The Mechanism of TBD-Catalyzed Ring-Opening Polymerization of Cyclic Esters

Efficiency and Mechanism of Catalytic Siloxane Exchange in Vitrimer Polymers: Modeling and Density Functional Theory Investigations

Of late, siloxane-containing vitrimers have gained significant interest due to their fast dynamic characteristics over a reasonable temperature range (180-220 °C), making them well-suited for diverse applications. The exchange reaction pathway in the siloxane vitrimers is accountable for the covalent adaptive network, with the reaction's effectiveness being regulated by either organic or organometallic catalysts. However, directly studying the exchange reaction pathway in the bulk phase using experimental approaches is challenging because of the intricate and interconnected structure of these vitrimers. Here, we perform comprehensive density functional theory (DFT) and experimental investigations to discover the detailed catalytic efficacy of siloxane exchange and provide direction for the reaction process using a 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) catalyst. The calculated transition barrier energy and catalytic efficiency of hexamethyldisiloxane and dihydroxy-dimethylsilane exchange derived from the nudged elastic band with transition-state calculations strongly agree with the experimental findings. In addition, Fukui indices, along with partial charges, are employed to evaluate the nucleophilic and electrophilic behaviors of silanol and siloxane molecules. Our analysis revealed that by utilizing the Fukui indices of both the acid and the base, we can make an approximate estimation of the respective kinetics of the SN2 process in the siloxane exchange reaction mechanism. These findings establish a foundation for comprehending a crucial aspect of the exchange mechanism in siloxane vitrimer systems and could aid in the development of novel catalysts.

Transesterification of Dimethyl Carbonate with Ethanol Catalyzed by Guanidine: A Theoretical Analysis

Density-functional theory (DFT) was performed to investigate the mechanistic features of different guanidine-based catalysts, namely, 1,1,3,3-tetramethyl guanidine (TMG) and 1,5,7-triaza-bicyclo-[4.4.0]dec-5-ene (TBD), for the transesterification reaction of dimethyl carbonate (DMC) with ethanol (EtOH). Different possible pathways were suggested in which these catalysts act as either nucleophile or base within a homogeneous system. The DFT results allowed not only the study of the thermochemistry aspects of all elementary reactions featured in the two different activation modes but also the accurate calculation of the free energy barriers for each case. Our findings showed that the catalyzed reaction proceeded through simultaneous activation of DMC and EtOH, facilitated by hydrogen bonding for both catalysts. This feature led to the formation of a stable intermediate with a relatively low free energy barrier. TBD exhibited a potentially more efficient mechanism, owing to its planar structure and dual-activation mode. The free energy barrier of the rate-limiting step, identified as the formation of a zwitterionic complex, then declined by approximately 50% when compared with the reaction without catalysts. Overall, the DFT approach provides good insight into the reactivity of both catalysts and helps to find possibilities for further enhancing the mechanistic features of both catalysts for this type of transesterification reaction.

Topology-Accelerated and Selective Cascade Depolymerization of Architecturally Complex Polyesters

Despite considerable recent advances already made in developing chemically circular polymers (CPs), the current framework predominantly focuses on CPs with linear-chain structures of different monomer types. As polymer properties are determined by not only composition but also topology, manipulating the topology of the single-monomer-based CP systems from linear-chain structures to architecturally complex polymers could potentially modulate the resulting polymer properties without changing the chemical composition, thereby advancing the concept of monomaterial product design. To that end, here, we introduce a chemically circular hyperbranched polyester (HBPE), synthesized by a mixed chain-growth and step-growth polymerization of a rationally designed bicyclic lactone with a pendent hydroxyl group (BiLOH). This HBPE exhibits full chemical recyclability despite its architectural complexity, showing quantitative selectivity for regeneration of BiLOH, via a unique cascade depolymerization mechanism. Moreover, distinct differences in materials properties and performance arising from topological variations between HBPE, hb-PBiLOH, and its linear analogue, l-PBiLOH, have been revealed where generally the branched structure led to more favorable interchain interactions, and topology-amplified optical activity has also been observed for chiral (1S, 4S, 5S)-hb-PBiLOH. More intriguingly, depolymerization of l-PBiLOH proceeds through an unexpected, initial topological transformation to the HBPE polymer, followed by the faster cascade depolymerization pathway adopted by hb-PBiLOH. Overall, these results demonstrate that CP design can go beyond typical linear polymers, and rationally redesigned, architecturally complex polymers for their unique properties may synergistically impart advantages in topology-augmented depolymerization acceleration and selectivity for exclusive monomer regeneration.

