The Preparation Of Alginic Acid Ester And Its Optimization Of Synthetic Conditions

Sodium alginate is a linear anion natural polysaccharide, composing of1,4-linked residues of β-D-mannuronic(M) acid and α-L-guluronic acid(G). The molecular chain is sequentially assembled GG blocks, MM blocks and GM alternate blocks. Sodium alginate is non-toxic, biocompatible, non-immunogenic, biodegradable and chemical modified polymer. So it is widely applied in various fields including food industry, pharmaceutical industry, daily chemistry, textile industry, biological technology, wastewater treatment and so on.Sodium alginate only has strong hydrophilicity, so it has some defects in the application of hydrophobic drug. For example, the capacity is not big and it is easy to burst release as control release material; the adhesion force is not big as mucosal adhesion agent, etc. In recent years, much reserch focus on grafting different compounds on sodium alginate through the different reaction mechanism according to its structure characteristic, in order to achieve different modification purpose. This paper grafted hydrophobic groups onto hydrophilic groups-COO-of sodium aginate so as to obtain a new kind of amphiphilic biomacromolecular, and this polymer can be used to expand applications fields of sodium aginate.Amphiphilic sodium aginate derivatives of different substitution degree and hydrophobic chain length were synthesized by the reaction of sodium alginate with aliphatic alcohol, using EDC as a coupling agent and DMAP as catalytic agent. The products were characterized by fourier transform infrared spectroscopy(FTIR), nuclear magnetic resonance spectroscopy (NMR), differential scanning calorimetry (DSC) and thermogravimetry(TG). The appearance of ester bond peaks in FTIR spectrum, the peaks of the methyl and methylene proton and the peaks of side chain alkyl carbon in NMR spectrum suggests that dodecyl groups successfully grafted onto sodium alginate. By DSC and TG, the conclusion is attained that, compared with NaAlg, when alginate ester releases CO2and H2O from adjacent hydroxyl groups, the hydrophobic side chain pyrolysis into micromolecule, in the process of temperature elevation. The preparation of alginate ester is further confirmed. The result show that under the same condition, the longer the carbon chain is. the more difficult the alcohol grafted to the sodium alginate.The degree of substitution(DS) of alginate ester was analysised by gas chromatography. The influences of molar ratio of alginate unit to alcohol, reaction time, reaction temperature, the mass of pTSA on DS were investigated systematacially. The result show that:the DS of alginate ester increased with the molar ratio of alginate unit to alcohol rised from1:1to1:5. but then the DS change little with the molar ratio of alginate unit to alcohol rised from1:5to1:15. The DS increased with prolonging reaction time, but DS change little after24h. As the reaction temperature rised, the DS of alginate ester increases. When the molar ratio of alginate unit to pTSA is1:0.6, the DS of alginate ester is highest. According to this rule, we obtain the optimal conditions of preparation alginate ester.The aggregation behavior, surface activity, electrical conductivity, viscosity and paticle size of amphiphilic alginate ester in aqueous solution were synthetically studied. The effect of the substitution degree and the length of carbon chain on the property of the aqueous solution was explored. With the solution concentration of alginate ester increased, the surface tension declined and electrical conductivity rised. In the same hydrophobic chain length, as the substitution degree increased, the surface tension, the electrical conductivity, the paticle size of aggregation and the critical micelle concentration of alginate ester decreased; In the similar substitution degree, as hydrophobic chain lengthened, the surface tension, the electrical conductivity, the paticle size of aggregation and the critical micelle concentration of alginate ester also gone down.