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Structure and Dynamics of Liquid Crystalline Polymers from Deuteron NMR
Author(s) -
Boeffel Ch.,
Hisgen B.,
Pschorn U.,
Ringsdorf H.,
Spiess H. W.
Publication year - 1983
Publication title -
israel journal of chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.908
H-Index - 54
eISSN - 1869-5868
pISSN - 0021-2148
DOI - 10.1002/ijch.198300055
Subject(s) - mesogen , chemistry , liquid crystal , thermotropic crystal , polymer , methylene , crystallography , alkyl , side chain , intermolecular force , deuterium nmr , molecular dynamics , pendant group , polymer chemistry , molecule , nuclear magnetic resonance spectroscopy , stereochemistry , organic chemistry , computational chemistry , materials science , liquid crystalline , optoelectronics
The molecular structures of thermotropic liquid crystalline polymers, which have been synthesized systematically in recent years, are described according to the model of decoupling the molecular motions of the mesogenic groups and the polymer chain by inserting a flexible spacer. The molecular structure is related to the properties of these systems, e.g., phase transition temperatures, mesophases formed, etc. The structure and mobility of a specific side chain, liquid crystalline polyacrylate with phenyl benzoate as a mesogenic group is investigated by deuteron NMR and compared with the behaviour of low molecular weight analogues selectively deuterated at equivalent positions, i.e., at the mesogenic group and at the spacer. The temperature dependence of the order parameter of the mesogenic group indicates significant differences between the intermolecular potential in polymeric liquid crystals and their low molecular weight analogues. The order parameter of the spacer (methylene group adjacent to the polymer chain) is reduced to 50% of the value of the mesogenic group, whereas the equivalent methylene group in the low molecular weight system exhibits a reduction by only 25%. This indicates a substantially higher fraction of gauche ‐conformers in the spacer of the polymeric liquid crystal than in the alkyl chains of low molecular weight liquid crystals. In the glassy state the order parameter of the mesogenic group is high, 0.85 and 0.65 for a frozen smectic‐A and a frozen nematic system, respectively. In the glassy state rapid rotational jumps by 180° are observed. This process can be followed by 2 H NMR line‐shape analysis down to temperatures 100K below the glass transition.