Synthesis of Lactide from Alkyl Lactate via a Prepolymer Route

• Published in: Industrial & engineering chemistry research Vol. 51; no. 13; pp. 4837 - 4842
• Main Authors: Upare, Pravin P, Hwang, Young Kyu, Chang, Jong-San, Hwang, Dong Won
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 04.04.2012
• Subjects: Applied sciences; Catalysts; Chemical engineering; Exact sciences and technology; Lactates; Molecular weight; Monomers; Oligomers; Prepolymers; Selectivity; Synthesis
• ISSN: 0888-5885; 1520-5045
• DOI: 10.1021/ie202714n

Poly(lactic acid) is a biodegradable polymer that has enormous potential for use as a replacement for some petroleum-based materials. However, the properties of this polymer depend strongly on the quality of the lactide monomer from which it is often synthesized. In this work, lactide was synthesized from alkyl lactate via a prepolymer route, and the reaction kinetics was compared with lactide synthesis from lactic acid. A number of different parameters were investigated in order to obtain the highest possible yield of lactide, as well as to achieve l-isomer selectivity. Among the various acid catalysts tested, Sn(Oct)2 was found to be the most effective for L-lactide selectivity as well as for producing a high oligomer yield from the alkyl lactate. The effect of the alkyl group length of the starting materials was investigated with the highest lactide yield being obtained from ethyl lactate, over methyl and butyl lactate. The deoligomerization reaction was also studied in detail. It was found that an oligomer with a molecular weight of 600–800 g/mol gave the highest lactide yield. The optimum depolymerization temperature for the oligomer with a molecular weight of 1274 g/mol was shown to be 180 °C, as above this temperature, the reaction rate of oligomerization for heavy residue was much faster than that of deoligomerization for crude lactide, which resulted in a lower lactide yield.