One-pot synthesis of poly(l-lactide) multi-arm star copolymers based on a polyester polyol macroinitiator

Using a hyperbranched poly(glycolide) (hbPGA) macroinitiator the synthesis of poly(l-lactide) (PLLA) multi-arm star polyesters has been achieved via a core-first approach. The star-shaped copolymers were prepared in a one-pot two-step process via Sn(Oct)2-catalyzed ring-opening polymerization (ROP) conducted in the melt. Complete conversion of the end groups of the hbpolyglycolide polyester polyols is ensured by the reactive primary hydroxyl termini. By adjusting the monomer/initiator ratio a series of star copolymers with varying PLLA arm length has been obtained with molecular weights in the range of 1500 to 10,000 g/mol (SEC). The successful coupling of the PLLA arms to the hbPGA core has been confirmed via detailed 1D and 2D NMR spectroscopy. Because of the different hydrodynamic volume of the star polymers in contrast to their linear analogs, the weight-average molecular weight (Mw) was determined both by SEC and static light scattering (SLS). The star-shaped poly(lactide)s reveal different thermal properties in comparison to linear poly(lactide) homopolymers.