Hydrophilic Block Research Articles

Synthesis of alternating copolymer PAspNa‐alt‐PAsp(Pr) for drug delivery system

AbstractAlternating copolymers (ACs) contain two distinct monomeric unit types dispersed in alternating order of hydrophilic block and hydrophobic block. ACs have extensive and versatile applications in both academia and industry, especially in drug delivery systems (DDS) due to their unique physical and chemical properties. In the present research, poly(β‐benzyl l‐aspartate) (PBLA) was prepared by ring‐opening polymerization of BLA‐NCA. The result obtained from GPC showed that PBLA was successfully synthesized with narrow weight distribution Mw/Mn = 1.055. The outcome of copolymer has the degree of polymerization (DP) of PBLA was 50 based on the 1H NMR spectroscopy. Further, alternating copolymer poly(aspartate‐sodium) alternating poly(aspartate‐R) (PAspNa‐alt‐PAsp(Pr)), which allows the installation of expected compounds into a polymer backbone of PBLA without unwanted side effects, was synthesized via 2 steps: (1) aminolysis by 0.5 fold primary amine to attach hydrophobic group and (2) hydrolysis slowly by NaOH solution to form the hydrophilic group on the side chain of the polymer. The novel alternating copolymer synthesized successfully in this study was expected to be a promising candidate for drug delivery devices.

Effect of aromatic substituents on thermoresponsive functional polycaprolactone micellar carriers for doxorubicin delivery.

Amphiphilic functional polycaprolactone (PCL) diblock copolymers are excellent candidates for micellar drug delivery. The functional groups on the backbone significantly affect the properties of PCL. A systematic investigation of the effect of aromatic substituents on the self-assembly of γ-functionalized PCLs and the delivery of doxorubicin (DOX) is presented in this work. Three thermoresponsive amphiphilic diblock copolymers with poly(γ-benzyloxy-ε-caprolactone) (PBnCL), poly(γ-phenyl- ε-caprolactone) (PPhCL), poly(γ-(4-ethoxyphenyl)-ε-caprolactone) (PEtOPhCL), respectively, as hydrophobic block and γ-tri(ethylene glycol) functionalized PCL (PME3CL) as hydrophilic block were prepared through ring-opening polymerization (ROP). The thermoresponsivity, thermodynamic stability, micelle size, morphology, DOX-loading, and release profile were determined. The LCST values of amphiphilic diblock copolymers PME3CL-b-PBnCL, PME3CL-b-PPhCL, and PME3CL-b-PEtOPhCL are 74.2°C, 43.3°C, and 37.3°C, respectively. All three copolymers formed spherical micelles in phosphate-buffered saline (PBS, 1×, pH = 7.4) at low concentrations ranging from 8.7 × 10-4g/L to 8.9 × 10-4g/L. PME3CL-b-PBnCL micelles showed the highest DOX loading capacity of 3.01 ± 0.18 (wt%) and the lowest drug release, while PME3CL-b-PEtOPhCL micelles exhibited the lowest DOX loading capacity of 1.95 ± 0.05 (wt%) and the highest drug release. Cytotoxicity and cellular uptake of all three micelles were assessed in vitro using MDA-MB-231 breast cancer cells. All three empty micelles did not show significant toxicity to the cells at concentrations high up to 0.5mg/mL. All three DOX-loaded micelles were uptaken into the cells, and DOX was internalized into the nucleus of the cells.

Ionic Strength Effect in the Equilibrium and Rheological Behavior of an Amphiphilic Triblock Copolymer at the Air/Solution Interface

This study investigates the effect of an inert salt (NaCl) on the equilibrium interfacial tension and dilatational modulus of Pluronic F-68 copolymer, a triblock copolymer consisting of two terminal blocks of poly(ethylene oxide) and a less hydrophilic central block of poly(propylene oxide). Interfacial tension measurements were carried out using a surface force balance and a drop shape tensiometer, while rheological measurements were carried out in two different frequency ranges. This involved the use of the oscillatory barrier/droplet method and electrocapillary wave measurements, complemented by an appropriate theoretical framework. This work aimed to elucidate the influence of NaCl on the interfacial behavior of Gibbs monolayers of Pluronic F-68. In addition, this study highlights some of the technical and theoretical limitations associated with obtaining reliable dilatational rheological data at high frequencies (<1 kHz) using electrocapillary wave measurements. The results provide valuable insights into the interplay between salt presence and interfacial properties of Pluronic F-68 and highlight the challenges of obtaining accurate dilatational rheological data under specific measurement conditions.

