Block Copolymer Architecture Research Articles

Structural Engineering of Cationic Block Copolymer Architectures for Selective Breaching of Prokaryotic and Eukaryotic Biological Species.

Positively charged antimicrobial polymers are known to cause severe damage to biological systems, and thus synthetic strategies are urgently required to design next-generation nontoxic cationic macromolecular architectures for healthcare applications. Here, we report a structural-engineering strategy to build cationic linear and star-block copolymer nanoarchitectures having identical chemical composition, molar mass, nanoparticle size, and positive surface charge, yet they differ distinctly in their biological action in breaching prokaryotic species such as E. coli (Gram-negative bacteria) without affecting eukaryotic species like red-blood and mammalian cells. For this purpose, linear and star-block structures are built on a polycaprolactone biodegradable platform having an imidazolium positive handle. Under physiological conditions, the linear architecture exhibits toxicity indiscriminately to all biological species, whereas its star counterpart is remarkably selective in membrane breaching action toward bacteria while maintaining inertness toward eukaryotic species. Confocal microscopy analysis of HPTS fluorescent dye-loaded star-polymer nanoparticles substantiated their antimicrobial action in E. coli. Tissue-penetrable near-infrared fluorescent dye (IR-780) loaded NP aided the in vivo biodistribution analysis and ex vivo quantification of cationic species' accumulations in vital organs in mice. Azithromycin, a clinical water-insoluble macrolide, is delivered from the star platform to accomplish synergistic antimicrobial activity by the combination of bactericidal-bacteriostatic action of the polymer carrier and drug together in a single system.

Visible light-driven photoreforming of polystyrene segmented glycopolymer architectures for enhanced hydrogen generation

In this report, a series of polystyrene segmented new glycopolymer architectures are synthesized, which are utilized in the photoreforming process to achieve a remarkable rate of hydrogen production. The primary building blocks of mono-, bi-, and tetra-functional photo-iniferter were employed in the RAFT polymerization process to design a series of block copolymer architectures using styrene and acetylated glucose methacrylate monomers. Acetylated polymer architectures exhibited higher thermal stability compared to deacetylated polymers. Deacetylated polymers showed lower Tg values than the acetylated polymers. In addition, a wide range of Tg values (55–96 °C) and variations in the Tm values of the acetylated polymers indicate the dependence on the nature of the pendant unit and macromolecular architecture. The deacetylated macromolecule, 1A-PS-b-PGMD diblock copolymer exhibits a hydrogen generation rate of ∼753 μmol/g/h with an AQY of ∼1.84% compared to that of the polystyrene segment alone (53 μmol/g/h, AQY of ∼0.02%). Within the range of possible synthesized glycopolymer architectures, linear and glucose-based triblock glycopolymers show promising activity. The kinetics of the water-splitting reaction are influenced by adjustments to both the solution's pH and the hydrophilicity of the glycomacromolecular chains.

Effect of Block Copolymer Self-Assembly on Phase Separation in Photopolymerizable Epoxy Blends.

Directing self-assembly of photopolymerizable systems is advantageous for controlling polymer nanostructure and material properties, but developing techniques for inducing ordered structure remains challenging. In this work, well-defined diblock or random copolymers were incorporated into cationic photopolymerizable epoxy systems to investigate the impact of copolymer architecture on self-assembly and phase separated nanostructures. Copolymers consisting of poly(hydroxyethyl acrylate)-x-(butyl acrylate) were prepared using photoiniferter polymerization to control functional group placement and molecular weight/polydispersity. Prepolymer configuration and concentration induced distinctly different effects on the resin flow and photopolymerization kinetics. The diblock copolymer self-assembled into nanostructured phases within the resin matrix, whereas the random copolymer formed an isotropic mixture. Rapid photopolymerization and ambient temperature conditions during cure facilitated retention of the self-assembled phases, leading to considerably different composite morphology and thermomechanical behavior. Increased loading of the diblock copolymer induced long-range ordered cocontinuous structures. Even with nearly identical prepolymer composition, controlled nanophase separation resulted in significantly enhanced tensile properties relative to those of the isotropic system. This work demonstrates that controlling phase separation with a block copolymer architecture allows access to nanostructured photopolymers with unique and enhanced properties.

