Ladder Polymer Research Articles

In-situ formed porous heteroatomic ladder polymer-based fibrous composite anode for high-rate and ultrastable lithium-ion batteries

Heteroatomic ladder polymers (HLPs) with high theoretical capacity are considered as the most promising electrode materials for next-generation green sustainable lithium-ion batteries (LIBs) due to their abundant resources, low cost, diverse structures and good safety features. However, the issues of low specific capacity and unsatisfactory reversibility, caused by underutilization and sluggish reaction kinetics, have thus far hindered the practical application of these materials. Herein, a porous heteroatomic ladder polymer-based fibrous composite anode (HLP/RGO/C) with interconnected conductive networks is designed and obtained by a simple electrospinning technique and in-situ heat treatment for LIB applications. Benefit from in-situ transformation and interconnected conductive porous networks, the obtained HLP/RGO/C anode achieves uniform distribution of HLP and rapid ionic/electronic transport, thereby realizing efficient utilization and rapid reaction kinetics of HLP in LIBs. Consequently, the HLP/RGO/C anode achieves a highly reversible specific capacity of 748 mA h g−1, ultra-long cyclic stability and exceptional rate performance for LIBs. Furthermore, the HLP/RGO/C anode also delivers superior electrochemical performance for LIBs over a broad temperature range, especially achieving ultrahigh reversible capacities of 186 mA h g−1 even at −30 °C. This research provides a straightforward method to construct green and sustainable polymer-based anode for LIBs.

On‐Surface Interchain Coupling and Skeletal Rearrangement of Indenofluorene Polymers

AbstractOn‐surface synthesis serves as a powerful approach to construct π‐conjugated carbon nanostructures that are not accessible by conventional wet chemistry. Nevertheless, this method has been limited by the types and numbers of available on‐surface transformations. While the majority of successful cases exploit thermally triggered dehalogenative carbon–carbon coupling and cyclodehydrogenation, rearrangement of appropriate functional moieties has received limited research attention. Here, the unprecedented interchain coupling and thermally induced skeleton rearrangement are described of (dihydro)indeno[2,1‐b]fluorene (IF) polymers on an Au(111) surface under ultrahigh vacuum conditions, leading to different ladder polymers as well as fully fused graphene nanoribbon segments containing pentagonal and heptagonal rings. Au‐coordinated nanoribbons are also observed. All structures are unambiguously characterized by high‐resolution scanning probe microscopy. The current results provide an avenue to fabricating a wider variety of π‐conjugated polymers and carbon nanostructures comprising nonhexagonal rings as well as rarely explored organometallic nanoribbons.

Secondary Structure Modulation of Triptycene-Based One-Handed Helical Ladder Polymers through π-Extension of Achiral Segments

A series of enantiopure triptycene-based one-handed helical ladder polymers containing π-extended achiral segments with naphthalene, fluorene, and carbazole spacers was synthesized through quantitative and chemoselective ladderization of the corresponding precursor polymers with random-coil conformations. The helical handedness (right- or left-handed) and geometry (loose coil or ribbon) of the resulting ladder polymers were readily modulated by tuning the structure of the achiral spacers despite the incorporation of the same point chirality of the triptycene unit. All the helical secondary structures are stable and robust due to the shape-persistent ladder structures, showing the characteristic and environment-independent chiroptical properties.

Chain‐Length Dependence of the Optical Activity of Helical Triptycene‐Based π‐Conjugated Ladder Polymers

AbstractHelical ladder polymers are designed by connecting planar indenofluorene chromophores by chiral triptycene linkers. The resulting hexagonal helices exhibit a substantial degree of homoconjugation across the triptycene knots, with saturation above ≈20 repeat units. The chiroptical anisotropy values gabs = Δε/ε of the lower‐energy lobes of the red‐most couplets in the circular dichroism (CD) spectra arise from the π−π* transition of the planar indenofluorene chromophores and increase almost sevenfold when going from a model dimer to the corresponding polymeric helical ladder structures. This increase represents a signature of “chiral amplification” that is observed at the molecular, single‐chain level. Here, the incorporated chiral linker units determine the chiroptical properties of the helical polymer chain, with chiral interactions arising across many achiral indenofluorene building blocks (>12). This behavior is observed for a fully covalently bound single polymer chain, in contrast to the more commonly studied supramolecular assemblies of appropriate chiral molecules.

