Polymerization of Lactide by Monomeric Sn(II) Alkoxide Complexes

Abstract

Monomeric Sn(II) alkoxide complexes of bulky amidinate ligands N,N′-bis(trimethylsilyl)benzamidinate, [L SiMe3 ] -, and N,N′-bis(dimethylphenylsilyl)benzamidinate, [L SiMe2Ph ] -, and the corresponding bis(amidinate) compounds were synthesized and structurally characterized by single-crystal X-ray diffraction. The monomeric nature of these complexes in the solid state was retained in solution as evinced by NMR spectroscopy. Both alkoxide complexes were active for DL-lactide (LA) polymerization in toluene solution at 80 °C. The controlled polymerization of LA by L SiMe2Ph Sn(OCPh3) was observed in the presence of 1.0 equiv of an exogenous alcohol. Under these conditions, the polymerization reaction was found to be first order in [LA] and about one-third order in [L SiMe2Ph Sn(OCPh3)]0. The polymerization kinetics were further analyzed by applying a model that invokes aggregation of the active species, with one inactive, aggregated form and one active, unaggregated form. The importance of aggregation in understanding catalyst reactivity is highlighted.

Mechanism of the Living Lactide Polymerization Mediated by Robust Zinc Guanidine Complexes

“…[1][2][3][4][5][6][7][10][11][12][13] The experimental results support the hypothesis that the neutral, but highly nucleophilic guanidine function can take on this crucial role, too. Herein, we propose the mechanism for the activation and insertion of the first lactide molecule (Scheme 2) to model the initiation step in analogy to the ring-opening reaction with tin ketiminate systems.…”

“…This plot shows a small positive intercept upon extrapolation for [1] = 0 m, which might be due to aggregation effects or reaction acceleration by acidic impurities. [13] Inspired by these polymerization characteristics, [10] we propose, analogously to classical metal alkoxide single-site initiators, that in the zinc guanidine initiator systems 1 and 2 the basic guanidine function acts as a nucleophilic ring-opening agent. To support this hypothesis we tried to identify the end group by spectroscopic techniques.…”

Improving the ring-opening polymerization of ε-caprolactone and l-lactide using stannous octanoate

“…However, the drawbacks include low polymerization activity and undesirable inter-and intramolecular transesterification reactions. Numerous researchers [22,[34][35][36][37][38][39][40] have attempted to synthesize Sn complexes to overcome these issues; however, they have encountered difficulties resulting from the sensitivity to air requiring that they be prepared under N 2 , making them difficult to manufacture or research without the glove box and vacuum lines.…”

Synthesis of lithium and aluminum complexes supported by [OC(But)CHP(Ph2)=NBut]− ligand and catalysis of [R2Al{OC(But)-CHP(Ph2)=NBut}] (R = Me, Et) and [Me2Al{1-{OC(Ph)CH}-3-R1-5-MeC3HN2}] (R1 = Me, But) in the ring-opening polymerization of ɛ-caprolactone

“…These polymers are usually synthesized by the ring-opening polymerization (ROP) of cyclic esters such as lactones and lactides initiated by metal complexes. The metal-initiated-ROP can enable control of polymer molecular weight and polymer architecture and can yield macromolecular samples with narrow molecular weight distributions [3][4][5][6][7][8]. Among the catalysts/initiators studied, aluminum complexes have attracted much attention due to their *Corresponding author (email: zxwang@ustc.edu.cn) high activity and selectivity as well as low toxicity of aluminum [9][10][11][12][13].…”