Chiral Transfer of Linear Polysiloxane with Preferred-Handed Helical Conformation.

We report the preparation of chiral silica using a linear polysiloxane main chain with a preferred-handed helical structure as the template. Poly(methylvinyl siloxane) (PMVS) with a cysteine derivative side chain designated as PMVS-Cys was prepared using anionic polymerization and an ene-thiol reaction. PMVS-Cys forms a helical conformation in both solution and film via hydrogen bonding between amide groups at side chains. The helical structure remains during the calcination process, resulting in silica with helical structure. The silica with a helical structure shows optical activity.

Core-Shell Double Gyroids Directed by Selective Solvation for ABC Triblock Terpolymers.

The formation of ABC triblock terpolymers through solution casting is still challenging. In this study, core-shell double gyroid network structures are fabricated via solution casting using poly(2,2,2-trifluoroethyl methacrylate) (PTFEMA) (F)-b-[poly(4-vinylpyridine) (P4VP) (P)]-b-[polystyrene (PS) (S)] (FPS) triblock terpolymers in N,N-dimethylformamide (DMF). Upon heat treatment, the polymer tends to form a sphere-in-lamellar structure at the F/S interface. Given the solubility properties of each component in DMF, it is anticipated that the effective volume fraction of F relative to P would increase in concentrated solutions and the effective volume fraction of S would decrease. The microphase-separated structure derived from the DMF solution consistently results in the formation of a network structure composed of a core-shell double gyroid, with F as the matrix, P as the shell, and S as the core, and their periodic lengths gradually increase to 110.8, 131.8, and 162.7 nm as increase molecular weights of PS blocks to 13.8, 20.7, and 28.8 kg mol-1. Based on the solubility properties of the polymer components highlighted in this study, the solvent selection strategy is broadly applicable to ABC triblock terpolymers featuring various polymer components, offering a more efficient avenue for fabricating core-shell double gyroid structures.

One-pot gram-scale rapid synthesis of MN4 complexes with 14-membered ring macrocyclic ligand as a precursor for carbon-based ORR and CO2RR catalysts.

Herein, CoN4, CuN4, and NiN4 complexes with a 14-membered ring hexaazamacrocycle ligand H2HAM were synthesised as precursors for ORR and CO2RR catalysts via a one-pot, gram-scale synthesis procedure, which involved microwave heating for only 10 min. Detailed structures of the obtained 14MR-MN4 complex were revealed by single-crystal X-ray diffraction measurements.

Controlling Circularly Polarized Luminescence Using Helically Structured Chiral Silica as a Nanosized Fused Quartz Cell.

Circularly polarized luminescence (CPL) is typically achieved with a chiral luminophore. However, using a helical nanosized fused quartz cell consisting of chiral silica, we could control the wavelength and helical sense of the CPL of an achiral luminophore. Chiral silica with a helical nanostructure was prepared by calcining a mixture of polyhedral oligomeric silsesquioxane (POSS)-functionalized isotactic poly(methacrylate) (it-PMAPOSS) and a small amount of chiral dopant. The chiral silica encapsulated functional molecules, including luminophores, along the helical nanocavity, leading to induced circular dichroism (ICD) and induced circularly polarized luminescence (iCPL). Because chiral silica can act as a helical nanosized fused quartz cell, it can encapsulate not only the luminophore but also solvent molecules. By changing the solvent in the luminophore-containing nanosized fused quartz cell, the wavelength of the CPL was controlled. This method provides an effective strategy for designing novel CPL-active materials.

An experimental and theoretical investigation into the self-assembly of a chemically modified high-χ coil-rod diblock copolymer.

A precursor diblock copolymer with a silicon backbone, polystyrene-block-poly(methylvinylsiloxane), was synthesized, and 1H,1H,2H,2H-perfluorodecanethiol was quantitatively introduced into the backbone via a thiol-ene reaction to yield a novel coil-rod diblock copolymer, poly(styrene-block-poly(2-((3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-heptadecafluorodecyl)thio)ethyl)methylsiloxane). The ultra-hydrophobicity of the introduced perfluoroalkyl side chain enhanced the segregation between counter-blocks and significantly increased the χ value, which is essential for minimizing the size of self-assembled domains for lithographic applications. Thus, self-assembled domains with a minimal spacing of approximately 10 nm were formed. A hexagonally packed array with significant anisotropy was observed in the self-assembled morphology by small-angle X-ray scattering and transmission electron microscopy. Such an array was precisely reproduced by modified self-consistent field theory (SCFT) calculation developed for the coil-rod structure. Furthermore, the phase diagram was estimated, and the morphological dependence on the relative scale of the rod unit was investigated by SCFT prediction.

