Cationic Ring-opening Polymerization Research Articles

Amphiphilic Heterograft Copolymers Bearing Biocompatible/Biodegradable Grafts.

The amphiphilic heterograft copolymers bearing biocompatible/biodegradable grafts [poly(2-methyl-2-oxazoline-co-2-pentyl-2-oxazoline)-g-poly(d-l-lactic acid)/poly(2-ethyl-2-oxazoline)] were synthesized successfully by the combination of cationic ring-opening polymerization and click chemistry via the ⟨"grafting to"⟩ approach. The challenge of this synthesis was to graft together hydrophobic and hydrophilic chains on a hydrophilic platform based on PMeOx. The efficiency of grafting depends on the chemical nature of the grafts and of the length of the macromolecular chains. The self-assembly of these polymers in aqueous media was investigated by DLS, cryo-TEM, and SANS. The results demonstrated that different morphologies were obtained from nanospheres and vesicles to filaments depending on the hydrophilic weight ratio in the heterograft copolymer varying from 0.38 until 0.84. As poly(2-ethyl-2-oxazoline) is known to be thermoresponsive, the influence of temperature rise on the nanoassembly stability was studied in water and in a physiological medium. SANS and DLS measurements during a temperature ramp allowed to show that nanoassemblies start to self-assemble in "raspberry like" primary structures at 50 °C, and these structures grow and get denser as the temperature is increased further. These amphiphilic heterograft copolymers may include hydrophobic drugs and should find important applications for biomedical applications which require stealth properties.

Synthesis of Amphiphilic Block Copolymer and Its Application in Pigment-Based Ink.

Amphiphilic block copolymers-based aqueous color inks show great potential in the field of visual communication design. However, the conventional step-by-step chemistry employed to synthesize the amphiphilic block copolymers is intricate, with low yield and high economic and environmental costs. In this work, we present a novel method for preparing an amphiphilic AB di-block copolymer of PCL-b-PAA by employing a combined polymerization strategy that involves both cationic ring-opening polymerization (ROP) of the ε-caprolactone monomer and the reversible addition-fragmentation chain-transfer (RAFT) polymerization on the acrylic acid monomer simultaneously. The corresponding polycaprolactone (PCL) and polyacrylic acid (PAA) serve as the hydrophobic and hydrophilic units, respectively. The effectiveness of the amphiphilic AB di-block copolymer as the polymeric pigment dispersant for water-based color inks is evaluated. The amphiphilic AB di-block copolymer of PCL-b-PAA exhibits a molecular weight of 1400 g mol-1, which is consistent with the theoretical value and suitable for polymeric dispersant application. The high surface excess (Γmax) of the PCL-b-PAA in water indicates a densely packed molecular morphology at the water/air interface. Additionally, micelles can be stably formed in the aqueous PCL-b-PAA solution at very low concentrations by demonstrating a low CMC value of 10-4 wt% and a micelle dimension of approximately 30 nm. The model ink dispersion is prepared using organic dyes (Disperse Yellow 232) and the amphiphilic block copolymer of PCL-b-PAA. The dispersion demonstrates near-Newtonian behavior, which is highly favorable for the application as inkjet ink. Furthermore, the ink dispersion displays a low viscosity, making it particularly suitable for visual communication design and printing purposes. Moreover, the ink dispersion demonstrates an unimodal distribution of the particle size, with an average diameter of approximately 500 nm. It retains exceptional stability of dispersion and even conducts a thermal aging treatment at 60 °C for 5 days. This work presents a facile and efficient synthetic strategy and molecular design of AB di-block copolymer-based dispersants for dye dispersions.

Characteristics of novel cycloaliphatic epoxides based on UV-induced cationic ring-opening polymerization for plastic coatings

Cationic ring-opening polymerization (CROP)-capable cycloaliphatic epoxide monomers bearing a benzyl ether group (CE-BEs) were developed as glass-replacement plastic coatings for lightweight automobiles. Three different monomers of bis(((7-oxabicyclo[4,1,0]heptan-3-yl)methoxy)methyl)benzene isomers were synthesized to provide the cycloaliphatic epoxide functional groups. 1H and 13C nuclear magnetic resonance and Fourier transform infrared (FT-IR) spectroscopic analyses confirmed that the monomers were successfully synthesized. The shear viscosity and real-time crosslinking behavior of the CROP coatings were investigated using a rheometer. In particular, the release of thermal energy via CROP under UV irradiation was monitored using differential scanning photocalorimetry. The reaction conversion of cycloaliphatic epoxides by CROP before and after UV irradiation was verified using FT-IR spectroscopy. The transparency of the CROP coating films cured on a polycarbonate substrate was measured using an ultraviolet–visible spectrophotometer, and their adhesion was confirmed using cross-cut tests. For characterization of the surface mechanical properties, a nanoindentation tester and a nanoscratch tester were used in conjunction with an atomic force microscope to evaluate the surface hardness and scratch resistance, respectively. In addition, the thermomechanical properties of the cured CROP coating films were investigated using a rigid-body pendulum tester operated in dynamic physical mode. The ternary coating systems with CE-BEs were found to exhibit high photoreactivity, a dense crosslinking density, a transparent appearance, and enhanced adhesion and mechanical properties, making it suitable for glass-replacement plastic coatings.

