Synthesis and properties of liquid crystalline polyurethane elastomers

Abstract

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.

Carotid stent‐supported angioplasty in a patient with symptomatic and critical aortic stenosis

“…The endotherm appearing at the lower temperature might be associated with a crystal–crystal transition because the polarizing microscope did not reveal any crystal–mesophase transition in this region. A similar observation was made by Lee et al33 The endotherms at 152.4 and 181.2 °C were the results of crystal–mesophase and isotropization temperatures, respectively, as confirmed with the polarizing optical microscope. The higher temperature melting endotherm at 193.7 °C was a result of the melting of microcrystalline hard segments, and this was observed in materials with longer aromatic urethane segments.…”

Synthesis and properties of new liquid crystalline polyurethanes containing mesogenic side chain

“…Conventionally, TLCPUs have been prepared by polymerization of mesogen-containing monomers, i.e. a mesogenic diisocyanate with an aliphatic diol [15] or a mesogenic diol with an aliphatic or aromatic diisocyanate [5,7,8,11,12,16,17]. Segmented liquid crystalline polyurethanes prepared from a polymeric diol, diisocyanate, and a mesogenic diol as a chain extender are being investigated with much interest.…”

“…Thermotropic liquid crystalline polyurethanes (TLCPUs) are being investigated with much interest owing to their application potential [7][8][9]. It is well known that hard segment of thermoplastic polyurethane can form thermotropic liquid crystalline phase when properly selected diisocyanate and diol are used for polyaddition reaction [9][10][11][12].…”

Synthesis and properties of transparent thermoplastic segmented polyurethanes

“…MDI has a tendency to dimerize at room temperature. Thus, MDI was purified by the hot sintering and filtering method 12 and placed in a sealed bottle and stored in a refrigerator at −30 • C. The equivalent weight of the purified MDI was determined by a di-n-butylamine back titration method 3 to be 125.4 g/mol. A poly(tetramethylene adipate)glycol derived from 1,4-butanediol and adipic acid, P3101, with a molecular weight of 2000, a hydroxyl number of 56 mg KOH/g, and an acid number of less than 0.5 mg KOH/g were supplied by Sumei Chemical Co., Ltd. (Taiwan).…”

“…8−11 Segmented polyurethanes are also our target. 12 Thermoplastic segmented polyurethane materials have been found in various applications because of their unique characteristics and diverse properties. 3,13 A lot of efforts have been made on these polyurethane materials.…”