Fluoroalkyl Side Chains Research Articles

Polymorph Screening of Core-Chlorinated Naphthalene Diimides with Different Fluoroalkyl Side-Chain Lengths.

In this work, naphthalenediimide (NDI) derivatives are widely studied for their semiconducting properties and the influence of the side-chain length on the crystal packing is reported, along with the thermal properties of three core-chlorinated NDIs with different fluoroalkyl side-chain lengths (CF3-NDI, C3F7-NDI and C4F9-NDI). The introduction of fluorinated substituents at the imide nitrogen and addition of strong electron-withdrawing groups at the NDI core are used to improve the NDI derivatives air stability. The new compound, CF3-NDI, was deeply analyzed and compared to the well-known C3F7-NDI and C4F9-NDI, leading to the discovery and solution of two different crystal phases, form α and solvate form, and a solid solution of CF3-NDI and CF3-NDI-OH, formed by the decomposition in DMSO.

Multifunctional polyzwitterion ionic liquid based solid-state electrolytes for enhancing the low-temperature performance of lithium-metal batteries

The extensive development of solid-state batteries (SSB) is still hindered by their insufficient charge transfer kinetics and severe interfacial problems at low temperatures. In this paper, a polyzwitterion ionic liquid based solid-state electrolyte (SSE) containing fluoroalkyl side chains is developed. The Lewis acid segment in the polymer backbone enhances the dissociation of lithium salts and modulates the Li+ transport. The experimental results showed that the −SO3- groups at the end of the zwitterions constructed a fast ion transport pathway, and the fluoroalkyl side chain can weaken the affinity between Li+ and the coupling site. In addition, the electrostatic shielding effect of zwitterions at the interface mitigated the tip effect, and the fluorinated alkyl side chains participated in the SEI film formation. As a result, the ionic conductivity of the designed electrolyte is as high as 1.39 × 10-4 S cm−1 at −30 °C, and the polarization rate of Li||Li symmetric battery at −10 °C is about 80 mV after 4000 h. The assembled Li||LiFePO4 pouch full cell delivers impressive performance in the wide temperature range from –23 to 99 °C. The proposed strategy has considerable potential for SSB application at low temperatures.

Transparent self-cleaning coatings repellent to ultralow surface tension liquids in extreme environments

Self-cleaning coatings have been garnering significant attention for their ability to reduce surface pollution by repelling liquids. However, creating transparent self-cleaning coatings that effectively repel ultralow surface tension liquids in harsh environments, like extremely high or low temperature environments, remains a challenge. Here, a transparent omniphobic coating (PMAPOSS-co-PFMA) is reported to achieve the repellency of droplets with surface tensions down to 15.5 mN·m−1 (n-pentane), even at temperatures up to 160 °C and down to −70 °C. The coating is engineered by grafting fluoropolymer with fluoroalkyl side chains onto the rigid polyhedral oligomeric silsesquioxane framework. The fluoroalkyl side chains tend to crystallize on the coating's surface, resulting in its low surface tension (measured at 9.39 mN·m−1). The incorporation of the robust POSS significantly enhances the coating's chemical, mechanical, and thermal stability. Moreover, with low roughness (Ra = 1 nm), the coating has a light transmittance of 90.5 %, surpassing untreated glass by 3.2 %. Heated at 80 °C, the migration of the long-fluorinated polymer chains within the PMAPOSS-co-PFMA coating enables its self-healing properties upon damage. These results provide a new perspective to develop versatile self-cleaning omniphobic coatings suitable for practical applications in extreme environments, such as asphalt transport pipes operating in high-temperature conditions.

