Conjugated Diblock Copolymers Research Articles

Correlating Optical Reflectance with the Topology of Aluminum Nanocluster Layers Growing on Partially Conjugated Diblock Copolymer Templates.

Large-scale fabrication of metal cluster layers for usage in sensor applications and photovoltaics is a huge challenge. Physical vapor deposition offers large-scale fabrication of metal cluster layers on templates and polymer surfaces. In the case of aluminum (Al), only little is known about the formation and interaction of Al clusters during sputter deposition. Complex polymer surface morphologies can tailor the deposited Al cluster layer. Here, a poly(methyl methacrylate)-block-poly(3-hexylthiophen-2,5-diyl) (PMMA-b-P3HT) diblock copolymer template is used to investigate the nanostructure formation of Al cluster layers on the different polymer domains and to compare it with the respective homopolymers PMMA and P3HT. The optical properties relevant for sensor applications are monitored with ultraviolet-visible (UV-vis) measurements during the sputter deposition. The formation of Al clusters is followed in situ with grazing-incidence small-angle X-ray scattering (GISAXS), and the chemical interaction is revealed by X-ray photoelectron spectroscopy (XPS). Furthermore, atomic force microscopy (AFM) and field emission scanning electron microscopy (FESEM) yield topographical information about selective wetting of Al on the P3HT domains and embedding in the PMMA domains in the early stages, followed by four distinct growth stages describing the Al nanostructure formation.

The Impacts of Polyisoprene Physical Interactions on Sorting of Single-Wall Carbon Nanotubes.

Conjugated polymer sorting is currently the best method to select large-diameter single-walled carbon nanotubes (SWCNTs) with tunable narrow chirality in the adaption of highly desired electronics applications. The acceleration on conjugated polymers-SWCNTs interaction with long-term stability through different molecular designs; for example, longer alkyl side-chains or conjugation moieties have been extensively developed in recent years. However, the importance of the macromolecules with abundant van der Waals (VDW) interaction in the conjugated-based block copolymer system acting during SWCNTs sorting is not clearly demonstrated. In this work, a conjugated diblock copolymer involving polyisoprene (PI) and highly dense π-interaction of poly (9,9-dioctylfluorene) (PFO) is utilized to investigate the impact of natural rubber PI physical interaction on sorting effectiveness and stability. Through the rational design of diblock copolymer, PFO with ≈1200 isoprene units can remarkably enhance SWCNTs sorting ability and selected few chiralities with a diameter of ≈0.83-1.1nm and highly stable solution for more than 1 year. The introduction of long-chain PI system is attributed not only to form weak VDW force with SWCNTs and strengthen the wrapping of PFO around the semiconducting SWCNTs but also to act as a barrier among nanotubes to prevent reaggregation of sorted SWCNTs.

Selective Silver Nanocluster Metallization on Conjugated Diblock Copolymer Templates for Sensing and Photovoltaic Applications

Polymer–metal composite films with nanostructured metal and/or polymer interfaces show a significant perspective for optoelectronic applications, for example, as sensors or in organic photovoltaics...

Three-Dimensional Spirals of Conjugated Block Copolymers Driven by Screw Dislocation

Three-dimensional spiral structures are common in nature but rare in nanoscale or mesoscale objects formed by self-assembly, and it is a challenge to obtain uniform and well-structured 3D spiral architecture. Here, we present a simple approach to preparation of 3D spiral micelles with conjugated diblock copolymer poly(p-phenylenevinylene)-block-poly(ethyleneglycol) by a dissolution-cooling-aging process. By controlling the concentration of the growing solution, the size of micelles can be regulated, and the transformation of assembly morphology from 2D square to 3D spiral can be realized. In view of the low crystallinity of compounds in this system, the 3D spiral structure is driven by relatively weak π–π intermolecular interactions of the conjugated core of the block copolymers. The surface potential of these 3D micelles is almost equally dispersed among the different positions of the spirals from the Kelvin probe force microscopy experiments, and the conductivity of the 3D spiral is inversely proportional to the numbers of spiral layers. Based on their electrical response features, these 3D spiral architectures composed of conjugated block copolymers, especially with well-controlled nanoscale sizes, should be a very promising candidate for the future photoelectronic device and switch applications.