Understanding the mechanism of a conjugated ladder polymer as a stable anode for acidic polymer-air batteries

Understanding the mechanism of a conjugated ladder polymer as a stable anode for acidic polymer-air batteries

Influence of Backbone Ladderization and Side Chain Variation on the Orientation of Diketopyrrolopyrrole-Based Donor-Acceptor Copolymers.

Ladder polymers with poly(diketopyrrolopyrrole) (DPP) moieties have recently attracted enormous interest for a large variety of opto-electronic applications. Since the rigidity of the backbone increases with ladderization, a strong influence on the self-organization of thin films is expected. We study the molecular orientation of DPP-based ladder polymers in about 50 nm thin films using polarization modulation-infrared reflection-absorption spectroscopy (PM-IRRAS). Exemplarily, for one polymer, the orientation in thicker films is qualitatively investigated by infrared spectroscopy in transmission. Further, this method allows us to rule out the effects of a possible azimuthal ordering, which would affect the analysis of the orientation by PM-IRRAS. For all polymers, the long axis of the polymer backbone is preferentially oriented parallel to the substrate surface, pointing to a high degree of ordering. It is suggested that the choice of the side chains might be a promising way to tune for face-on and edge-on orientations. The exemplarily performed investigation of interface properties on substrates with different work functions suggests that the choice of the side chains has a minor effect on the interfacial electronic interface structure.

Precise molecular sieving of ethylene from ethane using triptycene-derived submicroporous carbon membranes.

Replacement or debottlenecking of the extremely energy-intensive cryogenic distillation technology for the separation of ethylene from ethane has been a long-standing challenge. Membrane technology could be a desirable alternative with potentially lower energy consumption. However, the current key obstacle for industrial implementation of membrane technology is the low mixed-gas selectivity of polymeric, inorganic or hybrid membrane materials, arising from the similar sizes of ethylene (3.75 Å) and ethane (3.85 Å). Here we report precise molecular sieving and plasticization-resistant carbon membranes made by pyrolysing a shape-persistent three-dimensional triptycene-based ladder polymer of intrinsic microporosity with unparalleled mixed-gas performance for ethylene/ethane separation, with a selectivity of ~100 at 10 bar feed pressure, and with long-term continuous stability for 30 days demonstrated. These submicroporous carbon membranes offer opportunities for membrane technology in a wide range of notoriously difficult separation applications in the petrochemical and natural gas industry.

Ladder Polyphenylsilsesquioxanes and Their Niobium-Siloxane Composite as Coating Materials: Spectroscopy and Atomic Oxygen Resistance Study.

In order to expand the range of materials that can be used in outer space and in development of small spacecraft, ladder polyphenylsilsesquioxanes with different molar weights and the Nb-siloxane composites based on them were studied. The properties of the polymer films were studied, including tests in an oxygen plasma flow. Both initial and filled ladder polymers feature extremely low erosion coefficients in the region of 10-26 cm3/atom O at a high fluence of atomic oxygen of 1.0 × 1021 atom O/cm2. Ladder polyphenylsilsesquioxane films irradiated with atomic oxygen (AO) retain their integrity, do not crack, and exhibit good optical properties, in particular, a high transmittance. The latter slightly decreases during AO exposure. The Nb-siloxane filling retains the AO resistance and slight decrease in optical transmission due to diffuse scattering on the formed Nb-[(SiO)x] nanoparticles. Ladder polyphenylsilsesquioxanes demonstrate their suitability for creating protective, optically transparent coatings for small spacecraft that are resistant to the erosive effects of incoming oxygen plasma.