Amphiphilic Copolymer Thin Films with Short Fluoroalkyl Side Chains for Antibiofilm Properties at the Solid–Liquid–Air Interface

Amphiphilic Copolymer Thin Films with Short Fluoroalkyl Side Chains for Antibiofilm Properties at the Solid–Liquid–Air Interface

Repulsive segregation of fluoroalkyl side chains turns a cohesive polymer into a mechanically tough, ultrafast self-healable, nonsticky elastomer

Dynamic crosslinking of flexible polymer chains via attractive and reversible interactions is widely employed to obtain autonomously self-healable elastomers. However, this design leads to a trade-off relationship between the strength and self-healing speed of the material, i.e., strong crosslinks provide a mechanically strong elastomer with slow self-healing property. To address this issue, we report an “inversion” concept, in which attractive poly(ethyl acrylate-random-methyl acrylate) chains are dynamically crosslinked via repulsively segregated fluoroalkyl side chains attached along the main chain. The resulting elastomer self-heals rapidly (> 90% within 15 min) via weak but abundant van der Waals interactions among matrix polymers, while the dynamic crosslinking provides high fracture stress (≈2 MPa) and good toughness (≈17 MJ m−3). The elastomer has a nonsticky surface and selectively self-heals only at the damaged faces due to the surface segregation of the fluoroalkyl chains. Moreover, our elastomer strongly adheres to polytetrafluoroethylene plates (≈60 N cm−2) via hot pressing.

Strong Hydrophobic and Ultraviolet Reflective Film from Fluorinated Polyisoprene with Microphase Separation via Thiol–Epoxy Click Chemistry

AbstractPolyisoprene is widely used in the industrial production of tires, thermoplastic elastomers, pressure sensitive adhesives, coatings, plasticizers, lubricants, and other functional materials. However, due to the inherent molecular defect of containing many unsaturated double bonds, polyisoprene exhibits relatively weak environmental endurance, especially under extreme environmental conditions. To incorporate the excellent features of fluorinated polymer such as tough environmental endurance, a new type of fluorinated polyisoprene is tailored and a facile procedure of introducing fluoroalkyl side chains onto polyisoprene backbone is carried out via epoxidation and thiol–epoxy click chemistry under mild conditions. The results demonstrate that fluorinated alkyl side chains are successfully clicked onto backbone chains of polyisoprene and the corresponding film exhibits a microphase separation structure. As for the fluorinated polyisoprene film after the introduction of fluoroalkyl groups, the water contact angle enhances significantly from 79.4° to 114.8° and the UV reflectivity improves markedly. In addition, the surface chemical constituents confirm that the incorporated fluoroalkyl groups have a tendency to migrate and enrich spontaneously onto the film surface.

Persistent Water Repellency of Syndiotactic Polymethylene with Perfluoroethyl Hexyloxycarbonyl Side Chains.

Polyacrylates bearing long fluoroalkyl (Rf) side chains are known to have ultralow surface energies that are appropriate for functional coating and fabric finishing. However, these long Rf chains cause health concerns because of the risk of toxic and bioaccumulative perfluoroalcanoic acid emission via oxidative degradation. This work demonstrates that incorporating a short Rf chain of perfluoroethylene at the end of the side chains of syndiotactic poly(substituted methylene) (PM) produces hydrophobicity. A contact angle of 105° of PM remains constant for more than 50 s, whereas that of the polyacrylate (PA) with the same side chain rapidly decreases from 85° to 44° over the same period. Such persistent water repellency of the PM is ascribed to a liquid crystal structure comprised the main chains arranged in a 2D hexagonal lattice and side chains that extend perpendicularly from these main chains.

Chain Exchange Kinetics of Bottlebrush Block Copolymer Micelles

Chain exchange kinetics of the bottlebrush core micelles formed by poly(5-perfluorooctyl-2-norbornene-block-N-cyclohexyl-exo-norbornene-5,6-dicarboxyimide) (PF-b-PC) block copolymer in tetrahydrofuran (THF), selective for PC blocks, were investigated by time-resolved small-angle neutron scattering (TR-SANS). The bottlebrush PF core blocks are densely tethered with rigid fluoroalkyl side chains. Despite the unfavorable interaction between the PF cores and the medium, TR-SANS revealed that the chain exchange between the bottlebrush core micelles occurs within a measurable timescale (∼1 h) at 40 °C. The measured exchange kinetics were successfully described by the model based on the thermodynamic barrier for the core block extraction and the solvent plasticizing effect associated with partial swelling of the PF cores. This chain exchange rate is also partly attributed to the bottlebrush architecture of PF blocks, as supported by lower melt viscosities of PF homopolymers than those of the analogous fluorine-containing linear polymers. These results are discussed in terms of current understanding of molecular exchange between block copolymer micelles, and particular attention is paid to the issue of polymer architecture, given the bottlebrush type of the core block.

