Bis 6-hydroxyhexoxy Biphenyl Research Articles

Synthesis and characterization of thermotropic liquid crystalline polyurethanes from 4,4′‐bis(6‐hydroxyhexoxy) biphenyl and aliphatic diols

AbstractA series of thermotropic liquid crystalline polyurethanes (LCPUs) were synthesized by the polyaddition reactions of 2,4‐toluene diisocyanate (2,4‐TDI) with 4,4′‐bis(6‐hydroxyhexoxy)biphenyl (BHHBP) and aliphatic diol. The intrinsic viscosities of the polymers were measured by Ubbelohde viscometer, and the chemical structure was confirmed by Fourier transform infrared spectroscopy (FT‐IR). The LCPUs were examined by differential scanning calorimetry (DSC), polarized optical microscopy (POM), wide angle X‐ray diffraction (WAXD), and thermogravimetric analysis (TGA). The intrinsic viscosities were 0.56–0.83 dl/g. According to the melting point (Tm) and the isotropic temperature (Ti) of the LCPUs, the temperature range of the liquid crystalline phase became wider with increased number of methylene spacers in the polyurethane. The LCPUs exhibited a nematic phase with a threaded texture and had a wide mesophase temperature range. The decomposition temperature of the LCPUs was >300°C. On WAXD, the LCPUs give a dispersing peak at 2θ ≈ 20°, and a strong diffraction peak at 2θ ≈ 25°. Copyright © 2008 John Wiley & Sons, Ltd.

Shape memory polyurethane containing mesogenic moiety

The mechanical and thermal properties, in particular the shape memory effect, of TPUs synthesized from diol-terminated poly(caprolactone) (PCL diol), 4,4′-diphenylmethane diisocyanate (MDI), and mesogenic chain extenders, 4,4′-bis-(2-hydroxyethoxy)biphenyl (BEBP) or 4,4′-bis-(6-hydroxyhexoxy)biphenyl (BHBP) were examined and compared with results for PCL diol/MDI/1,4-butanediol (BD) based TPUs in a previous study. Some results related to the rigid structure of BEBP or BHBP were observed in the thermomechanical properties. Shape fixity was related to the crystallization of the PCL phase.

Properties of Polyurethanes Based on Mesogenic Diol and 4,4'-methylenebis(cyclohexyl Isocyanate)

New polyurethanes with mesogenic units in the main chain due to the use of a liquid crystalline chain extender were synthesized from 4,4'-methylenebis(cyclohexyl isocyanate) (HMDI)using diisocyanates of different trans, trans isomer content, a low molecular diol4,4'-bis(6-hydroxyhexoxy)biphenyl (BHHBP) and a high molecular poly(hexyleneadipate)diol (PHA). The growth of trans, trans isomer content in HMDI used to syntheses of PU induces monotonic growth of melting point, rectilinear growth of crystallization temperatures and the growth of crystallization enthalpy, both for hard segment polyurethanes and block polyurethanes. The increase of trans, trans isomer content in HMDI increases also glass transition temperatures and dynamic storage modulus of the polyurethanes.

Unusual Perpendicular Chain Orientation in a Smectic Liquid Crystal Polyester Subjected to Shear or Elongational Flow

Abstract In this work, we report on flow-induced orientation in two low molecular weight polyesters, both containing the smectic diol 4,1′-bis (6-hydroxy hexoxy) biphenyl (BHHBP) and either isophthalic acid (IA) or terephthalic acid (TA). The polyester of BHHBP and IA has a mesophase, while the polyester of BHHBP crystallises on cooling from the isotropic melt without any mesophase formation. When the TA polyester was subjected to flow, the chains were aligned parallel to the flow direction. In contrast, when the IA polyester was sheared or subjected to elongational flow in the mesophase state, it was found that the chains were surprisingly oriented perpendicular to the flow direction or the fibre axis. However, when the IA polyester was sheared or elongated in the isotropic molten state, the normal orientation with the chain axis parallel to the flow direction was observed. Thus, perpendicular orientation appears to have an association with deformation in the mesophase state. The orientation information ...

