Helical Polyacetylene Research Articles

Optically active thermosensitive amphiphilic polymer brushes based on helical polyacetylene: preparation through “click” onto grafting method and self-assembly

Optically active, thermosensitive, and amphiphilic polymer brushes, which consist of helical poly(N-propargylamide) main chains and thermosensitive poly(N-isopropylacrylamide) (PNIPAm) side chains, were prepared via a novel methodology combining catalytic polymerization, atom transfer radical polymerization (ATRP), and click chemistry. Helical poly(N-propargylamide) bearing α-bromoisobutyryl pendent groups was synthesized via catalytic polymerization, followed by substituting the –Br moieties with azido groups. Then, alkynyl terminated PNIPAm formed via ATRP was successfully grafted onto the azido functionalized helical polymer backbones via click chemistry, providing the expected polymer brushes. GPC, FT-IR, and 1H-NMR measurements indicated the successful synthesis of the novel amphiphilic polymer brushes. UV–vis and CD spectra evidently demonstrated the helical structures of the polymer backbones and the considerable optical activity of the final brushes. The polymer brushes self-assembled in aqueous solution forming core/shell structured nanoparticles, which were comprised of optically active cores (helical polyacetylenes) and thermosensitive shells (PNIPAm).

Cover Picture: Synthesis of Conjugated Polymers in Chiral Nematic Liquid Crystal Fields (Isr. J. Chem. 10/2011)

The cover illustration shows a schematic representation of the mechanism for acetylene polymerization in nematic liquid crystals. The helical polyacetylene with left-handed screw direction grows starting from the catalytic species in the right-handed N*-LC. See Synthesis of Conjugated Polymers in Chiral Nematic Liquid Crystal Fields by Matsushita and Akagi, p. 1075 in this issue.

Hierarchically Controlled Helical Graphite Films Prepared from Iodine-Doped Helical Polyacetylene Films Using Morphology-Retaining Carbonization

One-handed helical graphite films with a hierarchically controlled morphology were prepared from iodine-doped helical polyacetylene (H-PA) films using the recently developed morphology-retaining carbonization method. Results from scanning electron microscopy indicate that the hierarchical helical morphology of the H-PA film remains unchanged even after carbonization at 800 °C. The weight loss of the film due to carbonization was very small; only 10-29% of the weight of the film before doping was lost. Furthermore, the graphite film prepared by subsequent heating at 2600 °C retained the same morphology as that of the original H-PA film and that of the helical carbon film prepared at 800 °C. The screwed direction, twisted degree, and vertical or horizontal alignment of the helical graphite film were well controlled by changing the helical sense, helical pitch, and orientation state of the chiral nematic liquid crystal (N*-LC) used as an asymmetric LC reaction field. X-ray diffraction and Raman scattering measurements showed that graphitic crystallization proceeds in the carbon film during heat treatment at 2600 °C. Transmission electron microscopy measurements indicate that ultrasonication of the helical graphite film in ethanol for several hours gives rise to a single helical graphite fibril. The profound potentiality of the present graphite films is exemplified in their electrical properties. The horizontally aligned helical graphite film exhibits an enhancement in electrical conductivity and an evolution of electrical anisotropy in which conductivity parallel to the helical axis of the fibril bundle is higher than that perpendicular to the axis.

Synthesis of Conjugated Polymers in Chiral Nematic Liquid Crystal Fields

AbstractThis review presents the progress made on current research in the synthesis of π‐conjugated polymers in chiral nematic liquid crystal (N*‐LC) fields through either chemical or electrochemical polymerization. The following are noteworthy advances in the field of π‐conjugated polymers. (i) Helical aliphatic conjugated polymers of helical polyacetylene (H‐PA) were synthesized using asymmetric interfacial polymerization in N*‐LC fields. (ii) Helical aromatic conjugated polymers with electroactive properties, such as poly(3,4‐ethylenedioxythiophene) (PEDOT) and polybithiophene (PBT), were synthesized using asymmetric electrochemical polymerization in N*‐LC fields. (iii) Chiral aromatic conjugated copolymers, such as the poly(bithienylene‐phenylene) (PBTP) derivative, were synthesized using the asymmetric Stille polycondensation reaction in N*‐LC fields. Throughout the document, it has been emphasized that by using N*‐LC systems as asymmetric polymerization fields, helix formation is possible for aliphatic and aromatic π‐conjugated polymers without chiroptical substituents on the side chains.

