Fluorophilic Block Research Articles

Influence of Surfactant-Mediated Interparticle Contacts on the Mechanical Stability of Supraparticles.

Colloidal supraparticles are micron-scale spherical assemblies of uniform primary particles, which exhibit emergent properties of a colloidal crystal, yet exist as a dispersible powder. A prerequisite to utilize these emergent functionalities is that the supraparticles maintain their mechanical integrity upon the mechanical impacts that are likely to occur during processing. Understanding how the internal structure relates to the resultant mechanical properties of a supraparticle is therefore of general interest. Here, we take the example of supraparticles templated from water/fluorinated oil emulsions in droplet-based microfluidics and explore the effect of surfactants on their mechanical properties. Stable emulsions can be generated by nonionic block copolymers consisting of a hydrophilic and fluorophilic block and anionic fluorosurfactants widely available under the brand name Krytox. The supraparticles formed in the presence of both types of surfactants appear structurally similar, but differ greatly in their mechanical properties. While the nonionic surfactant induces superior mechanical stability and ductile fracture behavior, the anionic Krytox surfactant leads to weak supraparticles with brittle fracture. We complement this macroscopic picture with Brillouin light spectroscopy that is very sensitive to the interparticle contacts for subnanometer-thick adsorbed layers atop of the nanoparticle. While the anionic Krytox does not significantly affect the interparticle bonds, the amphiphilic nonionic surfactant drastically strengthens these bonds to the point that individual particle vibrations are not resolved in the experimental spectrum. Our results demonstrate that seemingly subtle changes in the physicochemical properties of supraparticles can drastically impact the resultant mechanical properties.

Structural Tunability of Multicompartment Micelles as a Function of Lipophilic-Fluorophilic Block Length Ratio.

Structural variation in multicompartment micelles consisting of lipophilic-hydrophilic-fluorophilic (hereafter referred to as BAC) triblock copolymers is investigated using the dissipative particle dynamics simulation method. It is demonstrated from our results that the structure of BAC multicompartment micelles is effectively tuned as a function of the lipophilic-fluorophilic ratio parameter, here termed [Formula: see text], of the constituent linear triblock copolymers. In particular, a morphological deviation from onion-like ABC micelles arises in BAC micelle systems as [Formula: see text] increases. The morphologies of BAC micelles with [Formula: see text] or [Formula: see text] display striking similarities, with the only notable difference being an inversion of the lipophilic and fluorophilic regions. When [Formula: see text], segmented worm-like structures with multiple cores are favored in BAC micelle systems. Through this study, it is confirmed that the block length ratio is an effective control parameter to tune the structure of multicompartment micelles.

Fluorophilic–Lipophilic–Hydrophilic Poly(2-oxazoline) Block Copolymers as MRI Contrast Agents: From Synthesis to Self-Assembly

This work focuses on the synthesis and self-assembly of triphilic poly(2-oxazoline) triblock copolymers with high fluorine content toward our future aim of developing poly(2-oxazoline) magnetic resonance imaging (MRI) contrast agents. A highly fluorinated 2-substituted-2-oxazoline monomer, namely 2-(1H,1H,2H,2H-perfluorooctyl)-2-oxazoline, was synthesized using the Grignard reaction. The polymerization kinetics of the synthesized monomer was studied, and it was used for the preparation of triblock copolymers with hydrophilic 2-methyl-2-oxazoline, hydrophobic 2-octyl-2-oxazoline, and fluorophilic blocks by cationic ring-opening polymerization yielding polymers with low relatively dispersity (1.2–1.4). The presence of the blocks with the different nature in one copolymer structure facilitated self-assembly of the copolymers in water and dimethyl sulfoxide as observed by dynamic light scattering, cryo-transmission electron microscopy, and small-angle neutron scattering. The nanoparticle morphology is strongl...

Fluorinated 2-Alkyl-2-oxazolines of High Reactivity: Spacer-Length-Induced Acceleration for Cationic Ring-Opening Polymerization As a Basis for Triphilic Block Copolymer Synthesis.

The synthesis of defined triphilic terpolymers with hydrophilic, lyophilic, and fluorophilic blocks is an important challenge as a basis for the development of multicompartment self-assembled structures with potential for, e.g., cascade catalysis and multidrug loading. The synthesis of fluorophilic poly(2-oxazoline)s generally suffers from a very low reactivity of fluorinated 2-oxazoline monomers in cationic ring-opening polymerization (CROP). We report a systematic study on overcoming the extremely low reactivity of 2-perfluoroalkyl-2-oxazolines in CROP by the insertion of methyl and ethyl hydrocarbon spacers between the 2-oxazoline ring and the trifluoromethyl group. The kinetic studies showed the gradual increase of the rate of polymerization with increasing of the hydrocarbon spacer length. The monomer with an ethyl spacer was found to have similar reactivity as 2-alkyl-2-oxazolines and allowed the synthesis of defined triphilic triblock copolymers.

