Block Copolymer Networks Research Articles

Digital Light Processing (DLP) 3D Printing of Caprolactone Copolymers with Tailored Properties through Crystallinity.

Digital light processing (DLP) 3D printing has shown great advantages such as high resolution in the fabrication of 3D objects toward a range of applications. Despite the rapid development of photocurable materials for DLP printing, tailoring properties to meet the specific demands for various applications remains challenging. Herein, we introduce copolymers of caprolactone and allyl caprolactone offering built-in functionality for thiol-ene photochemistry, thereby omitting the need for postfunctionalization. A crystalline block copolymer and an amorphous statistical copolymer were synthesized with the same comonomer composition and molecular weight. Thio-ene photocuring with a tetrafunctional thiol cross-linker was studied at different thiol to double-bond ratios for the copolymers and their blends. All formulations undergo rapid photocuring within several seconds of irradiation with slightly higher gel fractions observed for the statistical copolymer over the block copolymer under the same conditions, suggesting a somewhat higher cross-link density. Thermal properties of the networks were dependent on the presence of the semicrystalline block copolymer, where higher melting enthalpies were reached at higher block copolymer content. Similarly, crystallinity was found to be the main contributor to the mechanical properties. For a comparable composition, the modulus of a block copolymer network was found to be 31 times higher than that of the statistical copolymer network (27.7 vs 0.89 MPa). Intermediate moduli could be obtained by blending the two copolymers. DLP-printed scaffolds from these copolymers retained their thermal properties, therefore offering an efficient approach to tailoring mechanical properties, through crystallinity. Moreover, the printed scaffold displayed shape memory properties as the first example of poly(carprolactone) (PCL) copolymers in DLP printing. These materials are readily synthesized, offer fast and high-resolution 3D printing, and are degradable and cell compatible. They offer a straightforward approach to tailoring properties of PCL-based biomaterials and devices.

Supramolecular Association of a Block Copolymer via Strong Hydrogen Bonding to Form Self-Healable Ionogels.

The drive to enhance the operational durability and reliability of stretchable and wearable electronic and electrochemical devices has led to the exploration of self-healing materials that can recover from both physical and functional failures. In the present study, we fabricated a self-healable solid polymer electrolyte, referred to as an ionogel, using reversible hydrogen bonding between the ureidopyrimidone units of a block copolymer (BCP) network swollen in an ionic liquid (IL). The BCP consisted of poly(styrene-b-(methyl acrylate-r-ureidopyrimidone methacrylate)) [poly(S-b-(MA-r-UPyMA)], with the IL-phobic polystyrene forming micellar cores that were interconnected via intercorona hydrogen bonding between the ureidopyrimidone units. By precisely regulating the molecular weight and the composition of the hydrogen-bondable motifs, the mechanical, electrical, and self-healing characteristics of the ionogel were systematically evaluated. The resulting ionogel samples exhibited suitable stretchability, ionic conductivity, and room-temperature self-healability due to reversible hydrogen bonding. To highlight the applicability of the self-healing ionogel as a high-capacitance gate insulator, an electrolyte-gated transistor (EGT) was fabricated using a poly(3-hexylthiophene-2,5-diyl) semiconductor, and the performance of the EGT was fully recovered from a complete cut without any external stimuli.

Lithium Borate Polycarbonates for High-Capacity Solid-State Composite Cathodes.

Improving composite cathode function is key to the success of the solid-state battery. Maximizing attainable cathode capacity and retention requires integrating suitable polymeric binders that retain a sufficiently high ionic conductivity and long-term chemo-mechanical stability of the cathode active material-solid-electrolyte-carbon mixture. Herein, we report block copolymer networks composed of lithium borate polycarbonates and poly(ethylene oxide) that improved the capacity (200 mAh g-1 at 1.75 mA cm-2) and capacity retention (94 % over 300 cycles) of all-solid-state composite cathodes with nickel-rich LiNi0.8Co0.1Mn0.1O2 cathode active material, Li6PS5Cl solid electrolyte, and carbon. Tetrahedral B(OR)2(OH)2 - anions immobilized on the polycarbonate segments provide hydrogen-bonding chain crosslinking and selective Li-counterion conductivity, parameterized by Li-ion transference numbers close to unity (tLi+~0.94). With 90 wt % polycarbonate content and a flexible low glass transition temperature backbone, the single-ion conductors achieved high Li-ion conductivities of 0.2 mS cm-1 at 30 °C. The work should inform future binder design for improving the processability of cathode composites towards commercializing solid-state batteries, and allow use in other cell configurations, such as lithium-sulphur cathode designs.

