Effect of end-group modification of poly(lactide)s by cinnamoyl chloride on their thermal stability

In order to improve thermal stability of poly(l-lactide) (PLLA), the terminal hydroxy groups of PLLAs were converted to cinnamate esters by the treatment with cinnamoyl chloride. The resulting end-group modified PLLAs exhibited much higher thermal degradation temperature at 10% weight loss (Td10) at around 320 °C than those of the starting hydroxy-terminated PLLAs (ca. 240 °C). The amounts of the residual Sn in the PLLAs were estimated by ICP measurements before and after modification, which indicated the modified PLLAs were still contaminated with ca. 600 ppm of Sn. This suggested that the end-group modification is effective for improving thermal stability of PLLA even in the presence of Sn. The end-group modification was also applicable to the stabilization of stereocomplex poly(lactide)s, whose thermal stability is important due to their high processing temperature.