Cationic Polymerization Of Vinyl Ethers Research Articles

Recent Developments on Cationic Polymerization of Vinyl Ethers

Recent Developments on Cationic Polymerization of Vinyl Ethers

Asymmetric Ion-Pairing Photoredox Catalysis for Stereoselective Cationic Polymerization under Light Control.

By virtue of noninvasive regulations by light, photocontrolled polymerizations have attracted considerable attention for the precision synthesis of macromolecules. However, a cationic polymerization with simultaneous photocontrol and tacticity-regulation remains elusive so far. Herein, we introduce an asymmetric ion-pairing photoredox catalysis strategy that allows for the development of a stereoselective cationic polymerization with concurrent light regulation for the first time. By employing an ion pair catalyst (PC+/*A-) consisting of a photoredox active cation (PC+) and a sterically confined chiral anion (*A-) to deliver the stereochemical control, the cationic polymerization of vinyl ethers can be achieved with photocontrol and high isotactic selectivity (up to 91% m) at a remarkable low catalyst loading (50 ppm).

Dual control of stereoregularity and molecular weight in cationic polymerization of vinyl ether by tunable TADDOLs/TiCl4 initiating systems

The stereoregularity and molecular weight of poly(isobutyl vinyl ether) was simultaneously controlled by TADDOL/TiCl4 initiating systems with various aryl substituents on TADDOL.

Rapid, visible light‐controlled cationic polymerization of vinyl ethers for 3D printing of chemically reprocessable networks under ambient conditions

AbstractLight‐mediated 3D printing techniques have gained significant interest due to the inherent advantages of light as external stimuli, including spatiotemporal control and easy access. As 3D printing processes require rapid polymerization, free radical or cationic polymerization methods are used. However, these polymerization reactions are limited to the production of materials with properties that cannot be chemically altered post‐printing. In this work, a rapid, open‐to‐air photo‐controlled cationic reversible addition‐fragmentation chain‐transfer polymerization of vinyl ethers is demonstrated in the presence of a three‐component photoinitiating system comprising a photosensitizer, electron donor, and acceptor as co‐initiators under the irradiation with blue light. The polymerization mechanism shows rapid kinetics and controlled, living polymerization characteristics. Trithiocarbonate chain ends of poly(isobutyl vinyl ethers) are reactivated to produce block copolymers with cyclohexyl vinyl ethers. The rapid kinetics and water tolerance of the reported system enable the 3D printing of polymeric solids under ambient (e.g., room temperature and open to air) conditions, followed by the effective reactivation of trithiocarbonate chain ends to post‐synthetically modify the object with an acrylate‐based fluorescent monomer via a controlled radical polymerization strategy.

Ortho-Alkoxy-benzamide Directed Formation of a Single Crystalline Hydrogen-bonded Crosslinked Organic Framework and Its Boron Trifluoride Uptake and Catalysis.

Boron trifluoride (BF3 ) is a highly corrosive gas widely used in industry. Confining BF3 in porous materials ensures safe and convenient handling and prevents its degradation. Hence, it is highly desired to develop porous materials with high adsorption capacity, high stability, and resistance to BF3 corrosion. Herein, we designed and synthesized a Lewis basic single-crystalline hydrogen-bond crosslinked organic framework (HC OF-50) for BF3 storage and its application in catalysis. Specifically, we introduced self-complementary ortho-alkoxy-benzamide hydrogen-bonding moieties to direct the formation of highly organized hydrogen-bonded networks, which were subsequently photo-crosslinked to generate HC OFs. The HC OF-50 features Lewis basic thioether linkages and electron-rich pore surfaces for BF3 uptake. As a result, HC OF-50 shows a record-high 14.2 mmol/g BF3 uptake capacity. The BF3 uptake in HC OF-50 is reversible, leading to the slow release of BF3 . We leveraged this property to reduce the undesirable chain transfer and termination in the cationic polymerization of vinyl ethers. Polymers with higher molecular weights and lower polydispersity were generated compared to those synthesized using BF3 ⋅ Et2 O. The elucidation of the structure-property relationship, as provided by the single-crystal X-ray structures, combined with the high BF3 uptake capacity and controlled sorption, highlights the molecular understanding of framework-guest interactions in addressing contemporary challenges.

