Benzoate Side Groups Research Articles

Molecularly Oriented Liquid Crystalline Polymer Films Based on Axis-Selective Photo-Fries Rearrangement

Four kinds of liquid crystalline polymers (LCPs) with phenyl benzoate side groups were synthesized and their photoinduced reorientation behavior was investigated using linearly polarized (LP) UV light based on the axis-selective photo-Fries rearrangement and thermally induced self-organization of the mesogenic side groups of the materials. Due to different effect of the axis-selectively photoreacted side groups, reorientation direction and its performance depended on the chemical structure of the side groups. Both alignment ability and the molecular rotation of the photoreacted side groups played an important role in the reorientation behavior.

Photoinduced Reorientation of a Liquid Crystalline Polymer with Phenyl Benzoate Mesogenic Side Groups on the Basis of an Axis-Selective Photo-Fries Rearrangement

Many types of photoreactive polymers have been investigated to regulate their molecularly orientated structures for polarization-controlled optical and display applications. Herein, we demonstrate the axis-selective photoreaction of thin films and their molecular reorientation behaviors using four types liquid crystalline poly(meth)acrylates with phenyl benzoate side groups and linearly polarized (LP) 248 nm light. These simple liquid crystalline polymers (LCPs) exhibit sufficient photoinduced molecular reorientations. Photoinduced molecular reorientation based on an axis-selective photo-Fries rearrangement is simultaneously generated with an in-plane order parameter (S) up to 0.33 when the irradiation temperature is in the lower part of the LC temperature range of the material, but multidomain formation of the mesogenic groups inhibits reorientation. To prevent thermally generated multidomain formation, an axis-selective photoreaction of an amorphous film followed by thermally generated self-organization...

Axis-Selective Photo-Fries Rearrangement and Photoinduced Molecular Reorientation in Liquid Crystalline Polymer Films

The thermally enhanced photoinduced molecular reorientation based on an axis-selective photo-Fries rearrangement was explored for the first time using three liquid crystalline polymethacrylates with 4-(2′-(4″-methoxyphenyl)ethynyl)phenyl benzoate side groups (1a), 4-methoxybiphenyl benzoate side groups (1b), and 4-methoxyphenyl benzoate side groups (1c). All the polymeric films exhibited an axis-selective formation of the photo-Fries products at the phenyl benzoate derivatives side groups by irradiating with linearly polarized (LP) UV light. Annealing the films in the liquid crystalline temperature range of the material greatly amplified the photoinduced small optical anisotropy of the irradiated films. For 1a and 1b, the photoinduced small anisotropy was amplified in a direction parallel to the polarization (E) of LPUV light and the reorientational order (S) was greater than 0.7. In contrast, the orientation direction was perpendicular to E for 1c (S ∼ 0.57). Finally, a simple double-exposure method usin...

Mesophase structure of low-wetting liquid crystalline polyacrylates with new perfluoroalkyl benzoate side groups

The synthesis, thermal behavior, bulk microstructure, and wettability of new polyacrylates carrying spaced 4-perfluorohexylpropyl benzoate and 4-perfluorooctylpropyl benzoate units in the side groups were investigated. X-ray diffraction analysis proved the formation of different smectic mesophases (SmI 2 , SmF 2 , and SmC 2 ) and the evolution of their structures and lattice parameters with temperature. The mesophase polymorphic behavior depended on the length of the perfluorinated chain segment in the repeat unit. The electron density profiles along the smectic layer normal were drawn and provided a deeper insight into the packing of the side chains in a tilted, double layer structure. Thin polymer films were cast from solution, and their low wettability was established by measurements of contact angles with different probing liquids. We suggest that the hydrophobicity and lipophobicity of the films are enhanced by the mesophase surface structure which is mediated by the high-order, mesophase bulk structure.