Improved efficiency of single-component active layer photovoltaics by optimizing conjugated diblock copolymers

Using an A–B type monomer instead of an AA + BB type monomer to synthesise diblock copolymers, the PCE of a single-component photovoltaic device reached 1.22%.

Poly(3-alkylthiophene)- block-poly(3-alkylselenophene)s: Conjugated Diblock Co-polymers with Atypical Self-Assembly Behavior.

Understanding self-assembly behavior and resulting morphologies in block co-polymer films is an essential aspect of chemistry and materials science. Although the self-assembly of amorphous coil-coil block co-polymers is relatively well understood, that of semicrystalline block co-polymers where each block has distinct crystallization properties remains unclear. Here, we report a detailed study to elucidate the rich self-assembly behavior of conjugated thiophene-selenophene (P3AT- b-P3AS) block co-polymers. Using a combination of microscopy and synchrotron-based X-ray techniques, we show that three different film morphologies, denoted as lamellae, co-crystallized fibers, and patchy fibers, arise from the self-assembly of these block co-polymers over a relatively narrow range of overall degrees of polymerization (30 < N < 90). Crystallization-driven phase separation occurs at a very low N (<35), and lamellar films are formed. Conversely, at medium N (50-60) and high N (>80), the thiophene and selenophene blocks co-crystallize into nanofibers, where medium N leads to much more mixing than high N. The overall tendency for phase separation in these systems follows rather different trends than phase separation in amorphous polymers in that we observe the greatest degree of phase separation at the lowest N. Finally, we demonstrate how each morphology influences transport properties in organic thin-film transistors comprised of these conjugated polymers.

Influence of the Sequence in Conjugated Triblock Copolymers on Their Aggregation Behavior

Conjugated diblock copolymers can exhibit very promising properties, often based on microphase separation. However, both blocks can influence each other’s aggregation behavior, which might lead to a suboptimal aggregation behavior of the consecutive blocks. Herein, we investigate whether the introduction of a third, nonaggregating block can render triblock copolymers where the two blocks do not influence the aggregation behavior of one another. Different triblock copolymers consisting of solely thiophene units as well as triblock copolymers containing selenophene and (a)chiral thiophene units were designed to investigate the influence of the sequence of the blocks, the initiating unit, and the nonaggregating block on the aggregation behavior of the resulting triblock copolymers. The conjugated triblock copolymers were synthesized via a controlled Kumada catalyst transfer condensative polymerization (KCTCP), and their aggregation behavior was investigated via UV–vis and circular dichroism (CD) spectroscopy. For all synthesized polymers it was observed that when two aggregating blocks are separated from each other by a nonaggregating block, they do not influence each other’s aggregation behavior and aggregate separately. However, when the two aggregating blocks are situated next to each other, they influence each other’s aggregation behavior strongly and aggregate as one block.

Uniform two-dimensional square assemblies from conjugated block copolymers driven by \u03c0\u2013\u03c0 interactions with controllable sizes

Two-dimensional (2-D) micro- and nano-architectures are attractive because of their unique properties. However, the formation of 2-D supramolecular highly symmetrical structures with considerable control is still a major challenge. Here we present a simple approach for the preparation of regular and homogeneous 2-D fluorescent square non-crystallization micelles with conjugated diblock copolymers PPV12-b-P2VPn through a process of dissolving–cooling–aging. The scale of the formed micelles can be controlled by the ratio of PPV/P2VP blocks and the concentration of the solution. The results reveal that the micelles of PPV12-b-P2VPn initially form 1-D structures and then grow into 2-D structures in solution, and the growth is driven by intermolecular π–π interactions with the PPV12 blocks. The formation of 2-D square micelles is induced by herringbone arrangement of the molecules, which is closely related to the presence of the branched alkyl chains attached to conjugated PPV12 cores.

