Synthesis and X-ray diffraction of ferroelectric liquid crystalline polysiloxanes containing 4′-(2-chloro-3-methylpentanoyloxy)-4-alkanyloxybiphenyl side groups

Summary The synthesis and characterization of side-chain liquid crystalline polysiloxanes containing (2S,3S)-4-(2-chloro-3-methylpentanoyloxy)-4-alkanyloxybiphenyl side groups are presented. All the obtained polymers exhibit smectic mesomorphism. Those polymers containing a spacer length longer than 8 methylene units reveal respectively enantiotropic S_A, S _* ^C and S_B phases. The result demonstrates that the tendency toward the S _* ^C phase increases with increasing the spacer length.     

Infrared-spectroscopic investigations of molecular order in liquid crystalline side chain polymers

Summary Infrared dichroism was used to determine the order parameters of liquid crystalline side chain polymers. By this the order parameters of the main chain, of the spacer and of the mesogenic group can be obtained separately. Therefore spectra of two liquid crystalline polyacrylates were recorded with polarized light at different temperatures. In a poly(acrylate) with 6 CH₂ groups in the spacer a high order parameter was found not only for the mesogenic group, but also for the spacer and the main chain. The orientation of the poly(acrylate) with a spacer of only 2 CH₂ groups is lower due to the stronger interaction of main chain and mesogenic group.     

Investigation of liquid crystalline and photocrosslinkable poly[4‐x‐phenyl‐4′‐(m‐methacryloyloxyalkyloxy)cinnamate]s

Three series of liquid‐crystalline‐cum‐photocrosslinkable polymers were synthesized from 4‐x‐phenyl‐4′‐(m‐methacryloyloxyalkyloxy)cinnamates (x = ? H, ? OCH₃ and ? CN; m = 6, 8 and 10) by free radical solution polymerization using azobisisobutyronitrile as an initiator in tetrahydrofuran at 60 °C. All the monomers and polymers were characterized using intrinsic viscosity, and FTIR, ¹H NMR and ¹³C NMR spectroscopy. The liquid crystalline behavior of these polymers was examined using a hot stage optical polarizing microscope. All the polymers exhibited liquid crystalline behavior. The hexamethylene spacer‐containing polymers exhibited grainy textures; in contrast, the octamethylene and decamethylene spacer‐containing polymers showed nematic textures. Differential scanning calorimetry data confirmed the liquid crystalline property of the polymers. Thermogravimetric analysis revealed that all the polymers were stable between 236 and 344 °C in nitrogen atmosphere and underwent degradation thereafter. As the methylene chain length increases in the polymer side‐chain, the thermal stability and char yield of the polymers decrease. The photocrosslinking property of the polymers was investigated using the technique of exposing the polymer solution to UV light and using UV spectroscopy. The crosslinking reaction proceeds via 2π–2π cycloaddition reactions of the ? CH?CH? of the pendant cinnamate ester. The polymers containing electron‐releasing substituents (? OCH₃) showed faster crosslinking than the unsubstituted polymers and those containing electron‐withdrawing substituents (? CN). Copyright © 2007 Society of Chemical Industry     

Synthesis and characterization of liquid crystalline polymers containing aromatic ester mesogen and a nonmesogenic ferrocene unit in the spacer

A new series of liquid crystalline polymers containing aromatic triad ester mesogen and 1,1′‐disubstituted ferrocene as a nonmesogenic unit along with polymethylene spacer was synthesized. The polymer was synthesized by a room temperature polycondensation reaction between bis(4‐chloroformyl phenyloxy alkyl ferrocene dicarboxylate) and quinol. The alkyl groups have been varied by an even number of methylene groups with a range from two to ten groups. All the polymers were found to possess liquid crystalline properties. The identification of the mesophase is more transparent with an increase in the spacer. The thermal characteristics were studied using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The results reveal that the thermal stability of the polymers was decreased with increasing spacer length. The T_g, T_m, and T_i of the polymers decreased with increasing methylene groups. The incorporation of the ferrocene moiety also has a considerable effect on the glass transition temperature. The char yield of the polymer decreases with an increasing methylene chain length. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3494–3501, 2002     

