Bromine-functionalized poly(carbonate-co-lactide)s: Synthesis, characterization and post-polymerization functionalization

The ring-opening copolymerization of lactide with carbonate is an available strategy to incorporate reactive groups to the pendent sites of copolymer for further functional modification. A series of random and block copolymers were synthesized from l-lactide (L-LA) and 2-bromomethyl-2-methyltrimethylene carbonate (BMTC) using dodecanol as initiator and stannous octoate as catalyst. The structures of the copolymers were characterized by nuclear magnetic resonance (1H NMR, 13C NMR), gel permeation chromatography (GPC) and differential scanning calorimetry (DSC). The composition of the copolymers can be controlled through changing the feed ratios of nBMTC/nL-LA. It was found the random P(BMTC-co-LLA) copolymers had the semicrystalline characteristic due to the relative long block-like segments of PLLA (LL, PLLA = 5.3–7.3) and the polar interactions from bromo groups, but their crystallinity (Xc, PLLA) and melting temperature (Tm, PLLA) decreased when the BMTC content increased. The Xc, PLLA and Tm, PLLA of P(BMTC-b-PLLA) block copolymers were relatively higher than the corresponding random copolymers, and approached gradually to the pure PLLA with the increase of the molecular weight of PLLA block. Finally, the pendent bromo groups of P(BMTC-co-LLA) were easily transformed into azides, which could proceed the azide-alkyne click reaction smoothly and quantitatively at room temperature.