Synthesis and Characterization of White-Light Luminescent End-Capped Polyimides Based on FRET and Excited State Intramolecular Proton Transfer.

N-cyclohexylphthalimide-substituted trifluoroacetylamino (CF3CONH-) group (3TfAPI), which forms an intramolecular hydrogen bond, was synthesized, and it exhibited a bright yellow fluorescence owing to the excited-state intramolecular proton transfer (ESIPT) in the solution and crystalline states. In addition, CF3CONH-substituted phthalic anhydride (3TfAPA) was synthesized, which was attached to the termini of a blue-fluorescent semi-aromatic polyimide (PI) chain. Owing to the efficient Förster resonance energy transfer (FRET) occurring from the main chain to the termini and the suppression of deprotonation (anion formation) at the 3TfAPA moiety by H2SO4 doping, the resulting PI films display bright white fluorescence. Moreover, the enhancement of the chain rigidity by substituting the diamine moiety results in an increase in the quantum yield of white fluorescence (Φ) by a factor of 1.7, due to the suppression of local molecular motion. This material design strategy is promising for preparing thermally stable white-light fluorescent PIs applicable to solar spectral convertors, displays, and ICT devices.

High Durability of a 14-Membered Hexaaza Macrocyclic Fe Complex for an Acidic Oxygen Reduction Reaction Revealed by In Situ XAS Analysis.

Nonplatinum metal (NPM) catalysts for the oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFCs) have been developed; however, NPM catalysts still need to be improved in terms of both their catalytic activity and durability. To overcome these problems, an Fe active site contained within a more compact ligand than conventional, porphyrinic, 16-membered ring ligands, or more specifically, a hexaaza macrocyclic ligand with a 14-membered ring (14MR), was developed. In this study, the durability of the Fe-14MR complex was compared to that of Fe phthalocyanine (FePc), which has a 16-membered ring ligand, using in situ X-ray absorption spectroscopy; demetalation of the Fe complexes was directly observed during electrochemical experiments performed under acidic ORR conditions. It was found that Fe-14MR is significantly more resistant to demetalation than FePc during the ORR.

Topology-transformable block copolymers based on a rotaxane structure: change in bulk properties with same composition.

The topology of polymers affects their characteristic features, i.e., their microscopic structure and macroscopic properties. However, the topology of a polymer is usually fixed during the construction of the polymer chain and cannot be transformed after its determination during the synthesis. In this study, topology-transformable block copolymers that are connected via rotaxane linkages are introduced. We will present systems in which the topology transformation of block copolymers changes their 1) microphase-separated structures and 2) macroscopic mechanical properties. The combination of a rotaxane structure at the junction point and block copolymers that spontaneously form microphase-separated structures in the bulk provides access to systems that cannot be attained using conventional covalent bonds.

Chiral Silica with Preferred-Handed Helical Structure via Chiral Transfer.

A strategy to obtain chiral silica using an achiral stereoregular polymer with polyhedral oligomeric silsesquioxane (POSS) side chains is described herein. The preferred helical conformation of the POSS-containing polymer could be achieved by mixing isotactic polymethacrylate-functionalized POSS (it-PMAPOSS) and a chiral dopant. The array structure of POSS molecules, which are placed along the helical conformation, is memorized even after removing the chiral dopant at high temperatures, leading to a chiral silica compound with exclusive optical activity after calcination.

Exploring the Mesoscopic Morphology in Mussel Adhesive Proteins by Soft X-ray Spectromicroscopy.

