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1.
Thermotropic polyurethanes were prepared from three commercial diisocyanates of various flexibility and eight diols (based on diethanolamine derivatives) with mesogenic groups in side chain with stoichiometric ratio of reactive isocyanate and hydroxy groups. Polymers were studied by dynamic mechanical spectroscopy, X-ray scattering, differential scanning calorimetry and polarizing microscopy. The effect of structure changes in the diisocyanates and diols, in particular changes in the end substituents bound to the mesogen, were investigated. Introduction of mesogenic diols into the polymers suppresses the occurrence of mesophases in comparison with neat diols; in the case of simple end substituents (such as hydrogen, nitro and nitrile), the mesophases disappear completely regardless of the structure of diisocyanate. Stiff end substituents (phenyl and alkoxy groups) stabilize the mesophases to such an extent that the negative influence of long polymer chains is compensated and the liquid-crystalline (LC) properties are recovered. Generally, the polymers prepared from the stiffest 2(4)-methyl-1,3-phenylene diisocyanate exhibit a most pronounced LC behavior.  相似文献   

2.
X-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.  相似文献   

3.
Orientational elastic deformations in a magnetic field and phase transition temperatures of a thermotropically mesogenic “combined” aromatic polyester with mesogenic groups, both in the main and in the side chains, have been investigated in the range of 900 to 10,200 mol. wt. It was shown that in this molecular weight range the birefringence of a completely oriented nematic and correspondingly, the degree of its orientational order S are independent on molecular weight. When the relative temperature ΔT changes from −2 to −30°C the orientational order parameter increases from 0.35 to 0.55. The bend elasticity constants K3 coincide in the order of magnitude with those for high and low molecular weight nematics investigated previously and their dependence on molecular weight has not been detected.  相似文献   

4.
Abstract

The long range molecular dynamical behaviour of liquid-crystalline side chain polymers with the mesogenic groups linked laterally to the backbone have been studied by using dielectric relaxation spectroscopy over a broad temperature and frequency range. The samples were oriented homeotropically and homogenously by electric and magnetic fields and the relaxations were recorded during alignment and with the fully aligned samples. By fitting the data to theoretical relaxation curves, accurate relaxation parameters could be determined, allowing us to perform a comparison with end-fixed liquid-crystalline side chain polymers on the one hand and with low molecular weight liquid crystals on the other. The relaxation in homeotropic alignment for the laterally fixed compound has more analogies in some aspects, for example, the relaxation time distribution, with low molecular weight liquid crystals than with the corresponding end-fixed compounds, though the activation energy is very large (241 kJ/mol). We relate this to the length of the rigid mesogenic unit and the resulting stronger repulsion by the neighbouring side chains during reorientation. In homogeneous alignment the relaxation is very broad and also has a large activation energy. Different molecular processes are related to this relaxation regime. The relationship between the different relaxation processes and the molecular structure is discussed.  相似文献   

5.
The synthesis and characterization of nine polymethacrylates containing 4-alkoxy-4′-trifluoromethyltolane, 4-alkoxy-4′-cyanotolane, and 4-alkoxy-4′-nitrotolane side groups were described in this study. The phase behavior of the prepared monomers and polymers was characterized by differential scanning calorimetry, optical polarizing microscopy, and x-ray diffraction. All of the obtained monomers exhibit no mesophase, while most of the synthesized polymers reveal enantiotropic mesomorphism. The polymethacrylate containing 4-propanyloxy-4′-nitrotolane side groups was the only one which shows no mesomorphic behavior. Both the spacer length and the nature of terminal groups have profound influence on the phase transition temperatures and thermal stability of the mesophase. The polymers with longer spacers tend to form a more ordered mesophase with a wider temperature range. Among three polymers with the same spacer length, the polymer with a trifluoromethyl terminal end group is inclined to form a more ordered mesophase than the other two polymers. No side chain crystallization occurred for all obtained polymers. © 1994 John Wiley & Sons, Inc.  相似文献   

