基于Diels-Alder点击反应构建壳聚糖-O-聚乙二醇接枝共聚物

通过Diels-Alder(D-A)反应,合成了具有规整化学结构的接枝共聚物,壳聚糖-O-聚乙二醇(CS-O-PEG).D-A反应所需双烯体(呋喃环)通过糠基硫醇与端甲基丙烯酸酯聚乙二醇之间的巯基-丙烯酸酯(thio-acrylate)反应合成得到;马来酰亚胺基丙酸通过活泼酯法偶联到十二烷基硫酸钠-壳聚糖复合物(SCC)羟基上,从而获得亲双烯体.采用红外光谱(FTIR)和核磁共振(1H-NMR)表征了中间产物与最终产物的结构,并用原位核磁监测D-A反应及其逆反应过程.结果表明,聚乙二醇双烯体可在水介质中温和条件下定量接枝到壳聚糖羟基上,反应具有点击特征;同时,聚乙二醇与壳聚糖之间的连接键在高温下(90℃)可通过D-A逆反应而发生断裂.

SYNTHESIS OF CHITOSAN-O-POLY(ETHYLENE GLYCOL) THROUGH DIELS-ALDER REACTION

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).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.