Patchy Nanofibers from the Thin Film Self-Assembly of a Conjugated Diblock Copolymer.

An unexpected morphology comprising patchy nanofibers can be accessed from the self-assembly of an all-conjugated, polyselenophene-block-polythiophene copolymer. This morphology consists of very small (<10 nm), polythiophene- and polyselenophene-rich domains and is unprecedented for both conjugated polymers and diblock copolymers in general. We propose that the patchy morphology occurs from the enhanced miscibility of the blocks arising from the longer alkyl chains in comparison to similar block copolymers with shorter alkyl chains, which fully phase separate, as well as the difference in rigidity between the polythiophene and polyselenophene blocks. This work demonstrates a facile way to tune the self-assembly behavior of conjugated block copolymers by modification of the side chain substituents.

Patchy Nanofibers from the Thin Film Self‐Assembly of a Conjugated Diblock Copolymer

AbstractAn unexpected morphology comprising patchy nanofibers can be accessed from the self‐assembly of an all‐conjugated, polyselenophene‐block‐polythiophene copolymer. This morphology consists of very small (&lt;10 nm), polythiophene‐ and polyselenophene‐rich domains and is unprecedented for both conjugated polymers and diblock copolymers in general. We propose that the patchy morphology occurs from the enhanced miscibility of the blocks arising from the longer alkyl chains in comparison to similar block copolymers with shorter alkyl chains, which fully phase separate, as well as the difference in rigidity between the polythiophene and polyselenophene blocks. This work demonstrates a facile way to tune the self‐assembly behavior of conjugated block copolymers by modification of the side chain substituents.

Synthesis and Transfer of Chirality in Supramolecular Hydrogen Bonded Conjugated Diblock Copolymers

The synthesis of a block copoly(3-alkylthiophene) consisting of two different P3AT blocks equipped with an H-donor and -acceptor functionality is presented. The P3ATs were synthesized using a functionalized Ni-initiator. By a series of postpolymerization reactions, including click chemistry, an H-donor and -acceptor entity was attached to the end of the polymer chains. Evidence for a quantitative functionalization of the polymers was provided by 1H NMR and MALDI-ToF analyses. Chiral side chains were implemented on one of both blocks, allowing the study of the influence of the H-bond formation on the chiral self-assembly using UV–vis and circular dichroism spectroscopy.

N-Containing 1,7-Octadiyne Derivatives for Living Cyclopolymerization Using Grubbs Catalysts.

Synthesis of a new class of conjugated polyenes containing N-heterocyclic six-membered rings was demonstrated via cyclopolymerization of N-containing 1,7-octadiyne derivatives using Grubbs catalysts. Successful cyclopolymerization was achieved by introducing protecting groups to the amines in the monomers. Moreover, a hydrazide-type monomer containing a di-tert-butyloxycarbonyl group (6) promoted the living cyclopolymerization to give poly(6) with a controlled molecular weight and narrow dispersity. This living polymerization allowed us to prepare various conjugated diblock copolymers using poly(6) as the first block.

Strategies to Enhance Cyclopolymerization using Third-Generation Grubbs Catalyst

Cyclopolymerization (CP) of 1,6-heptadiyne derivatives using the Grubbs catalysts has been known to afford conjugated polyenes in low yields in dichloromethane (DCM), the most common solvent for olefin metathesis polymerization and a good solvent for typical conjugated polymers. Based on our previous work that showed highly efficient CP using the Grubbs catalysts in tetrahydrofuran (THF), we developed a new polymerization system using weakly coordinating additives with the third-generation Grubbs catalyst in DCM. The polymerization efficiency of various monomers and their controls dramatically increased by adding 3,5-dichloropyridine, yielding polymers with narrow polydispersity indices (PDIs) at low temperatures. These new reaction conditions not only expand the monomer scope by resolving the solubility concerns of conjugated polymers but also more effectively reduced the chain transfer. Consequently, fully conjugated diblock copolymer was successfully prepared. Additionally, kinetic analysis has revealed that low CP efficiency in DCM resulted from the rapid decomposition of the propagating carbene. This decomposition was effectively suppressed by both pyridine additives and THF, suggesting that weakly coordinating additives stabilize the living chain end. Furthermore, we observed that the turnover number of CP was higher at lower temperatures (0-10 °C) than at ambient temperatures, consistent with the understanding that the lifetime of a propagating carbene is greater at lower temperatures. Steric protection was also shown to increase the stability of the propagating carbene, as shown by a higher turnover number for the 3,3-dimethyl-substituted 1,6-heptadiyne compared to the nonfunctionalized monomer.