Hollow Two‐Layered Chiral Nanoparticles Consisting of Optically Active Helical Polymer/Silica: Preparation and Application for Enantioselective Crystallization

AbstractThis article reports for the first time a novel category of hollow organic@inorganic hybrid two‐layered nanoparticles (NPs), in which the inner layer is formed by optically active helical polyacetylene, and the outer layer by silica. Such NPs show remarkable optical activity and are successfully used for enantioselective crystallization. To prepare such NPs, n‐butyl acrylate undergoes radical polymerization to first form poly(n‐butyl acrylate) (PBA) cores two shells by catalytic polymerization of substituted acetylene and sol–gel approach of TEOS (tetraethyl orthosilicate), respectively. Removal of the PBA cores provides the expected hollow core/shell NPs. The intense dircular dichroism (CD) effects demonstrate that the hollow chiral NPs possess considerable optical activity, arising from the helical substituted polyacetylenes forming the inner layer. The hollow NPs are further used as chiral templates to induce enantioselective crystallization of racemic alanines, demonstrating the significant potential applications of the hollow chiral NPs in chiral technologies. Also of particular significance is the detailed process of the induced crystallization observed by TEM. The strategy for preparing the hollow hybrid chiral NPs should be highlighted since it combines free radical polymerization and catalytic polymerization with sol–gel process in a single system, by which numerous advanced materials will be accessible.

Optically Active Amphiphilic Polymer Brushes Based on Helical Polyacetylenes: Preparation and Self-Assembly into Core/Shell Particles

The article reports on the first preparation and self-assembly of a unique class of amphiphilic polymer brushes, which consist of hydrophobic optically active helical polyacetylene backbones and hydrophilic thermosensitive poly(N,N-dimethylamino-2-ethyl methacrylate) (PDMAEMA) side chains. The polymer brushes were prepared by a two-step process: substituted acetylene monomers underwent catalytic copolymerizations to form optically active helical polymer backbones bearing −Br moieties in side chains, which were employed as macroinitiators for the subsequent atom transfer radical polymerization (ATRP) of a vinyl monomer DMAEMA. High specific rotations and intense circular dichroism effects demonstrated that the polymer brushes possessed optical activities, derived from the helical polyacetylene backbones. The polymer brushes could self-assemble in water/tetrahydrofuran mixture solvent to form core/shell structured nanoparticles, which showed considerable optical activity originated in the helical polyacetyl...

Optically Active Helical Polyacetylene@silica Hybrid Organic−inorganic Core/Shell Nanoparticles: Preparation and Application for Enantioselective Crystallization

This article reports on a novel category of hybrid nanoparticles (NPs) consisting of a unique organic core (composed of optically active helical polyacetylene) and an inorganic shell (composed of silica). The NPs were synthesized by combining in one system the aqueous catalytic microemulsion polymerization of substituted acetylene monomer to form the core and the sol−gel approach of TEOS to form the shell. The substituted polyacetylene forming the core adopted helical conformations of predominant one handedness while the silica shell provided desirable protection for the core. The obtained emulsions exhibited high stability. The NPs possessed large optical activities, arising from the helical polymer chains constituting the core. The investigations are important in chemistry since two diverse research fields (organic helical polymers and inorganic materials) were combined for the first time in a specific system. The obtained hybrid core/shell NPs induced enantioselective crystallization of alanine enantio...