Controlled architecture of multi-defense anti-fouling forward osmosis membrane for efficient shale gas wastewater treatment

Forward osmosis (FO) membrane process facilitates effective treatment of shale gas wastewater (SGW) due to its tolerance to high salinity and exceptional separation performance. However, serious membrane fouling remains a challenge regarding the complexity of realistic SGW. To address the fouling issues, controlled block copolymer architecture was constructed on the FO membrane surface to achieve combined effect of oil-resistance, self-regenerating, and fouling mitigation. In the modification process, zwitterionic polymer with strong hydrophilicity and fluoropolymers with low surface energy were successively grafted to the membrane active layer by atom transfer radical polymerization. The outermost fluoropolymer layer with low surface energy imparts the membrane with anti-oil and self-regenerating capabilities. Meanwhile, the strong hydration effect of the zwitterionic polymer ensures that nonspecific foulants breaking through the outermost defense are kept away from the membrane surface. According to the Extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory, the modified FO membrane exhibited a significantly higher total interaction energy (ΔGTOT) compared to the pristine membrane when exposed to various types of model foulants (bovine serum albumin, humic acid, sodium alginate, mineral oil). Furthermore, the advantage of having multiple defense mechanisms was further substantiated through dynamic filtration tests with realistic SGW. In comparison to the pristine TFC membrane, the modified membrane not only experienced a much smaller decrease in water flux (reduced by 52%) during fouling but also an exceptional flux recovery after cleaning (∼97%). These findings underscore that the modified FO membranes greatly mitigated membrane fouling associated with SGW through the synergistic interplay between a zwitterionic polymer and a low surface energy material, highlighting its promising potential in SGW treatment via membrane technology.

Enhanced performance of phototransistor memory by optimizing the block copolymer architectures comprising Polyfluorenes and hydrogen-bonded insulating coils

Photonic transistor memory, which adopts the structure of a field-effect transistor, combines optical and electronic principles. Conjugated block copolymers (BCPs) are promising electret materials for optoelectronic applications. In this study, a series of BCPs comprising poly[2,7-(9,9-dioctylfluorene)] (PFO: A block) and poly(n-butyl acrylate-random-2-ureido-4[1H]pyrimidinone acrylate) (nBA-r-UPyA: B block), with linear-diblock (AB), branched (AB2), and linear-triblock (BAB) architectures, are synthesized to investigate hydrogen bonding effect stemming from UPyA groups. After thermal annealing, the soft segments of BCPs lead to self-assembled arrangements and smoother morphologies, providing an excellent interface for the deposition of the semiconducting channel layer. Furthermore, forming vertical phase-separated structures through thermal annealing significantly enhances the electron-capture capability. Subsequently, the BCP materials are applied in photonic transistor memory and conducted with electrical characterization. Our study reveals that different compositions of BCP architectures have a corresponding impact on the performance of photonic transistor memory devices. Consequently, AB of PFO-b-P(nBA-r-UPyA)s with a linear-diblock architecture presents an outperforming memory ratio of ∼105, outstanding memory stability over 104 s, and durability to consecutive write/erase processes.