Intensified Continuous Flow Process for the Scalable Production of Bio-Based Glycerol Carbonate

A subtle combination of fundamental and applied organic chemistry toward process intensification is demonstrated for the large-scale production of bio-based glycerol carbonate under flow conditions. The direct carbonation of bio-based glycidol with CO2 is successfully carried out under intensified flow conditions, with Barton's base as a potent homogeneous organocatalyst. Process metrics for the CO2 coupling step (for the upstream production, output: 3.6 kg day-1 , Space Time Yield (STY): 2.7 kg h-1  L-1 , Environmental factor (E-factor): 4.7) outclass previous reports. High conversion and selectivity are achieved in less than 30 s of residence time at pilot scale with a stoichiometric amount of CO2 . Supporting DFT computations reveal the unique features of the mechanism in presence of Brønsted bases.

Next-Generation Vitrimers Design through Theoretical Understanding and Computational Simulations

Vitrimers are an innovative class of polymers that boast a remarkable fusion of mechanical and dynamic features, complemented by the added benefit of end-of-life recyclability. This extraordinary blend of properties makes them highly attractive for a variety of applications, such as the automotive sector, soft robotics, and the aerospace industry. At their core, vitrimer materials consist of crosslinked covalent networks that have the ability to dynamically reorganize in response to external factors, including temperature changes, pressure variations, or shifts in pH levels. In this review, the aim is to delve into the latest advancements in the theoretical understanding and computational design of vitrimers. The review begins by offering an overview of the fundamental principles that underlie the behavior of these materials, encompassing their structures, dynamic behavior, and reaction mechanisms. Subsequently, recent progress in the computational design of vitrimers is explored, with a focus on the employment of molecular dynamics (MD)/Monte Carlo (MC) simulations and density functional theory (DFT) calculations. Last, the existing challenges and prospective directions for this field are critically analyzed, emphasizing the necessity for additional theoretical and computational advancements, coupled with experimental validation.

Non-activated Esters as Reactive Handles in Direct Post-Polymerization Modification

Non-activated esters are prominently featured functional groups in polymer science, as ester functional monomers display great structural diversity and excellent compatibility with a wide range of polymerization mechanisms. Yet, their direct use as a reactive handle in post-polymerization modification has been typically avoided due to their low reactivity, which impairs the quantitative conversion typically desired in post-polymerization modification reactions. While activated ester approaches are a well-established alternative, the modification of non-activated esters remains a synthetic and economically valuable opportunity. In this review, we discuss past and recent efforts in the utilization of non-activated ester groups as a reactive handle to facilitate transesterification and aminolysis/amidation reactions, and the potential of the developed methodologies in the context of macromolecular engineering.

Recent Advances in Polycaprolactones for Anticancer Drug Delivery

Poly(ε-Caprolactone)s are biodegradable and biocompatible polyesters that have gained considerable attention for drug delivery applications due to their slow degradation and ease of functionalization. One of the significant advantages of polycaprolactone is its ability to attach various functionalities to its backbone, which is commonly accomplished through ring-opening polymerization (ROP) of functionalized caprolactone monomer. In this review, we aim to summarize some of the most recent advances in polycaprolactones and their potential application in drug delivery. We will discuss different types of polycaprolactone-based drug delivery systems and their behavior in response to different stimuli, their ability to target specific locations, morphology, as well as their drug loading and release capabilities.

