Ring-opening Polymerization Of Lactones Research Articles

Weak Interaction Activates Esters: Reconciling Catalytic Activity and Turnover Contradiction by Tailored Chalcogen Bonding.

The activation of esters by strong Lewis acids via the formation of covalent adducts is a classic strategy to give reactivity; however, this approach frequently incurs limited turnover due to the low efficiency in the dissociation of catalyst from a stable catalyst-product complex. While the use of some weak interaction catalysts that can easily dissociate from any bonding complexes in the reaction system would solve this catalyst turnover problem, the poor catalytic activity in the ester activation that can be provided by these noncovalent forces in turn sets up a formidable challenge. Herein, we describe the activation and catalytic transformation of esters by weak interactions, which provides a promising platform to reconcile the catalytic activity and turnover problems. Several tailored chalcogen-bonding catalysts were developed for the activation of esters, enabling achieving several inherently low reactive Diels-Alder reactions as well as the ring-opening polymerization of lactones through weak chalcogen bonding interactions. This supramolecular catalysis approach is particularly highlighted by its capability to promote some uncommon Diels-Alder reactions involving using dienes bearing electron-withdrawing groups coupled by α,β-unsaturated ester as dienophiles and substrate incorporating competitive Lewis basic sites, in which typical strong Lewis acids showed low catalytic efficiency, while representative hydrogen and halogen bonding catalysts were inactive.

Visible Light-Regulated Ring-Opening Polymerization of Lactones by Employing Indigo as a Photoacid Catalyst.

The development of visible light-regulated polymerizations for precision synthesis of polymers has drawn considerable attention in the past years. In this study, an ancient dye, indigo, is successfully identified as a new and efficient photoacid catalyst, which could readily promote the ring-opening polymerization of lactones under visible light irradiation in a well-controlled manner, affording the desired polyester products with predictable molecular weights and narrow dispersity. The enhanced acidity of indigos by excitation is crucial to the H-bonding activation of the lactone monomers. Chain extension and block copolymer synthesis are also demonstrated with this method. This article is protected by copyright. All rights reserved.

Unexpected Periodicity in Cationic Group 5 Initiators for the Ring-Opening Polymerization of Lactones.

ε-Caprolactone (ε-CL) adducts of cationic, amine tris(phenolate)-supported niobium(V) and tantalum(V) ethoxides initiate the ring-opening polymerization of lactones. The Ta(V) species prepared and applied catalytically herein exhibits higher activity in the ring-opening polymerization (ROP) of ε-caprolactone than the previously reported, isostructural Nb(V) complex, contradicting literature comparisons of Nb(V)- and Ta(V)-based protocols. Both systems also initiate the ROP of δ-valerolactone and rac-β-butyrolactone, kinetic studies confirming retention of higher activity by the Ta congener. Polymerizations of rac-β-butyrolactone and δ-valerolactone were previously unrealized under Group V- or Ta-mediated conditions, respectively, although the former has afforded only low molecular weight, cyclic poly-3-hydroxybutyrate. Cationic ethoxo-Nb(V) and -Ta(V) δ-valerolactone adducts are also reported, demonstrating the facility of δ-valerolactone as a ligand and the generality of the synthetic method. Both δ-valerolactone-bearing complexes initiate the ROP of ε-caprolactone, δ-valerolactone, and rac-β-butyrolactone. Accordingly, we have elucidated trends in reactivity and investigated the initiation mechanism for such systems, the insertion event being predicated upon intramolecular nucleophilic attack on the coordinated lactone by the adjacent alkoxide moiety. This mechanism enables quantitative, stoichiometric installation of a single monomer residue distinct from the bulk of the polymer chain, and permits modification of polymer properties via both manipulation of the molecular architecture and tuning of the polymerization kinetics, and thus dispersity, through hitherto inaccessible independent control of the initiation event.

Investigation of monomer reactivity, polymer microstructure and solubility in the copolymerization of 1,5-dioxepan-2-one with alkyl substituted lactones

Ring Opening Polymerization of lactones is an excellent synthetic tool for the production of polyesters with tuned microstructure. In copolyesters, the polymer microstructure is an important feature that can greatly influence the properties. Therefore, it is desirable to investigate the copolymerization behaviour of monomers. In this work, the copolymerization of 1,5-dioxepan-2-one (DXP) with the potentially renewable alkyl substituted lactones δ-undecalactone (UDL) and β,δ-trimethyl-ε-caprolactone (TMCL) was investigated. The reactivity ratios were determined for both monomer pairs, and revealed that both substituted lactones react significantly different with DXP. Furthermore, the microstructure of copolymers from DXP and UDL with different monomer feed ratios was characterized by quantitative 13C NMR and MALDI-ToF MS analysis. The resulting copolymers exhibited a varying degree of randomness depending on the monomer feed ratio. The lactones in this study were selected for their different solubility properties. The Hansen solubility spheres were determined for the homo-and copolymers of DXP and UDL. Using this, we demonstrated that the polymer solubility properties can be tuned by copolymerization of polar and apolar monomers.

