Thermally Stabilized Poly(lactide)s Stereocomplex with Bio-Based Aromatic Groups at Both Initiating and Terminating Chain Ends

In order to improve the thermal stability of polylactides (PLA), conjugation approaches have been applied to both the terminal and initiating chain end of PLA. We selected benzyl alcohol as the initiator to introduce an aromatic group at one end. The terminal hydroxyl group of the resultant PLAs was conjugated with 3,4-diacetoxycinnamic acid (DACA). The modified polymers showed a dramatic improvement in their thermal decomposing temperature (T-10) from 326 to 355 degrees C. The stereocomplexation of the modified PLAs could be achieved by a variety of molecular weight (M-n) combination. The melting temperature (T-m) increased after stereocomplexation with any size of polymer mixture, but the best improvements on thermal properties in both T-m and T-10 were obtained by a mixture of specific M-n ranges of enantiomeric PLAs (M-n = 11 400 and 9600). In contrast, the longer and shorter M-n discouraged the simultaneous improvements in the T-m and T-10, suggesting that a balance of chain end groups and stereocomplexation efficiency was important.