Development of crystallinity in a polyurethane containing mesogenic units. 1. Morphology and mechanism

Abstract

This work extends prior studies of a polyurethane containing mesogenic moieties. Optical and thermal methods reveal that this polyurethane exhibits monotropic mesomorphic behavior. Two distinct crystallization mechanisms and crystal morphologies are identified, one arising from the isotropic melt and producing a spherulitic texture and the other arising from the mesophase and producing a threaded texture. A combination of thermal analysis, X-ray diffraction, and dynamic rheological studies reveals that crystals grown from the mesophase are readily perfected to a higher melting form by annealing whereas spherulitic crystals are less amenable to perfection. The development and perfection of the crystalline state were also found to be dependent on polyurethane molecular weight.

Synthesis and Thermotropic Properties of Polyurethanes Prepared from 2,5-Tolylene Diisocyanate and 2,6-Bis(ω-hydroxyalkoxy)naphthalenes

“…On the other hand, in the series of l,4-PDI/BHNm (m=2, 3,5,6,8,11) without methyl substituent on the phenylene unit, no explicit mesomorphic behavior was observed by DSC measurement and polarizing microscope. They showed a colored sand-like texture characteristic of highly crystalline para-linked polyurethanes.…”

“…2, 6-Bis( w-hydroxyalkoxy )naphthalenes (BHNm; m=2, 3,5,6,8,11) were synthesized by the reaction of 2,6-dihydroxynaphthalene with w-halogenated alkanols. A mixture of sodium hydroxide (5.4 g, 0.13 mol), 2,6-dihydroxynaphthalene (5.1 g, 0.032mol), and wbromo-or chloro-1-alkanol (0.13 mol) in 150 mL of ethanol was refluxed for 12 h, and then poured into cold water.…”

Synthesis and properties of liquid crystalline polyurethane elastomers

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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.

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Synthesis and Characterization of Thermotropic Liquid Crystalline Main-Chain Polyurethanes from High-Aspect Ratio Mesogenic Diols

“…[2] Because of strong intermolecular interaction resulting from the hydrogen bonding of urethane linkages, synthesizing thermotropic liquid crystalline polyurethanes (LCPU) seems more difficult than synthesizing other liquid crystalline polymers. To prepare a LCPU, many methods to minimize the hydrogen bonding effect have been developed, e. g., by inserting flexible spacers into the mesogenic unit, [3] by introducing a substituted mesogenic segment, [4] or by using a secondary amine reacted with dichloroformates. [5] In the last decade, a number of articles on LCPUs have been reported.…”