Synthesis of Functionalized Poly(lactic acid) Using 2-Bromo-3-hydroxypropionic Acid

Brominated poly(lactic acid) (PLB) and brominated poly(lactic acid-co-glycolic acid) (PLGB) were synthesized by acid-catalyzed melt copolyesterifications of glycolic acid and/or lactic acid with 2-bromo-3-hydroxypropionic acid, which is a brominated constitutional isomer of lactic acid. Molecular weights up to Mn = 104 Da were achieved by adding diphenyl ether to the copolymerizations (100% w/v comonomer concentration) performed at 90–130 °C in vacuo. GPCPSt underestimates the molecular weight of PLB when it contains at least approximately 6 mol % brominated units. The bromine atoms of PLB5050 (MnPSt = 5.32 × 103 Da; absolute Mn ∼ 1.70 × 104 Da) were replaced quantitatively with iodide using sodium iodide in acetone at room temperature, with a modest decrease in the molecular weight (MnPSt = 4.62 × 103 Da). PLB was also reacted with 0.25 equiv of sodium azide in DMF at 0 °C to replace the corresponding amount of bromine atoms in 88% efficiency, again with a slight decrease in the apparent molecular weight...