Cocatalyst Binding Effects in Organocatalytic Ring-Opening Polymerization of l-Lactide

Crafting sustainable solutions: architecting biodegradable copolymers through controlled ring-opening copolymerization

Polylactic acid (PLA) is a biodegradable and biocompatible polymer with versatile applications in packaging and medicine. It is derived from lactic acid and thus represents an eco-friendly option sourced from renewable raw materials. Despite its advantages, PLA exhibits few drawbacks, such as brittleness and relatively high melting and glass transition temperatures. However, these limitations can be addressed through copolymerization with other monomers like ε-caprolactone (ε-CL), resulting in a composite material with improved physical properties. This paper comprehensively reviews achievements in PLA-PCL copolymerization using organometallic catalysts, discussing scientific findings and various copolymer architectures obtained, including random or block configurations. It also demonstrates various sustainable catalysts for achieving the required microstructure under mild reaction conditions without the aid of any external initiator.

Organo-catalyzed/initiated ring opening co-polymerization of cyclic anhydrides and epoxides: an emerging story

This review deals with recent organo-catalyzed/initiated developments of co-polymerization of cyclic anhydrides and epoxides to access polyesters.

Synthesis of macrocyclic poly(α-hydroxyl acids) via DABCO-mediated ROP of O-carboxylanhydrides derived from l-phenylalanine even in the presence of an alcohol

On exploration of a catalytic system including simple 1,4-diazabicyclo-[2.2.2]octane (DABCO), triethylboron (TEB) and benzylalcohol (BnOH), a new pathway to achieve cyclic PAHAs was developed via ROP of OCAs.

DFT Modeling of Organocatalytic Ring-Opening Polymerization of Cyclic Esters: A Crucial Role of Proton Exchange and Hydrogen Bonding

Organocatalysis is highly efficient in the ring-opening polymerization (ROP) of cyclic esters. A variety of initiators broaden the areas of organocatalysis in polymerization of different monomers, such as lactones, cyclic carbonates, lactides or gycolides, ethylene phosphates and phosphonates, and others. The mechanisms of organocatalytic ROP are at least as diverse as the mechanisms of coordination ROP; the study of these mechanisms is critical in ensuring the polymer compositions and architectures. The use of density functional theory (DFT) methods for comparative modeling and visualization of organocatalytic ROP pathways, in line with experimental proof of the structures of the reaction intermediates, make it possible to establish these mechanisms. In the present review, which continues and complements our recent manuscript that focused on DFT modeling of coordination ROP, we summarized the results of DFT modeling of organocatalytic ROP of cyclic esters and some related organocatalytic processes, such as polyester transesterification.

Covalent Poly(lactic acid) Nanoparticles for the Sustained Delivery of Naloxone

The opioid epidemic currently plaguing the United States has been exacerbated by an alarming rise in fatal overdoses as a result of the proliferated abuse of synthetic mu opioid receptor (MOR) agonists, such as fentanyl and its related analogues. Attempts to manage this crisis have focused primarily on widespread distribution of the clinically approved opioid reversal agent naloxone (Narcan); however, due to the intrinsic metabolic lability of naloxone, these measures have demonstrated limited effectiveness against synthetic opioid toxicity. This work reports a novel polymer-based strategy to create a long-acting formulation of naloxone with the potential to address this critical issue by utilizing covalent nanoparticle (cNP) drug delivery technology. Covalently loaded naloxone nanoparticles (Nal-cNPs) were prepared via the naloxone-initiated, ring-opening polymerization (ROP) of l-lactide in the presence of a bifunctional thiourea organocatalyst with subsequent precipitation of the resulting naloxone-poly(l-lactic acid) polymer. This protocol afforded well-defined nanoparticles possessing a drug loading of approximately 7% w/w. The resulting Nal-cNPs demonstrated excellent biocompatibility, while exhibiting sustained linear release kinetics in vitro and blocking the effects of high dose (10 mg/kg) acute morphine for up to 98 h in an in vivo rodent model of neuropathic pain.

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.

