Series Of Liquid Crystalline Polyesters Research Articles

주사슬에 X-자 모양의 메소젠기를 갖는 액정폴리에스터의 합성 및 성질

주사슬에 X-모양의 메소젠기를 갖는 액정폴리에스터 시리즈가 단위체인 2,5-디(4-치환된 벤조에이트)하이드로퀴논과 4,4'-디카르복시-1,8-디페녹시옥테인으로부터 용액중합에 의해 합성되었다. 합성된 중합체의 구조와 물성들은 <TEX>$^1H$</TEX>-NMR, FT-IR, DSC, TGA, POM, WXRD를 이용하여 조사되었다. 1,1,2,2-테트라클로로에탄 내에서 측정된 중합체의 고유점성도(<TEX>${\eta}_{inh}$</TEX>)는 0.35~0.66 dL/g로 측정되었으며, 본 실험에서 용해도 조사에 사용된 대부분의 유기용매에 잘 용해되었다. 모든 중합체들은 비교적 낮은 용융전이온도(<TEX>$T_m$</TEX>)와 결정성을 나타내었으며, <TEX>$T_m$</TEX> 이상으로 가열했을 때 열방성 네마틱 액정성을 보였다. 중합체의 이러한 특성은 주사슬에 결합되어 있는 벌키한 4-치환된 벤조에이트기에 때문인 것으로 보인다. A series of liquid crystalline polyesters containing X-shaped mesogenic groups in main chain were synthesized through the solution polymerization of 2,5-di(4-substituted benzoate)hydroquinones and 4,4'-dicarboxy-1,8-diphenoxyoctane. The structures and properties of synthesized polymers were investigated by <TEX>$^1H$</TEX>-NMR, FT-IR, differential scanning calorimetry (DSC), thermogravimetry analysis (TGA), polarized optical microscopy (POM) and wide angel X-ray diffraction (WXRD). Inherent viscosities (<TEX>${\eta}_{inh}$</TEX>) of polymers were measured between 0.35 and 0.66 dL/g in 1,1,2,2-tetrachloroethane, and they were easily soluble in most of organic solvents used for this experiment. All polymers revealed relatively low melting transition temperature (<TEX>$T_m$</TEX>) and crystallinity, and also showed thermotropic nematic liquid crystallinity when they were heated to their melting temperatures. These properties of polymers were presumably due to the presence of the bulky substituting groups on the hydroquinone unit in mesogenic group.

Two New Thermotropic Liquid Crystalline Polyesters and their Composites: Synthesis and Characterization

Two new series of liquid crystalline polyesters were synthesized using melt polycondensation reaction.Glass fiber,as a reinforcement,was meltpolymerized with 4-acetoxybenzoic(ABA),4,4＇-diacetoxybiphenyl, isophthalic acid(IA) and terephthalic acid(TA) to make TLCP/GF composites with a good mechanical properties.All the obtained compounds were characterized by conventional spectroscopic methods. The structure of the target compounds and intermediates was conformed by the IR, 1H NMR and SEM. The thermal behavior of the polymers has been characterized using polarized optical microscopy and differential scanning calorimetry. The effect of monomer structure and mechanical properties has been investigated on the prepared polyesters. These compounds show a high birefringent Schlierene texture characteristic of the nematic phase on heating and cooling experiments. This was further confirmed using differential scanning calorimetric investigations.The melting points of polymers having a central 4,4’-biphenyldicarboxylate residue have broad endotherms. The glass transition temperature values of polyesters are not effect by the glass fiber.According to the SEM result showed that the composite had strong fiber-matrix adhesion.The effect of copolymerization with added glass fiber in synthesis process is compared with that of the anlogous homopolyesters by other processing mode.Our finding shows that the copolymers exhibit reduced technical process and maintained mechanical properties.

Callimatic and T-shaped liquid crystalline compounds with fluorinated terminal groups

A series of liquid crystalline polyesters with a rigid T-shaped or a stick-like mesogenic fragment and fluorinated terminal groups of various structures was synthesized and studied by means of polarization optical microscopy, differential scanning calorimetry, and IR and 1H NMR spectroscopy. It was shown that the effect of the fluorinated group on the thermostability of the mesophase depends on the shape of the mesogenic fragment. The thermostability of the mesophase in callimatic liquid crystalline compounds with perfluorinated terminal groups is higher and in those with difluoromethyl terminal groups containing one hydrogen atom is lower compared with their alkyl analogs. This is connected with the possibility of weak hydrogen bonding that destroys the liquid crystalline order. The thermostability of the mesophase in compounds with a T-shaped mesogenic fragment and any fluorinated terminal groups is always higher compared with their alkyl analogs.

