Comparison of three elements (In, Sn, and Sb) in the same period as catalysts in the ring-opening polymerization of l-lactide: from amorphous to semicrystalline polyesters

The ring-opening polymerization (ROP) of l-lactide (l-LA) is the main method for synthesizing poly(l-lactide) (PLLA), in which choosing the catalyst is one of the most important parameters. In this work, we focused on the systematic study of catalysts based on p-block elements from period 5, such as indium(iii), tin(ii), tin(iv) and antimony(iii) acetates, which displayed contrasting performances influenced by the oxidation state of the metal center. Analysis of the obtained oligomers by different techniques, including nuclear magnetic resonance (NMR), differential scanning calorimetry (DSC), polarized optical microscopy (POM) and matrix-assisted laser desorption ionization-time-of-flight (MALDI-TOF), revealed the selectivity of each catalyst toward the ROP of l-LA. Tin(ii) acetate showed the best performance, making it the best catalyst of this series for synthesizing PLLA. Indium(iii) and tin(ii) acetates induced an amorphous and semicrystalline polyester, respectively. The kinetic study evidenced the excellent performance of tin(ii) acetate in the ROP of l-LA. This catalyst reached high conversions in a quarter of the total reaction time, positioning it as the most catalytically active of the selected p-block acetate catalysts. Finally, the coordination-insertion mechanism by the catalyst in the initiation step was corroborated through the development of a mechanistic study applying the density functional theory (DFT).

Structural subtleties and catalytic activity of sodium aminophenolate complexes in polylactide degradation: towards sustainable waste management solutions

This study explores the intricate coordination chemistry of sodium aminophenolate species and their significant role in the depolymerization of polylactide (PLA), offering novel insights into catalytic degradation processes. By examining sodium coordination entities, including dimers and larger aggregates such as tetramers, we reveal how structural modifications, particularly the manipulation of steric hindrances, influence the formation and stability of these complexes. The dimers, characterized by a unique four-center core (Na-O-Na-O), serve as a foundational motif, which is further elaborated to obtain complexes with varied coordination environments through strategic ligand design. Our research delves into the lability of the amino arm in these complexes, a critical factor that facilitates the coordination of PLA to the sodium center, thereby initiating the depolymerization process. Moreover, DFT studies have been pivotal in identifying the most energetically favorable structures for catalysis, highlighting a distinct preference for an eight-membered ring motif stabilized by intramolecular hydrogen bonds. This motif not only enhances the catalyst's efficiency but also introduces a novel structural paradigm for sodium-based catalysis in PLA degradation. Experimental validation of the theoretical models was achieved through NMR spectroscopy, which confirmed the formation of the active catalyst forms and monitored the progress of PLA degradation. The study presents a comprehensive analysis of the influence of ligand structure on the catalytic activity, underscoring the importance of the eight-membered ring motif. Furthermore, we demonstrate how varying the steric bulk of substituents on the amino arm affects the catalyst's performance, with benzyl-substituted ligands exhibiting superior activity. Our findings offer a profound understanding of the structural factors governing the catalytic efficiency of sodium aminophenolate complexes in PLA degradation. This research not only advances the field of coordination chemistry but also presents a promising avenue for the development of efficient and environmentally friendly catalysts for polymer degradation.

Synthesis and characterization of new Na+ complexes of N-benzyl cyclic peptoids and their role in the ring opening polymerization of l-lactide

Na⁺ complexes of cyclic peptoid were employed for the first time as catalyst for the l-lactide polymerization.