The mechanistic duality of (thio)urea organocatalysts for ring-opening polymerization

Among the various catalysts for ROP, H-bonding organocatalysts stand out in the precise level of reaction control they are able to render during ROP. The H-bonding class of organocatalysts are thought to effect ROP via dual activation of both monomer and chain end. (Thio)urea mediated ROP has experienced a renaissance as a new polymerization mechanism - mediated by imidate or thioimidate species - facilitates new modes of reactivity and new synthetic abilities. Indeed, the urea class of H-bond donors has been shown to be more active than their corresponding thioureas. The imidate mechanism remains highly active in polar solvents and exhibits remarkable control - and 'living' behavior - under solvent-free conditions, and a broad range of temperatures is accessible. The advancements in synthetic abilities have all evolved through a greater understanding of reaction mechanism. Through the continued synergistic advances of catalysis and material, the (thio)urea class of catalyst can find use in a host of potential applications, research and industrial environments.

N-Heterocyclic olefins and thioureas as an efficient cooperative catalyst system for ring-opening polymerization of δ-valerolactone

An organocatalytic ring-opening polymerization of δ-valerolactone has been developed.

Triclocarban: Commercial Antibacterial and Highly Effective H-Bond Donating Catalyst for Ring-Opening Polymerization

The antibacterial compound, triclocarban (TCC), is shown to be a highly effective H-bond donating catalyst for ring-opening polymerization (ROP) when applied with an H-bond accepting base cocatalyst. These ROPs exhibit the characteristics of "living" polymerizations. TCC is shown to possess the high activity characteristic of urea (vs thiourea) H-bond donors. The urea class of H-bond donors is shown to remain highly active in H-bonding solvents, a trait that is not displayed by the corresponding thiourea H-bond donors. Two H-bond donating ureas that are electronically similar to TCC are evaluated for their efficacy in ROP, and a mechanism of action is proposed. This "off-the-shelf" H-bond donor is among the most active and most controlled organocatalysts for the ROP of lactones.

Squaramide and amine binary H-bond organocatalysis in polymerizations of cyclic carbonates, lactones, and lactides

Multiple combinations of six squaramides and eight amines as co-catalysts were success in ROPs of cyclic monomers by H-bond donor and acceptor binary catalysis that established a general protocol.

Bis- and Tris-Urea H-Bond Donors for Ring-Opening Polymerization: Unprecedented Activity and Control from an Organocatalyst

A new class of H-bond donating ureas was developed for the ring-opening polymerization (ROP) of lactone monomers, and they exhibit dramatic rate acceleration versus previous H-bond mediated polymerization catalysts. The most active of these new catalysts, a tris-urea H-bond donor, is among the most active organocatalysts known for ROP, yet it retains the high selectivity of H-bond mediated organocatalysts. The urea cocatalyst, along with an H-bond accepting base, exhibits the characteristics of a "living" ROP, is highly active, in one case, accelerating a reaction from days to minutes, and remains active at low catalyst loadings. The rate acceleration exhibited by this H-bond donor occurs for all base cocatalysts examined. A mechanism of action is proposed, and the new catalysts are shown to accelerate small molecule transesterifications versus currently known monothiourea catalysts. It is no longer necessary to choose between a highly active or highly selective organocatalyst for ROP.

Controlled Organocatalytic Ring-Opening Polymerization of ε-Thionocaprolactone

For the first time, the controlled ring-opening polymerization (ROP) of ε-thionocaprolactone (tnCL) is conducted. The organocatalytic ROP of tnCL occurs without carbonyl scrambling, leading to homopoly(ε-thionocaprolactone) (PtnCL). The ROP by base catalysts alone is proposed to proceed via a nucleophilic mechanism, while the addition of an H-bond donating thiourea (TU) is shown to provide excellent reaction control. The increased reaction control provided by the TU occurs in the virtual absence of binding between tnCL and TU, and a mechanistic account for this observation is discussed. The monomer ring strain is measured and found to be similar to δ-valerolactone (VL). Copolymers with VL are synthesized, and the resulting analysis of the copolymer materials properties provides the only known physical characterizations of poly(thio(no)ester-co-ester)s.

Synthesis, characterization, and catalytic activity of sodium ketminiate complexes toward the ring-opening polymerization of l-lactide

Na complexes bearing ketiminate ligands revealed the greater catalytic activity and polymer controllability than that of Na complexes bearing Schiff base ligands.

Photoswitchable ring-opening polymerization of lactide catalyzed by azobenzene-based thiourea

An azobenzene-based thiourea compound 1 as a catalyst was successfully used in the ring-opening polymerization of rac-lactide. The reactivity of a catalytic polymerization system using photoresponsive azobenzene-based thiourea/PMDETA as a catalyst could be switched between slow and fast states by alternating exposure to UV and ambient light.