Self-assembled buffer layer from conjugated diblock copolymers with ethyleneoxide side chains for high efficiency polymer solar cells

A remarkable improvement of 7.3% in the PCE is obtained through the spontaneous migration of diblock copolymers during the spin-coating process.

Self-Assembly of Amphiphilic Conjugated Diblock Copolymers into One-Dimensional Nanoribbons

The colloidal self-assembly of a new conjugated diblock copolymer of a polythiophene derivative, poly[3-(2,5,8,11-tetraoxatridecanyl)thiophene]-block-poly(ethylene glycol) (PTOTT-b-PEG), led to various well-defined assembly structures such as vesicles, sheets, and nanoribbons. A unique and technologically relevant nanoribbon structure with a dimension reaching tens of micrometers was formed in water when polar protic solvents were used as initial cosolvents. Self-assembly of PTOTT-b-PEG in various solvent compositions and polymer concentrations indicated that the hydrogen bonding between the diblock copolymer and the self-assembly medium plays an important role in determining the self-assembly structure and that the final assembly structure should be the result of a delicate interplay between hydrogen bonding and π–π interactions. This study demonstrates that the addition of hydrogen bonding capability and amphiphilicity in the self-assembly of conjugated polymers can lead to many interesting well-defined assembly structures that are not typically found in conjugated polymers.

Fine dispersion and self-assembly of ZnO nanoparticles driven by P3HT-b-PEO diblocks for improvement of hybrid solar cells performance

The rod-coil conjugated diblock copolymers of poly(3-hexylthiophene)-b-poly(ethylene oxide) (P3HT-b-PEO), acting as an electron donor, were blended with ZnO nanoparticles to fabricate the hybrid bulk-heterojunction (BHJ) solar cells. According to the ultraviolet-visible (UV-vis) absorption spectroscopy, the intensity at 610 nm, derived from a strong inter-molecular interaction of π–π stacking and the high crystallizability of the P3HT main chains, was higher in P3HT-b-PEO/ZnO blend films than that in P3HT/ZnO blend films especially after thermal treatment, revealing that PEO segments could make P3HT form more densely stacked and orderly structured. Due to the nature of block copolymers and the interaction between the oxygen atoms of the PEO chains and the ZnO polar surface, the surface defects of ZnO were passivated and the fine dispersion and self-assembly of ZnO in the polymer matrix driven by the P3HT-b-PEO diblock copolymer was obtained, leading to the improvement of device power conversion efficiency and thermal stability. Overall, this work demonstrated that the application of conjugated block copolymers in hybrid BHJ solar cells was a promising approach to improve the device performance and thermal stability.

Selenophene–Thiophene Block Copolymer Solar Cells with Thermostable Nanostructures

The nanostructure morphology and electron donor performance of a poly(3-hexylselenophene)-block-poly(3-hexylthiophene) (P3HS-b-P3HT) copolymer was studied in a photovoltaic device with a [6,6]-phenyl C61 butyric acid methyl ester (PCBM) acceptor. P3HS-b-P3HT forms fiberlike nanostructures spontaneously, which leads to an initial optimal device performance. Furthermore the nanostructure morphology is not greatly affected by annealing, which leads to a device stability that outperforms P3HT, P3HS, or a P3HS/P3HT mixture under identical conditions. External quantum efficiency, hole mobility, and current-voltage measurements show that the block copolymer also outperforms a ternary blend that consists of a physical mixture of P3HS, P3HT, and PCBM with the same overall composition. Overall, the observation of optimal device performance and morphology without annealing as well as enhanced thermal stability demonstrates the advantage of fully conjugated diblock copolymers in nanostructured devices.

