Ring-opening Polymerization Research Articles

Copolymerization of β-Butyrolactones into Functionalized Polyhydroxyalkanoates Using Aluminum Catalysts: Influence of the Initiator in the Ring-Opening Polymerization Mechanism.

Within bioplastics, natural poly(3-hydroxybutyrate) (PHB) stands out as fully biocompatible and biodegradable, even in marine environments; however, its high isotacticity and crystallinity limits its mechanical properties and hence its applications. PHB can also be synthesized with different tacticities via a catalytic ring-opening polymerization (ROP) of rac-β-butyrolactone (BBL), paving the way to PHB with better thermomechanical and processability properties. In this work, the catalyst family is extended based on aluminum phenoxy-imine methyl catalyst [AlMeL2], that reveals efficient in the ROP of BBL, to the halogeno analogous complex [AlClL2]. As well, the impact on the ROP mechanism of different initiators is further explored with a particular focus in dimethylaminopyridine (DMAP), a hardly studied initiator for the ROP of BBL. A thorough mechanistic study is performed that evidences the presence of two concomitant DMAP-mediated mechanisms, that lead to either a DMAP or a crotonate end-capping group. Besides, in order to increase the possibilities of PHB post-polymerization functionalization, the introduction of a side-chain functionality is explored, establishing the copolymerization of BBL with β-allyloxymethylene propiolactone (BPLOAll), resulting in well-defined P(BBL-co-BPLOAll) copolymers.

Tailoring the Structure-Property Relationship of Ring-Opened Metathesis Copolymers for CO2-Selective Membranes.

In this work, we explore the use of ring-opening metathesis polymerization (ROMP) facilitated by a second-generation Grubbs catalyst (G2) for the development of advanced polymer membranes aimed at CO2 separation. By employing a novel copolymer blend incorporating 4,4'-oxidianiline (ODA), 1,6-hexanediamine (HDA), 1-adamantylamine (AA), and 3,6,9-trioxaundecylamine (TA), along with a CO2-selective poly(ethylene glycol)/poly(propylene glycol) copolymer (Jeffamine2003) and polydimethylsiloxane (PDMS) units, we have synthesized membranes under ambient conditions with exceptional CO2 separation capabilities. The strategic inclusion of PDMS, up to a 20% composition within the PEG/PPG matrix, has resulted in copolymer membranes that not only surpass the 2008 upper limit for CO2/N2 separation but also meet the commercial targets for CO2/H2 separation. Comprehensive analysis reveals that these membranes adhere to the mixing rule and exhibit percolation behavior across the entire range of compositions (0-100%), maintaining robust antiplasticization performance even under pressures up to 20 atm. Our findings underscore the potential of ROMP in creating precisely engineered membranes for efficient CO2 separation, paving the way for their application in large-scale environmental and industrial processes.

Leveraging Electron Push‐Pull Effect for Catalytic Polymerization and Degradation of a Cyclobutane Monomer System

Ring‐opening polymerization (ROP) offers a striking solution to solve problems encountered in step‐growth condensation polymerization, including precise control over molecular weight, molecular weight distribution, and topology. This has inspired our interest in ROP of cycloalkanes with an ultimate goal to rethink polyolefins, which clearly poses a number of challenges. Practicality of ROP of cycloalkanes is actually limited by their low polymerizability and elusive mechanisms which arise from significantly varied ring size and non‐polar C–C bonds in monomers. In this work, by using Lewis acid/Brønsted base/C(sp3)–H initiator system previously developed in our laboratory, we focus on cyclobutanes and explore the positional and electronic effects of substituents on the ring, namely electron push‐pull effect, in promoting controlled polymerization to afford densely functionalized poly(cyclobutanes), as well as catalytic degradation of obtained polymers for upcycling. More importantly, experiments and DFT calculations unveil considerable population of Lewis‐acid‐induced thermostabilized 1,4‐zwitterions, which distinguish cyclobutanes from cyclopropanes and others. All these findings would shed light on catalytic synthesis and degradation of saturated all‐carbon main‐chain polymers, as well as small molecule transformations of cyclobutanes.