6.
A new series of carbosilane liquid crystalline (LC) dendrimers from the first to the third generations with 8, 16 and 32 chiral terminal mesogenic groups, respectively, has been synthesized. The molecular structures and purity of all new compounds were confirmed by 1H NMR spectroscopy and GPC analysis. Data of polarization microscopy and SAX analysis demonstrated that all LC dendrimers synthesized form a chiral smectic SmC* phase at temperatures below 50 °C. It has been found that bistable electrooptical switching is observed for all dendrimers. The influence of chiral mesogenic fragment length on phase behavior and ferroelectric properties of carbosilane LC dendrimers is discussed.  相似文献   

7.
The viscoelastic behavior of phosphonate derivatives of phosphonylated low-density polyethylene (LDPE) was studied by dynamic mechanical techniques. The polymers investigated contained from 0.2 to 9.1 phosphonate groups per 100 carbon atoms and included the dimethyl phosphonate derivative and two derivatives for which the phosphonate ester group was an oligomer of poly(ethylene oxide) (PEO). The temperature dependences of the storage and loss moduli of the dimethyl phosphonate derivatives were qualitatively similar to those of LDPE. At low phosphonate concentrations, the α, β, and γ dispersion regions characteristic of PE were observed, while at concentrations greater than 0.5 pendent groups per 100 carbons atoms, only the β and α relaxations could be discerned. At low degrees of substitution, the temperature of the β relaxation Tβ decreased from that of PE, but above a degree of substitution of 0.1, Tβ increased. This behavior was attributed to the competing influences of steric effects which tend to decrease Tβ and dipolar interactions between the phosphonate groups which increase Tβ. For the phosphonate containing PEO, a new dispersion region designated as the β′ relaxation was observed as a low-temperature shoulder of the β relaxation. The temperature of the β′ loss was consistent with Tg(U) of the PEO oligomers as determined by differential scanning calorimetry, and it is suggested that the β′-loss process results from the relaxation of PEO domains which constitute a discrete phase within the PE matrix.  相似文献   

8.
Two new thermotropic liquid-crystalline side group polymers were synthesized, characterized and compared with the liquid-crystalline monomeric analogues. Some packing features of these polymeric liquid crystals are discussed.

Investigations were carried out by differential calorimetry (D.S.C.), polarization microscopic observation and X-ray diffraction on non-aligned and magnetic field-aligned samples in the wide and small angle region.

The synthesized polymers contain as mesogenic moiety a benzylideneaniline group which is attached in the 4 position via a hexamethylene spacer to a poly-methacrylate backbone. The benzylideneaniline group is substituted in 4′ position with an ethoxy or butoxy group (PEt or PBu). The monomeric analogues are denoted MEt and MBu. The two polymers show a phase sequence crystalline-smectic A-nematic-isotropic. The liquid-crystalline temperature range is observed between 90 and 150°C. The monomeric MEt exhibits only a monotropic nematic, MBu an enantiotropic nematic and a smectic A phase.  相似文献   

9.
Dynamic mechanical, differential scanning calorimetry and X-ray scattering behavior of ordered polyurethane systems, based on a diol with rigid (mesogenic) group in side chain (D), 2(4)-methyl-1,3-phenylene diisocyanate (DI) and two triols (T)--stiff trimethylolpropane (TMP) or flexible poly(oxypropylene)triol (PPT), was investigated during crosslinking and on the networks. The networks were prepared at various stoichiometric initial molar ratios of the reactive groups, [OH]T/[NCO]DI/[OH]D ranging from 1/2/1 to 1/20/19. From our measurements it follows that: (a) Power-law parameters, which are characteristic of the structure at the gel point (the gel strength S and the relaxation exponent n), are dependent on the initial ratio of the reactants. With increasing content of mesogenic diol in the system (increasing length of elastically active network chains, EANCs), the gel strength S increases and the relaxation exponent n decreases; higher S and lower n are found for stiffer TMP networks in comparison with more flexible PPT ones. (b) Introduction of crosslinks reduces the flexibility of the network chains in fully cured samples and inhibits conformational rearrangements required for ordering. A more complex thermal behavior was found for networks based on TMP in comparison with those based on PPT. (c) Strong physical interactions between the mesogens promote cyclization in the course of crosslinking; the fraction of bonds lost in intramolecular cycles is ∼15% for fully cured networks.  相似文献   