Ring Opening Copolymerization of Boron-Containing Anhydride with Epoxides as a Controlled Platform to Functional Polyesters.

Boron-functionalized polymers are used in opto-electronics, biology, and medicine. Methods to produce boron-functionalized and degradable polyesters remain exceedingly rare but relevant where (bio)dissipation is required, for example, in self-assembled nanostructures, dynamic polymer networks, and bio-imaging. Here, a boronic ester-phthalic anhydride and various epoxides (cyclohexene oxide, vinyl-cyclohexene oxide, propene oxide, allyl glycidyl ether) undergo controlled ring-opening copolymerization (ROCOP), catalyzed by organometallic complexes [Zn(II)Mg(II) or Al(III)K(I)] or a phosphazene organobase. The polymerizations are well controlled allowing for the modulation of the polyester structures (e.g., by epoxide selection, AB, or ABA blocks), molar masses (9.4 < Mn < 40 kg/mol), and uptake of boron functionalities (esters, acids, "ates", boroxines, and fluorescent groups) in the polymer. The boronic ester-functionalized polymers are amorphous, with high glass transition temperatures (81 < Tg < 224 °C) and good thermal stability (285 < Td < 322 °C). The boronic ester-polyesters are deprotected to yield boronic acid- and borate-polyesters; the ionic polymers are water soluble and degradable under alkaline conditions. Using a hydrophilic macro-initiator in alternating epoxide/anhydride ROCOP, and lactone ring opening polymerization, produces amphiphilic AB and ABC copolyesters. Alternatively, the boron-functionalities are subjected to Pd(II)-catalyzed cross-couplings to install fluorescent groups (BODIPY). The utility of this new monomer as a platform to construct specialized polyesters materials is exemplified here in the synthesis of fluorescent spherical nanoparticles that self-assemble in water (Dh = 40 nm). The selective copolymerization, variable structural composition, and adjustable boron loading represent a versatile technology for future explorations of degradable, well-defined, and functional polymers.

Synthesis of ROS-responsive poly(thioacetal)s with narrow molecular weight distributions via lactone ring-opening polymerization

Poly(thioacetal)s with narrow molecular weight distributions were synthesized via lactone ring-opening polymerization. They showed ROS-responsive degradability according to their electronic structures.

Visible Light-Regulated Organocatalytic Ring-Opening Polymerization of Lactones Using Hydroxybenzophenones as Photocatalyst

Visible Light-Regulated Organocatalytic Ring-Opening Polymerization of Lactones Using Hydroxybenzophenones as Photocatalyst

Stereoselective Ring-Opening Polymerization of Lactones with a Fused Ring Leading to Semicrystalline Polyesters

Stereoselective Ring-Opening Polymerization of Lactones with a Fused Ring Leading to Semicrystalline Polyesters

Kinetic Modeling of Ring Opening Polymerization of Lactones under Microwave Irradiation

AbstractA kinetic study on the mathematical modeling of polymerization rate and molar mass development in the ring opening bulk polymerization (ROP) of lactones under microwave irradiation (MI), for the production of biodegradable green polymers used in the biomedical sector, is presented. Two modeling approaches, one based on calculation of average properties using a self‐developed code based on the method of moments, and the other one providing calculation of full molar mass distributions with the aid of the Predici software are contrasted. The observed enhancement on polymerization rate under MI is captured well by using a non‐thermal microwave effect modeling approach, namely, a microwave‐enhanced propagation model. The proposed approach is validated with available experimental data for ROP of ε‐caprolactone, a monomer which can be obtained from biomasses, using benzyl alcohol (BzOH) and stannous octoate (SnOc)2 as initiator and catalyst, respectively, at 150 °C. Seven case studies are analyzed, including ROPs carried out under both conventional heating (CH) and MI. The effect of initiator and alcohol initial concentrations on polymerization rate and molar mass distributions is analyzed. The advantages of using MI in ROP are assessed.