Marine mussels efficiently adhere under wet conditions by precisely controlling the hierarchical structure of the adhesive plaque through sequential mussel foot protein secretion in the foot-tip cavity. Chemical analysis of the non-uniform mussel plaque morphology has been performed using spectromicroscopy; however, the mesoscopic morphology has not been elucidated yet because of the limited spatial resolution of conventional chemical imaging techniques. We investigated the chemical speciation in the non-uniform mussel plaque morphology employing scanning transmission soft X-ray spectromicroscopy (STXM). The high-spatial-resolution STXM chemical imaging with C 1s near-edge X-ray absorption fine structure yields the distribution of the hydroxy-substituted aromatic residues in the sub-micron scale non-uniform mussel plaque morphology. The matrix consists of a high-protein-density cured product containing a large number of hydroxy-substituted aromatic carbons, including tyrosine and 3,4-dihydroxyphenylalanine (Dopa), whereas the microdomains are poor-protein-density regions with a low aromatic residue relative content. The adhesive interface was covered with the matrix phase to ensure adhesion. The cuticle layer involves a moderate Dopa content, which appears to be optimized for the mechanical performance of the skin.

Highly Ordered Nanocellular Polymeric Foams Generated by UV-Induced Chemical Foaming.

Nanocellular polymer foams have shown significant potential for industrial applications because of their superior thermal, mechanical, and optical properties. Some of these properties may be further improved by enhancing the ordering of cell structures. However, it is challenging for conventional foaming methods to control both the cell size and ordering at the nanoscale. Here, we show an innovative method to produce highly ordered nanocellular polymer foams by incorporating the self-assembly of an asymmetric diblock copolymer with the UV-induced chemical foaming technique. The minor domains are designed to generate a gaseous compound from the partial cleavage of the functional group. It is demonstrated that the gas-producing reaction can be accelerated at a temperature low enough to prevent melting of the whole self-assembled template, by mixing a small amount of photoacid generator into the copolymer, followed by UV irradiation. The result is the production of polymer foams with the nanoscale cells highly aligned to the self-assembled domains.

Block copolymers containing stable radical and fluorinated blocks with long-range ordered morphologies prepared by anionic polymerization.

We report a facile synthetic approach to create stable radical block copolymers containing a secondary fluorinated block via anionic polymerization using a bulky, sterically hindered countercation composed of a sodium ion and di-benzo-18-crown-6 complex. The synthetic conditions described in this report allowed for controlled molecular weights and dispersity (<1.3) of both homopolymers: poly(2,2,6,6-tetramethyl-1-piperidinyloxy-methacrylate) (PTMA) and poly(2,2,2-trifluoroethyl methacrylate) (PTFEMA) as well as their block copolymers (PTMA-b-PTFEMA). The stable radical concentration of the polymers was determined by electron spin resonance (ESR) and showed radical content above 70%. An analysis of the microphase morphologies in PTMA-b-PTFEMA thin films via atomic force microscopy (AFM) and grazing incidence small angle X-ray scattering (GISAXS) showed clear evidence of long-range ordering of lamellar and cylindrical morphologies with 32 and 36 nm spacing, respectively. The long-range ordering of the morphologies was developed with the aid of two separate neutral layers: PTMA-ran-PTFEMA-ran-poly(hydroxyl ethyl methacrylate) (PHEMA) and poly(isobutyl methacrylate) (PiBMA)-ran-PTFEMA-ran-PHEMA, which helped us corroborate, along with the Zisman method, the surface energy estimation of PTMA to be 30.1 mJ/m2.

Chemically tailored high-χ block copolymers for perpendicular lamellae via thermal annealing.

A chemically tailored high-χ block copolymer (BCP), polystyrene-block-poly[2-hydroxy-3-(2,2,2-trifluoroethylsulfanyl)propyl methacrylate] (PS-b-PHFMA), was designed to incorporate tailored surface affinities and chemical incompatibilities for engineering perpendicular lamellae using thermal annealing. PS-b-PHFMA was synthesized via the sequential anionic polymerization of styrene and glycidyl methacrylate and the post-polymerization functionalization of the glycidyl moieties with 2,2,2-trifluoroethanethiol. The bulk studies revealed lamellae with a minimum domain spacing of 9.6 nm and a large effective Flory-Huggins interaction parameter (χeff) of 0.191 at 25 °C. Furthermore, atomic force microscopy and scanning electron microscopy showed perpendicular lamellae of the PS-b-PHFMA prepared on thermally-annealed thin films. The introduction of hydrophobic trifluoroethyl moieties onto the hydrophilic glycidyl moieties successfully balanced the surface affinity of the PHFMA block relative to PS, while simultaneously increasing the strength of segregation. Thus, χeff of the chemically tailored BCP increased, and a perpendicular orientation was facilitated on the thin films using thermal annealing.

