Starch-cl-PEG hydrogels synthesized via click reaction as novel delivery device for sustained release of imidacloprid insecticide

Although the appearance of agrochemicals has extended the efficiency of food considerably, the non-judicious application of these essential chemical agents not only result in crucialecological problems because of their leaching and volatilization but also contaminate surface water and groundwater due to their potential health hazards. The new controlled pesticide formulations are superior conventional formulations in avoidance of treating excess amounts of active agents, highefficiency activity, reduced leaching, volatilization and degradation, the least residues on food and decreased dermaltoxicity. Hydrogels, three-dimensional hydrophilic polymer networks which are cross-linked physically (ionic-, van der Waals-, hydrophobic, or hydrogen bond interactions) or chemically (covalent bonds) and can absorb water many times over than their dry mass and outstandingly increase in theirvolume, possess significant potential application in different fields e.g. biomedical application and pharmaceuticalcontrolled release technology and more recently in theagrochemichals field [1]. Click chemistry has been succeeded in fabricating various hydrogels, due to its high efficiency and selectivity [2]. However one of the hydrogel preparation methods, crosslinking by Cu-catalyzed Huisgen-type [3+2] cycloadditionreaction between azide and alkynes, can be accomplished with a high reaction rate, no by-products and acceptable stability under physiological conditions. The present study is an attempt, to synthesize starch-based hydrogels, using Poly(ethylene glycol)-Diazide as crosslinkerthrough Cu-catalyzed [3+2] cycloaddition reaction. To estimate the feasibility of prepared hydrogels as novel pesticide carriers, imidacloprid, a systemic neonicotinoidinsecticide that is highly active against sucking insects [3], was applied as a model for this investigation.