Dielectric properties of liquid-crystalline copolymers with side cyanobiphenyl groups and acrylic acid units

Dielectric properties of a number of liquid-cry stalline comb-shaped copolymers with different ratios of side-chain mesogenic cyanobiphenyl groups and acrylic acid units are studied. In the electric-field frequency range 300 Hz-100 MHz, temperature dependences of dielectric permittivity are obtained for nematic and isotropic phases. The times of relaxation and the energies of activation for processes responsible for dielectric-permittivity dispersion are measured. The quantitative relationship between the dielectric characteristics and the content of acrylic acid units in the copolymer is established.     

Synthesis and mesomorphic structures of comb liquid-crystalline polymers with lipopeptidic side chains

Lipopeptidic macromonomers were synthesized from bi-functional lipids by two methods and transformed into comb copolymers with lipopeptidic side chains by radical polymerization of their acrylate, methacrylate, acrylamide or methacrylamide terminal group. X-ray diffraction and differential scanning calorimetry studies showed that comb copolymers exhibit both a thermotropic and a lyotropic behaviour and present smectic and nematic mesophases. The influence of the solvent concentration, the degree of polymerization of the peptidic chains and the nature of the main chains on the structural parameters of the smectic mesophases were established in the case of copolymers with liposarcosine side chains.     

Synthesis and characterization of graft copolymers containing poly(p-phenylene) main chains and mesogen-jacketed liquid-crystalline polystyrene side chains

A series of novel comblike mesogen-jacketed liquid-crystalline graft copolymers, poly(p-phenylene)-g-poly{2,5-bis[(4-methoxyphenyl)oxycarbonyl]styrene} (PPP-g-PMPCS) copolymers, have been designed and successfully synthesized by a Yamamoto coupling reaction and subsequent atom transfer radical polymerization (ATRP). ¹H NMR spectroscopy, ultraviolet–visible spectra, and gel permeation chromatography (GPC) have been used to confirm the molecular structure of the macroinitiator and the copolymers. A study of the polymerization kinetics of ATRP has shown that the molecular weight of the copolymer increases linearly with the conversion of the monomer, whereas the polydispersity remains narrow (≤1.28), indicating that the ATRP of 2,5-bis[(4-methoxyphenyl)oxycarbonyl]styrene is well controlled. Thermogravimetric analysis and differential scanning calorimetry (DSC) measurements have indicated that the PPP-g-PMPCS copolymers have better thermal stabilities than the macroinitiator, and their thermal stabilities increase with increasing molecular weight. The liquid-crystalline behavior has been examined with polarized optical microscopy, DSC, one-dimensional wide-angle X-ray diffraction (1D WAXD), and two-dimensional wide-angle X-ray diffraction (2D WAXD). The results show that all the comblike copolymers exhibit obvious liquid-crystalline behaviors, even though the GPC molecular weight of the segments of poly{2,5-bis[(4-methoxyphenyl)oxycarbonyl]styrene} (PMPCS) have been determined to be far less than the critical value of linear PMPCS. Moreover, 1D WAXD measurements show that the temperature at which the comblike mesogen-jacketed liquid-crystalline copolymers can transform into a liquid-crystalline phase is low; about 20 °C in comparison with the linear ones. 2D WAXD analysis has revealed that these comblike copolymers should be assigned to a hexatic columnar nematic (Φ_HN) phase. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2543–2555, 2007     

Characteristics of liquid-crystalline cholesteryl and cyanobiphenyl side chains pendent to trans-polypentenamer

trans-Polypentenamers with thermotropic liquid-crystalline side chains cholesteryl and cyanobiphenyl were prepared by ring-opening polymerization of vinylcyclopropane monomers with proper substituents. Molecular weights of the polymers were in the range of 25000 to 80000 and the ratios of weight- to number-average molecular weights M _w/M _n were between 3.3 and 3.8. The glass transition temperature values of the polymers were 35°C ( 4a ) and 39°C ( 4b ). Monomers 3a and 3b present cholesteric and smectic mesomorphism, respectively. On the other hand, polymers 4a and 4b present only a smectic mesophase.     

