Synthesis and Characterization of Hybrid Biopolymers of L-lactic Acid and 2-Pyrone-4,6-dicarboxylic Acid

Abstract

Copolymers of L-lactic acid (LA) and 2-pyrone-4,6-dicarboxylic acid (PDC), a chemically stable metabolic intermediate of lignin, were prepared by dehydrated polycondensation based on stepwise oligomerization followed by post-polymerization in vacuo. When the polymerization was performed in the presence of methanesulfonic acid as a catalyst, the molecular weights of the resulting copolymers were sufficiently high. Furthermore, expansion of the polymeric surface area was found to be an important factor in facilitating dehydration and thereby producing high molecular weight polymers. PDC feed ratio significantly affected the molecular weight because of the different polymerization capability from LA. Relationship between the PDC feed ratio and the molecular weight of the resulting polyesters was for the first time demonstrated quantitatively. The obtained copolymers were characterized by ¹H- and ¹³C-NMR, IR, and thermal analysis. The high molecular weight copolymers possessed the higher decomposition temperatures than PLLA and their fusible temperature ranges were reasonably expanded.

Keywords:

• Biomass
• lignin
• polycondensation
• polyester
• polylactide

Acknowledgments

This work was supported, in part, by a Grant-in-Aid for Scientific Research from the Ministry of Education, Science, Sports and Culture, Japan, and General Sekiyu Research Promotion. We thank Prof. S. Kajita (Tokyo University of Agriculture and Technology) for useful discussion.