Lithium Borate Polycarbonates for High‐Capacity Solid‐State Composite Cathodes

AbstractImproving composite cathode function is key to the success of the solid‐state battery. Maximizing attainable cathode capacity and retention requires integrating suitable polymeric binders that retain a sufficiently high ionic conductivity and long‐term chemo‐mechanical stability of the cathode active material‐solid‐electrolyte‐carbon mixture. Herein, we report block copolymer networks composed of lithium borate polycarbonates and poly(ethylene oxide) that improved the capacity (200 mAh g−1 at 1.75 mA cm−2) and capacity retention (94 % over 300 cycles) of all‐solid‐state composite cathodes with nickel‐rich LiNi0.8Co0.1Mn0.1O2 cathode active material, Li6PS5Cl solid electrolyte, and carbon. Tetrahedral B(OR)2(OH)2− anions immobilized on the polycarbonate segments provide hydrogen‐bonding chain crosslinking and selective Li‐counterion conductivity, parameterized by Li‐ion transference numbers close to unity (tLi+~0.94). With 90 wt % polycarbonate content and a flexible low glass transition temperature backbone, the single‐ion conductors achieved high Li‐ion conductivities of 0.2 mS cm−1 at 30 °C. The work should inform future binder design for improving the processability of cathode composites towards commercializing solid‐state batteries, and allow use in other cell configurations, such as lithium‐sulphur cathode designs.

Fundamental Principles and Emerging Opportunities for Selectively‐Solvated Block Copolymer Networks in Nonpolar Media: A Perspective

AbstractBlock polymers remain an extensively studied class of macromolecules due to their ability to self‐organize spontaneously as a result of microphase separation into a variety of ordered nanostructures, depending on the number of contiguous sequences (“blocks”) present and their sequential arrangement. These polymers are classified as multifunctional since they exhibit two or more different property sets during application. In this work, the focus is on bicomponent block copolymers composed of soft and hard segments arranged as linear triblock or higher‐order multiblock copolymers and possessing the properties of a thermoplastic elastomer (TPE). Of particular interest are selectively‐solvated TPEs, designated as TPE gels (TPEGs), with precisely‐ and composition‐tunable properties. An important aspect of TPEs and their TPEG analogs is their elasticity, which reflects the ability of the soft block(s) to form a contiguous molecular network connected by dispersed microdomains composed of the hard block. Here, the origins of microphase separation and network formation in styrenic TPEs and TPEGs are explored, and experimental, theoretical, and simulation results are examined to elucidate chemistry‐structure‐property‐processing (CSPP) relationships in these self‐networking materials. Once such relationships are established, several unconventional technologies that can directly benefit from TPEGs, along with TPEGs fabricated from TPEs possessing different chemical moieties, are likewise considered.

Block Copolymer Networks Composed of Poly(ε-caprolactone) and Polyethylene with Triple Shape Memory Properties

Block Copolymer Networks Composed of Poly(ε-caprolactone) and Polyethylene with Triple Shape Memory Properties

Tuning the Double Gyroid Phase Window in Block Copolymers via Polymer Chain Conformation Near the Interface

Block copolymer network morphologies have been proven interesting for applications ranging from mechanical to transport and optical properties. The shape of the polymer chain and its ability to stretch across an interface can be used as handles to target these network morphologies. Here, we show that the double gyroid phase window is broadened when there is a flexible segment near the interface and narrowed when a more constrained segment is placed there by using a series of poly(styrene-b-peptoid) block copolymers in which the polypeptoid block chain conformation can be tuned to adopt either a helical or a coil conformation (NRpe6 vs Npe6). The double gyroid phase is accessed in both block copolymer series, while the phase boundaries are shifted toward larger polypeptoid volume fractions in the helix-forming PS–(NRpe6Nmey) series, due to the more compact helix segment (i.e., the helix segment has the same chain volume as its random coil counterpart but occupies less space). The space-filling difference between the helix and coil segment is further confirmed by the smaller domain spacing of PS–(NRpe6Nme39) compared to PS–(Npe6Nme36) (13.9 nm vs 14.3 nm) despite the former having a longer polypeptoid block. Furthermore, a broadened double gyroid phase window is accessed in the PS–(Npe6Nmey) series that has a flexible coil segment near the interface. These results demonstrate the possibility of tuning the double gyroid phase in linear block copolymers by chain conformation near the interface alone, highlighting chain conformation as a versatile handle in block copolymer design.

