“In Situ” Formation of Yttrium Alkoxides: A Versatile and Efficient Catalyst for the ROP of ε-Caprolactone

Abstract

[Tris(hexamethyldisilyl)amide] yttrium is a catalyst for the controlled ring-opening polymerization of ε-caprolactone when reacted with an excess of alcohol. Up to an alcohol-to-yttrium molar ratio of 50, the chain transfer to the alcohol is quantitative, and the molecular weight of the chains can be predicted from the monomer-to-alcohol molar ratio. At alcohol-to-yttrium ratios higher than 100, the alcohol is quantitatively consumed provided that 1,1,1,3,3,3-hexamethyldisilazane, which is formed as a byproduct, is removed from the reation medium. Depending on the structure of the alcohol, end-functional polyesters can be prepared (e.g., with N-pyrrolyl and 3-thienyl end groups). Well-defined block and random copolymers of ε-CL with lactides and γ-bromo-ε-caprolactone, respectively, have also been synthesized. Compared to aluminum alkoxides, the in situ formed yttrium alkoxides have the advantage of a much faster polymerization kinetics while preserving control.

A high-throughput approach to lanthanide complexes and their rapid screening in the ring opening polymerisation of caprolactone

“…1 H NMR spectra were referenced to residual protons in the deuterated solvent and 13 C NMR spectra to the 13 C atoms therein. Elemental analyses were performed by Elemental Microanalysis Ltd., Devon.…”

“…The resulting white solids were isolated in 68-83% yield and were characterised by 1 H NMR spectroscopy. In addition to this, selected ligands were also characterised by 13 View Article Online…”

Ring-opening polymerization of cyclic esters in the presence of choline/SnOct2 catalytic system

“…Polylactide (PLA), polyglycolide (PGA), and poly(ecaprolactone) (PCL) are regarded as a soft and hard-tissue compatible material, which has found use in resorbable sutures, drug-delivery systems, and bone graft substitutes [1][2][3][4]. For their synthesis, various cationic or anionic initiators, catalysts, and enzymes have been used [1,[5][6][7][8][9][10][11][12][13][14][15].…”

Ring‐opening polymerization of lactones using RuCl2(PPh3)3 as initiator: Effect of hydroxylic transfer agents

“…Many groups of researchers [2][3][4][5][6] have reported using alkoxides derived from alkaline metals and rare earth elements containing unoccupied p, d, and f orbitals (such as Mg, Zn, Al, Sn, Ti, Zr, Sm, and Y alkoxides) as initiators in the polymerization of cyclic esters. The effectiveness of these compounds has mainly relied on the ability of the particular alkoxide to induce formation of the initiation species, which involves the complexation of the monomer with the initiator via free p or d orbitals, followed by cleavage of the lactone acyl-oxygen bond.…”