Liquid crystalline side-chain polymers (3b-3f) crosslinked by a trans Pt(II) complex were synthesized by a ligand exchange reaction with dichlorobis(benzonitrile)platinum(II) and poly(methylsiloxane) (3a) bearing a p-cyanobiphenyloxy mesogen unit attached to the polymer backbone by a flexible spacer group. The amount (x) of p-cyanobiphenyloxy mesogen coordinating to the Pt(II) ion in polymers 3b, 3c, 3d, 3e, and 3f was 4.9, 9.7, 14.8, 20.2, and 49.6 mol%, respectively. The effect of Pt(II) coordination on the thermotropic liquid crystalline behavior of 3a was examined by DSC, x-ray diffraction, and polarizing microphotography. Polymers 3a-3d exhibited a nematic mesophase between Tg and Tc. On the other hand, 3e-3f, which have a large amount of Pt(II)-coordinating mesogen, did not show a definite nematic mesophase, but exhibited an ambiguous one. The introduction of Pt(II) ion into 3a resulted in a crosslinked structure and consequently prevented the formation of the ordered nematic mesophase.
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Hanabusa et al. (1990) studied this question.
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