An accelerated route for ladder polymers

An accelerated route for ladder polymers

Recent Progress in Synthesis of Conjugated Ladder Polymers

AbstractConjugated ladder polymers (cLPs) are macromolecules consisting of fully fused aromatic backbones, which have emerged as an intriguing research area due to their unique electronic and optoelectronic properties. They possess a highly ordered, ladder‐like structure, which leads to improved charge transport properties and enhanced stability compared to conventional conjugated polymers. The synthesis of cLPs involves two main strategies: single‐step ladderization and stepwise ladderization. However, due to the extremely low solubility of the desired cLPs and the limited synthetic methods for preparing defect‐free cLPs, the field of solution‐based synthesis and processing of cLPs encountered synthetic and processing challenges. This review provides an overview of recent achievements in the synthesis of conjugated ladder polymers, emphasizing the challenges and potential in this fascinating field of research.

Defect-Free Synthesis of a Fully π-Conjugated Helical Ladder Polymer and Resolution into a Pair of Enantiomeric Helical Ladders.

Fully π-conjugated ladder polymers with a spiral geometry represent a new class of helical polymers with great potential for organic nanodevices, but there is no precedent for an optically-active helical ladder polymer totally composed of achiral units. We now report the defect-free synthesis and resolution of a fully π-conjugated helical ladder polymer with a rigid helical cavity, which has been achieved by quantitative and chemoselective acid-promoted alkyne benzannulations of a rationally designed, random-coil achiral polymer followed by chromatographic enantioseparation. Because of a sufficiently high helix-inversion barrier, the isolated excess one-handed helical ladder polymer with the degree of polymerization of more than 15 showed a strong circular dichroism with the dissymmetry factor of up to 1.7 × 10-2 and is thermally stable, maintaining its optical activity in solution even at 100 °C, as well supported by molecular dynamics simulation.

Defect‐Free Synthesis of a Fully π‐Conjugated Helical Ladder Polymer and Resolution into a Pair of Enantiomeric Helical Ladders**

AbstractFully π‐conjugated ladder polymers with a spiral geometry represent a new class of helical polymers with great potential for organic nanodevices, but there is no precedent for an optically active helical ladder polymer totally composed of achiral units. We now report the defect‐free synthesis and resolution of a fully π‐conjugated helical ladder polymer with a rigid helical cavity, which has been achieved by quantitative and chemoselective acid‐promoted alkyne benzannulations of a rationally designed, random‐coil achiral polymer followed by chromatographic enantioseparation. Because of a sufficiently high helix‐inversion barrier, the isolated excess one‐handed helical ladder polymer with a degree of polymerization of more than 15 showed a strong circular dichroism with a dissymmetry factor of up to 1.7×10−2 and is thermally stable, maintaining its optical activity in solution even at 100 °C, as well‐supported by molecular dynamics simulation.

Exploring the effect of intra-chain rigidity on mixed-gas separation performance of a Triptycene-Tröger's base ladder polymer (PIM-Trip-TB) by atomistic simulations

Atomistic simulations were performed to investigate pure- and mixed-gas CO2/CH4 separation properties of a ladder polymer of intrinsic microporosity, PIM-Trip-TB. Despite expected intra-chain rigidity of the polymer, previous experimental reports observed significant loss in CO2/CH4 perm-selectivity under high-pressure mixed-gas conditions. In this work, all-atomistic simulations were applied to accurately predict density, gas uptakes and gas diffusion properties of PIM-Trip-TB. Competitive sorption favoring CO2 over CH4 was apparent in mixed-gas sorption simulations, as previously demonstrated by experimental studies from our group. This effect resulted in enhanced mixed-gas CO2/CH4 solubility selectivity. However, this increase did not translate to increased mixed-gas perm-selectivity because a significant increase in CH4 permeability was observed by co-permeation of CO2 relative to the pure-gas value. Back-calculated diffusion coefficients indicated very low CO2/CH4 diffusion selectivity under mixed-gas conditions, eliminating any gain from competitive sorption. Structural analysis confirmed intact intra-chain rigidity of the polymer; on the other hand, a significant increase in fractional free volume (FFV) and shift to larger pores in the pore size distribution was revealed by our simulations which may be attributed to polymer dilation due a reduction in inter-chain packing.

