Block Oligomers Research Articles

Excitation-Wavelength-Dependent Charge Injection and Hole Localization in Diblock Oligomers Anchored to TiO2.

A series of diblock oligomers containing oligothiophene (Tn, n = 4, 5) and 4,7-di(thiophen-2-yl)benzo[c][1,2,5]thiadizole (TBT) segments, functionalized with carboxylic acid anchoring groups, were prepared and anchored to mesoporous TiO2 films to study wavelength-dependent interfacial electron transfer mechanisms. Thin films of the surface-anchored diblock oligomers contained two absorption bands centered at 400 and 500 nm, corresponding to the Tn and TBT blocks, respectively. Pulsed-laser excitation of the oligomer-sensitized films yielded local excited-states that promoted electron injection into TiO2. The injection pathway was dependent on the excitation wavelength, as electron injection occurred from the oligomer block that was locally excited. Recombination between the injected electron and the oxidized oligomer was sensitive to the bridging unit that separates the oligomer conjugated segments (-C≡C- vs trans-Pt(PBu3)2-). When the bridge facilitated strong coupling between the two blocks (-C≡C- bridge), the excitation wavelength had no effect on the recombination pathway, as the hole was delocalized over the entire oligomer. However, in the weak coupling case (Pt(PBu3)2- bridge), selective excitation resulted in wavelength-dependent hole localization that persisted to the μs time scale, providing control over the recombination pathway by varying the excitation wavelength. Dye-sensitized solar cells (DSSCs) were fabricated by using the diblock oligomers as sensitizers. The photocurrent action spectra were measured, and the absorbed photon-to-current efficiency (APCE) provided further insight into the electron-transfer mechanisms that are operative under continuous illumination.

Stabilizing a Double Gyroid Network Phase with 2 nm Feature Size by Blending of Lamellar and Cylindrical Forming Block Oligomers

Molecular dynamics simulations are used to study binary blends of an AB-type diblock and an AB2-type miktoarm triblock amphiphiles (also known as high-χ block oligomers) consisting of sugar-based (A) and hydrocarbon (B) blocks. In their pure form, the AB diblock and AB2 triblock amphiphiles self-assemble into ordered lamellar (LAM) and cylindrical (CYL) structures, respectively. At intermediate compositions, however, the AB2-rich blend (0.2 ≤ xAB ≤ 0.4) forms a double gyroid (DG) network, whereas perforated lamellae (PL) are observed in the AB-rich blend (0.5 ≤ xAB ≤ 0.8). All of the ordered mesophases present domain pitches under 3 nm, with 1 nm feature sizes for the polar domains. Structural analyses reveal that the nonuniform interfacial curvatures of DG and PL structures are supported by local composition variations of the LAM- and CYL-forming amphiphiles. Self-consistent mean field theory calculations for blends of related AB and AB2 block polymers also show the DG network at intermediate compositions, when A is the minority block, but PL is not stable. This work provides molecular-level insights into how blending of shape-filling molecular architectures enables network phase formation with extremely small feature sizes over a wide composition range.

Development of a PointNet for Detecting Morphologies of Self-Assembled Block Oligomers in Atomistic Simulations.

Molecular simulations with atomistic or coarse-grained force fields are a powerful approach for understanding and predicting the self-assembly phase behavior of complex molecules. Amphiphiles, block oligomers, and block polymers can form mesophases with different ordered morphologies describing the spatial distribution of the blocks, but entirely amorphous nature for local packing and chain conformation. Screening block oligomer chemistry and architecture through molecular simulations to find promising candidates for functional materials is aided by effective and straightforward morphology identification techniques. Capturing 3-dimensional periodic structures, such as ordered network morphologies, is hampered by the requirement that the number of molecules in the simulated system and the shape of the periodic simulation box need to be commensurate with those of the resulting network phase. Common strategies for structure identification include structure factors and order parameters, but these fail to identify imperfect structures in simulations with incorrect system sizes. Building upon pioneering work by DeFever et al. [Chem. Sci. 2019, 10, 7503-7515] who implemented a PointNet (i.e., a neural network designed for computer vision applications using point clouds) to detect local structure in simulations of single-bead particles and water molecules, we present a PointNet for detection of nonlocal ordered morphologies of complex block oligomers. Our PointNet was trained using atomic coordinates from molecular dynamics simulation trajectories and synthetic point clouds for ordered network morphologies that were absent from previous simulations. In contrast to prior work on simple molecules, we observe that large point clouds with 1000 or more points are needed for the more complex block oligomers. The trained PointNet model achieves an accuracy as high as 0.99 for globally ordered morphologies formed by linear diblock, linear triblock, and 3-arm and 4-arm star-block oligomers, and it also allows for the discovery of emerging ordered patterns from nonequilibrium systems.

