Thermal and rheological properties of a liquid-crystalline polyurethane

Abstract

A novel liquid-crystalline polyurethane (LCPU) was synthesized by the condensation of 2,4-toluenediisocyanate and 4,4'-bis(6-hydroxyhexoxy)biphenyl. Solution polymerization in dimethylformamide produced intrinsic viscosities in the range 0.30457 dL/g. Differential scanning calorimetry shows a crystalline melting transition that is highly dependent on molecular weight and thermal history and a clearing transition that is virtually independent of both. Parallel-plate rheometry results are consistent with the presence of a liquid-crystalline phase, coexisting with a small amount of three-dimensional crystallinity, between 152 and 166 "C. Dynamic mechanical measurements reveal an unusually high elastic modulus of 180 MPa in the plateau region above Tg, compared with 6 MPa for an amorphous polyurethane with a chemical structure based on 1,4-butanediol.

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.…”

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

“…11 and 12. Figure 1 2 shows the texture of polyurethane M/BAG/BH( 1/6) heated to 220"C, cooled down to room temperature with a rate of 1 K/min.…”

The influence of 4,4’-bis(6-hydroxyhexoxy)biphenyl moieties on properties of polyurethanes based on 4,4’-methylenebis(cyclohexyl isocyanate)

“…In recent years considerable attention has been paid on the structure -property relationships of polyurethanes (PUs) based on 4,4'-bis(ω-hydroxyalkoxy)biphenyls (BHn) [1][2][3][4][5][6][7][8][9][10][11][12][13]. Some PUs based on BHn are thermoplasts due to relatively low melting point of polymers in which macromolecules contain only short rigid mesogenic 4,4'-bis(oxy)biphenyl moieties.…”

“…Both non segmented [1][2][3][4][5][6][7] and block [8][9][10][11][12][13][14] polymers have been described. Intensive work was focused on PUs based on tolylene 2,4-diisocyanate (TDI) [1][2][3][4][8][9][10][11]. Penczek and co-workers investigated the influence of a 4,4'-bis(2-hydroxyethoxy)biphenyl (BH2) amount [8] and a high molecular diol length [9] on segmented PUs properties and microphase structure.…”