Chiral helical polyacetylene–vinyl polymer core/shell nanoparticles: preparation and application to optically active composite films

Optically active core/shell nanoparticles (NPs) were prepared by combining aqueous catalytic microemulsion polymerization of a monosubstituted N-propargylsulfamide monomer and free-radical polymerization of two vinyl monomers (MMA and BA) in one specific system. In such novel NPs, poly(N-propargylsulfamide) forming the cores took helical conformations of a predominant handedness, endowing the NPs with interesting optical activities. The use of two vinyl monomers simultaneously in one system led to NPs with desirable dispersity and morphology. From the NP emulsions, optically active composite films were prepared with poly(vinyl alcohol) as supporting material, attesting to the potential applications of the optically active core/shell NPs. Following the strategy, other novel core/shell NPs and advanced materials can be anticipated. The current investigations provide large possibilities to realize practical applications of highly interesting helical polyacetylenes.

Formation Mechanism of Helical Polyacetylene with Spiral Morphology in Asymmetric Reaction Field Consisting of Chiral Nematic Liquid Crystal

The formation mechanism of helical polyacetylene (H-PA) in chiral nematic liquid crystal (N*-LC) used as an asymmetric reaction field was investigated by taking into account the relationship in morphology between the H-PA and N*-LC. The spiral texture characteristic of N*-LC observed in polarized optical microscopy was examined and compared with the spiral morphology of the resultant H-PA. The distance between the fibril bundles of H-PA was determined to be half of a helical pitch of N*-LC; in addition, the helical axis of H-PA is orthogonal to that of N*-LC. Interestingly, the screw direction of the H-PA fibrils was found to be opposite to that of N*-LC. On the basis of these experimental facts, we propose a chemically graspable formation mechanism of H-PA in N*-LC.

ChemInform Abstract: From Helical Polyacetylene to Helical Graphite: Synthesis in the Chiral Nematic Liquid Crystal Field and Morphology‐Retaining Carbonization

AbstractReview: 70 refs.

Macroscopically Aligned Helical Polyacetylene Synthesized in Magnetically Oriented Chiral Nematic Liquid Crystal Field

We have succeeded in synthesizing macroscopically aligned helical polyacetylene (H-PA) by using magnetically oriented chiral nematic liquid crystal (N*-LC) with monodomain structure. The N*-LC with monodomain structure was prepared by applying a magnetic field as an external perturbation to a N*-LC with polydomain structure. Because of the positive anisotropy of the diamagnetic susceptibility of N*-LC, the helical axis of the N*-LC was oriented perpendicular to the direction of the applied magnetic field. The monodomain N*-LC enabled us to synthesize macroscopically aligned H-PA. The bundles of fibrils were aligned parallel to the direction of the magnetic field and perpendicular to the axis of the N*-LC. It is anticipated that the macroscopically aligned H-PA film might be available for novel organic electromagnetic materials and also for the promising precursor of aligned helical graphite by using the morphology-retaining carbonization method.

From helical polyacetylene to helical graphite: synthesis in the chiral nematic liquid crystal field and morphology-retaining carbonisation

This tutorial review presents current progress in the synthesis of helical polyacetylene (H-PA) using a chiral nematic liquid crystal reaction field as an asymmetric polymerisation solvent. In addition, we review the morphology-retaining carbonisation for helical graphite using H-PA as a carbonisation precursor. Carbonisation of H-PA films, via iodine doping, is demonstrated to produce carbon and graphitic films bearing completely preserved morphologies and even helical nanofibril structures.

Chiroptically Active Photonics Polymers: Synthesis and Chiroptically Switching Properties of Helical Polyacetylene Bearing Electrochromic Viologens in the Side Chains

Toward near-infrared chiroptically active photonics polymers, a new type of optically active polyacetylene bearing l-alanine and electrochromic viologen in the side chains was prepared and carefully studied for the chiroptical properties. The resulting polymer exhibited much larger optical rotation ([m]25D = −1310°, DMF) than the model compound ([φ]25D = 201°, DMF) as well as a strong negative circular dichroism (CD) signal attributable to backbone absorption, indicating the formation of a single-handed helical structure of the polymer main chain. The content of viologen in the polymer was determined to be >70 mol % relative to the repeat unit by NMR and X-ray photoelectron spectrscopy. Because of the chiral perturbation of the helical main chain, the viologens in the side chains are asymmetrically positioned and interacted to yield a new strong negative CD band at long wavelengths (i.e., 450−800 nm) upon reduction to radical cations. The intensity of this CD signal could be easily switched between nearly...

