(27) Macromolecules 2013, 46, 3965−3974


27_pub

“PLA-PHB-PLA triblock copolymers: Synthesis by sequential addition and investigation of mechanical and rheological properties”

The dinuclear indium catalyst [(NNO)InCl]2(μ-OEt)(μ-Cl), previously reported to be highly active for the living ring-opening polymerization of cyclic esters lactide (LA) and β-butyrolactone (BBL), was used to generate a series of triblock copolymers of poly(lactic acid) (PLA) and poly(hydroxybutyrate) (PHB). Copolymers PLLA−PDLLA−PLLA and
PLLA−PDLLA−PDLA, synthesized via sequential monomer addition, showed low molecular weight distributions and excellent correlation between the calculated and experiment molecular weights. Significantly, triblock copolymers of the type PLA−PHB−PLA were also synthesized for the first time through a sequential addition technique. Analysis of polymers after each addition of monomer showed that although only 85% conversion was achieved after addition of BBL, the remaining chain ends were active and addition of more lactide yielded a triblock. Rheological studies of PLLA−PHB−PDLA indicated solid like behavior even well above the temperature at which stereocomplex formation was observed. These elastomeric triblocks exhibited elongations at break 5−10 times greater than those of corresponding PLLA−PDLLA−PLDA triblocks.