Synthesis and characterization of thermotropic liquid crystalline polyesters with biphenyl unit in the main chain

Two new series of liquid crystalline polyesters containing central biphenylene moiety in the mesogenic unit with ester and ether linkages to the different lengths of flexible spacers (series I and II, respectively) were synthesized using melt polycondensation reaction. All the obtained compounds were characterized by conventional spectroscopic methods. The copolymer compositions were obtained from 1H NMR. The thermal behavior of the polymers has been characterized using polarized optical microscopy and differential scanning calorimetry. The effect of monomer structure and methylene spacer length has been investigated on the prepared polyesters and is also compared with that of the analogous polyester having central phenylene unit. Optical microscopy showed a highly threaded liquid crystalline texture to a high birefringent Schlierene texture characteristic of the nematic phase for all polyesters. DSC experiments were also found in accord with mesophase formation. The melting points and isotropization temperature values of series I polymers having a central 4,4′-biphenyldicarboxylate residue were significantly higher than those of the series II having a central 4,4′-biphenol moiety due to different molecular geometry. The glass transition temperature values of series I polyesters are also higher than those for series II because of increased chain rigidity. The effect of copolymerization on liquid crystallinity has been studied on the prepared copolymers from equimolar mixture of monomer with different lengths of spacers (n=4, 6) and it is compared with that of the analogous homopolyesters. Our finding shows that the copolymers exhibit reduced melting point and extended liquid crystalline range.

Synthesis of Liquid Crystalline Polyesters of Various Types by Acyclic Diene Metathesis Polymerization

A series of liquid crystalline polyesters of different types were prepared by the acyclic diene metathesis polymerization method. These polymers are of main-chain, side-chain, and combined types. Polymerizations were conducted at 25−50 °C either in solution or in bulk using the so-called Grubbs' catalyst, bis(tricyclohexylphosphine)benzylideneruthenium dichloride. The monomers utilized in this investigation are all isolated dienes containing a built-in aromatic type mesogenic unit or an aromatic ester type mesogen bearing the cholesterol pendant through oxydodecyloxy spacer or monomesogenic terephthalate ester unit bearing the cholesterol pendant through a spacer. Bulk polymerization produced higher MW polymers than solution polymerization as expected from the known polymerization mechanism. Liquid crystallinity and phase transition properties of obtained polymers were studied by differential scanning calorimetry, optical microscopy, and X-ray diffraction.

New Bilaterally Linked Mesogens in Main-Chain Polymers with Exhibition of Biaxial Fluctuation in Nematic Phase

The synthesis of a new series of liquid crystalline polyesters with bilaterally linked mesogens is described. The investigation of their mesomorphic behaviors by differential scanning calorimetry, ...

High-pressure DTA study on liquid crystalline polyesters with biphenyl as mesogen

The phase transition of a homologous series of liquid crystalline polyesters was studied under hydrostatic pressures up to 300 MPa by using a high-pressure DTA apparatus. The thermotropic polyesters, abbreviated as PB- n (where n is an even number of methylene units), were prepared from 4,4′-dihydroxybiphenyl and aliphatic dibasic acids containing an even number of methylene groups from 8 to 22 units. The T vs. P phase diagrams of the PB-10, PB-12, PB-14 and PB-18 polyesters were constructed. PB-10 shows a simple phase transition of melt (I) over the whole pressure region. PB-12 shows a similar region. PB-12 shows a similar KS H-I KS HI transition in the low-pressure region below about 100 MPa. At high pressures above 100–120 MPa, however, PB-12 exhibits a T vs. P relation that is different from that in the low-pressure region. The phase diagram supports the existence of the pressure-induced smectic phase which was assigned to be the smectic-B (S B) phase. The PB-14, PB-16, and PB-18 samples show an additional first-order transition just below the KS H transition at atmospheric pressure. The new transition peak increases with increasing space n in the PB- n samples, in contrast to the decrease in the KS H transition peak. The transition is a kind of crystal transition between the low- and high-temperature phases, denoted here as K 1 and K 2. The thermal behavior of these samples can be understood as enantiotropic transitions through the K 1K 2S HI route. They show the same type of T vs. P phase diagram, indicating the K 1K 2, K 2S H and S HI transition lines. The phase diagrams indicate that the stable region of the S H phase broadens with increasing pressure. However, the K 2S H transition peak becomes too small to be detected under pressures of 300–400 MPa.

Liquid crystalline polyesters with 1,4‐cyclohexylene units

AbstractA new series of liquid crystalline polyesters (5a – f) containing 1,4‐cyclohexylene dibenzoate moieties as mesogenic units in the main chain was prepared and characterized. The rigid segments in the polymers are connected by α,ω‐alkanedioyl units containing 4–8 or 10 methylene groups.