From Order to Disorder: Computational Design of Triblock Amphiphiles with 1 nm Domains.

Using molecular dynamics simulations and transferable force fields, we designed a series of symmetric triblock amphiphiles (or high-χ block oligomers) comprising incompatible sugar-based (A) and hydrocarbon (B) blocks that can self-assemble into ordered nanostructures with sub-1 nm domains and full domain pitches as small as 1.2 nm. Depending on the chain length and block sequence, the ordered morphologies include lamellae, perforated lamellae, and hexagonally perforated lamellae. The self-assembly of these amphiphiles bears some similarities, but also some differences, to those formed by symmetric triblock polymers. In lamellae formed by ABA amphiphiles, the fraction of B blocks "bridging" adjacent polar domains is nearly unity, much higher than that found for symmetric triblock polymers, and the bridging molecules adopt elongated conformations. In contrast, "looping" conformations are prevalent for A blocks of BAB amphiphiles. Above the order-disorder transition temperature, the disordered states are locally well-segregated yet the B blocks of ABA amphiphiles are significantly less stretched than in the lamellar phases. Analysis of both hydrogen-bonded and nonpolar clusters reveals the bicontinuous nature of these network phases. This simulation study furnishes detailed insights into structure-property relationships for mesophase formation on the 1 nm length scale that will aid further miniaturization for numerous applications.

Controlling the block sequence of multi-block oligomer ligands for neutralization of a target peptide

A series of block oligomers consisting of the same monomer composition but a different block sequence was prepared via reversible addition–fragmentation chain transfer (RAFT) polymerization to screen high affinity ligands for a toxic peptide.

Effect of increasing hydrophilic–hydrophobic block length in quaternary ammonium-functionalized poly(ether sulfone) block copolymer for anion exchange membrane fuel cells

Quaternary ammonium-functionalized poly(ether sulfone) (QA-PES) block copolymers with different block chain lengths were prepared as anion exchange membranes. Copolymers with similar hydrophilic/hydrophobic block ratios and hence similar IEC values, but with various oligomer block chain lengths were synthesized to investigate, for the first time, how the length of each oligomer included in the block copolymers affected the chemophysical and electrical properties of the obtained QA-PES anion exchange membranes. The copolymer with the optimal hydrophilic:hydrophobic block chain length (QA-PES-16-30) showed good phase separation. This led to the optimal formation of ionic clusters, and the highest ion conductivity of 81.01mScm−1 at 80°C, as well as excellent physicochemical stability even after alkaline treatment in 1M NaOH at 60°C for 500h, due to strengthening of the hydrophobic regions, strongly suggesting that the block chain length of each of the hydrophilic and hydrophobic blocks can affect the physicochemical properties of the polymer membranes. The H2/O2 single cell performance using the QA-PES-16-30 membrane showed a maximum power density of 260mWcm−2, much higher than that obtained from the Tokuyama A201.

Quaternary ammonium-functionalized poly(ether sulfone ketone) anion exchange membranes: The effect of block ratios

Anion exchange membranes based on quaternary ammonium-functionalized poly(ether sulfone ketone) block copolymers (QA-PESK) with various hydrophilic–hydrophobic oligomer block ratios (10:7, 10:18, and 10:26) were synthesized, and the block length effect on the membranes' physicochemical and electrical properties were systematically investigated. The QA-PESK-10-18 membrane, prepared using a hydrophilic and hydrophobic block ratio of 10:18, displayed well-balanced hydrophilic/hydrophobic phase separation, the highest conductivity of 23.19 mS cm−1 at 20 °C and 57.84 mS cm−1 at 80 °C, and the highest alkaline stability among the three block ratios tested, indicating that the membranes' properties were closely related to their morphologies, which were determined by the hydrophilic/hydrophobic ratio of the block copolymer. The H2/O2 single cell performance using the QA-PESK-10-18 revealed a maximum power density of 235 mW cm−2.

Telechelic Helical Poly(quinoxaline-2,3-diyl)s Containing a Structurally Defined, Circularly Polarized Luminescent Terquinoxaline Core: Synthesis by Core-Initiated Bidirectional Living Polymerization.