Synthesis of side chain liquid crystalline poly(vinyl ether)s containing 2,2′-dimethyl-4-methoxy-4′-[undecanyloxy-4-benzoyl]ester biphenyl side group

The synthesis and characterization of 2,2′-dimethyl-4-methoxy-[(11-vinyloxy)undecanyloxy-4-benzoyl]ester biphenyl (7), its cationic polymerization to side chain liquid crystalline polymers with relative number average degrees of polymerization (DP) of 2, 8 and 19 are presented. The mesogenic vinyl ether monomer displays an inverse monotropic nematic phase. The oligomers with DP = 2 and DP = 8 display an enantiotropic nematic, while the polymer with DP = 19 exhibits an inverse monotropic smectic A and an enantiotropic nematic phase. All the liquid crystalline polymers display only liquid crystalline phases and do not undergo side chain crystallization even though eleven methylenic units are used as the flexible spacer. Received: 28 February 1997/Accepted: 23 May 1997     

Synthesis and characterization of optically active liquid crystalline polyacrylates containing mesogenic phenylbenzoate groups

A series of novel side chain liquid crystalline polyacrylates with pendant chiral groups were synthesized. It was found that monomers with electron releasing -OC₄H₉ terminal groups seem beneficial for the formation of liquid crystalline phases. Copolymerization of the monomers was carried out and the physical properties of the copolymers were investigated. All synthesized polymers revealed liquid crystalline phases and appeared highly thermally stable with decomposition temperatures (T_d) at 10% weight loss greater than 384 °C and about 50% weight loss occurred beyond 442 °C under nitrogen atmosphere. Two miscible chiral compounds were also synthesized and used as chiral dopants to induce cholesteric liquid crystalline phases of polymers. Liquid crystalline phases of the polymers were investigated using DSC and XRD, and confirmed with POM technique. The optical properties of the induced cholesteric liquid crystalline polymers were investigated using UV-vis spectrometer. The appearance and the color variation of the polymer films before and after UV irradiation were also investigated. Typical helical morphology of the cholesteric liquid crystalline film was analyzed by SEM technique.     

Synthesis and characterization of chiral smectic side‐chain liquid crystalline polysiloxanes and ionomers containing sulfonic acid groups

The synthesis of new chiral smectic A (S_A) side‐chain liquid crystalline polysiloxanes (LCPs) and ionomers (LCIs) containing 4‐allyloxy‐benzoyl‐4‐(S‐2‐ethylhexanoyl) p‐benzenediol bisate (ABB) as mesogenic units and 4‐[[4‐(2‐propenyloxy)phenyl]azo]benzenesulfonic acid (AABS) as nonmesogenic units is presented. The chemical structures of the monomers and polymers are confirmed by FTIR spectroscopy or ¹H–NMR. Differential scanning calorimetry (DSC), optical polarizing microscopy, and X‐ray diffraction measurements reveal that all the polymers P_I–P_IV and ionomers P_V–P_VI exhibit S_A texture. The results seem to demonstrate that the tendency toward the S_A‐phase region increases with increasing sulfonic acid concentration, and the thermal stability of the S_A phase is determined by the flexibility of the polymer backbones and the interactions of sulfonic acid groups. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2335–2340, 2001     

Synthesis and characterization of side‐chain liquid‐crystalline polyacrylates containing azobenzene moieties