Synthesis, structure, and surface properties of Poly(meth)acrylates bearing a vinylene-bridged fluoroalkyl side chain

In this study, unprecedented polyacrylates with vinylene-bridged fluoroalkyl side chains (–(CF2)6–CHCH-(CF2)5CF3) were successfully synthesized. These polyacrylates comprise short perfluoroalkyl groups, thus allowing to prevent the formation of bioaccumulative polyfluorinated compounds including perfluorooctanoic acid (PFOA). The bulk organization and surface properties of these polymers were investigated by differential scanning calorimetry, X-ray diffraction analysis, and contact angle measurements. Thin films of the novel polyacrylates bearing the –(CF2)6–CHCH-(CF2)5CF3 groups exhibited excellent water and oil repellency comparable to those made by conventional polyacrylates bearing C8F17 groups. A novel polymethacrylate bearing the –(CF2)6–CHCH-(CF2)5CF3 group showed low surface energy and low contact angle hysteresis despite of its amorphousness in the bulk state, which is very different from conventional polymethacrylates bearing a C6F13 group. Therefore, these polyacrylates bearing vinylene-bridged fluoroalkyl side chains are promising alternatives to conventional analogues containing long perfluoroalkyl side chains.

Synthesis and performances of 9,9‐bis(perfluorohexylethyl propionate) fluorene copolymers

Abstract2,7‐dibromo‐9,9‐bis(perfluorohexylethyl propionate) fluorene was synthesized by Michael addition reaction using 2,7‐dibromofluorene and perfluorohexyl ethyl acrylate as the reactants. 9,9‐Bis(perfluorohexylethyl propionate) fluorene copolymers were then synthesized by Suzuki coupling reaction with 2,7‐bis(4,4,5,5‐tetramethyl‐1,3,2‐dioxaborane‐diyl)‐9,9 ‐dioctyl fluorene, 2,7‐dibromo‐9,9‐dioctyl fluorene and 2,7‐dibromo‐9,9‐bis(perfluorohexylethyl propionate) fluorene as the monomers. The fluorinated fluorene copolymers were characterized and investigated via Fourier infrared spectroscopy (FTIR), hydrogen nuclear magnetic resonance spectroscopy (1HNMR), ultraviolet absorption spectroscopy (UV–vis), cyclic voltammetry (CV) and photoluminance spectroscopy (PL). Because of the long fluorine‐containing alkyl side chain, the ultraviolet absorption peak of 9,9‐bis(perfluorohexylethyl propionate) fluorene is blue‐shifted compared with poly(9,9‐dioctylfluorene)(PF8). The LUMO energy level increases and the energy band gap of copolymers widens. Due to the self‐assembly of the long fluoroalkyl side chain, the photoluminance spectra of 9,9‐bis(perfluorohexylethyl propionate) fluorene copolymers exhibit a new excimer emission peak at 550 nm. The photoluminance stabilities of the copolymers under irradiation and humid conditions are significantly improved due to protective effect from the long fluoroalkyl side chain. After being irradiated under 500 W iodine tungsten lamp or kept under 70% relative humid conditions, the 9,9‐bis(perfluorohexylethyl propionate) fluorene copolymers showed much better photoluminance stability than that of poly(9,9‐dioctylfluorene) (PF8). These show that introducing long fluoroalkyl side chain into conjugated polymer main chain is a promising strategy to improve environmental stability of devices based on organic conjugated polymers.

