Preparation And Characterization Of Intelligent Hydrogel Microspheres Based On Spray Drying And Diels-Alder Click Reaction

Diels-Alder reaction can be carried out in water without catalyst or initiator.At the same time,it has attracted much attention in the preparation of hydrogels due to its high selectivity and atomic economy.Spray drying is an attractive technique of preparing microspheres on a large scale due to its convenience and rapidity.In this study,Diels-Alder reaction was used to form cross-linking to obtain hydrogel microspheres during spray drying,which provided a new method for rapid preparation of hydrogel microspheres.In this paper,a binary copolymer was synthesized by free radical polymerization,and then modified to prepare macromolecular diene and macromolecular dienophiles.Finally,three kinds of hydrogel microspheres which could response to environmental stimuli were respectively prepared by spray drying.The structures and morphologies of the samples were characterized by FT-IR,NMR,SEM,XRD,TGA and Raman spectroscopy.The swelling and sustained release properties of the hydrogel microspheres were studied.The specific research contents are as follows:(1)First,anhydride-containing copolymer was synthesized by free radical polymerization using N,N-dimethacrylamide and maleic anhydride as monomers,and the copolymer was modified with 2-furfurylamine to prepare a macromolecular diene.Hydroxyl-containing copolymer was synthesized by free radical polymerization using N-vinylpyrrolidone and N-methylol acrylamide as monomers.The copolymer was modified by N-maleoyl alanine(AMI)under the dehydrating agent to synthesize a macromolecular dienophile.Then,an aqueous solution of macromolecular diene and dienophile was prepared,and a kind of pH-sensitive hydrogel microsphere is prepared by in situ Diels-Alder reaction in spray dryer to produce chemical crosslinking points.The performance of the hydrogel microspheres was adjusted by varying the mass concentration of the solution used for spray drying.Then the structure and properties of the intermediate products and final products were characterized.Finally,urea was used as a model molecule to study the sustained release behavior of urea-loaded hydrogel microspheres.The results show that the prepared hydrogel microspheres were pH sensitive and the swelling degree increases with the increase of pH.Similarly,the release rate of urea also increases with increasing pH.(2)First,anhydride-containing copolymer was prepared by free radical polymerization using itaconic anhydride and N-isopropylacrylamide as monomers,and the copolymer was modified with 2-furfurylamine to obtain a macromolecular diene.The hydroxyl-containing copolymer was prepared by free radical polymerization using N,N-dimethacrylamide and hydroxyethyl methacrylate as monomers,and modified by AMI under the dehydrating agent to synthesize a macromolecular dienophile.Then,aqueous solution of macromolecular diene and dienophile was prepared,and a kind of sensitive hydrogel microsphere is prepared by in situ Diels-Alder reaction in spray dryer to produce chemical crosslinking points.The performance of the hydrogel microspheres was adjusted by varying the mass concentration of the solution used for spray drying.Then the structure and properties of the intermediate products and final products were characterized.Finally,salicylic acid was used as a model molecule to study the sustained release behavior of hydrogel microspheres containing salicylic acid.Swelling studies show that the prepared hydrogel microspheres have pH/temperature dual sensitivity,and the swelling degree increases with the increase of temperature and pH.Similarly,the release rate of salicylic acid also increases with the increase of temperature and pH.(3)First,a macromolecular diene was synthesized by modifying the copolymer of N,N-dimethacrylamide and maleic anhydride with 2-furfurylamine.The AMI was used to modify the copolymer of N,N-dimethacrylamide and hydroxyethyl methacrylate to synthesize a macromolecular dienophile,and the mixed solution of macromolecular dienes and dienes was prepared.Microspheres with temperature/pH were prepared by chemical cross-linking through Diels-Alder click reaction during spray drying.The structure and properties of intermediate and final products were characterized by FT-IR,NMR,TGA and SEM.The swelling behavior of microspheres at different temperatures and pH was studied by weighing method.Finally,urea was used as a model molecule to study the controlled release behavior of urea-loaded hydrogel microspheres.Studies have shown that the degree of swelling of the microspheres increases with increasing temperature and pH.The rate of urea release can be adjusted by changing the pH or temperature.The method described here has wide application prospects in the preparation of hydrogel microspheres due to its advantages such as simple operation,low cost and easy industrialization.These advantages are attributed to its combination of Diels-Alder reaction and spray drying.