Liquid Crystalline Copoly Research Articles

One-pot synthesis of soluble wholly aromatic liquid crystalline copoly(ester amide)s with high thermal and dimensional stability

Thermotropic liquid crystalline polymers (LCPs) have been of great interest for electronic packaging. Herein, we introduce a series of wholly aromatic, thermotropic LCPs from copoly(ester amide)s of 6-hydroxy-2-naphthalic acid, isophthalic acid, terephthalic acid, and 4-aminophenol, prepared by a convenient one-pot melt polycondensation. Almost synthesized copoly(ester amide)s exhibited good solubility in common organic solvents at room temperature. Furthermore, they possessed high thermal stability with 2% degradation temperatures (Tid) of 359–368 °C and the char yields (at 600 °C) of 50.3–55.6%. The synthesized copoly(ester amide)s had relatively low coefficient of thermal expansion (CTE) values, which were 35.85–41.21 ppm °C−1 in the temperature range of 50–200 °C. Furthermore, an annealing process could be employed to improve the thermomechanical properties of synthesized polymers. For instance, the CTE of sample LCP3 in range temperature of 275–315 °C was reduced by more than 90% after annealing at 320 °C for 1 h, implying the feasibility for electronic packaging.

Liquid crystalline polymers XV. Synthesis, properties and cytotoxicity of photoresponsive thermotropic liquid crystalline copoly(arylidene-ether)s based on 4-tert-butylcyclohexanone and cyclohexanone moieties in the main chain

ABSTRACTA new series of photoresponsive thermotropic liquid crystalline copoly(arylidene-ether)s based on both 4-tert-butylcyclohexanone and cyclohexanone moieties in the main chain were synthesised using solution polycondensation technique of both with different 4,4ʹ-diformyl-α,ω-diphenoxyalkane derivatives. Two model compounds were synthesised from the reaction of each cycloalkanone monomer with benzaldehyde, and their structures were determined using single crystal X-ray diffraction. The structure of the monomers and copolymers was confirmed by elemental and spectral analyses. In addition, the thermal stabilities of these copolymers were evaluated by thermogravimetric analysis. We performed both differential scanning calorimertric and polarised optical microscopic measurements to investigate the thermotropic liquid crystalline properties of synthesised copolymers. The UV−Vis absorption spectroscopy of the liquid crystalline copoly(arylidene-ether) 6f revealed that the system undergoes Entgegen/Zusammen (E/Z) photoisomerisation using UV lamp (450 nm). Moreover, the various characteristics of the prepared copolymers including: solubility, X-ray diffraction analysis, gel permeation chromatography (GPC) and scanning electron microscopy were determined and discussed. The cytotoxicity of the model compounds and selected examples of these copolymers was tested against MCF-7 breast cancer cells. All tested samples showed considerable results, where 6c copolymer gave the best result; it showed cytotoxicity against MCF-7 cell line with IC50 of 0.26 µM.

Liquid crystalline polymers XIV. Main chain thermotropic copoly(arylidene-ether)s based on 4-methyl-cyclohexanone and 4-tertiary-butyl-cyclohexanone moieties linked with polymethylene spacers

A new interesting class of thermotropic liquid crystalline copoly(arylidene-ether)s based on cyclohexanone derivative moieties was synthesised by solution polycondensation of 4,4′- diformyl-α,ω-diphenoxyalkanes (Ia−f) or 4,4′- diformyl-2,2′- dimethoxy-α,ω-diphenoxyalkanes (IIa−f) with methyl-cyclohexanone and 4-tertiary-butyl-cyclohexanone monomers. A model compound III was synthesised from X with benzaldehyde and characterised by elemental and spectral analyses. The inherent viscosities of the resulting polymers were in the range 0.23−0.91 dL/g. All the copoly(arylidene-ether)s were insoluble in common organic solvents but partially soluble in halogenated solvents. The mesomorphic properties of these polymers were studied as a function of the diphenoxyalkane space length. Their thermotropic liquid crystalline properties were examined by differential scanning calorimetry (DSC) and optical polarising microscopy and it was demonstrated that the resulting polymers form nematic mesophases over wide temperature ranges. The thermal properties of those polymers were evaluated by thermogravimetric analysis and DSC measurements and correlated to their structural units. X-ray analysis showed that polymers have some degree of crystallinity in the region 2θ = 5−60°. In addition, the morphological properties of the selected examples were tested by scanning electron microscopy (SEM).