Multivalent Salt-Induced Self-Assembly of Amphiphilic Polyelectrolytes of Different Charge Fractions: A Coarse-Grained Molecular Dynamics Simulation Study.

Amphiphilic polymers with both hydrophobic and hydrophilic blocks are of great interest for their potential applications in drug delivery. Their self-assembly behavior in response to environmental factors like ion charge and multivalent salt concentration has been the subject of recent investigation. Our study utilizes coarse-grained molecular dynamics simulations to investigate the aggregation behavior of amphiphilic copolymers upon introducing tetravalent salt at varying charge fractions. We identify a critical concentration, Cs*, where the aggregation number reaches its maximum for each charge fraction, followed by a subsequent decrease at the excessive salt regime. This study reveals distinct morphological transitions in response to increasing salt concentration and decreasing charged fractions, namely, (i) stable dispersed micelles, (ii) a singular micelle comprising all copolymer chains, and (iii) redispersed micelles, particularly evident at lower charged fractions. Our study highlights the significant influence of tetravalent salt and charge fractions of polyelectrolyte chains on the self-assembly behavior of polyelectrolyte copolymers.

Relationship between molecular structure and corrugations in self-assembled polypeptoid nanosheets revealed by cryogenic electron microscopy

Designing conformationally dynamic molecules that self-assemble into predictable nanostructures remains an important unmet challenge. This paper describes how atomic-scale cryogenic transmission electron microscopy (cryo-TEM) can be used to explore the relationship between molecular structure and self-assembly of block copolymers. We examined sheetlike micelles formed in water using a series of diblock copolypeptoids with the same hydrophilic block and three distinct crystalline hydrophobic blocks. Our cryo-TEM images revealed all the structures share nansoscale features, but differ in their intermolecular packing geometries. Different molecular arrangements, parallel and antiparallel V-shaped crystal motifs, were revealed by two-dimensional atomic-scale through-plane images. However, images from tilted samples revealed an unexpected feature when the hydrophobic polypeptoid block comprised phenyl rings with substituted bromine atoms at the para position. The nanosheets contained atomic-scale corrugations that were absent in the other systems which comprised unsubstituted aliphatic and aromatic side chains. We hypothesize that these corrugations are due to the dipolar characteristics of the brominated phenyl group and interactions between this group and water molecules. Published by the American Physical Society 2024

Coordinative Double Hydrophilic All-Polyether Micelles for pH-Responsive Delivery of Cisplatin.

Despite its widespread use in the treatment of numerous cancers, the use of cisplatin still raises concerns about its high toxicity and limited selectivity. Consequently, the necessity arises for the development of an effective drug delivery system. Here, we present an effective approach that introduces a double hydrophilic block copolyether for the controlled delivery of cisplatin. Specifically, poly(ethylene glycol)-block-poly(glycidoxy acetic acid) (mPEG-b-PGA) was synthesized via anionic ring-opening polymerization using the oxazoline-based epoxide monomer 4,4-dimethyl-2-oxazoline glycidyl ether, followed by subsequent acidic deprotection. The coordinative metal-ligand interaction between cisplatin and the carboxylate group within the PGA block facilitated the formation of micelles from the double hydrophilic mPEG-b-PGA copolyether. Cisplatin-loaded polymeric micelles had a high loading capacity, controlled pH-responsive release kinetics, and high cell viability. Furthermore, in vitro biological assays revealed cellular apoptosis induced by the cisplatin-loaded micelles. This study thus successfully demonstrates the potential use of double hydrophilic block copolyethers as a versatile platform for biomedical applications.

Block Sequence Effects on the Self-Assembly Behaviors of Polypeptide-Based Penta-Block Copolymer Hydrogels.

