Thermotropic Polyurethanes Research Articles

Synthesis of thermotropic polyurethanes containing ester mesogen units and their mesophase behavior

AbstractA series of novel thermotropic liquid crystalline was synthesized from bi(p-hydroxyl benzoic acid)hydroquinone ester (PHQ), triethylene glycol and 2,4- toluenediisocyanate (2,4-TDI) by altering the molar ratio of PHQ and diol, and PHQ was prepared by using hydroquinone and p-hydroxybenzoic acid as raw materials. The thermotropic mesophase behavior, the melting point temperature (Tm) and the isotropization temperature (Ti) of the synthesized polyurethanes were characterized by FT-IR, DSC and POM. It showed that all of the polyurethane polymers exhibited nematic textures at temperature of 110~230 °C. The shift of the melting and isotropization temperature (Tm, Ti) to lower temperature is discussed to be a consequence of the increasing amount of diol content.

Synthesis of Thermotropic Polyurethanes Containing Biphenylnate and Imide Units and their Mesophase Behavior

A series of novel liquid crystal polyurethanes containing biphenylnate and imide units were synthesized through the polyaddition reaction of 4,4′-Bis-(2-hydroxyhexoxy)biphenyl (BP2), 2,4-toluenediisocyanate (2,4-TDI) with N,N′-bis(2-hydroxyhexyl)-dicarboxyimide (BHDI) by altering the molar ratio of BP2 and BHDI. The effects of structure difference molar ratio between BP2 and BHDI on the liquid crystalline behavior and thermal stability were studied. Results showed that all of the polyurethane polymers exhibited thermotropic nematic liquid crystalline textures in the range of 160~190°C. The melting temperatures (Tm) and the thermal stability increased with increasing BHDI content.

SYNTHESIS AND CHARACTERIZATION OF NEW THERMOTROPIC LIQUID CRYSTALLINE POLYURETHANES WITH BIPHENYL MOIETY

A new series of thermotropic polyurethanes containing biphenyl units was synthesized by polyaddition reaction of diisocyanates such as 2,6-tolylene diisocyanate, 2,5-tolylene diisocyanate, 2,4-tolylene diisocyanate, and 1,4-phenylene diisocyanate, with 4,4□-bis(9-hydroxynonoxy)biphenyl (BP9). Structures of the monomer and the corresponding polymers were identified using FT-IR and 1 H NMR spectroscopic methods. BP9 exhibited a smectic type mesophase, however, nematic phase was found for all synthesized liquid crystalline polyurethanes except for 1,4-phenylene diisocyanate/BP9 based polyurethane. Their phase transition temperatures and thermal stability were investigated by differential scanning calorimetry (DSC), optical polarizing microscopy, and X-ray scattering. The infrared study indicated that the hydrogen bonding among urethane linkages attributed to the mesomorphism. Thermal gravimetric analysis (TGA) of synthesized polyurethanes showed that no weight loss of the polymers observed up to 280°C.

Characterization of molecular structures and properties of polyurethanes using molecular dynamics simulations.

Thermotropic polyurethanes with mesogenic groups in side chains were prepared from two diisocyanates and four diols with stoichiometric ratios of reactive isocyanate (NCO) and hydroxy (OH) groups. Their thermal behavior was determined by differential scanning calorimetry. The effect of structure modifications of the diisocyanates and diols, in particular changes in the mesogen, were investigated. Introduction of mesogenic segments into the polymers suppresses the ordering. Stiff end substituents (phenyl and alkoxy groups) of the mesogens stabilize the mesophases to such an extent that the negative influence of long polymer chains is compensated and the liquid-crystalline properties are recovered. All-atom molecular dynamics simulations in the Cerius2 modeling environment were carried out to characterize the structures of the polymers. Analysis of the dynamic trajectories at 20, 100, 120 and 170 degrees C revealed changes in conformation of macromolecules, which correlate with DSC measurements.

Thermal and dynamic mechanical behavior of polyurethanes based on diisocyanates and diethanolamine derivatives with mesogenic groups in side chain

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.

Synthesis of thermotropic polyurethanes containing imide units and their mesophase behavior

Thermotropic polyurethanes were synthesized from 1,6-hexane diisocyanate (HDI) as a diisocyanate, 1,6-hexane diol (HD), and rigid diols containing imide unit such as N,N′-bis(4-hydroxyphenyl)-3,4,3′,4′-biphenyl-dicarboxyimide (BPDI) or bis-N-(4-hydroxyphenyl)-4,4′-oxydiphthalimide (ODPI). The effects of structure difference between BPDI and ODPI and composition of HD/BPDI (ODPI) on the thermal and liquid crystalline behavior were studied. Thermotropic polyurethanes with an inherent viscosity of 0.59–0.70 were obtained. The melting temperature of BPDI-based polyurethanes were in the range of 150–290°C, however, those of ODPI-based polyurethanes were in the range of 150–190°C. All the polyurethanes based on ODPI (25–100 mole %) clearly exhibited a stable liquid crystalline phase, and BPDI-based polyurethane having 5–25% of BPDI showed a mesophase. The melting and isotropization temperatures (T m , T i ) andΔT(T i −T m ) increased with increasing BPDI and ODPI content. The polyurethanes based on BPDI has higher melting points and thermal stability compared to ODPI-based polyurethanes.

Changes of Mechanical Properties and Phase Separated Structure of Thermotropic Polyurethane Fiber under the Periodic Elongation and Recovery.

