Helical Polymers Research Articles

Helical Network Polymers Embodying High Dissymmetry Factors in Circularly Polarized Luminescence: Photocrosslinking Polymerization of Acrylate Derivatives in Chiral Smectic Liquid Crystals

Radical photocrosslinking polymerizations of functional acrylate derivatives are achieved in a chiral smectic C liquid crystal (SC*-LC) used as an asymmetric medium to synthesize helical network polymers (HNPs) with thermally and chemically stable chiroptical properties that are represented by circularly polarized luminescence (CPL). Two types of acrylate derivatives that bear an LC moiety and a fluorene moiety as luminophores are synthesized and used as functional monomers for photocrosslinking polymerizations. A trisubstituted acrylate derivative is used as a crosslinker to enhance the amount of photocrosslinking to produce a spatially linked network structure of polymers. The synthesized HNPs show a striated fan-shaped texture that is characteristic of the SC*-LC, and they exhibit notable Cotton effects owing to their circular dichroism in the absorption and luminescence processes. The CPL of the (R)- and (S)-HNP films shows considerably high dissymmetry factors (|glum|) of 2.4 × 10–2 and 2.5 × 10–2, respectively. The CPL further increases in intensity by more than 4 times after heating the HNP film at 150 °C to provide |glum| values of 1.0 × 10–1 and 1.1 × 10–1 for (R)- and (S)-HNP films, respectively. This increase in CPL intensity is ascribed to the thermally stimulated progress of the crosslinking between the monomers that still remain unreacted during photopolymerization at room temperature, thus leading to the completion of the helical network in the HNP film. The higher structural order of the HNP films prepared with the SC*-LC than those prepared with a chiral nematic LC (N*-LC) is confirmed through X-ray diffraction measurements. The present work is the first successful asymmetric polymerization using the SC*-LC as a chiral medium.

Axial Motion Characterization of a Helical Ionic Polymer Metal Composite Actuator and Its Application in 3-DOF Micro-Parallel Platforms

In this work, a helical ionic polymer metal composite (IPMC) was fabricated by thermal treatment in a mold with helix grooves. The axial actuation behaviors of the helical IPMC actuator were observed, and the electromechanical and electrochemical characteristics were evaluated. The experimental results showed that as the voltage increased and the frequency decreased, the axial displacement, axial force, and electric current of the actuator all increased. Compared with square wave and sinusoidal signals, the actuator exhibited the most satisfactory motion under the direct current (DC) signal. For the electrochemical test, as the scanning rate decreased, the gravimetric specific capacitance increased. Within a suitable voltage range, the actuator was chemically stable. In addition, we coupled the Electrostatics module, Transport of Diluted Species module, and Solid Mechanics module in COMSOL Multiphysics software to model and analyze the helical IPMC actuator. The simulation data obtained were in good agreement with the experimental data. Finally, by using three helical IPMC actuators as driving components, an innovative three-degree-of-freedom (3-DOF) micro-parallel platform was designed, and it could realize a complex coupling movement of pitch, roll, and yaw under the action of an electric field. This platform is expected to be used in micro-assembly, flexible robots, and other fields.

Helical Covalent Polymers with Unidirectional Ion Channels as Single Lithium-Ion Conducting Electrolytes

Single-ion conducting polymer electrolytes have attracted great attention as safe alternatives to liquid electrolytes in high energy density lithium-ion batteries. Herein, we report the first examp...

Helical Polymers with Dynamic and Static Macromolecular Helicity Memory: The Power of Helicity Memory for Helical Polymer Synthesis and Applications

Abstract In this Account, we describe the recent progress in the synthesis and unique features and functions of helical polymers with a controlled handedness based on the noncovalent helicity induction and subsequent memory of the helicity strategy that we have developed during the past two decades. Remarkable progress has been achieved in the emerging research area of helical polymers over the past decades, producing a number of helical polymers with various structures and functions. Nevertheless, the helical polymers with dynamic and static helicity memory have been proved to be exceptional and like no other among a huge number of helical polymers prepared so far because of their unique and exclusively outstanding features, such that an excess handed helicity, once induced by noncovalent weak chiral interactions, is immediately memorized accompanied by a significant amplification of the helical chirality, leading to a long-lasting helicity memory. This finding has a significant impact on the development of novel advanced chiral materials, such as switchable chiral stationary phases for separating enantiomers and asymmetric catalysts, which will also be described in this Account.

