Synthesis and ring-opening polymerization of new monoalkyl-substituted lactides

New monoalkyl-substituted lactides were synthesized by reaction of α-hydroxy acids with 2-bromopropionyl bromide, and polymerized with various catalysts in the presence of benzyl alcohol by ring-opening polymerization (ROP). The classic tin(II) 2-ethylhexanoate (Sn(Oct)2) catalyst was leading to polymers with narrow distribution and predictable molecular weights, in polymerizations in bulk or toluene at 100 °C. The polymerization rate was corresponding to the steric hindrance of the alkyl substituents, such as butyl, hexyl, benzyl, isopropyl, and dimethyl groups. A yield of 83% was obtained with the hexyl-substituted lactide after 1 h of polymerization. Excellent conversions (97%) could be achieved by using the alternative catalyst 4-(dimethylamino)pyridine (DMAP). This latter organic catalyst was most efficient in polymerizing the more steric-hindered lactides with good molecular weight and polydispersity control, in comparison to the tin(II) 2-ethylhexanoate and tin(II) trifluoromethane sulfonate [Sn(OTf)2] catalysts. The efficiency of the DMAP catalyst and the variability of the monomer synthesis route for new alkyl-substituted lactides allow to prepare and to envision a wide range of new functionalized polylactides for the elaboration of tailored materials. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4379–4391, 2004