Dual-Labelled Nanoparticles Inform on the Stability of Fluorescent Labels In Vivo

Fluorescent labelling is commonly used to monitor the biodistribution of nanomedicines. However, meaningful interpretation of the results requires that the fluorescent label remains attached to the nanomedicine. In this work, we explore the stability of three fluorophores (BODIPY650, Cyanine 5 and AZ647) attached to polymeric hydrophobic biodegradable anchors. Using dual-labelled poly(ethylene glycol)-b-poly(lactic acid) (PEG-PLA) nanoparticles that are both radioactive and fluorescent, we investigated how the properties of the fluorophores impact the stability of the labelling in vitro and in vivo. Results suggest that the more hydrophilic dye (AZ647) is released faster from nanoparticles, and that this instability results in misinterpretation of in vivo data. While hydrophobic dyes are likely more suitable to track nanoparticles in biological environments, quenching of the fluorescence inside the nanoparticles can also introduce artefacts. Altogether, this work raises awareness about the importance of stable labelling methods when investigating the biological fate of nanomedicines.

DFT Investigations on the Ring-Opening Polymerization of Trimethylene Carbonate Catalysed by Heterocyclic Nitrogen Bases

Organocatalysts for polymerization have known a huge interest over the last two decades. Among them, heterocyclic nitrogen bases are widely used to catalyse the ring-opening polymerization (ROP) of heterocycles such as cyclic carbonates. We have investigated the ring-opening polymerization of trimethylene carbonate (TMC) catalysed by DMAP (4-dimethylaminopyridine) and TBD (1,5,7-triazabicyclo[4.4.0]dec-5-ene) as case studies in the presence of methanol as co-initiator by Density Functional Theory (DFT). A dual mechanism based on H-bond activation of the carbonyl moieties of the monomer and a basic activation of the alcohol co-initiator has been shown to occur more preferentially than a direct nucleophilic attack of the carbonate monomer by the heterocyclic nitrogen catalyst. The rate-determining step of the mechanism is the ring opening of the TMC molecule, which is slightly higher than the nucleophilic attack of the TMC carbonyl by the activated alcohol. The calculations also indicate TBD as a more efficient catalyst than DMAP. The higher energy barrier found for DMAP vs. TBD, 23.7 vs. 11.3 kcal·mol−1, is corroborated experimentally showing a higher reactivity for the latter.

Guanidinates as Alternative Ligands for Organometallic Complexes

For decades, ligands such as phosphanes or cyclopentadienyl ring derivatives have dominated Coordination and Organometallic Chemistry. At the same time, alternative compounds have emerged that could compete either for a more practical and accessible synthesis or for greater control of steric and electronic properties. Guanidines, nitrogen-rich compounds, appear as one such potential alternatives as ligands or proligands. In addition to occurring in a plethora of natural compounds, and thus in compounds of pharmacological use, guanidines allow a wide variety of coordination modes to different metal centers along the periodic table, with their monoanionic chelate derivatives being the most common. In this review, we focused on the organometallic chemistry of guanidinato compounds, discussing selected examples of coordination modes, reactivity and uses in catalysis or materials science. We believe that these amazing ligands offer a new promise in Organometallic Chemistry.

Tunable and recyclable polyesters from CO2 and butadiene

Carbon dioxide is inexpensive and abundant, and its prevalence as waste makes it attractive as a sustainable chemical feedstock. Although there are examples of copolymerizations of CO₂ with high-energy monomers, the direct copolymerization of CO₂ with olefins has not been reported. Here an alternative route to functionalizable, recyclable polyesters derived from CO₂, butadiene and hydrogen via an intermediary lactone, 3-ethyl-6-vinyltetrahydro-2H-pyran-2-one, is described. Catalytic ring-opening polymerization of the lactone by 1,5,7-triazabicyclo[4.4.0]dec-5-ene yields polyesters with molar masses up to 13.6 kg mol^-1 and pendent vinyl side chains that can undergo post-polymerization functionalization. The polymer has a low ceiling temperature of 138 °C, allowing for facile chemical recycling, and is inherently biodegradable under aerobic aqueous conditions (OECD-301B protocol). These results show that a well-defined polyester can be derived from CO₂, olefins and hydrogen, expanding access to new polymer feedstocks that were once considered unfeasible.

