4 Characterization of the Nematic Conformation of the Flexible Spacer . . . . . . . . . . . . . . . . . . 113
4.1 RIS Analysis of the Orientational Correlation of the Neighboring Mesogens . . . . . 113
4.2 Validity of the Assumption Adopted for Mesogenic Core Axis . . . . . . . . . . . . . . . . . . . . 115
4.3 Rotational Characteristics of the Bonds Constituting the Spacer . . . . . . . . . . . . . . . . . . . 115
5 Elucidation of the Nematic Conformation and Its Contribution to the NI Transition
Entropy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116
6 Comparison with the Constant-Volume Transition Entropy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
7 Concluding Remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120
1 Introduction
Various aspects of segmented liquid crystalline (LC) polymers have been exclusively documented in the literature [1–3]. These molecules often exhibit an
enatiotropic nematic (N) LC phase over a certain temperature range between the
crystal (C) and isotropic melt (I), and are conventionally called mainchain LCs.
Customarily LC-forming molecules comprising a single mesogen, often with a
short tail, are called a monomer, and those having two mesogens joined with a
flexible spacer are called a dimer, and so forth. In this part of the article, I would like
to discuss the sensible way of long flexible spacers adjusting themselves into a
partially ordered LC fluid.
As is known from the pioneering work of Vorla ¨nder [4], the dimer LC compounds having mesogenic groups on each end of an intervening spacer often exhibit
a very profound odd-even trend in their melting behaviors when plotted against the
constituent atoms of the spacer. When properly designed, amazingly long flexible
segments can be accommodated in an ordered nematic fluid. The effect of the
functional group (X) joining the mesogenic unit (Ms) and the spacer in polymers
such as –[Ms–X–(CH 2 ) n X] x – was first pointed out by Roviello and Sirigu [5], who
found that the odd-even oscillation of the latent entropy ΔS NI with n (the number of
spacer atoms) became substantially weaker when the carbonate group was
employed for X in place of ether or ester linkages. The odd-even characteristics
of the NI phase transition behaviors T NI ¼ ΔH NI /ΔS NI have been extensively
studied for dimers, trimers, and polymers, and the results are well-documented in
several review articles [6–8]. Various spectroscopic analyses have demonstrated
that the orientational correlation among the mesogenic units dispersively located
along the backbone is strongly coupled with the geometrical structure and conformational characteristics of intervening spacers. Such a structure-sensitive
cooperativity along the flexible chain may be regarded as an example in line with
Staudinger’s macromolecular concept, brought up in his early days [9].
110
A. Abe
4.1 RIS Analysis of the Orientational Correlation of the Neighboring Mesogens . . . . . 113
4.2 Validity of the Assumption Adopted for Mesogenic Core Axis . . . . . . . . . . . . . . . . . . . . 115
4.3 Rotational Characteristics of the Bonds Constituting the Spacer . . . . . . . . . . . . . . . . . . . 115
5 Elucidation of the Nematic Conformation and Its Contribution to the NI Transition
Entropy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116
6 Comparison with the Constant-Volume Transition Entropy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
7 Concluding Remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120
1 Introduction
Various aspects of segmented liquid crystalline (LC) polymers have been exclusively documented in the literature [1–3]. These molecules often exhibit an
enatiotropic nematic (N) LC phase over a certain temperature range between the
crystal (C) and isotropic melt (I), and are conventionally called mainchain LCs.
Customarily LC-forming molecules comprising a single mesogen, often with a
short tail, are called a monomer, and those having two mesogens joined with a
flexible spacer are called a dimer, and so forth. In this part of the article, I would like
to discuss the sensible way of long flexible spacers adjusting themselves into a
partially ordered LC fluid.
As is known from the pioneering work of Vorla ¨nder [4], the dimer LC compounds having mesogenic groups on each end of an intervening spacer often exhibit
a very profound odd-even trend in their melting behaviors when plotted against the
constituent atoms of the spacer. When properly designed, amazingly long flexible
segments can be accommodated in an ordered nematic fluid. The effect of the
functional group (X) joining the mesogenic unit (Ms) and the spacer in polymers
such as –[Ms–X–(CH 2 ) n X] x – was first pointed out by Roviello and Sirigu [5], who
found that the odd-even oscillation of the latent entropy ΔS NI with n (the number of
spacer atoms) became substantially weaker when the carbonate group was
employed for X in place of ether or ester linkages. The odd-even characteristics
of the NI phase transition behaviors T NI ¼ ΔH NI /ΔS NI have been extensively
studied for dimers, trimers, and polymers, and the results are well-documented in
several review articles [6–8]. Various spectroscopic analyses have demonstrated
that the orientational correlation among the mesogenic units dispersively located
along the backbone is strongly coupled with the geometrical structure and conformational characteristics of intervening spacers. Such a structure-sensitive
cooperativity along the flexible chain may be regarded as an example in line with
Staudinger’s macromolecular concept, brought up in his early days [9].
110
A. Abe