Photoinduced reorientation processes in thin films of photochromic LC polymers on substrates with a photocontrollable command surface

Orientation and reorientation processes that occur in nematic and cholesteric LC polymer systems under irradiation with plane-polarized light are studied. A copolyacrylate containing phenyl benzoate and azobenzene side groups is synthesized as a nematic polymer; the cholesteric mixture is prepared via doping of the nematic copolymer with the chiral dopant, the derivative of D-isosorbide. Thin layers of the azobenzene-containing photoorientant SD-1 are first used as orienting substrates for polymer liquid crystals. Thin layers of the copolymer and of the mixture are spin-coated on the substrate after irradiation of the photoorientant layer with polarized light. It is shown that after annealing phenyl benzoate and azobenzene side groups of the nematic copolymer orient strictly along the direction of orientation of surface molecules, whereas in the case of the cholesteric mixture, a partial formation of the helical structure is observed. It is demonstrated that all the systems under examination can experience the repeated cyclic reorientation of the cooperative type under irradiation and subsequent annealing of the films.

Chiral liquid-crystalline copolyacrylates with biphenyl and phenyl benzoate side groups

The phase behavior and structure of liquid-crystalline phases of three series of copolymers with mesogenic units belonging to the families of biphenyls and phenyl benzoates have been studied, with the former mesogenic units containing a chiral center in a flexible spacer. A variation in the isotropization temperature as a function of composition is well described by the additivity rule, whereas the tilt angle of mesogenic groups in smectic layers changes nonlinearly. This angle decreases beginning from homopolymers and attains the minimum value for the copolymers of the equimolar composition, which show the highest ferroelectric activity among the polymer systems under study.

New liquid-crystalline homo-and copolymers with phenyl benzoate side groups and a chiral center in a flexible spacer

The phase behavior and structure of liquid-crystalline homo-and copolymers based on structurally isomeric units belonging to the family of phenyl benzoates that differ in orientation of an ester link situated between benzene rings have been studied with X-ray diffraction, scanning calorimetry, and polarization optical microscopy. The orientation of this link in the monomer unit affects the temperature of phase transition, the type of the smectic phase, and the packing mode of side mesogenic groups in smectic layers of homopolymers. When monomer units commensurable with the monomer units of the basic component in terms of geometry but not identical to them in terms of smectogenity are randomly incorporated into macromolecules of the LC polymer, the resulting copolymer is characterized by layered packing not typical of either of the components.

Synthesis and characterization of novel side-chain liquid crystalline polycarbonates, 5. Mesophase characterization of side-chain liquid crystalline polycarbonates with tails of different lengths

The mesomorphic properties and thermal stability of side-chain LC polycarbonates with alkoxyphenyl benzoate side groups having a short spacer and alkoxy tails ranging from 1 to 8 carbon atoms were studied by DSC, X-ray diffraction and polarized light optical microscopy. All polymers have a smectic A structure. Mesogens having short tails organize preferably in a monolayer structure, and mesogens having long tails in a double layer structure. A sharp increase in the clearing temperatures and enthalpies as a function of tail length was observed. No clear relation between the tail length and the glass transition temperature was found. Both the Tg and the clearing temperature show a strong dependence on the molecular weight. Up to about Mw = 20000 a rapid increase in phase transition temperatures with increasing molecular weight was observed, eventually levelling off to a constant maximum value. The LC polycarbonates were found to be thermally stable up to about 200°C. At higher temperatures, random chain scission, resulting in a rapid decrease in molecular weight, and unzipping, resulting in the formation of a five-membered cyclic carbonate, are the main initial degradation mechanisms. The degraded polymers have lower transition temperatures than the original ones.

Effect of lateral substituents on the mesomorphic properties of side‐chain liquid crystalline polysiloxanes containing 4‐[(S)‐2‐methyl‐1‐butoxy]phenyl 4‐(alkenyloxy)benzoate side groups

Effect of lateral substituents on the mesomorphic properties of side‐chain liquid crystalline polysiloxanes containing 4‐[(S)‐2‐methyl‐1‐butoxy]phenyl 4‐(alkenyloxy)benzoate side groups

Effect of lateral substituents on the mesomorphic properties of side-chain liquid crystalline polysiloxanes containing 4-[(S)-2-methyl-1-butoxy]phenyl 4-(alkenyloxy)benzoate side groups