Poly(ethylene terephthalate)‐polyethylene block copolymer architecture effects on interfacial adhesion and blend compatibilization

AbstractIn this study, poly(ethylene terephthalate)‐block‐polyethylene (PET‐PE) multiblock copolymers (MBCPs) with block molar masses of ~4 or 7 kg mol−1 and either alternating or random block sequencing, and a PE‐PET‐PE triblock copolymer (TBCP) of comparable total molar mass, were synthesized. To explore the effect of molecular architecture on compatibilization, both MBCPs and TBCPs were blended into 80/20 wt/wt mixtures of PET/linear low‐density PE (LLDPE). Compatibilization was remarkably efficient for all MBCP types, with the addition of 0.2 wt% yielding blends nearly as tough as PET homopolymer. Addition of MBCP also significantly decreases LLDPE dispersed phase sizes compared to PET/LLDPE neat blends, as much as 80% in as‐mixed blends and by a factor of 10 in post‐mixing thermally annealed samples. Conversely, the TBCP was less efficient at decreasing domain sizes of the blends and improving the mechanical properties, requiring loadings of 1 wt% to produce comparably tough blends. Peel tests of PET/BCP/LLDPE trilayer films showed that both MBCPs and TBCP all improve interfacial strength over a PET‐PE bilayer film by two orders of magnitude; however, when the BCPs were preloaded into LLDPE, only the MBCP containing films showed strong adhesion highlighting their potential utility as adhesive agents in multilayer films.

Flexible biomimetic block copolymer composite for temperature and long-wave infrared sensing.

Biological compounds often provide clues to advance material designs. Replicating their molecular structure and functional motifs in artificial materials offers a blueprint for unprecedented functionalities. Here, we report a flexible biomimetic thermal sensing (BTS) polymer that is designed to emulate the ion transport dynamics of a plant cell wall component, pectin. Using a simple yet versatile synthetic procedure, we engineer the physicochemical properties of the polymer by inserting elastic fragments in a block copolymer architecture, making it flexible and stretchable. The thermal response of our flexible polymer outperforms current state-of-the-art temperature sensing materials, including vanadium oxide, by up to two orders of magnitude. Thermal sensors fabricated from these composites exhibit a sensitivity that exceeds 10 mK and operate stably between 15° and 55°C, even under repeated mechanical deformations. We demonstrate the use of our flexible BTS polymer in two-dimensional arrays for spatiotemporal temperature mapping and broadband infrared photodetection.

Synthesis and microphase separation of dendrimer-like block copolymers by anionic polymerization strategies

Anionic polymerization for the preparation of polystyrene-b-polybutadiene is well-established and leads to thermoplastic elastomers on industrial scale. The classical ABA block copolymer (BCP) architecture and composition usually forms a cylindrical morphology in the bulk state. Their anisotropic mechanical properties are, however, unfavorable for many applications. The gyroid microphase is entirely isotropic, but it is only formed in a narrow compositional area of around 35 vol% of the minority polymer block. In the present study, a second-generation dendrimer-like block copolymer structure ((AB)2B)3 is described. This BCP architecture is expected to show a higher curvature on the microphase boundaries, which leads to a larger morphological range for the gyroid phase. Three compositionally different polymers are synthesized by living anionic polymerization strategies and the resulting morphology is analyzed via transmission electron microscopy (TEM) and small angle X-ray scattering (SAXS). The dendrimer-like BCPs are compared to their less branched analogues, namely the asymmetric star polymers and H-shape stars. The expected influence of the dendrimer-like BCP architecture on the microphase separation is investigated paving the way to a promising synthetic platform for interesting mechanical and optical properties.

Modifying the Properties of Microemulsion Droplets by Addition of Thermoresponsive BAB* Copolymers.

