Kinetics and mechanism of epsilon-caprolactone and L,L-lactide polymerization coinitiated with zinc octoate or aluminum acetylacetonate: The next proofs for the general alkoxide mechanism and synthetic applications

摘要

Following our previous papers on mechanism of cyclic esters' polymerization coinitiated by tin(II) octoate [tin(II) bis-(2-ethylhexanoate), (Sn(Oct)_2)] in the presence of either the low molar mass coinitiator (an alcohol, hydroxy acid, or H_2O) or a macromolecule fitted with a hydroxy end group (ROH), the present work deals with epsilon-caprolactone (CL) and L,L-lactide (LA) polymerizations coinitiated with zinc octoate (Zn(Oct)_2) or aluminum acetylacetonate (Al(Acac)3). A series of kinetic measurements revealed that similarly as in the Sn(Oct)_2 coinitiated process, these polymerizations proceed by simple monomer insertion into the ...Mt-OR bond, reversibly formed in the reaction -Mt-L + ROH <=> ...-Mt-OR + LH (where Mt = Sn, Zn or Al; L = Oct or Acac), taking place throughout the whole polymerization process. MtL_n itself does not play an active role in the polymerization. Applicability of the commercially available Zn(Oct)_2 or Al(Acac)_3 for the aliphatic polyester (10~3 <= M_n <= 4 x 10~5) synthesis is also discussed.