Thermal Transformation of Polyacrylonitrile Accelerated by the Formation of Ultrathin Nanosheets in a Metal–Organic Framework

In this study, polyacrylonitrile (PAN) nanosheets with unimolecular thickness were successfully synthesized by cross-linking polymerization in the 2D nanospaces of a metal-organic framework. In contrast to 1D and 3D analogues, crystallization could be inhibited by the topological constraint of the ultrathin 2D network structure, allowing for an efficient thermal transformation reaction of PAN. The amorphous nature of the PAN nanosheets led to an increase in the access of oxygen molecules to the polymer chains, facilitating the thermal dehydroaromatization reactions to yield a ladder polymer structure with a highly extended conjugated system. Notably, further carbonization of this ladder polymer afforded graphitic carbon with a highly ordered structure because of the well-defined precursor structure.

A Flexible Aromatic Amphiphilic Trication for the Solubilization of Hydrophobic Organic Semiconductors in Water

Amphiphiles are widely explored for the solubilization of various hydrophobic molecules especially drugs in water. Recently, aromatic amphiphiles emerged as a new class of molecules for the solubilization of hydrophobic organic semiconductors in water. However, the synthesis of these systems involves several steps and often requires the use of expensive metal catalysts. Here we describe the design and synthesis of a new type of flexible aromatic amphiphilic trication (FAT) and its application for solubilization of hydrophobic organic semiconductors in water. FAT has been synthesized in two steps without the use of any expensive metal catalysts. We observed that FAT self-assembles in water into bilayer two-dimensional (2D) nanosheets composed of hydrophobic naphthalimide units. FAT is found to be effective for the solubilization of various hydrophobic organic semiconductors such as perylene, perylene diimide and C60 in water by encapsulating them into its hydrophobic domains. Moreover, FAT was also explored for the solubilization of a 2D conjugated ladder polymer, TQBQ (triquinoxalinylene and benzoquinone), in water.

Phenazine-Substituted Poly(benzimidazobenzophenanthrolinedione): Electronic Structure, Thin Film Morphology, Electron Transport, and Mechanical Properties of an n-Type Semiconducting Ladder Polymer

Unlike naphthalene diimides, perylene diimides, and other classes of n-type conjugated polymers with numerous derivatives that enable understanding of structure–property relationships, the electronic structure and properties have not been reported for any derivative of ladder poly(benzimidazobenzophenanthroline) (BBL). Herein, we report the synthesis and properties of BBL-P, a phenazine derivative of BBL. In acid solution, BBL-P has a broad absorption spectrum with a lowest energy absorption peak at 840 nm due to protonation-enhanced intramolecular charge transfer. Compared to BBL, BBL-P thin films have decreased crystallinity with face-on molecular orientations on substrates, resulting in a substantially decreased field-effect electron mobility of 1.2 × 10–4 cm2/V s. BBL-P films have excellent mechanical properties exemplified by a Young modulus of 11 GPa. The results demonstrate that BBL-P is a promising n-type semiconducting polymer and provide new insights into the effects of backbone structure on electronic structure, thin film microstructure, and charge transport properties of conjugated ladder polymers.

3,11-Diaminodibenzo[a,j]phenazine: Synthesis, Properties, and Applications to Tröger's Base-Forming Ladder Polymerization.

