Thermal stability of poly ( l-lactide): influence of end protection by acetyl group

• Published in: Polymer degradation and stability 2004-04, Vol.84 (1), p.143-149
• Main Authors: Fan, Yujiang, Nishida, Haruo, Shirai, Yoshihito, Endo, Takeshi
• Format: Article
• Language: English
• Subjects: Acetylation; Applied sciences; Chemical reactions and properties; Degradation; End-protection; Exact sciences and technology; Kinetics; Organic polymers; Physicochemistry of polymers; PLLA; Poly ( l-lactic acid); Poly ( l-lactide); Pyrolysis; Thermal degradation; Thermal stability
• ISSN: 0141-3910; 1873-2321
• DOI: 10.1016/j.polymdegradstab.2003.10.004

Thermal stability of end-protected poly ( l-lactide) (PLLA) was studied by dynamic thermal degradation and pyrolyzate analyses. The treatment of PLLA by acetic anhydride resulted in the acetylation of end hydroxyl groups, and at the same time a decrease in the residual Sn content in the polymer. The thermal degradation of the acetylated PLLA-Ac showed a shift to a 40–50 °C higher degradation temperature range than that of untreated, high Sn content PLLA, but exhibited nearly the same degradation behavior as the untreated PLLA with a comparable Sn content. Purified metal-free PLLA-H showed good thermal stability, having the highest degradation temperature range. Interestingly, despite the end-protection, the acetylated metal-free PLLA-H/Ac decomposed at almost the same temperature as that of PLLA-H. From pyrolyzate and kinetic analyses, it was found that the contribution of the hydroxyl-end acetylation to the stability of PLLA was negligible, except for the stabilization effect due to the elimination of residual Sn during the acetylation process.