Peptide-based hydrogels have great potential for applications in tissue engineering, drug delivery, and so on. We systematically synthesize, characterize, and investigate the self-assembly behaviors of a series of polypeptide-based penta-block copolymers by varying block sequences and lengths. The copolymers contain hydrophobic blocks of poly(γ-benzyl-l-glutamate) (PBG, Bx) and two kinds of hydrophilic blocks, poly(l-lysine) (PLL, Ky) and poly(ethylene glycol) (PEG, EG34), where x and y are the number of repeating units of each block, where PBG and PLL blocks have unique functions for nerve regeneration and cell adhesion. It shows that a sufficient length of the middle hydrophilic segment capped with hydrophobic end PBG blocks is required. They first self-assemble into flower-like micelles and sequentially form transparent hydrogels (as low as 2.3 wt %) with increased polymer concentration. The hydrogels contain a microscale porous structure, a desired property for tissue engineering to facilitate the access of nutrient flow for cell growth and drug delivery systems with high efficiency of drug storage. We hypothesize that the structure of Bx-Ky-EG34-Ky-Bx agglomerates is beyond micron size (transparent), while that of Ky-Bx-EG34-Bx-Ky is on the submicron scale (opaque). We establish a working strategy to synthesize a polypeptide-based block copolymer with a wide window of sol-gel transition. The study offers insight into rational polypeptide hydrogel design with specific morphology, exploring the novel materials as potential candidates for neural tissue engineering.

Influence of Peptoid Sequence on the Mechanisms and Kinetics of 2D Assembly.

Two-dimensional (2D) materials have attracted intense interest due to their potential for applications in fields ranging from chemical sensing to catalysis, energy storage, and biomedicine. Recently, peptoids, a class of biomimetic sequence-defined polymers, have been found to self-assemble into 2D crystalline sheets that exhibit unusual properties, such as high chemical stability and the ability to self-repair. The structure of a peptoid is close to that of a peptide except that the side chains are appended to the amide nitrogen rather than the α carbon. In this study, we investigated the effect of peptoid sequence on the mechanism and kinetics of 2D assembly on mica surfaces using in situ AFM and time-resolved X-ray scattering. We explored three distinct peptoid sequences that are amphiphilic in nature with hydrophobic and hydrophilic blocks and are known to self-assemble into 2D sheets. The results show that their assembly on mica starts with deposition of aggregates that spread to establish 2D islands, which then grow by attachment of peptoids, either monomers or unresolvable small oligomers, following well-known laws of crystal step advancement. Extraction of the solubility and kinetic coefficient from the dependence of the growth rate on peptoid concentration reveals striking differences between the sequences. The sequence with the slowest growth rate in bulk and with the highest solubility shows almost no detachment; i.e., once a growth unit attaches to the island edge, there is almost no probability of detaching. Furthermore, a peptoid sequence with a hydrophobic tail conjugated to the final carboxyl residue in the hydrophilic block has enhanced hydrophobic interactions and exhibits rapid assembly both in the bulk and on mica. These assembly outcomes suggest that, while the π-π interactions between adjacent hydrophobic blocks play a major role in peptoid assembly, sequence details, particularly the location of charged groups, as well as interaction with the underlying substrate can significantly alter the thermodynamic stability and assembly kinetics.

Spatial-Arrangement-Assisted Emission Energy Fine Tuning of CdSe Quantum Dots (QDs) in QD–Block Copolymer Complexes

Quantum dots (QDs) exhibit size-dependent optical properties, where both the absorption and fluorescence energy levels vary with QD size. However, this dependence results in a discontinuity of intrinsically accessible energy levels for the bandgap, posing challenges in achieving precise energy tuning within a specific range. Herein, we demonstrate emission energy control of QDs with identical absorption energy levels by manipulating the spatial arrangement of QDs within QD–polymer complexes through hydrophobic interactions. The phase behavior of the QD–polymer complexes was modulated by adjusting the mass fraction of hydrophilic and hydrophobic blocks in the block copolymer, utilizing two types of amphiphilic block copolymers and varying temperatures. The QDs were spontaneously trapped within the hydrophobic region of the polymer template in water, resulting in spherical, cylindrical, and vesicle structures of QD–polymer complexes, corresponding to spherical, cylindrical, and layered assemblies of QDs, respectively. Depending on the QDs’ location within the QD–polymer complex, the surface area in contact with water varied, leading to different degrees of oxidation and, consequently, a change in the fluorescence energy level of QDs. This study introduces a novel method to fine tune the emission energy (<15 eV) of QDs by adjusting the polymer form factor without complicated procedures.

