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) 2 M 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.