Sequential Atom Transfer Radical Polymerization Research Articles

Responsive polymer thin films

Responsive polymer thin films play an important role as structural components in the emerging fields of soft actuators, wearable electronics, and biomedical devices. These films are capable of changing their physical and/or chemical properties significantly in response to environmental stimuli, such as temperature, light, pH, magnetic fields, and ion strength. The integration of multifunctional designs in the polymer networks enables these films to possess advanced capabilities, including, but not limited to, structure color, self-healing, adhesion, conductivity, antimicrobial properties, and antifatigue properties. Polymer and hydrogel films are typically thinner than bulk polymer materials, ranging from nanometers to several hundred micrometers, and are usually made up of thin layers of natural or synthetic polymers. These films can be free-standing or coated on substrates. They offer faster response times, high flexibility, good adaptivity, and versatility via integrating with other functional materials. This special issue on responsive polymer and hydrogel films collects a series of review articles that detail the latest progress in this rapidly developing field, as well as original research articles that propose novel approaches to tackle practical challenges. The review article by Dong et al. provides a comprehensive overview of recent progress in the fabrication and application of functional hydrogel films. The authors focus on two main areas: (i) the methods used to fabricate hydrogel films, and (ii) the various applications of hydrogel films in the fields of biomedicine and emerging technologies. Hydrogel films with controllable thickness, fast response times, good compliance, and tunable mechanical properties are ideal for use in artificial muscles, wound dressing, and the construction of soft actuators and flexible electronics. The review article also highlights current challenges, and provides future perspectives on the development of hydrogel films. Yang et al. reported on the successful fabrication of self-healable, electromagnetic interference (EMI) shielding composite films that exhibit dual responsiveness to temperature and strain. To create these multifunctional films, the team incorporated carbon nanotubes into hydroxyl-terminated polybutadiene (HTPB), which was dynamically crosslinked by boric acid (BA). The HTPB-BA substrate showed excellent self-healing ability at room temperature, facilitating the autonomous recovery of electric conductivity and mechanical strength of the composite films. Dual responsiveness to temperature and strain was observed in the composite films, with electric resistance actively changing in response to variation of temperature and strain. In addition, the composite films exhibited excellent EMI shielding ability, with an effectiveness beyond 28 dB, making them ideal for commercial applications. The EMI shielding efficiency was also found to be responsive to temperatures. These responsive, EMI shielding, and self-healable composite films have broad potential applications in the fields of flexible electronics and protection of sensitive instruments. Amphiphilic block copolymer (BCP) thick films with stimuli-responsive pores are emerging as promising candidates for next-generation ultrafiltration (UF) membranes, due to their stimuli-responsive, smart nanochannels which facilitate the removal of fouling, among the biggest challenges in membrane technology. Bouzit et al. prepared a well-defined, polystyrene-block-poly(2-vinylpyridine)-block-poly(N-isopropylacrylamide) (PS-b-P2VP-b-PNIPAM) terpolymer using reversible addition-fragmentation chain transfer polymerization. They used a combination of nonsolvent-induced phase separation process and solvent vapor annealing treatment to produce nanostructured pH- and thermo-double sensitive ABC-type, BCP thick films. The NIPS-made PS-b-P2VP-b-PNIPAM thick film, comprising a microporous spinodal-type network substructure topped by a dense thin layer of poorly defined nanopores, was transformed into a monolith composed entirely of a well-ordered, perforated lamellar (PL) phase upon exposure to a chloroform vapor. These PL-structured monoliths, show excellent permeance and temperature cyclability and are highly desirable for the manufacturing of smart, separation-based UF materials that can transition their pore state from hydrophilic to hydrophobic (and vice versa), leading to much more efficient detachment of foulants during the cleaning process. Dolmat et al. developed a method for the dynamic assembly of hydrogen-bonded multilayers of (poly(N-vinylpyrrolidone/poly(methacrylic acid)) [PVPON/PMAA]) and compared it with static multilayers. They found that dynamic multilayers, in which a planar substrate is shaken during polymer adsorption, leads to a 15-times faster deposition of the planar coatings than with static multilayer films. The thickness and roughness of the dynamic coatings were found to be approximately 30% larger than those of static multilayer films, as measured by spectroscopic ellipsometry and atomic force microscopy. The researchers examined the film growth, mechanical properties, wettability, hydration, and pH stability of the planar static and dynamic multilayers, and found that these properties were minimally affected by the assembly mode. They discovered that upon release of the multilayer films into a solution to produce free-standing films (either as planar membranes or multilayer capsule shells), the molecular chain rearrangements resulted in decreased roughness for both static and dynamic multilayers and decreased thickness of dynamic multilayers. These findings can aid in developing a rapid synthesis of thicker nanostructured polymer coatings for sensing and controlled delivery applications. Poly(vinylidene fluoride) (PVDF) has garnered significant attention in recent decades due to its properties, particularly pyro- and piezo-electricity, which are linked to its electro-active β-phase in PVDF. The production of β-PVDF through mechanical stretching of nonpolar α-PVDF have been reported, but the impact of strain and temperature on phase changes in spin-coated PVDF thin films has been unclear. In a recent study by Pilla et al., the mechanical properties of spin-coated PVDF freestanding thin films were investigated with a focus on the effects of thermal annealing and in-plane anisotropy. Full-field deformation was measured under in situ tensile loading, in conjunction with digital image correlation to observe correlations between the stress–strain behavior of spin-coated β-PVDF/α-PVDF and the mechanical stretch-induced phase transformation in α-PVDF. The study found that spin-coated and annealed