Controlled Random Terpolymerization of β -Propiolactone, Epoxides, and CO 2 via Regioselective Lactone Ring Opening

The random ring-opening terpolymerization of CO2, epoxides, and lactones remains challenging, mainly because CO2/epoxide copolymerization and lactone ring-opening polymerization typically proceed a...

Structure and activity relationship studies of N-heterocyclic olefin and thiourea/urea catalytic systems: application in ring-opening polymerization of lactones

Structure–activity relationship studies of N-heterocyclic olefin and thiourea/urea catalytic systems were performed and applied to ROP of lactones.

Visible light-induced living/controlled cationic ring-opening polymerization of lactones

Ring-opening polymerization of lactones has served as one of the most resourceful and versatile methods for the production of polyesters. However, the photocontrolled ring-opening polymerization of lactones with the advantages of being inexpensive, green, and noninvasive, is still rarely reported. In this work, we developed a series of composite photoacid generators containing a common photocatalyst and an onium salt to induce the living/controlled cationic ring-opening polymerization of lactones using benzyl alcohol or butyl alcohol as an initiator under visible light. The wavelength of the light could be easily adjustable by applying different photocatalysts. Moreover, radical species are generated concurrently during the electron transfer processes; as a result, simultaneous living/controlled cationic ring-opening polymerization of lactones and reversible addition–fragmentation chain transfer radical (RAFT) polymerization can be performed using hydroxy group capped trithiocarbonate to produce hybrid block copolymers. Photocontrolled ring-opening polymerization of lactones with the advantages of being inexpensive, green, and noninvasive, is still rarely reported. In this work, we developed a series of composite photoacid generators containing a common photocatalyst and an onium salt to induce the living/controlled cationic ring-opening polymerization of lactones using alcohol compound as an initiator under visible light. The wavelength of the light could be easily adjustable by applying different photocatalysts. Moreover, simultaneous living/controlled cationic ring-opening polymerization of lactones and reversible addition–fragmentation chain transfer radical (RAFT) polymerization of methyl acrylate can be performed using hydroxy group capped trithiocarbonate to produce hybrid block copolymers in one step.

High Molecular‐Weight Cyclic Polyesters from Solvent‐Free Ring‐Opening Polymerization of Lactones with a Pyridyl‐Urea/MTBD

Abstract(Thio)urea/base systems have been widely used in the ring‐opening polymerization (ROP) of lactones based on their superior performance in activity and selectivity. Herein, a pyridyl‐urea (6C‐PU)/7‐methyl‐1,5,7‐triazabicyclo[4.4.0]dec‐5‐ene catalytic system is used to prepare the polyesters with cyclic topology via the ROP of lactones in the absence of initiator under solvent‐free conditions. The catalytic system shows high activity in the ROP of δ‐valerolactone (δ‐VL) and cyclic polyvalerolactones (PVLs) with high molecular weights and narrow molecular weight distribution are obtained despite the existence of some linear products generated during the precipitation process. The structure of the resulting polymers is determined by proton and carbon nuclear magnetic resonance spectra, matrix assisted laser desorption/ionization time of flight mass spectrometry, and intrinsic viscosity studies. A possible mechanism is proposed on the basis of NMR analysis and characteristics of polymerization. Thermal and mechanical properties of cyclic PVLs are investigated through differential scanning calorimetry, thermogravimetric analysis, and tensile test.

Imidodiphosphorimidate (IDPi) as an efficient organocatalyst for controlled/living ring-opening polymerization of lactones

Imidodiphosphorimidate (IDPi) is demonsatreted as a novel and efficient acid/base bifunctional organocatalyst for controlled/living ring-opening polymerization of lactones, which delivered the metal-free poly(δ-valerolactone) and poly(ε-caprolactone) with excellent control over the molecular weight and narrow dispersity at a low catalyst loading under mild conditions. NMR and MALDI-TOF characterizations, kinetic study, and chain extension experiment suggest a well-controlled/living nature of the current ROP of lactones catalyzed by the IDPi catalyst.

Readily Prepared and Tunable Ionic Organocatalysts for Ring-opening Polymerization of Lactones

Highly potent ionic organocatalyst is developed for room-temperature controlled ring-opening polymerization (ROP) of lactones, including δ-valerolactone, ε-caprolactone, and δ-hexalactone. The catalysts are prepared by simply mixing tetra-n-butyl ammonium hydroxide and a (thio)urea at elevated temperature under vacuum, and used in cooperation with an alcoholic initiator. The performance of the catalyst is readily adjusted and optimized through variation of the (thio)urea precursor, catalyst composition, and reaction condition. Urea-derived catalysts are generally superior to thiourea-derived ones. Provided with proper N-substituents, the catalyst affords both high polymerization efficiency and high selectivity for monomer enchainment over macromolecular transesterification, even at high monomer conversion and/or substantially extended reaction time. In addition to acidity, structural symmetry of the urea also proves decisive for the catalytic activity, which enables a catalyst-assisted proton transfer process for the ring-opening of lactone and thus provides a novel mechanistic insight for ROP catalyzed by hydrogen-bonding type bifunctional ionic organocatalysts.