Enhancement of air-stability, π-stacking ability, and charge transport properties of fluoroalkyl side chain engineered n-type naphthalene tetracarboxylic diimide compounds

In this study, the impact of fluoroalkyl side chain substitution on the air-stability, π-stacking ability, and charge transport properties of the versatile acceptor moiety naphthalene tetracarboxylic diimide (NDI) has been explored. A density functional theory (DFT) study has been carried out for a series of 24 compounds having different side chains (alkyl, fluoroalkyl) through the imide nitrogen position of NDI moiety. The fluoroalkyl side chain engineered NDI compounds have much deeper highest occupied molecular orbitals (HOMO) and lowest unoccupied molecular orbitals (LUMO) than those of their alkyl substituted compounds due to the electron withdrawing nature of fluoroalkyl groups. The higher electron affinity (EA > 2.8 eV) and low-lying LUMO levels (<−4.00 eV) for fluoroalkyl substituted NDIs reveal that they may exhibit better air-stability with superior n-type character. The computed optical absorption spectra (∼386 nm) for all the investigated NDIs using time-dependent DFT (TD-DFT) lie in the ultra-violet (UV) region of the solar spectrum. In addition, the low value of the LOLIPOP (Localized Orbital Locator Integrated Pi Over Plane) index for fluoroalkyl side chain comprising NDI compounds indicates better π–π stacking ability. This is also in good agreement for the predicted π–π stacking interaction obtained from a molecular electrostatic potential energy surface (ESP) study. The π–π stacking is thought to be of cofacial interaction for the fluoroalkyl substituted compounds and herringbone interaction for the alkyl substituted compounds. The calculated results shed light on why side chain engineering with fluoroalkyl groups can effectively lead to better air-stability, π-stacking ability and improved charge transport properties.

Structural Analysis of Bottlebrush Block Copolymer Micelles Using Small-Angle X-ray Scattering.

We present structural analysis of spherical diblock copolymer micelles where core blocks have bottlebrush architecture. The dependence of the core radius (Rcore) and the corona thickness (Lcorona) on the core block length (Ncore) is investigated using small-angle X-ray scattering (SAXS) and discussed in terms of the stiffness of a core-forming polymer posed by its long fluoroalkyl side chains. The conformation of the core block is strongly stretched, and the measured exponents α and β from power-law correlations, Rcore ∼ Ncoreα and Lcorona ∼ Ncoreβ, respectively, are greater than those from any scaling predictions for block copolymer micelles with a flexible, linear core-block. Such deviations are attributed to the appreciable chain stiffness of the bottlebrush core block, and a simple model is suggested to understand how the core block stiffness influences both the dimensions of core and corona.

A waterborne coating for robust superamphiphobic surfaces

Although recent progress has been made in the development of superamphiphobic fabrics, durability has been an obstacle to their wide application in practice. In this work, a robust water-borne superamphiphobic coating was successfully prepared using poly(vinylidene fluoride) (PVDF) latex particles (225 nm) modified with a cationic fluorocarbon surfactant (Zonyl 321) and an fluoroalkylsilane (FAS). It is demonstrated that the superamphiphobic coating could strongly adhere to various substrates (fabric, sponge, wood, and filter paper) to efficiently repel water and hexadecane under harsh environments such as strong ultraviolet (UV) irradiation, abrasion, plasma cleaning, boiling water, and strong acid/base corrosion. Furthermore, this coating could exhibit good thermal healing capability upon thermal annealing. Through a thorough study of the self-assembly structure of the composite PVDF/Zonyl 321/FAS particles, the robust superamphiphobic property was considered to relate to the following reasons. First, PVDF latex particles provided nanoscale roughness and good UV/chemical resistance. Second, cationic Zonyl 321 self-assembled onto negatively charged PVDF latex particles to form a shell structure with inner fluoroalkyl groups protected by the outer positive charges, which could provide strong adhesion to various fabrics. Third, FAS self-assembled into the fluoroalkyl shell and subsequent self-condensed to render a lightly crosslinked structure. After forming a dense coating onto a substrate, further crosslinking via self-condensation of FAS provided robustness for the coating. Subsequent thermal annealing at 130 °C drove the fluoroalkyl side chains to accumulate at the top surface for superamphiphobicity. This understanding of the composite PVDF/Zonyl 321/FAS system will help us design even better superamphiphobic coatings in the future.