α-PVDF exhibited significantly higher mechanical strength and failure strain (~35 MPa and ~5.5) than spin-coated β-PVDF (~10 MPa and ~0.45). Fourier transform infrared and Raman spectroscopy were used to confirm that mechanical stretching at room temperature caused α-PVDF to transition to β-PVDF beyond a stretch ratio of ~1.2. Furthermore, the study suggested that the in-plane anisotropy observed in β-PVDF is due to the spin-coating process. The unique properties of Janus two-dimensional (2D) polymeric materials, with asymmetric dual surfaces, make them ideal for applications such as biosensors, catalysts, and drug delivery systems. In their recent paper, Zhao et al. successfully constructed micro/macro-scale Janus polypeptoid-based 2D structures at the air–water interface using evaporation-induced interfacial self-assembly of amphiphilic BCP poly(ethylene glycol)-b-poly(N-(2-phenylethyl) glycine) (PEG-b-PNPE). Initially, the PEG-b-PNPE was assembled into a monolayer with a uniform thickness of ~2.5 ± 0.1 nm, which was then mechanically compressed into a bilayer structure by Langmuir–Blodgett (LB) technology by increasing surface pressure beyond the critical collapse pressure. The resulting monolayer and bilayer nanostructure spanned hundreds of microns in both dimensions, and exhibited asymmetric wettability on the air and water sides, as determined by dynamic/static optical contact angle/interface tensiometer. The evolution from a monolayer to a bilayer was further tracked using atomic force microscope. The team was also able to prepare macroscopic Janus films with a diameter of ~3.5 mm using the same methods. These micro/macro-scale 2D materials have potential applications in nanoscience and biomedicine, and the results of this study provide a valuable contribution to the field of Janus 2D materials. In another example, Kashem et al. developed a high-performance and multifunctional film using poly(diallyldimethylammonium chloride) (PDDA) and poly(acrylic acid) (PAA) via a spin-spray-assisted layer-by-layer (SSA-LbL) assembly. The SSA-LbL method was found to be highly efficient and timesaving, resulting in a homogeneous thick film in the tens of micrometer range compared with the conventional immersive assembly method, which typically produces thin films in the nanometer range. When scratches occurred, the film displayed a quick and durable self-healing capability, thanks to the dynamic movement of the flexible polyelectrolyte complex chains at the scratch edges. In addition, the film effectively blocked UV rays by incorporating graphene oxide (GO) and titanium dioxide (TiO2) nanoparticles as UV-blocking additives. Because of the hydrophilic feature of the PDDA/PAA molecules, the film also showed antifog characteristics in different environmental conditions. The researchers investigated the effect of GO and TiO2 nanoparticle concentration on self-healing and UV-protection properties, and identified the optimum concentration range of GO and TiO2 nanoparticles in polyelectrolyte solutions for producing the film with self-healing, UV-blocking, and antifogging features. Silk is renowned as the “queen of fibers” due to its lightness, smoothness, and luster. A study by Zhu et al. reported an easy care solution for silk fabrics by crosslinking a thermo-responsive copolymer film onto the surface. The thermo-responsive copolymer—poly(N-isopropylacrylamide-co-oligo[ethylene glycol] methyl ether methacrylate-co-ethylene glycol methacrylate) (P(NM-co-OA300-co-EA360))—was synthesized using sequential atom transfer radical polymerization. By using 1,2,3,4-butanetetracarboxylic acid as crosslinker, the thermos-responsive P(NM-co-OA300-co-EA360) film can be placed onto silk fabric with a transition temperature of around 46 °C. The reversible transition behavior effectively reduces the attachment between lipophilic stains and the film, leading to efficient stain removal. A 30-s rinse with deionized water at 25 °C (below its transition temperature) can remove 60% of stains. Moreover, during outdoor activities or drying, the crosslinked P(NM-co-OA300-co-EA360) film becomes hydrophobic, allowing water molecules to quickly evaporate from the silk fabrics; the drying process was found to be 25% faster than without the crosslinked film. These excellent properties make silk fabric crosslinked with the thermo-responsive copolymer film suitable for designing silk-based clothing. In recent years, researchers have made significant advancements in the development of soft actuators that can morph into complex shapes, taking inspiration from nature. One noteworthy example of this is the work of Peeketi et al., who have reported a new type of thin-film-based bioinspired actuator. Drawing inspiration from the calla lily, they demonstrated a splay-nematic liquid crystal polymer network tapered actuator that can morph from a flat film to a cone, mimicking the blooming of a calla lily flower. Using both finite element simulations and experiments, Peeketi et al. have successfully produced conical tubes. The researchers analyzed the influence of tapering and alignment orientations with respect to the edge of the film on the cones through simulations, and found that the design with tapering and splayed alignments oriented at 45 °C to the edge is the optimal choice for forming conical tubes. This collection offers a glimpse into the many recent works published in the Journal of Polymer Science on responsive polymer thin films. Our aim is to provide a summary of these selected publications, which will, we hope, inspire readers to develop new approaches to solve fundamental problems and explore novel functional devices for practical applications. We thank all the authors, reviewers, and editorial staff for their significant contributions to this special issue. Wei Li is an Associate Professor in the Chemical Engineering Department at Texas Tech University. He obtained his PhD in Polymer Chemistry and Materials at the University of Toronto. He was an Natural Sciences and Engineering Research Council of Canada (NSERC) Postdoctoral Fellow at MIT. Dr. Li's research combines microfluidics and nanoassembly techniques to develop novel functional polymer materials and smart microdevices for biological, optical, and energy applications. Jouha Min is an Assistant Professor of Chemical Engineering at the University of Michigan. Dr. Min has a PhD in Chemical Engineering from MIT, and postdoctoral research experience from Harvard Medical School/Massachusetts General Hospital. Dr. Min's research group focuses on developing advanced biomaterials and biosensors using fundamental chemical engineering principles, with the goal of creating robust engineering solutions to significant health problems such as cancer and life-threatening infectious diseases.