Crystallization of side chains in copolymers of ethylene and 1-alkenes

The phase structure of random copolymers of ethylene and ethylene-d₄ with 1-octadecene and other 1-alkenes has been investigated. CPMAS ¹³C NMR spectra show that a fraction of the central sections of C₁₆H₃₃ side chains in ethylene-d₄ copolymers are in ordered environments at 298 K. They give rise to resonances from 32.9 ppm to 33.8 ppm, which show that they are in trans conformations; T_1C values for this group of resonances range from 1 s to 7 s. The remaining side chains are in an amorphous environment, the internal methylenes having a chemical shift of 30.8 ppm and a T_1C close to 0.4 s. A Raman band at 1062 cm⁻¹ in the spectrum of an ethylene-d₄-1-octadecene copolymer is consistent with partial crystallization of side chains. Some side-chain crystallization also occurs in a 1-tetradecene copolymer. X-ray diffraction studies suggest that smaller side chains do not crystallize to a significant extent at 298 K. © 1996 John Wiley & Sons, Inc.     

Dynamic mechanical and thermal behavior of liquid-crystalline polybutadiene-diols with mesogenic groups in side chains

Liquid-crystalline polybutadiene-diols (LCPBDs) with the comb-like architecture were synthesized by reaction of a LC thiol with the double bonds of telechelic HO-terminated polybutadiene (PBD). LCPBDs with various initial molar ratios of thiol to double bonds of PBD, R₀, in the range from 0.15 to 1, were prepared by the radical reaction at temperature 60 °C for 48 h. The experimentally obtained degree of modification, R_e, after the reaction and purification, was determined from elemental analysis - from the amount of sulphur bounded in LCPBDs, GPC and from ¹H NMR spectra. The physical properties were investigated by differential scanning calorimetry and dynamic mechanical spectroscopy. With increasing R_e ratio the glass transition temperature of LCPBDs, T_g, increases from ∼ − 45 °C (neat PBD) to ∼20 °C (R_e ∼ 0.5). LC transition starts at R_e ∼ 0.27 (the transition temperature T_m ∼ 27 °C). With increasing R_e temperature T_m increases and for R_e ∼ 0.5 reaches the value T_m ∼ 74 °C; at the same time also the change in enthalpy at LC transition increases. The LC transition could be detected also by the dynamic mechanical spectroscopy; especially shape and position of mechanical functions on frequency and free volume parameters strongly depend on degree of modification.     

Molecular and conformational properties of comb-like polymers with ionically bound side chains studied in organic solvent

Conformational and dynamo-optical properties of a homologous series of poly(cetyltrimethylammonium 2-acrylamido-2-methylpropane sulfonates) with molecular masses ranging from 80 to 700?kDa were studied in chloroform solutions by viscometry, dynamic light scattering, sedimentation, and flow birefringence. The Mark–Kuhn–Houwink Equations for this polymer in chloroform were obtained; the values of hydrodynamic diameter and the Kuhn segment length as well as the value of intrinsic anisotropy of polarizability of the monomer unit were defined.     

Polyaniline copolymers with solvent‐mimic side chains

We investigated new polyaniline copolymers with solvent‐mimic side chains for enhanced processability in various solvents. The solvent‐mimic side chains, benzyloxypropoxy (BOP), phenoxybutoxy (POB), and dihydroxypropoxy (DHP), were introduced into copolymers and used with nonpolar aromatic and polar alcoholic solvents, respectively. Compared to a polyaniline homopolymer, polyaniline copolymers with a small amount of side chains (<4 mol %) exhibit different physical properties, including film‐forming ability. This can be attributed to the solvent‐mimic side chains strongly interacting with the solvent and/or the polyaniline backbone. Especially, in nonpolar aromatic solvents, polyaniline copolymers with nonpolar aromatic BOP and POB side chains exhibit good film‐forming ability leading to high electrical conductivity, while the polyaniline homopolymer did not form a film. Therefore, introducing solvent‐mimic side chains in conducting polymers is a very attractive method of enhancing their processability and physical properties. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1986–1995     

Specific features of the field-induced effects in comb-like liquid-crystalline polymers