A new class of diamino-substituted π-extended phenazine compound was synthesized, and its photophysical properties were investigated. The U-shaped diaminophenazine displayed photoluminescence in solution with moderate quantum yield. The diamino aromatic compound was found applicable to the poly-condensation with formaldehyde to form Tröger's base ladder polymer. The obtained microporous ladder polymer features high CO2 adsorption selectivity against N2 , most likely due to the presence of basic nitrogen atoms in the phenazine rings.

One-Handed Helical Tubular Ladder Polymers for Chromatographic Enantioseparation.

Defect-free one-handed contracted helical tubular ladder polymers with a π-electron-rich cylindrical helical cavity were synthesized by alkyne benzannulations of the random-coil precursor polymers containing 6,6'-linked-1,1'-spirobiindane-7,7'-diol-based chiral monomer units. The resulting tightly-twisted helical tubular ladder polymers showed remarkably high enantioseparation abilities toward a variety of chiral hydrophobic aromatics with point, axial, and planar chiralities. The random-coil precursor polymer and analogous rigid-rod extended helical ribbon-like ladder polymer with no internal helical cavity exhibited no resolution abilities. The molecular dynamics simulations suggested that the π-electron-rich cylindrical helical cavity formed in the tightly-twisted tubular helical ladder structures is of key importance for producing the highly-enantioseparation ability, by which chiral aromatics can be enantioselectively encapsulated by specific π-π and/or hydrophobic interactions.

One‐Handed Helical Tubular Ladder Polymers for Chromatographic Enantioseparation**

AbstractDefect‐free one‐handed contracted helical tubular ladder polymers with a π‐electron‐rich cylindrical helical cavity were synthesized by alkyne benzannulations of the random‐coil precursor polymers containing 6,6′‐linked‐1,1′‐spirobiindane‐7,7′‐diol‐based chiral monomer units. The resulting tightly‐twisted helical tubular ladder polymers showed remarkably high enantioseparation abilities toward a variety of chiral hydrophobic aromatics with point, axial, and planar chiralities. The random‐coil precursor polymer and analogous rigid‐rod extended helical ribbon‐like ladder polymer with no internal helical cavity exhibited no resolution abilities. The molecular dynamics simulations suggested that the π‐electron‐rich cylindrical helical cavity formed in the tightly‐twisted tubular helical ladder structures is of key importance for producing the highly‐enantioseparation ability, by which chiral aromatics can be enantioselectively encapsulated by specific π‐π and/or hydrophobic interactions.

Hydration of a Side-Chain-Free n-Type Semiconducting Ladder Polymer Driven by Electrochemical Doping

We study the organic electrochemical transistor (OECT) performance of the ladder polymer poly(benzimidazobenzophenanthroline) (BBL) in an attempt to better understand how an apparently hydrophobic side-chain-free polymer is able to operate as an OECT with favorable redox kinetics in an aqueous environment. We examine two BBLs of different molecular masses from different sources. Regardless of molecular mass, both BBLs show significant film swelling during the initial reduction step. By combining electrochemical quartz crystal microbalance gravimetry, in-operando atomic force microscopy, and both ex-situ and in-operando grazing incidence wide-angle X-ray scattering (GIWAXS), we provide a detailed structural picture of the electrochemical charge injection process in BBL in the absence of any hydrophilic side-chains. Compared with ex-situ measurements, in-operando GIWAXS shows both more swelling upon electrochemical doping than has previously been recognized and less contraction upon dedoping. The data show that BBL films undergo an irreversible hydration driven by the initial electrochemical doping cycle with significant water retention and lamellar expansion that persists across subsequent oxidation/reduction cycles. This swelling creates a hydrophilic environment that facilitates the subsequent fast hydrated ion transport in the absence of the hydrophilic side-chains used in many other polymer systems. Due to its rigid ladder backbone and absence of hydrophilic side-chains, the primary BBL water uptake does not significantly degrade the crystalline order, and the original dehydrated, unswelled state can be recovered after drying. The combination of doping induced hydrophilicity and robust crystalline order leads to efficient ionic transport and good stability.