SummarySingle-site calcium initiators containing chelating tmhd
(H-tmhd = 2,2,6,6-tetramethylheptane-33-dione) ligands
[(THF)Ca(tmhd)]2[μ-N(SiMe3)2](μ-tmhd)
(2) and
[(THF)Ca(tmhd)]2[μ-OCH(Me)Ph](μ-tmhd)
(3) have been synthesized and
applied for the ring-opening polymerization of L-lactide and
ε-caprolactone. Both 2 and
3 were highly reactive and
promoted a fast polymerization of L-lactide and ε-caprolactone
to high monomer conversions under mild conditions (THF as a
solvent, room temperature). More importantly, results showed
that the ring-opening polymerizations of lactides and lactones
initiated by either 3 or
2 in the presence of equivalent
2-propanol are living, to provide polymers and block copolymers
of controlled molecular weights and tailored end-groups. The
polymerizations were first-order in monomer up to high
conversions, in which the in
situ initiating system 2/2-propanol revealed no induction period
and much faster polymerization kinetics as compared to
3.