Liquid Crystalline Polymers XIII Main Chain Thermotropic Copoly (Arylidene-Ether)s Containing 4-Teriary Butyl-Cyclohexanone Moiety Linked with Polymethylene Spacers

A new homologous series of thermotropic liquid crystalline copoly(arylidene-ether)s based on 4-teriary butyl cyclohexanone moiety were synthesized by solution polycondensation of 4,4’-diformyl-α,ω-diphenoxyalkanes, Ia-d or 4,4’- diformyl-2,2’-dimethoxy-α,ω-diphenoxyalkanes IIa-d with the 4-teriary butyl-cyclohexanone III and cyclopentanone. A model compound IV was synthesized from the monomer III with benzaldehyde and characterized by elemental and spectral analyses. The inherent viscosities of the resulting polymers were in the range 0.22 - 0.92 dI/g. All the copoly(arylidene-ether)s were insoluble in common organic solvents but dissolved completely in concentrated H2SO4 and formic acid. The mesomorphic properties of these polymers were studied as a function of the diphenoxyalkane space length. Their thermotropic liquid crystalline properties were examined by DSC and optical polarizing microscopy and demonstrated that the resulting polymers form nematic mesophases over wide temperature ranges. The thermogravimetric analyses of those polymers were evaluated by TGA and DSC measurements and correlated to their structural units. X-Ray analysis showed that copolymers having some degree of crystallinity in the region 2q = 5° -60°. In addition, the morphological properties of selected examples were tested by Scanning electron microscopy.

Thermal, dielectric, and rheological properties of aluminum nitride/liquid crystalline copoly(ester amide) composite for the application of thermal interface materials

AbstractIn this article, thermally conductive and relatively low dielectric constant polymer matrix composites of an aluminum nitride filler (AlN) and a novel liquid crystalline copoly(ester amide) (LCP) were prepared via a solution blending method in the presence of a phosphate containing dispersant. The viscosities, thermal conductivities, and dielectric properties of the prepared AlN/LCP composites were investigated as a function of AlN loading. Our experimental results demonstrated that the AIN/LCP composite with AlN concentration of 50 wt% had 2.5 times higher thermal conductivity than pure LCP (2.020 and 0.817 W/mK for composite with 50 wt% of AlN and pure LCP, respectively), but its dielectric constant remained at low level, i.e., < 9.0 at frequency of 900 Hz. In addition, viscosities of AlN/LCP pastes in the N‐methyl‐2‐pyrrolidinone solvent remained at acceptable levels with the high AlN loading of 50 wt%. The morphologies of the prepared composites were also investigated by scanning electron microscopy. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers

Improvements in thermal, mechanical, and dielectric properties of epoxy resin by chemical modification with a novel amino-terminated liquid-crystalline copoly(ester amide)

We used a novel amino end-capped aromatic liquid crystalline copoly(ester amide) (LCP) to improve the thermal and mechanical properties of glycidyl end-caped poly(bisphenol A-co-epichlorohydrin) (DGEBA) cured with 4,4′-diaminodiphenylsulfone (DDS). The thermal and mechanical properties of the blends were investigated as a function of LCP loading. Upon addition of 10phr of LCP, the impact strength of the modified epoxy was dramatically increased from 35.8J/m to 51.8J/m, which is an approximately 30% improvement compared to the un-modified system. In addition, an increase in the fracture toughness and decreases in the dielectric constant and the dielectric loss were found with increases in LCP loading in the blend. These improvements were achieved even when LCP was dispersed in an epoxy network within a homophase structure.