Amino-modified 2-oxazoline copolymers for complexation with DNA

Novel amino-functionalized 2-oxazoline-based copolymers able to form complexes with DNA were obtained. Their efficiency of DNA condensation into polyplexes of scales appropriate for effective cellular internalization was studied.

Protecting group free synthesis of nitroxide-functionalized poly(2-oxazoline)s: direct access to electroactive polynitroxides.

Herein, we report the simple and direct cationic ring opening polymerization (CROP) of a nitroxide bearing 2-oxazoline monomer to yield redox-active poly[1-oxyl-2,2,6,6-tetramethylpiperidin-4-(2-oxazoline)] (PTOx) with no requirement for protecting group chemistries. The spin and redox activity of the polymer are quantitatively retained as confirmed by cyclic voltammetry and electron paramagnetic resonance spectroscopy, while yielding a comparable oxidation potential to that of PTMA in preliminary electrochemical characterization.

Mechanism of cationic ring-opening polymerisation of ε-caprolactone using metallocene/borate catalytic systems: a DFT and NCI study on chain initiation, propagation and termination.

We present a comprehensive DFT investigation on the cationic ring-opening polymerisation (CROP) of ε-caprolactone (CL) using zirconocene/borate catalyst systems. All possible pathways of the interaction between cationic species [Cp2ZrMe+] and counteranions, [A-] = [MeB(C6F5)3]- and [B(C6F5)4]-, were examined during chain initiation, propagation, and termination steps. The calculations reveal an active chain-end mechanism with O-alkyl bond cleavage of the polymerisation. The catalytic performance of the two counteranions is found to be identical, and they influence the initial process through stabilisation of the cationic species via non-covalent interactions (NCI), with the [MeB(C6F5)3]- anion stabilising the catalyst-monomer complex more effectively than the [B(C6F5)4]- anion by 24.3 kJ mol-1. The first two propagations are likely the rate-determining step, with calculated free-energy barriers of 61.4-71.2 and 73.9-80.6 kJ mol-1 with and without the anions (A-), respectively. The presence of the counteranion significantly affects the third propagation rate, lowering the barriers up to 20 kJ mol-1. Comparison of the first termination and the third propagation shows that they are not competitive, with the termination being less facile. We also studied the initiation and propagation steps for the hafnocene catalyst and found that the Hf catalyst slightly favours the CL CROP in comparison to the Zr catalyst. Analysis of solvent and dispersion interaction demonstrates that both factors play an important role in the process. NCI analysis reveals weak (van der Waals) interactions at the contacts between the cationic species and the counteranions during the reaction course. Overall, our results offer insights into the structures and interactions involved in the polymerisation.

Metal-free living cationic ring-opening polymerization of cyclic esters using selenonium salts as Lewis acids

Selenonium salts were employed as a new class of metal-free Lewis acid catalysts for the cationic ring-opening polymerization (ROP) of various cyclic esters.

Stereoregular poly(2-phenylthiirane) via cationic ring-opening polymerization.

Herein, we describe an effective strategy for synthesizing polythioethers with a well-defined structure through the cationic polymerization of thiirane with electron-withdrawing substituents. This strategy allows for precisely controlling the regio- and stereochemistry of the ring-opening polymerization of 2-phenylthiirane, thus allowing for producing poly(2-phenylthiirane) with high stereoregularity using enantiomeric pure thiirane.