Preparation of helical carbon and graphite films using morphology-retaining carbonization

Helical carbon and graphite films were prepared from iodine-doped helical polyacetylene (H-PA) film using currently developing morphology-retaining carbonization. It was found from scanning electron microscopy (SEM) observations that the hierarchical helical morphology of the H-PA film remains unchanged even after the carbonization at 800 °C. Besides, the weight loss of the film due to the carbonization was very small, which was only a few percent to the weight of the film before doping. Furthermore, the graphite film prepared by the subsequent heating at 2600 °C still retained the same morphology as those in the original H-PA film and in the helical carbon film prepared at 800 °C. X-ray diffraction (XRD) and Raman scattering measurements were then pursued. The results showed that graphitic crystallization proceeds in the carbon film through the heat treatment at 2600 °C. Transmission electron microscopy (TEM) image of a single helical graphitic fibril was also observed by ultrasonicating the graphite film in ethanol. Carbonization of the H-PA films by way of iodine doping was found to afford helical carbon and graphite films, where spiral morphologies and even helical fibril structures were completely preserved.

Helical polyacetylene—a conductive material for self-contained molecular electronic deviceuse**The contents of this paper were presented at the 2007 European Conference on MolecularElectronics, 5–8 September 2007, Metz, France.

We describe mono-substituted helical poly(phenyl)acetylene, a structural variation ofpolyacetylene that may overcome its problem: the lack of chemical stability. Helicalpolyacetylene shows an intrinsic stiff rod structure, which can be enhanced by the choice ofsuitable side groups. The structure looks like a narrow spiral with a conjugatedelectron system, covered by attached side groups spiralling in the opposite sense. Weconsider this unique material as a prototype for molecular electronic device use. Itprovides the electronic function, mechanical packaging and electrical insulationthrough a variety of side groups and exhibits useful self-assembly properties.We provide evidence that such materials, in many variations, show the expected overallstructure, can be synthesized through living polymerization (which is necessary for thefabrication of monomers by monomer controlled structures), do show enhanced chemicalstability, are amenable to self-assembly, may be deposited in an oriented fashion and doshow electrical conductivity.

Helical Carbon and Graphitic Films Prepared from Iodine-Doped Helical Polyacetylene Film Using Morphology-Retaining Carbonization

In this communication, we report a novel preparation of the helical carbon nanofibril-fabricated thin film from the iodine-doped filmy helical polyacetylene through a carbonization process. Carbonization of the helical polyacetylene films by way of iodine doping is found to afford carbon and graphitic films completely preserving morphologies and even helical nanofibril structures.

Helical polyacetylene—Origins and synthesis

We present the origins and synthesis of helical polyacetylene (H-PA) by focusing on its peculiar spiral morphology. Interfacial polymerization of acetylene was carried out in an asymmetric reaction field consisting of chiral nematic liquid crystal (N*-LC) and Ziegler-Natta catalyst. As the N*-LC is composed of nematic liquid crystal and a chiral compound such as a binaphthyl derivative with either the R- or S-configuration, the screw directions of the polyacetylene chain and fibril bundle--and even the spiral morphology--are rigorously controlled by the chirality of the selected compound. Interestingly, the screw directions of the fibril and the bundle in H-PA were found to be opposite to that of N*-LC. It is worthwhile to emphasize that the hierarchical spiral morphology involving the primary to higher order structure is generated in a synthetic polymer such as polyacetylene by using N*-LC as an asymmetric polymerization solvent.