We have designed and synthesized divalent initiators that contain a fluorescent terquinoxaline unit with two palladium groups for the living polymerization of 1,2-diisocyanobenzenes. Using these divalent initiators, the bidirectional living polymerization of a monomer bearing (S)-butoxymethyl side chains afforded telechelic helical poly(quinoxaline-2,3-diyl)s (PQXs), which consist of a terquinoxaline unit at the center of the polymer chain and chiral oligomeric blocks on both sides. The location of the core unit was confirmed by NMR spectroscopy and photoluminescence measurements. Upon changing the solvent from CHCl3 to 1,1,2-trichloroethane, these PQXs exhibit both left- and right-handed circularly polarized luminescence with dissymmetry factors of approximately 1.0 × 10-3.

Design and synthesis of PEGylated amphiphilic block oligomers as membrane anchors for stable binding to lipid bilayer membranes

Cell surface engineering is a potentially powerful method for manipulating living cells by decorating the cell membrane with specific molecules. Possible applications include cell therapy, drug delivery systems, bio-imaging, and tissue engineering. The stable binding of synthetic molecules to serve as artificial membrane protein anchors is a promising approach for appending functional molecules to the cell surface. However, such synthetic molecules have previously shown limitations, including cytotoxicity and low cell surface affinity. We synthesized amphiphilic block oligomers, using ruthenium-catalyzed living radical polymerization, as novel membrane anchors for stable binding to lipid bilayer membranes. AB and ABA-type amphiphilic block oligomers were synthesized with poly(ethylene glycol) methacrylate (PEGMA) and varying butyl methacrylate (BMA) contents (PEGMA/BMA ratios of 25/5–25/50). These PEGylated oligomers showed high binding efficiencies (up to 92%) for liposomes, which served as model cell membranes, and low cytotoxicity in K562 cells. Both the BMA content and the block segment sequence in the copolymers strongly affected their binding efficiencies. Oligomers with an ABA-type block structure were much more effective than AB-type block oligomers, random oligomers, or PEGMA homo-oligomers for stable membrane binding. Thus, precise control of the primary structures of the amphiphilic oligomers enabled tuning of their binding efficiencies. These amphiphilic block oligomers hold promise as novel membrane anchors in many biomedical applications. A series of amphiphilic block oligomers were designed and synthesized using ruthenium-catalyzed living radical polymerization with poly(ethylene glycol) and butyl methacrylates (BMA). These PEGylated oligomers showed high binding efficiencies for liposomal preparations as model cell membranes, and also had low cytotoxicity. BMA contents and monomer sequences in the copolymers strongly affected their binding efficiencies. Current method enabled precise control of the primary structures of amphiphilic oligomers, allowing tuning of their binding efficiencies. These amphiphilic block oligomers have promise as novel membrane anchors for many biomedical applications.

Computational Design of High-χ Block Oligomers for Accessing 1 nm Domains.

Molecular dynamics simulations are used to design a series of high-χ block oligomers (HCBOs) that can self-assemble into a variety of mesophases with domain sizes as small as 1 nm. The exploration of these oligomers with various chain lengths, volume fractions, and chain architectures at multiple temperatures reveals the presence of ordered lamellae, perforated lamellae, and hexagonally packed cylinders. The achieved periods are as small as 3.0 and 2.1 nm for lamellae and cylinders, respectively, which correspond to polar domains of approximately 1 nm. Interestingly, the detailed phase behavior of these oligomers is distinct from that of either solvent-free surfactants or block polymers. The simulations reveal that the behavior of these HCBOs is a product of an interplay between both "surfactant factors" (headgroup interactions, chain flexibility, and interfacial curvature) and "block polymer factors" (χ, chain length N, and volume fraction f). This insight promotes the understanding of molecular features pivotal for mesophase formation at the sub-5 nm length scale, which facilitates the design of HCBOs tailored toward particular desired morphologies.

Oligomer–oligomer modification upon the synthesis of epoxy polymers with a “shape-memory” effect

The results of studies of the oligomer–oligomer modification of epoxyamine compositions with amine adducts, oligomers, block oligomers, and oligocyclocarbonates differing in their structure and molecular weight upon hardening under the conditions of a general epoxide–amine polycondensation reaction, and competitive epoxide–amine and cyclocarbonate–amine reactions are given. The parameters of the structure and the elastic-deformation properties required for the preparation of high-quality thermally contracting epoxy polymers with a “shape-memory” and for their reliable application are established.

