Chiral Side Groups Research Articles

Photosensitive chiral polyisocyanates

AbstractThe dynamic polyisocyanate helix amplifies changes in the conformation of its side groups. Thereby it acts like a fast responding switch for optical properties. Here we show how the photoisomerization of chiral azo side groups can be used to induce large changes of chirooptical properties. These changes can be detected by CD measurements or by ORD measurements far from the absorption region. Large changes of the optical rotation can be induced reversibly in a multicycle process.

Correlation between the Isomerization of Side Groups and the Helical Main Chain in Chiral Polyisocyanates

In polyisocyanates with chiral azo chromophores a change of the helical conformation can be triggered photochemically. In this investigation we studied the correlation between the isomerization of the main chain and the photoisomerizable side groups by CD measurements. A few minutes of irradiation are enough to reach a new helix equilibrium of the polymer chain. Also during slow thermal back-relaxation, the helical conformation of the polymer chain follows the isomerization of the side groups reversibly. The relation between the ratio of cis and trans isomer and the preference for one helical conformation can be linear or nonlinear. For low concentrations/inductions of the chiral side groups a linear relation is found. For higher concentrations/inductions the stronger inducting species dictates the helical conformation in accordance with the “sergeants and soldiers” principle.

Optical suppression of ferroelectricity in polysiloxane copolymers with chiral and photochromic side groups

The ferroelectricity of surface-stabilized aligned films of polysiloxane copolymers containing chiral esters and photochromic azobenzene moieties within the side groups is suppressed on UV irradiation and is rebuilt on visible irradiation. The liquid crystalline polymer (Sc* 64 SA 80 i) shows ferroelectric behavior below 64°C. The photoinduced modification of supramolecular order and the corresponding changes in its dynamics are studied by polarized UV/vis spectroscopy and broad band dielectric spectroscopy (10−2–105 Hz). The dielectric measurements show that UV irradiation causes a loss of ferroelectricity within an interval of 10 K below the phase transition temperature. The photochemical change of intermolecular interactions results in the disappearance of the Sc* phase and the Goldstone mode. Polarized absorption spectroscopy indicates the degree of order, the orientational direction as well as the establishment of different steady states of the EZ photoisomerization by UV and visible exposure. The photoisomerization of only a small amount of azobenzene moieties causes a decrease of the phase transition temperature between the ferroelectric Sc* and the nonferroelectric SA mesophase. This is connected with a reversible modification of the degree of order and of the director orientation characteristic for the Sc* and SA phases. Thus, the photoinduced modification of the intermolecular interactions results in an opto-dielectric effect. © 1998 John Wiley & Sons, Ltd.

Methacrylate networks containing chiral calamitic liquid crystalline side groups

A one-step copolymerization of ferroelectric methacrylate monomers leading to networks is presented. Oriented networks are obtained and electro-optical investigations are described. Smectic C * and another smectic phase are found in slightly crosslinked networks. For higher crosslinking densities, only the high temperature smectic C * phase was found. Electro-optical measurements were performed on the networks, and significant changes in the ferroelectrical properties were found. For crosslinking densities higher than 0.5 mol-%, switching times increased dramatically and the spontaneous polarization decreased. Networks with crosslinking densities of 2 mol-% did not exhibit ferroelectric properties.

Methacrylate networks containing chiral calamitic liquid crystalline side groups

Methacrylate networks containing chiral calamitic liquid crystalline side groups

Methacrylate networks containing chiral calamitic liquid crystalline side groups

Methacrylate networks containing chiral calamitic liquid crystalline side groups

Photo-optical properties of new combined chiral photochromic liquid crystalline copolymers

For the first time, a series of cholesteric copolymers containing combined chiral photochromic side groups has been synthesized and the phase behaviour and optical properties of the copolymers have been characterized. Specific features of the photochemical and photo-optical behaviour of such systems were studied, and the quantum yields of the photo-induced process in solution and in the condensed state of the cholesteric copolymers were calculated. The selective light reflection wavelength was found to be controlled by the UV radiation. The synthesized polymers were shown to be promising candidates for colour data recording.

A TGB-Like, Poorly Birefringent Smectic Phase of Side Chain Polymers

Abstract An almost optically isotropic smectic phase has been observed for some side chain polymers having main chains of different nature (homo-and copolymethacrylates, polysiloxanes) but the same chiral mesogenic side group. Structure and optical properties of the mesophase are investigated.

