Cationic Ring-opening Copolymerization Research Articles

Organo-Catalyzed Cationic Ring-Opening Copolymerization of Cyclic Anhydrides with Oxolanes: Access to Structurally Diverse Polyesters

Organo-Catalyzed Cationic Ring-Opening Copolymerization of Cyclic Anhydrides with Oxolanes: Access to Structurally Diverse Polyesters

Multifunctional Poly(2-ethyl-2-oxazoline) Copolymers Containing Dithiolane and Pentafluorophenyl Esters as Effective Reactive Linkers for Gold Surface Coatings.

Surface functionalization with biological macromolecules is an important task for the development of sensor materials, whereby the interaction with other biological materials should be suppressed. In this work, we developed a novel multifunctional poly(2-ethyl-2-oxazoline)-dithiolane conjugate as a versatile linker for gold surface immobilization of amine-containing biomolecules, containing poly(2-ethyl-2-oxazoline) as antifouling polymer, dithiolane for surface immobilization, and activated esters for protein conjugation. First, a well-defined carboxylic acid containing copoly(2-ethyl-2-oxazoline) was synthesized by cationic ring-opening copolymerization of 2-ethyl-2-oxazoline with a methyl ester-containing 2-oxazoline monomer, followed by postpolymerization modifications. The side-chain carboxylic groups were then converted to amine-reactive pentafluorophenyl (PFP) ester groups. Part of the PFP groups was used for the attachment of the dithiolane moiety, which can efficiently bind to gold surfaces. The final copolymer contained 1.4 mol% of dithiolane groups and 4.5 mol% of PFP groups. The copolymer structure was confirmed by several analytical techniques, including NMR spectroscopy and size-exclusion chromatography. The kinetics of the PFP ester aminolysis and hydrolysis demonstrated significantly faster amidation compared to hydrolysis, which is essential for subsequent protein conjugation. Successful coating of gold surfaces with the polymer was confirmed by spectroscopic ellipsometry, showing a polymer brush thickness of 4.77 nm. Subsequent modification of the coated surfaces was achieved using bovine serum albumin as a model protein. This study introduces a novel reactive polymer linker for gold surface functionalization and offers a versatile polymer platform for various applications including biosensing and surface functionalization.

Cationic ring-opening copolymerization of a cyclic acetal and γ-butyrolactone: monomer sequence transformation and polymerization–depolymerization control by vacuuming or temperature changes

Polymerization–depolymerization equilibrium is a promising strategy for the construction of polymerization systems through which sustainable polymers can undergo reversible polymer–monomer transformations. In this study, we perform monomer sequence transformation and copolymer depolymerization, which are based on transacetalization reactions and polymerization–depolymerization equilibrium, in the cationic ring-opening copolymerization of 2-methyl-1,3-dioxepane and γ-butyrolactone with a protonic acid. The removal of monomer molecules from the copolymerization solution by vacuuming with a vacuum pump caused monomer sequence to transform into pseudo-alternating copolymer chains and subsequently depolymerize into oligomers. Increasing the temperature during copolymerization also resulted in depolymerization, while copolymers were regenerated by the subsequent decrease in temperature.

Synthesis and Comparative Study of Polyether-b-polybutadiene-b-polyether Triblock Copolymers for Use as Polyurethanes.

In this paper, the effects of HTPBs with different main-chain microstructures on their triblock copolymers and polyurethane properties were investigated. Three polyether-modified HTPB triblock copolymers were successfully synthesized via a cationic ring-opening copolymerization reaction using three HTPBs with different microstructures prepared via three different polymerization methods as the macromolecular chain transfer agents and tetrahydrofuran (THF) and propylene oxide (PO) as the copolymerization monomers. Finally, the corresponding polyurethane elastomers were prepared using the three triblock copolymers as soft segments and toluene diisocyanate (TDI) as hard segments. The results of an analysis of the triblock copolymers showed that the triblock copolymers had lower viscosity and glass transition temperature (Tg) values as the HTPB 1,2 structure content decreased, although the effect on the thermal decomposition temperature was not significant. An analysis of the polyurethane elastomers revealed that as the content of the 1,2 structure in HTPB increased, its corresponding polyurethane elastomers showed a gradual increase in breaking strength and a gradual decrease in elongation at break. In addition, PU-1 had stronger crystallization properties compared to PU-2 and PU-3. However, the differences in the microstructures of the HTPBs did not seem to have much effect on the surface properties of the polyurethane elastomers.

