Polyaspartic Acid Synthesis Method, The Ionic Liquid System

Liquid-phase polymerization method of polyaspartic acid (PASP) was improved and it was the first time to be synthesizd in ionic liquids using L-aspartic acid (L-ASP) as raw material. A series of problems like poor solubility, chemical and thermal unstability, uncontrollable polymerization method were solved.Three ionic liquids AlCl3-NaCl-KCl, [Bmim]BF4 and AlCl3-Et3NHCl have been chosen as reaction medium. The influence of L-ASP solubility in ionic liquids, viscosity and acidic properties of ionic liquids on PASP polymerization have been studied. The structure of the product, the yield and scale inhibition performance to calcium carbonate were as judge basis to select the best ionic liquids. First, analyze the characteristics of the infrared spectrum, nuclear magnetic resonance spectrum of ionic liquids and products. Second, optimize synthesis process of PASP in AlCl3-Et3NHCl ionic liquids. Last, investigate the influence of reaction conditions on yield, molecular weight and scale inhibition rate of PASP, and analyze the relationship between molecular weight and scale inhibition rate of PASP. Variation of L-ASP structure and electrical property was preliminarily studied by infrared spectroscopy and ultraviolet spectroscopy, and polymerization process could be speculated.The results show that PASP can be synthesized in the medium of three kinds of ionic liquids. It has high yield and excellent scale inhibition performance. The obtained PASP is a singleβ-bonded configuration and the ratio reaches 95%. The optimal condition of polymeric reaction are the molar ratio of anhydrous aluminum chloride, triethylamine hydrochloride is 2.2:1, reaction temperature is 220℃, concentration of L-aspartic is 0.2 g·mL-1, and reaction time is 2.0 hour. Under conditions above, the PASP yield ratio reaches to 35.5%, molecular weight is 4 750, the scale inhibition rate to calcium carbonate reaches to 96.8% when concentration of Ca2+ is 250 mg·L-1 and it is increased compared with the traditional liquid-phase polymerization process. Al2Cl7- and H+ in AlCl3-Et3NHCl can promote carbonyl carbon of L-ASP with more positive electrical property and they have catalysis on polymerization reaction.