Preparation of itaconic acid bio-based cross-linkers for hydrogels

Itaconic acid (IA) is a bio-based unsaturated monomer, which has been limitedly used in free-radical polymerization due to low reactivity of its carbon-carbon double bond and lack of tendency toward homo-polymerization. In the present work, IA was modified with glyceryl methacrylate (GMA) or epichlorohydrin (ECH) to synthesize two new IA-based materials, i.e., IA-GMA and IA-ECH, respectively. After the characterization of the crosslinkers by 1H NMR and FTIR, IA-GMA containing two methacrylate groups in the structure was used as an internal crosslinker for the preparation of a superabsorbent polymer (SAP). The obtained IA-GMA crosslinked SAP showed a high water absorbency under load (AUL) up to 23.9 g/g compared to commercial SAPs (14–18 g/g), so it can be a potential crosslinker for SAP preparation without a requirement of the surface treatment process as a time and energy-consuming process. Moreover, the application of IA-ECH, possessing hydroxyl or epoxy functionalities as an internal and surface crosslinker in the synthesis of SAPs was investigated. The unique ion structure of IA-ECH as an external crosslinker resulted in improvement in gel strength, as well as AUL up to 30.7 g/g. The SAPs crosslinked by IA-ECH as internal crosslinker presented a high water absorbency (Qw) and saline absorbency (Qs).