Introducing SuFEx click chemistry into aliphatic polycarbonates: a novel toolbox/platform for post-modification as biomaterials

As a biodegradable and biocompatible biomaterial, aliphatic polycarbonates (APCs) have attracted substantial attention in terms of post-polymerization modification (PPM) for functionalization. A strategy for the introduction of sulfur(VI)-fluoride exchange (SuFEx) click chemistry into APCs for PPM is proposed for the first time in this work. 4'-(Fluorosulfonyl)benzyl 5-methyl-2-oxo-1,3-dioxane-5-carboxylate (FMC) was designed as a SuFEx clickable cyclic carbonate for APCs via ring-opening polymerization (ROP), and an operational and nontoxic synthetic route was achieved. FMC managed to undergo both ROP and PPM through the SuFEx click chemistry organocatalytically without constraining or antagonizing each other, using 1,5,7-triazabicyclo[4,4,0]dec-5-ene (TBD) as a co-organocatalyst here. Its ROP was systematically investigated, and density functional theory (DFT) calculations were performed to understand the acid-base catalytic mechanism in the anionic ROP. Exploratory investigations into PPM by SuFEx of poly(FMC) were conducted as biomaterials, and the one-pot strategies to achieve both ROP and SuFEx were confirmed.

Preparing Well-Defined Polyacrylamide-b-Polycarbonate by Integrating Photoiniferter Polymerization and TBD-Catalyzed ROP

The dual-initiator technique allows the polymerization of different monomers from orthogonal polymerization mechanisms to obtain block copolymers (BCPs). In this study, it is attempted to combine photoiniferter living free radical polymerization and organocatalytic ring-opening polymerization (ROP) to design a hydroxyl-functionalized carbamodithioate, i.e., 4-(hydroxymethyl)benzyl diethylcarbamodithioate (HBDC), which can integrate photoiniferter polymerization of acrylamide monomers and ROP of cyclic carbonates. As a proof of concept, the monomer applicability is further extended to acrylates and lactones. The results confirm that the two polymerization systems are experimentally compatible in a stepwise sequence as well as in a simultaneous one-pot process to synthesize BCPs. It is reasonable to assume that HBDC can allow for simple and efficient one-pot access to well-defined BCPs from a larger range of monomers, which is more advantageous from the operational, economical, and environmental points of view.

Complexities of Regioselective Ring-Opening vs Transcarbonylation-Driven Structural Metamorphosis during Organocatalytic Polymerizations of Five-Membered Cyclic Carbonate Glucose Monomers

Rigorous investigations of the organobase-catalyzed ring-opening polymerizations (ROPs) of a series of five-membered cyclic carbonate monomers derived from glucose revealed that competing transcarbonylation reactions scrambled the regiochemistries of the polycarbonate backbones. Regioirregular poly(2,3-α-d-glucose carbonate) backbone connectivities were afforded by 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD)-catalyzed ROPs of three monomers having different cyclic acetal protecting groups through the 4- and 6-positions. Small molecule studies conducted upon isolated unimers and dimers indicated a preference for Cx-O2 vs Cx-O3 bond cleavage from tetrahedral intermediates along the pathways of addition-elimination mechanisms when the reactions were performed at room temperature. Furthermore, treatment of isolated 3-unimer or 2-unimer, having the carbonate linkage in the 3- or 2-position as obtained from either Cx-O2 or Cx-O3 bond cleavage, respectively, gave the same 74:26 (3-unimer:2-unimer) ratio, confirming the occurrence of transcarbonylation reactions with a preference for 3-unimer vs. 2-unimer formation in the presence of organobase catalyst at room temperature. In contrast, unimer preparation at -78 °C favored Cx-O3 bond cleavage to afford a majority of 2-unimer, presumably due to a lack of transcarbonylation side reactions. Computational studies supported the experimental findings, enhancing fundamental understanding of the regiochemistry resulting from the ring-opening and subsequent transcarbonylation reactions during ROP of glucose carbonates. These findings are expected to guide the development of advanced carbohydrate-derived polymer materials by an initial monomer design via side chain acetal protecting groups, with the ability to evolve the properties further through later-stage structural metamorphosis.