A monotropic liquid crystal polyester with a biphasic nematic-smectic phase

The polyesters made from the condensation of isophthalic acid (IA) or terephthalic acid (TA) with the mesogenic diol 4,4′-bis (6-hydroxy hexoxy)biphenyl (BHHBP) are both reported to show a smectic mesophase. However, in our previous work, we found evidence for a mesophase in the polyester containing BHHBP and IA, but not in the one with BHHBP and TA. For the BHHBP-IA polyester, we thought the phase sequence on cooling was I → SA → K, while on heating the situation was unresolved; there was some indication that on heating, a K → I transition occurs without any intervening mesophase. In other words, it was suspected that the mesophase in the IA polyester was monotropic. In this work, we have now obtained firm evidence that the mesophase behavior of the BHHBP-IA polyester is indeed monotropic. Further, an additional complexity has been found: on cooling, there is in fact a nematic phase, besides a smectic A, and a crystal phase. However, the mesophase appears to be complex. As the nematic and smectic textures occurred simultaneously, it seems that the mesophase is a nematic-smectic biphase. © 1996 John Wiley & Sons, Inc.

Adherence of Liquid Crystalline TDI-Polyurethanes to Steel

Abstract Linear liquid crystalline polyurethane (LC-PU) were synthesized by the reaction of 2,4-toluene diisocyanate (TDI), 4,4′-bis-(6-hydroxyhexoxy)biphenyl (BHHBP), and poly(butylene adipate) (PBA). The BHHBP as mesogenic unit was incorporated into the hard segment formed by the reaction with the TDI. The hard segments are incompatible with the PBA soft segments. The mesomorphic behaviour is influenced by both the soft segment length and the hard segment concentration. The adhesion of such polyurethanes used as primer in composites based on steel as substrate and alkyd melamine resin as coating is dependent on the polyurethane structure, the thickness of the polyurethane layer and its drying conditions. The highest wet adhesion stability is achieved by the hard-segment-type polyurethane composed of TDI and the mesogenic unity BHHBP. Partial substitution of BHHBP by 2,2-bis-(hydroxymethyl)propionic acid (BHMPA) in this LC polyurethane enhances the effectiveness of the primer.

Miscibility of a liquid crystalline polyurethane with common segmented polyurethanes

Abstract The phase behaviour of blends of a liquid crystalline polyurethane A, based on 4,4′-bis(6-hydroxyhexoxy)-biphenyl (BHHBP) as the mesogenic diol and toluene 2,4-diisocyanate (TDI), with common segmented polyurethanes B (based on poly(tetramethylene adipate), methylene di- p -phenylene isocyanate (MDI) or toluene 2,4-diisocyanate (TDI) and 1,4-butanediol) with various segment lengths was studied by differential scanning calorimetry (d.s.c.) and electron microscopy. No miscibility of the polyurethane A and the hard segments of the different polyurethanes B, independent of the length of the hard segments and the type of diisocyanate used, was observed. With decreasing length of the soft segment an increasing amount of the liquid crystalline polymer (LCP) can be mixed with the amorphous phase of the soft segment in the case of the MDI-polyurethanes, whereas the TDI-polyurethanes B are completely immiscible with polyurethane A.

Correlation of observations made by DSC and hot-stage optical microscopy of the thermal properties of a monotropic liquid-crystal polyester

The polyester formed by condensation of 4,4′-bis(6-hydroxyhexoxy)biphenyl (BHHBP) and isophthalic acid has been reported to show many interesting and intriguing thermal properties. By optical microscopy, we established that the polymer shows monotropic liquid-crystalline behaviour. Thus, on heating, no mesophases are formed and the crystal melts directly to the isotropic state; on cooling, however, the material transforms from the isotropic melt to a nematic and smectic A mesophase before crystallizing. However, the DSC heating scan of this polymer was very complex, showing an exotherm and two endotherms; further, unlike the phenomenon of cold crystallization, the exotherm occurred between the two endotherms. If there is only a single phase transition (crystal-isotropic) on heating, then the multiple peaks need to be explained. In this work, we have shown that the multiple peaks in the heating scan are solely related to the thermal history of the sample. The nascent polymer and quench-cooled material showed multiple peaks during heating, whereas slowly crystallized polymer showed a single melting endotherm. By quench cooling from the isotropic melt, it was not possible to obtain the material in an amorphous form, because this polyester had a propensity for fast ordering. In the previous work, on cooling, we only found two instead of three DSC peaks. Here, we have attempted to see if three peaks (corresponding to I-N, N-S A and S A-K) can be resolved by going to very slow cooling rates (0.1°C min −1). It was found that even at such low cooling rates, I-N and the N-S A transitions could not be separated into distinct peaks. This is in accord with optical microscope observations which indicated that the transformation to the smectic phase from the nematic was never complete and was overtaken eventually by crystallization. This kind of incomplete phase transformation appears to be a feature of this monotropic liquid-crystalline polymer.

