Cationic Polymerization of L,L-Lactide

Cationic bulk polymerization of L,L-lactide (LA) initiated by trifluromethanesulfonic acid Itriflic acid (TfA)] has been studied. At temperatures 120-160 degrees C, polymerization proceeded to high conversion (>90% within similar to 8 h) giving polymers with M-n similar to 2 x 10(4) and relatively high dispersity Thermogravimetnc analysis of resulting polylactide (PLA) indicated that its thermal stability was considerably higher than the thermal stability of linear PLA of comparable molecular weight obtained with ROH/Sn(Oct)(2) initiating system Also hydrolytic stability of canonically prepared PLA was significantly higher than hydrolytic stability of linear PLA Because thermal or hydrolytic degradation of PLA starting from end-groups is considerably faster than random chain scission, both thermal and hydrolytic stability depend on molecular weight of the polymer High thermal and hydrolytic stability, in spite of moderate molecular weight of canonically prepared PLA, indicate that the fraction of end-groups is considerably lower than in linear PLA of comparable molecular weight According to proposed mechanism of cationic LA polymerization growing macromolecules are fitted with terminal -OH and C(O)OSO2CF3 end-groups. The presence of those groups allows efficient end-to-end cyclization Cyclic nature of resulting PLA explains its higher thermal and hydrolytic stability as compared with linear PLA (C) 2010 Wiley Periodicals, Inc. J Polym Sci Part A Polym Chem 48 2650-2658, 2010