Syntheses of novel liquid‐crystalline polymers containing azobenzene moieties were performed by a convenient route with an acrylate backbone. The azobenzenes were key intermediates of the monomers, and side‐chain liquid‐crystalline polymers were prepared, that is, poly[α‐{4‐[(4‐acetylphenyl)azo]phenoxy}alkyloxy]acrylates, for which the spacer length was 3 or 11 methylene units. In addition, poly[3‐{4‐[(3,5‐dimethylphenyl)azo]phenoxy}propyloxy]acrylate was prepared with a spacer length of 3 methylene units. The structures of the precursors, monomers, and polymers were characterized with Fourier transform infrared, ¹H‐NMR, and ¹³C‐NMR techniques. The polymers were obtained by conventional free‐radical polymerization with 2,2′‐azobisisobutyronitrile as an initiator. The phase‐transition temperatures of the polymers were studied with differential scanning calorimetry, and the phase structures were evaluated with a polarizing optical microscopy technique. The results showed that two of the monomers and their corresponding polymers exhibited nematic liquid‐crystalline behavior, and one of the monomers and its corresponding polymer showed smectic liquid‐crystalline behavior. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2653–2661, 2002     

Novel thermotropic liquid crystalline polyphosphonates

Main chain liquid crystalline polyphosphonates containing semi-flexible phenylester mesogen with even number of methylene spacers (2-10) have been synthesized. The monomers and polymers were characterized by IR, ¹H, ¹³C and ³¹P NMR spectroscopy. The spectral details are in accordance with the structures. All the polymers were exhibited liquid crystalline property in the Hot stage optical polarized microscope (HOPM). DSC thermal analysis confirms the mesophase formation for all the polymers. The grain size of the liquid crystalline mesophase is increasing with increasing methylene chain. T_g, T_m and T_i of the polymers decreased with increase in spacer length. The T_g of these phosphorus-containing polymers is much lower than that of non-phosphorus polymers containing triad ester mesogens. Energy minimized structures for the molecules which mimic the polymer chain suggests that the reduction in T_g may be due to entanglement raised by incorporation of phosphorus heterogeneity.     

Polymers with terminally cyanobiphenyl-substituted side chains

Summary Two acrylate side chain polymers in which the mesogenic moiety is a 4-cyano-biphenyl-4-yl group have been synthesized and characterized by d.s.c., optical microscopy and X-ray diffraction. If the mesogenic moiety is linked to the polymer backbone by a -O-CO-(CH₂)-₅ group, the resultant polymer is nematic. For a -O-(CH₂)-₆ group, the unusual NS_AN_re sequence is observed. X-ray diffraction has shown that the S_A phase has a partially bilayer structure : the molecules are arranged in an antiparallel, overlapping interdigitated structure with a layer spacing of about 1.4 times the length of the side chains. Monolayer fluctuations are also observed in this S_A phase.     

Synthesis, characterization and liquid crystalline behavior of poly(monomethyl itaconate)s with new pendant cholesterol moieties

In order to investigate the effects of cholesteryl pendant groups on inducing liquid crystalline (LC) phase formation, a new series of cholesteryl-modified poly(monomethyl itaconate) (PMMI-Chol-C₆) have been synthesized from poly(monomethyl itaconate) (PMMI) and 6-(cholesteryloxycarbonyloxy) hexanol (Chol-C₆) with different degrees of substitution (DS_chol). All the obtained compounds were characterized by conventional spectroscopic methods. The DS_chol values of the modified PMMI were obtained by ¹H NMR spectroscopy and conductometric titration. The inherent viscosities of polymers were determined by an Ubbelohde viscometer at 35 °C in DMSO solution. The resulting products of modified PMMA polymers were soluble in a variety of organic solvents, and the solubility improved by increasing the DS_chol. Thermal behavior and optical properties of Chol-C₆ and PMMI-Chol-C₆ polymers were investigated by thermal gravimetric analysis, differential scanning calorimetry and hot-stage polarizing optical microscopy. The glass transitions of the modified PMMI polymers occurred at lower temperatures than the parent PMMI. It was found that among the synthesized polymers with different molar ratios of the substitution, only the PMMI-Chol-C₆ (1) polymer bearing 77 mol% of the side chains, with reduced melting point and increased thermal stability, formed thermotropic liquid crystalline smectic phases. This polymer exhibited wider mesophase than the mesogenic side chain Chol-C₆ and amorphous morphology. The results of a comparative study on the structure and properties of the polymers showed that liquid crystalline polymers may be achieved through the attachment of mesogenic cholesterol side chain onto the main chain via methylene chains of side branches.     