The periodic structure, which is composed of hard and soft domains, oriented along the fiber axis in the melt spun thermotropic polyurethane fiber. The phenomena of structure and mechanical properties change can be divided into three extension ratio ranges, less than 1.2, from 1.2 to 1.5, and more than 1.7. There are little changes in the structure and the properties observed for extension ratio less than 1.2. The periodic structure became apparent at the extension ratio 1.2-1.5. The short relaxation time component, the maximum stress, and the energy loss were steeply increased at that extension range. The periodic structure vanished by over 1.7 times extension, but it reconstructed by the relaxation process. The residual strain and the loss energy decreased obviously by the previous extension-recovery. For example, the ratio of 2nd cycle residual strain to the 1st cycle one was about 30% for extension ratio 1.5 and 1.7, whereas it was 13-19% for extension ratio more than 2.

Side-chain liquid crystalline polyurethanes on the basis of biphenyl mesogenic units

Liquid crystalline diols containing a biphenyl mesogenic core, methoxy or cyano terminal groups and spacers of various lengths were synthesized and used for the preparation of side-chain thermotropic polyurethanes. The structure of the synthesized diols and polymers was confirmed by elemental analysis, FTIR and NMR spectroscopy. Phase transition temperatures were studied by DSC, while optical textures were characterized by polarizing microscopy. A smectic type arrangement was found for the mesophases of all products.

Studies on thermotropic liquid crystalline polyurethanes. III. Synthesis and properties of polyurethane elastomers by using various mesogenic units as chain extender

Four series of thermotropic polyurethane elastomers (TPUEs) were synthesized in this study. The hard segments were formed by using 4,4′-methylenedicyclohexyl diisocyanate (H12MDI) reacted with various mesogenic units, such as benzene-1,4-di(4-iminophenoxy-n-hexanol), benzene-1,4-di(4-iminophenol), and 3,3′-(4,4′-biphenylene)dipropanol, which also acted as the chain extender. Poly(oxytetramethylene)glycols (PTMEGs), PTMEG-2000 (Mn 2,000) and PTMEG-1000 (Mn 1,000) were used as a soft segment. The structures of all synthesized thermotropic liquid crystalline polyurethanes (TLCPUs) were characterized by FTIR spectroscopy. The effects of mesogenic units on the LC properties and elastic behaviors of LCPUs were studied. It was difficult to show LC behaviors for the PU elastomers derived from the mesogenic units with a lower aspect ratio, such as 3,3′-(4,4′-biphenylene)dipropanol, or the long soft segments, PTMEG-2000. In addition, these PU elastomers show better elastic properties by using a higher aspect ratio mesogenic unit as the chain extender, such as benzene-1,4-di(4-iminophenoxy-n-hexanol and benzene-1,4-di(4-imino-phenol)). The thermal properties were investigated by DSC measurements, thermal optical polarized microscopy, wide angle X-ray diffraction, dynamic mechanical analysis, and thermogravimetric analysis. The mechanical properties were measured by a tensilemeter. © 1996 John Wiley & Sons, Inc.

Synthesis and Liquid Crystalline Properties of New Thermotropic Polyurethanes

Abstract The synthesis and liquid crystal behavior of new thermotropic polyurethanes derived from different mesogenic diols, alkylene di[4-(ω-hydroxyalkyloxy-4-oxybenzoyI)oxybenzoate]s, and 2,4-toluenediiso-cyanate are reported. Depending upon the chemical structure of the repeat unit, the polyurethanes formed either one or two mesophases extending over a fairly broad (>60 K) and accessible range of temperature (T, < 430 K). A cybotactic nematic mesophase was identified in each polyurethane sample.

Synthesis and liquid-crystalline properties of thermotropic polyurethanes prepared from 1,4-diisocyanates and 4,4'-bis(.omega.-hydroxyalkoxy)biphenyls

Thermotropic polyurethanes [O(CH 2 ) m OPHPhO(CH 2 ) m OCONHPh(R)NHCO] n (m= 2-6,8,11; R= H, Me) with intrinsic viscosities in the range of 0.41-0.99 dL/g were synthesized. DSC thermograms for these polymers exhibited two endothermic peaks corresponding to phase transitions of melting and isotropization. IR study indicated that the hydrogen bonding between urethane linkages affected the mesomorphism.

Development of crystallinity in a semiflexible thermotropic polyurethane. 2. Structure and dynamics

The monotropic liquid-crystalline polyurethane [CONHPh(CH 3 )NHCOO(CH 2 ) 6 OPhPhO(CH 2 ) 6 O] n is studied. The development of crystallinity is found to increase the conformational regularity of the polymer and, in particular, lead to development of two unique conformations of TDI urethane linkage in hydrogen bonding. Secondary relaxation processes involving reorientational motion of the inner hexamethylene spacer carbons, possibly a three-bond conformational jump motion, and the biphenyl mesogen are also identified and correlated with mechanically active relaxation processes

Polymers from multifunctional isocyanates, 6. Thermotropic di‐ and oligo(urethane)s from novel triad diisocyanatodiesters

AbstractThe first examples of triad diisocyanatodiesters with a substituent in the central aromatic ring, namely methyl‐, trimethyl‐, tert‐butyl‐, and phenyl‐substituted 1,4‐phenylene bis(4‐isocyanato‐benzoates), and bis(4‐isocyanatophenyl) trans‐1,4‐cyclohexanedicarboxylate are described. The diisocyanatodiesters melt in the range of 160°C, give nematic mesophases and have a clearing transition above 300°C except for the phenyl‐substituted diisocyanate which exhibits a monotropic mesophase. Due to the more favourable aspect ratio of the mesogens thermotropic diurethanes were obtained by reaction with butanol and oligomeric thermotropic polyurethanes resulted from the reaction with butanol and diethylene glycol, triethylene glycol, or 3‐methyl‐1,5‐pentanediol. The phase behaviour of the urethanes in relation to their structure is discussed. The thermal stability of the urethanes is limited by the occurrance of urethane cleavage.