Living Helix

Key words helical polymers - organocatalysis - cyclization - cyclopolymerization - living polymers

Unimolecular Transmembrane Na + Channels Constructed by Pore-Forming Helical Polymers with a 2.3 Å Aperture

To understand the relationships between channel size and ion selectivity, we have developed a new type of artificial ion channel based on pore-forming helical polymers consisting of phenanthroline-...

SuFExable polymers with helical structures derived from thionyl tetrafluoride.

Sulfur(VI) fluoride exchange (SuFEx) is a category of click chemistry that enables covalent linking of modular units through sulfur(VI) connective hubs. The efficiency of SuFEx and the stability of the resulting bonds have led to polymer chemistry applications. Now, we report the SuFEx click chemistry synthesis of several structurally diverse SOF4-derived copolymers based on the polymerization of bis(iminosulfur oxydifluorides) and bis(aryl silyl ethers). This polymer class presents two key characteristics. First, the [-N=S(=O)F-O-] polymer backbone linkages are themselves SuFExable and undergo precise SuFEx-based post-modification with phenols or amines to yield branched functional polymers. Second, studies of individual polymer chains of several of these new materials indicate helical polymer structures. The robust nature of SuFEx click chemistry offers the potential for post-polymerization modification, enabling the synthesis of materials with control over composition and conformation.

Distance Matters: Biasing Mechanism, Transfer of Asymmetry, and Stereomutation in N-Annulated Perylene Bisimide Supramolecular Polymers.

The synthesis of two series of N-annulated perylene bisimides (PBIs), compounds 1 and 2, is reported, and their self-assembling features are thoroughly investigated by a complete set of spectroscopic measurements and theoretical calculations. The study corroborates the enormous influence that the distance between the PBI core and the peripheral groups exerts on the chiroptical properties and the supramolecular polymerization mechanism. Compounds 1, with the peripheral groups separated from the central PBI core by two methylenes and an ester group, form J-type supramolecular polymers in a cooperative manner but exhibit negligible chiroptical properties. The lack of clear helicity, due to the staircase arrangement of the self-assembling units in the aggregate, justifies these features. In contrast, attaching the peripheral groups directly to the N-annulated PBI core drastically changes the self-assembling properties of compounds 2, which form H-type aggregates following an isodesmic mechanism. These H-type aggregates show a strong aggregation-caused quenching (ACQ) effect that leads to nonemissive aggregates. Chiral (S)-2 and (R)-2 experience an efficient transfer of asymmetry to afford P- and M-type aggregates, respectively, although no amplification of asymmetry is achieved in majority rules or “sergeants-and-soldiers” experiments. A solvent-controlled stereomutation is observed for chiral (S)-2 and (R)-2, which form helical supramolecular polymers of different handedness depending on the solvent (methylcyclohexane or toluene). The stereomutation is accounted for by considering the two possible conformations of the terminal phenyl groups, eclipsed or staggered, which lead to linear or helical self-assemblies, respectively, with different relative stabilities depending on the solvent.

Emergence of Highly Enantioselective Catalytic Activity in a Helical Polymer Mediated by Deracemization of Racemic Pendants.

