Side-chain liquid crystalline poly(N-maleimides). 5. Dielectric relaxation behavior of liquid crystalline side-chain and amorphous poly(N-maleimides). A comparative structural study

Abstract

A series of five nonaligned comblike polyUV-maleimides) have been studied by frequency (200 Hz-100 kHz) and temperature (from 123 to 423 K) dependent dielectric measurements. Three of them are smectic side-chain liquid crystal polymers (SCLCPs) and the other two are amorphous materials. These samples also allow us to study the possible influence of the smectic field. By a change of the chemical nature of the structure of mesogens, a self-consistent assignment of the different relaxational processes has been possible. Six main relaxation processes have been found and assigned: (i) Two relaxations, ft and ft, are produced at temperatures below T" due to rotational motions and torsional oscillations of the mesogens, respectively. They can be attributed to the reorientation of the perpendicular component to the major axis of the permanent dipolar moment located at the center of the mesogenic groups. In polymer V, these two relaxations are reduced to one ft. Here the second type of motion is no longer possible because of the absence of an oblong moiety with interphenylenic ester groups and because of the presence of a tetramethylbutane group as a substituent in the phenylene group, (ii) Two relaxations, 72 and 71, are located at the lower temperature and attributed to localized motions of n-alkoxy pendant groups linked to mesogens in para position and to the spacer with its interconnecting functional groups which link it to the main chain and the mesogen, respectively, (iii) Two relaxations, a and 5, respectively, are produced at temperatures above T, which are assigned respectively to dipole reorientation of the main chain motions and to displacements of the mesogens which are able to reorientate the dipolar moment component parallel to the long axis of the mesogens. The absence of a ¿-process in polymers I and II may be due to the absence of orientational rotation of the anisodiametrical mesogenic group; as a result, the orientation of the parallel component µ; of the dipole moment of the mesogen does not take place. It is possible that topological constraints imposed by a strong smectic field due to the existence of a long range order in the smectic layer of these two highly ordered polymers may be responsible for this behavior by hindering such a motion. The structure and phase transitions of the five polymers were studied by optical polarizing microscopy, small and wide-angle X-ray diffraction on aligned and unaligned samples, and differential scanning calorimetry.

Propriétés diélectriques de polysiloxanes cristaux liquides à groupements mésogènes diphényles et espaceurs de type thioéther. Dielectric properties of liquid crystalline polysiloxanes with mesogenic diphenyl groups and thioether spacers

“…1 a, b), caractéristique des polymères cristaux liquides à groupements pendants fortement polaires (Kresse et al 23,24) , Krupicka et al 34) , Hsiue et al 20) ). Quand l'espaceur est trop court 17) ). Le mécanisme de cette relaxation d consiste en une rotation du groupement latéral autour de la chaîne principale.…”

“…De nombreux travaux ont été réalisés ou sont encore effectués sur la caractérisation des propriétés diélectri-ques des polymères cristaux liquides à groupements pendants (Attard et al 14) , Bormuth et al 15) , Zhong et al 16) , Romero Colomer et al 17) , Kim et al 18) , Akins et al 19) , Hsiue et al 20) ). Ces polymères permettent par vitrification d'obtenir des mésophases solides.…”

Synthesis and characterization of polymaleimides containing 4-cyanobiphenyl-based side groups for nonlinear optical applications

“…[15][16][17] In the first example, poly-and copolymaleimides, in which the cholesteroxycarbonyl mesogenic group was attached to the polymer backbone through a paraffinic spacer containing one, 15 5, or 11 methylenic units, 16 were synthesized and investigated for their chirooptical properties. It was shown that asymmetric induction polymerization took place in all the investigated systems.…”

“…The second SCLC polymaleimide series is based on phenylbenzoate mesogenic groups attached to the backbone through 10 methylenic units. 17 These polymaleimides exhibit smectic phases.…”

Dynamic and photochemical behavior of amorphous comb-like copolymers with photochromic azobenzene side groups

“…-relaxation: This relaxation process is neither present in the common polymethacrylates nor in corresponding liquid crystalline materials. Only for poly(N-maleimides) with two ester linkages and a range of mesogenic units two b -processes are described 3,32) . For the investigated polymers the b…”