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

Abstract

Abstract 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