Real-time and in situ observation of structural evolution of giant block copolymer thin film under solvent vapor annealing by atomic force microscopy.

An instrumentation technique for real-time, in situ and real space observation of microphase separation was proposed for ultra-high molecular weight block copolymer thin films (1010 kg mol-1, domain spacing of 180 nm) under high solvent vapor swelling conditions. This is made possible by a combination of a homebuilt chamber which is capable of supplying sufficient amount of vapor, and force-distance curve measurements which gives real-time swollen film thickness and allow active feedback for controlling the degree of swelling. We succeeded in monitoring the domain coarsening of perpendicular lamellar structures in polystyrene-block-poly(methyl methacrylate) thin films for eight hours via tapping mode imaging. During the annealing process, the thickness reached a maximum of 8.5 times that of the original film. The series of temporal real space topographic images obtained via this method allowed us to study, for the first time, the growth exponent of the correlation length under solvent vapor annealing.

Dynamic Ordering in High-χ Block Copolymer Lamellae Based on Cross-Sectional Orientational Alignment.

Further development of next-generation block copolymer (BCP) lithography processes is contingent on comprehensive studies of the ordering dynamics of high-χ BCPs that can form sub-10 nm features on thin films. However, quantitative analyses of the degree of ordering on the surface and cross sections of thin films have been difficult to execute. To tackle this challenge, we employ a perpendicular lamella-forming high-χ BCP, poly(polyhedral oligomeric silsesquixone-block-2,2,2-trifluoroethyl methacrylate) (PMAPOSS-b-PTFEMA), and reveal that the high-χ PMAPOSS-b-PTFEMA requires three times the activation energy (Ea) compared to that of poly(styrene-block-methyl methacrylate) (PS-b-PMMA) for defect annihilation, at Ea = 2600 ± 420 kJ mol-1, and a transition from a fast ordering regime with a growth exponent of Φ = 0.30 at lower orientational order parameters (ψ2 < 0.36) to a slow ordering regime with Φ < 0.05 at ψ2 > 0.36, where well-aligned lamellae restrict defect annihilations to enthalpically unfavorable glide mechanisms that require BCP intermixing.

Self-Assembly of Hierarchical Structures Using Cyclotriphosphazene-Containing Poly(substituted methylene) Block Copolymers.

The cyclotriphosphazene-substituted diazoacetate homopolymer (polyPNDA') (PNDA' = hexaphenoxy-substituted phosphazene-containing methylene) and a novel poly(substituted methylene) block copolymer, polyPNDA'-block-poly(hexyloxycarbonylmethylene) (polyPNDA'-b-polyHDA'), were synthesized, and the self-assembly behavior of these polymers was studied in detail. A hexagonally packed aggregated structure was observed in the self-assembled structure of polyPNDA', whereas a lamellar structure was observed in the microphase-separated nanoassembly of polyPNDA'-b-polyHDA'. These results indicate that a hierarchical structure composed of highly regular polyPNDA' nanoaggregates and the long-range microphase-separated polyPNDA' and polyHDA' domains had formed.

Star-Shaped Thermoresponsive Polymers with Various Functional Groups for Cell Sheet Engineering.

This study demonstrates the facile preparation of poly(N-isopropylacrylamide) (PNIPAM)-immobilized Petri dishes by drop-casting a star-shaped copolymer of hyperbranched polystyrene (HBPS) possessing PNIPAM arms (HBPS-g-PNIPAM) functionalized with polar groups. HBPS was synthesized via reversible addition-fragmentation chain transfer (RAFT) self-condensing vinyl polymerization (SCVP), and HBPS polymers with different terminal structures were prepared by changing the monomer structure. HBPS-g-PNIPAM was synthesized by the grafting of PNIPAM from each terminal of HBPS. To tune the cell adhesion and detachment properties, polar functional groups such as carboxylic acid and dimethylamino groups were introduced to HBPS-g-PNIPAM. Based on surface characterization using scanning transmission electron microscopy (STEM), X-ray photoelectron spectroscopy (XPS), and contact angle measurements, the advantage of the hyperbranched structure for the PNIPAM immobilization was evident in terms of the uniformity, stability, and thermoresponsiveness. Successful cell sheet harvesting was demonstrated on dishes coated with HBPS-g-PNIPAM. In addition, the cell adhesion and detachment properties could be tuned by the introduction of polar functional groups.