Synthesis and improved mechanical properties of twin-mesogenic epoxy thermosets using siloxane spacers with different lengths

A series of twin-mesogenic epoxy resins with siloxane (di-, tri-, and tetra-siloxane) chain spacers of different lengths were successfully synthesized. Results showed that the melting point of the twin-mesogenic epoxy monomers decrease by more than 50 °C due to the change of siloxane spacer length. In particular, the tri- and tetra-incorporated siloxane twin-mesogenic epoxy monomers showed a liquid crystalline (LC) phase below 100 °C during the cooling process. Epoxy thermosets with isotropic and smectic (S_m) LC phases were then prepared using an aromatic amine and the dependence on curing temperature was investigated. Furthermore, the relationship between the ordered network chain structure and mechanical properties was investigated. Results were compared with isotropic and S_m LC phases. The tensile strain and fracture energy in the S_m type LC thermosets increased without a decrease in the tensile modulus, and this occurred in all systems irrespective of siloxane spacer length. The maximum value of the fracture energy (283 kJ m⁻²) reached by LC thermosets with increased spacer lengths was twice as large as that using the alkyl chain spacer (144 kJ m⁻²). © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47891.     

Side chain polysiloxane liquid crystals and their behaviour in electric fields

Optical and electro-optical properties of side chain liquid crystalline polymers are described. The polymers studied were homopolysiloxanes with mesogenic side groups separated from the polymer backbone by flexible polymethylene spacers of varying length. The effect of the flexible spacer on the phase properties and electric field effects will be discussed. Low frequency a.c. fields induced a turbulent scattering texture, whilst at higher frequencies (> 1 kHz) a homeotropic alignment was obtained. The latter effect leads to high contrast displays which are durably stored at temperatures well above the glass transition. Various parameters affecting the response of the polymers to applied fields will also be discussed. These include temperature, frequency and magnitude of the electric field, film thickness and the length of the flexible spacer.     

Side-Chain Liquid Crystalline Polymers with [α-terpineol-co-MMA] Main Chain: Synthesis and Characterization of Polymers with Phenyl Benzoate Mesogenic Group

Summary Side chain liquid crystalline (SCLC) [α-terpineol-co-MMA] polymers with a phenyl benzoate mesogenic group with polymethylene spacers have been synthesized and characterized in which the spacer length is taken 9 methylene units. The thermal behavior and liquid crystallinity of the polymer has been characterized using Differential Scanning Calorimetry (DSC) and Polarized Optical Microscopy (POM) techniques . The DSC curve of the LCpolymer shows glass transition at 52 °C followed by nematic phase which undergoes isotropization at 120 °C without undergoing side chain crystallization. Under optical polarized microscope the appearance of characteristic schlieren texture confirms the presence of nematic phase .     

Synthesis and characterization of biphasic liquid crystalline polysiloxanes containing 4-undecanyloxy-4′-cyanobiphenyl side-groups

Summary The synthesis and characterization of liquid crystalline polysiloxanes and copolysiloxanes containing 4-undecanyloxy-4-cyanobiphenyl side-groups is presented. The polysiloxane presents a single glass transition temperature followed by a S_c and a S_A mesophase. Copolysiloxanes presenting around 50% weight fraction of side-groups exhibit two glass transition temperatures i.e., one due to the independent motion of the main chain and the other due to the cooperative but independent motion of the side groups, and in addition to the S_c and S_A phases exhibited by the homopolymer, present also side-chain crystallization.     

