Synthesis of Liquid Crystalline Phosphazenes Containing Chiral Mesogens

Phosphazene cyclic trimers and high polymers containing biphenyl side groups with (S)-2-methyl-1-butoxy as a terminal unit were synthesized. The chiral biphenyl units [4,4′-C₆H₄C₆H₄OCH₂-CH(CH₃)CH₂CH₃] were linked to the skeletal phosphorus atoms of the small-molecule phosphazene cyclic trimers and high polymers through -C(CH₂CH₂O)_m- spacer linkages, where m = 2 or 3. Of the cyclic trimers synthesized, with the formula N₃P₃[O(CH₂CH₂O)_mC₆H₄C₆H₄OCH₂CH(CH₃)CH₂CH₃]₆ where m = 2 (4) or 3 (5), only 5 was liquid crystalline, as determined by differential scanning calorimetry (DSC). Single-substituent high-polymeric poly(organophosphazenes) were synthesized that contained the chiral biphenyl unit linked to the backbone through spacer units m = 2(6) and 3 (8). Cosubstituent polymers were also synthesized which contained both the chiral biphenyl derivative linked to the backbone through varying spacer lengths and with nonmesogenic cosubstituents, OCH₂CH₂OCH₂CH₂OCH₃ and OCH₂CF₃. The liquid crystalline behavior of these polymers was studied with respect to spacer length and nonmesogenic cosubstituents. All the polymers synthesized showed enantiotropic liquid crystallinity. Morphologies and thermal behavior of these compounds were investigated with the use of DSC, X-ray diffraction, and optical hot stage microscopy.