Biobased Copolymers via Cationic Ring-Opening Copolymerization of Levoglucosan Derivatives and ε-Caprolactone.

Simultaneous ring-opening copolymerization is a powerful strategy for the synthesis of highly functional copolymers from different types of cyclic monomers. Although copolymers are essential to the plastics industry, environmental concerns associated with current fossil-fuel-based synthetic polymers have led to an increasing interest in the use of renewable feedstock for polymer synthesis. Herein, we report a scalable synthetic platform to afford unique polysaccharides with different pendant functional groups from biomass-derived levoglucosan and ε-caprolactone via cationic ring-opening copolymerization (cROCOP). Biocompatible and recyclable bismuth triflate was identified as the optimal catalyst for cROCOP of levoglucosan. Copolymers from tribenzyl levoglucosan and ε-caprolactone, as well as from tribenzyl and triallyl levoglucosan, were successfully synthesized. The tribenzyl levoglucosan monomer composition ranged from 16% to 64% in the copolymers with ε-caprolactone and 22% to 79% in the copolymers with triallyl levoglucosan. The allylic levoglucosan copolymer can be utilized as a renewably derived scaffold to modify copolymer properties and create other polymer architectures via postpolymerization modification. Monomer reactivity ratios were determined to investigate the copolymer microstructure, indicating that levoglucosan-based copolymers have a gradient architecture. Additionally, we demonstrated that the copolymer glass transition temperature (Tg, ranging from -44.3 to 33.8 °C), thermal stability, and crystallization behavior could be tuned based on the copolymer composition. Overall, this work underscores the utility of levoglucosan as a bioderived feedstock for the development of functional sugar-based copolymers with applications ranging from sustainable materials to biomaterials.

Newly developed gel polymer electrolytes based on crosslinked poly(2-oxazolines)

Advanced materials based on polyoxazoline chemistry are presented as electrochemically, mechanically and thermally stable, efficient and versatile “green” gel polymer electrolytes (GPEs). A series of GPEs was prepared by cationic ring-opening copolymerization (CROP) of two 2-oxazolines with different ratios of the comonomers and their subsequent crosslinking and swelling in Li salt solution. The samples were investigated in terms of their ionic conductivity, thermal properties and ionic diffusion. Finally, a lithium stripping/plating experiment was used to evaluate their electrochemical stability. Promising electrolytes possessing high conductivity (3.7·10−4 S/cm at 20 °C) and excellent durability were obtained.

Synthesis and Degradation of Vinyl Polymers with Evenly Distributed Thioacetal Bonds in Main Chains: Cationic DT Copolymerization of Vinyl Ethers and Cyclic Thioacetals.

We report a novel method to synthesize degradable poly(vinyl ether)s with cleavable thioacetal bonds periodically arranged in the main chains using controlled cationic copolymerization of vinyl ethers with a 7-membered cyclic thioacetal (7-CTA) via degenerative chain transfer (DT) to the internal thioacetal bonds. The thioacetal bonds, which are introduced into the main chain by cationic ring-opening copolymerization of 7-CTA with vinyl ethers, serve as in-chain dormant species to allow homogeneous propagation of vinyl ethers for all internal segments to afford copolymers with controlled overall and segmental molecular weights. The obtained polymers can be degraded into low- and controlled-molecular-weight polymers with narrow molecular weight distributions via hydrolysis. Various vinyl ethers with hydrophobic, hydrophilic, and functional pendants are available. Finally, one-pot synthesis of multiblock copolymers and their degradation into diblock copolymers are also achieved.

Ternary hybrid materials based on the photoinduced cationic polymerization of functional twin monomer and epoxides

Homogeneous ternary silicone hybrid materials comprising phenolic resins and disubstituted polysiloxane with crosslinked epoxy resin were conveniently prepared by the photoinduced cationic ring-opening copolymerization of twin monomer (2-methyl-2-(3-glycidoxypropyl)-4H-1,3,2-benzodioxa-siline, MGS) and epoxy monomer (3,4-epoxycyclohexylmethyl-3′,4′-epoxycyclohexane, EPOX). The two monomers had good compatibility, and no phase separation occurred during long-term storage. Under the excitation, the cationic ring-opening polymerization of MGS rapidly occurred to form polysiloxane and phenolic resin, and EPOX played the role of a crosslinking agent. The reaction mechanism was explicitly proven by infrared spectroscopy, solid-state 13C and 29Si nuclear magnetic resonance spectroscopy, surface contact angle, and X-ray photoelectron spectroscopy. SEM showed that the photocured film had no macroscopic phase separation, and the film had very good light transmittance. This study provided a new rapid method of preparing highly transparent ternary hybrid materials at room temperature through photopolymerization. It has potential applications in the fields of coatings, photoresists, and optical devices.

