Study On Synthetic Pathways & Structure-Activity Relationship Of Hydroxyethyl Starch And Its Derivatives

Distribution of hydroxyethyl groups along starch chains makes great influence on the water-solubility,viscosity,stability of hydroxyethyl starch(HES)and its application performance in pharmaceutical and paper-making industry.The research of substituents distribution in HES is of great significance for the development of additional value of home-made HES and the application of HES with different substituents distribution.However,it is difficult that the substituents distribution is analyzed in detail because of the complex structure of HES,especial to the HES with the degree of molar substitution(MS)>0.5 which contains polyethylene glycol oligomer side chain.The substituents distribution of HES was detected by GC-MS in this paper and the possible breaking pathway of mono-and di-substituted hydroxyethyl glucose derived from HES was deduced.The GC-MS analysis method of substituents distribution along HES(MS=0.02-1.2)chains was advanced.The HES with different substituents distribution was further prepared by ethylene carbonate(EC)and ethylene oxide(EO)respectively based on the analytic method.In this research,the substituents distribution inside HES-EC(The HES prepared via ethylene carbonate)was regulated by the change of reaction conditions,for instance,the amount of ethylene carbonate,the amount of activator alkaline,etherification temperature and etherification time on the basis of the high selectivity of EC to C2-OH of anhydrous glucose unit(AGU)onto starch main chains and the inhibition capability against polysubstitution of hydroxyethyl groups.HES-EC with a relative uniform distribution of hydroxyethyl groups was obtained.The research result displays that the HES-EC with MS of 0.58,the total degree of substitution(DSt)of 0.43 and the polyethylene glycol oligomer side chain average length(MS/DSt)of 1.35 possesses uniform hydroxyethyl distribution.The corresponding reaction conditions are as follows,n(AGU):n(EC):n(NaOH)is 1:3:1,etherification temperature is 140? and etherification time is 11 h.Additionally,C2 monohydroxylates are predominant and account for 31.21%of the total substituted constituents derived from HES-EC.Simultaneously,the distribution of hydroxyethyl groups inside HES-EO(The HES prepared via ethylene oxide(EO))was detected.The result shows that the MS/DSt values of HES-EO with MS of 0.20-1.22 cover the range from 2 to 6.5.Consequently,it is hard to obtain the HES-EO with uniform substituents distribution,which possessing a high DSt value as well as low MS/DSt value.HES-EC has a higher DSt 0.43 and lower MS/DSt values of about 1.35 than HES-EO in spite of the same MS value 0.58 between HES-EC and HES-EO.Accordingly,HES-EC has more homogeneous hydroxyethyl distribution along starch main chains than HES-EO.Compared with the three generations of plasma substitute HES-EO,the molecular weight(Mw),MS and C2/C6 of HES-EC(MS=0.42,Mw=6.2×104 g/mol,C2/C6=15)complies with the structural requirement of plasma substitute HES,and HES-EC has potential development prospect.The results of rheological characteristics,surface tension and emulsion ability of the HES with different substituents distribution indicates that the viscosity of HES-EC is low,MS and MS/DSt make little influence on the rheological characteristics of HES-EC.Additionally,HES-EC exhibits notable surface activity and emulsion ability.Especially,the surface tension and emulsion stabilizing time of HES-EC with MS of 0.58 reaches 30.20 mN/m and 840 min,respectively.The main factor is that substituents uniform distribution is benefit for the extension of HES-EC macromolecular chains in aqueous solution and the formation of dense adsorption layer where the macromolecular was arranged closely.Therefore,HES-EC can effectively reduce the surface tension of aqueous solution.On the other hand,HES-EO almost has no surface activity.The 1 wt%HES-EO(MS=0.58-1.00,Mw>106)and the HES-EO(Mw=60000-90000 g/mol)obtained by acid hydrolysis exhibit ideal shear resistance at shear rate of 0-1000 s-1.MS makes greater effect on the rheological characteristics of HES-EO(Mw=60000-90000 g/mol)than MS/DSt.The more MS is,the lower viscosity HES-EO has on the case of the equal MS/DSt among all HES-EO samples possessing the equal number grade molecular weight.On the other hand,MS/DSt makes little influence on the viscosity of HES-EO.On the basis of the desired shear resistance,water-solubility,ion interference resistance and suitable viscosity(10-50 mPa·s)for dispersing other additives in foam concrete slurry,the amphipathic HES-EO derivatives 2,4-di(4'-tertbutylphenoxyl-6-chloro-[1,3,5]-triazine hydroxyethyl starch(B-HES)possessing foam stabilization abilities were designed and synthesized by the regulation of MS of HES-EO(MS=0.58-1.00,Mw 60000-90000 g/mol)and DS of hydrophobic reagent 2,4-di(4'-tertbutylphenoxyl-6-chloro-[1,3,5]-triazine(BPCT).B-HES was further used as foam stabilizer in the preparation of foam concrete containing tailing sands,the results show that the compressive strength of the foam concrete block containing B-HES is higher than those blocks added the equal amount of traditional petroleum-based surfactant calcium stearate and unmodified HES-EO.Especially,the foam concrete block using B-HES 10(MS=1.00,DS=0.03)as stabilizers,which has even pore distribution,the highest compressive strength 0.97 MPa and a relative low bulk density 460 kg/m3.