Thermal stability of poly(L-lactide) prepared by polymerization of L,L-dilactide with Sn(II)-based initiators

摘要

alpha-Ester-co-hydroxy terminated poly(L-lactide) [C_4H_9OC(O)--PLA-OH] was prepared by the ring-opening polymerization of L,L-dilactide using tin(II) 2-ethylhexanoate [tin octoate,Sn(Oct)_2]/BuOH system or tin(II) butoxide as initiators in a wide range of molecular weights (M_n):from 10~3 up to 7 o 10~5.Thermal degradation behavior of C_4H_9OC(O)-PLA-OH was then compared with that of its esterified counterpart [C_4H_9OC(O)-PLA--OC(O)CH(C_2H_5)C_4H_9].Thermogravimetric measurements versus M_n revealed,as a result of M_n->infinity extrapolation,the upper limit of thermal resistance of poly(L-lactide) (PLA).The onset temperature of the thermal degradation (OT) and the temperature of maximum degradation rate (MDT) of PLA are equal to 337 and 376degC,respectively.Despite the deteriorating effect on the PLA molecular weight caused by in situ esterification of the hydroxyl chain ends with Sn(Oct)_2,largely unreacted in polymerization,certain im-pr.ovement of PLA thermal stability due to this side reaction was also observed.