Aerobic Oxidations via Organocatalysis: A Mechanistic Perspective

This review focuses on recent advances and mechanistic views of aerobic C(sp3)–H oxidations catalyzed by organocatalysts, where metal catalysis and photocatalysis are not included.

1 Introduction

2 Carbanion Route: TBD-Catalyzed C(sp3)–H Oxygenation

2.1 α-Hydroxylation of Ketones

2.2 Carbonylation of Benzyl C(sp3)–H

3 Radical Route: NHPI-Catalyzed C(sp3)–H Oxidation

3.1 N-Oxyl Radicals and Mechanisms

3.2 Oxygenation of Benzyl C(sp3)–H

3.3 Solvent Effects

4 Hydride-Transfer Route: TEMPO-Catalyzed Oxidations

4.1 Oxoammonium Cation and Mechanisms

4.2 Dehydrogenation of Alcohols

4.3 Oxygenation of Benzyl C(sp3)–H

5 Conclusions and Outlook

Pathway to fully-renewable biobased polyesters derived from HMF and phenols

Building on previous work where 5-hydroxymethylfurfural (HMF) was selectively functionalized by etherification with phenols, we demonstrated that the oxidized versions of these HMF ethers can be converted to functionalized δ-hexalactones...

Green and sustainable synthesis of poly(δ-valerolactone) with a TBD catalyzed ring-opening polymerization reaction

A green and sustainable method is proposed for the TBD catalyzed ring-opening polymerization of δ-valerolactone.

Degradable Polymer Structures from Carbon Dioxide and Butadiene

The utilization of carbon dioxide as a polymer feedstock is an ongoing challenge. This report describes the catalytic conversion of carbon dioxide and an olefin comonomer, 1,3-butadiene, into a polymer structure that arises from divergent propagation mechanisms. Disubstituted unsaturated δ-valerolactone 1 (EVL) was homopolymerized by the bifunctional organocatalyst 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) to produce a hydrolytically degradable polymer. Isolation and characterization of reaction intermediates using ¹H, ¹³C, COSY, HSQC, and MS techniques revealed a vinylogous 1,4-conjugate addition dimer forms in addition to polymeric materials. Polymer number-average molecular weights up to 3760 g/mol and glass transition temperatures in the range of 25-52 °C were measured by GPC and DSC, respectively. The polymer microstructure was characterized by ¹H, ¹³C, FTIR, MALDI-TOF MS, and ESI tandem MS/MS. The olefin/CO₂-derived materials depolymerized by hydrolysis at 80 °C in 1 M NaOH. This method and the observed chemical structures expand the materials and properties that can be obtained from carbon dioxide and olefin feedstocks.

Remarkable thermoplasticity of branched cellulose copolymers: Graft-chain-dependent structural transition and thermoplasticity

In this study, we designed novel methods to prepare a cellulose graft copolymer series (Cell-g-PDLs) with varied graft chain lengths, via direct ring-opening polymerization (ROP) of unmodified cellulose with alkyl-branched lactones. With increasing alkyl-branched graft chain length of the Cell-g-PDLs, the crystalline phase of cellulose became increasingly weakened, while the glass transition temperature significantly decreased. The latter was attributed to the extended free volume derived from the increased chain end-group concentrations of the branched graft chains. These results suggested that the incorporation of a highly alkyl-branched graft chain into unmodified cellulose is an effective way to improve its thermo-plasticity. Notably, the Cell-g-PDL with the longest graft chain (Cell-g-PDL9) was demonstrative of highly sufficient thermo-plasticity, owing to the enhanced molecular mobility resulting from the reduced frictional forces between the cellulose molecules.