Thermal and ferroelectric properties of two series of coloured chiral liquid crystalline side group copolymers

AbstractTwo series of liquid crystalline side group copolymethacrylates were synthesized and their thermal and ferroelectric properties determined. All copolymers contain the same azobenzene mesogen spaced from the backbone by a heptamethylene sequence but different chiral co‐compounds were used. The samples show either a monolayer or a bilayer smectic C* phase but only four polymers with a low content of the azo‐dye could be switched ferroelectrically. The formation of the smectic C* phase of some samples was found to be hindered. In order to study this phenomenon as a function of the molecular weight one copolymer was fractionated.

Piezoelectric and pyroelectric properties of new polysiloxane smectic C ∗ elastomers

We investigated the pyroelectric and piezoelectric effects of new smectic C ∗ liquid crystalline elastomers. The materials are made up of a flexible polysiloxane backbone bearing chiral mesogenic side groups and are cross-linked via alkylene chains. The polar structure of the mesophase is evidenced by the observation of piezoelectric and pyroelectric effects. Integration of the pyroelectric coefficient over the whole smectic C ∗ stability range allows the determination of the spontaneous polarization ( P S = 3–6 nC/cm 2). Due to the rubber elasticity, these materials exhibit a high piezoelectric response. The piezosignal at room temperature does not vanish after annealing at temperatures even much higher than the Curie point. The piezoelectric coefficient d 31 ranges from 0.5 pC/N for non-poled samples to 2.5 pC/N after application of a poling field.

Electrooptical investigation on the three switching states of a chiral smectic side group polymer

Electrooptical properties of a polyacrylate with 1,3-dioxolane-4-carboxylic acid as chiral building block terminally attached to phenylpyridine mesogenic moiety and linked via a C11 spacer were studied. Results showed that the formation of 3 switching states for the polymer occurred upon conformational interactions between the side groups and the main chain.

Highly conjugated, substituted polyacetylenes via the ring‐opening metathesis polymerization of substituted cyclooctatetraenes

Soluble polyacetylenes with high conjugation length and high molecular weight are a goal of polymer scientists. The ring‐opening metathesis polymerization of substituted cyclooctatetraenes (COT) to form soluble substituted polyacetylenes which display iodine doped conductivities in the range 0.1 to 50 S/cm are reported. The solubility is imparted by the alkyl groups which occupy, on average, every eighth carbon atom of the polymer backbone.

Chiral Smectic Liquid Crystalline Polymers

Abstract The synthesis of side-chain liquid crystalline polysiloxanes, copolysiloxanes and of tetracyclosiloxanes containing chiral mesogenic side groups, i.e, trans- 2[p-(l-undecanyl-ll-oxy)phenyl]-5-[(p-2(S)- methyl-1-butoxy)pheny1]-1,3-dioxane, trans- 2-[p-(2(S)-methyl-1-butoxy)phenyl]-5-(11- undecalenyl)-1,3-dioxane and 2-[4-(2(S)- methyl-butoxy)-phenyl]-5-(w-alkl)-l,3,2- dioxaborlnane with alkyl being undecanyl, octyl, and hexyl is discussed. Differential scanning calorimetry and thermal optical polarization microscopy revealed chiral smectic mesomorphism for polymers containing eleven methylene units in the flexible spacer. The polymers containing undecanyl spacers present a chiral smectic C mesophase. The polysiloxanes with hexyl spacers exhibit a chiral nematic mesophase.

Single Crystals from Optically Active Diacetylenes and Polydiacetylenes

AbstractDiacetylene monomers with chiral side groups have been synthetized. The monomer crystals polymerize upon irradiation or thermal annealing. The thermal polymerization was studied and the potential use of the resulting polymer crystals as optical devices was discussed. A characterization of the monomers and one polymer in solution with regard to specific rotation was obtained.

New chiral polysiloxanes prepared from derivatives of (+)- or (-)-2-phenyl-3-butehoic acid, (r)-l-hepten-3-ol and (r)-l-cyclohexyl-2-propen-1-ol

A series of new polysiloxanes containing chiral side groups has been prepared. These polymers were prepared by hydrosilylating chiral alkene derivatives onto polyhydromethylsiloxane. The alkene derivatives were prepared from (+) or (-)-2-phenyl-3-butenoic acid, (R)-1-hepten-3-ol and (R)-1-cyclohexyl-2-propen-1-ol. Polysiloxanes containing racemic substituents were also prepared fron derivatives of racemic 3-buten-2-ol. The polysiloxanes containing biphenyl carboxylate derivatives (11a–13a) had liquid crystalline properties. These polymers were prepared for use as stationary phases for capillary gas and supercritical fluid chromatography.