posted on 2016-09-07, 00:00authored byTomer Rosen, Israel Goldberg, Vincenzo Venditto, Moshe Kol
Poly(lactic acid) (PLA) is a biodegradable
polymer prepared by
the catalyzed ring opening polymerization of lactide. An ideal catalyst
should enable a sequential polymerization of the lactide enantiomers
to afford stereoblock copolymers with predetermined number and lengths
of blocks. We describe a magnesium based catalyst that combines very
high activity with a true-living nature, which gives access to PLA
materials of unprecedented microstructures. Full consumption of thousands
of equivalents of L-LA within minutes gave PLLA of expected molecular
weights and narrow molecular weight distributions. Precise PLLA-b-PDLA diblock copolymers having block lengths of up to
500 repeat units were readily prepared within 30 min, and their thermal
characterization revealed a stereocomplex phase only with very high
melting transitions and melting enthalpies. The one pot sequential
polymerization was extended up to precise hexablocks having “dialed-in”
block lengths.