Solving fundamental concepts in supramolecular science with functionality-tolerant living polymerizations of self-assembling monomers and dendronized monomers

The evolution and development of several examples of functionality-tolerant living polymerizations to the level of perfection that they could be employed to solve fundamental concepts in supramolecular science by living polymerization of self-assembling monomers and self-organizable dendronized monomers is briefly reviewed. The review focuses on the development of the living polymerization methodology with brief examples on how they impacted the field of self-assembly and self-organization. The first polymerization reaction discussed is the stereoselective polymerization of phenylacetylene and of other arylacetylenes to generate helical poly(arylacetylene) stereoisomers. The transition from functionality non-tolerant to functionality-tolerant stereoselective polymerizations and the evolution to functionality-tolerant living stereoselective polymerization of phenylacetylene is used as the main example of this brief review. This living polymerization methodology is followed by living polymerization of vinyl ethers, oxazolines, of group transfer polymerization, of cationic ring-opening polymerization of cyclic siloxanes combined with hydrosilylation, of ROMP of cylooxanorbornene. This brief review is concluded by a brief discussion of the capabilities of the above-mentioned living methodologies with living radical polymerizations. The numerous applications in the field of supramolecular science of these living methodologies are not reviewed. However, the reader is directed to numerous comprehensive review articles discussing these applications. The challenges that remain to be solved in all these functionality-tolerant living polymerizations are presented.

Designing Polymer Electrolytes via Ring‐Opening Polymerization for Advanced Lithium Batteries

AbstractReplacing liquid electrolytes with solid‐state polymer electrolytes (SPEs) can solve the safety hazards of Li metal batteries (LMBs) while increasing their energy density. However, there has been limited success so far in preparing advanced SPEs with controllable molecular structure and chemical composition, posing great obstacles to further promoting its application in LMBs. Recently, ring‐opening polymerization (ROP), including cationic ROP, anionic ROP, and ring‐opening metathesis polymerization, has become a dazzling new star in achieving SPEs due to its mild polymerization conditions and controllable chemical composition (molecular structure, functional group), etc. Besides, there is no small molecule released during the polymerization process, which means reduced interfacial side reaction. Hence, in this review, the merits of ROP in preparing SPEs and its mechanism as well as interfering factors, etc are evaluated from the perspective of synthetic chemistry. Furthermore, the review focuses on outlining the existing cases related to ROP as much as possible and summarize them from different ring structures (from triple ring to multivariate ring) and polymerization methods, hoping to provide a comprehensive understanding and serve as strategic guidance for designing high‐performance SPEs. Challenges and opportunities regarding this burgeoning field are also discussed at the end.

Synthesis and cure kinetics of bisoxazoline monomers during cationic ring‐opening polymerization

AbstractIn this work, the synthesis and characterization of highly aromatic bisoxazoline (BOX) monomers containing diphenyl ether, furan, and thiophene backbones are presented. Preliminary investigations of the cure and reaction kinetics are performed to understand the impact of these moieties on polymerization and their glass transition temperatures. To do this, two catalysts are used, methyl triflate (MT) and dodecyl benzene sulfonic acid (DBS) to explore their role in controlling the cationic ring‐opening polymerization (CROP) mechanism. Polymerization was monitored using non‐isothermal differential scanning calorimetry and characterized according to the Kissinger and Ozawa models. Kinetic modeling using the Malek and Sestak‐Berggren methods showed excellent agreement with experimental values and was used to determine reaction rate constants. The polymerization of BOX monomers in the presence of both MT and DBS is shown to be highly latent, being stable until the melting point is reached, after which reaction occurs rapidly.

Cationic ring-opening polymerization of 2-oxazolines and 2-oxazines in biomass-derived solvents

In this study, we investigate the cationic ring-opening polymerization (CROP) of 2-oxazolines and 2-oxazines in two biomass-derived solvents, namely isosorbide dimethyl ether (DMI) and dihydrolevoglucosenone (Cyrene), environmentally friendly alternatives to conventional, fossil-based solvents such as acetonitrile and chlorobenzene. DMI matched the CROP kinetics and control of acetonitrile, with the advantage of being a non-toxic and biodegradable solvent. Furthermore, the living character of the polymerization process in DMI enabled us to synthesize well-defined, low-dispersity polymers with precise length and chain-end functionality. Furthermore, the potential of DMI is showcased by the successful synthesis of a triblock copolymer comprising three different monomers, as well as poly(2-ethyl-2-oxazoline) with a wide range of chain lengths. In turn, the polymerization rates were faster in Cyrene, but its application is limited by potential chain transfer reactions. Overall, this study may help to evaluate greener solvents and methods for polymer production, thereby mitigating the environmental impact of the increasing demand for polymer materials.

Microstructural Analysis of Benzoxazine Cationic Ring-Opening Polymerization Pathways.

Herein, an evaluation of the initial step of benzoxazine polymerization is presented by mass spectrometry, with a focus on differentiating the phenoxy and phenolic products formed by distinct pathways of the cationic ring opening polymerization (ROP) mechanism of polybenzoxazine formation. The use of infrared multiple photon dissociation (IRMPD) and ion mobility spectrometry (IMS) techniques allows for differentiation of the two pathways and provides valuable insights into the ROP mechanism. The results suggest that type I pathway is favored in the initial stages of the reaction yielding the phenoxy product, while type II product should be observed at later stages when the phenoxy product would interconvert to the most stable type II phenolic product. Overall, the findings presented here provide important information on the initial step of the benzoxazine polymerization, allowing the development of optimal polymerization conditions and represents a way to evaluate other multifunctional polymerization processes.