Impact of Unsymmetrical Alkyl–Fluoroalkyl Side Chains over Coil-to-Rod Transition of Soluble Polyacetylenes: Modulation of Electronic Conjugation of Isolated Chains and Their Self-Assembly

Soluble all-trans polyacetylenes (PAs) are most ideal models to study the spectroscopic properties of conjugated polymers for precise control of their backbone configurations, resulting in semiconducting properties for optoelectronic applications. Herein, we report precise control of the backbone configuration and subsequent self-assembly of soluble PAs flanked with alkyl–fluoroalkyl side chains, using light and temperature stimuli respectively in solution. PAs with symmetric alkyl and unsymmetrical alkyl–fluoroalkyl side chains were successfully polymerized by living cyclopolymerization with the olefin metathesis reaction mediated by third-generation Grubbs catalysts. Coil-to-rod-like conformational transition was observed for all of the PAs under ambient light due to photoisomerization, monitored by UV–vis spectroscopy and discussed in terms of the Huang–Rhys parameter. Enrichment of the trans configuration in the conjugated backbones opened up the possibility of aggregation between the isolated conjuga...

Evaluation of 4-oxo-quinoline-based CB2 PET radioligands in R6/2 chorea huntington mouse model and human ALS spinal cord tissue

The cannabinoid receptor 2 (CB2) has been implicated in a series of neurodegenerative disorders and has emerged as an interesting biological target for therapeutic as well as diagnostic purposes. In the present work, we describe an improved radiosynthetic approach to obtain the previously reported CB2-specific PET radioligand [18F]RS-126 in higher radiochemical yields and molar activities. Additionally, the study revealed that prolongation of the [18F]RS-126 fluoroalkyl side chain ultimately leads to an improved stability towards mouse liver enzymes but is accompanied by a reduction in selectivity over the cannabinoid receptor 1 (CB1). Huntington-related phenotypic changes as well as striatal D2R downregulation were confirmed for the transgenic R6/2 mouse model. CB2 upregulation in R6/2 Chorea Huntington mice was observed in hippocampus, cortex, striatum and cerebellum by qPCR, however, these results could not be confirmed at the protein level by PET imaging. Furthermore, we evaluated the utility of the newly developed [11C]RS-028, a potent [18F]RS-126 derivative with increased polarity and high selectivity over CB1 in post-mortem human ALS spinal cord and control tissue. Applying in vitro autoradiography, the translational relevance of CB2 imaging was demonstrated by the specific binding of [11C]RS-028 to post-mortem human ALS spinal cord tissue.

Model Amphiphilic Block Copolymers with Tailored Molecular Weight and Composition in PDMS-Based Films to Limit Soft Biofouling.

A set of controlled surface composition films was produced utilizing amphiphilic block copolymers dispersed in a cross-linked poly(dimethylsiloxane) network. These block copolymers contained oligo(ethylene glycol) (PEGMA) and fluoroalkyl (AF6) side chains in selected ratios and molecular weights to control surface chemistry including antifouling and fouling-release performance. Such properties were assessed by carrying out assays using two algae, the green macroalga Ulva linza (favors attachment to polar surfaces) and the unicellular diatom Navicula incerta (favors attachment to nonpolar surfaces). All films performed well against U. linza and exhibited high removal of attached sporelings (young plants) under an applied shear stress, with the lower molecular weight block copolymers being the best performing in the set. The composition ratios from 50:50 to 60:40 of the AF6/PEGMA side groups were shown to be more effective, with several films exhibiting spontaneous removal of the sporelings. The cells of N. incerta were also removed from several coating compositions. All films were characterized by surface techniques including captive bubble contact angle, atomic force microscopy, and near edge X-ray absorption fine structure spectroscopy to correlate surface chemistry and morphology with biological performance.