Any polymers composed of racemic repeating units are obviously optically inactive and hence chiral functions, such as asymmetric catalysis, will not be expected at all. Contrary to such a preconceived notion, we report an unprecedented helical polymer-based highly enantioselective organocatalyst prepared by polymerization of a racemic monomer with no catalytic activity. Both the right- and left-handed helical poly(biarylylacetylene)s (PBAs) composed of dynamically racemic 2-arylpyridyl-N-oxide monomer units with N-oxide moieties located in the vicinity of the helical polymer backbone can be produced by noncovalent interaction with a chiral alcohol through deracemization of the biaryl pendants. The macromolecular helicity and the axial chirality induced in the PBAs are retained ("memorized") after complete removal of the chiral alcohol. Accordingly, the helical PBAs with dual static memory of the helicity and axial chirality show remarkable enantioselectivity (86% ee) for the asymmetric allylation of benzaldehyde. The enantioselectivity is slightly lower than that (96% ee) of the homochiral PBAs prepared from the corresponding enantiopure (R)- and (S)-monomers, but is comparable to that (88% ee) of the helical PBA composed of nonracemic monomers of ca. 60% ee.

A close look at the conformational transitions of a helical polymer in its response to environmental stimuli

We present a study of the conformational transitions of a helical polymer by using coarse-grained molecular dynamics simulations. With focus on the variation of the dihedral angles, we are able to obtain the monomer-level details of the response of the polymer chain to environmental stimuli (e.g., temperature variation and mechanical forces). Specifically, during the thermo-induced helix–coil transition, all the helices break synchronously. On the contrary, the force-induced helix breaking always starts from the termini, and then the chain behaviors become divergent and temperature dependent. Particularly, at intermediate temperatures, we find that our polymer chain can adopt an asymmetrical half-trans conformation during the stretching procedures, although the chain itself has quite uniform and homogeneous composition.

Chiral Recognition and Resolution Based on Helical Polymers

Chiral Recognition and Resolution Based on Helical Polymers

Single-Chirality Near-Infrared Carbon Nanotube Sub-Cellular Imaging and FRET Probes.

Applications of single-walled carbon nanotubes (SWCNTs) in bioimaging and biosensing have been limited by difficulties with isolating single-chirality nanotube preparations with desired functionalities. Unique optical properties, such as multiple narrow near-infrared bands and several modes of signal transduction, including solvatochromism and FRET, are ideal for live cell/organism imaging and sensing applications. However, internanotube FRET has not been investigated in biological contexts. We developed single-chirality subcellular SWCNT imaging probes and investigated their internanotube FRET capabilities in live cells. To functionalize SWCNTs, we replaced the surfactant coating of aqueous two-phase extraction-sorted single-chirality nanotubes with helical polycarbodiimide polymers containing different functionalities. We achieved single-chirality SWCNT targeting of different subcellular structures, including the nucleus, to enable multiplexed imaging. We also targeted purified (6,5) and (7,6) chiralities to the same structures and observed internanotube FRET within these organelles. This work portends the use of single-chirality carbon nanotube optical probes for applications in biomedical research.

Cholesteric Soft Matter Molded Helical Photonic Architecture toward Volatility Monitoring of Organic Solvent

Volatility monitoring of a tiny amount of organic solvent, which reflects the profound understanding of the micro‐environmental chemical physics effect, plays a significant role in chemical reactions. Common approaches, such as microfluidic technology, undeniably encounter the issue of complicated fabrication or high cost, impeding their large‐scale application for monitoring the processes of chemical physics in micro‐reactions. Herein, a helical polymer film (HPF) molded by a cholesteric liquid crystal (CLC) is reported to record the helical arrangement. By infiltrating less than 1.0 μL volatile solvent into the HPF and monitoring the corresponding reflection spectral behaviors, an intrinsic dynamic chemical physics process, solvent properties, and molecular interactions between the solvent and the polymer network are quantitatively evaluated. Furthermore, to further explore the underlying interaction mechanism that results in spectral band shift, a dynamical model is established and elucidated, providing remarkable information and understanding of the dynamic chemical physics processes and interfacial molecular interactions between the solvent and the polymer. This work has tied a close bond among chemical engineering, photonics, and soft condensed physics, which can provide an avenue for the new field of application of LC photonics beyond display and optics.