Oil-in-water (O/W) microemulsions (ME) typically feature a low viscosity and exhibit ordinary viscosity reduction as a function of temperature. However, for certain applications, avoiding or even reverting the temperature trend might be required. This can be conceived by adding thermoresponsive (TR) block copolymers that induce network formation as the temperature increases. Accordingly, various ME-polymer mixtures were studied for which three different block copolymer architectures of BAB*-, B2AB*-, and B(AB*)2-types were employed. Here, "B" represents a permanently hydrophobic, "A" a permanently hydrophilic, and "B*" a TR block. For the TR-block, three different poly(acrylamide)s, namely poly(N-n-propylacrylamide) (pNPAm), poly(N,N-diethylacrylamide) (pDEAm), and poly(N-isopropylacrylamide) (pNiPAm), were used, which all exhibit a lower critical solution temperature. For a well-selected ME concentration, these block copolymers lead to a viscosity enhancement with increasing temperature. At a polymer concentration of about 22 g L-1, the most pronounced enhancement was observed for the pNPAm-based systems with factors up to 3, 5, and 8 for BAB*, B2AB*, and B(AB*)2, respectively. This phenomenon is caused by the formation of a transitory network mediated by TR-blocks, as evidenced by the direct correlation between the attraction strength and the viscosity enhancement. For applications requiring a high hydrophobic payload, which is attained via ME droplets, this kind of tailored temperature-dependent viscosity control of surfactant systems should therefore be advantageous.

Linear Block Copolymer Synthesis.

Block copolymers form the basis of the most ubiquitous materials such as thermoplastic elastomers, bridge interphases in polymer blends, and are fundamental for the development of high-performance materials. The driving force to further advance these materials is the accessibility of block copolymers, which have a wide variety in composition, functional group content, and precision of their structure. To advance and broaden the application of block copolymers will depend on the nature of combined segmented blocks, guided through the combination of polymerization techniques to reach a high versatility in block copolymer architecture and function. This review provides the most comprehensive overview of techniques to prepare linear block copolymers and is intended to serve as a guideline on how polymerization techniques can work together to result in desired block combinations. As the review will give an account of the relevant procedures and access areas, the sections will include orthogonal approaches or sequentially combined polymerization techniques, which increases the synthetic options for these materials.

Concentration Threshold for Membrane Protection by PEO-PPO Block Copolymers with Variable Molecular Architectures.

Poloxamer 188, a poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) (PEO-PPO-PEO) triblock copolymer, protects cell membranes in several injury models. However, the nature of the copolymer/membrane interaction and the mechanism of membrane protection remain unknown. Systematic variations of the block copolymer architecture - including PPO-PEO-PPO triblocks and PPO-PEO diblocks - were used to probe the mechanism and evaluate the potential for alternative architectures to yield superior protection. To test the polymers, murine myoblasts were subjected to an osmotic stress, and membrane integrity was quantified by measuring lactate dehydrogenase (LDH) leakage. These experiments exposed a concentration threshold effect where all tested polymers reach 50% leakage of LDH compared to a non-treated buffer only control over a narrow concentration range of 0.8-4 μM. Differences in polymer protection at lower concentrations indicate that protection increases with the PPO-PEO-PPO molecular architecture and increasing hydrophobicity.

Exploring the effect of block copolymer architecture and concentration on the microstructure, electrical conductivity and rheological properties of PP/PS blend nanocomposites

The interface between polymer matrices and nanofillers is critical for efficient interaction to achieve the desired final properties. In this work, block copolymers were utilized to control the interface and achieve optimum interfacial interaction. Specifically, we studied the compatibilizing effects of styrene-ethylene/butadiene-styrene (SEBS) and styrene-ethylene/propylene (SEP) block copolymers on the morphology, conductivity, and rheological properties of polypropylene-polystyrene (PP/PS) immiscible blend with 2 vol% multiwall carbon nanotube (MWCNT) at different blend compositions of PP/PS 80:20, 50:50 and 20:80.MWCNTs induced co-continuity in PP/PS blends and did not obstruct with the copolymer migration to the interface. Copolymers at the interface led to blend morphology refinement. Adding block copolymers at a relatively low concentration of 1 vol% to compatibilize the PP/PS 80:20 blend substantially increased the electrical conductivity from 5.15*10−7S/cm for the uncompatibilized blend to 1.07*10−2S/cm for the system with SEP and 1.51*10−3S/m for the SEBS system. These values for the compatibilized blends are about 4 orders of magnitude higher due to the interconnection of the droplet domains. For the PP/PS 50:50 blend, the SEBS copolymer resulted in a huge increase in conductivity at above 3 vol% concentration (conductivity increased to 3.49*10−3S/cm from 5.16*10−7S/cm). Both the conductivity and the storage modulus increased as the SEBS copolymer content was increased. For the PP/PS 20:80 blend, we observed an initial decrease in conductivity at lower copolymer concentrations (1–3 vol%) and then an increase in conductivity to values higher than the uncompatibilized system, but only at a higher copolymer concentration of 10 vol%. The triblock copolymer (SEBS), which had 60 wt% PS content, shows a more significant increase in rheological properties compared to the diblock copolymer (SEP). The morphology shows that the interaction between MWCNT and PS is stronger than the interaction between MWCNT and PP, hence there is selective localization of the nanofiller in the PS phase as predicted by Young’s equation and by molecular simulation.