Polymersomes as the Next Attractive Generation of Drug Delivery Systems: Definition, Synthesis and Applications.

Polymersomes are artificial nanoparticles formed by the self-assembly process of amphiphilic block copolymers composed of hydrophobic and hydrophilic blocks. They can encapsulate hydrophilic molecules in the aqueous core and hydrophobic molecules within the membrane. The composition of block copolymers can be tuned, enabling control of characteristics and properties of formed polymersomes and, thus, their application in areas such as drug delivery, diagnostics, or bioimaging. The preparation methods of polymersomes can also impact their characteristics and the preservation of the encapsulated drugs. Many methods have been described, including direct hydration, thin film hydration, electroporation, the pH-switch method, solvent shift method, single and double emulsion method, flash nanoprecipitation, and microfluidic synthesis. Considering polymersome structure and composition, there are several types of polymersomes including theranostic polymersomes, polymersomes decorated with targeting ligands for selective delivery, stimuli-responsive polymersomes, or porous polymersomes with multiple promising applications. Due to the shortcomings related to the stability, efficacy, and safety of some therapeutics in the human body, polymersomes as drug delivery systems have been good candidates to improve the quality of therapies against a wide range of diseases, including cancer. Chemotherapy and immunotherapy can be improved by using polymersomes to deliver the drugs, protecting and directing them to the exact site of action. Moreover, this approach is also promising for targeted delivery of biologics since they represent a class of drugs with poor stability and high susceptibility to in vivo clearance. However, the lack of a well-defined regulatory plan for polymersome formulations has hampered their follow-up to clinical trials and subsequent market entry.

Enhanced stability of gold nanoparticles capped with double hydrophilic block copolymers synthesized by eATRP

AbstractIn this study, the gold nanoparticles (Au NPs) are capped with a novel, well‐defined double hydrophilic block copolymer, poly (ethylene glycols)‐block‐poly(mono‐2‐(methacryloyloxy) ethyl succinate) (PEG‐b‐PSEMA). The PEG‐b‐PSEMA, with long side chains and relatively narrow dispersity index, is successfully prepared by aqueous electrochemically mediated atom transfer radical polymerization using a PEG‐Br macroinitiator (Mn≈2000 g mol−1). By simply mixing PEG‐b‐PSEMA and Au precursor before adding reductants, coulombic interactions occur between the Au precursor and the carboxylate group of the PSEMA, as a result dense Au NPs are formed. This enables the Au NPs to remain dispersed even in the presence of temperature variations, pH adjustments, and incubation in organic solvents. Au NPs were endowed by PEG‐b‐PSEMA with more remarkable catalytic activity in organic solvents of 4‐nitrophenol into 4‐aminophenol than by sodium citrate (Au@citrate) and MeO‐PEG‐OH (Au@PEG). In addition, PEG‐b‐PSEMA‐stabilized Au NPs (Au@PEG‐b‐PSEMA) were also tested for the dye degradation property against Rhodamine‐B in only pH 10 basic solution, and over 99% of dye degradation can be achieved in 9 min. PEG‐b‐PSEMA induces coulombic interactions with Au NPs, providing outstanding stability for catalytic applications in organic or specific acidic‐base environments.

