Liquid crystal polymers—11. Structure-property relationships in a series of thermotropic poly(2-n-alkyl-1,4-phenylene terephthalates)

Majnusz, J.; Catala, J.‐M.; Lenz, Robert W.

doi:10.1016/0014-3057(83)90070-8

Cited by 158 publications

(48 citation statements)

References 7 publications

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“…Many studies have been devoted to decrease the melting point to a melt processable temperature range as well as to improve the solubility without destroying the liquid crystal formation. [1][2][3][4][5][6][7][8] For the thermoplastic polyurethanes, because of the strong intermolecular interaction resulting from the hydrogen bonding of urethane linkages, many studies were developed to minimize the hydrogen bonding effects using chain modifications. 9 -11 In liquid crystalline polyurethane elastomers (LCPUEs), it was revealed that the incorporation of mesogenic diol as a chain extender into the backbone could produce liquid crystalline character.…”

Section: Introductionmentioning

confidence: 99%

Synthesis and properties of liquid crystalline polyurethane elastomers

Lee

Kim

2000

J. Appl. Polym. Sci.

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Novel type of mesogenic chain extenders used in this study are N, 4,3Ј, and N, phenyl]-3,4,3Ј,4Ј-biphenyldicarboxyimide (BHDI). BHDI has a flexible spacer of 6-methylene units but BPDI does not. The liquid crystalline polyurethane elastomers were synthesized from BPDI or BHDI as a mesogenic chain extender, 4,4Ј-diphenylmethane diisocyanate, and poly(oxytetramethylene)glycol (MW 1000) as a soft segment. Polyurethane based on BHDI exhibited two melting transitions. However, any melting behavior was not shown in the BPDI-based polyurethanes because of higher melting temperature than decomposition temperature. The composition of polyurethanes was varied as a means of manipulating liquid crystalline behavior and physical properties. The BHDI-based polyurethanes containing above 50 wt % of hard segment content exhibited nematic liquid crystal behaviors. As the hard segment content of the BHDIbased polyurethanes increased, the glass transition temperature (T g ), strength, modulus, and the amount of hydrogen bonding increased.

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Section: Introductionmentioning

confidence: 99%

Synthesis and properties of liquid crystalline polyurethane elastomers

Lee

Kim

2000

J. Appl. Polym. Sci.

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“…30 Moreover, TLCP clearing temperatures depend on molecular weight below a certain critical value. [30][31][32][33][34][35]51,52 Therefore, the temperature (T NI ) at which η goes through a maximum in Figure 10 corresponds to the clearing of the highest molecular weight fractions while the minimum (at a lower temperatures) corresponds to the clearing of the lowest molecular weight TLCP chains. If the polymer were monodisperse, the biphasic region in Figure 10 would be extremely narrow.…”

Section: Growth Of Shear Stress and Normal Stress Difference Upon Stamentioning

confidence: 99%

“…30 000 g/mol). [30][31][32][33][34][35] Therefore, concerning phase behavior and rheooptical changes associated with the clearing transition, the choice of T NI as a reference temperature minimizes, if not eliminating completely, the effect of molecular weight on ∆n + (t,γ ) and ∆n. More specifically, it has been amply demonstrated in the literature 21,[36][37][38] that the viscosity of TLCPs in the nematic state first decreases, going through a minimum, and then increases, going through a maximum at T NI , finally decreasing again as the temperature is increased from the nematic state to the isotropic state.…”

Section: Birefringence In Startup Of Shear Flow In the Nematicmentioning

confidence: 99%

Optical and Mechanical Rheometry of Semiflexible Main-Chain Thermotropic Liquid-Crystalline Polymers with Varying Pendant Groups