Segmented polyurethanes with 4,4?-bis-(6-hydroxyhexoxy)biphenyl as chain extender. Part 2. Synthesis and properties of MDI-polyurethanes in comparison with 2,4-TDI-polyurethanes

Linear segmented polyurethanes based on poly(butylene adipate)s (PBA) of different molecular weight (Mn 2000, 1000, and 600), 4,4′-diphenylmethane diisocyanate (MDI) and the mesogenic diol 4,4′-bis-(6-hydroxyhexoxy)biphenyl (BHHBP) as well as the unsegmented polyurethane consisting of MDI/BHHBP units have been synthesized and characterized by elemental analysis, 13C-NMR and SEC. The thermal behavior and the morphology were studied by DSC, polarizing microscopy, and DMA. The properties of the MDI-polyurethanes were discussed in relation to the BHHBP chain extended 2,4-TDI-polyurethanes and common 1,4-butanediol chain-extended MDI products. MDI polyurethanes based on PBA (Mn 2000) exhibit a glass transition temperature Tg of about −40°C independent of the hard segment content up to ∼50% hard segments. At higher hard segment contents increasing Tgs were observed. Polyurethanes, based on the shorter polyester soft segments PBA (Mn 1000 or 600), reveal an increase in the glass transition temperatures with growing hard segment content. The thermal transitions caused by melting of the MDI/BHHBP hard segment domains are found at 50 K higher temperatures in comparison with the analogous TDI products with mesogenic BHHBP/TDI hard segments. Shortening of the PBA chain length causes a shift of the thermal transitions to lower temperatures. Polarizing microscopy experiments indicate that liquid crystalline behavior is influenced by both the content of mesogenic hard segments and the chain length of the polyester. © 1996 John Wiley & Sons, Inc.

Segmented polyurethanes with 4,4′‐bis‐(6‐hydroxyhexoxy)biphenyl as chain extender. Part 2. Synthesis and properties of MDI‐polyurethanes in comparison with 2,4‐TDI‐polyurethanes

Linear segmented polyurethanes based on poly(butylene adipate)s (PBA) of different molecular weight (Mn 2000, 1000, and 600), 4,4′-diphenylmethane diisocyanate (MDI) and the mesogenic diol 4,4′-bis-(6-hydroxyhexoxy)biphenyl (BHHBP) as well as the unsegmented polyurethane consisting of MDI/BHHBP units have been synthesized and characterized by elemental analysis, 13C-NMR and SEC. The thermal behavior and the morphology were studied by DSC, polarizing microscopy, and DMA. The properties of the MDI-polyurethanes were discussed in relation to the BHHBP chain extended 2,4-TDI-polyurethanes and common 1,4-butanediol chain-extended MDI products. MDI polyurethanes based on PBA (Mn 2000) exhibit a glass transition temperature Tg of about −40°C independent of the hard segment content up to ∼50% hard segments. At higher hard segment contents increasing Tgs were observed. Polyurethanes, based on the shorter polyester soft segments PBA (Mn 1000 or 600), reveal an increase in the glass transition temperatures with growing hard segment content. The thermal transitions caused by melting of the MDI/BHHBP hard segment domains are found at 50 K higher temperatures in comparison with the analogous TDI products with mesogenic BHHBP/TDI hard segments. Shortening of the PBA chain length causes a shift of the thermal transitions to lower temperatures. Polarizing microscopy experiments indicate that liquid crystalline behavior is influenced by both the content of mesogenic hard segments and the chain length of the polyester. © 1996 John Wiley & Sons, Inc.

Phase transitions in two polyesters containing a smectic diol

AbstractThis work reports the phase behavior of the polyesters made from the condensation of isophthalic acid (IA) and terephthalic acid (TA) with the mesogenic diol 4,4′‐bis (6‐hydroxy hexoxy) biphenyl (BHHBP). The latter monomer forms a smectic mesophase in the interval 98‐179°C. Fischer et al., who investigated the room temperature x‐ray patterns of the oriented polyesters of BHHBP and IA, as well as BHHBP and TA, claimed that both polymers also showed smectic mesophases. However, they showed no other evidence to support their interpretation. In the present work, examination of these polyesters under the optical microscope revealed focal conic textures for the IA polyester, but spherulitic textures for the TA polyester. DSC studies revealed thermograms with two peaks in the cooling scan for the IA polyester, at different cooling rates, which supported the view that there were two phase transitions. The heating scans of the TA polyester showed multiple peaks that depended on heating rate whereas on cooling, only a single exothermic peak was observed at all cooling rates. Thus, the current results definitely support the case for a smectic A mesophase in the IA polyester but, contrary to Fischer et al.'s opinion, do not suggest any mesophase formation in the TA polyester. © 1995 John Wiley & Sons, Inc.