AMPHIPHILIC BLOCK COPOLYMERS AS STABILIZERS OF SILICA AND SILICON NANOPARTICLES SYNTHESIZED IN PLASMA DISCHARGE UNDER ULTRASONIC CAVITATION

A range of tailor-made amphiphilic block copolymers of acrylic acid as a hydrophilic block and styrene as a hydrophobic block, as well as their homo- and random copolymers, were utilized for colloidal stabilization of silica and silicon nanoparticles in their hydrocarbon suspensions. Silicon-containing nanoparticles were synthesized in plasma discharge under intensive ultrasonic cavitation by decomposition of tetraethoxysilane. The influence of the molecular characteristics and architecture of the applied copolymers on the stabilization effect was examined. Random copolymers of styrene and acrylic acid were shown to provide poor stabilization effects, while diblock and triblock copolymers acted as effective suspension stabilizers. As a result of this study, the optimal molecular structure for diblock copolymers and the optimal molecular architecture for triblock copolymers were established. These findings allowed us to conduct a short reconnaissance study of the structure-dependent stabilization effects, opening prospective routes for tunable compatibilizers with stability varied as a function of composition.

Star-polymer unimolecular micelle nanoparticles to deliver a payload across the blood-brain barrier.

Nanocarrier-mediated therapeutic delivery to brain tissue is impeded by tightly controlled transportation across the blood-brain barrier (BBB). Herein, we report a well-defined core-shell star-shaped unimolecular micelle (star-UMM; a single polymer entity) as an efficient BBB-breaching nanoparticle for brain-specific administration of the fluorescent anticancer drug doxorubicin and in vivo mapping of brain tissues by the near-infrared biomarker IR780 in mice. The star-UMM was engineered by precisely programming the polymer topology having hydrophobic and hydrophilic polycaprolactone blocks and in-built with lysosomal enzyme-biodegradation stimuli to deliver the payloads at intracellular compartments. In vivo imaging in mice revealed prolonged circulation of star-UMM in blood for >72 h, and whole-organ image-quantification substantiated its efficient ability to breach the BBB. Star UMM exhibited excellent stability in blood circulation and reduced cardiotoxicity, was non-hemolytic, had substantial uptake in the cortical neurons of the mouse brain, had lysosomal enzymatic-biodegradation, and exhibited negligible immunogenicity or necrosis. This newly designed star-UMM could have long-term applications in brain-specific drug delivery.

Impact of a poly(ethylene glycol) corona block on drug encapsulation during polymerization induced self-assembly.

Polymerization induced self-assembly (PISA) provides a facile platform for encapsulating therapeutics within block copolymer nanoparticles. Performing PISA in the presence of a hydrophobic drug alters both the nanoparticle shape and encapsulation efficiency. While previous studies primarily examined the interactions between the drug and hydrophobic core block, this work explores the impact of the hydrophilic corona block on encapsulation. Poly(ethylene glycol) (PEG) and poly(2-hydroxypropyl methacrylate) (PHPMA) are used as the model corona and core blocks, respectively, and phenylacetic acid (PA) is employed as the model drug. Attachment of a dithiobenzoate end group to the PEG homopolymer - transforming it into a macroscopic reversible addition-fragmentation chain transfer agent - causes the polymer to form a small number of nanoscopic aggregates in solution. Adding PA to the PEG solution encourages further aggregation and macroscopic phase separation. During the PISA of PEG-PHPMA block copolymers, inclusion of PA in the reaction mixture promotes faster nucleation of spherical micelles. Although increasing the targeted PA loading from 0 to 20 mg mL-1 does not affect the micelle size or shape, it alters the drug spatial distribution within the PISA microenvironment. PA partitions into either PEG-PHPMA micelles, deuterium oxide, or other polymeric species - including PEG aggregates and unimer chains. Increasing the targeted PA loading changes the fraction of drug within each encapsulation site. This work indicates that the corona block plays a critical role in dictating drug encapsulation during PISA.

Influence of hydrophilic block length on the aggregation properties of polyglycidol-polystyrene-polyglycidol copolymers.