10.
Several novel mesogenic spiro-orthoester monomers such as 1,6,10-trioxaspiro[4,5]decanes 4 , containing biphenyl mesogens at the C-8 positions of the five- and six-membered spirocyclic ring, through the alkylene spacers of different lengths were prepared by condensation reaction of the corresponding biphenyl mesogenic 1,3-propanediol 3 with 2,2-diethoxytetrahydrofuran, with 50–75% yields. Through cationic double ring-opening polymerization, carried out with boron trifluoride etherate as an initiator (5 mol % vs. monomer) in bulk at 150°C, spiro-orthoester monomers 4 afforded a novel class of side-chain thermotropic LC polymers with a poly(ether ester) as the main chain 8 . The liquid-crystalline properties of the spiro-orthoester monomers and the resulting polymers were examined by differential scanning calorimetry and optical polarized microscopy. Biphase separation was observed in the side-chain liquid-crystalline poly(ether ester)s upon annealing in the broad isotropic region. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. A Polym. Chem. 36: 2439–2455, 1998  相似文献   

11.
A new side chain liquid crystalline polymers have been synthesized and characterized in which [geraniol-co-MMA] polymer are used as a backbone linked via polymethylene spacer to phenyl benzoate mesogenic group. The polymer exhibits enantiotropic liquid crystallinity with nematic phase and does not exhibit side chain crystallization .A clear difference between the nature of the mesophase is evidenced between [Geraniol-co-MMA] main chain and methacrylate polymers .The LC polymer exhibit glass transition at 40 °C. In a comparative analysis, we discuss the relevance of polymer backbone in the synthesis of side chain liquid crystalline polymers.  相似文献   

12.
Blends of polyamide12 (PA12) and isotactic polypropylene (PP) were prepared by melt mixing, in an internal mixer, in the presence and absence of compatibiliser. The compatibiliser used was maleic anhydride grafted PP (PP-g-MA). The dynamic mechanical properties of the blends with and without compatibiliser were studied. Although compatibilization shifted the glass transition temperatures (Tg's) of component polymers only marginally, it significantly enhanced the storage modulus of the blends. The storage moduli of the uncompatibilised blends were compared with those predicted by theoretical models. Correlation between the dynamic mechanical properties of both compatibilised and uncompatibilised blends and their phase morphology was made.  相似文献   

13.
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.  相似文献   

14.
Liquid crystalline materials display unique properties, which can be exploited in organic light emitting diodes. Polythiophene model compounds containing phenyl groups linked with azomethine, ester, and alkoxy groups [thiophene‐3‐alkyloxy benzoyloxy aniline series (N series) and thiophene‐3‐alkoxy phenoxy amino benzoate series (R Series)] were synthesized. Molecular orbital calculations were performed and the predicted band gaps compared to understand the effects of spacer length and linkage. The experimental photoabsorption characteristics are compared with the theoretically predicted band gap. Photoabsorption and emission studies on N series and R series polymers as the function of polarizer angle suggest that polymers of both series emit polarized light in all base color ranges. The electroemission characteristics of the above‐synthesized polymers were also recorded as the function of polarizer angle. The results show that the compounds also emit polarized electroemission, and the EL polarization ratio decreases with the increase of alkoxy chain length for N and R polymers. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1463–1477, 2008  相似文献   

15.
Using solution polycondensation, a new polyazomethine with m-tolylazo side groups (PAz) exhibiting thermotropic liquid crystalline phase was synthesised and its chemical structure was characterised with generally accepted methods. Its phase transition temperatures were detected with both polarising optical microscopy and differential scanning calorimetry. Using dielectric spectroscopy method, both real and imaginary parts of the permittivity were investigated in wide regions of temperature (from ?100°C to 170°C) and frequency (from 1 Hz to 1 MHz). Analysis of frequency dependent permittivity allowed finding three relaxations (α, β1 and β2) in PAz. β-relaxations were described with the Arrhenius equation, whereas α-relaxation was described with the Vogel–Fulcher–Tammann equation. The alternating current conductivity (ACC) of PAz was studied in the same regions of temperature and frequency. The frequency dependent ACC was described with an exponent power equation. Presentation of ACC as a function of inverse temperature allowed us to describe ACC with the Arrhenius equation.  相似文献   