The main problems concerning the liquid crystalline polymers and their behaviour in outer fields are discussed. The influence of the mesophase structure type of the side-chain LC polymers on the orientation processes in mechanical, electrical and magnetical fields is shown. The field effects in polymers permit to evaluate the specific peculiarities of the polymeric state of liquid crystals. During the last 10 years the field of Liquid-Crystalline (LC) polymers has been developed and is going to expand so intensively that one could not predict this at the time when first lyotropic and thermotropic LC-systems were discovered. Not only thousand of new LC polymers were synthesized and our Symposium gives a good example of very interesting papers devoted to this area, but it became clear that LC-state of polymers should be considered as normal, thermodynamically stable, widespread state of macromolecular substances - the idea which you hardly could find in textbooks a decade ago. First applications of thermotropic LC-polymers start to be described (memory devices, optical filters, ferroelectric polymers) while lyotropic systems continue its victorial march in the field of high tenacity fibers and films. It is absolutely impossible to give in one lecture an overall review of what is going on in this area because this would need at least 5–6 lectures of two hours each. That is why on preparing this talk we decided to concentrate ourself onto only one side of this rich picture - the field induced effects in comb-like LC thermotropic polymers.     

Influence of side chains assembly on the structure and transport properties of comb-like polysiloxanes in hydrocarbon separation

We have synthesized a number of comb-like polysiloxanes with linear, branched, cyclic and silicon-containing substituents; most of them are new and previously not studied polymers. The physicochemical properties of comb-like polysiloxanes have been systematically investigated. Differential-scanning calorimetry and wide-angle X-ray scattering data revealed the side-chain microphase assembly for polymers with linear aliphatic substituents, while the polymers with bulky substituents did not form a microphase. It is shown that the ratio of microphase in the polymer is greater, the closer the values of the thickness of the microphase layer and the length of the cross-link. The effect of the side-chain substituent on the hydrocarbon transport properties of comb-like polysiloxanes was studied. All synthesized polymers are promising as membrane materials for a vital process of hydrocarbon separation. This is associated with an increase in the solubility selectivity of n-butane/methane because the solubility coefficient of methane sharply decreases when long side chains are introduced into the polysiloxane. It was shown for the first time that microphase forming polymers have a significantly higher butane/methane selectivity (23.2–27.5) than polysiloxanes not forming a microphase (selectivity 12.3–20.0). The effect is demonstrated on polysiloxanes with various types of side substituents. It was revealed that for the comb-like polysiloxanes, the diffusivity selectivity and permselectivity are proportional to the fraction of the side-chain microphase in the polymer. With the increase in the hydrocarbon microphase share, the diffusion coefficient of the permanent gas methane is decreasing more rapidly than n-butane, which dissolves well in hydrocarbons and plasticizes polymer. Consequently, the polymers forming the microphase have a higher selectivity C₃₊/CH₄ in the separation of a multicomponent hydrocarbons mixture.     

Specific features of liquid-crystalline comb-like polymers with mesogenic groups

The results of structural investigation of the new type of the liquid-crystalline thermotropic methacrylic polymers are discussed. These polymers contain mesogenic groups as models for cholesteric, nematic and smectic types of low-molecular liquid crystals. The groups are attached to the backbone through methylene bridges of various lengths. The polymers of the first group have amorphous structure; the polymers of the second group are characterized by liquid crystalline structure and those of the third group can exist in both crystalline and liquid-crystalline states, manifesting properties of enantiotropic liquid crystals. The temperatures and heats of phase transitions have been determined. It is shown that the ability to realize the liquid-crystalline state of comb-like polymers with mesogenic groups depends on and is determined by the proceess of ordering of these groups.     

Synthesis of comb-like polyurethanes containing hydrophilic phosphatidylcholine analogues in the main chains and hydrophobic long chain alkyl groups in the side chains

Three new amphiphilic phospholipid diols containing hydrophilic phosphatidylcholine analogues in the main chains and hydrophobic octadecyl, hexadecyl or dodecyl alkyl groups in the side chains were synthesized. The typical phospholipid diol based on an octadecyl group was further reacted with diisocyanates such as hexamethylene diisocyanate (HDI), 2,4-tolylene diisocyanate (TDI) and 4,4′-methylenediphenyl diisocyanate (MDI), respectively. Preliminary studies suggest that polyurethane based on MDI shows a viscosity behavior similar to common polyelectrolytes and exhibits a therm decomposition peak at 244°C due to the phospholipid moiety and a melting point at 218°C.     