Highly Twisted Helical Polyacetylene with Morphology Free From the Bundle of Fibrils Synthesized in Chiral Nematic Liquid Crystal Reaction Field

We synthesized novel axially chiral binaphthyl derivatives with highly twisting powers by substituting phenylcyclohexyl (PCH) mesogenic moieties into 2,2' positions or 2,2',6,6' positions of binaphthyl rings. The di- and tetrasubstituted binaphthyl derivatives, abbreviated as D-1 and D-2, respectively, were adopted as chiral dopants to induce chiral nematic liquid crystals (N*-LCs) available for synthesis of helical polyacetylene. The helical twisting power (betaM) of D-2 was 449 microm(-1), which was ca. 2.6 times larger than that of D-1 (171 microm(-1)). We prepared two kinds of induced N*-LCs with 5 microm and 270 nm in helical pitch by adding the chiral dopants D-1 and D-2 into the host N-LCs, respectively. The helical polyacetylene synthesized in the N*-LC containing D-2 exhibited highly screwed fibrils, but not a bundle of fibrils. This result is in quite contrast to the usual fibril morphology, where the screwed fibrils are gathered to form the bundle of fibrils, as observed in the helical polyacetylene synthesized in the N*-LC containing a chiral dopant with moderate helical twisting power, such as D-1. It is of keen interest that the helical pitch (270 nm) of the N*-LC including D-2 is much smaller than the diameter (ca. 1 microm) of the bundle of fibrils, which should depress the formation of the bundle of fibrils. The morphology free from the bundle of fibrils might enable us to evaluate more precisely intrinsic electromagnetic properties of a single screwed fibril of helical polyacetylene.

Helical Polyacetylenes Synthesized in Helical Sense and Pitch Controllable Chiral Nematic Liquid Crystal with Unprecedented Temperature Dependence

We have synthesized two types of novel chiral compounds, D-1 and D-2−D-5, where D-1 is an asymmetric center-containing chiral compound of (S)-configuration, and D-2−D-5 are so-called double chiral compounds consisting of axially chiral binaphthyl moiety of (S)-configuration and asymmetric center moieties of (S)-, (S)-, (R)- and racemic configuration, linked with methylene spacers of 6, 12, 12 and 12, respectively. These chiral compounds were adopted as chiral dopants to induce chiral nematic liquid crystals (N*-LCs). The N*-LC including the double chiral dopant D-3, abbreviated as N*-LC with D-3 (system 2), showed an extraordinary increase in helical pitch (decrease in helical twisting power) in polarizing optical microscope (POM) when the temperature increased from 0 to 30 °C. This is due to a substantial cancellation in twisting power between the double chiral moieties having opposite screw directions, although both of them have the same (S)-configuration. Meanwhile, the N*-LC including the two types of chiral dopants D-1 and D-3, abbreviated as N*-LC with both D-1 and D-3 (system 3), exhibited a temperature-dependent helical inversion; It showed a notable increase in left-handed helical pitch when the temperature increased from 0 to 15 °C, and became a nematic phase giving no helicity in the temperature range of 16−19 °C, and then showed a right-handed N* phase giving a decrease in helical pitch when the temperature increased from 20 to 25 °C. The changes in helical sense and helical pitch in the N*-LC were found to be thermally reversible. The helical pitch-controllable N*-LC (system 2) enabled us to control the screw structure and the spiral morphology of the helical polyacetylene by changing only the polymerization temperature.

Hyperstructured polyacetylene

AbstractCurrent progress in the synthesis and properties of conjugated polymers is presented by focusing on recently put forward hyperstructured helical polyacetylene. Interfacial polymerization of acetylene has been carried out in an asymmetric reaction field consisting of chiral nematic liquid crystal (N*‐LC) and Ziegler–Natta catalyst. Since the chiral nematic liquid crystal is composed of nematic liquid crystal and a chiral compound such as axially chiral binaphthyl derivative with R‐ or S‐configuration, the screw directions of the polyacetylene chain and fibril bundle and even the spiral morphology are rigorously controlled by selecting the chirality of the chiral compound. Surprisingly, the screw directions of the fibril and the bundle of fibrils in helical polyacetylene were found to be opposite to that of N*‐LC. It is worthwhile to emphasize that the hierarchical spiral morphology involving the primary to higher order structure is generated in a synthetic polymer such as polyacetylene by using N*‐LC as an asymmetric polymerization solvent. Copyright © 2007 Society of Chemical Industry