Fluoropolymer synthesis in supercritical carbon dioxide

Fluoropolymers in biomedical applications: state-of-the-art and future perspectives

Biomedical applications of fluoropolymers in gene delivery, protein delivery, drug delivery, ¹⁹F MRI, PDT, anti-fouling, anti-bacterial, cell culture, and tissue engineering.

Simultaneous Wrinkle-Patterning and In Situ Foaming in Polymer Films Using Supercritical Carbon Dioxide

Unique and random wrinkle features are desired for applications, especially in anticounterfeiting. Multifunctional wrinkled materials as well as simple wrinkling methods are desired for more applications. In this study, free-standing wrinkle-patterned porous polymer films were prepared using a modified supercritical CO₂ foaming strategy. Spontaneous wrinkling was generated by applying moderate normal stress to the polymer films while foaming in situ. The wrinkle characteristics (wavelength and amplitude) were shown to be governed by the film thickness and the magnitude of the applied stress. Excessive (>5000 N) or no stress produced no obvious wrinkling or foaming whatsoever. Moreover, different morphologies of the wrinkles such as brain coral and herringbone patterns were achieved depending upon the shape of the mold used to apply the stress. Thus, the patterns show unique features for each batch process. Notwithstanding, geometric shape of the foamed wrinkle area is customizable. The reported wrinkling strategy offers the complementary advantage of patterning a foam in a polymer film and templating a PDMS stamp for different applications such as "mask-less" soft lithography, anticounterfeiting, pattern transfer, flexographic printing, and displays.

Insight into the Intermolecular Interaction and Free Radical Polymerizability of Methacrylates in Supercritical Carbon Dioxide

High pressure in situ Fourier transfer infrared/near infrared technology (HP FTIR/NIR) along with theoretical calculation of density functional theory (DFT) method was employed. The solvation behaviors and the free radical homopolymerization of methyl methacrylate (MMA), methacrylate acid (MAA), trifluoromethyl methacrylate (MTFMA) and trifluoromethyl methacrylate acid (TFMAA) in scCO2 were systematically investigated. Interestingly, the previously proposed mechanism of intermolecular-interaction dynamically-induced solvation effect (IDISE) of monomer in scCO2 is expected to be well verified/corroborated in view that the predicted solubility order of the monomers in scCO2 via DFT calculation is ideally consistent with that observed via HP FTIR/NIR. It is shown that MMA and MAA can be easily polymerized, while the free radical polymerizability of MTFMA is considerably poor and TFMAA cannot be polymerized via the free radical initiators. The α trifluoromethyl group (-CF3) may effectively enhance the intermolecular hydrogen bonding and restrain the diffusion of the monomer in scCO2. More importantly, the strong electron-withdrawing inductive effect of -CF3 to C=C may distinctly decrease the atomic charge of the carbon atom in the methylene (=CH2). These two factors are believed to be predominantly responsible for the significant decline of the free radical polymerizability of MTFMA and the other alkyl 2-trifluoromethacrylates in scCO2.

Sustainable synthesis and precise characterisation of bio-based star polycaprolactone synthesised with a metal catalyst and with lipase

Development of a sustainable route for the synthesis of star-shaped poly(ε-caprolactone) using renewable feedstocks in clean solvents (scCO₂ and bulk) with the catalysts Sn(Oct)₂ or the enzyme Novozym 435.

Fundamental properties and practical applications of ionic liquids: concluding remarks

The Faraday Discussion on Ionic Liquids: From Fundamental Properties to Practical Applications took place in Cambridge in September 2017. A summary of the conference and a vision for the future of ionic liquids are presented.

Prospective Symbiosis of Green Chemistry and Energetic Materials

A global increase in environmental pollution demands the development of new "cleaner" chemical processes. Among urgent improvements, the replacement of traditional hydrocarbon-derived toxic organic solvents with neoteric solvents less harmful for the environment is one of the most vital issues. As a result of the favorable combination of their unique properties, ionic liquids (ILs), dense gases, and supercritical fluids (SCFs) have gained considerable attention as suitable green chemistry media for the preparation and modification of important chemical compounds and materials. In particular, they have a significant potential in a specific and very important area of research associated with the manufacture and processing of high-energy materials (HEMs). These large-scale manufacturing processes, in which hazardous chemicals and extreme conditions are used, produce a huge amount of hard-to-dispose-of waste. Furthermore, they are risky to staff, and any improvements that would reduce the fire and explosion risks of the corresponding processes are highly desirable. In this Review, useful applications of almost nonflammable ILs, dense gases, and SCFs (first of all, CO₂ ) for nitration and other reactions used for manufacturing HEMs are considered. Recent advances in the field of energetic (oxygen-balanced and hypergolic) ILs are summarized. Significant attention is paid to the SCF-based micronization techniques, which improve the energetic performance of HEMs through an efficient control of the morphology and particle size distribution of the HEM fine particles, and to useful applications of SCFs in HEM processing that makes them less hazardous.