Effects of surface-active block copolymers with oxyethylene and fluoroalkyl side chains on the antifouling performance of silicone-based films

Block copolymers made from a poly(dimethyl siloxane) (Si) and a poly(meth)acrylate carrying oxyethylene (EG) or fluoroalkyl (AF) side chains were synthesized and incorporated as surface-active components into a silicone matrix to produce cross-linked films with different surface hydrophilicity/phobicity. Near-edge X-ray absorption fine structure (NEXAFS) studies showed that film surfaces containing Si-EG were largely populated by the siloxane, with the oxyethylene chains present only to a minor extent. In contrast, the fluorinated block was selectively segregated to the polymer–air interface in films containing Si-AF as probed by NEXAFS and X-ray photoelectron spectroscopy (XPS) analyses. Such differences in surface composition were reflected in the biological performance of the coatings. While the films with Si-EG showed a higher removal of both Ulva linza sporelings and Balanus amphitrite juveniles than the silicone control, those with Si-AF exhibited excellent antifouling properties, preventing the settlement of cyprids of B. amphitrite.

Fluoroalkylation of Silsesquioxanes-Modified Polysiloxane and Its Surface Property

Poly(silsesquioxane)methylsiloxane (PSS) was prepared by the hydrosilylation and hydrolysis reactions using trichlorovinylsilane and dimethyldichlorosilane as starting materials. Poly(fluorosilsesquioxane)methylsiloxane (FPSS) was obtained via a single electron transfer addition reaction of PSS with perfluorobutyl iodide followed by Zn-mediated reduction of iodide. FT-IR, 1H NMR, 19F NMR and 13C NMR indicated the structures of PSS and FPSS. The surface chemical composition and element distribution of polymer films were measured using X-ray Photoelectron Spectroscopy. In addition, Atomic Force Microscopy images showed that there were numerous pinnacles that were generated on the rough surface of films by the segregation of fluoroalkyl side chains at the polymer-air interface. The relative static contact angles of PSS and FPSS films toward water were 105.1° and 119.3°, respectively. The FPSS was characterized to possess of better water repellent property because of the segregation and enrichment of fluoroalkyl chains on the surface of FPSS.

Effect of α-substituents on molecular motion and wetting behaviors of poly(fluoroalkyl acrylate) thin films with short fluoroalkyl side chains

The effect of α-substituent on the molecular motion and wetting behavior of poly{2-(perfluorobutyl)ethyl acrylate} [PFA-C4], poly{2-(perfluorobutyl)ethyl methacrylate} [PFMA-C4], poly{2-(perfluorobutyl)ethyl α-fluoroacrylate} [PFFA-C4], and poly{2-(perfluorobutyl)ethyl α-chloroacrylate} [PFClA-C4] films were characterized by dynamic contact angle measurement, lateral force microscopy (LFM), wide angle X-ray diffraction (WAXD), and X-ray photoelectron spectroscopy (XPS). WAXD of oriented PFClA-C4 fiber suggested the presence of rod-like chain due to the presence of bulky α-substituent. The glass transition temperature (Tg) of PFFA-C4 and PFClA-C4 were well above the room temperature. The water repellencies of PFFA-C4 and PFClA-C4 were as high as that of PFMA-C4 and their oil repellency of PFFA-C4 and PFClA-C4 was higher than the PFMA-C4. This result was originated from the low main chain mobility of PFFA-C4 and PFClA-C4 due to the presence of bulky α-substituents. The effect of molecular motion on water repellency was clarified by the results of temperature dependence studies of dynamic contact angle, LFM, and surface chemical composition measured by XPS.

Homeotropic alignment of dendritic columnar liquid crystal induced by hydrogen-bonded triphenylene core bearing fluoroalkyl chains.

A 1:3 molar complex of the fluoroalkyl side chain-substituted 2,6,10-tris-carboxymethoxy-3,7,11-tris(4,4,5,5,6,6,7,7,7-nonafluoroheptyloxy)triphenylene (TPF4) with the second generation dendron 3,5-bis(3,4-bis-dodecyloxybenzyloxy)-N-pyridin-4-yl-benzamide (DN) assembled through complementary hydrogen bonding to form a supramolecular columnar liquid crystal, which exhibited homeotropic alignment when sandwiched between octadecyltrichlorosilane (OTS)-coated or indium tin oxide (ITO)-coated glass plates due to specific interactions between the fluoroalkyl side chains and the substrates.