2000

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A specially designed flow cell was used to investigate birefringence in transient shear flow, ∆n + (γ ,t), of three semiflexible main-chain thermotropic liquid-crystalline polymers (TLCPs), poly[(x)-pphenylene 1,10-decamethylenebis(4-oxybenzoate)] (PxHQ10) with varying pendant side groups (x ) oxyethyleneethoxy, tert-butyl, or phenylsulfonyl). Also, shear rheometry was used to investigate the growth of shear stress σ + (γ ,t) and first normal stress difference N1 + (γ ,t) during transient shear flow of the same TLCPs. Upon startup of shear flow, ∆n + (γ ,t) initially increases rapidly, follows two minor overshoots, and then levels off to attain a steady-state value ∆n in all three TLCPs. The steady-state value of ∆n for PSHQ10 (PxHQ10 with x ) phenylsulfonyl pendant side group) was found to be greater than that for PEHQ10 (PxHQ10 with x ) ethoxy pendant side group) and PTHQ10 (PxHQ10 with x ) tert-butyl pendant side group). This behavior is strongly correlated to the large van der Waals volume of phenylsulfonyl pendant side groups in PSHQ10 compared to that of ethoxy pendant side groups in PEHQ10 and tertbutyl pendant side groups in PTHQ10. It is also observed that N 1 + (γ ,t) exhibits a very large overshoot followed by an oscillatory decay to attain a steady-state value N1, while σ + (γ ,t) shows a very large overshoot followed by a rapid monotonic decrease to attain a steady-state value, σ. The peak values of N1 + (γ ,t) and σ + (γ ,t) for PSHQ10 were found to be 3-4 times greater than those for both PEHQ10 and PTHQ10, which we again attribute to the bulky phenylsulfonyl pendant side groups in PSHQ10. Only positive values of N1 + (γ ,t) and N1 were observed over the entire range of shear rates investigated. Variations of the ratio N1 + (γ ,t)/σ + (γ ,t) with shear strain (γ t) were found to be very similar to variations of ∆n + (γ ,t) with γ t for all three TLCPs investigated, except for that the ratio N1 + (γ ,t)/σ + (γ ,t) reached a steady state sooner than ∆n + (γ ,t). In steady-state shear flow, it is observed that the ratio N1/σ overlaps ∆n over the entire range of temperatures investigated; specifically, both the ratio N1/σ and ∆n remain constant at temperatures far below the clearing temperature (TNI), decrease gradually as the temperature approaches TNI, and drop precipitously to zero value at and near TNI.

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“…Substantial decreases in Tm and T; values were only achieved when fairly long pendant alkyl substituents were used, so polymers containing n-alkyl groups ranging from the hexyl to the dodecyl (n = 5 to II in Series I) were prepared for this purpose, with the results shown in Table II. 33 Because the polymer samples in Table II varied quite widely in molecular weight, as indicated by their solution viscosities, it is not possible to make exact comparisons of the effects of substituent length on their liquid crystalline properties, but as the data in Table II show, there was only a surprisingly small variation in both T m and T; with alkyl group length. What is also unexpected is that some of the polymers in Series I, particularly those with the decyl substituent, appear to form a smectic phase on melting, but additional characterization studies are needed to verify this conclusion.…”

Section: Pendant Group Flexible Unitsmentioning

confidence: 97%

Synthesis and Properties of Thermotropic Liquid Crystal Polymers with Main Chain Mesogenic Units

Lenz¹

1985

Polym J

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ABSTRACT:The molecular variables which control the structure-property relationships in thermotropic liquid crystalline polyesters are under investigation in this laboratory. A wide variety of polymers based on rigid, linear aromatic ester mesogenic units, with and without flexible or rigid spacers, have been prepared and characterized for their ability to form a liquid crystalline melt, the type of phase formed, their transition temperatures, and the morphology of the mesophase. Flexible spacers reduce both the melting and clearing temperatures, and the type and length of the spacer can determine whether either a nematic, cholesteric or smectic phase is formed. Variations in the structure of the rigid mesogenic group, both in the specific type and arrangement of the aromatic ester groups and the presence of pendant substituent, also cause profound changes in the properties of the mesophase melt formed.

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Liquid crystal polymers—11. Structure-property relationships in a series of thermotropic poly(2-n-alkyl-1,4-phenylene terephthalates)

Cited by 158 publications

References 7 publications

Synthesis and properties of liquid crystalline polyurethane elastomers

Synthesis and properties of liquid crystalline polyurethane elastomers

Optical and Mechanical Rheometry of Semiflexible Main-Chain Thermotropic Liquid-Crystalline Polymers with Varying Pendant Groups

Synthesis and Properties of Thermotropic Liquid Crystal Polymers with Main Chain Mesogenic Units

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