Leveraging Electron Push-Pull Effect for Catalytic Polymerization and Degradation of a Cyclobutane Monomer System.

Ring-opening polymerization (ROP) offers a striking solution to solve problems encountered in step-growth condensation polymerization, including precise control over molecular weight, molecular weight distribution, and topology. This has inspired our interest in ROP of cycloalkanes with an ultimate goal to rethink polyolefins, which clearly poses a number of challenges. Practicality of ROP of cycloalkanes is actually limited by their low polymerizability and elusive mechanisms which arise from significantly varied ring size and non-polar C-C bonds in monomers. In this work, by using Lewis acid/Brønsted base/C(sp3)-H initiator system previously developed in our laboratory, we focus on cyclobutanes and explore the positional and electronic effects of substituents on the ring, namely electron push-pull effect, in promoting controlled polymerization to afford densely functionalized poly(cyclobutanes), as well as catalytic degradation of obtained polymers for upcycling. More importantly, experiments and DFT calculations unveil considerable population of Lewis-acid-induced thermostabilized 1,4-zwitterions, which distinguish cyclobutanes from cyclopropanes and others. All these findings would shed light on catalytic synthesis and degradation of saturated all-carbon main-chain polymers, as well as small molecule transformations of cyclobutanes.

Advances in the Synthesis of Poly(phenolic ester)s via Ring‐Opening Polymerization

The poly(phenolic ester)s are attracting growing attention due to their essential role in the application as biodegradable plastics. Thus, extensive efforts have been devoted to the development of methodology that allows facile preparation of poly(phenolic ester)s with controlled molecular weights for widespread utilities. However, it is highly challenging to introduce phenolic ester bond structure into polyesters from ring‐opening polymerization (ROP) to yield aromatic/semiaromatic poly(phenolic ester)s due to severe transesterification reactions. To synthesize poly(phenolic ester)s with desired structures and properties, scientists have developed various ring‐opening polymerization systems with distinct advantages. Here, we have summarized basic features and recent progresses of these methods, including the cyclic phenolic lactone polymerization system, the salicylic acid O‐carboxyanhydride polymerization system, and the dissymmetric cyclic phenolic lactide polymerization system, as well as other copolymerization routes. Furthermore, the advantages and unsettled problems in various synthetic ways are discussed for readers to choose fast and controllable ROP systems for poly(phenolic ester)s.

Synthesis, Structural Characterization of Substituted Phenoxyimine Based Ti(IV) Complexes for Ring Opening Polymerization and DFT Studies

AbstractA series of 4 new titanium complexes bearing phenoxyimine ligands that differ in their steric and electronic properties have been synthesized and investigated for the polymerization of ethylene and rac‐lactide. X‐ray crystal structures of these catalysts reveal compounds 1–3 exhibit distorted octahedral geometry while complex 4 shows distorted trigonal bipyramidal. The substituents on the phenoxyimine framework have a profound influence on the catalytic activities of these compounds in the polymerization reactions. All four complexes afforded polylactide with a heterotactic bias in ring opening polymerization of rac‐lactide. In addition to this, density functional theory calculations using (B3LYP) with the 6‐311++G (d, p) basis set and no constraints were used while doing geometry optimizations and compared with experimental results. Hirshfeld surface analysis, MEP and Mulliken charge also reported an unexpected relationship between the nitrogen, oxygen on the ligands, titanium isopropoxide, and good relation between the experimental findings.