Synthesis of amphiphilic ABA triblock oligomer via ATRP and its surface properties

A series of novel amphiphilic ABA-type poly(tridecafluorooctylacrylate)-poly(ethylene glycol)-poly(tridecafluorooctylacrylate) (henceforth referred to as p-TDFA-PEG-p-TDFA) triblock oligomers were successfully synthesized via atom transfer radical polymerization (ATRP) using well-defined Br-PEG-Br as macroinitiator and copper as catalyst. The block oligomers were characterized by Fourier transform infrared (FTIR) spectroscopy and 1H and 19F nuclear magnetic resonances (NMR). Gel permeation chromatography (GPC) showed that the block oligomers have been obtained with narrow molecular weight distributions of 1.22–1.33. X-ray photoelectron spectroscopy (XPS) was carried out to confirm the attachment of p-TDFA-PEG-p-TDFA onto the silicon substrate, together with the chemical compositions of p-TDFA-PEG-p-TDFA. The wetabilities of the oligomer films were measured by water contact angles (CAs). Water CAs of p-TDFA-PEG-p-TDFA film were measured and their morphologies were tested by atomic force microscopy (AFM). The result showed that the CAs of the oligomer films, which possess fluoroalkyl groups assembled on the outer surface, increase after heating due to the migration of fluoroalkyl groups and the resulted microphase separation of the p-TDFA-PEG-p-TDFA.

Influence of Defined Hydrophilic Blocks within Oligoaminoamide Copolymers: Compaction versus Shielding of pDNA Nanoparticles.

Cationic polymers are promising components of the versatile platform of non-viral nucleic acid (NA) delivery agents. For a successful gene delivery system, these NA vehicles need to comprise several functionalities. This work focuses on the modification of oligoaminoamide carriers with hydrophilic oligomer blocks mediating nanoparticle shielding potential, which is necessary to prevent aggregation or dissociation of NA polyplexes in vitro, and hinder opsonization with blood components in vivo. Herein, the shielding agent polyethylene glycol (PEG) in three defined lengths (12, 24, or 48 oxyethylene repeats) is compared with two peptidic shielding blocks composed of four or eight repeats of sequential proline-alanine-serine (PAS). With both types of shielding agents, we found opposing effects of the length of hydrophilic segments on shielding and compaction of formed plasmid DNA (pDNA) nanoparticles. Two-arm oligoaminoamides with 37 cationizable nitrogens linked to 12 oxyethylene units or four PAS repeats resulted in very compact 40–50 nm pDNA nanoparticles, whereas longer shielding molecules destabilize the investigated polyplexes. Thus, the balance between sufficiently shielded but still compact and stable particles can be considered a critical optimization parameter for non-viral nucleic acid vehicles based on hydrophilic-cationic block oligomers.

The effect of adjusting the hydrophilic–hydrophobic block length in densely sulfonated poly(fluorenyl ether sulfone) block copolymer membranes

Densely sulfonated poly(fluorenyl ether sulfone) block copolymers (DS-PFESs) of various hydrophilic and hydrophobic oligomer block lengths were prepared, and the effect of the block length on the membranes' physicochemical and electrical properties was systematically investigated. Although the conductivity increased with the block length, a morphological analysis identified an optimal chain length. Further increases in the chain length resulted in the formation of larger ionic cluster clumps that caused a significant loss in the phase separation and, hence the dimensional/mechanical stability. The DS-9-32 membrane, prepared with a hydrophilic and hydrophobic block length of 9:32, displayed a well-balanced hydrophilic/hydrophobic phase separation and a high conductivity, together with a high dimensional/mechanical stability.

Effect of an organosilicon modifier on the structure of polyether urethanes

Structures of amorphous polyether urethanes modified with oligomeric organosilicon blocks are studied via AFM, SEM, and TEM. The main structural unit of the investigated polymers is found to be a globule. The effect the silicon modifier has on the polyether urethane structure is determined.

Synthesis of Amphiphilic Naturally-Derived Oligosaccharide-block-Wax Oligomers and Their Self-Assembly.