Easy access to oxygenated block polymers via switchable catalysis

Oxygenated block polyols are versatile, potentially bio-based and/or degradable materials widely applied in the manufacture of coatings, resins, polyurethanes and other products. Typical preparations involve multistep syntheses and/or macroinitiator approaches. Here, a straightforward and well-controlled one-pot synthesis of ABA triblocks, namely poly(ether-b-ester-b-ether), and ABCBA pentablocks, of the form poly(ester-b-ether-b-ester’-b-ether-b-ester), using a commercial chromium catalyst system is described. The polymerization catalysis exploits mechanistic switches between anhydride/epoxide ring-opening copolymerization, epoxide ring-opening polymerization and lactone ring-opening polymerization without requiring any external stimuli. Testing a range of anhydrides, epoxides and chain-transfer agents reveals some of the requirements and guidelines for successful catalysis. Following these rules of switch catalysis with multiple monomer additions allows the preparation of multiblock polymers of the form (ABA)n up to 15 blocks. Overall, this switchable catalysis delivers polyols in a straightforward and highly controlled manner. As proof of potential for the materials, methods to post-functionalize and/or couple the polyols to make higher polymers are demonstrated.

Amides as Non-polymerizable Catalytic Adjuncts Enable the Ring-Opening Polymerization of Lactide With Ferrous Acetate Under Mild Conditions

Sn-based catalysts are effective in the ring-opening polymerization (ROP) but are toxic. Fe(OAc)2 used as an alternative catalyst is suitable for the ROP of lactide only at higher temperatures (>170°C), associated with racemization. In the ROP of ester and amide group containing morpholinediones with Fe(OAc)2 to polydepsipeptides at 135°C, ester bonds were selectively opened. Here, it was hypothesized that ROP of lactones is possible with Fe(OAc)2 when amides are present in the reactions mixture as Fe-ligands could increase the solubility and activity of the metal catalytic center. The ROP of lactide in the melt with Fe(OAc)2 is possible at temperatures as low as 105°C, in the presence of N-ethylacetamide or N-methylbenzamide as non-polymerizable catalytic adjuncts (NPCA), with high conversion (up to 99 mol%) and yield (up to 88 mol%). Polydispersities of polylactide decreased with decreasing reaction temperature to ≤ 1.1. NMR as well as polarimetric studies showed that no racemization occurred at reaction temperatures ≤145°C. A kinetic study demonstrated a living chain-growth mechanism. MALDI analysis revealed that no side reactions (e.g., cyclization) occurred, though transesterification took place.

Performance Comparison of Commercial and Home-Made Lipases for Synthesis of Poly(δ-valerolactone) Homopolymers

Novozyme 435, which is the commercially available immobilized form of Candida antarctica lipase B, has been successfully conducted ring opening polymerization of lactones in organic solvents. In this paper, it was aimed to in... | Find, read and cite all the research you need on Tech Science Press

Hydrogen Bonding-Based Non-Metallic Organocatalysts for Ring-Opening Polymerization of Lactones

Hydrogen Bonding-Based Non-Metallic Organocatalysts for Ring-Opening Polymerization of Lactones

H-Bonding Organocatalysts for the Living, Solvent-Free Ring-Opening Polymerization of Lactones: Toward an All-Lactones, All-Conditions Approach

The developing urea class of H-bond donors facilitates the solvent-free ROP of lactones at ambient and elevated temperatures, displaying enhanced rates and control versus other known organocatalysts for ROP under solvent-free conditions. The ROPs retain the characteristics of living polymerizations despite solidifying prior to full conversion, and copolymers can be accessed in a variety of architectures. One-pot block copolymerizations of lactide and valerolactone, which had previously been inaccessible in solution phase organocatalytic ROP, can be achieved under these reaction conditions, and one-pot triblock copolymers are also synthesized. For the ROP of lactide, however, thioureas remain the more effective H-bond donating class. For all (thio)urea catalysts under solvent-free conditions and in solution, the more active catalysts are generally more controlled. A rationale for these observations is proposed. The triclocarban (TCC) plus base systems are particularly attractive in the context of solvent-f...