Converting inorganic sulfur into degradable thermoplastics and adhesives by copolymerization with cyclic disulfides

Converting elementary sulfur into sulfur-rich polymers provides a sustainable strategy to replace fossil-fuel-based plastics. However, the low ring strain of eight-membered rings, i.e., S8 monomers, compromises their ring-opening polymerization (ROP) due to lack of an enthalpic driving force and as a consequence, poly(sulfur) is inherently unstable. Here we report that copolymerization with cyclic disulfides, e.g., 1,2-dithiolanes, can enable a simple and energy-saving way to convert elementary sulfur into sulfur-rich thermoplastics. The key strategy is to combine two types of ROP—both mediated by disulfide bond exchange—to tackle the thermodynamic instability of poly(sulfur). Meanwhile, the readily modifiable sidechain of the cyclic disulfides provides chemical space to engineer the mechanical properties and dynamic functions over a large range, e.g., self-repairing ability and degradability. Thus, this simple and robust system is expected to be a starting point for the organic transformation of inorganic sulfur toward sulfur-rich functional and green plastics.

Supersoft Norbornene-Based Thermoplastic Elastomers with High Strength and Upper Service Temperature.

With over 6 million tons produced annually, thermoplastic elastomers (TPEs) have become ubiquitous in modern society, due to their unique combination of elasticity, toughness, and reprocessability. Nevertheless, industrial TPEs display a tradeoff between softness and strength, along with low upper service temperatures, typically ≤100°C. This limits their utility, such as in bio-interfacial applications where supersoft deformation is required in tandem with strength, in addition to applications that require thermal stability (e.g., encapsulation of electronics, seals/joints for aeronautics, protective clothing for firefighting, and biomedical devices that can be subjected to steam sterilization). Thus, combining softness, strength, and high thermal resistance into a single versatile TPE has remained an unmet opportunity. Through de novo design and synthesis of novel norbornene-based ABA triblock copolymers, we fill this gap. Ring-opening metathesis polymerization (ROMP) is employed to prepare TPEs with an unprecedented combination of properties, including skin-like moduli (<100kPa), strength competitive with commercial TPEs (>5MPa), and upper service temperatures akin to high-performance plastics (∼260°C). Furthermore, the materials are elastic, tough, reprocessable, and shelf stable (≥2 months) without incorporation of plasticizer. Structure-property relationships identified herein inform development of next-generation TPEs that are both biologically soft yet thermomechanically durable. This article is protected by copyright. All rights reserved.

Polymerization/Depolymerization-Induced Self-Assembly under Coupled Equilibria of Polymerization with Self-Assembly.

Depolymerization breaks down polymer chains into monomers like unthreading beads, attracting more attention from a sustainability standpoint. When polymerization reaches equilibrium, polymerization and depolymerization can reversibly proceed by decreasing and increasing the temperature. Here, we demonstrate that such dynamic control of a growing polymer chain in a selective solvent can spontaneously modulate the self-assembly of block copolymer micellar nano-objects. Compared to polymerization-induced self-assembly (PISA), where irreversible growth of a solvophobic polymer block from the end of a solvophilic polymer causes micellization, polymerization/depolymerization-induced self-assembly presented in this study allows us to reversibly regulate the packing parameter of the forming block copolymer and thus induce reversible morphological transitions of the nano-objects by temperature swing. Under the coupled equilibria of polymerization with self-assembly, we found that demixing of the growing polymer block in a more selective solvent entropically facilitates depolymerization at a substantially lower temperature. Taking ring-opening polymerization of δ-valerolactone initiated from the hydroxyl-terminated poly(ethylene oxide) as a model system, we show that polymerization/depolymerization/repolymerization leads to reversible morphological transitions, such as rod-sphere-rod and fiber-rod-fiber, during the heating and cooling cycle and accompanied by changes in macroscopic properties such as viscosity, suggesting their potential as dynamic soft materials.

