Novel acrylate/organophosphorus-based hydrogels for agricultural applications. New outlook and innovative concept for the use of 2-(methacryloyloxy)ethyl phosphate as a multi-purpose monomer

Abstract

Novel hydrogels with phosphoric acid-bearing units suitable for agricultural applications have been obtained. Introducing phosphate moieties into acrylate-based hydrogels could result in better swelling properties, especially under acidic conditions as the dissociation constants of phosphoric acid are much lower than that of acrylic acid. The presence of phosphate groups could also increase hydrogels’ biocompatibility and biodegradability, what in the case of agricultural application may be of great advantage. Presented hydrogels, besides acting as a water reservoir, have a potential to be an additional source of phosphorus - preliminary studies confirmed phosphate release as a result of hydrolysis. To obtain novel hydrogels, two organophosphorus compounds were chosen: 2-(methacryloyloxy)ethyl phosphate (MEP) acting as functional monomer and bis[2-(methacryloyloxy)ethyl] phosphate (BMEP) acting as a crosslinking agent. To the best of our knowledge, the use of these monomers in combination with acrylic acid has not been reported earlier in hydrogel synthesis. Hydrogels with nominal BMEP and MEP concentration 0.5–5.0 wt.% and 1.0–4.0 wt.%, respectively and water regain ranging from 105.5 g/g up to 2837.5 g/g were obtained. Swelling properties and response to different stimuli (pH, ionic strength etc.) were determined, indicating that synthesized materials could be successfully applied in agriculture. Moreover, obtained results gave new information about the properties of MEP, BMEP, products of their polymerization and, simultaneously, on their potential applications.