Thermoresponsive dynamic BAB block copolymer networks synthesized by aqueous PISA in one-pot

The incorporation of neutral hydrophilic monomer units in the hydrophobic B blocks of BAB copolymers produces transient networks exhibiting a thermoresponsive behavior with a maximum of viscosity in water.

A new waterborne chitosan-based polyurethane hydrogel as a vehicle to transplant bone marrow mesenchymal cells improved wound healing of ulcers in a diabetic rat model

Foot ulcers, a common complication of diabetes, can cause physical incapacity and are derived from several factors, including poor wound healing. New therapeutic strategies are needed to minimize this complication for the sake of patients’ health. We therefore developed a new chitosan- polyurethane hydrogel membrane (HPUC) and the test results confirmed that HPUC present low cytotoxicity and improved wound healing when used with mononuclear bone marrow fraction cells in the diabetic rat model. The biodegradable hydrogels were produced in block copolymer networks with a combination of chitosan blocks and biodegradable polyurethane. The membranes were characterized by FTIR, 13C-NMR and thermogravimetry. Swelling and hydrolytic degradation were also evaluated. The non-solubility of the membranes in good solvents and the chemical characterization confirmed that the network structure was formed between the PU and the chitosan through urea/urethane bonds. The findings confirm that the HPUC have interesting properties that make them suitable for wound healing applications.

Toughened polymer electrolyte membranes composed of sulfonated poly(arylene ether ketone) block copolymer and organosiloxane network for fuel cell

The semi-interpenetrating polymer network (semi-IPN) based electrolyte membrane was synthesized from the poly(arylene ether ketone)-b-ketone sulfonated poly(arylene ether ketone) multi-block copolymer (PAEK-b-KSPAEK) and the organosiloxane organic-inorganic hybrid polymer network (OSPN) pre-synthesized. The chemical structure of the synthesized PAEK-b-KSPAEK and semi-IPN was identified using 1H and 19F nuclear magnetic resonance spectroscopy and Fourier transform infrared spectroscopy, and the dimension of the phase separated ionic clusters was examined by small angle X-ray scattering spectroscopy. Introduction of OSPN to PAEK-b-KSPAEK improved not only the thermal and mechanical stability (toughness) but also the oxidative stability. The performance of the membrane electrode assembly fabricated with the semi-IPN electrolyte membranes was superior to that of the pure block copolymer membrane because of the enhanced proton conductivity and toughness. While the semi-IPN24 membrane showed the comparable proton conductivity and cell performance to Nafion 115 membrane, its methanol permeability was significantly lower than that of Nafion 115 membrane.

Shape Memory Properties of Polystyrene-block-poly(ethylene-co-butylene)-block-polystyrene (SEBS) ABA Triblock Copolymer Thermoplastic Elastomers

This work demonstrates that neat polystyrene-block-poly(ethylene-co-butylene)-block-poly styrene (SEBS) displays thermally responsive shape memory properties. The shape memory properties were quantitatively investigated under uniaxial tension using a dynamic mechanical analyzer and manual stretching. The shape memory properties of SEBS were found to depend on both the molecular weight of the polymer and on the shape programming conditions, including the programming temperature, applied strain, and annealing time at elevated temperature under load. The shape memory mechanism is proposed to be a result of partial stress relaxation of the block copolymer network under load and the formation of a second network with a lower glass transition temperature. This second network counterbalances the initially stretched network producing fixity and weakens first on heating, allowing recovery. Due to the unique mechanism of shape memory where the secondary network is generated from the initial network, achieving highe...

Spray-Processed Composites with High Conductivity and Elasticity.

Highly conductive elastic composites were constructed using multistep solution-based fabrication methods that included the deposition of a nonwoven polymer fiber mat through solution blow spinning and nanoparticle nucleation. High nanoparticle loading was achieved by introducing silver nanoparticles into the fiber spinning solution. The presence of the silver nanoparticles facilitates improved uptake of silver nanoparticle precursor in subsequent processing steps. The precursor is used to generate a second nanoparticle population, leading to high loading and conductivity. Establishing high nanoparticle loading in a microfibrous block copolymer network generated deformable composites that can sustain electrical conductivities reaching 9000 S/cm under 100% tensile strain. These conductive elastic fabrics can retain at least 70% of their initial electrical conductivity after being stretched to 100% strain and released for 500 cycles. This composite material system has the potential to be implemented in wearable electronics and robotic systems.