1,5,7-Triazabicyclo[4.4.0]dec-5-ene Enhances Activity of Peroxide Intermediates in Phosphine-Free α-Hydroxylation of Ketones

The critical role of double hydrogen bonds was addressed for the aerobic α-hydroxylation of ketones catalyzed by 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD), in the absence of either a metal catalyst or phosphine reductant. Experimental and theoretical investigations were performed to study the mechanism. In addition to initiating the reaction by proton abstraction, a more important role of TBD was revealed, that is, to enhance the oxidizing ability of peroxide intermediates, allowing DMSO to be used rather than commonly used phosphine reductants. Further characterizations with nuclear Overhauser effect spectroscopy (NOESY) confirmed the presence of double hydrogen bonds between TBD and the ketone, and kinetic studies suggested the attack of dioxygen on the TBD-enol adduct to be the rate-determining step. This work should encourage the application of TBD as a catalyst for oxidations.

Transesterification in Vitrimer Polymers Using Bifunctional Catalysts: Modeled with Solution-Phase Experimental Rates and Theoretical Analysis of Efficiency and Mechanisms

Recently, thermoset vitrimer polymers have shown significant promise for structural applications because of their ability to be reshaped and remolded due to their covalent adaptive network (CAN). In these vitrimers, the transesterification reaction is responsible for the CAN, where the efficiency of the reaction is controlled either by organic or by organometallic catalysts. Understanding the mechanism of the transesterification reaction in the bulk phase using direct experimental techniques is extremely difficult due to the highly cross-linked complex structure of thermosetting vitrimers. Therefore, we use solution-phase experiments to investigate the catalytic efficiency and to guide density functional theory (DFT) simulations of the transesterification reaction mechanism with catalysts triazabicyclodecene (TBD), zinc acetate (Zn(OAc)₂), 1-methylimidazole (1-MI), and dibutyltin oxide (DBTO). The estimated catalytic efficiency from the detailed DFT reaction path calculations follows the order TBD ≳ DBTO ≳ Zn(OAc)₂ > 1-MI, which agrees with the experimental results. In addition to reaction path modeling, the mechanism and the relative rates of the transesterification reaction are analyzed with the assistance of Fukui indices as a measure of electrophilicity and nucleophilicity of atomic sites and with partial charges. It was found that the sum of the nucleophilicity index of the base and the electrophilicity index of the acid of the bifunctional catalysts correlates with the S_N2 transition state and tetrahedral intermediate energies, which are related to the barrier of the rate-limiting step. This correlation provides a hypothesis for computational prescreening of potentially better catalysts that have an index in a range of values. These results provide a basis for understanding an important part of the mechanism of transesterification in vitrimer systems and may assist with designing new catalysts.

Synthesis of poly(caprolactone)-block-poly[oligo(ethylene glycol)methyl methacrylate] amphiphilic grafted nanoparticles (AGNs) as improved oil dispersants

Amphiphilic polymers have been covalently grafted from a SiO2 core with room temperature polymerizations. These amphiphilic grafted nanoparticles have been found to uptake up to 30 times their mass in crude oil within a 24 hour window.

Neodymium catalysts for polymerization of dienes, vinyl monomers, and ε-caprolactone

This review discusses various neodymium catalysts for stereospecific polymerization of dienes, vinyl monomers, and ε-caprolactone.

Stoichiometric Control over Partial Transesterification of Polyacrylate Homopolymers as Platform for Functional Copolyacrylates

Only recently, post-polymerization modification reactions of unactivated polyacrylates have been emerging as an attractive alternative to utilizing reactive monomers, enabling the synthetic upcycling of these widely applied polymers. Within this contribution, the triazabicyclodecene-catalyzed transesterification of polyacrylates is reported, including the reaction kinetics and the broad scope for macromolecular design of functional copolyacrylates. More specifically, the transesterification is performed under equilibrium conditions with a set of primary alcohols whereby the reaction kinetics and the obtained conversion as a function of stoichiometric excess of alcohol are evaluated. The results show that the obtained conversion is dependent on the polarity of the solvent and of the alcohol. Through this approach, the transesterification degree can be accurately controlled by stoichiometry, enabling the precise modulation of the macromolecular structure. Finally, the utility of this approach is demonstrated to incorporate functional side chains that are incompatible with radical polymerization, to facilitate Diels-Alder and thiol-ene reactions, enabling access to a broad range of functional materials from simple polyacrylate homopolymer precursors.