Anti-biofouling properties of comblike block copolymers with amphiphilic side chains

Surfaces of novel block copolymers with amphiphilic side chains were studied for their ability to influence the adhesion of marine organisms. The surface-active polymer, obtained by grafting fluorinated molecules with hydrophobic and hydrophilic blocks to a block copolymer precursor, showed interesting bioadhesion properties. Two different algal species, one of which adhered strongly to hydrophobic surfaces, and the other, to hydrophilic surfaces, showed notably weak adhesion to the amphiphilic surfaces. Both organisms are known to secrete adhesive macromolecules, with apparently different wetting characteristics, to attach to underwater surfaces. The ability of the amphiphilic surface to undergo an environment-dependent transformation in surface chemistry when in contact with the extracellular polymeric substances is a possible reason for its antifouling nature. Near-edge X-ray absorption fine structure spectroscopy (NEXAFS) was used, in a new approach based on angle-resolved X-ray photoelectron spectroscopy (XPS), to determine the variation in chemical composition within the top few nanometers of the surface and also to study the surface segregation of the amphiphilic block. A mathematical model to extract depth-profile information from the normalized NEXAFS partial electron yield is developed.     

Elastic behavior of comb-like polymer chains

<正>Three-dimensional Monte Carlo simulations of comb-like polymer chains with various backbone lengths N_b,arm lengths N_a and arm densities m are carried out to study the elastic behavior of comb-like polymer chains.The radius of gyration,the shape factors and bond length in different cases during elastic process are calculated,and it is found that the comb-like polymer molecules with longer backbone or shorter arm are more close to linear chains.But the arm density m affects the chain conformation non-monotonously.Some thermodynamic properties are also studied.Average Helmholtz free energy and elastic force f all increase with elongation ratioλfor all chains.     

High-efficiency electrophosphorescent copolymers containing charged iridium complexes in the side chains

A convenient approach to novel charged Ir polymers for optoelectronic devices to achieve red emission was developed. 2-(Pyridin-2-yl)benzimidazole units grafted into the side chains of macroligands (PFCz and PFP) served as ligands for the formation of charged Ir complex pendants with 1-phenylisoquinoline (1-piq). The charged Ir polymers (PFPIrPiq and PFCzIrPiq) showed exclusive Ir(1-piq)(2){N-[2-(pyridin-2-yl)benzimidazole]hexyl}(+)BF(4)(-) (IrPiq) emission, with the peak at 595 nm. The best device performances were obtained from PFCzIrPiq4 with the device configuration of ITO/PEDOT:PSS/PFCzIrPiq4+PBD (30 wt %)/TPBI/Ba/Al (PBD: 5-(4-tert-butylphenyl)-2-(biphenyl-4-yl)-1,3,4-oxadiazole; TPBI: 1,3,5-tris-(2-N-phenylbenzimidazolyl)benzene). A maximum external quantum efficiency (EQE) of 7.3 % and a luminous efficiency (LE) of 6.9 cd A(-1) with a luminance of 138 cd m(-2) were achieved at a current density of 1.9 mA cm(-2). The efficiencies remained as high as EQE=3.4 % and LE=3.3 cd A(-1) with a luminance of 3770 cd m(-2) at a current density of 115 mA cm(-2). The single-layer devices based on charged Ir polymers also showed high efficiency with the high work-function metal Ag as cathode. The maximum external quantum efficiencies of the devices were 0.64 % and 0.66 % for PFPIrPiq2 and PFPIrPiq10, respectively. A possible mechanism of an electrochemical cell associated with its electrochemical redox pathway for single-layer devices has been proposed. The results showed that the charged Ir polymers are promising candidate materials for polymer optoelectronic devices.     