Synthesis of helical branched carbodiimide polymers with liquid crystalline properties

ABSTRACT Carbodiimide polymers are synthetic helical polymers that display unique properties depending on the functional groups attached to the polymer backbone. The amidine groups of the backbone present alternating amine- and imine-like groups. The properties of the polycarbodiimides have been studied by varying the sidechains of the polymer from linear to branched. In previous work, different arenes and straight aliphatic chains substituted polycarbodiimides have been used to evaluate the thermal and liquid crystalline properties of these polymers. In this study, we introduced bulky branched aliphatic and octadecyl side chains to the polymer backbone to generate a branched homopolymer and different branched/linear-chain copolymers. The effect of these side-chain combinations on the solid and solution properties of these polycarbodiimides was studied. It was observed that polycarbodiimides containing octadecyl and branched bulky alkyl groups showed different thermal events in the DSC plot at ~30°C. Also, we observed a decrease in thermal stability in the TGA thermogram as we increase the branched alkyl side chains of the polymers. The lyotropic liquid crystallinity was observed in all the branched copolymers that consist of both branched alkyl side chains and octadecyl functional groups in different ratios.

Helical springs as a color indicator for determining chirality and enantiomeric excess.

Chirality plays a key role in the physiological system, because molecular functionalities may drastically alter due to a change in chirality. We report herein a unique color indicator with a static helicity memory, which exhibits visible color changes in response to the chirality of chiral amines. A difference of less than 2% in the enantiomeric excess (ee) values causes a change in the absorption that is visible to the naked eyes. This was further quantified by digital photography by converting to RGB values. This system relies on the change in the tunable helical pitch of the π-conjugated polymer backbone in specific solvents and allows rapid on-site monitoring of chirality of nonracemic amines, including drugs, and the simultaneous quantitative determination of their ee values.

Super Chirality Promotion of Helical Poly(Phenyl Isocyanide)s by Grafting onto Ethyl Cellulose

AbstractChiral property of cellulose can be transferred to final materials, here artificial helical polymer, right‐handed helical poly(phenyl isocyanide) (PPI) is grafted onto ethyl cellulose (EC) with expecting to enhance the chiral effect of PPI. EC‐2,3‐g‐PPIn copolymers are prepared via “click” chemistry of copper‐catalyzed alkyne‐azide cycloaddition, and confirmed by high‐resolution 1H and 13C NMR, Fourier transform infrared spectroscopy (FTIR), and gel permeation chromatography (GPC). The resulting EC‐2,3‐g‐PPIn copolymer takes a right‐handed helical structure with super circular dichroism intensity which is 302% higher than that of PPI, which indicates that EC backbone promotes the right‐handed chirality of PPIn. Furthermore, EC‐2,3‐g‐PPIn exhibits good chiral recognition ability of the D/L‐Ala‐DNSP fluorescent probe, and induces a uniquely visible blue shift for L‐Ala‐DNSP. Therefore, a novel facile strategy is provided to highly improve chiral property and chiral recognition ability of artificial helical polymers by grafting onto EC.

Tuning the helical sense and elongation of polymers through the combined action of the two components of tetraalkylammonium-anion salts

The helical sense and elongation of a helical polymer that bears the 4-ethynylanilide of (R)-α‑methoxy-α-phenylacetic acid [m-(R)-1] can be tuned by the action of the two components of tetraalkylammonium-anion salts. Thus, while the supramolecular PPA-anilide/anion interaction creates a chiroptical switch, inducing either P or M helical senses in the poly(phenylacetylene) (PPA) depending on the nature of the anion —P helix: fluoride (F−) or cyanide (CN−); M helix: acetate (OAc−), benzoate (OBz−) or azide (N3−)—, deprotonation of the anilide group by these anions in dry conditions makes it possible to play with the elongation of the PPA, depending on the size of the tetraalkylammonium group, which results in a colorimetric switch. Thus, a color change from yellow to deep red is obtained by deprotonation of the anilide group when a tetraabutylammonium salt is used, while yellow/light-red and yellow/orange color changes are obtained when the size of the tetraalkylammonium group is reduced. Structural and mechanistic studies confirm that the color change occurs when the counterion accommodates itself close to the pendant group once the anilide hydrogen is removed. This PPA/tetraalkylammonium association is responsible of elongation changes in the PPA and therefore on the conjugation of the polyene backbone that is accompanied with color changes. Moreover, this colorimetric switch also operates in the solid state and can be switched in a vacuum/air moisture cycle.

