Liquid Crystalline Homopolymers Research Articles

New side-chain liquid crystalline terpolymers with anhydrous conductivity: Effect of azobenzene substitution on light response and charge transfer

We have prepared and characterised a series of side-chain liquid crystalline homopolymers and terpolymers containing different azobenzene derivatives (RAzB), sulfonic groups (2-acrylamido-2-methyl-1-propanesulfonic acid, AMPS), and methyl(methacrylate) groups (MMA), as monomeric units. We have evaluated the effect of different para-substitutes of 6-(4-azobenzene -4′-oxy)hexyl methacrylate, at the side chains, OCH3, NO2 and H, on the phase behaviour and conductivity of the new polymers. The copolymers can form smectic and nematic phases, depending on their composition, and have light responsiveness, conferred by the azobenzene chromophores. The terpolymer with methoxy terminations, MeOAzB/AMPS/MMA, exhibits the highest conductivity values of the series (10−2/10−3 S·cm−1 range) through liquid crystalline phases and with signs of decoupling from polymeric segmental motions. These materials are promising candidates to develop new light-responsive polymeric electrolytes for electrochemical conversion devices in which ionic conductivity under anhydrous conditions can be controlled by their nanostructure.

Strategies to Stabilize the Photoinduced Supramolecular Chirality in Azobenzene Liquid Crystalline Polymers.

This paper describes the synthesis, thermal characterization and optical properties of liquid crystalline homopolymers and block copolymers with a repeating unit consisting of two functional units, with at least one of them being an azobenzene. Films of these polymers have been irradiated with circularly polarized light at room temperature, evaluating the intensity of the photoinduced chiral signal and its temporal stability upon storage. The paper also explores two different strategies to restrict the relaxation of the photoinduced order. Firstly, block copolymers have been prepared to confine the photoaddressable segments into nanoscopic domains where relaxation should be restricted. Secondly, an alternative homopolymer has been synthesized where the repeating unit combines two chromophores that can be separately photoaddressed, an azobenzene unit to efficiently photoinduce chirality and a cinnamate to fix the chiral signal by photocrosslinking.

Synthesis and Mesomorphic Properties of New Side Chain Liquid Crystalline Oligomers Containing Salicylaldimine Mesogenic Groups

New liquid crystalline salicylaldimine-based homopolymers PLC1 and PLC2 have been synthesized from their corresponding monomers 5-(10-undecenyloxy)-2-[[(4-(hexyloxy)phenyl)imino]methyl]phenol (LC1 ) and 5-(10-undecenyloxy)-2-[[(4-(hexyl)phenyl)imino]methyl]phenol (LC2 ) via free radical polymerization. The polymers were characterized by 1H-NMR, differential scanning calorimetry (DSC) and optical microscopy in polarized light (polarizing microscope). The synthesized polymers have low molecular weights, and so are in the oligomeric domain. The oligomers behave very similarly to their monomers that exhibit smectic mesophases. Replacing the hexyloxy chain by a hexyl chain of the mesogenic unit generates an additional SmC mesophase in the temperature range of both the monomer and oligomer. All the observations suggest that the oligomerization of the liquid crystalline salicylaldimine monomers gives rise to decreased transition temperatures whereas it has no influence on the type and stability of the mesophase formed.

Cholesteric mesophase in side-chain liquid crystalline polymers: influence of mesogen interdigitation and motional decoupling

In this paper, the thermal, optical and mesomorphic properties of side-chain liquid crystalline (SCLC) homopolymers (PNBCh-n), in which cholesteryl mesogens are linked to a polynorbornene backbone by different lengths of methylene spacer (n = 4, 5, 9, 10 and 15), are investigated. By doing so, the impact of flexible spacer length on the formation of different types of LC mesophase is explained. Because of comb-shaped SCLC polymer architecture, smectic mesophases are primarily found in PNBCh-n. Interestingly, cholesteric mesophases are identified only in PNBCh-9 and 10, which are proved by (1) the selective light reflection in UV-Vis analysis, (2) the characteristic oily streak texture under polarized optical microscope (POM) and (3) a long range periodicity in the cross-sectioned films from transmission electron microscope (TEM) investigation. Moreover, temperature-controlled X-ray scattering measurements are performed to examine mesomorphic structure evolution. By comparing the mesomorphic structures in this series of SCLC homopolymers, both extent of mesogen interdigitation and motional decoupling between backbone and mesogenic side-chains are found to play a critical role in the development of cholesteric mesophase. This structure–property study of PNBCh-n will help elucidate the importance of molecular structure, particularly the length of spacers, on the formation of cholesteric mesophase and its importance in the design of thermochromic devices.