The packing structure of side chains of liquid-crystalline side-chain polymers before and during heat treatment

Six varieties of liquid-crystalline side-chain polymers, poly (cholesteryl ω-(methacryloyloxy)alkanoates) (p-ChMO-n, n = 1,2,3,4,5,7, the carbon number of the alkyl chain), were studied by differential scanning calorimetry (DSC) and small-angle X-ray scattering (SAXS). On and after the first cooling run from the isotropic state, these polymethacrylates gave the same smectic phase. However, on the first heating run for virgin samples, unique phenomena were observed, similar to those frequently observed on the first heating run for thermotropic liquidcrystalline polymers. The thermal properties of the first heating run for these six polymers showed different tendencies between pChMO-n (n-1-3) and pChMO-n (4-7). Although the DSC curve of pChMO-n (n = 4, 5 and 7) exhibited the melting and clearing points on the first heating run, the DSC curve of pChMO-n (n = 1,2 and 3) exhibited an exothermal peak between the glass transition and the clearing point on the first heating run. This difference, probably due to the difference in the spacer length of these polymers, was investigated quantitatively by small-angle X-ray scattering by which the micro-change of the packing structure of the side chains of the polymers was traced.     

Coexistence of two different side chain packing structures in a smectic phase of liquid-crystalline side chain polymers

Ten varieties of liquid-crystalline side chain polymers, poly(cholesteryl-ω-(methacryloyloxy)alkanoates) (pChMO-n, n = 1, 2, 3, 4, 5, 7, 9, 10, 11 and 15; the carbon number of the alkyl chain), were studied by differential scanning calorimetry and small angle X-ray scattering. On and after the first cooling run from the isotropic state, these polymethacrylates gave the same smectic phase. X-ray investigations showed that pChMO-n with short spacers (n = 1-7) has a two layer (bilayer) S_A packing structure, and pChMO-n with a longer spacer (n= 15) has a single layer (monolayer) S_A packing structure. However, these two types of packing structure appear simultaneously in pChMO-n (n = 9s-11) below their phase transition temperature. To clarify the manner of the coexistence of the two different structures the smectic layer spacing and X-ray diffraction patterns were examined by small angle X-ray scattering at various temperatures.     

Selectively degradable alternating copolymers of isobutyl vinyl ether and plant‐derived aldehydes with acyclic side chains: Effects of side group structures on copolymerization behaviors

Side group structures of aldehydes were demonstrated to have decisive effects on cationic copolymerizations with alkyl vinyl ether (VE). Alternating copolymerizations of isobutyl VE (IBVE) and plant‐derived aldehydes with acyclic side chains such as trans‐2,cis‐6‐nonadienal, trans‐2‐nonenal, and citral proceeded under appropriate reaction conditions with the EtSO₃H/GaCl₃ initiating system. In addition, some aldehydes copolymerized in a well‐controlled fashion to yield alternating copolymers with controlled molecular weights and narrow molecular weight distributions. Quantitative and selective acid hydrolysis of the resulting alternating copolymers, based on the acetal structures in the main chains, was also achieved to give other conjugated aldehydes as nearly sole degradation products. Copolymerization results of IBVE and various plant‐derived aldehydes with acyclic or cyclic side groups suggested that electron‐donating ability and bulkiness of the side groups were most likely responsible for the alternating and/or controlled copolymerization behaviors. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4684–4693     

Dielectric relaxations in linear aliphatic polyesters

Molecular motions in a series of linear aliphatic polyesters [poly(ethylene adipate), poly(ethylene sebacate), poly(hexamethylene sebacate), and poly(decamethylene 1,16-hexadecanedicarboxylate)] were studied by dielectric measurements. Two loss maxima were observed for each polymer in the temperature range from ?196 to about 60°C and in the frequency range from 110 to 10⁵ Hz. The loss maxima of these polyesters, lying between ?17 and ?38°C at 110 Hz (β-relaxation), are due to the micro-Brownian motions of amorphous main chains. It was found that these β-relaxations are well described by the WLF equation. The loss maxima in the range from ?88 to ?109°C at 110 Hz (γ-relaxation), are attributed both to local mode motions of main chains in the amorphous region and to motions of the polar groups involved at the chain ends. For the β-relaxation, no simple relation between the methylene sequence length and the loss peak temperature was found. Furthermore, as the methylene sequence length decreased, the effective dipole moment of the polyesters increased gradually. These facts were explained in terms of interchain dipole attraction.