Copolymerizability Evaluation in Cationic Vinyl-Addition and Ring-Opening Copolymerization of Vinyl Ethers and Oxiranes: Effects of Bulkiness and the Number of Substituents Introduced into Oxiranes

Copolymerizability Evaluation in Cationic Vinyl-Addition and Ring-Opening Copolymerization of Vinyl Ethers and Oxiranes: Effects of Bulkiness and the Number of Substituents Introduced into Oxiranes

Synthesis and properties of l-lactide/1,3-dioxolane copolymers: preparation of polyesters with enhanced acid sensitivity

Herein, we report the first example of cationic ring-opening copolymerization of 5-membered cyclic acetal (1,3-dioxolane (DXL)) with l-lactide (LA) to afford polylactide containing acetal units.

Inspired by mussel adhesive protein: hydrophilic cationic copoly(2-oxazoline)s carrying catecholic side chains

The cationic ring-opening copolymerization of 2-ethyl-2-oxazoline and 3,4-dimethoxyaryl-substituted 2-oxazolines yields gradient or random copolymers, which can be converted into adhesive copolymers carrying catecholic and cationic groups.

Thiol-Substituted Poly(2-oxazoline)s with Photolabile Protecting Groups-Tandem Network Formation by Light.

Herein, we present a novel polymer architecture based on poly(2-oxazoline)s bearing protected thiol functionalities, which can be selectively liberated by irradiation with UV light. Whereas free thiol groups can suffer from oxidation or other spontaneous reactions that degrade polymer performance, this strategy with masked thiol groups offers the possibility of photodeprotection on demand with spatio-temporal control while maintaining polymer integrity. Here, we exploit this potential for a tandem network formation upon irradiation with UV light by thiol deprotection and concurrent crosslinking via thiol-ene coupling. The synthesis of the novel oxazoline monomer 2-{2-[(2-nitrobenzyl)thio]ethyl}-4,5-dihydrooxazole (NbMEtOxa) carrying 2-nitrobenzyl-shielded thiol groups and its cationic ring-opening copolymerization at varying ratios with 2-ethyl-2-oxazoline (EtOxa) is described. The tandem network formation was exemplarily demonstrated with the photoinitator 2-hydroxy-2-methylpropiophenone (HMPP) and pentaerythritol tetraacrylate (PETA), a commercially available, tetrafunctional vinyl crosslinker. The key findings of the conducted experiments indicate that a ratio of ~10% NbMEtOxa repeat units in the polymer backbone is sufficient for network formation and in-situ gelation in N,N-dimethylformamide.

Antibacterial and pH-responsive Quaternized Hydroxypropyl Cellulose-g-Poly(THF-co-epichlorohydrin) Graft Copolymer: Synthesis, Characterization and Properties

The novel quaternized hydroxypropyl cellulose-g-poly(THF-co-epichlorohydrin) graft copolymers, HPC-g-QCP(THF-co-ECH), have been successfully synthesized to combine the properties from hydrophilic hard HPC biomacromolecular backbone and hydrophobic flexible polyether branches. Firstly, the P(THF-co-ECH) living chains were synthesized by cationic ring-opening copolymerization of THF with ECH. Secondly, P(THF-co-ECH) living chains were grafted onto HPC backbone by reaction with —OH groups along HPC to produce HPC-g-P(THF-co-ECH) graft copolymers. Thirdly, the mentioned graft copolymers were quaternized by reaction with ternary amine to generate functionalized HPC-g-QCP(THF-co-ECH). The HPC-g-QCP(THF-co-ECH) graft copolymers exhibited good antibacterial ability against S. aureus or E. coli bacteria. The ibuprofen (IBU)-loaded microparticles of HPC-g-(QC)P(THF-co-ECH) graft copolymers were prepared by electrospraying. The in vitro pH-responsive drug-release behavior of IBU reached up to 75% of drug-loaded at pH = 7.4. This quaternized graft copolymer was beneficial to solving the problems of a burst effect and fast release of HPC as drug carriers.