Silver Nanocrystal Array with Precise Control via Star-like Copolymer Nanoreactors.

Silver nanocrystal arrays had attracted much attention due to the unique plasmonic effect of their ordered nanostructure and the synergy among adjacent nanocrystals. Conventional preparation methods had several limitations, such as high cost, harsh preparation conditions, and complicated influencing factors, which could not be employed to fabricate the nanocrystal arrays in highly controlled fashion. To solve these issues, we reported ordered arrays of different Ag nanocrystals with precise control prepared by utilizing amphiphilic star-like poly(4-vinylpyridine)-block-polystyrene diblock copolymers as nanoreactors synthesized by sequential atom transfer radical polymerization. Moreover, this unimolecular nanoreactor method based on star-like copolymers with stable and predesigned nanostructures was proved to be a universal approach to prepare other nanocrystal arrays. This strategy had low cost, simple process flow, wide applicability, and structural stability that could fabricate nanocrystal array with precise control and continuously prepare more complex nanostructure units in a large scale to meet different functions and applications.

Easy care of silk fabrics realized by crosslinking thermo‐responsive copolymer film on its surface

AbstractAn easy care of silk fabrics is realized by crosslinking a thermo‐responsive copolymer film onto its surface. The thermo‐responsive copolymer poly(N‐isopropylacrylamide‐co‐oligo[ethylene glycol] methyl ether methacrylate‐co‐ethylene glycol methacrylate), abbreviated as P(NM‐co‐OA300‐co‐EA360), is synthesized by sequential atom transfer radical polymerization. By applying 1,2,3,4‐butanetetracarboxylic acid as crosslinker, the thermo‐responsive P(NM‐co‐OA300‐co‐EA360) film can be immobilized onto the silk fabrics. The transition temperature (TT) of the P(NM‐co‐OA300‐co‐EA360) film crosslinked on silk fabrics is around 46 °C. The reversible transition behavior can effectively reduce the attachment between lipophilic stains and P(NM‐co‐OA300‐co‐EA360) film, inducing a high efficiency of stain removal. Simply rinsing with deionized water at 25 °C (below its TT) for 30 s, 60% of stains can be removed. Moreover, the crosslinked P(NM‐co‐OA300‐co‐EA360) film turns hydrophobic during outdoor activities or drying. Thus, the repelled water molecules can be easily evaporated from the silk fabrics and the drying process is 25% faster than that without crosslinked P(NM‐co‐OA300‐co‐EA360) film. Based on the excellent performance of stain removal and quick drying, the silk fabrics crosslinked with thermo‐responsive copolymer film can be broadly used to design silk‐based costumes for daily use.

General Route to Colloidal Nanocrystal Clusters with Precise Hierarchical Control via Star-like Nanoreactors.

A colloidal nanocrystal cluster (CNC) is a hierarchical nanostructure formed by clustering several nanocrystals into one nano-ensemble, which may exhibit unique optical or catalytic properties different from individual nanocrystals owing to the mutual interactions among neighboring component nanocrystals. However, there is still no universal synthetic route that could be applicable to diverse material compositions with precisely controlled hierarchical structures (i.e., nanocrystal number density, component nanocrystal size, and overall diameter of the CNC) up to now. Herein, a general and novel synthetic strategy was reported for crafting a wide range of inorganic CNCs (i.e., noble metal, semiconductor, and metal oxide) via utilizing amphiphilic star-like poly(4-vinylpyridine)-block-polystyrene diblock copolymers as nanoreactors prepared by sequential atom transfer radical polymerization. The hierarchical structure of rationally designed CNCs could be readily tailored by varying the P4VP molecular weight of star-like nanoreactors and the parameter optimization during the CNC preparation process, which was inaccessible by conventional synthetic methods.