Amphiphilic triblock copolymers, polyglycidol-polystyrene-polyglycidol (PGL-PS-PGL), were synthesised via anionic polymerization starting from the synthesis of a polystyrene macroinitiator with 60 styrene units in the block terminated by ethylene oxide. Poly(ethoxyethyl glycidyl ether) blocks of different lengths were created on both sides of the macroinitiator. By removing the ethoxyethyl blocking groups, PGL-PS-PGL copolymers containing polyglycidol blocks with DP 11, 23, 44 and 63 were received. Their structures were determined by NMR and FTIR. The hydrophilicity of PLG-PS-PGL films was studied upon exposure to water vapour. To perform the copolymers' aggregation in water, the samples were dialysed from DMF into water. The critical concentration of their micellisation (CMC) was determined by measuring the absorbance of the 1,6-diphenylhexa-1,3,5-triene (DPH) probe and the intensity of light scattered by the copolymers' solution as a function of concentration. CMC values increased with increasing the number of hydrophilic glycidol units in the copolymer chain. The sizes of aggregates formed slightly above the critical concentration were measured by dynamic light scattering (DLS), and particles were imaged by cryo-TEM. Cryo-TEM pictures showed the presence of regular micelles in copolymer dispersions. For copolymers with shorter PGL chains aggregated partices were detected. Moreover, cryo-TEM demonstrated that the copolymers with a polyglycidol block of DP = 63 formed regular spherical micelles that formed 2D ordered organisation on the surface. X-ray measurements showed the formation of a partially crystallised PS core in the micelle's interior. The aggregates of all copolymers were stable. Their sizes did not change after one year of storage. The particles did not disassociate even after diluting their dispersions to a concentration 10 times lower than the critical concentration.

Formation of a planar biomimetic membrane with a novel zwitterionic polymer for nanopore sequencing.

Biological membranes containing transmembrane channels play a crucial role in numerous cellular processes, and mimicking of cell membranes has garnered significant interest in various biomedical applications, particularly nanopore sequencing technology, where remarkable progress has been made with nanopore membranes. Considering the fragility of biomimetic membranes formed by artificial lipids and the limited mimicry of those formed by common block copolymers, this study developed a novel amphiphilic polymer by covalently linking hydrophilic heads of phospholipids to the ends of hydrophobic poly(dimethyl siloxane) (PDMS) chains. The absence of hydrophilic blocks allowed for good control over the polydispersity of this polymer within a narrow range. The high flexibility of PDMS chains, combined with relatively uniform molecular weights, would confer enhanced stability and robustness to polymeric membranes. Dynamic light scattering measurements and microdroplet formation tests demonstrated good amphipathic properties of these novel polymers when maintaining an appropriate hydrophilic-hydrophobic ratio. Moreover, the high similarity between the hydrophilic heads and natural phospholipids makes this polymer more compatible with biomolecules. A successful protein insertion experiment confirmed both the stability of this polymeric membrane and its compatibility with membrane proteins. As a result, this novel amphiphilic polymer exhibits great potential for biomembrane mimicking and paves a new path for material design in biomedical applications.

Azonia‐Naphthalene: A Cationic Hydrophilic Building Block for Stable N‐Type Organic Mixed Ionic‐Electronic Conductors**

AbstractConjugated polymers that can efficiently transport both ionic and electronic charges have broad applications in next‐generation optoelectronic, bioelectronic, and energy storage devices. To date, almost all the conjugated polymers have hydrophobic backbones, which impedes efficient ion diffusion/transport in aqueous media. Here, we design and synthesize a novel hydrophilic polymer building block, 4a‐azonia‐naphthalene (AN), drawing inspiration from biological systems. Because of the strong electron‐withdrawing ability of AN, the AN‐based polymers show typical n‐type charge transport behaviors. We find that cationic aromatics exhibit strong cation‐π interactions, leading to smaller π–π stacking distance, interesting ion diffusion behavior, and good morphology stability. Additionally, AN enhances the hydrophilicity and ionic‐electronic coupling of the polymer, which can help to improve ion diffusion/injection speed, and operational stability of organic electrochemical transistors (OECTs). The integration of cationic building blocks will undoubtedly enrich the material library for high‐performance n‐type conjugated polymers.

Azonia-Naphthalene: A Cationic Hydrophilic Building Block for Stable N-Type Organic Mixed Ionic-Electronic Conductors.