Enhancement of elongation at break and UV-protective properties of poly(lactic acid) film with cationic ring opening polymerized (CROP)-lignin

In this study, the intrinsic brittleness of poly(lactic acid) (PLA) was overcome by chemical modification using ethyl acetate-extracted lignin (EL) via cationic ring-opening polymerization (CROP). The CROP was conducted to promote homopolymerization under starvation of the initiator (oxyrane). This method resulted in the formation of lignin-based polyether (LPE). LPE exhibited enhanced interfacial compatibility with nonpolar and hydrophobic PLA owing to the fewer hydrophilic hydroxyl groups and a long polyether chain. In addition, because of the UV-protecting and radical-scavenging abilities of lignin, LPE/PLA exhibited multifunctional properties, resulting in improved chemical properties compared with the neat PLA film. Notably, one of the LPE/PLA films (EL_MCF) exhibited excellent elongation at break of 297.7% and toughness of 39.92MJ/m3. Furthermore, the EL_MCF film showed superior UV-protective properties of 99.52% in UVA and 88.95% in UVB ranges, both significantly higher than those of the PLA film, without sacrificing significant transparency in 515nm. In addition, the radical scavenging activity improved after adding LPE to the PLA film. These results suggest that LPEs can be used as plasticizing additives in LPE/PLA composite films, offering improved physicochemical properties.

Design, synthesis and curing mechanism of two novel photothermal dual-curing adhesives for propellants and explosives

Photothermal dual-curing adhesive is not only required to realize the basic curing function, but also has the characteristics of rapid setting and strong curing, which possesses a vital role in the molding speed, stability and structure integrity for 3D-printed propellants and explosives. Herein, the acrylate hydroxyl terminated polybutadiene, as novel photothermal dual-curing binders, were designed and synthesized utilizing cationic ring opening polymerization and active monomer mechanism as the strategy of photothermal dual-curing reaction. The mechanical properties and thermal stability of the photothermal dual-curing elastomers were systematically investigated. The results suggested that the target MAHTPB(Acrylate hydroxy‑terminated polybutadiene)-based adhesives could be cured rapidly within 5 s under UV light irradiation and completely cured in 1.5 h under heating conditions. Specifically, the elastomer film formed by MAHTPB-based photothermal dual-curing has a tensile strength of 4.63 MPa and an elongation of 386%, which exhibits stronger mechanical properties than the elastomer film formed by single photo- or thermal-curing. As a result, the synthesized photothermally cured adhesives have performed 3D printing experiments and achieved relatively satisfactory printing effects. Our study aims to solve the problems of short photocuring time, slow curing rate and incomplete curing for traditional photocuring, which lays a solid foundation to achieve rapid prototyping and precise performance control in 3D printing of propellants and explosives.

Solvation structure reorganization and interface regulation of poly (glycidyl POSS)-based electrolyte for quasi-solid-state lithium-ion batteries

The interfacial stability and some unexpected side reactions in quasi-solid-state lithium-ion batteries (LIBs) impede the practical application of the in-situ crosslinked polymer electrolytes. Herein, a novel in-situ crosslinked polymer electrolyte with eight-armed crosslinked supramolecular structure is constructed via cationic ring-opening polymerization of glycidyl polyhedral oligomeric silsesquioxane (POSS). The strong electrostatic and hydrogen bonding interactions of the POSS blocks with anions reorganize the solvation structure, and the overall oxidation resistance of anions can be also effectively enhanced benefiting from the relatively electron-withdrawing effect of the POSS blocks. Simultaneously, a hierarchical cathode-electrolyte interphase with flexibility and oxidation resistance is constructed involving the boron difluoride radical-catalyzed cleavage of Si-O-Si linkages in POSS frameworks. The poly (glycidyl POSS)-based electrolyte enables the Li||NCM83 cell to possess a high capacity retention of 79.1 % after 500 cycles. Moreover, the SiOx||NCM83 battery shows a capacity retention of 87.6 % after 200 cycles. These insights gained form this work opens up an avenue for the development and practical application of quasi-solid-state LIBs.

Mechanism of Action of Oxazoline-Based Antimicrobial Polymers Against Staphylococcus aureus: In Vivo Antimicrobial Activity Evaluation.