Synthesis and properties of novel phosphorus‐containing thermotropic liquid crystalline copoly(ester imide)s

AbstractA series of novel phosphorus‐containing polyesterimides were prepared from diols—a mixture of a new aromatic phosphorus‐containing bisphenol, namely 1,4‐bis[N‐(4‐hydroxyphenyl)phthalimidyl‐5‐carboxylate]‐2‐(6‐oxido‐6H‐dibenz<c,e><1,2>oxaphosphorin‐6‐yl)‐naphtalene, with aliphatic diols such as 1,3‐propanediol, 1,4‐butanediol, 1,5‐pentanediol, 1,6‐hexanediol, and 1,12‐dodecanediol—and an aromatic diacid chloride containing two preformed ester groups, namely terephthaloyl‐bis‐(4‐oxibenzoyl‐chloride), via high‐temperature polycondensation in o‐dichlorobenzene. The structures of monomers and polymers were verified by means of Fourier transform infrared (FTIR) spectroscopy and 1H NMR spectroscopy. The molar ratio of aromatic bisphenol to aliphatic diol was varied to generate a series of copolyesterimides with tailored physicochemical properties, structure–properties relationships being established. The effect of the phosphorus content on the thermal properties and the flame retardancy was evaluated by means of thermogravimetric analysis (TGA), TGA–FTIR, and scanning electron microscopy. The polymers were stable up to 340 °C showing a 5% weight loss in the range of 340–395 °C and a 10% weight loss in the range of 370–415 °C. The char yields at 700 °C were in the range of 13.6–38% increasing with the content of phosphorus‐containing bisphenol. The effect of the aliphatic content on the liquid crystalline behavior was investigated by polarized light microscopy, differential scanning calorimetry, and X‐ray diffraction. The transition temperatures from crystal to liquid crystalline melt were in the range of 209–308 °C. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010

Synthesis and properties of novel thermotropic liquid crystalline copoly(ester-imide)s

Four novel copoly(ester-imide)s based on 3,3′,4,4′-biphenyltetracarboxylic dianhydride, bis(trimellitic acid anhydride) phenyl ester and di-p-aminophenyl ester of dicarboxylic acids were synthesized via two-step method in order to investigate whether two imide mesogenic units with different conformation and polarity could control the formation of LC-phase. Polarizes light microscopy (PLM) and differential scanning calorimetry (DSC) have shown that three polymers formed the nematic phase with “thread schlieren texture” and a polymer formed the nematic phase with “Inversion walls texture”.

Light-Induced Orientation of Liquid Crystalline Terpolymers Containing Azobenzene and Dye Moieties

Films of liquid crystalline copoly(methacrylate)s with photochromic azobenzene and benzanilide side groups and related terpolymers with additional dye side groups were oriented by the irradiation with linearly polarized visible or, alternatively, UV light. The orientational behaviors of the terpolymers with benzoxazole, stilbene, and anthracene moieties were compared. The irradiation conditions for the photoorientation process were optimized concerning wavelength and dose with respect to the absorption of the dyes and their limited photostability. Caused by the cooperativity of the photoorientation process, the light-induced ordering of the azobenzene group is connected with the alignment of the nonphotochromic co-mesogenic and the dye side groups even below the glass transition temperature. The light-induced orientational order generated in the glassy state was significantly amplified by the subsequent annealing of the irradiated films at temperatures within the mesophase of the co- and terpolymers. Amplification factors up to 30 were found in this series of polymers. The photoinduction process and the subsequent amplification by thermotropic self-organization were investigated in dependence of the polymer composition, the irradiation dose, and the wavelength of the incident light. The required dose or the irradiation time was significantly reduced by the optimization of light-induced and thermal processing, respectively. In this way, dichroic polymer films containing different types of dyes were created.

New Fluorinated Liquid Crystalline Copoly(vinylcyclopropane)s with Unusual Macromolecular Structure

New liquid crystal polymers with unusual macromolecular structure were prepared by copolymerization of a fluorinated vinylcyclopropane (1) with methyl methacrylate (2). The copolymers pol(1-co-2) formed a mesophase despite the high dilution of the perfluorinated side chains along the polymer main chain. The onset of mesomorphism is attributed to the microphase separation of the incompatible fluorocarbon-hydrocarbon components.