The synthesis of side-chain liquid crystalline polysiloxanes containing ei- ther 4-((S)-2-methyl-1-butoxy)phenyl 4-(alkenyloxy)benzoate or laterally fluoro-, chloro-, bromo-, and methoxy-substituted 4-((S)-2-methyl-1-butoxy)phenyl 4-(alkenyl- oxy)benzoate mesogenic side groups is presented. The mesomorphic properties of the synthesized polymers have been characterized by optical polarizing microscopy, differ- ential scanning calorimetry, and X-ray diffraction measurements. The effects of spacer length and lateral substituent on the mesomorphic properties of the obtained polymers are examined. The five polymers which contain three methylene units in the spacers show no mesophase, while the five polymers which contain eleven methylene units in the spacer display smectic mesomorphism. Among the other fifteen polymers which contain respectively four, five, or six methylene units in the spacers, those with small fluoro and chloro substituents reveal respectively an SA phase, while those with bulky bromo and methoxy substituents show no liquid crystalline behavior. The experimental results demonstrate that introducing a bulky lateral substituent into the mesogenic core of a polymer depresses the tendency to form a mesophase. Furthermore, the tech- nique of thermally stimulated current has been used to study the dipolar relaxation mechanisms in a side-chain liquid crystalline polysiloxane. q 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 2793-2800, 1997

Synthesis of Liquid Crystalline Polysiloxanes Containing Naphthalene-Based Mesogens and Chiral Side Chains

The synthesis and characterization of side-chain liquid crystalline polysiloxanes containing (2S)-2-chloro-4-methylpentyl 4-[(6-alkanyloxynaphthyl-2-yl)carbonyloxy]benzoate and (2S, 3S)-2-chloro-3-methylpemtyl 4-[(6-alkanyloxynaphthyl-2yl)carbonyloxy]benzoate side groups are presented. All of the obtained polymers reveal respectively an enantiotropic smectic A phase. The phase transition temperatures of the obtained polymers depend on the spacer length. As the spacer length increases the glass transition temperature decreases while the isotropization temperature increases. The thermal stability of the obtained polymers increases as the spacer length increases. All of the obtained polymers present no chiral smectic C phase. The result seems to demonstrate that incorporation of a naphthalene ring in the mesogenic core decreases the tendency to form a chiral smectic C phase.

Dielectric study of ferroelectric side-chain liquid crystalline polysiloxanes with broad temperature ranges of the chiral smectic c phase 1. Structure dependence of dielectric relaxation

The dielectric behavior of a series of ferroelectric side-chain liquid crystalline polysiloxanes containing 1–3 oligooxyethylene units as spacers, and 4-(S)-2-methyl-1-butyl[[[(4-hydroxy-biphenyl-4′-yl)]carbonyl]oxy] benzoate or 4-(S)-2-methyl-1-butyl[[(4-hydroxy-biphenyl-4′-yl)carbonyl]oxy]-3-fluoro benzoate side groups was studied by broadband dielectric spectroscopy. The increase of the spacer length, and incorporation of a strong dipole moment fluoro-substituent into the mesogenic group, resulted in a decrease of the relaxation activation energy and an increase in the intensity of the relaxation. Moreover, the relaxation peak of the Goldstone mode has only been observed for the FLCP with a lateral fluoro-substituent. The relationship between the thermal dynamic behavior and chemical structure is discussed in detail. Furthermore, analysis of the dielectric relaxation behavior of these FLCPs showed that the molecular relaxations could be described by the Cole-Cole equation. © 1996 John Wiley & Sons, Inc.

An infrared spectroscopic study of photo-induced reorientation in dye containing liquid-crystalline polymers

Abstract Infrared spectroscopy is used to study simultaneously the orientational behaviour of different segments of dye containing liquid-crystalline side group copolymers in sandwich type films of about 2 μm thickness. Under continuous irradiation with polarized light above and below T g of the polymers both azobenzene and phenyl benzoate side groups reorient preferentially normal to the film plane leading to a strongly biaxial orientation distribution. The analysis of the kinetics reveals that the reorientation is essentially a mono-exponential process with an additional faster process only found for the azobenzene dye and assigned to the initial trans to cis isomerization step. Investigation of an isotropic copolymer system containing azobenzene in the side groups shows that an anisotropy can be induced through irradiation with polarized light that is strongly dependent on temperature.