Ortho‐Alkoxy‐benzamide Directed Formation of a Single Crystalline Hydrogen‐bonded Crosslinked Organic Framework and Its Boron Trifluoride Uptake and Catalysis

AbstractBoron trifluoride (BF3) is a highly corrosive gas widely used in industry. Confining BF3 in porous materials ensures safe and convenient handling and prevents its degradation. Hence, it is highly desired to develop porous materials with high adsorption capacity, high stability, and resistance to BF3 corrosion. Herein, we designed and synthesized a Lewis basic single‐crystalline hydrogen‐bond crosslinked organic framework (HCOF‐50) for BF3 storage and its application in catalysis. Specifically, we introduced self‐complementary ortho‐alkoxy‐benzamide hydrogen‐bonding moieties to direct the formation of highly organized hydrogen‐bonded networks, which were subsequently photo‐crosslinked to generate HCOFs. The HCOF‐50 features Lewis basic thioether linkages and electron‐rich pore surfaces for BF3 uptake. As a result, HCOF‐50 shows a record‐high 14.2 mmol/g BF3 uptake capacity. The BF3 uptake in HCOF‐50 is reversible, leading to the slow release of BF3. We leveraged this property to reduce the undesirable chain transfer and termination in the cationic polymerization of vinyl ethers. Polymers with higher molecular weights and lower polydispersity were generated compared to those synthesized using BF3 ⋅ Et2O. The elucidation of the structure–property relationship, as provided by the single‐crystal X‐ray structures, combined with the high BF3 uptake capacity and controlled sorption, highlights the molecular understanding of framework‐guest interactions in addressing contemporary challenges.

Organocatalytic stereoselective cationic polymerization of alkenyl vinyl ethers and post-functionalization via click chemistry

Vinyl polymer tacticity is critical for regulating the thermal and physical properties of materials. Stereoselective cationic polymerization of vinyl ethers has gained significant progress in recent years, while monomer scope beyond simple alkyl vinyl ethers to access functionalized isotactic polymer materials remains to be explored but highly desirable. Herein, we report the successful development of a stereoselective cationic polymerization of alkenyl vinyl ethers by employing confined Brønsted acid organocatalysis. This organocatalytic system shows high efficiency and stereoselectivity in the polymerization of several alkenyl vinyl ethers, as well as good compatibility to the diolefinic monomers without touching the C=C bonds in the alkenyl part during the cationic polymerization, thus allowing for further modification on these C-C double bonds after polymerization to construct functionalized, isotactic polymer materials. Further, a series of thermoplastic copolymers with tunable properties and variable and predictable contents of side-chain C=C bonds can be synthesized through the corresponding stereoselective copolymerization. Sequential post-polymerization modification of both isotactic homopolymers and copolymers by combining thiol-ene and sulfur(VI) fluoride exchange (SuFEx) click reactions is also demonstrated.

The development of highly efficient monophosphonium photocatalysts for the visible light-regulated metal-free cationic polymerization of vinyl ethers

Monophosphonium salts designed via P+-doping of benzo-anthracene have been identified as a new and highly efficient class of tunable photocatalysts for the visible light-regulated cationic RAFT polymerization of vinyl ethers.

Suspension and emulsion aqueous cationic homopolymerization and copolymerization of cyclohexyl vinyl ether by B(C6F5)3 initiating system

Aqueous cationic suspension polymerization and emulsion polymerization of cyclohexyl vinyl ether (CHVE) were successfully achieved by CumOH/B(C6F5)3/Et2O initiating system. The effects of the main initiator concentration, reaction temperature, and surfactant types on the conversion and polymerization rate were investigated. This work broke through the aqueous cationic polymerization of vinyl ether monomer at −15 °C and significantly improved the molecular weight of the polymer. The copolymerization behavior of CHVE with IBVE, n-BVE aqueous suspension polymerization, and emulsion polymerization was investigated. The mechanism of aqueous cationic polymerization of cyclohexyl vinyl ether was proposed.

Photoredox Catalysis in Photocontrolled Cationic Polymerizations of Vinyl Ethers.