A four-in-one multifunctional self-assembly hydrogel composed of natural drugs for repairing myocardial infarction

To meet the multiple demands of myocardial repair, it would be a novel strategy for myocardial repair if multiple drugs could be constructed into an integrated multifunctional drug formulation. In this study, four drugs with different functions (thioctic acid with antioxidant effects, quercetin with anti-inflammatory and antioxidant effects, arginine with pro-angiogenic effects, and Mn2+ with imaging functions) were selected to construct a four-in-one injectable hydrogel (thioctic acid-arginine-quercetin-Mn2+) through chemical bonding and supramolecular interactions. First, thioctic acid polymerized to a redox-sensitive degradable polymer—poly(thioctic acid) containing disulfide bonds in the main chains through ring-opening polymerization. Quercetin was conjugated to the main chain of the poly(thioctic acid) molecules via thiyl radical-polyphenol Michael addition. Arginine cross-linked the carboxyl groups side chains of the poly(thioctic acid) molecules through hydrogen bonding. Mn2+ further cross-linked the carboxyl groups' side chains of the poly(thioctic acid) molecules through ionic bonding. The hydrogel has antioxidant properties, promotes neovascularization, inhibits inflammatory, improves intracellular Ca2+ overload and mitochondrial dysfunction, protects adenosine triphosphatase (ATPase) activity, and maintains intracellular energy supply, which can reduce the size of myocardial infarcts, and improves cardiac function. This construction method of preparing integrated multifunctional hydrogels from natural drugs will provide a new therapeutic strategy for myocardial repair.

Ring-Opening Polymerization of Cyclohexene Oxide and Cycloaddition with CO2 Catalyzed by Amine Triphenolate Iron(III) Complexes.

A series of novel amine triphenolate iron complexes were synthesized and characterized using UV, IR, elemental analysis, and high-resolution mass spectrometry. These complexes were applied to the ring-opening polymerization (ROP) of cyclohexene oxide (CHO), demonstrating excellent activity (TOF > 11050 h-1) in the absence of a co-catalyst. In addition, complex C1 maintained the dimer in the presence of the reaction substrate CHO, catalyzing the ring-opening polymerization of CHO to PCHO through bimetallic synergy. Furthermore, a two-component system consisting of iron complexes and TBAB displayed the ability to catalyze the reaction of CHO with CO2, resulting in the formation of cis-cyclic carbonate with high selectivity. Complex C4 exhibited the highest catalytic activity, achieving 80% conversion of CHO at a CHO/C4/TBAB molar ratio of 2000/1/8 and a CO2 pressure of 3 MPa for 16 h at 100 °C, while maintaining >99% selectivity of cis-cyclic carbonates, which demonstrated good conversion and selectivity.

In Vitro Biocompatibility and Endothelial Permeability of Branched Polyglycidols Generated by Ring-Opening Polymerization of Glycidol with B(C6F5)3 under Dry and Wet Conditions.

Polyglycidol or polyglycerol (PG), a polyether widely used in biomedical applications, has not been extensively studied in its branched cyclic form (bcPG), despite extensive research on hyperbranched PG (HPG). This study explores the biomedical promise of bcPG, particularly its ability to cross the blood-brain barrier (BBB). We evaluate in vitro biocompatibility, endothelial permeability, and formation of branched linear PG (blPG) as topological impurities in the presence of water. Small angle X-ray scattering in solution revealed a fractal dimension of approximately two for bcPG and the mixture bc+blPG, suggesting random branching. Comparisons of cytotoxicity and endothelial permeability between bcPG, bc+blPG, and HPG in a BBB model using hCMEC/D3 cells showed different biocompatibility profiles and higher endothelial permeability for HPG. bcPG showed a tendency to accumulate around cell nuclei, in contrast to the behavior of HPG. This study contributes to the understanding of the influence of polymer topology on biological behavior.

Reprocessability in Engineering Thermosets Achieved Through Frontal RingOpening Metathesis Polymerization.