Unconventional Approach to Fabricating a TiO2 Nanoring with Precise Dimension Control Based on Starlike Polymeric Nanoreactors.

The past few years witnessed the rapid development of bottom-up synthesis strategies for preparing various nanostructures (i.e., nanoparticles, nanorods, nanowires, etc.) with distinct morphology-dependent properties. In this study, we reported a facile and efficient synthesis method for preparing anatase titanium dioxide (TiO2) nanorings based on multiarm, starlike amphiphilic polystyrene-b-poly(acrylic acid) (PS-b-PAA) diblock copolymers as nanoreactors which were prepared via a sequential atom-transfer radical polymerization (ATRP) technique followed by the conversion of polystyrene-b-poly(tert-butyl acrylate) (PS-b-PtBA) to PS-b-PAA. The outer PAA block of nanoreactors possessed carboxylic acid groups which could coordinate with a titanium precursor followed by high-temperature calcination to form crystalline TiO2 nanorings. The living nature of ATRP enabled the precise preparation of starlike diblock copolymer nanoreactors with a controlled length of each block (i.e., PtBA and PS), thereby tailoring the inner diameter and wall thickness of the resulting TiO2 nanorings, which were inaccessible to conventional routes.

Design and synthesis of novel di‐ and triblock amphiphilic polyelectrolytes: Improving salt‐induced viscosity reduction of water solutions for potential application in enhanced oil recovery

AbstractIn the present study, three different block copolymers based on styrene, tert‐butyl methacrylate, and glycidyl methacrylate (GMA) were synthesized via sequential atom transfer radical polymerization. The addition of the GMA block was found to be best performed at 60°C. The polymers were then hydrolyzed and neutralized, to afford amphiphilic block copolymers, and the rheological properties of their aqueous solutions were measured, in order to investigate solution properties relevant for enhanced oil recovery, as a function of the polymer structure. It was observed that these polymers behave as thickening agents with shear thinning behavior. As expected, the polymers were sensitive to the presence of salt, as lower viscosities were recorded in saline water. However, the viscosity is less affected by high salinity, when compared to previously studied analogous diblock systems. In the best case, the viscosity only decreased by a factor of 1.8 upon salt addition whereas it decreased by a factor of 10 in previously reported non‐GMA containing polymers. Finally, thermo‐responsive behavior was found for one of the synthesized polymers. In particular, a hydrolyzed triblock poly[styrene‐b‐tert‐butyl methacrylate‐b‐glycidyl methacrylate], which synthesis is reported here for the first time, showed a thermothickening behavior, promising for the intended application in oil recovery.

Ion transport in topological all‐solid‐state polymer electrolyte improved via graphene‐oxide

AbstractDesigning and constructing novel topological all‐solid‐state polymer electrolyte (SPE) matrices can improve the ionic conducting ability of the prepared SPEs compared with the linear ones. Here, we construct a novel topological polymer electrolyte matrix using triphenylene as core and block poly(methyl methacrylate)‐poly(poly[ethylene glycol] methyl ether methacrylate) as arm. Specifically, the arm is attached onto the core via sequential atom transfer radical polymerization. The molecular weight of the polymers is well controlled via adjusting the inventory rating of monomers, the optimal SPE obtained via solution casting has an ambient temperature ionic conductivity of 3.69 × 10−5 S cm−1, which is higher than typical linear poly(ethylene oxide)‐based SPE (usually 10−6–10−8 S cm−1). The electrochemical performance is further improved through adding given contents of graphene‐oxide into the SPE. Thus, we believe, through molecular designing and the widely used composite tactics, new class of electrolytes with high‐electrochemical performance for all‐solid‐state Li‐ion batteries can be developed.

Renewable Fabric Surface-Initiated ATRP Polymerizations: Towards Mixed Polymer Brushes.

A totally new approach in the synthesis of mixed polymer brushes tethered on polyamide (PA) surfaces is presented herein. As a proof of concept, two types of homopolymers were synthesized in sequential surface-initiated atom transfer radical polymerization (SI-ATRP) reactions: poly(methyl methacrylate)/poly((2-dimethylamino)ethyl methacrylate) and polystyrene /poly((2-dimethylamino)ethyl methacrylate). The ATRP initiator was immobilized on the surface through PA chain-end groups in two subsequent steps, separated by homo-polymerizations. The amount of the PA chains’ end groups available on the modified surface was tuned by the thermal rearrangement of the surface.

Main Chain-Type Block Copolymers through Atom Transfer Radical Polymerization from Double-Decker-Shaped Polyhedral Oligomeric Silsesquioxane Hybrids.