Antimicrobial-resistant pathogens have reached alarming levels, becoming one of the most pressing global health issues. Hence, new treatments are necessary for the fight against antimicrobial resistance. Synthetic nanoengineered antimicrobial polymers (SNAPs) have emerged as a promising alternative to antimicrobial peptides, overcoming some of their limitations while keeping their key features. Herein, a library of amphiphilic oxazoline-based SNAPs using cationic ring-opening polymerization (CROP) is designed. Amphipathic compounds with 70% cationic content exhibit the highest activity against clinically relevant Staphylococcus aureus isolates, maintaining good biocompatibility in vitro and in vivo. The mechanism of action of the lead compounds against S. aureus is assessed using various microscopy techniques, indicating cell membrane disruption, while the cell wall remains unaffected. Furthermore, a potential interaction of the compounds with bacterial DNA is shown, with possible implications on bacterial division. Finally, one of the compounds exhibits high efficacy in vivo in an insect infection model.

Simultaneous Interpenetrating Polymer Networks Based on Poly(2‐Oxazoline)s

AbstractInterpenetrating polymer networks (IPNs), comprised of two or more independent crosslinked networks in which the individual networks are interlaced, can be used to enhance material properties and increase functionality for applications such as tissue engineering, drug delivery, and biofabrication. IPNs can be formed by either simultaneous or sequential crosslinking, with sequential crosslinking being complicated by the need to infiltrate the constituents of the second network into the first network. Herein, the study reports the first simultaneous IPN based on the cationic ring‐opening polymerization (CROP) of 2‐methyl‐2‐oxazoline (MeOx) with bis(butyl‐2‐oxazoline) (BBOx) crosslinker and the reversible addition‐fragmentation chain‐transfer (RAFT) polymerization of N,N‐dimethylacrylamide (DMAAm) with N,N`‐methylene bis(acrylamide) (BAM) crosslinker. Specifically, the compatibility of the synthesis techniques is demonstrated for the preparation of simultaneous IPNs, and it is shown that, by varying the amounts of the two crosslinkers and comparing to single‐component networks, the equilibrium degree of swelling (EDS) in water and compressive modulus can be tuned. The results reported demonstrate the utility of CROP and RAFT for preparing IPNs and suggest that with appropriate optimization the technique can be expanded to other monomer pairs which are polymerizable via CROP and RAFT.

Lamp vs Laser: A Visible Light Photoinitiator That Promotes Radical Polymerization at Low Intensities and Cationic Polymerization at High Intensities.

A visible light absorbing anthraquinone derivative 1-tosyloxy-2-methoxy-9,10-anthraquinone (QT) mediates both cationic and radical polymerizations depending on the intensity of visible light used. A previous study showed that this initiator generates para-toluenesulfonic acid through a stepwise, two-photon excitation mechanism. Thus, under high-intensity irradiation, QT generates acid in sufficient quantities to catalyze the cationic ring-opening polymerization of lactones. However, under low-intensity (lamp) conditions, the two-photon process is negligible, and QT photooxidizes DMSO, generating methyl radicals which initiate the RAFT polymerization of acrylates. This dual capability was utilized to switch between radical and cationic polymerizations to synthesize a copolymer using a one-pot procedure.

Synthesis and characterization of dendronized side chain liquid crystalline Poly(2-oxazoline)s towards biomimetic ion channels

The polymerization of dendronized monomers is an attractive option to synthesize liquid crystalline columnar polymers with side chain dendrons. Following this approach, we report for the first time in the present study the synthesis of a family of side chain liquid crystalline (SCLC) poly(2-oxazoline)s, poly(2-(3,4,5-tris(4-dodecyloxybenzyloxy)phenyl)-2-oxazoline) (PTOx) from its oxazoline monomer precursor, 2-(3,4,5-tris(4-dodecyloxybenzyloxy)phenyl)-4,5-dihydro-1,3-oxazole) (TAPOx), by cationic ring-opening polymerization (CROP). The optimisation of the reaction parameters (temperature, type of initiator, terminating agent, solvent and monomer concentration), combined with the nature of the CROP allowed us to obtain high molecular weight SCLC poly(2-oxazoline)s. NMR investigations were consistent with the targeted molecular weights of the synthesized PTOx and the living nature of TAPOx polymerization. Regarding the mesomorphic characterization, all synthesized acyl-substituted poly(ethyleneimine)s exhibited liquid crystalline mesophases in a broad temperature range. XRD studies demonstrated that these dendronized poly(2-oxazoline)s self-assemble into columnar structures. Mesomorphic and thermal properties suggest that these family of poly(2-oxazoline)s could be excellent candidates to build up membranes for proton transport applications.