Advances in photocontrolled polymerizations have expanded the scope of polymer architectures and structures that can be synthesized for various applications. The majority of these polymerizations have been developed for radical processes, which limits the diversity of monomers that can be used in macromolecular design. More recent developments of photocontrolled cationic polymerizations have taken a step toward addressing this limitation and have expanded the palette of monomers that can be used in stimuli-regulated polymerizations, enabling the synthesis of previously inaccessible polymeric structures. This Account will detail our group's studies on cationic polymerization processes where chain growth is regulated by light and highlight how these methods can be combined with other stimuli-controlled polymerizations to precisely dictate macromolecular structure.Photoinitiated cationic polymerizations are well-studied and important processes that have control over initiation. However, we wanted to develop systems where we had spatiotemporal control over both polymer initiation and chain growth. This additional command over the reaction provides the ability to manipulate the growing polymer with an external stimulus during a polymerization, which can be used to control structure. To achieve this goal, we set out to develop a method to photoreversibly generate a cation at a growing chain end that could participate in a controlled polymerization process. We took inspiration from previous work on cationic degenerate chain transfer polymerizations of vinyl ethers that used thiocarbonylthio chain transfer agents. These polymerizations were initiated by a strong acid and gave well-defined poly(vinyl ether)s. We posited that we could remove the acid initiator in these systems and reversibly oxidize the thiocarbonylthio chain ends in these reactions with a photocatalyst to give a photocontrolled cationic polymerization of vinyl ethers. This Account will focus on our journey to discover cationic photocontrolled polymerizations. We will summarize our initial developments and detail our mechanistic understanding of these reactions using both organic and inorganic based photocatalysts, and we will outline more recent efforts to expand cationic degenerate chain transfer polymerizations to other thioacetal initiators. Finally, we will detail how these photocontrolled cationic polymerizations can be used to switch monomer selectivity in situ using light to control polymer structure. At the end of the Account, we will discuss our vision for future potential applications of these photocontrolled cationic polymerizations in the synthesis of novel block copolymers and next generation cross-linked networks.

Controlled microflow cationic polymerization of vinyl ethers under ambient conditions

Living cationic polymerization is a well-established method for preparing polymers with controlled molecular weights and complex architectures, but rigorous polymerization conditions limit its widespread application. Here, we report a facile strategy for simplifying the strict conditions required for traditional living cationic polymerizations of various vinyl ethers including ethyl vinyl ether (EVE), propyl vinyl ether (PVE), butyl vinyl ether (BVE) and isobutyl vinyl ether (IBVE) by utilizing continuous microflow reactors and a weak Lewis acid, zinc chloride (ZnCl2). Well-defined polymers with controlled molecular weights and narrow molecular weight distributions (<1.20) can be obtained under ambient conditions without monomer purification, temperature control or strictly anhydrous conditions. The living nature of the polymerization was verified by kinetic experiments and successful in situ chain extension.

Organocatalytic, Stereoselective, Cationic Reversible Addition-Fragmentation Chain-Transfer Polymerization of Vinyl Ethers.

Tacticity is a crucial factor affecting the properties of synthetic polymer materials. Here, we introduce a type of chiral organic Brønsted acid catalyst, 1,1'-bi-2-naphthol-derived N,N'-bis(triflyl)phosphoramidimidates (PADIs), for the cationic polymerization of vinyl ethers, which enables the development of the first organocatalytic, highly stereoselective, cationic reversible addition-fragmentation chain-transfer (RAFT) polymerization of vinyl ethers with a trithiocarbonate chain-transfer agent. This metal-free RAFT process could afford isotactic poly(vinyl ethers) with high stereoselectivity, controllable molecular mass, and narrow dispersity at low catalyst loadings (as low as 200 ppm). Moreover, the trithiocarbonate chain-end allows for chain extension to synthesize diblock copolymers comprising an isotactic poly(vinyl ether) block, by a mechanistic switching from stereoselective cationic RAFT polymerization to visible-light-regulated cationic and radical RAFT polymerization.

Organocatalytic stereoselective cationic polymerization of vinyl ethers by employing a confined brønsted acid as the catalyst

Organocatalytic stereoselective cationic polymerization of vinyl ethers by employing a confined brønsted acid as the catalyst

Organophotocatalytic Strict Temporally Controlled Cationic Polymerization of Vinyl Ethers

Organophotocatalytic Strict Temporally Controlled Cationic Polymerization of Vinyl Ethers

Synthesis and Post-Polymerization Modification of Defined Functional Poly(vinyl ether)s.

Living cationic polymerization is known for a good control over chain growth yielding polymers with well-defined molar mass distributions and low dispersities. However, the practical challenges involved in the synthesis of poly(vinyl ether)s limited suitable post-polymerization modifications (PPM) via chemoselective click reactions. Herein the successful controlled cationic polymerization of vinyl ethers bearing pendant CC double and C≡C triple bonds using a single-component initiation under ambient conditions is reported. Furthermore, the PPM via thiol-ene/-yne and copper(I)-catalyzed alkyne-azide cycloaddition reaction of the obtained polymers is successfully realized laying the foundation for the synthesis of unprecedented functional poly(vinyl ether)s.