Perpendicular Orientation Control without Interfacial Treatment of RAFT-Synthesized High-χ Block Copolymer Thin Films with Sub-10 nm Features Prepared via Thermal Annealing.

In this study, a series of perpendicular lamellae-forming poly(polyhedral oligomeric silsesquioxane methacrylate-block-2,2,2-trifluoroethyl methacrylate)s (PMAPOSS-b-PTFEMAs) was developed based on the bottom-up concept of creating a simple yet effective material by tailoring the chemical properties and molecular composition of the material. The use of silicon (Si)-containing hybrid high-χ block copolymers (BCPs) provides easy access to sub-10 nm feature sizes. However, as the surface free energies (SFEs) of Si-containing polymers are typically vastly lower than organic polymers, this tends to result in the selective segregation of the inorganic block onto the air interface and increased difficulty in controlling the BCP orientation in thin films. Therefore, by balancing the SFEs between the organic and inorganic blocks through the use of poly(2,2,2-trifluoroethyl methacrylate) (PTFEMA) on the organic block, a polymer with an SFE similar to Si-containing polymers, orientation control of the BCP domains in thin films becomes much simpler. Herein, perpendicularly oriented BCP thin films with a χeff value of 0.45 were fabricated using simple spin-coating and thermal annealing processes under ambient conditions. The thin films displayed a minimum domain size of L0 = 11 nm, as observed via atomic force microscopy (AFM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Furthermore, directed self-assembly (DSA) of the BCP on a topographically prepatterned substrate using the grapho-epitaxy method was used to successfully obtain perpendicularly oriented lamellae with a half pitch size of ca. 8 nm.

Pt-free carbon-based fuel cell catalyst prepared from spherical polyimide for enhanced oxygen diffusion.

The development of a non-precious metal (NPM) fuel cell catalyst is extremely important to achieve globalization of polymer electrolyte fuel cells due to the cost and scarcity of platinum. Here, we report on a NPM cathode catalyst prepared by the pyrolysis of spherical polyimide nanoparticles that contain small amounts of Fe additive. 60 nm diameter Fe-containing polyimide nanoparticles were successfully synthesized by the precipitation polymerization of pyromellitic acid dianhydride and 1,3,5-tris(4-aminophenyl)benzene with Fe(acac)3 (acac = acetylacetonate) as an additive. The particles were subsequently carbonized by multistep pyrolysis to obtain the NPM catalyst while retaining the small particle size. The catalyst has good performance and promising durability for fuel cell applications. The fuel cell performance under a 0.2 MPa air atmosphere at 80 °C of 1.0 A cm(-2) at 0.46 V is especially remarkable and better than that previously reported.

Perpendicularly oriented sub-10-nm block copolymer lamellae by atmospheric thermal annealing for one minute.

The directed self-assembly (DSA) of block co-polymers (BCPs) can realize next-generation lithography for semiconductors and a variety of soft materials. It is imperative to simultaneously achieve many requirements such as a high resolution, orientation control of micro-domains, etch selectivity, rapid and mild annealing, a low cost, and compatibility with manufacturing for developing suitable BCPs. Here, we describe a new design for modified polysiloxane-based BCPs targeted for sub-10-nm-wide lines, which are able to form perpendicularly oriented lamellar structures in thin films. The hydroxyl groups in the side chains introduced in the polysiloxane block provide a good balance with the polystyrene surface free energy, thereby leading to the perpendicular orientation. Moreover, this orientation can be completed in only one minute at 130 °C in an air atmosphere. Oxygen plasma etching for the thin films results in the achievement of a line width of 8.5 nm.