a soap-free emulsion polymerization method. Then P(St-BA)-COOH LMs were added into an aqueous solution composed of acrylamide (AAm) and acrylic acid (AAc). The P(AAm-co-AAc)-MBA/LMs hydrogel was fabricated after adding redox initiators and N,N’-methylene diacrylamide (MBA) as covalent crosslinker by a free radical copolymerization. Subsequently, P(AAm-co-AAc)-MBA/LMs hydrogels were soaked into a ferric solution to achieve a tough hybrid hydrogel with covalent crosslinking and ionic coordination interaction between ferric ions and negative carboxylic groups arising from LMs and P(AAm-co-AAc) chains. The resultant P(AAm-co-AAc)-MBA/LMs-Fe3+ hydrogels possessed high fracture stress of 1440 kPa, large strain of 1140% and fracture energy of 6983 kJ/m3. This would help us to deeply understand the relationship between the structure and performance of LMs-reinforced hydrogels.