Self-assembly characteristics of amphiphilic macromolecules into micelles, nanoparticles and vesicles has been of fundamental interest for many applications including designed nanoscale therapeutic delivery systems and enzymatic reactors. In this work, a class of amphiphilic block oligomers was synthesized from naturally occurring oligosaccharides and aliphatic alcohol precursors, which are all currently prominent in the pharmaceutical, food, and supplement industries. These block oligomer materials were synthesized by functionalization of the precursor materials followed by subsequent coupling by azide-alkyne cycloaddition and their bulk self-assembly was investigated after solvent vapor annealing. Self-assembly of the amphiphilic materials into liposomes in aqueous solution was also investigated after preparing solutions using a nanoprecipitation method. Encapsulation of hydrophobic components was demonstrated and verified using dynamic light scattering, transmission electron microscopy, and fluorescence spectroscopy experiments.

Morphology control of porous epoxy resin by rod-coil block oligomer: a self-assembly-induced phase separation by diphenyl fluorene-modified silicone epoxy

Self-assembly of amphiphilic rod-coil polymers into well-ordered structures has attracted significant interest over the last decade.

Synthesis and characterization of sulfonated cardo based poly(arylene ether sulfone) multiblock copolymers for proton exchange membrane

Abstract Sulfonated multiblock poly(arylene ether sulfone) copolymers (SMPESs) containing phenolphthalein anilide (PPA) as a cardo group were prepared from the precursors of hydrophilic and hydrophobic block oligomers. The hydrophobic oligomer was prepared by 4,4′-dihydroxydiphenylsulfone and 4,4′-dichlorodiphenylsulfone. On the other hand, hydrophilic oligomer prepared by disodium-3,3′-disulfonate-4,4′-dichlorodiphenylsulfone (SDCDPS) and PPA. Post-sulfonation process was applied to add sulfonic acid group on PPA unit of MPES copolymers by using concentrated sulfuric acid. Sulfonated multiblock copolymers (SMPESs) with hydrophilic units of 15, 20 and 25 mol% were successfully synthesized by varying the different mole ratios to control the degree of sulfonation. SMPESs were studied by FT-IR, 1H-NMR spectroscopy, and thermo gravimetric analysis (TGA). Sorption experiment resulted the water uptake of SMPESs that was 16%–62% at 80 °C. The resulted ion exchange capacities (IEC) were 1.14–1.78 (meq/g), and proton conductivities were 65–93 (mS/cm) evaluated as increasing IEC by altering the temperature and relative humidity (RH).

Supramolecular nanostructures from self‐assembly of T‐shaped rod building block oligomers

ABSTRACTT‐shaped coil–rod–coil oligomers, consisting of a dibenzo[a,c]phenazine unit and phenyl groups linked together with acetylenyl bonds at the 2,7‐position of dibenzo[a,c]phenazine as a rigid segment have been synthesized. The coil segments of these new molecules composed of poly(ethylene oxide) (PEO)–poly(propylene oxide) (PPO) incorporating lateral methyl groups between the rod and coil segment and two flexible alkyl groups connecting with the rigid segment at the 4,6‐position of dibenzo[a,c]phenazine, respectively. The experimental results reveal that the length of the flexible PEO coil chain influence construction of various supra‐nanostructures from lamellar structure to rectangular columnar structure. It is also shown that introduction of different length of alkyl side chain groups in the backbone of the T‐shaped molecules affect the self‐organization behavior to form hexagonal perforate layer or oblique columnar structures. In addition, lateral methyl groups attached to the surface of rod and coil segments, dramatically influence the self‐assembling behavior in the crystalline phase. T‐shaped molecules containing a lateral methyl group at the surface of rod and PEO coil segments, self‐assemble into 3D body‐centered tetragonal structures in the crystalline phase, while molecules without a lateral methyl group based on PEO coil chain self‐organize into 2D oblique columnar crystalline structures. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 5021–5028

Photopolymerization of acryl composites for producing waveguides with high transparency within telecommunication spectral regions

The photopolymerization of hydrocarbon and fluorine-containing monomers and oligomers synthesized in this work for the creation of planar polymer waveguides has been studied. The kinetics of the copolymerization of hydrocarbon and fluorinated compounds hardly depends on the number and structure of fluorinated moieties. The overall kinetics of the photoinitiated polymerization of acryl oligomers with different chemical nature of their oligomer block, molecular masses, and local and macroscopic viscosities has been studied by IR spectroscopy. At high initiation rates, the oligomer block’s flexibility, which is governed by the number of groups with a low potential rotational barrier, e.g., carbonate groups, is the principal factor that influences the kinetics of polymerization. At low initiation rates, the viscosity of oligomers becomes an essential factor. The optimal conditions for molding optical articles from hydrocarbon and fluorinated acryl oligomer composites have been determined.