Solvent- and Coating Mode-induced Surface Patterns of a Ternary Hydrophilic–Lipophilic–Fluorophilic Block Copolymer

Solvent and coating mode play crucial roles on the formation of polymeric surface patterns. Investigation by AFM revealed that a ternary hydrophilic–lipophilic–fluorophilic block copolymer can self...

Self-Assembly into Multicompartment Micelles and Selective Solubilization by Hydrophilic−Lipophilic−Fluorophilic Block Copolymers

Amphiphilic linear ternary block copolymers (ABC) were synthesized in three consecutive steps by the reversible addition−fragmentation chain transfer (RAFT) method. Using oligo(ethylene oxide) monomethyl ether acrylate, benzyl acrylate, and 1H,1H-perfluorobutyl acrylate monomers, the triblock copolymers consist of a hydrophilic (A), a lipophilic (B), and a fluorophilic (C) block. The block sequence of the triphilic copolymers was varied systematically to provide all possible variations: ABC, ACB, and BAC. All blocks have glass transition temperatures below 0 °C. Self-assembly into spherical micellar aggregates was observed in aqueous solution, where hydrophobic cores undergo local phase separation into various ultrastructures as shown by cryogenic transmission electron microscopy (cryo-TEM). Selective solubilization of substantial quantities of hydrocarbon and fluorocarbon low molar mass compounds by the lipophilic and fluorophilic block, respectively, is demonstrated.

Synthesis of Ternary, Hydrophilic−Lipophilic−Fluorophilic Block Copolymers by Consecutive RAFT Polymerizations and Their Self-Assembly into Multicompartment Micelles

Linear amphiphilic diblock and ternary triblock copolymers were synthesized by the RAFT method in three successive steps, using oligo(ethylene oxide) monomethyl ether acrylate, butyl or 2-ethylhexyl acrylate, and 1H,1H,2H,2H-perfluorodecyl acrylate. The diblock and the triblock copolymers, which consist of a hydrophilic, a lipophilic, and a fluorophilic block, self-assemble in water into spherical micellar aggregates. Imaging by cryogenic transmission electron microscopy (cryo-TEM) revealed that the cores of the micellar aggregates made from these “triphilic” copolymers undergo local phase separation to form various ultrastructures, which depend sensitively on the given block sequence. While the sequence hydrophilic−lipophilic−fluorophilic resulted in multicompartment cores with core−shell−corona morphology, the sequence lipophilic−hydrophilic−fluorophilic provided new “patched double micelle” and larger “soccer ball” structures.

Synthesis and Micellar Self-Assembly of Ternary Hydrophilic−Lipophilic−Fluorophilic Block Copolymers with a Linear PEO Chain

Linear amphiphilic diblock and ternary triblock copolymers were synthesized by the RAFT method in two successive steps using a poly(ethylene oxide) (PEO) macrochain transfer agent, butyl or 2-ethylhexyl acrylate, and 1H,1H,2H,2H-perfluorodecyl acrylate. The diblock and the triblock copolymers, which consist of a hydrophilic, a lipophilic, and a short fluorophilic block, self-assemble in water into spherical micellar aggregates. Imaging by cryogenic transmission electron microscopy (cryo-TEM) revealed that the micellar cores of the aggregates made from these "triphilic" copolymers can undergo local phase separation to form a unique ultrastructure. In these multicompartment micelles, it appears that extended nonspherical domains, presumably made of nanocrystallites of the fluorocarbon block, are embedded in the hydrocarbon matrix forming the spherical micellar core. This novel internal structure of a micellar core is attributed to the mutual incompatibility of the fluorocarbon and hydrocarbon side chains in combination with the tendency of the used fluorocarbon acrylate monomer to undergo side-chain crystallization.