Conjugated polymers that can efficiently transport both ionic and electronic charges have broad applications in next-generation optoelectronic, bioelectronic, and energy storage devices. To date, almost all the conjugated polymers have hydrophobic backbones, which impedes efficient ion diffusion/transport in aqueous media. Here, we design and synthesize a novel hydrophilic polymer building block, 4a-azonia-naphthalene (AN), drawing inspiration from biological systems. Because of the strong electron-withdrawing ability of AN, the AN-based polymers show typical n-type charge transport behaviors. We find that cationic aromatics exhibit strong cation-π interactions, leading to smaller π-π stacking distance, interesting ion diffusion behavior, and good morphology stability. Additionally, AN enhances the hydrophilicity and ionic-electronic coupling of the polymer, which can help to improve ion diffusion/injection speed, and operational stability of organic electrochemical transistors (OECTs). The integration of cationic building blocks will undoubtedly enrich the material library for high-performance n-type conjugated polymers.

Hybrid polyionic complexes as nanoreactors for the synthesis of iron oxide nanoparticles: From size control to modulation of magnetic and catalytic properties

Hybrid polyion complexes (HPICs) obtained from the complexation in aqueous solution of a double hydrophilic block copolymers and metal ions can act as efficient precursors for the controlled synthesis of hybrid nanoparticles. Hence, HPICs based on a mixture of ferrous and ferric ions with poly(ethylene oxide)-block-poly(acrylic acid) were used to initiate, after the addition at 70 °C of a solution of NH4OH, the formation of iron oxide nanoparticles. The careful choice of the molar ratio between polymer and metal ions within HPICs enables to tune the morphology and size of the obtained iron oxide nanoparticles while maintaining the same surface composition. This control of size and composition was further used to highlight the relationship between the size of these particles and their catalytic and magnetic properties.

Next Generation Fluorine-Free Proton Exchange Membranes for Electrochemical Energy Applications

Most commercially available proton exchange membrane (PEM)-based fuel cell and electrolyser systems currently employ perfluorinated sulfonic acid (PFSA)-based PEMs, e.g., Nafion. The use of these fluorinated polymers presents serious health and environmental concerns as their production, degradation, and disposal results in the release of hazardous perfluorinted compounds that have been shown to accumulate in the environment and are toxic to living organisms.[1] Developing non-toxic, safe-by-design hydrocarbon PEMs is therefore crucial to ensure that renewable technologies that rely on proton exchange membranes remain an environmentally friendly solution. Additional shortcomings of PFSA-based PEMs include their expensive synthetic cost, inherently high hydrogen crossover, and limited operating temperature range due to poor thermo-mechanical properties above 90 °C. Hydrocarbon (HC)-based membranes offer advantages over their perfluorinated counterparts in these specific areas, however, the main drawback of HC-PEMs is that they require a much greater density of sulfonic acid groups to achieve similar proton conductivities as PFSA-based polymers.[2] This leads to greater water uptake and excessive swelling which ultimately leads to reduced mechanical stability of HC membranes.More recently there has been an increasing number of reports exploring the use of block copolymer strategies to limit the water uptake and swelling properties of hydrocarbon PEMs while maintaining good ionic conductivity.[3] As the ion, liquid, and gas transport properties of the membrane are largely attributed to the hydrophilic blocks (i.e., with sulfonic acid groups) and the mechanical, chemical, and thermal stability of the resulting membrane is determined by the hydrophobic blocks (i.e., no sulfonic acid groups), it is postulated that the resulting membrane properties can be tuned by varying the fraction of hydrophilic/hydrophobic blocks.The overall goal of this project is to synthesise hydrocarbon block copolymer PEMs with reduced gas crossover and enhanced the mechanical properties while maintaining sufficiently high ionic conductivity, ultimately leading to higher performance and greater durability inelectrochemical energy conversion and storage systems, e.g., fuel cells and electrolysers. In this project we have compared the ex-situ properties of novel hydrocarbon block copolymers with PFSA-based Nafion membranes, e.g., water uptake and swelling, conductivity measurements, oxidative stability via Fenton's test, etc., as well as in-situ performance tests in single cell fuel cell and electroylzers.[1]Feng, M.; Wang, Z. et al. Sci. Rep. 2015, 5, 9859.[2]Holdcroft, S. Chem. Mater. 2014, 26, 381.[3]Guiver, M. et al. Chem. Rev. 2017, 117, 4759.