Inimer-Promoted Synthesis of Branched and Hyperbranched Polylactide Copolymers

A series of (hyper)branched poly(l-lactide)(PLLA) copolymers has been prepared by ring-opening multibranching copolymerization of l-lactide with a hydroxyl-functional (ABB′) lactone inimer, 5HDON (5-hydroxymethyl-1,4-dioxane-2-on). Polymerization was conducted in bulk and solution and catalyzed either by stanneous-2-ethyl hexanoate (Sn(Oct)2) or an organic base, 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD). Precise structural characterization of the resulting branched copolyester structures was accomplished by a combination of 2D NMR techniques, relying on the comparison with model compounds. The 5HDON inimer was employed in 1% to 20% fractions and is incorporated either as a dendritic unit or as a focal structure, but hardly in the linear mode. A detailed reaction mechanism was derived from kinetic investigation of the polymerization via NMR spectroscopy, preparative and analytical SEC and MALDI-TOF MS. The evolution and the extent of branching have been monitored and quantified. Both the degree of branchin...