Rates of transesterification in epoxy-thiol vitrimers

Vitrimers, an important subset of dynamically crosslinked polymer networks, have many technological applications for their excellent properties, and the ability to be re-processed through plastic flow above the so-called vitrification temperature. We report a simple and efficient method of generating such adaptive crosslinked networks relying on transesterification for their bond exchange by utilising the 'click' chemistry of epoxy and thiols, which also has the advantage of a low glass transition temperature. We vary the chemical structure of thiol spacers to probe the effects of concentration and the local environment of ester groups on the macroscopic elastic-plastic transition. The thermal activation energy of transesterification bond exchange is determined for each chemical structure, and for a varying concentration of catalyst, establishing the conditions for the optimal, and for the suppressed bond exchange. However, we also discover that the temperature of elastic-plastic transition is strongly affected by the stiffness (dynamic rubber modulus) of the network, with softer networks having a much lower vitrification temperature even when their bond-exchange activation energy is higher. This combination of chemical and physical control factors should help optimise the processability of vitrimer plastics.

Stereoselective ROP of rac- and meso-Lactides Using Achiral TBD as Catalyst

1,5,7-Triazabicyclo[4.4.0]dec-5-ene (TBD) polymerizes rac-lactide (rac-LA) to form highly isotactic polylactide (PLA) with a Pm = 0.88, while meso-LA yields heterotactic PLA (Pm ~ 0.8) at −75 °C. The stereocontrol of the cryogenic-based ring-opening polymerization comes from a perfect imbrication of both chiral LA and the propagating chiral end-group interacting with the achiral TBD catalyst.

Substituted glycolides from natural sources: preparation, alcoholysis and polymerization

Herein we present a comparative study of substituted glycolides MeGL, iPrGL, iBuGL, BnGL, PhGL and MePhGL, synthesized from natural sources and polymers therefrom.

Nanoformulation-by-design: an experimental and molecular dynamics study for polymer coated drug nanoparticles

Experimental studies of drug–polymer nanoparticle formation combined with molecular dynamics simulations provide atomistic explanations for the high drug loadings obtained.

Formation of bis-benzimidazole and bis-benzoxazole through organocatalytic depolymerization of poly(ethylene terephthalate) and its mechanism

One-pot syntheses of bis-benzimidazole and bis-benzoxazole from poly(ethylene terephthalate) waste bottles were successful through two-step nucleophilic attacks promoted by TBD.

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.

Ionic Organocatalyst with a Urea Anion and Tetra-n-butyl Ammonium Cation for Rapid, Selective, and Versatile Ring-Opening Polymerization of Lactide

A highly active and chemoselective ionic organocatalyst is developed for room-temperature living/controlled ring-opening polymerization of lactide. The catalysts are prepared by a simple dehydration reaction between tetra-n-butyl ammonium hydroxide and an N,N'-diarylurea and used in cooperation with hydroxy initiators. Typically, poly(l-lactide) with near perfect isotacticity and widely tunable molar mass (4-130 kg mol^-1) can be produced in <2 min (turnover frequency up to 120 000 h^-1). Low molar mass distribution is observed in both short and substantially extended reaction times, clearly demonstrating the selectivity of catalyst for monomer enchainment over macromolecular transesterification. Versatile design and construction of diverse polylactide-based macromolecular structures are allowed thanks to the livingness of the polymerization and independence of initiator and catalyst. In addition to the hydrogen bond donor-acceptor type bifunctional activation mechanism, direct nucleophilic attack of the urea anion on the monomer and polymer is also shown which can be suppressed by the added hydroxy initiator.