In this study, we synthesized two main chain–type block copolymers featuring hydrogen bond donor and acceptor segments through atom transfer radical polymerization (ATRP) using a bifunctionalized polyhedral oligomeric silsesquioxane (POSS) nanoparticle as the initiator. Hydrosilylation of vinylbenzyl chloride at the two corners of a double-decker silsesquioxane (DDSQ) provided the bifunctionalized benzyl chloride initiator VBC-DDSQ-VBC, which we applied as a platform to prepare a main chain–type polystyrene homopolymer (PS-DDSQ-PS), the diblock copolymer poly(styrene–b–4-vinylpyridine) (P4VP-b-PS-DDSQ-PS-b-P4VP), and the diblock copolymer poly(styrene–b–tert-butoxystyrene) (PtBuOS-b-PS-DDSQ-PS-b-PtBuOS) through sequential ATRP. Selective hydrolysis of the tert-butoxyl units of PtBuOS-b-PS-DDSQ-PS-b-PtBuOS yielded the strongly hydrogen bonding diblock copolymer poly (styrene-b-vinylphenol) (PVPh-b-PS-DDSQ-PS-b-PVPh). We used Fourier transfer infrared spectroscopy, nuclear magnetic resonance spectroscopy, size exclusion chromatography, differential scanning calorimetry, mass-analyzed laser desorption ionization mass spectrometry, and transmission electron microscopy to investigate the chemical structures, thermal behavior, and self-assembled nanostructures formed by these main chain–type block copolymers based on DDSQ.

Enhanced Stain Removal and Comfort Control Achieved by Cross-Linking Light and Thermo Dual-Responsive Copolymer onto Cotton Fabrics.

Enhanced capabilities of stain removal and comfort control are simultaneously achieved by the light and thermo dual-responsive copolymer poly(triethylene glycol methyl ether methacrylate- co-ethylene glycol methacrylate- co-acrylamide azobenzene) (P(MEO3MA- co-EGMA- co-AAAB)) cross-linked on cotton fabrics. P(MEO3MA- co-EGMA- co-AAAB) is synthesized by sequential atom transfer radical polymerization with a molar ratio of 8 (MEO3MA):1 (EGMA):1 (AAAB). The MEO3MA units induce a thermoresponsive behavior to the copolymer. The hydrophilicity of the copolymer films can be further improved by the light-induced trans- cis isomerization of the AAAB units with UV radiation. The copolymer is facilely immobilized onto cotton fabrics with 1,2,3,4-butane tetracarboxylic acid as cross-linker. Due to the immobilization of P(MEO3MA- co-EGMA- co-AAAB), the hydrophilicity of the fabric surface is increased under UV radiation. Therefore, by simply installing a UV light source in the washing machine, better capability of stain removal is realized for the cross-linked cotton fabrics. It can prominently reduce the consumption of energy, water, and surfactants in laundry. In addition, the trans-AAAB units of the copolymer cause the cross-linked P(MEO3MA- co-EGMA- co-AAAB) layer to be more hydrophobic under ambient conditions. Hence, the copolymer can more easily collapse and form a porous structure on the fabrics. Thus, the air permeability of cotton fabrics cross-linked with P(MEO3MA- co-EGMA- co-AAAB) is enhanced by 13% at human body temperature as compared to P(MEO3MA- co-EGMA), giving improved comfort control during daily wear.

Triple-Responsive Block Copolymer Micelles with Synergistic pH and Temperature Response

Multifunctional, stimuli-responsive block copolymers have been prepared via the sequential atom transfer radical polymerization (ATRP) of 2-(dimethylamino)ethyl methacrylate (DMAEMA) and the in-house synthesized 1′-(2-methacryloxyethyl)-3′,3′-dimethyl-6-nitrospiro-(2H-1-benzopyran-2,2′-indoline) (SPMA) monomer. Two PDMAEMA-b-PSPMA diblock copolymers, containing 3 and 14 mol % SPMA, were synthesized. The amphiphilic nature of the PDMAEMA-b-PSPMA diblock copolymers led to the formation of well-defined spherical micelles, comprising a hydrophobic PSPMA core and a hydrophilic PDMAEMA shell, in water. The combination of the pH- and temperature-responsive character of PDMAEMA with the pH-, temperature-, and light-sensitive properties of the PSPMA block has resulted in a complex responsive behavior of the copolymer micelles in aqueous solution, when applying three different external stimuli (i.e., light irradiation, pH, and temperature). More importantly, the synergistic response of the block copolymer micelles ...