Synthesis and characterization of ferroelectric side chain liquid crystal polymers bearing banana-shaped chiral mesogens

A series of ferroelectric liquid crystal polymers having banana-shaped side chain mesogens were synthesized through photo-polymerization of epoxide moiety. 2,5-disubstituted-thiophene sub-unit was used in synthesizing the banana-shaped monomers. These liquid crystal compounds were characterized by NMR, differential scanning calorimetry (DSC) and optical polarized microscopy (POM). Mesomorphism was investigated as a function of spacer units. All the synthesized low molar mass banana-shaped compounds exhibit smectic blue phase, but chiral smectic C phase could be observed only on compounds having longer spacer. The clearing temperature of low molar mass compounds fluctuated a little when spacer length varies. All polymers exhibit cholesteric mesophase and an observable glass transition. These liquid crystalline compounds reveal strong photoluminescence at visible region (λ_max = 475 nm for M9EPX) and have potential use in polarized organic light emitting diode materials.     

The Effect of the Structural Elements on the Properties of Side Chain Mesomorphic Polymers

The thermal properties of mesomorphic polymers depend on the relative amounts of the different structural elements (hard core, flexible chains, main chain) of the polymer. Literature data are compared with the conclusions obtained from the three-component thermodynamic model of side chain mesomorphic polymers. The effects of the different soft elements (main chain, spacer and p-alkyl or alkoxy chain) depend first of all on the length of the spacer and its interaction with the main chain. The thermal properties of the polymer can be well regulated by varying the different structural elements of the homo- and co-polymers. The glass transition temperature (T_g) of the polymer can be reduced by building O and N atoms into the main chain and/or by binding the side chains on 3rd, 4th, etc. atoms of the main chain. The T_g can be further reduced by increasing the length of the spacer. If the spacers are long enough, the layer type structures are favored, with p-alkoxy chains behaving also as a plasticizer of the main chain. The clearing point can be influenced by copolymerization of monomers with different hard cores. The three-component thermodynamic model of side-chain mesomorphic polymers well explains the effect of different structural elements on the structure and properties of these polymers.     

液晶高分子的分子设计

简单介绍了液晶高分子的结构特点，分类及其应用状况，详细介绍了主链型和侧链型液晶高分子设计的新进展，根据溶臻主链型液晶高分子和热臻主链型液晶高分子分子结构的不同，提出今后设计主链液晶高分子的主要任务，从主链结构，液晶基元类型和柔性间隔出发介绍了侧链液晶高分子分子设计的关键，最后介绍了液晶高分子分子设计的发展趋势。     

Polymers with rigid anisotropic side groups: 2. Synthesis and properties of some side chain acrylate and methacrylate liquid crystal polymers containing the 4′-alkylbiphenyl-4-yl moiety

A number of acrylate and methacrylate side chain polymers in which the mesogenic moiety is either a 4′-n-pentyl- or 4′-(2-methylbutyl)-biphenyl-4-yl group have been synthesized. A systematic investigation into the effect on the thermal properties of the acrylate polymers containing the n-pentylbiphenylyl moiety, by changing the size of the flexible spacer group, has revealed large differences in the smectic thermal stability of these polymers with respect to whether the flexible spacer group contains an even or odd number of methylene groups. An explanation is given as to why this alternation effect was observed. X-ray diffraction has shown the smectic phase to be S_A in type with a near perfect bilayered structure for the polyacrylates, but a more disordered bilayered structure for the methacrylates. Two of the acrylate polymers exhibit a second smectic phase which has not yet been identified.     

Naphthoic acid derivatives as hydrogen bond donors in supramolecular materials

The synthesis of a series of 6‐hydroxy‐2‐naphthoic acid derivatives is described. These have been used to form supramolecular main‐chain liquid crystalline polymers. These hydrogen bond donors are complexed with a series of bisfunctionalized rigid pyridine species. These associative chain structures were analyzed through differential scanning calorimetry and polarizing light thermal optical microscopy. The liquid crystalline phases formed displayed mainly enantiotropic nematic phases that display an increase in clearing temperature as the rigid portions of the supramolecular system increased in length. A decrease in the clearing temperature was observed as the length of the flexible spacer group increased. Both of these observations follow established trends in liquid crystalline behavior. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 5890–5894, 2006