Tandem Unzipping and Scrambling Reactions for the Synthesis of Alternating Copolymers by the Cationic Ring-Opening Copolymerization of a Cyclic Acetal and a Cyclic Ester.

Cationic copolymerization of different types of monomers, 4-hydroxybutyl vinyl ether (HBVE) and ε-caprolactone (CL), was explored using EtSO3H as an acid catalyst, producing copolymers with a remarkably wide variety of compositions and sequences. In the initial stage of the reaction, HBVE was unexpectedly isomerized to 2-methyl-1,3-dioxepane (MDOP), followed by concurrent copolymerization of MDOP and CL via active chain end and activated monomer mechanisms, respectively. The compositions and sequences of the copolymers were tunable, depending on the initial monomer concentrations. Moreover, a unique method was developed for transforming a copolymer with no CL homosequences into an "alternating" copolymer by removing MDOP from the system using a vacuum pump. This was achieved by the tandem reactions of depolymerization (unzipping) and random transacetalization (scrambling) under thermodynamic control. Specifically, the unzipping of HBVE homosequences proceeded at the oxonium chain end until a nondissociable ester bond emerged next to the chain end, while the scrambling of the main chain via transacetalization transferred midchain HBVE homosequences into the polymer chain end.

Facile Synthesis of Functional Poly(ε-caprolactone) via Janus Polymerization

Functionalized aliphatic polyesters attract increasing attentions as biocompatible and biodegradable polymers with broad applications in biological science. In this contribution, we propose a facile and controllable synthetic technique for functional poly(ε- caprolactone) (PCL) via Janus polymerization, which comprises cationic ring-opening copolymerization (ROP) of ε-caprolactone (CL) with 3,3-bis(chloromethyl) oxacyclobutane (CO) and (coordinated) anionic ROP of CL at a single propagating chain by rare earth metal triflates (RE(OTf)3) and propylene oxide, thus generating block copolymers in one step. The compositions of the copolymers of poly(CLb-( CL-r-CO)) can be modulated by various RE(OTf)3. Scandium triflate catalyzes Janus polymerization to yield the copolymers containing the highest CO contents among all the RE(OTf)3 catalysts used with complete conversion of CL. The chlorine in CO repeating units is ready to be transferred into azide group which affords the modification sites to react with 9-ethynyl-9-fluorenol and mPEG-alkyne, respectively, via copper(I)-catalyzed azide-alkyne cycloaddition reaction with quantitative conversions of azides, as confirmed by FTIR analyses. According to NMR and SEC analyses, copolymers (PCC-g-PEG) bearing a homo-PCL block and a PEG-grafted block of poly(CO-co-CL) demonstrate well-defined chemical structures. The investigations on thermal properties reveal the strong phase separation between PCL and PEG blocks. The amphiphilic PCC-g-PEG is able to self-assemble into micelles in aqueous solution while cylindrical and lamellar morphologies are observed in bulk. We provide an efficient protocol to synthesize functional PCL combining onestep Janus polymerization and precise post-polymerization click reaction.

Generation of “Living” Species Using Perfluoroalkylsulfonic Acids in Concurrent Cationic Vinyl-Addition and Ring-Opening Copolymerization via Crossover Reactions

“Living” species-mediated propagation reactions were demonstrated to occur in the cationic vinyl-addition and ring-opening copolymerization of isopropyl vinyl ether and isobutylene oxide (IBO) with CF3SO3H (TfOH) as an initiator. The polymerization proceeded by the carbocations as propagating species formed by the dissociation of a terminal covalent carbon–OTf bond. Importantly, the covalent species were generated exclusively at the IBO-derived propagating end, which was indicated by both the incorporation of a quencher fragment into the ω-end of the product copolymer and 19F NMR analysis of the copolymerization reaction. The generation of reversibly dissociable covalent species, or “dormant” species, from one of the two monomers was crucial for allowing the even propagation of the propagating chains. Moreover, the reaction conditions were optimized to suppress side reactions such as chain transfer via β-proton elimination. Copolymers with molecular weights that agree relatively well with the theoretical values were produced using C4F9SO3H as an initiator in less polar solvents at lower temperature.