Synthesis and characterization of side‐chain liquid crystalline polymers bearing cholesterol mesogen

AbstractA series of new norbornene carboxylic cholesteryl ester monomers with and without alkyl spacers, NBCh, and NBCh‐n, respectively, were synthesized. New side‐chain liquid crystalline homopolymers, PNBCh and PNBCh‐n, were cleanly prepared using NBCh and NBCh‐n, respectively, with Grubbs 2nd generation catalyst. Molecular and structural characterization of monomers and polymers were carried out by nuclear magnetic resonance, NMR, Fourier transform infrared, FT‐IR, spectroscopy, and gel permeation chromatography, GPC. The thermal and liquid crystalline properties of the homopolymers were investigated by differential scanning calorimetry, DSC, thermogravimetric analysis, TGA, and polarized optical microscopy, POM. Small angle and wide angle X‐ray studies of PNBCh‐n in powder and fiber states not only confirmed the formation of smectic A mesophases, but also established their morphologies. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2690–2701, 2009

Synthesis of novel three‐arm star azo side‐chain liquid crystalline polymer via ATRP and photoinduced surface relief gratings

AbstractA three‐arm star azo side‐chain liquid crystalline (LC) homopolymer, poly[6‐(4‐methoxy‐4‐oxy‐azobenzene) hexyl methacrylate] (PMMAZO), was synthesized by atom transfer radical polymerization (ATRP) method. The polymerization of 6‐(4‐methoxy‐4‐oxy‐azobenzene) hexyl methacrylate proceeded in a controlled/“living” way. A series of three‐arm star LC block copolymers (PMMAZO‐b‐PMMA) were also synthesized. The polymers were characterized by 1H NMR, gel permeation chromatograph, and UV–vis spectra, respectively. The both polymers of PMMAZO and copolymers of PMMAZO‐b‐PMMA exhibited a smetic phase and a nematic phase. As concern to the PMMAZO, the glass‐transition temperature (Tg) and phase‐transition temperature from the smetic to nematic phase and from the nematic to isotropic phase increased with the increase of molecular weight (Mn(GPC)) of PMMAZO. The phase transition temperature of the block copolymers, PMMAZO‐b‐PMMA, with the same PMMA block was similar to that of PMMAZO. However, the Tg of the PMMAZO‐b‐PMMA decreased at low azo content and then increased with the increasing Mn(GPC) when azo content was above 61.3%. With illumination of linearly polarized Kr+ laser beam at modest intensities (35 mW/cm2), significant surface relief gratings formed on PMMAZO films with different molecular weights were observed. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 777–789, 2008

Photoinduced Chiral Nematic Organization in an Achiral Glassy Nematic Azopolymer

AbstractA liquid crystalline homopolymer that has photoisomerizable methoxyazobenzene groups in the side chain has been synthesized and characterized. Thin films of the nematic glassy phase of this polymer have been processed in order to study the absorption spectra and the vibrational and electronic circular dichroism responses by irradiation with 488 nm circularly polarized light (CPL). Selective reflection of visible light demonstrates that the irradiation of this glassy nematic azopolymer induces a helix as a consequence of the chiral arrangement of the azobenzene units. Moreover, a wedge cell with an aligning layer for planar orientation was filled with the polymer with the aim of investigating the change in the macroscopic optical properties and optical textures of the azopolymer on irradiation with CPL. The transfer of chirality from CPL to azopolymer through chiral conformations is proposed as a model for explaining the supramolecular chirality.

