Preparation Of Maleoyl Chitosan Microspheres From Self-Assembly-Crosslinking

Chitosan is the only positively charged natural polysaccharide, however, chitosan is only soluble in acid. In order to expand its use, water-soluble chitosan derivative was prepared. With water as reaction medium, a novel water-soluble chitosan derivative was prepared from the acylation of maleic anhydride and chitosan, which was catalysised by sodium carbonate.The effects of the molar ratio of reactant, the amount of water, reaction time and reaction temperature on the degree of substitution and water-soluble were studied, the best reaction condition was determined. Maleoyl chitosan is a gender polymer, so it is a negative polymer under certain condition. 7nm nano-silica was treated by poly(diallydimethylammonium chloride)(PDDA), TEM results showed that nano-silica was properly distributed with particle size of 10-40nm, and the surface of modified nano-silica was positively charged.Maleoyl chitosan /SiO2 composites was prepared by electrostatic self-assembly with negative maleoyl chitosan and positive PDDA/SiO2, SEM and TEM results showed that maleoyl chitosan attached to PDDA/SiO2.With K2S2O8/Na2SO3 as initiator and N, N-Methylene-bis-acrylamide(MBA) as the crosslinking agent, The maleoyl chitosan microspheres were prepared from cross-linking maleoyl chitosan/SiO2 composites. TEM results showed that narrow distributed cross-linked microspheres were well-shaped spheres with a diameter from 100nm to 300nm.The effects of reaction temperature, reaction time, stirring speed, amount of initiator, amount of crosslinking agent on the properties of microspheres were discussed. The optimum conditions were determined as follows: the volume of PDDA/SiO2 composites was 20ml, reaction temperature was 50℃, reaction time was 1h, stirring speed was 800r/min, the content of initiator was 0.3%(in maleic anhydride chitosan, wt%), the volume of 1% MBA was 10ml, chitosan degree of deacetylation was greater than 80%. Compared with microspheres prepared in emulsion-crosslinking method, the microspheres prepared from directly cross-linking in aqueous solution were less distributed, but had a smaller particle size. At the same time, the prepared microspheres were almost free from organic solvent pollution, which make it more useful.