Cationic polymerization of vinyl monomers in aqueous media: from monofunctional oligomers to long-lived polymer chains

Characterization and mechanism study of aqueous cationic polymerization of p-methylstyrene

Aqueous cationic polymerization has attracted considerable interest as a novel polymerization technique, because it conforms to the “green chemistry” trend and challenges the concept of traditional cationic polymerization. In this paper, a CumOH/B(C₆F₅)₃/Et₂O system was used to initiate the aqueous polymerization of p-methylstyrene through suspension and emulsion methods. Several types of surfactants were used, including the cationic surfactant CTAB, non-ionic surfactant NP-40, and anionic surfactant SDBS, and the influences of initiator concentration and temperature on polymerization were investigated. Consistent with previous literature, initiator activity was positively correlated with temperature unlike in traditional cationic polymerization. Gaussian 09W simulation software was used to calculate and optimize changes in the bond lengths and angles of B(C₆F₅)₃ after ether was added to the system. The addition of ether increased the polarity of B(C₆F₅)₃, rendering it soluble in water. ¹H-NMR was used in identifying the main chain and terminal structures of the polymer, and the mechanism of p-methylstyrene aqueous phase cationic polymerization was proposed.

The co-initiator B(C₆F₅)₃ first complexed with ether. Then the complex deprives the OH⁻ of CumOH at the water–oil interface, and initiates the polymerization of p-methylstyrene at the interface.

Cationic Polymerization of Hexamethylcyclotrisiloxane in Excess Water

Ring-opening ionic polymerization of cyclosiloxanes in dispersed media has long been discovered, and is nowadays both fundamentally studied and practically used. In this short communication, we show some preliminary results on the cationic ring-opening polymerization of hexamethylcyclotrisiloxane (D₃), a crystalline strained cycle, in water. Depending on the catalyst or/and surfactants used, polymers of various molar masses are prepared in a straightforward way. Emphasis is given here on experiments conducted with tris(pentafluorophenyl)borane (BCF), where high-molar polymers were generated at room temperature. In surfactant-free conditions, µm-sized droplets are stabilized by silanol end-groups of thus generated amphiphilic polymers, the latter of which precipitate in the course of reaction through chain extension. Introducing various surfactants in the recipe allows generating smaller emulsions in size with close polymerization ability, but better final colloidal stability, at the expense of low small cycles’ content. A tentative mechanism is finally proposed.

On the limitations of cationic polymerization of vinyl monomers in aqueous dispersed media

We investigate the effects of chain transfer to monomer and chain transfer to water on the molecular weight of polymers obtained by cationic polymerization in aqueous dispersed media.

Interfacial Water Mediates Oligomerization Pathways of Monoterpene Carbocations

The air-water interface plays central roles in "on-droplet" synthesis, living systems, and the atmosphere; however, what makes reactions at the interface specific is largely unknown. Here, we examined carbocationic reactions of monoterpene (C₁₀H₁₆ isomer) on an acidic water microjet by using spray ionization mass spectrometry. Gaseous monoterpenes are trapped in the uppermost layers of a water surface via proton transfer and then undergo a chain-propagation reaction. The oligomerization pathway of β-pinene (β-P), which showed prompt chain-propagation, is examined by simultaneous exposure to camphene (CMP). (CMP)H⁺ is the most stable isomer formed via rearrangement of (β-P)H⁺ in the gas phase; however, no co-oligomerization was observed. This indicates that the oligomerization of (β-P)H⁺ proceeded via ring-opening isomerization. Quantum chemical calculations for [carbocation-(H₂O)_n=1,2] complexes revealed that the ring-opened isomer is stabilized by hydrogen-π bonds. We propose that partial hydration is a key factor that makes the interfacial reaction unique.

Lewis acid-surfactant complex catalyzed polymerization in aqueous dispersed media: cationic or radical polymerization?

Evidence is presented that shows Lewis acid-surfactant complex catalyzed polymerization proceeds via a radical, not a cationic, mechanism.