Biodegradable chitosan-poly(Ɛ-caprolactone) dialdehyde copolymer networks for soft tissue engineering

Chitosan/PCL block-copolymer networks were synthesized using different amounts of aldehyde end-capped polycaprolactone as crosslinking agent. The crosslinking reaction was performed by dissolving both components in the common solvent hexafluoroisopropanol (HFIP). The formation of the network was confirmed by solubility tests in good solvents of both components. The resulting composition was determined by thermogravimetric analysis. The hydrophilic/hydrophobic networks behave as hydrogels; water sorption at pH7 is around 70% that of pure chitosan for a network containing 36% PCL blocks. The PCL domains were not able to crystallize, except for the CHT-64 sample as shown by DSC and X-ray diffraction. Enzymatic degradation of these networks is quite fast, thus, the network with 36% PCL presented a remaining weight of 22± 1% of their initial mass after 28 days of degradation in lipase. Nevertheless in purely hydrolytic degradation, the remaining weight was 86± 3% for the same time and composition.

Shape-memory behavior of cross-linked semi-crystalline polymers and their blends

The present study deals with thermally induced one-way and invertible two-way shape-memory effect (SME) in covalent networks on the basis of crystallizable (co)polymers and their blends and is an attempt to generalize the results of own investigation received by the authors in the last ten years. The main focus of work clearly lies on research of covalently crosslinked binary and ternary blends having two and three crystalline phases with different thermal stability, respectively. The existence of two or three crystalline phases possessing different melting and crystallization temperatures in heterogeneous polymer networks can lead to triple-shape or even quadruple-shape behavior of such networks. However, the performed investigations point to crucial effect of phase morphology of crosslinked polymer blends on multiplicity of their shapememory behavior beside the influence of blend content, crystallinity and cross-link density of blend phases as well as of processing conditions. For instance, triple-shape memory behavior in binary blends can be realized only if the continuous phase has a lower melting temperature than the dispersed phase. Cross-linked polymer blends are a facile alternative to expensive and complex synthesis of interpenetrating or block-copolymer networks used for shape memory polymers. In addition to findings of experimental investigation of SME in crystallizable covalent polymer networks, the results of modeling their shape-memory behavior on the basis of self-developed physically reasonable model have been briefly described and discussed. Thereby, good accordance between results of theory and experiment was achieved with physically justified fitting parameters.

Thermoresponse improvement of poly(N-isopropylacrylamide) hydrogels via formation of poly(sodium p-styrenesulfonate) nanophases.

The block copolymer networks composed of poly(N-isopropylacrylamide) (PNIPAM) and poly(sodium p-styrenesulfonate) were synthesized via sequential reversible addition-fragmentation chain transfer (RAFT) polymerization with α,ω-didithiobenzoate-terminated poly(sodium p-styrenesulfonate) (PSSNa) as the macromolecular chain transfer agent. It was found that the block copolymer networks were microphase-separated as evidenced by means of transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS). In the block copolymer networks, spherical or cylindrical PSSNa microdomains were finely dispersed into continuous PNIPAM matrixes. In comparison with unmodified PNIPAM hydrogel, the nanostructured hydrogels displayed improved thermoresponsive properties. In addition, the swelling ratios of the PSSNa-modified PNIPAM hydrogels were significantly higher than that of plain PNIPAM hydrogel. The improvement of thermoresponse was attributable to the formation of the PSSNa nanophases, which promoted the transportation of water molecules in the cross-linked networks.

Poly(N-isopropylacrylamide)-block-poly(acrylic acid) hydrogels: synthesis and rapid thermoresponsive properties

In this contribution, we reported the synthesis of poly(N-isopropylacrylamide)-block-poly(acrylic acid) (PNIPAAm-b-PAA) copolymer networks via sequential reversible addition-fragmentation chain transfer (RAFT) polymerization. The PNIPAAm-b-PAA block copolymer networks were characterized by means of Fourier transform infrared spectroscopy (FTIR) and small angle X-ray scattering (SAXS). The volume phase transition (VPT) temperatures of the PNIPAAm-b-PAA hydrogels were measured by means of micro-differential scanning calorimetry (micro-DSC). It was found that the block copolymer hydrogels displayed the VPT temperatures lower than the control PNIPAAm hydrogel. Compared to the control PNIPAAm hydrogel, the deswelling and reswelling properties of the block copolymer hydrogels were significantly improved. The improved thermoresponsive properties of the PNIPAAm-b-PAA hydrogels have been interpreted on the basis of the formation of the architecture of the block copolymer networks.