Bismuth subsalicylate, a low-toxicity catalyst for the ring-opening polymerization (ROP) of l-lactide (l-LA) with aliphatic diol initiators: synthesis, characterization, and mechanism of initiation

The ring-opening polymerization (ROP) of l-lactide (l-LA) was induced by the catalytic action of bismuth subsalicylate (BiSS) using linear aliphatic diols [HO(CH₂)_nOH, where n = 2, 3, 4, 5, 6, and 8] as initiators and chain transfer agents. The theoretical and experimental degree of polymerization (DP) in all samples of α,ω-hydroxy telechelic poly(l-lactide) (HOPLLAOH) had a good agreement in all samples, an effect attributed to the interaction of BiSS with HO(CH₂)_nOH inducing a transfer reaction. HOPLLAOH was synthesized and characterized by a range of analytical techniques, confirming the insertion of methylene groups from the initiator into the main chain of the polyester. The glass-transition temperature (T_g) of HOPLLAOH was found to be proportional to the number of methylene groups present in the diol. Various parameters regarding the ROP of l-LA were studied, such as temperature, time of reaction, amount of catalyst, and the nature of the diols. A kinetic study of the reaction allowed the determination of the rate constants (k) and activation energy (E_a). A mechanism of initiation is proposed based on a computational study using density functional theory (DFT), evidencing the role of the alkyl diol as an initiator, producing an alkoxide (Bi–OROH). This species then acts as a nucleophile, attacking the carbonyl group, inducing its insertion, and ultimately completing the ring-opening of l-LA.

Bismuth subsalicylate (BiSS) acted as a catalyst in the ring-opening polymerization of l-lactide (l-LA) in the presence of alkyl diols as initiators.

Heterolepic β-Ketoiminate Zinc Phenoxide Complexes as Efficient Catalysts for the Ring Opening Polymerization of Lactide

Zinc phenoxide complexes L1ZnOAr 1-4 (L1=Me2NC2H4NC(Me)CHC(Me)O) and L2ZnOAr 5-8 (L2=Me2NC3H6NC(Me)CHC(Me)O) with donor-functionalized β-ketoiminate ligands (L1/2) and OAr substituents (Ar=Ph 1, 5; 2,6-Me2-C6H3 2, 6; 3,5-Me2-C6H3 3, 7; 4-Bu-C6H4 4, 8) with tuneable electronic and steric properties were synthesized and characterized. 1-8 adopt binuclear structures in the solid state except for 5, while they are monomeric in CDCl3 solution. 1-8 are active catalysts for the ring opening polymerization (ROP) of lactide (LA) in CH2Cl2 at ambient temperature and the catalytic activity is controlled by the electronic and steric properties of the OAr substituent, yielding polymers with high average molecular weight (M n) and moderately controlled molecular weight distribution (MWDs). 1 and 5 showed a living polymerization character and kinetic studies on the ROP of L-LA with 1 and 5 proved first order dependencies on the monomer concentration. Homonuclear decoupled 1H-NMR analyses of polylactic acid (PLA) formed with rac-LA proved isotactic enrichment of the PLA microstructure.

Recent progress in the application of group 1, 2 & 13 metal complexes as catalysts for the ring opening polymerization of cyclic esters

This review focuses on recent developments concerned with the use of well-defined main group complexes as (pre-)catalysts for the ROP of cyclic esters to give aliphatic polyesters; factors influencing catalytic activity, selectivity and polymer properties are all discussed.

Ring-opening polymerization of rac-lactide catalyzed by crown ether complexes of sodium and potassium iminophenoxides

Crown ether complexes of sodium and potassium iminophenoxides were demonstrated to catalyze the stereoselective polymerization of rac-lactide.

Crown ether complexes of potassium quinolin-8-olates: synthesis, characterization and catalysis toward the ring-opening polymerization of rac-lactide

Crown ether complexes of potassium quinolin-8-olates were synthesized and demonstrated to catalyze the stereoselective polymerization of rac-lactide.

Synthesis of aluminum complexes supported by 2-(1,10-phenanthrolin-2-yl)phenolate ligands and their catalysis in the ring-opening polymerization of cyclic esters

Phenanthroline-phenolate based N,N,O-chelate aluminum complexes were demonstrated to catalyze the ROP of ε-caprolactone, rac-lactide, and rac-β-butyrolactone, as well as their block copolymerization.