Synthesis and characterization of liquid crystalline side‐chain block copolymers containing luminescent 4,4′‐bis(biphenyl)fluorene pendants

AbstractA series of new liquid crystalline homopolymers, copolymers, and block copolymers were polymerized from styrene‐macroinitiator (SMi) and methacrylates with pendent 4,4′‐bis(biphenyl)fluorene (M1) and biphenyl‐4‐ylfluorene (M2) groups through atom transfer radical polymerization (ATRP). The number‐average molecular weights (Mn) of polymers P1‐P4 were 10,007, 14,852, 6,275, and 10,463 g mol−1 with polydispersity indices values of 1.21, 1.15, 1.31, and 1.22, respectively. All polymers exhibit the nematic phase. The thermal, mesogenic, and photoluminescent properties of all polymers were investigated. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4564–4572, 2007

Synthesis and characterization of side-chain liquid crystalline homopolymers and block copolymers containing biphenyl-4-ylthiophene and biphenyl-4-ylfluorene pendants

A series of new liquid crystalline homopolymers ( P1 and P2) and block copolymers ( P3 and P4) composed of methacrylates containing pendant biphenyl-4-ylthiophene ( M1) and biphenyl-4-ylfluorene ( M2) units were synthesized by atom transfer radical polymerization (ATRP). The number-average molecular weights ( M n) of the homopolymer ( P2) and diblock copolymers ( P3 and P4) were in the range of 5153–8713 g mol −1 with polydispersity indices (PDIs) between 1.17 and 1.25. The thermal, mesogenic, and photoluminescence (PL) properties of all polymers were investigated. Except for the absence of mesogenic properties in block copolymer P4, polymers P1 and P3 possessed the smectic A phase and polymer P2 exhibited the nematic phase. Moreover, the mesomorphism and the layer d-spacing values of the smectic A phase in polymers P1 and P3 were confirmed and characterized by X-ray diffraction (XRD) patterns.

Photoinduced supramolecular chirality in side-chain liquid crystalline azopolymers

A series of liquid crystalline homopolymers that have photoisomerizable cyanoazobenzene groups in the side chain has been synthesized and characterized. Thin films of these polymers have been processed in order to study the absorption spectra and circular dichroism responses after illumination with 488 nm circularly polarized light. The tendency of the azobenzene units to aggregate and the modification of the electronic spectra by illumination were studied by UV-vis spectroscopy. Illumination with circularly polarized light of the azopolymers gave rise to a photoinduced circular dichroism response, which suggests supramolecular structures with a chiral orientation of the azobenzene chromophores in H-aggregates. The photoinduced supramolecular order depends on the polymer structure, i.e., on the Tg and the length of the flexible spacer, and the nature of the liquid crystal phase. Identical absorption spectra and reverse circular dichroism spectra were obtained after irradiation with circularly polarized light of opposite handedness and this is due to the photoinduction of enantiomeric supramolecular structures. The thermal stability above Tg of the photoinduced supramolecular chirality is determined by the polymer structure.

Synthesis, Nanostructures, and Functionality of Amphiphilic Liquid Crystalline Block Copolymers with Azobenzene Moieties

A series of liquid crystalline (LC) homopolymers of poly{11-[4-(4-butylphenylazo)phenoxy]undecyl methacrylate}containing an azobenzene mesogen with different degrees of polymerization were synthesized by using the atom transfer radical polymerization (ATRP) method. The homopolymers were prepared with a range of number-average molecular weights from 6100 to 23 500 with narrow polydispersities of less than 1.17. Thermal investigation showed that the homopolymers exhibit monolayer smectic A, smectic C, and an unknown smectic X phases. The transition temperatures increase slightly with the increase of the molecular weights and level off at around 21 500. Novel amphiphilic LC-coil diblock copolymers with a defined length of a flexible poly(ethylene glycol) segment as the hydrophilic coil were also prepared by the ATRP method. The LC-coil diblock copolymers exhibit narrow polydispersities of less than 1.11. Morphologies of the thin films of the block copolymers were investigated by using transmission electron microscopy (TEM). Microphase separation with small size in the range of 10−20 nm (nanoseparated structures) was observed. Different photophysical and photochemical behaviors were observed between annealed homopolymer and block copolymer films, which is thought to be caused by the formation of nanostructures of the block copolymers.