Effect of Molecular Architecture and Symmetry on Self-Assembly: A Quantitative Revisit Using Discrete ABA Triblock Copolymers.

The inherent statistical heterogeneities associated with chain length, composition, and architecture of synthetic block copolymers compromise the quantitative interpretation of their self-assembly process. This study scrutinizes the contribution of molecular architecture on phase behaviors using discrete ABA triblock copolymers with precise chemical structure and uniform chain length. A group of discrete triblock copolymers with varying composition and symmetry were modularly synthesized through a combination of iterative growth methods and efficient coupling reactions. The symmetric ABA triblock copolymers self-assemble into long-range ordered structures with expanded domain spacings and enhanced phase stability, compared with the diblock counterparts snipped at the middle point. By tuning the relative chain length of two end blocks, the molecular asymmetry reduces the packing frustration, and thus increases the order-to-disorder transition temperature and enlarges the domain sizes. This study would serve as a quantitative model system to correlate the experimental observations with the theoretical assessments and to provide quantitative understandings for the relationship between molecular architecture and self-assembly.

Novel super-hydrophilic coatings with enhanced adhesion on polyolefin substrate obtained by gravure deposition of true amphiphilic block co-polymer water dispersions

The aim of this study was to produce and characterise durable, high-performance super-hydrophilic anti-drip coatings based on water dispersions of true amphiphilic block copolymers, to be utilised on agricultural films. The performance of coated low density poly(ethylene) (LDPE) samples, obtained by varying both the coating dispersion formulation and process conditions, were evaluated by means of: hot-fog testing; mechanical wear resistance testing; surface free energy measurements; UV–vis spectroscopy, and; scanning electron microscopy. This study clearly demonstrated that durable super-hydrophilic coatings could be successfully deposited onto LDPE using the proposed approach. In this study, the novel coatings showed excellent adhesion on LDPE substrates, exhibiting anti-drip properties after 100 complete abrasion cycles in an in-house developed test. These levels of mechanical wear resistance, as demonstrated by the optimised coatings, are much greater than those previously reported for antifog films on polyolefins. The molecular architecture of the true amphiphilic block copolymers showed them to be responsible for both the antifogging and enhanced adhesion performance of the coated surfaces. It was demonstrated that the new solvent-free, water-based co-polymer solutions developed, offer important advantages over traditional agricultural films in terms of both their initial and long-term performance, thereby, making them attractive for use in agricultural and other industrial applications.

Synthesis of block copolymers containing 3-chloro-2-hydroxypropyl methacrylate by NMP – a versatile platform for functionalization

This study highlights the potential of 3-chloro-2-hydroxypropyl methacrylate (ClHPMA) as a functional building block in nanostructured block copolymer architectures.

Hybrid polymer/lipid vesicles: Influence of polymer architecture and molar mass on line tension

Hybrid polymer/lipid vesicles are self-assembled structures that have been the subject of an increasing number of studies in recent years. They are particularly promising tools in the development of cell membrane models because they offer the possibility to fine-tune their membrane structure by adjusting the distribution of components (presence or absence of “raft-like” lipid domains), which is of prime importance to control their membrane properties. Line tension in multiphase membranes is known to be a key parameter on membrane structuration, but remains unexplored, either experimentally or by computer modeling for hybrid polymer/lipid vesicles. In this study, we were able to measure the line tension on different budded hybrid vesicles, using a micropipette aspiration technique, and show the influence of the molar mass and the architecture of block copolymers on line tension and its consequences for membrane structuration.