Metal-Free Cationic Polymerization of Vinyl Ethers with Strict Temporal Control by Employing an Organophotocatalyst.

By virtue of spatiotemporal control over the chain propagating, visible-light-regulated organocatalytic photoredox cationic polymerization provides an appealing approach for the construction of metal-free, well-defined polymers and materials. However, so far, organic photocatalysts capable of mediated cationic polymerization of vinyl ethers are quite limited, and the photocontrol or efficiency is often eroded due to the difficulty in achieving a good activation-deactivation balance, which is greatly dependent on the redox property of the catalyst. Here, we introduce a new type of organic photocatalysts, bisphosphonium salts, which show high performance in the photoregulated reversible addition-fragmentation chain transfer cationic polymerization of vinyl ethers and allow the synthesis of poly(vinyl ethers) with predictable molecular weights and narrow dispersities at low ppm catalyst loadings under visible light. In particular, the tunable redox potential and excellent stability endow the bisphosphonium salts strict temporal control, thus enabling the metal-free polymerization with a halt in a long dark period.

Living cationic polymerization of vinyl ethers initiated by electrophilic selenium reagents under ambient conditions

We present a living cationic polymerization of vinyl ethers utilizing electrophilic selenium reagents as initiators and pentacarbonylbromomanganese (Mn(CO)5Br) as the catalyst.

Hydrogen Bond Donor Catalyzed Cationic Polymerization of Vinyl Ethers

AbstractThe synthesis of high‐molecular‐weight poly(vinyl ethers) under mild conditions is a significant challenge, since cationic polymerization reactions are highly sensitive to chain‐transfer and termination events. We identified a novel and highly effective hydrogen bond donor (HBD)–organic acid pair that can facilitate controlled cationic polymerization of vinyl ethers under ambient conditions with excellent monomer compatibility. Poly(vinyl ethers) of molar masses exceeding 50 kg mol−1 can be produced within 1 h without elaborate reagent purification. Modification of the HBD structure allowed tuning of the polymerization rate, while DFT calculations helped elucidate crucial intermolecular interactions between the HBD, organic acid, and polymer chain end.

Hydrogen Bond Donor Catalyzed Cationic Polymerization of Vinyl Ethers.

The synthesis of high-molecular-weight poly(vinyl ethers) under mild conditions is a significant challenge, since cationic polymerization reactions are highly sensitive to chain-transfer and termination events. We identified a novel and highly effective hydrogen bond donor (HBD)-organic acid pair that can facilitate controlled cationic polymerization of vinyl ethers under ambient conditions with excellent monomer compatibility. Poly(vinyl ethers) of molar masses exceeding 50 kg mol-1 can be produced within 1 h without elaborate reagent purification. Modification of the HBD structure allowed tuning of the polymerization rate, while DFT calculations helped elucidate crucial intermolecular interactions between the HBD, organic acid, and polymer chain end.

Mechanistic Insight into the Stereoselective Cationic Polymerization of Vinyl Ethers.

The control of the tacticity of synthetic polymers enables the realization of emergent physical properties from readily available starting materials. While stereodefined polymers derived from nonpolar vinyl monomers can be efficiently prepared using early transition metal catalysts, general methods for the stereoselective polymerization of polar vinyl monomers remain underdeveloped. We recently demonstrated asymmetric ion pairing catalysis as an effective approach to achieve stereoselective cationic polymerization of vinyl ethers. Herein, we provide a deeper understanding of stereoselective ion-pairing polymerization through comprehensive experimental and computational studies. These findings demonstrate the importance of ligand deceleration effects for the identification of reaction conditions that enhance stereoselectivity, which was supported by computational studies that identified the solution-state catalyst structure. An evaluation of monomer substrates with systematic variations in steric parameters and functional group identities established key structure-reactivity relationships for stereoselective homo- and copolymerization. Expansion of the monomer scope to include enantioenriched vinyl ethers enabled the preparation of an isotactic poly(vinyl ether) with the highest stereoselectivity (95.1% ± 0.1 meso diads) reported to date, which occurred when monomer and catalyst stereochemistry were fully matched under a triple diastereocontrol model. The more complete understanding of stereoselective cationic polymerization reported herein offers a foundation for the design of improved catalytic systems and for the translation of isotactic poly(vinyl ether)s to applied areas.