Synthesis Of Chitosan-O-poly(Ethylene Glycol) Through Diels-Alder Reaction

In this study, the feasibility of employing Diels-Alder reaction for improving the grafting efficiency and controllability of poly(ethylene glycol) (PEG) towards chitosan (CS) was evaluated. Diene-capped PEG (PEG-diene) was conveniently obtained through thio-acrylate reaction between furfuryl mercaptan and poly(ethylene glycol) methyl ether methacrylate (PEGMEMA). By using sodium dodecyl sulphate-chitosan complex (SCC) as an organo-soluble precursor, the dienophile, (N-(2-carboxyethyl)maleimide), was regioselectively conjugated to the hydroxy groups of chitosan backbone through conventional coupling method. Sodium dodecyl sulphate (SDS) was then removed from the conjugate simply by precipitating the reaction solution into tris(hydroxymethyl)aminomethane (Tris) solution to give the chitosan intermediate carrying dienophile moieties (CS-dienophile). The products are characterized by FT-IR,1H NMR and GPC in water phase. In situ 1H NMR was further used for studying the Diels-Alder reactions between CS-dienophile and PEG-diene. It was found that PEG could be grafted onto chitosan backbone in aqueous media under mild conditions. In addition, the PEG grafts could be detached from the graft copolymers at high temperature through retro Diels-Alder reaction.The diene which can serve as an initiator of ATRP, was synthesized by 9-anthracenemethanol and 2-Bromoisobutyryl bromide. The brush PEG was prepared through ATRP method and reacted with CS-MI.