Silver-Catalyzed Reduction of Quinolines in Water

A ligand- and base-free silver-catalyzed reduction of quinolines and electron-deficient aromatic N-heteroarenes in water has been described. Mechanistic studies revealed that the effective reducing species was Ag-H. This versatile catalytic protocol provided facile, environmentally friendly, and practical access to a variety of 1,2,3,4-tetrahydroquinoline derivatives at room temperature.

Characteristics and Mechanism of Vinyl Ether Cationic Polymerization in Aqueous Media Initiated by Alcohol/B(C₆F₅)₃/Et₂O

Aqueous cationic polymerizations of vinyl ethers (isobutyl vinyl ether (IBVE), 2-chloroethyl vinyl ether (CEVE), and n-butyl vinyl ether (n-BVE)) were performed for the first time by a CumOH/B(C₆F₅)₃/Et₂O initiating system in an air atmosphere. The polymerization proceeded in a reproducible manner through the careful design of experimental conditions (adding initiator, co-solvents, and surfactant or decreasing the reaction temperature), and the polymerization characteristics were systematically tested and compared in the suspension and emulsion. The significant difference with traditional cationic polymerization is that the polymerization rate in aqueous media using B(C₆F₅)₃/Et₂O as a co-initiator decreases when the temperature is lowered. The polymerization sites are located on the monomer/water surface. Density functional theory (DFT) was applied to investigate the competition between H₂O and alcohol combined with B(C₆F₅)₃ for providing a theoretical basis. The effectiveness of the proposed mechanism for the aqueous cationic polymerization of vinyl ethers using CumOH/B(C₆F₅)₃/Et₂O was confirmed.

R–Cl/SnCl4/n-Bu4NCl-induced direct living cationic polymerization of naturally-derived unprotected 4-vinylphenol, 4-vinylguaiacol, and 4-vinylcatechol in CH3CN

A R–Cl/SnCl₄/n-Bu₄NCl-initiating system induced direct living cationic polymerization of naturally derived styrene monomers with phenol and catechol groups in CH₃CN.

Synthesis of highly reactive polyisobutylenesviacationic polymerization in ionic liquids: characteristics and mechanism

The cationic polymerization of isobutylene (IB) was systematically studied in a 1-butyl-3-methylimidazolium hexafluorophosphate ([Bmim][PF₆]) ionic liquid at −10 °C.

Naturally-Derived Amphiphilic Polystyrenes Prepared by Aqueous Controlled/Living Cationic Polymerization and Copolymerization of Vinylguaiacol with R⁻OH/BF₃·OEt₂

In this study, we investigated direct-controlled/living cationic polymerization and copolymerization of 4-vinylguaiacol (4VG), i.e., 4-hydroxy-3-methoxystyrene, which can be derived from naturally-occurring ferulic acid, to develop novel bio-based amphiphilic polystyrenes with phenol functions. The controlled/living cationic polymerization of 4VG was achieved using the R⁻OH/BF₃·OEt₂ initiating system, which is effective for the controlled/living polymerization of petroleum-derived 4-vinylphenol in the presence of a large amount of water via reversible activation of terminal C⁻OH bond catalyzed by BF₃·OEt₂, to result in the polymers with controlled molecular weights and narrow molecular weight distributions. The random or block copolymerization of 4VG was also examined using p-methoxystyrene (pMOS) as a comonomer with an aqueous initiating system to tune the amphiphilic nature of the 4VG-derived phenolic polymers. The obtained polymer can be expected not only to be used as a novel styrenic bio-based polymer but also as a material with amphiphilic nature for some applications.