Polymethylene Brushes via Surface-Initiated C1 Polyhomologation.

Surface-initiated polymerization reactions are a powerful tool to generate chain-end-tethered polymer brushes. This report presents a synthetic strategy that gives access to structurally well-defined hydrocarbon polymer brushes of controlled molecular weights, which can be further modified to generate more complex surface-attached polymer architectures. The hydrocarbon brushes reported in this study are polymethylene brushes that are obtained via surface-initiated C1 polyhomologation of dimethylsulfoxonium methylide. The strategy outlined here is based on the use of an alkylboronic acid pinacol ester initiator, which allows for controlled, unidirectional chain growth by monomer insertion into only the C-B bond of the initiator and which presents the polymerization active group at the growing polymer chain end. This surface-initiated C1 polyhomologation methodology is compatible with photopatterning strategies and can be used to generate micropatterned polymethylene brush films. Furthermore, conversion of the boronic ester chain-end functionalities to hydroxyl groups allows for selective chain-end modification and enables access to a variety of surface-anchored block copolymer architectures by chain extension via, for example, ring-opening or atom transfer radical polymerization chemistries.

Temperature Variation Enables the Design of Biobased Block Copolymers via One‐Step Anionic Copolymerization

The bio-based monomer, myrcene, attracts significant interest as a green alternative for the preparation of polydiene-based materials and for polymer architectures. In article number 2000513, Markus Gallei and co-workers introduce a convenient statistical, i.e. one-pot anionic copolymerization, strategy for the design of myrcene-based block copolymer architectures.

Pluronic-based lamellar phases: influence of polymer architecture on bilayer bending elasticity

ABSTRACT In this study, we investigate the influence of the block copolymer architecture on the bending elasticity of polymer-rich lamellar phases. In detail, we study the polymer-rich system water/o-xylene/Pluronic triblock copolymer/CTAB and change the polymer while keeping the mass ratios constant. We use neutron spin echo measurements (NSE) to determine κ. With the measurements we determine the relaxation rate of the bilayer bending mode and subsequently calculate the bilayer bending modulus κ using the Zilman-Granek approach [Zilman et al., Phys. Rev. Lett. 77, 4788–4791 (1996)]. Moreover, we have investigated the lamellar phases via small-angle X-ray scattering (SAXS) and have analysed the data with the modified Caillé theory to obtain the Caillé parameter η. Based on κ the bulk compression modulus can be calculated. Increasing values of κ are found with increasing EO and PO block size in the range of 3.8 to 13.4 T. The computed values of are in the range of 10 to 10 Pa.

Scattering Function and Spinodal Transition of Linear and Nonlinear Block Copolymers Based on a Unified Molecular Model

This work uses a block copolymer architecture [(A′B)nA2]m to unify the scattering function and spinodal transition of typical AB-type block copolymers. The key roles of block number, junction points and asymmetry ratios of block length are (1) to determine the form factor of each block copolymer at the molecular scale; (2) to affect the entropy loss across the spinodal transition and may result in deflection of spinodal curves. The common features are validated in typical linear and nonlinear block copolymers, including AB diblock, asymmetric A′BA triblock, miktoarm stars of ABn, AnBn, (AB)n, (A′B)nA, A′BAm, and multi-graft combs of (BnA2)m and [(A′B)nA2]m. The explicit scattering functions and form factors of various block copolymers can be directly applied in radiation experiments (i.e. neutron or X-ray scattering) to unravel the effect of molecular architecture in solution and microphase separation in disordered melt. The molecular model used in this study is also helpful to guide the chemical synthesis to explore more potentially interesting block copolymers.