From Regioirregular Linear Main-Chain Liquid-Crystal Polyethers Exhibiting Two Uniaxial Nematic Phases to Macrocyclic Main-Chain Oligoethers Displaying Nematic and Smectic Phases

The synthesis and characterization of regioirregular macrocyclics based on the conformationally flexible 1-(4-hydroxyphenyl)-2-(2-methyl-4-hydroxyphenyl)ethane (MBPE) and α,ω-dibromoalkanes, i.e ., MBPE-(c) X ( z ) (where c stands for cyclic, X = 4, 5, 9, and 11 represents the number of methylenic groups in the flexible spacer and z = 1−5 is the degree of oligomerization of the macrocyclic) and the comparison of their phase behavior with that of the corresponding high molecular weight linear polymers MBPE-(l)X (where l stands for linear and X has the same meaning as in the case of cyclics) are described. The effects of X and z on the phase behavior of MBPE-(c) X ( z ) is discussed. For proper ( X, z ) pairs such as (4, 5), (5, 4), (9, 3), (9, 4), (11, 3), and (11, 4), MBPE-(c)X(z) have a higher ability to generate and stabilize liquid-crystalline (LC) phases than the corresponding linear polymers. MBPE-(l) X with X = odd numbers exhibit two uniaxial nematic phases. MBPE-(c) X ( z ) do not display the second uniaxial nematic phase that is exhibited by the linear polymers. This second nematic phase is converted to a smectic A phase through cyclization. An explanation for this behavior is suggested.