Strongly polar molecules with the general formula: show a great variety of interesting polymorphism such as reentrant phases and some new smectic phases. The importance of the relative longitudinal dipolar moment of the cyano or nitro group and of the different X and Y linkages has been clearly underlined. For this purpose four families of polar mesogens belonging to the above structure with X, Y = -COO-, -CH = N -, -OCO-, - N = CH- have been synthesized. Some interesting results are given: - Reentrant sequences: - Transition SC - SC - Existence of different smectic A and C phases:
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Tình et al. (1984) studied this question.
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