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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...

The atom transfer radical polymerization (ATRP) of styrene was investigated using the popular alkyne-functional initiator prop-2-yn-1-yl 2-bromo-2-methylpropanoate (PBiB). The polymerization kinetics and evolution of molecular weight as a function of monomer conversion were systematically studied with PBiB and similar initiators with protecting groups at the reactive propargylic and terminal acetylenic sites. These studies were compared to control studies using the nonfunctional initiator ethyl 2-bromoisobutyrate. As confirmed by NMR analysis of a model reaction, the terminal alkynes undergo oxidative alkyne–alkyne coupling under ATRP conditions, resulting in polymers with bimodal molecular weight distributions. This side reaction is significant because it diminishes the orthogonality of ATRP/copper-catalyzed azide–alkyne cycloaddition procedures as well as the control of ATRP.