Six-arm star polymer based on discotic liquid crystal as high performance all-solid-state polymer electrolyte for lithium-ion batteries

All-solid-state polymer electrolyte (SPE) matrices prepared by molecular design are still needed to be further perfected with excellent performance. In this paper, a controlled-structure discotic liquid crystal (DLC)-based six-arm star copolymer was designed and synthesized from a DLC initiator (2,3,6,7,10,11-hexakis(2-bromoisobutyryloxy)triphenylene) via the sequential atom transfer radical polymerization (ATRP) of styrene and poly(ethylene glycol) methyl ether methacrylate (PEGMA). Here, this class of discotic liquid crystal star polymer is applied as an SPE in LIBs for the first time. By solution casting, a suitable self-standing SPE film composed of the six-arm copolymer and lithium bis(trifluoromethanesulfonimide (LiTFSI)) can be easily formed, and the film shows long-range molecular orientation after annealing. It is confirmed that the electrolyte shows wide electrochemical window (5.1 V) and high lithium-ion transference number (0.37). Especially, the ionic conductivity (1.46 × 10−4, S cm−1, 30 °C) of the obtained SPE is more than 8 times higher than that of the corresponding linear copolymer electrolytes. Furthermore, the results of battery performance demonstrate that the polymer electrolyte displays eminently reversible electrochemical reaction and outstanding cycling performance. The present work not only shows the advantages of DLC-based star SPE for LIBs but also paves the way for the design of SPE with excellent performances.

Preparation and characterization of gel polymer electrolyte based on electrospun polyhedral oligomeric silsesquioxane-poly(methyl methacrylate)8/polyvinylidene fluoride hybrid nanofiber membranes for lithium-ion batteries

As a kind of organic–inorganic hybrid materials with nanocage structure, polyhedral oligomeric silsesquioxane (POSS) has the advantages of good interaction with polymer and excellent thermal and mechanical stability. Star-shaped polyhedral POSS-poly(methyl methacrylate) (POSS-(PMMA n )8) with different molecular weights had been synthesized by sequential atom transfer radical polymerization (ATRP) with POSS-(C3H6Cl)8 as the initiator. Electrospun polyvinylidene fluoride (PVDF) composite gel polymer electrolytes (GPEs) modified by POSS-(PMMA n )8 were prepared, and their electrochemical and mechanical properties were assessed. The POSS-(PMMA n )8 particles were found to improve thermal stability and mechanical strength of the GPEs without decreasing electrochemical properties. Among all composite GPEs studied, the best comprehensive performance was obtained from PVDF-[POSS-(PMMA46)8] GPE: the porosity was 60.0%, and the tensile strength and the elongation at break were 4.94 MPa and 52.2%, respectively. Besides, the ionic conductivity was 4.85 × 10−3S cm−1 at room temperature, the electrochemical window could reach 6.0 V, and the interfacial impedance with Li electrode was 256.15 Ω. The cells with POSS-(PMMA)8-modified composite electrolytes also have good cycle performance. These results suggest that the PVDF-[POSS-(PMMA)8] composite GPEs are suitable for lithium-ion battery applications.

Stimuli-responsive and micellar behaviors of star-shaped poly[2-(dimethylamino)ethyl methacrylate]-b-poly[2-(2-methoxyethoxy)ethyl methacrylate] with a β-cyclodextrin core

A series of star-shaped block copolymers (CDPDPM) of 2-(dimethylamino)ethyl methacrylate (DMAEMA) and 2-(2-methoxyethoxy)ethyl methacrylate (MEO2MA) with tunable stimuli-responsive behavior are synthesized via sequential atom transfer radical polymerization (ATRP) with the 2-bromoisobutyryl-terminated β-cyclodextrin (β-CD) as a core. The properties of these star-shaped copolymers are characterized by FT-IR, NMR and GPC analyses. Meanwhile, the thermo-sensitive behaviors of CDPDPM with different compositions and pH values are investigated by dynamic light scattering (DLS) and UV–vis measurements. The results have shown that the synthesized polymer CDPDPM exhibits both pH- and thermo-responsive behaviors in aqueous solutions. The star-shaped copolymers with the nearly equal mole fraction of DMAEMA and MEO2MA show two-step thermo-induced aggregation behavior in water at a pH near the isoelectric point (IEP), which corresponds to the formation of branch aggregates and large aggregates consisting of clustered branch aggregates, respectively. The mole fraction of DMAEMA and MEO2MA in polymer affects the thermal-responsive behaviors of polymer itself. Moreover, the micellar behaviors of the synthesized copolymers in aqueous solution are explored. The aggregation process of the copolymer can be generalized into intramolecular aggregation of the hydrophobic chains (corresponding to CI), formation of premicelles, the aggregation and rearrangement of the premicelles (namely CMC), as well as the formation of multicore structures. The CI and CMC values depend on both the MEO2MA molar fraction and the carbon backbone length of polymers. The aggregation number (N) and the sizes of polymer micelles (Dh) vary with the polymer composition, polymer concentration and ambient environment.

Bottlebrush-Guided Polymer Crystallization Resulting in Supersoft and Reversibly Moldable Physical Networks

The goal of this study is to use ABA triblock copolymers with central bottlebrush B segments and crystalline linear chain A segments to demonstrate the effect of side chains on the formation and mechanical properties of physical networks cross-linked by crystallites. For this purpose, a series of bottlebrush copolymers was synthesized consisting of central amorphous bottlebrush polymer segments with a varying degree of polymerization (DP) of poly(n-butyl acrylate) (PnBA) side chains and linear tail blocks of crystallizable poly(octadecyl acrylate-stat-docosyl acrylate) (poly(ODA-stat-DA)). The materials were generated by sequential atom transfer radical polymerization (ATRP) steps starting with a series of bifunctional macroinitiators followed by the growth of two ODA-stat-DA linear-chain tails and eventually growing poly(nBA) side chains with increasing DPs. Crystallization of the poly(ODA-stat-DA) tails resulted in a series of reversible physical networks with bottlebrush strands bridging crystalline cr...