Synthesis and mesomorphic behavior of poly(methylsiloxane)s containing trans-cyclohexane-based mesogenic side groups

The synthesis and characterization of poly(methylsiloxane)s containing either trans-4-methylcyclohexyl 4-alkenyloxybenzoate or trans-4-methylcyclohexyl 4-alkenyloxybiphenyl-4-carboxylate mesogenic side groups are presented. All polymers except two which contain either trans-4-methylcyclohexyl 4-allyloxybenzoate or trans-methylcyclohexyl 4-(5-hexene-1-yloxy)benzoate side groups, display liquid crystalline phases. The dependence of phase trasition temperature on the spacer length and the mesogenic core length as well as the thermal stalility of the prepared liquid crystalline polymers (LCPs) are described.

Ferroelectric liquid-crystalline polymethacrylates

Abstract The ferroelectricity in the chiral smectic C phase of two comb-shaped liquid-crystalline polymers with a methacrylic main chain, phenyl benzoate side groups and chiral fragments of different types have been studied using the pulse pyroelectric method. The spontaneous polarization, pyroelectric coefficient and some relaxation times associated with two different molecular motions have been evaluated.

High-ordered smectic phases and polymorphic transformations in comb-like liquid crystal polymers

The structural ordering of high-ordered smectic phases in comb-liquid crystalline polymers having main chains (backbones) of different nature (acrylate and methacrylate) but identical phenyl benzoate side groups and also the structural transitions between than are studied. The correlational lengths along the layer plane and normal to it are evaluated from small and wide angle X-ray scattering data, and it is concluded that low and high temperature smectic phases of the acrylate polymer can be assigned to type B and A smactic types respectively. The polymorphic transformations of the methacrylate polymer follow the scheme: F smectic-C smectic-A smectric isotropic liquid.

Dielectric relaxation in two liquid crystalline polyacrylates under high hydrostatic pressure

For two polyacrylates with p-cyano-phenyl benzoate side groups and different spacer lengths the dielectric relaxation was measured in the nematic and isotropic phase at pressures up to 5000 bar. The relaxation of the cyano groups was observed as a separate relaxation process; it seems to be closely correlated with the glass relaxation. The pressure dependence of the glass temperature and of the clearing temperature could be derived from the experiments.

Structure of Polymers With Phenyl Benzoate Side Groups By X-Ray Evidence

Abstract Structure of four polymers were studied: poly-p-methacryloyloxy phenyl esters of p-n-hexyloxy benzoic acid (PMB-6), p-n-heptyl benzoic acid (PMH-7) and p-n-heptyl - trans-cyclohexane carboxylyc acid (PMC-7) and poly-p-n-hexyloxy phenyl ester of pmethacryloyloxy benzoic acid (PM-06). Diffractions parameters and polymer organization were discussed in terms of both crystallinity and paracrystal. The structural organization of PMB-6, PMH-7 and PM-06 was interpreted on the basis of block model. Structure of PMC-7 assumed to be organized similar to cybotactic nematics.

Thermal effects on liquid‐crystalline order in polymers with mesogenic side groups

AbstractX‐ray studies on polymers with phenyl benzoate side groups separated from the main chain by spacer groups of various lengths have been performed. It was found that the dimensions of liquid‐crystalline regions are 15–20 nm, and they contain four to six close‐packed layers. Thermal changes in x‐ray scattering are associated with the variation of sizes and concentration of liquid‐crystalline regions determined by the mobility of the main chain.

Influence of length of the aliphatic group on the character of liquid-crystalline orderliness in polymers with phenyl benzoate side groups

An X-ray investigation has been made of a number of polymers with side mesogenic groups and different degrees of bonding of side groups and the main chain. Models of layered packing are proposed for the members of the series studied. It was found that with increase in the length of the spacer groups by more than 1·2 nm separate packing of the chains and side mesogenic groups takes place. The corresponding polymer is crystalline at room temperature. On melting this polymer the smectic B-phase forms. Rise in temperature leads to increase in the concentration and size of the regions of liquid crystalline orderliness in polymers with strong bonding of the main chains and side groups and worsening of the orderliness in the polymer with independent packing of the main chains and side groups.