Electro-Controlled Living Cationic Polymerization

Cationic polymerizations have long been industrialized; however, stimulus-regulated cationic polymerization remains to be developed. An electrochemically controlled living cationic polymerization is presented for the first time. In the presence of external potential and organic-based electrocatalyst, a series of monomers can be polymerized under a cationic chain-transfer mechanism. The resulting polymers exhibit well-defined molecular mass, narrow dispersity, and good chain-end fidelity. By controlling the external potential to switch the electrocatalyst between its oxidized and reduced states, ON/OFF polymerization can be achieved. This method is a versatile way to a large range of monomers, including vinyl ether-type and p-substituted styrene-type monomers. Given the sustainability feature and broad interest of electrochemical synthetic techniques, we envisaged that this method would lead a new direction of external regulated living ionic polymerization.

Aqueous cationic homo- and co-polymerizations of β-myrcene and styrene: a green route toward terpene-based rubbery polymers

A green and cost-efficient approach for the synthesis of bio-based poly(β-myrcene) and poly(β-myrcene-co-styrene) via emulsion cationic polymerization is developed.

Chain-propagation, chain-transfer, and hydride-abstraction by cyclic carbocations on water surfaces

New mechanisms for the growth and increase in complexity of atmospheric aerosol particles are elucidated. The present findings will also be useful for interfacial polymer/oligomer synthesis.

Nucleophile-initiated anionic polymerization of zwitterionic monomers derived from vinylpyridines in aqueous media under ambient aerobic conditions

Anionic polymerization of vinylpyridine based zwitterionic monomers using nucleophile initiators under natural conditions and DFT calculations for such polymerization are reported here.

Controlling factors of oligomerization at the water surface: why is isoprene such a unique VOC?

The interfacial oligomerization of isoprene is facilitated by the resonance stabilization through the formation of a tertiary carbocation with a conjugated CC bond pair, and electron enrichment induced by the neighboring methyl group.

New catalysts for the synthesis of highly reactive polyisobutylene: chloroaluminate imidazole-based ionic liquids in the presence of diisopropyl ether

The use of [emim]Cl–AlCl₃ in combination with ⁱPr₂O allowed the synthesis of HR PIB with high exo-olefin end group content (≥90%) and a relatively narrow MWD (Mw/Mn ≤ 2.0) at a high reaction temperature (>0 °C) and monomer concentration (5.2 M–7.8 M).

Electrophilic bis-fluorophosphonium dications: Lewis acid catalysts from diphosphines

Stepwise oxidation of 1,8-bis(diphenylphosphino)naphthalene and a series of (oligo)methylene-linked diphosphines with XeF2 followed by fluoride abstraction yields a family of compounds featuring phosphine, phosphonium and phosphorane moieties in close proximity. The bisphosphonium ions [(C10H6)(Ph2PF)2]2+ (5) and [CH2(Ph2PF)2]2+ (9a) exhibit remarkable Lewis acidity arising from the proximity of the phosphonium centers. The effectiveness of bisphosphonium dications (5, 9a-e) is examined in a series of Lewis acid catalysed transformations.

Recent progress in the Lewis acid co-initiated cationic polymerization of isobutylene and 1,3-dienes

This article reviews recent approaches towards the synthesis of exo-olefin terminated polyisobutylenes and well-defined poly(1,3-diene)s based on their scientific and industrial relevance.

Sulfide synthesis through copper-catalyzed C–S bond formation under biomolecule-compatible conditions

We report here an efficient, mild and biomolecule-compatible method for constructing C–S bonds.

Generation of gold carbenes in water: efficient intermolecular trapping of the α-oxo gold carbenoids by indoles and anilines

The efficient intermolecular reaction of gold carbene intermediates, generated via gold-catalyzed alkyne oxidation, with indoles and anilines has been realized in aqueous media.

Metal-free controlled ring-opening polymerization of ε-caprolactone in bulk using tris(pentafluorophenyl)borane as a catalyst

Controlled/living ring-opening polymerization of ε-caprolactone utilizing tris(pentafluorophenyl)borane as the metal-free catalyst was demonstrated, leading to block, end-functionalized and macrocyclic poly(ε-caprolactone) containing macromolecules.