Thermoreversible Order−Order Transition of a Triblock Copolymer Containing a Mesogen‐Jacketed Liquid Crystalline Polymer with a Re‐Entrant Phase Behavior

Poly{2,5‐bis[(4‐butoxyphenyl)‐oxycarbonyl]styrene} (PBPCS) with a re‐entrant phase behavior is used to synthesize a new kind of ABC triblock copolymers (triBCPs), poly(dimethylsiloxane)‐b‐polystyrene‐b‐PBPCS (PDMS‐b‐PS‐b‐PBPCS, DSB). Two well‐defined triBCPs D120S100B50 and D120S100B120 with different molecular weights (MWs) and narrow MW distributions are synthesized by sequential atom transfer radical polymerization. The volume fractions of PDMS, PS, and PBPCS in D120S100B50 are 0.24, 0.26, and 0.50, respectively, while the values in D120S100B120 are 0.14, 0.16, and 0.70, respectively. At low temperatures, PBPCS is amorphous. Both samples form a core–shell hexagonally packed cylindrical (CSH) morphology. At high temperatures, PBPCS in the triBCPs can form a liquid crystalline (LC) phase, the transformation of which can induce an order−order transition (OOT) of D120S100B120. The nanostructure changes from a CSH structure to a three‐phase‐four‐layer lamellar structure, and the transition is thermoreversible. The sequence of the OOT is opposite to that of a coil−coil−coil triBCP. The unusual LC behavior of PBPCS plays an important role on the thermoreversible morphological transition of the triBCP. image

Electron Propagation within Redox-Active Microdomains in Thin Films of Ferrocene-Containing Diblock Copolymers.

This paper reports the electrochemical behavior of redox-active microdomains in thin films of ferrocene-containing diblock copolymers, polystyrene-block-poly(2-(acryloyloxy)ethyl ferrocenecarboxylate) (PS-b-PAEFc). PS-b-PAEFc with different PAEFc volume fractions (PS154-b-PAEFc51, PS154-b-PAEFc26, and PS154-b-PAEFc12, where the subscripts represent the polymerization degree of each block; f(PAEFc) = 0.47, 0.30, and 0.17, respectively) was synthesized by sequential atom transfer radical polymerization. PS-b-PAEFc films of controlled thicknesses (20-160 nm) were prepared on gold substrates via spin-coating and characterized by ellipsometry. Microdomains were observed via atomic force microscopy on the surfaces of PS154-b-PAEFc51 and PS154-b-PAEFc26 thin films but not on the surfaces of PS154-b-PAEFc12 thin films. Electrochemical behavior of films was assessed by cyclic voltammetry and chronocoulometry in acetonitrile solution. The redox potential of ferrocene moieties was similar (ca. + 0.29 V vs Fc(+)/Fc) regardless of fPAEFc and film thickness. For PS154-b-PAEFc51 and PS154-b-PAEFc26, thicker films afforded larger faradaic peak currents and exhibited diffusion-controlled voltammograms at faster sweep rates. PS154-b-PAEFc26 produced voltammograms less influenced by solvent-induced swelling than PS154-b-PAEFc51, reflecting the improved morphological stability of PAEFc microdomains by redox-inert PS frameworks. In contrast, PS154-b-PAEFc12 films yielded similar faradaic peak currents regardless of film thickness and exhibited voltammograms indicative of surface-confined species. These observations suggest that PS154-b-PAEFc51 and PS154-b-PAEFc26 films contain continuous PAEFc microdomains extending from the electrode to the surface, in contrast to the PS154-b-PAEFc12 films which contain isolated PAEFc microdomains buried within the PS matrix. Electron propagation took place only through PAEFc microdomains that could electrically communicate with the underlying electrode. Apparent diffusion coefficients within PAEFc microdomains were similar (≈ 2 × 10(-11) cm(2)/s) for PS154-b-PAEFc51 and PS154-b-PAEFc26. The relatively low efficiency in electron propagation was attributable to ineffective electron self-exchange reaction within the PAEFc microdomains and/or limited counterion migration through the acetonitrile-swollen microdomains. These results provide guidance in design of redox-active metalloblock copolymers for various applications, which include electrocatalysis, electrochemical mediation in enzyme sensors, and redox-controlled molecular deposition.