Side-Chain Liquid-Crystalline Homopolymers and Copolymers. Structure and Rheology

We report on the structure and the viscoelastic properties of two side-chain liquid-crystalline polymers with different spacer length in the melt and fiber states and of their copolymers with a semicrystalline block. Optical microscopy, X-ray scattering, and differential scanning calorimetry are employed for the structure investigation and rheology for the dynamics. The smectic and nematic liquid-crystalline polymers exhibit non-Newtonian low-frequency response and violate the empirical principle of time−temperature superposition with the effect being more pronounced in the former. Fibers drawn from the melt exhibit significantly different structure from the melt samples. In the diblock copolymer composed of smectic/crystalline blocks, the strong first-order isotropic-to-smectic transition induces the weak disorder-to-lamellar transition between the dissimilar blocks in the diblock.

Synthesis and characterization of non-covalent liquid crystalline diblock copolymers

Poly(dimethylaminoethylmethacrylate)-b-poly(sodium methacrylate) diblocks, (polyDMAEMA-b-polyMA), were synthesized as precursors of liquid crystalline (LC) copolymers. These LC copolymers were prepared by proton-transfer between a carboxylic acid-containing mesogen (A) and the dimethylamino substituent of the polyDMAEMA block and by electrostatic interactions between the polyMA subunits and an ammonium-containing mesogen (B). When mesogen A is complexed with DMAEMA units, a dramatic enhancement of the mesophase stability is noted. The mesogenic properties of these LC copolymers were compared to those ones of the parent LC homopolymers, in relation to the copolymer composition. The supramolecular organization of the LC diblock copolymers was studied by small-angle X-ray scattering (SAXS), and smectic mesophases were observed in some LC (co)polymers. For samples containing a major LC block, a smectic mesophase coexists with microphases formed by the second amorphous block. Different organizations, including a body-centered lattice of spheres and a hexagonal array of cylinders, were observed, depending on the investigated copolymers and their composition. When the LC block is the minor component, it forms microdomains too small for a liquid crystalline order to emerge. Moreover, no supramolecular organization of these dispersed microdomains was detected by SAXS. A homogeneous smectic mesophase was observed when the two blocks are bearing liquid crystalline moieties.

FT-IR studies of side chain liquid crystalline thermoplastic elastomers

Side chain liquid crystalline polyurethanes are a new class of materials that show promise for mechanooptic applications. The rich morphology afforded by these materials also provides a chance to understand the interplay between polyurethane morphology and liquid crystalline ordering. In this paper, we study the response of a polyurethane with liquid crystals pendant to the soft segments to an applied strain using fourier transform infrared (FT-IR) linear dichroism. We find that this complex material follows the trend established in the literature for both side chain liquid crystalline homopolymers and segmented polyurethanes. At low strains, the soft segments align with strain inducing an orientation in “lone” hard segments. Up to strains of 40%, the LC mesogens align with the strain field and the hard segments in hydrogen bonded domains align perpendicular to the field. At strains above 40%, we find a rearrangement of the ordering that result in smectic layers and the hard segments aligning parallel to the field. A model is proposed to represent these findings, and reflections on the cooperative movement of the different macromolecular components of the polyurethane are offered.

Synthesis of Side-Chain Liquid Crystalline Homopolymers and Block Copolymers with Cyanobiphenyl Moieties as the Mesogen by Living Anionic Polymerization and Their Thermotropic Phase Behavior

We performed the anionic living polymerization of 6-[4-(4‘-cyanophenyl)phenoxy]hexyl methacrylate. By a selection of suitable initiations, the cyano group was completely stable toward the propagating enolate anion, and the anionic polymerization proceeded with a living nature. The homopolymers could thus be prepared with a wide range of molecular weights from 6000 to 20 000, a narrow molecular weight distribution of less than 1.14, and different tacticities. All the polymers exhibited the smectic A phase in which two mesogenic groups were included within a smectic layer of thickness 36.0 Å. The isotropization temperature of the smectic A phase increased with the increase of the molecular weight and leveled off at around 15 000. No crystallization took place so that the smectic A phase was glassified. Well-controlled block copolymers with methyl methacrylate and styrene were also prepared by living anionic polymerization, and their thermotropic phase behavior and structures are described in a relation to a microphase separation of the two different segments.