Phase Transition and Transition Kinetics of a Thermotropic Poly(amide−imide) Derived from 70 Pyromellitic Dianhydride, 30 Terephthaloyl Chloride, and 1,3-Bis[4-(4‘-aminophenoxy)cumyl]benzene

The phase transition and transition kinetics of a liquid crystalline copoly(amide−imide) (PAI37), which was synthesized from 70 mol % pyromellitic dianhydride, 30 mol % terephthaloyl chloride, and 1,3-bis[4-(4‘-aminophenoxy)cumyl]benzene, was characterized by differential scanning calorimetry, polarized light microscopy, X-ray diffraction, and rheology. PAI37 exhibits a glass transition temperature at 182 °C followed by multiple phase transitions. The crystalline phase starts to melt at ∼220 °C and forms smectic C (SC) phase. The SC phase transforms into smectic A (SA) phase when the temperature is above 237 °C. The SC to SA transition spans a broad temperature range in which the SA phase vanishes and forms isotropic melt. The WAXD fiber pattern of PAI37 pulled from the anisotropic melt revealed an anomalous chain orientation, which was characterized by its layer normal perpendicular to the fiber direction. The transition kinetics for the mesophase and crystalline phase formation was also studied.

Miscibility in blends of liquid crystalline copolyester and semicrystalline poly(ethylene-2,6-naphthalene dicarboxylate)

The miscibility in blends of random liquid crystalline copoly(oxybenzoate-ethylene terephthalate) at a molar ratio of 60:40 (P64) and semicrystalline poly(ethylene-2,6-naphthalene dicarboxylate) (PEN) were investigated with differential scanning calorimetry, wide angle X-ray diffraction and polarized optical micrography. It was found that P64 and PEN were partially miscible as evidenced from the appearance of a single glass transition temperature for each blend at different compositions. Furthermore, the Flory–Huggins interaction parameter, χ12, for P64 and PEN was determined to be −1.13 through the melting point depression analysis, indicating miscibility in blends of P64 and PEN at the melt state. The coherence lengths of PEN in the presence of a small amount of P64, around 3%, were larger than that in pure PEN, implying the regularity of PEN crystals in the blends with low P64 content being more perfect than that of the pure PEN.

Induced γ → α Crystal Transformation in Blends of Polyamide 6 and Liquid Crystalline Copolyester

The equilibrium melting temperatures and the induced γ → α crystal transformation in blends of random liquid crystalline copoly(oxybenzoate−ethylene terephthalate) at molar ratio 60/40 (P64) and polyamide 6 (PA6) under different thermal treatments were investigated with differential scanning calorimetry and wide-angle X-ray diffraction, respectively. It was found that the equilibrium melting temperatures of P64/PA6 blends depended strongly on the amount of P64, and the presence of a small amount of P64 in PA6, around 5%, induced additional crystallization of the α-form crystal in the quenched PA6. Moreover, the onset temperature for the γ → α crystal transformation in the 5/95 P64/PA6 blend was reduced by 30 °C as compared to that in the pure PA6 case (160 °C vs 130 °C).

Structure and high-resolution thermogravimetry of liquid-crystalline copoly(p-oxybenzoate-ethylene terephthalate-p-benzamide)