Segmented polyurethanes with 4,4′‐bis‐(6‐hydroxyhexoxy) biphenyl as chain extender. I. Synthesis and characterization of 2,4‐tdi‐polyurethanes

AbstractPolyurethanes composed of 2,4‐toluene diisocyanate (TDI), poly (butylene adipate) diols (PBA) of different molecular weights, and 4,4′‐bis‐(6‐hydroxyhexoxy) biphenyl (BHHBP) were prepared by a two‐step solution polymerization process. The polyurethanes were char‐acterized by elemental analysis, NMR, and SEC. The thermal properties were investigated by DSC, DMA, and optical polarizing microscopy. Dependent on the molecular weight of the PBA, a shift in the glass transition temperature Tg of the polyurethanes has been observed by DSC and DMA. Polyurethanes based on poly (butylene adipate)s of Mn ∼ 2000 exhibited a Tg nearly independent on the hard‐segment content up to 50% LC hard segments, indicating the existence of mainly phase separated soft and hard segments. By shortening the PBA chain length up to 1,000 and further to 600, the Tg of the polyester soft‐segment phase increases with growing hard‐segment content, a consequence of enhanced interaction between the hard and soft segments. This tendency is observed to the greatest extent at polyurethanes with the shortest, polyester diol and can be interpreted as a partial miscibility or compatibility of hard and soft segments. Although in polyurethanes with PBA 2000 the mesophase can be proven at a hard‐segment content of ∼ 40%, its appearance in polyure‐thances prepared with PBA 1000 or PBA 600 requires a hard‐segment content > 60%. © 1995 John Wiley & Sons, Inc.

Phase behavior and structure in mesogen containing polyurethanes

AbstractThe mesophase to crystal phase transition observed upon heating the monotropic liquid crystal polyurethane (2,6‐LCPU‐6), based on the mesogenic biphenol 4,4′‐bis(6‐hydroxyhexoxy)biphenyl (BHHBP) and 2,6‐toluenediisocyanate (2,6‐TDI), has been investigated by differential scanning calorimetry (DSC), wide angle x‐ray scattering (WAXS) and infrared (IR) spectroscopy. Hexafluoroisopropanol (HFIP) fast solvent‐evaporation casting resulted in 2,6‐LCPU‐6 thin films with a glassy mesophase morphology. The mesophase to crystal exothermic transition has been observed by DSC between 130 and 140°C, depending on sample preparation. It is accompanied by a substantial increase of H‐bonding between urethane C=O and N‐H, as observed by IR. Curve fitting analysis of the conformationally sensitive amide I region revealed three bands; ordered H‐bonded carbonyl groups, disordered H‐bonded carbonyl groups, and “free” carbonyl groups. The prime feature of the 130°C transition is the substantial increase of ordered H‐bonded carbonyl groups at the expense of disordered H‐bonded carbonyl groups. Crystal melting occurs between 180 and 210°C and is accompanied by the complete disappearance of the ordered H‐bonded peak along with substantial changes in the frequency and width at half‐height of the disordered H‐bonded peak

Structure in mesogenic diol-containing polyesters

Copolyesters synthesized from two mesogenic monomers have been investigated. The monomers are 4,4′-bis(6-hydroxyhexoxy)biphenyl (BHHBP) and the p-diester made from terephthaloyl dichloride and p-hydroxybenzoic acid. The incorporation of a very rigid, second mesogen increases the ability of BHHBP to form tilted mesophases. An untilted smectic A phase is formed initially, but the final, stable phase is a highly ordered, tilted smectic phase. Similar behavior is observed when BHHBP is combined with a mixture of the diacids of the crown ether dibenzo-18-crown-6. A copolymer of this type also forms a smectic A phase. For both types of copolymers, there is good agreement between the measured and calculated values for the layer distances.