While valued for their durability and exceptional performance, crosslinked thermosets are challenging to recycle and reuse. Here, inherent reprocessability in industrially relevant polyolefin thermosetsis unveiled. Unlike prior methods, this approach eliminates the need to introduce exchangeable functionality to regenerate the material, relying instead on preserving the activity of the metathesis catalyst employed in the curing reaction. Frontal ring-opening metathesis polymerization (FROMP) proves critical to preserving this activity. Conditions controlling catalytic viability are explored to successfully reclaim performance across multiple generations of material, thus demonstrating long-term reprocessability. This straightforward and scalable remolding strategy is poised for widespread adoption. Given the anticipated growth in polyolefin thermosets, these findings represent an important conceptual advance in the pursuit of a fully circular lifecycle for thermoset polymers.

Polypeptide and Protein-Based Conjugate Nanoparticles via Aqueous Ring-Opening Polymerization-Induced Self-Assembly (ROPISA).

Protein-polymer conjugates and polymeric nanomaterials hold great promise in many applications including biomaterials, medicine or nanoelectronics. In this work, we present the first PISA (polymerization-induced self-assembly) approach performed in aqueous medium enabling protein-polymer conjugates and nanoparticles entirely composed of amino acids by using ring-opening polymerization (ROP). We indeed show that aqueous ROPISA can be used with protein or peptidic macroinitiators without prior chemical modification and afford the simple preparation of nanomaterials with protein-like property, for example to implement biomimetic thermoresponsivity in drug delivery. This article is protected by copyright. All rights reserved.

Dextran Macroinitiator for Synthesis of Polysaccharide-b-Polypeptide Block Copolymers via NCA Ring-Opening Polymerization.

Synthesis of polysaccharide-b-polypeptide block copolymers represents an attractive goal because of their promising potential in delivery applications. Inspired by recent breakthroughs in N-carboxyanhydride (NCA) ring-opening polymerization (ROP), we present an efficient approach for preparation of a dextran-based macroinitiator and the subsequent synthesis of dextran-b-polypeptides via NCA ROP. This is an original approach to creating and employing a native polysaccharide macroinitiator for block copolymer synthesis. In this strategy, regioselective (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) oxidation of the sole primary alcohol located at the C-6 position of the monosaccharide at the nonreducing end of linear dextran results in a carboxylic acid. This motif is then transformed into a tetraalkylammonium carboxylate, thereby generating the dextran macroinitiator. This macroinitiator initiates a wide range of NCA monomers and produces dextran-b-polypeptides with a degree of polymerization (DP) of the polypeptide up to 70 in a controlled manner (Đ < 1.3). This strategy offers several distinct advantages, including preservation of the original dextran backbone structure, relatively rapid polymerization, and moisture tolerance. The dextran-b-polypeptides exhibit interesting self-assembly behavior. Their nanostructures have been investigated by dynamic light scattering (DLS) and transmission electron microscopy (TEM), and adjustment of the structure of block copolymers allows self-assembly of spherical micelles and worm-like micelles with varied diameters and aspect ratios, revealing a range of diameters from 60 to 160 nm. Moreover, these nanostructures exhibit diverse morphologies, including spherical micelles and worm-like micelles, enabling delivery applications.

Effect of Keratin Waste on Poly(ε-Caprolactone) Films: Structural Characterization, Thermal Properties, and Keratinocytes Viability and Proliferation Studies

Keratin extracted (KE) from chicken feathers was used for the production of composite films comprising poly(ε-caprolactone) (PCL) and keratin (PCL/KE films). The process involved the extraction of keratin from chicken feathers using a 0.1 M NaOH solution, followed by characterization via sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The PCL was synthesized through the ring-opening polymerization (ROP) of ε-caprolactone (ԑ-CL) with Sn(Oct)2 as a catalyst. Films were prepared via solvent casting, including pure PCL films and those enriched with different weight percentages of KE (10%, 15%, 25%, and 30%). The films were characterized by differential scanning calorimetry (DSC), thermogravimetric analysis (TG), and scanning electron microscopy (SEM). SEM analysis revealed a more uniform incorporation of KE within the PCL matrix in the case of the 15% keratin-enriched film (PCL/KE15) as compared to other keratin percentages. The thermal analysis showed a positive influence of keratin on the thermal stability of the films. Keratinocytes viability and proliferation tests on the PCL/KE15 film demonstrated compatibility with cells. Collectively, these results hold relevance for potential biomedical applications of PCL/KE films.