Simulation of Stimuli-Responsive Polymer Networks

The structure and material properties of polymer networks can depend sensitively on changes in the environment. There is a great deal of progress in the development of stimuli-responsive hydrogels for applications like sensors, self-repairing materials or actuators. Biocompatible, smart hydrogels can be used for applications, such as controlled drug delivery and release, or for artificial muscles. Numerical studies have been performed on different length scales and levels of details. Macroscopic theories that describe the network systems with the help of continuous fields are suited to study effects like the stimuli-induced deformation of hydrogels on large scales. In this article, we discuss various macroscopic approaches and describe, in more detail, our phase field model, which allows the calculation of the hydrogel dynamics with the help of a free energy that considers physical and chemical impacts. On a mesoscopic level, polymer systems can be modeled with the help of the self-consistent field theory, which includes the interactions, connectivity, and the entropy of the polymer chains, and does not depend on constitutive equations. We present our recent extension of the method that allows the study of the formation of nano domains in reversibly crosslinked block copolymer networks. Molecular simulations of polymer networks allow the investigation of the behavior of specific systems on a microscopic scale. As an example for microscopic modeling of stimuli sensitive polymer networks, we present our Monte Carlo simulations of a filament network system with crosslinkers.

Self‐Assembly: Reinforcement of Shear Thinning Protein Hydrogels by Responsive Block Copolymer Self‐Assembly (Adv. Funct. Mater. 9/2013)

Triblock copoylmers with associative protein midblocks and thermoresponsive endblocks form shear thinning hydrogels that can be injected at low temperature. On page 1182, Bradley D. Olsen and co-workers report that when warmed to body temperature, the gel is responsively reinforced as the endblocks self-assemble into a secondary block copolymer network, leading to large increases in modulus and yield stress, and decreased erosion and creep compliance.

Poly(N-isopropylacrylamide)-block-poly(vinyl pyrrolidone) block copolymer networks: Synthesis and rapid thermoresponse of hydrogels

In this work, we reported the synthesis of poly(N-isopropyl acrylamide)-block- poly(N-vinylpyrrolidone)-block-poly(N-isopropylacrylamide) triblock copolymer (PNIPAAm-b-PVPy-b-PNIPAAm) via reversible addition-fragmentation chain transfer polymerization/macromolecular design via the interchange of xanthate (RAFT/MADIX) process. This approach was further employed to prepare the PNIPAAm-b-PVPy block copolymer networks with N,N′-methylenebisacrylamide as the crosslinker. The results of small angle X-ray scattering (SAXS) indicate that the PNIPAAm-b-PVPy block copolymer networks were microphase-separated, in which PVPy was dispersed into PNIPAAm matrix as the microdomains. The architecture of block copolymer networks allows investigating the effect of the blocked permanently hydrophobic chains (viz. PVPy) on the deswelling and reswelling behavior of the PNIPAAm hydrogels. It was found that the diffusion of water molecules in PNIPAAm-b-PVPy block copolymer networks was in a non-Fickian and accelerating manner. The swelling ratios of the PNIPAAm-b-PVPy hydrogels were significantly higher than that of control PNIPAAm hydrogel. Compared to control PNIPAAm hydrogel, the PNIPAAm-b-PVPy hydrogels displayed an accelerated response to the external temperature changes in terms of deswelling and reswelling tests. The accelerated thermoresponsive properties is ascribed to the presence of the PVPy blocks in the PNIPAAm-b-PVPy block copolymer networks, which could act as the hydrophilic tunnels to facilitate the diffusion of water molecules in the PNIPAAm networks.

Hydrazone self-crosslinking of multiphase elastin-like block copolymer networks

Biosynthetic strategies for the production of recombinant elastin-like protein (ELP) triblock copolymers have resulted in elastomeric protein hydrogels, formed through rapid physical crosslinking upon warming of concentrated solutions. However, the strength of physically crosslinked networks can be limited, and options for non-toxic chemical crosslinking of these networks are not optimal. In this report, we modify two recombinant elastin-like proteins with aldehyde and hydrazide functionalities. When combined, these modified recombinant proteins self-crosslink through hydrazone bonding without requiring initiators or producing by-products. Crosslinked materials are evaluated for water content and swelling upon hydration, and subject to tensile and compressive mechanical tests. Hydrazone crosslinking is a viable method for increasing the mechanical strength of elastin-like protein polymers, in a manner that is likely to lend itself to the biocompatible in situ formation of chemically and physically crosslinked ELP hydrogels.