Functional Polyesters with Pendant Double Bonds Prepared by Coordination–Insertion and Cationic Ring-Opening Copolymerizations of ε-Caprolactone with Renewable Tulipalin A

The synthesis of functional copolyesters that contain pendant double bonds in their structures is reported by ring-opening copolymerization of renewable monomer Tulipalin A (α-methylene-γ-butyrolactone, MBL) and e-caprolactone (CL) using either coordination–insertion or monomer activated mechanisms. Aluminum tris(isopropoxide) (Al(OiPr)3) was successfully used as a cheap and commonly available catalyst for the coordination–insertion ring-opening copolymerization, and functional copolyesters with dispersities below 1.2 and with contents of MBL units in the copolymer up to 25 mol % were prepared. In addition, linear or multiarm copolymers of MBL with CL were synthesized by cationic ring-opening copolymerization that was conducted using protic acid as a “metal-free” catalyst in combination with mono- or multihydroxyl alcohols as initiators. The molecular characteristics and composition of the functional copolyesters were determined by GPC, NMR, two-dimensional NMR, and MALDI-TOF spectroscopy. The effect of M...

Functional polylactide by cationic ring-opening copolymerization of lactide with epoxides

Sequential and simultaneous cationic copolymerizations of lactide with commercial functional epoxides: allyl glycidyl ether, glycidyl propargyl ether, and epichlorohydrin, catalyzed by a protic acid in a one-pot process were studied. Block and gradient polylactide-based medium-molecular-weight copolymers with several alkene, alkyne, or chloromethyl groups at one chain end or with gradient distribution along the polymer chain were successfully synthesized, as proven by 1H NMR, SEC, and MALDI TOF analyses. Functional polylactides were further subjected to thiol-ene addition, cycloaddition of azide, or reaction with tertiary amine, respectively, to demonstrate the reactivity of the introduced functional groups.

Concurrent Cationic Vinyl-Addition and Coordination Ring-Opening Copolymerization via Orthogonal Propagation and Transient Merging at the Propagating Chain End.

Controlled cationic vinyl-addition polymerization of an alkyl vinyl ether (VE) and ring-opening polymerization of ε-caprolactone (CL) simultaneously proceeded using HfCl4/Hf(OBu)4 as a dual-role catalyst for both mechanisms, yielding a graft copolymer consisting of a poly(VE) main chain and several poly(CL) side chains. The copolymer of conventionally incompatible monomers was generated via the unprecedented mechanisms consisting of orthogonal propagating reactions and transient merging. Specifically, the poly(CL) chains were incorporated into a poly(VE) chain through an exchange reaction between the VE-derived alkoxy group and the propagating poly(CL) chain at the acetal moiety of the propagating end of the poly(VE) chain. An appropriate ratio of HfCl4 and Hf(OBu)4 was indispensable for both the simultaneous vinyl-addition and ring-opening polymerizations and the alkoxy group exchange reaction.

Poly(THF-co-cyano ethylene oxide): Cyano Ethylene Oxide (CEO) Copolymerization with THF Leading to Multifunctional and Water-Soluble PolyTHF Polyelectrolytes

Cyano-functional polyether copolymers based on THF were prepared via cationic ring-opening copolymerization of THF with cyano ethylene oxide (CEO). The CEO content of poly(tetrahydrofuran) (polyTHF) based copolymers varied from 3.3 to 29.3%, and molecular weights ranged from 5100 to 31900 g·mol–1 with Mw/Mn in the range of 1.31 to 1.74 (SEC in THF, PS standards). The polymerization was conducted with methyl trifluoromethanesulfonate (MeOTf) as an initiator. Kinetic studies concerning incorporation of both monomers were performed via NMR spectroscopy. The cyano groups at the poly(THF-co-CEO) copolymers enable direct access to amino (polyTHF–NH2) and carboxyl groups (polyTHF–COOH) in facile one-step procedures, respectively. The modified copolymers were characterized via NMR, MALDI–ToF mass, and FT-IR spectroscopy. Thermal properties of the materials were studied via differential scanning calorimetry (DSC), demonstrating a gradual decrease of the melting points with increasing amount of CEO in the copolymer...