Sidechain polymers

Table 6.12 Molecular structure of some sidechain polymers (62-64)...

Fig. 3.2.4 [Wiel] Orientation dependent C NMR spectra of the liquid crystalline sidechain polymer (a) before (b) and after (c) irradition with light. The shaded regions are C resonances from nuclei in natural abundance. The angle measures the orientation of optical axis of the film relative to the magnetic field Bo- (d) Moments of the orientational distribution function before and after inadition.

The influence of the crosslinking density on the birefringence has been studied [11]. For weakly crosslinked materials the results obtained coincide with the previous ones while for strongly crosslinked liquid crystalline elastomers the birefringence is only weakly affected in the vicinity of the phase transition as can be seen in Fig. 17. We stress, however, that the strongly crosslinked LSCE are duromers for which there are no independent macroscopic director degrees of freedom anymore, which are characteristic for the nematic liquid crystalline phase in low molecular weight materials, in sidechain polymers and in weakly crosslinked liquid crystalline elastomers. 

Since there are very few dynamic experimental investigations of pretransitional effects [8], not much modeling has been reported to date either. Based on work for the macroscopic dynamics of the nematic-isotropic transition in sidechain polymers [27 -29], it has been suggested [28] that the non-meanfield exponent observed in dynamic stress-optical experiments [8] can be accounted for at least qualitatively by the mode-coupling model [28, 29]. Intuitively this qualitatively new dynamic behavior can be traced back to static nonlinear coupling terms between the nematic order parameter and the strain tensor. 

Macroscopic properties of nematic elastomers have been discussed [56, 60]. De Gennes focused on the static properties, emphasizing especially the importance of coupling terms associated with relative rotations between the network and the director field [60]. The electrohydrodynamics of nematic elastomers has been considered generalizing earlier work by the same authors [54,55] on the macroscopic properties of nematic sidechain polymers [56]. The static considerations of earlier work [60] were extended to incorporate electric effects in addition a systematic overview of all terms necessary for linear irreversible thermodynamics was given [56]. 

Finkehnaim, H., Liquid-crystaUine sidechain polymers, in Liquid Crystallinity in Polymers, Ciferri, A., Ed. VCH, New York, 1991. 

Finkelmann H (1991) Liquid-crystalline sidechain polymers. In Ciferri A (ed) Liquid crystallinity in polymers. VCH, Weinheim... 

Progressing from guest-host systems (chromophores dissolved in a polymer matrix) to sidechain polymer systems (chromophores chemically attached to a polymer backbone), one arrives at another class of materials where the dipole is actually part of the polymer backbone, i.e., mainchain polymer systems. In fact, there are some reports on mainchain chromophoric copolymers in which the chromophores are attached head to tail. Figure 1 summarizes the four types of polarized organic materials. 

Important technological applications are critically dependent on the influence of light on the structure and dynamics of a polymer. For example, liquid crystalline sidechain polymers are used for reversible optical data storage and... 

Research into liquid-crystalline ferrocene sidechain polymers has been conducted by the research groups of Zentel and Deschenaux. One such liquid-crystalline polymer, polymethacrylate (18) and its monomer, showed enantiotropic smectic C and smectic A phases. This polymer also exhibited a weight average molecular weight of 100,000. ... 

Figure 14 A schematic representation of crosslinking in liquid-crystalline sidechain polymers. (Adapted from Ref. 43.)...

---