Controlled Polymerization of dl-Lactide and ε-Caprolactone by Structurally Well-Defined Alkoxo-Bridged Di- and Triyttrium(III) Complexes

Abstract

We have prepared the yttrium(III) alkoxides [(L Me2 )(HL Me2 )Y3(OCH2C6H5)4] (3) and [(S-L Me )Y]2‚2(HOCH2C6H5) (1‚2BnOH) through treatment of two previously developed complexes with benzyl alcohol. Complex 3 possesses a novel cluster structure that appears to be retained in solution and is capable of polymerizing both DL-lactide (LA) and -caprolactone (CL). The polymerizations are controlled as evidenced by the linear nature of molecular weight versus conversion plots and [M]/[3] ratios. The kinetics of LA polymerization using 3 are first-order with respect to the monomer at low [LA]/[Y] ratios. The polymerization of CL is zero-order in monomer. Complex 1‚2BnOH possesses a dimeric structure previously seen in both the solid and solution state. However, the added presence of benzyl alcohol moieties in 1‚2BnOH increases the rate of LA polymerization and allows for control over the molecular weights of isolated polylactide, a feature unseen in earlier reported dimers. The complex 1‚2BnOH is not active for the polymerization of CL.

A Strategy for Control of “Random” Copolymerization of Lactide and Glycolide: Application to Synthesis of PEG-b-PLGA Block Polymers Having Narrow Dispersity

“…These include zinc or aluminum alkoxides 11,14,15,16,17 and rare earth metal compounds. 14,17,18,19,20 Some of these catalysts also raise health safety concerns. Enzymatic ROP of lactones, lactide ( 1 ), and glycolide ( 2 ) has also been studied to address concerns about possible toxicity of heavy metal catalysts and initiators.…”

A series of rare earth phenolates substituted by alkyl groups for D,L-lactide ring-opening polymerization

“…Although several methods for the synthesis of PDLLA exist, the most convenient route is the ring-opening polymerization of D, L-lactide (DLLA), which has many advantages over traditional step condensation polymerizations. Many kinds of organometallic and coordination complexes have been reported to be effi cient catalysts for the ring-opening polymerization of DLLA [2][3][4][5][6][7][8][9] . Complete removal of the catalysts residues from the polymer is not possible, and therefore low toxicity catalysts should be used for biomedical application, among which rare earth catalysts have received most considerable interest due to their high activity [10,11] , very few toxicological data [12,13] and therapeutical application.…”

Ring-opening polymerization of lactides by (pyrazol-1-ylmethyl)pyridine Zn(II) and Cu(II) complexes: Kinetics, mechanism and tacticity studies

“…20 The narrow PDIs coupled with the relatively high Mw observed in L-LA polymerization indicate absence/minimum transesterification reactions. 33,34 However, low molecular weights of poly(D,L-LA) is consistent with the occurrence of intramolecular transesterification reactions. 34 The narrow PDIs achieved for complexes 1-4 bearing acetate groups is in fact unusual as most acetate complexes give broad PDI in comparison to the alkoxide initiators.…”