Synthesis of Miktoarm Star‐Shaped Polymers with POSS Core via a Combination of CuAAC Click Chemistry, ATRP, and ROP Techniques

Well‐defined AB‐type miktoarm star‐shaped polymers with a polyhedral oligomeric silsesquioxane (POSS) core are prepared by combination of the “core‐first” and “arm‐first” approaches using ring‐opening polymerization (ROP) and copper‐catalyzed azide–alkyne cycloaddition (CuAAC) click reactions. The clickable octakis‐azido‐hydroxyl‐POSS as the core molecule and alkyne end‐functionalized precursor polymers (methoxypoly(ethylene glycol), poly(methyl methacrylate) (PMMA), and polystyrene) are synthesized independently according to the well‐known procedures including ring‐opening reaction of octaglycidyldimethylsilyl POSS using sodium azide, etherification of poly(ethylene glycol) (PEG) monomethyl ether using propargyl bromide and sequential atom transfer radical polymerization of methyl methacrylate or styrene and following nucleophilic substitution reactions of the these polymers with sodium azide. In subsequent step, octa‐armed poly(ε‐caprolactone) star‐shaped polymer ((PCL)8‐POSS‐(N3)8) containing azido functionalities in the core is synthesized via “core‐first” approach through ROP of ε‐caprolactone (ε‐CL). Finally, alkyne end‐functionalized polymers are introduced to the (PCL)8‐POSS‐(N3)8 via “arm‐first” approach using the CuAAC click reaction under ambient conditions, yielding AB‐type miktoarm star‐shaped polymers. Based on 1H NMR spectroscopy calculations, the number of PEG, PMMA, and PSt arms in (PCL)8‐POSS‐(mPEG)7, (PCL)8‐POSS‐(PMMA)5, and (PCL)8‐POSS‐(PSt)6 star‐shaped polymers is found as 7.1, 4.9, and 5.9, respectively. image

Preparation of multicompartment micelles from amphiphilic linear triblock terpolymers by pH-responsive self-assembly

Multicompartment micelles, as an intriguing class of self-assembled aggregates with subdivided solvophobic cores, show high potentials for various applications. Their unique morphologies and sequestration properties depend highly on structure and chemical composition of the building blocks as well as self-assembly environments. To further understand their relationships, a series of well-defined amphiphilic triblock terpolymers poly(methyl methacrylate)-block-poly(2-(cinnamoyloxy)ethyl methacrylate)-block-poly(2-dimethylaminoethyl methacrylate) (PMMA-b-PCEMA-b-PDMAEMA) was synthesized via sequential atom transfer radical polymerization (ATRP) followed by selective modification of the middle block, and the self-assembly of PMMA-b-PCEMA-b-PDMAEMA via direct dispersing in water and step-wise procedures through solvent exchange was studied, respectively. Dynamic laser scattering (DLS) studies showed the existence of large-sized aggregates formed through direct self-assembly of PMMA-b-PCEMA-b-PDMAEMA triblock terpolymers in water, and the aqueous solutions were found to exhibit the surface tension reduction. This is probably caused by the frozen micelles adsorbed on the air/water interface which play the role of Pickering emulsifiers. However, PMMA-b-PCEMA-b-PDMAEMA multicompartment micelles could be successfully prepared by the step-wise self-assembly method, inhibiting the formation of frozen micelles and large aggregates. Prepared from different PMMA-b-PCEMA-b-PDMAEMA triblock terpolymers, the homogeneously nano-sized multicompartment micelles of oval morphologies with distinct subdivided core domains were confirmed by transmission electron microscope (TEM). Besides, various morphologies of the multicompartment micelles were obtained simply by altering the pH value of water. This multicompartment micelle system with adjustable pH response holds potential for therapeutic delivery of multiple incompatible drug payloads and is believed to contribute to enriching the research field of tunable polymer self-assemblies.

Macrocyclic poly(methyl acrylate) and macrocyclic poly(methyl acrylate-block-styrene) synthesized by radical trap-assisted atom transfer radical coupling

Dibrominated poly(methyl acrylate) (BrPMABr) was prepared by atom transfer radical polymerization (ATRP), and this unpurified reaction mixture was used directly in a radical trap-assisted atom transfer radical coupling (RTA-ATRC) reaction to achieve cyclic PMA by intramolecular chain-end coupling. When the polymerization-to-cyclization crossover was performed as a one pot-two step sequence simply by the addition of the radical trap 2-methyl-2-nitrosopropane (MNP) and increased amounts of ligand-catalyst complex, cyclic PMA could be formed in yields up to 65% by adjusting the total volume and reactant ratios during the intramolecular RTA-ATRC, based on gel permeation chromatography (GPC) analysis. In analogous intramolecular ATRC trials lacking the radical trap, cyclization was not successful and instead chain extension by continuation of ATRP was observed. When the ATRP reaction mixture containing the BrPMABr precursor was added drop-wise into a redox active solution containing MNP, yields of cyclic polymer were increased up to 85%. The effect of the ligand was studied, with the highest amounts of cyclic product obtained in intramolecular RTA-ATRC reactions using tris[2-(dimethylamino)ethyl]amine (Me6TREN) as the ligand. Cyclic diblock copolymers were also prepared by this method, using telechelic poly(methyl acrylate-block-styrene-block-methyl acrylate) (PMA-b-PS-b-PMA) linear precursors prepared by sequential ATRP reactions.