Liquid crystalline main chain polymers containing the ferrocene unit as a side group, 2. Variation of the spacer length

Four new ω‐ferrocenylalkyl diethyl malonates with varying length of the alkyl group from 4 to 10 methylene units were incorporated via Ti(OiPr)4‐catalyzed copolymerization into smectic liquid crystalline main‐chain polymers in contents of about 10 mol‐%. As mesogenic unit 4,4′‐bis(6‐hydroxyhexyloxy)azoxybenzene was used as diol component and diethyl phenyl malonate as diester component. Polymer analogous oxidation of the ferrocene units leads to liquid crystalline ionomers, which also form smectic phases. The ferrocene containing polymers were investigated in the oxidized and non‐oxidized state of the ferrocene unit. Differential scanning calorimetry (DSC) data show a shift towards higher phase transition temperatures after oxidation, which is in agreement with the behaviour of classical ionomers. Small angle X‐ray scattering (SAXS) experiments show an excess scattering to small angles, which is a hint for dispersed particles in the polymer matrix (ionic clusters). In one polymer series the ferrocene content was varied. Increasing the ferrocene content changes the type of the LC phase from smectic A to nematic presumably because of the bulkiness of the neutral ferrocene group. It is, however, possible to restore the smectic A phase by an oxidation of the ferrocene units to ferrocenium ions. This is a result of microphase separation in ionic domains and non‐ionic domains, which supports the formation of layered structures.