Bio‐safe synthesis of linear and branched PLLA

The catalytic activities of Bi(III) acetate (Bi(OAc)₃) and of creatinine towards the ring‐opening polymerization of L ‐lactide have been compared with those of a stannous (II) ethylhexanoate ((SnOct)₂)‐based system and with those of a system catalyzed by enzymes. All four were suitable catalysts for the synthesis of high and moderate molecular weight poly(L ‐lactide)s and the differences in reactivity and efficiency have been studied. Linear and branched poly(L ‐lactide)s were synthesized using these bio‐safe initiators together with ethylene glycol, pentaerythritol, and myoinositol as coinitiators. The polymerizations were performed in bulk at 120 and 140 °C and different reactivities and molecular weights were achieved by adding different amounts of coinitiators. A molecular weight of 105,900 g/mol was achieved with 99% conversion in 5 h at 120 °C with a Bi(OAc)₃‐based system. This system was comparable to Sn(Oct)₂ at 140 °C. The reactivity of creatinine is lower than that of Bi(OAc)₃ but higher compared with enzymes lipase PS (Pseudomonas fluorescens). A ratio of Sn(Oct)₂M_o/I_o 10,000:1 was needed to achieve a polymer with a reasonable low amount of tin residue in the precipitated polymer, and a system catalyzed by creatinine at 140 °C has a higher conversion rate than such a system. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1214–1219, 2010