Formation of Multiple‐Helical Core‐Shell Structure from Polyphenyl and Boron Nitride Nanotube

AbstractIn this manuscript, a multiple‐helical core‐shell structure is studied from polyphenyl and boron nitride nanotube (BNNT) through the molecular dynamics simulation. The results exhibited that polyphenyl is constrained in the inside of BNNT and self‐coiled to a helical configuration. In these systems, both the van der Waals potential well and the π–π stacking interaction between the polyphenyl and BNNT play a key role in the formation of helical nanostructures. The final configuration of composites can be influenced by many factors such as the diameter of BNNT, the chain number of polymer, the length of polymer, and the simulation temperature which are investigated in detail. This theory research about polyphenyl and BNNT may supply more theoretical foundation in chemical functionalization and helical polymer synthesis, which can be helpful for fabricating nanoscale devices.

Axially oriented guest induced crystallization in syndiotactic polystyrene unstretched fibers

Guest-induced crystallization of amorphous s-PS fibers, although prepared with slow take-up speeds (e.g., 80 m/min) and in the absence of mechanical stretching, unexpectedly leads to high degrees of axial orientation (0.7 < fc < 0.8) of co-crystalline phases. Similar high degrees of axial orientation can be maintained after suitable guest removal procedures, leading to nanoporous-crystalline (NC) phases. High degrees of orientation are even maintained after high temperature (e.g., 200 °C) treatments leading to dense crystalline α phases, although this phase transition implies change of polymer conformation from helical to zig-zag planar. Hence, guest induced crystallization of amorphous s-PS fibers not only leads to NC forms (suitable for removal of organic pollutants from the environment) or to co-crystalline forms with active guests (e.g., suitable for antimicrobial release) but also lead, without stretching, to axial orientation. For the disordered NC form, fiber patterns are for the first time reported, showing only four diffraction peaks, which suggest the occurrence of a hexagonal packing of chain axes of s(2/1)2 polymer helices. The NC nature of this disordered crystalline form is clearly confirmed by tests of perchloroethylene uptake, from dilute aqueous solutions (500 ppb).

Consequences of Amide Connectivity in the Supramolecular Polymerization of Porphyrins: Spectroscopic Observations Rationalized by Theoretical Modelling.

The correlation between molecular structure and mechanism of supramolecular polymerizations is a topic of great interest, with a special focus on the pathway complexity of porphyrin assemblies. Their cooperative polymerization typically yields highly ordered, long 1D polymers and is driven by a combination of π‐stacking due to solvophobic effects and hydrogen bonding interactions. Subtle changes in molecular structure, however, have significant influence on the cooperativity factor and yield different aggregate types (J‐ versus H‐aggregates) of different lengths. In this study, the influence of amide connectivity on the self‐assembly behavior of porphyrin‐based supramolecular monomers was investigated. While in nonpolar solvents, C=O centered monomers readily assemble into helical supramolecular polymers via a cooperative mechanism, their NH centered counterparts form short, non‐helical J‐type aggregates via an isodesmic pathway. A combination of spectroscopy and density functional theory modelling sheds light on the molecular origins causing this stunning difference in assembly properties and demonstrates the importance of molecular connectivity in the design of supramolecular systems. Finally, their mutual interference in copolymerization experiments is presented.