Donor–Donor Block Copolymers for Ternary Organic Solar Cells

We describe a fully conjugated diblock copolymer, poly(3-thiohexylthiophene)-block-(3-hexylthiophene) (P3THT-b-P3HT), which is composed of two equally proportioned blocks that have distinct electronic structure and is suitable for testing in a donor–donor–acceptor solar cell. Calculations and optoelectronic characterization demonstrate communication between blocks in silico and in solution. In the solid state, powder X-ray diffraction and atomic force microscopy show that the polymer is semicrystalline and has a distinct morphology (relative to a 1:1 physical blend of its constituent homopolymers), both with and without a fullerene-derivative (PC71BM) acceptor. When tested in a device configuration (P3THT-b-P3HT:PC71BM), the deep HOMO level of the P3THT block increases the open circuit voltage (Voc) to a value that is equal to a P3THT:PC71BM control device. This shows that the Voc of an equally proportioned ternary organic solar cell can reach the upper limit of the corresponding binary devices. The block...

Synthesis of conjugated diblock copolymers: two mechanistically distinct, sequential living polymerizations using a single catalyst

Block copolymers comprised of poly(3-hexylthiophene) and three different poly(isocyanide)s were synthesized in a single pot via the sequential addition of 2-bromo-3-hexyl-5-chloromagnesiothiophene followed by 2-(2-methoxyethoxy)ethyl 4-isocyanobenzoate, tert-butyl 4-isocyanobenzoate, or 1-isocyanohexadecane to a solution of 1,3-bis(diphenylphosphino)propane dichloronickel. Similarly, block copolymers of poly(1-dodecylpyrrole) along with poly(2,5-bis(hexyloxy)phenylene) and a poly(arylisocyanide) were also prepared using an analogous methodology. The respective mechanistically distinct polymerizations proceeded in a controlled fashion, were mediated by a common catalyst, and afforded well-defined block copolymers with tunable molecular weights and compositions. Selected block copolymers exhibited higher-order structures in solution and microphase separation characteristics in the solid state.

Synthesis, morphology, and field-effect transistor characteristics of new crystalline-crystalline diblock copolymers of poly(3-hexylthiophene-block -steryl acrylate)

We report the synthesis, morphology, and charge-transporting characteristics of new crystalline–crystalline diblock copolymers, poly(3-hexylthiophene-block-stearyl acrylate) (P3HT-b-PSA). Three different diblock copolymers, P1, P2, and P3, with P3HT/PSA polymerization degree block ratios of 60/26, 60/50, and 60/360, respectively, were prepared for investigating the morphology-property relationship and the dependence of optoelectronic properties on the block copolymer structure. Small- and wide-angle X-ray scattering indicated the presence of both P3HT and PSA crystalline domains and the presence of microphase separation among blocks. The transmission electron microscopy and atomic force microscopy results revealed that the diblock copolymers cast from chlorobenzene, tended to form needle-like morphologies. The field-effect mobilities of the diblock copolymers deposited on untreated SiO2 substrates, decreased with increasing PSA block length. In a sharp contrast, the mobilities enhanced with increasing PSA content when the P3HT-b-PSA was deposited on phenyltrichlorosilane (PTS)-treated substrates. The copolymers with a 60/360 P3HT/PSA ratio showed a good mobility of 4 × 10−3 cm2 V−1 s−1 and a high on/off ratio of 7 × 106 on PTS-treated substrates. This study highlighted the importance of the block ratio, the substrate and self-assembly structures on the charge transport characteristics of the crystalline–crystalline conjugated diblock copolymers. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012