16.
Two resins were synthesized containing triple bonds in the side chains. The polymers were characterized by IR and NMR spectroscopy. DSC and thermal decomposition temperatures were determined. These resins show high thermal stability.  相似文献   

17.
A study of a liquid crystal side chain copolymer with a siloxane backbone has been carried out using dielectric relaxation spectroscopy and optical microscopy. We have found that this particular copolymer, a mixture of longitudinally and laterally attached mesogens, can be aligned both homeotropically and planarly between two electrodes using a directing AC field of specific frequency by cooling from the melt or more importantly at temperatures below the clearing point (Tc). The switching of the material from homeotropic to planar and the reverse has been studied at temperatures below Tc. It is shown that the kinetics of realignment are strongly dependent on the electrical/thermal history of the sample. The dielectric data allows the state of alignment of the sample to be monitored and the molecular dynamics to be studied. The optical textures of the polymer which were subjected to different AC electric fields have been observed and provide complementary information to the dielectric work on the state of the aligned sample.  相似文献   

18.
Two polybenzoxazines are cured in an autoclave from the polyfunctional benzoxazine monomers, 8,8′-bis(3,4-dihydro-3-phenyl-2H-1,3-benzoxazine) and 6,6′-bis(2,3-dihydro-3-phenyl-4H-1,3-benzoxazinyl) ketone. The density and tensile properties of these polybenzoxazines are measured at room temperature. Dynamic mechanical tests are performed to determine the Tg, crosslink density, and the activation enthalpy of the glass-transition process for these two polybenzoxazines. The effect of postcure temperature on the Tg of the polymers is investigated and discussed in terms of crosslink density. Fourier transform infrared (FTIR) spectroscopy is also applied for the molecular characterization of the curing systems. Thermal properties of these polybenzoxazines are studied in terms of isothermal aging and decomposition temperature via thermogravimetric analysis. These two polybenzoxazines show mechanical and thermal properties similar to or better than bismaleimides and some polyimides. They also show very high char yield after being carbonized in a nitrogen atmosphere. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 3257–3268, 1999  相似文献   

19.
Liquid crystalline materials display unique properties, which can be exploited in various optoelectronic device applications. The Langmuir‐Blodgett (LB) film characteristics of polythiophene model compounds containing phenyl rings linked with azomethine, ester, and alkoxy functional groups poly‐4‐{[(E)‐thiophen‐3‐ylmethylidene]amino}phenyl 4‐alkyloxybenzoate (PTAPAB series) and poly‐4‐alkyloxy phenyl 4‐{[(E)‐thiophen‐3‐ylmethylidene]amino}benzoate (PAPTAB Series) were explored in this study. The AM1 optimized geometries of the aforementioned compounds showed that the films have different type of orientation in space because of the change in the linking functional group. The LB film characteristics were studied by applying the concepts of the failure mechanism in tensile failure. The compression‐expansion hysteresis cycle of the LB films at predetermined area per repeat unit was used to study the viscous, elastic, and plastic nature of the films. The results showed that in PAPTAB series compounds, the LB films were more flexible and took less surface energy than its PTAPAB series homologues, which formed into LB films of rigid nature. The LB films of PAPTAB series compounds were of more viscoplastic in nature. The studies suggested that PAPTAB series structures exhibited good thin film forming nature than its PTAPAB series homologues. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 173–182, 2009  相似文献   

20.
Properties of a poly(arylene ether ketone) with carboxyl side groups, copolymers containing units of this homopolymer, and their salts with different degrees of neutralization by alkali metals were studied by the methods of dynamic mechanical analysis, thermogravimetric analysis, and differential scanning calorimetry. By varying the nature of a metal atom and the degree of neutralization of carboxylic groups of a homopolymer and their content in copolymers, one may change the properties of polymers, including their ability to form ion pairs and, hence, their glass transition temperatures. For polymer salts at the 100% neutralization of carboxylic groups, the storage modulus and the glass transition temperature are shown to increase with decreasing the radius of the metal ion. The thermal stability of poly(arylene ether ketone) with carboxylic side groups and copolymers with different contents of such groups may be controlled by varying the nature and content of the introduced metal.  相似文献   

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