Characterization and Electro-Optical Properties of the Homopolymer and Copolymers of Ferroelectric Side-Chain Liquid Crystalline Polysiloxanes Containing Two Chiral Center Side Groups

Aggregation and electro-optical effects in the chiral smectic C phase of the ferroelectric liquid crystalline homopolymer and two copolymers were investigated. The smectic layers of homopolymer and copolymer were constructed by overlapping about 1.2 and 1.4 times the length of the side-chain mesogenic groups, respectively. The transient scattering mode was obtained by repeated voltage polarity reversal. Ferroelectric liquid crystalline polysiloxanes (FLCPs) exhibit large spontaneous polyarization (Ps) and Ps of homopolymers are larger than those of copolymers. The response times of homopolymers are longer than that of copolymers due to high viscosity. Reversible and bistable transparent-opaque change was successfully realized for the chiral smectic C phase upon applications of dc electric fields with a response time of several milliseconds at room temperature.

Dielectric relaxation spectra of two side chain liquid crystalline homopolymers and their copolymers

Dielectric relaxation spectra have been measured for a complete series of siloxane-based side chain liquid crystalline copolymers (with two mesogenic side groups of similar structure but having flexible spacer groups of different length) and the effect of the copolymer chemical structure on thermal properties and dielectric motion is presented. The qualitative behaviour observed in the spectra of two of the polymers with regard to their change in peak height of the loss relaxation with temperature is discussed in terms of influences on relaxation strength and alignment with temperature. The speed of motion of the mesogens is compared between different members of the copolymer series by normalising the experimental temperature by either the glass transition temperature of the material or its clearing point (liquid crystalline to isotropic temperature). The effect of an increased content of the side group with a very long flexible spacer is to increase the frequency of motion due to greater mesogen mobility if the data is compared at temperatures normalised by the clearing point. However, if the temperature is normalised by the glass transition, the peak frequencies of motion are much closer (although the material with a longer spacer group still moves slightly faster), indicating the important role the motion of the polymer backbone plays in determining the mesogenic mobility. The activation energy of motion is found to be less for the copolymer with the longer spacer length and consequently in the copolymers with greater content of the long spacer unit side chain.

Liquid crystalline block copolymers by sequential cationic or promoted cationic and free‐radical polymerizations

AbstractThe scope for the study of the synthesis and properties of liquid crystalline (LC) block copolymers is briefly outlined. While there are many approaches to the synthesis of LC block copolymers, the use of azo macroinitiators is very versatile and allows one to produce diverse block copolymer architectures. Azo macroinitiators are prepared by cationic or promoted cationic polymerization of tetrahydrofuran (1) or cyclohexene oxide (2), and are then used to initiate the free‐radical polymerization of various methacrylates 3,4 or acrylates 5–9 containing mesogenic azobenzene or biphenyl units thereby yielding block copolymers. The AB or ABA block copolymers are microphase‐separated and form smectic and/or nematic mesophases similar to the respective LC homopolymers.

Synthesis of Side-Chain Liquid Crystalline Homopolymers and Block Copolymers with Well-Defined Structures by Living Anionic Polymerization and Their Thermotropic Phase Behavior

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTSynthesis of Side-Chain Liquid Crystalline Homopolymers and Block Copolymers with Well-Defined Structures by Living Anionic Polymerization and Their Thermotropic Phase BehaviorMasayuki Yamada, Akira Hirao, Seiichi Nakahama, Tsukasa Iguchi, and Junji WatanabeCite this: Macromolecules 1995, 28, 1, 50–58Publication Date (Print):January 1, 1995Publication History Published online1 May 2002Published inissue 1 January 1995https://doi.org/10.1021/ma00105a006RIGHTS & PERMISSIONSArticle Views722Altmetric-Citations93LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (5 MB) Get e-Alerts Get e-Alerts

Effects of non‐mesogenic comonomers on the phase behaviour, the structure and the miscibility of side chain liquid‐crystalline polymers

AbstractThe phase behaviour of methacrylic side chain liquid‐crystalline (LC) copolymers, with a spacer‐decoupled mesogen in one comonomer and a methyl (MMA) or stearyla (SMA) substituent in the other comonomer, was studied. The mesogen is of the phenyl benzoate type and has a methoxy end group. The LC homopolymer (PLC) has a smectic and a nematic phase. The comonomers MMA and SMA destabilize the LC phase. This effect is compared to the destabilisation caused by end groups in oligomers of PLC. The SMA side chains crystallize so that the SMA copolymers assume a smectic‐crystalline bilayer structure. Finally, it is shown that the order of the copolymers affects their mutual miscibility.