Thermotropic liquid-crystalline copoly(ester-amide)s consisting of three units of p-oxybenzoate (B), ethylene terephthalate (E) and p-benzamide (A) were studied by proton nuclear magnetic resonance at 200 and 400 MHz, wide-angle X-ray diffraction, and high-resolution thermogravimetry to ascertain their molecular and supermolecular structures, thermostability and kinetics parameters of thermal decomposition in both nitrogen and air. The assignments of all resonance peaks of [1H]NMR spectra for the copoly(ester-amide)s are given and the characteristics of X-ray equatorial and meridional scans are discussed. Overall activation energy data of the first major decomposition have been evaluated through three calculating techniques. The thermal degradation occurs in three steps in nitrogen and air. The degradation temperatures are higher than 447 °C in nitrogen and 440 °C in air and increase with increasing B-unit content at a fixed A-unit content of 5 mol%. The temperatures at the first maximum weight-loss rate are higher than 455 °C in nitrogen and 445 °C in air and also increase with an increase in B-unit content. The first maximum weight-loss rates range between 11.1 and 14.5%min−1 in nitrogen and between 11.9 and 13.5%min−1 in air. The char yields at 500 °C in both nitrogen and air range from 45.8 to 54.3 wt% and increase with increasing B-unit content. But the char yields at 800 °C in nitrogen and air are quite irregular with the variation of copolymer composition and testing atmosphere. The activation energy and Ln (pre-exponential factor) for the first major decomposition are usually higher in nitrogen than in air and increase slightly with an increase in B-unit content at a given A-unit content of 5 mol%. The activation energy, decomposition order, and Ln (pre-exponential factor) of the thermal degradation for the copoly(ester-amide)s in two testing atmospheres, are situated in the ranges of 210–292 kJmol−1, 2.0–2.8, 33–46 min−1, respectively. The three kinetic parameters of the thermal degradation for the aromatic copoly(ester-amide)s obtained by high-resolution thermogravimetry at a variable heating rate are almost the same as those by traditional thermogravimetry at constant heating rate, suggesting good applicability of kinetic methods developed for constant heating rate to the variable heating-rate method. These results indicate that the copoly(ester-amide)s exhibit high thermostability. The isothermal decomposition kinetics of the copoly(ester-amide)s at 450 and 420 °C are also discussed and compared with the results obtained based on non-isothermal high-resolution thermogravimetry. © 1999 Society of Chemical Industry

Thermal analysis of vectra B950 liquid crystal polymer

AbstractThe melting and crystallization behavior of Vectratm B950, a random liquid crystalline copoly(ester amide), was studied by differential scanning calorimetry (DSC). Nonisothermal experiments showed the existence of some interesting and peculiar transition behavior, which may depend on the crystallization conditions (cooling rate). In isothermal experiments, both the thermal and crystallization behavior have been studied as functions of annealing temperature and annealing time. Different thermal behaviors were observed, indicating the possibility of multiple states of mesophase aggregation In addition, the thermal decomposition of Vectra B950 was also studied by TGA‐FTIR in both nitrogen and air environments. A single‐stage decomposition process was found when heating in nitrogen atmosphere, and the decomposition is due to the easter linkage rupture. A double‐stage decomposition process was found when heating in air, and the decompositions are mainly due to the ester linkage rupture for the first decomposition step and the oxidative reaction for the second decomposition step. Annealing slightly changes the decomposition composition occuring in the early stage of thermal degradation.

X-ray analysis of the structure of a copoly(ester-imide)

The structure of a thermotropic liquid crystalline copoly(ester-imide) prepared from p-hydroxybenzoic acid (48 mol %), 4,4'-dihydroxybenzophenone (26 mol %), and N,N'-bis(trimellitimide)hexane (26 mol %) has been investigated by X-ray diffraction. X-ray fiber diagrams of as-spun and annealed fibers contain a series of aperiodic layer lines reminiscent of those seen for fibers of other copolymers that have extended chain conformations and completely random monomer sequences. The positions of these layer lines were reproduced approximately in simulation of the X-ray scattering by a fully extended chain of completely random sequence, and the match was improved to within experimental error when we considered a stereochemically acceptable sinuous chain. This agreement was lost when the sequence statistics deviated were completely random.