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.

Monomer-Recyclable Polyester from CO2 and 1,3-Butadiene.

Synthesis of monomer-recyclable polyesters solely from CO2 and bulk olefins holds great potentials in significantly reducing CO2 emissions and addressing the issue of plastic pollutions. Due to the kinetic disadvantage of direct copolymerization of CO2 and bulk olefins compared to homopolymerization of bulk olefins, considerable research attention has been devoted to synthesis of polyester via the ring-opening polymerization (ROP) of a six-membered disubstituted lactone intermediate, 1,2-ethylidene-6-vinyl-tetrahydro-2H-pyran-2-one (𝜹-L), obtained from telomerization of CO2 and 1,3-butadiene. However, the conjugate olefin on the six-membered ring of 𝜹-L leads to serious Michael addition side reactions. Thus, selective ROP of 𝜹-L, which can precisely control the repeating unit for the production of polyesters potentially amenable to efficient monomer recycling, remains an unresolved challenge. Herein, we report the first example of selective ROP of 𝜹-L using a combination of organobase and N,N'-Bis[3,5-bis(trifluoromethyl)phenyl]urea as the catalytic system. Systematic modifications of the substituent of the urea shows that the presence of electron-deficient 3,5-bis(trifluoromethyl)-phenyl groups is the key to the extraordinary selectivity of ring opening over Michael addition. Efficient monomer recovery of oligo(𝜹-L) was also achieved under mild catalytic conditions. This article is protected by copyright. All rights reserved.

Remarkable impact of chain backbone on the performance of Poly(norbornene derivatives)-based anion exchange membranes

Chemical stability and the trade-off between ion conductivity and dimensional stability are two primary challenges for the development of suitable anion exchange membranes (AEMs). Herein, a series of non-crosslinked poly(norbornene derivatives)-based AEMs containing a bulky steric hindrance hydrophobic arylene substituent were prepared by vinyl addition polymerization (VAP), ring-opening metathesis polymerization (ROMP), and ROMP followed post-hydrogenation, respectively. Compared with ROMP and hydrogenated type membranes, VAP-type membranes, especially the VAP-N-50, exhibited excellent dimensional stability with limited swelling ratio (SR = 27.9 %) while higher water uptake (WU = 213.8 %) at 80 °C, which is attributed to its rigid VAP-type cyclic chain backbone. Microtopography study demonstrated the existence of nanoscale phase separation in VAP-type AEMs and its association with water uptake and swelling behavior. VAP-N-60 showed excellent hydroxide conductivity up to 105.5 mS cm−1 at 80 °C, while exhibited superior alkaline stability that was not found in ROMP-type membrane ROMP-N-50 and the hydrogenated-type membrane H-ROMP-N-50. After being immersed in 2 M NaOH solution at 80 °C for 1200 h, the hydroxide conductivity loss of VAP-N-60 was only 3.0 %. Furthermore, a H2/O2 single cell using VAP-N-50 membrane achieved the highest peak power density of 722 mW cm−2 at 60 °C without back pressure.

From Health Supplement to Versatile Monomer: Radical Ring-Opening Polymerization and Depolymerization of α-Lipoic Acid

The radical ring-opening polymerization (rROP) of α-lipoic acid (LA) and its derivatives represents a synthetically accessible, efficient, and scalable strategy to impart degradability into functional copolymers. This review highlights recent advances in the design of sustainable materials containing LA through rROP driven by heat and/or light.