Novel non-ionic block copolymers tailored for interactions with phospholipids

The bulk of literature on phospholipid membrane interactions with non-ionic amphiphilic block copolymers deals with ABA triblock copolymers of poly(ethylene oxide)- b-poly(propylene oxide)- b-poly(ethylene oxide). This is partially the result of their commercial availability. In recent years novel block copolymers have been synthesized and their interactions with phospholipids structured as Langmuir monolayers, liposomes, bilayer lipid membranes, tethered bilayers, and living cells have been studied. This review describes some new block copolymers with potential to interact with phospholipids. There is a tremendous progress in synthesis of amphiphilic block copolymers triggered by new controlled polymerization techniques as atom transfer radical polymerization or nitroxide mediated polymerization and by the possibility to ‘click’ preformed blocks together using quantitative reactions of functional endgroups. A special focus is given to novel water soluble amphiphilic triblock copolymers of poly(glycerol monomethacrylate)- b-poly(propylene oxide)- b-poly(glycerol monomethacrylate) and their interactions with phosphatidylcholine lipids. Also block copolymers containing hydrophobic blocks with perfluoroalkyl groups are discussed since they are special in a sense that their fluorophilic blocks are neither hydrophilic nor oleophilic as this is the case for conventional amphiphilic block copolymers. Experimental methods to study block copolymer–phospholipid interactions are summarized and selected results based on special experimental techniques such as isothermal titration calorimetry, infrared reflection absorption spectroscopy and ion conductance are presented. This work is intended to convey a better quantitative understanding of amphiphilic block copolymers used for in vitro and in vivo experiments in medicine and pharmacy.

Micellar Structures of Hydrophilic/Lipophilic and Hydrophilic/Fluorophilic Poly(2‐oxazoline) Diblock Copolymers in Water

AbstractAmphiphilic poly(2‐alkyl‐2‐oxazoline) diblock copolymers of 2‐methyl‐2‐oxazoline (MOx) building the hydrophilic block and either 2‐nonyl‐2‐oxazoline (NOx) for the hydrophobic or 2‐(1H,1H′,2H,2H′‐perfluorohexyl)‐2‐oxazoline (FOx) for the fluorophilic block were synthesized by sequential living cationic polymerization. The polymer amphiphiles form core/shell micelles in aqueous solution as evidenced using small‐angle neutron scattering (SANS). Whereas the diblock copolymer micelles with a hydrophobic NOxn block are spherical, the micelles with the fluorophilic FOxn are slightly elongated, as observed by SANS and TEM. In water, the micelles with fluorophilic and lipophilic cores do not mix, but coexist.magnified image

Synthesis of ABC and CABAC Triphilic Block Copolymers by ATRP Combined with ‘Click’ Chemistry

AbstractATRP using poly(propylene oxide) monofunctional macroinitiator was carried out with solketal methacrylate (SMA) and the non‐reactive PPO having two N3 terminal groups was removed by dissolution in an excess of n‐hexane. The resulting azido terminated AB diblock copolymer was ‘clicked’ with an α‐alkyne fluorinated compound, followed by acid hydrolysis of the SMA units, a triphilic ABC triblock copolymer was prepared. ATRP of SMA with a difunctional PPO macroinitiator to give ABA triblock copolymer was also carried out. The terminal Br was again exchanged with N3, ‘clicked’ with the α‐alkyne fluorinated compound and likewise hydrolyzed to give a triphilic CABAC pentablock copolymer, i.e., hydrophilic, oleophilic, and fluorophilic blocks were combined.magnified image

Atrp synthesis of abc lipophilic–hydrophilic–fluorophilic triblock copolymers

AbstractNew ABC triblock copolymers that contain lipophilic, hydrophilic, and fluorophilic blocks are reported. These new block copolymers were synthesized via sequential controlled/living atom transfer radical polymerization. The formation of block copolymers was confirmed by size exclusion chromatography, 1H, and 19F NMR. In direct comparison to the ABC copolymer, the corresponding ABA′ polymer did not produce a gel up to 45 wt % polymer. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2601–2608, 2007

SYNTHESIS AND CHARACTERIZATION OF WATER-SOLUBLE BLOCK COPOLYMERS WITH AN END-TAGGED NAPHTHALENE PROBE

Water-soluble A-B block copolymers of 2-perfluoroethyl-2-oxazoline or 2-pentyl-2-oxazoline as hydrophobic monomers and 2-methyl-2-oxazoline as hydrophilic monomer were prepared by means of the living cationic ring-opening polymerization. The polymerization was initiated with N-methyl-2-(1-naphthyl)-2-oxazolinium trifluoromethanesulfonate as fluorescence label followed by sequential addition of the hydrophobic and the hydrophilic monomer. The polymerization was monitored by 1H NMR spectroscopy and gel permeation chromatography(GPC) measurements. The results revealed that fluorophilic block copolymers can be prepared by this method while lipohilic block copolymers are not accessible by this monomer sequence. Micelle formation of the fluorophilic block copolymers in aqueous solution was studied by means of steady-state fluorescence spectroscopy which confirmed strong intermolecular excimer formation of the terminal bounded naphthalene moiety. In chloroform as a good solvent for both blocks, only monomer fluorescence could be observed.