Synthesis and characterization of novel thermotropic liquid crystalline copoly(ester imide)s

Novel liquid crystalline copoly(ester imide)s were synthesized via polyesterification of triethyleneglycol bis(4-carboxyphenyl) ether (le), diacetoxybiphenyl, and diacids with imide moieties. The effects of composition on the changes of T g , T m , and T i were examined by global TSC and DSC. Thermal gravimetric analyses (TGA) found that 4a-d and 5a-g possess higher thermal stability. Strong stir opalescence phenomenon and observations from polarized optical microscopy identified that 2b-e and 3a-d possess the typical schlieren texture of an enantiotropic nematic mesophase. The birefrigent melts of 4a-d and 5a-g, however, displayed particular liquid crystalline behavior. Copolymers with higher aromatic imide ring content (4a-d, 5a-g) form a layered structure and an enantiotropic smectic mesophase in the melting state. The melt viscosity of the semetic mesophase was higher than the nematic mesophase which was observed by capillary rheometer.

The role of partial miscibility on the properties of ternary blends of liquid crystalline copolyesters and polyetherimide

Binary blends of liquid crystalline copoly(oxybenzoate-p-ethylene terephthalate) at molar ratio 60/40, POB-PET, and polyetherimide (PEI) were investigated with differential scanning calorimetry and polarised optical microscopy. It was found that POB-PET and PEI were partially miscible when PEI was the major component. Adding a small amount (5 phr) of POB-PET to the originally immiscible blends of liquid crystalline copoly(oxybenzoate-naphthalate) (73/27), Vectra, and PEI resulted in better interfacial adhesions between Vectra and PEI as evidenced by the morphological observations with scanning electron microscopy. The enhancement in the interfacial adhesions caused an increase in the ultimate tensile strength and the impact strength of these ternary blends of Vectra, POB-PET and PEI as compared to that of the corresponding binary blends of Vectra and PEI in an injection molding process.

Interactions of a liquid crystalline polymer with polycarbonate and poly(ethylene terephthalate)

Thermal behaviour of blends of a liquid crystalline copoly(ester amide) (Vectra B950) with two isotropic polymers has been studied by differential scanning calorimetry. One of the isotropic polymers is an amorphous polymer – polycarbonate, the other is a semi-crystalline polymer – poly(ethylene terephthalate). It was found that the glass transition temperature of polycarbonate decreases with increasing Vectra concentration in the blend, suggesting a partial miscibility between the Vectra liquid crystalline polymer (LCP) and polycarbonate. The miscibility is enhanced through heat treatment at elevated temperatures presumably due to a transesterification reaction. Moreover, the presence of the amorphous poly- carbonate hinders the crystallization of the liquid crystalline polymer in the blends. It was also observed that heat treatment of the Vectra LCP and poly(ethylene terephthalate) blends causes a loss in crystallinity and shifts in transition temperatures of poly(ethylene terephthalate), indicating that exchange reactions occur between Vectra B950 and poly(ethylene terephthalate). Based on these results, a new strategy, in situ compatibilization, is proposed to improve the interfacial adhesion between an LCP and an isotropic polymer.

Effects of Monomeric Sequence Distributions on Physical Properties of Thermotropic Liquid Crystalline Copoly(ester-imide)s

Thermotropic liquid crystalline copoly(ester-imide)s were synthesized from n-(ω-carboxyalkylene) trimellitic imide, 2,6-dihydroxynaphthalene, and p-hydroxybenzoic acid. The synthesized polymers were abbreviated as PEIM, CPHA, CPHB, CPHC, and CPHD, corresponding to mole fractions of p-hydroxybenzoic acid (PHB) to PEIM varied from 0 to 1/3, 1/2, 2/3, and 3/4. We investigated the monomeric sequence distributions by high resolution 13C NMR and their effects on the thermal, viscoelastic properties and molecular orientation of copoly(ester-imide)s. The solids of CPHA and CPHB with short runs of PHB blocks in a main chain preserved a nematic glassy state during the cooling process because of the slow crystallization. The low degree of crystallinity and slow crystallization rate were considered to be caused by the absence of long runs of PHB blocks. But CPHC with long runs of PHB blocks showed a high tendency to crystallize and, therefore, the hysteresis of viscoelastic properties in heating and cooling was observed. The residual crystallites of CPHC were considered to hinder the molecular orientation during melt spinning.