Light-Mediated Atom Transfer Radical Polymerization of Semi-Fluorinated (Meth)acrylates: Facile Access to Functional Materials

A highly efficient photomediated atom transfer radical polymerization protocol is reported for semi-fluorinated acrylates and methacrylates. Use of the commercially available solvent, 2-trifluoromethyl-2-propanol, optimally balances monomer, polymer, and catalyst solubility while eliminating transesterification as a detrimental side reaction. In the presence of UV irradiation and ppm concentrations of copper(II) bromide and Me₆-TREN (TREN = tris(2-aminoethyl amine)), semi-fluorinated monomers with side chains containing between three and 21 fluorine atoms readily polymerize under controlled conditions. The resulting polymers exhibit narrow molar mass distributions (Đ ≈ 1.1) and high end group fidelity, even at conversions greater than 95%. This level of control permits the in situ generation of chain-end functional homopolymers and diblock copolymers, providing facile access to semi-fluorinated macromolecules using a single methodology with unprecedented monomer scope. The results disclosed herein should create opportunities across a variety of fields that exploit fluorine-containing polymers for tailored bulk, interfacial, and solution properties.

Organic Polymer Chemistry in the Context of Novel Processes

This article was written to shed light on a series of what some have stated are not so obvious connections that link polymer synthesis in supercritical CO₂ to cancer treatment and vaccines, nonflammable polymer electrolytes for lithium ion batteries, and 3D printing. In telling this story, we also attempt to show the value of versatility in applying one's primary area of expertise to address pertinent questions in science and in society. In this Outlook, we attempted to identify key factors to enable a versatile and nimble research effort to take shape in an effort to influence diverse fields and have a tangible impact in the private sector through the translation of discoveries into the marketplace.

Structure-Property Relationships in CO2-philic (Co)polymers: Phase Behavior, Self-Assembly, and Stabilization of Water/CO2 Emulsions

This Review provides comprehensive guidelines for the design of CO2-philic copolymers through an exhaustive and precise coverage of factors governing the solubility of different classes of polymers. Starting from computational calculations describing the interactions of CO2 with various functionalities, we describe the phase behavior in sc-CO2 of the main families of polymers reported in literature. The self-assembly of amphiphilic copolymers of controlled architecture in supercritical carbon dioxide and their use as stabilizers for water/carbon dioxide emulsions then are covered. The relationships between the structure of such materials and their behavior in solutions and at interfaces are systematically underlined throughout these sections.

Towards sustainable polymeric nano-carriers and surfactants: facile low temperature enzymatic synthesis of bio-based amphiphilic copolymers in scCO2

We demonstrate that useful bio-based amphiphilic polymers can be produced enzymatically at a mild temperature, in a solvent-free system and using renewably sourced monomers, by exploiting the unique properties of supercritical CO₂(scCO₂).

Green process for green materials: viable low-temperature lipase-catalysed synthesis of renewable telechelics in supercritical CO2

We present a novel near-ambient-temperature approach to telechelic renewable polyesters by exploiting the unique properties of supercritical CO(2) (scCO(2)). Bio-based commercially available monomers have been polymerized and functional telechelic materials with targeted molecular weight prepared by end-capping the chains with molecules containing reactive moieties in a one-pot reaction. The use of scCO(2) as a reaction medium facilitates the effective use of Candida antarctica Lipase B (CaLB) as a catalyst at a temperature as low as 35°C, hence avoiding side reactions, maintaining the end-capper functionality and preserving the enzyme activity. The functionalized polymer products have been characterized by (1)H nuclear magnetic resonance spectroscopy, matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry, gel permeation chromatography and differential scanning calorimetry in order to carefully assess their structural and thermal properties. We demonstrate that telechelic materials can be produced enzymatically at mild temperatures, in a solvent-free system and using renewably sourced monomers without pre-modification, by exploiting the unique properties of scCO(2). The macromolecules we prepare are ideal green precursors that can be further reacted to prepare useful bio-derived films and coatings.

Supercritical carbon dioxide: a solvent like no other

Supercritical carbon dioxide (scCO2) could be one aspect of a significant and necessary movement towards green chemistry, being a potential replacement for volatile organic compounds (VOCs). Unfortunately, carbon dioxide has a notoriously poor solubilising power and is famously difficult to handle. This review examines attempts and breakthroughs in enhancing the physicochemical properties of carbon dioxide, focusing primarily on factors that impact solubility of polar and ionic species and attempts to enhance scCO2 viscosity.

Selective free radical reactions using supercritical carbon dioxide

We report herein a means to modify the reactivity of alkenes, and particularly to modify their selectivity toward reactions with nonpolar reactants (e.g., nonpolar free radicals) in supercritical carbon dioxide near the critical point. Rate constants for free radical addition of the light hydrogen isotope muonium to ethylene, vinylidene fluoride, and vinylidene chloride in supercritical carbon dioxide are compared over a range of pressures and temperatures. Near carbon dioxide's critical point, the addition to ethylene exhibits critical speeding up, while the halogenated analogues display critical slowing. This suggests that supercritical carbon dioxide as a solvent may be used to tune alkene chemistry in near-critical conditions.

On the ionizing properties of supercritical carbon dioxide: uncatalyzed electrophilic bromination of aromatics

scCO₂, a non-polar solvent with a dielectric constant lower than n-pentane, promotes the electrophilic bromination of aromatics as efficiently as strongly ionizing solvents such as aqueous acetic and trifluoroacetic acids.