Flexible spacer nature/length

The side chains in these structures can rearrange into positions either parallel or perpendicular to the deformed chain backbone. [178]. The outcome depends particularly on the nature and length of the flexible spacer connecting the mesogenic groups to the chain backbone. As expected the physical properties can become strongly anisotropic [179]. 

The length of the flexible spacer determines the nature of the mesophase. Long spacers favour smectic phases while short spacers favour nematic phases. This effect is similar to that observed in low molar mass liquid crystals. 

Let us first consider very briefly the influence of various parameters (i.e., nature of flexible spacer and its length, nature and flexibility of the polymer backbone and its degree of polymerization) on the phase behavior of a side chain liquid crystalline polymer. According to some thermodynamic schemes which were described elsewhere, the increase of the degree of polymerization decreases the entropy of the system and therefore, if the monomeric structural unit exhibits a virtual or monotropic mesophase, the resulting polymer should most probably exhibit a monotropic or enantiotropic mesophase. Alternatively, if the monomeric structural unit displays an enantiotropic mesophase, the polymer should display an enantiotropic mesophase which is broader. It is also possible that the structural unit of the polymer exhibits more than one virtual mesophase and therefore, at high molecular weights the polymer will increase the number of its mesophases. All these effects were observed with various polymer systems. ... 

Calorimetric data also demonstrated that the low temperature first-order transition occurs in quenched samples independent of the particular chemical nature and length of the flexible spacers. Since the structure of the rigid core of the mesogenic groups is the same for all the polyesters examined, it can be reasonably assumed that such a transition involves exclusively the aromatic moiety of the repeating unit. This conclusion is also supported by the calorimetric data obtained for copolyesters HTH-C3/C5 and HTH-C5/C10, which still exhibit the double-peaked transition in their DSC curves at the same temperature as that of the corresponding homopolymers (Fig. 1). It must be noted, however, that copolymer samples quenched from the LC state had very poor crystallinity and attempts to clarify the nature and state of order of the supercooled mesophase by x-ray analysis have been unsuccessful to date. 

Similar, if less pronounced, effects are also found in other non-polar SCLCPs. A simple estimate of dipolar-induced dipolar forces in these systems suggests that the core overlap is due to the action of these forces between the mesogenic side groups. SCLCPs may exhibit A and C phases which have a monolayer, a perfect bilayer or an interdigitated structure, depending on the nature of the polymer backbone, the number of atoms in the flexible spacer and the length of the terminal... 

The four synthetic isomers of rir-solamin were indistinguishable from each other and from natural rir-solamin on the basis of their IR, MS, H-NMR, and 13C-NMR spectra, owing to the length and flexibility of the spacer connecting the tetrahydrofurandiol and butenolide moieties. Optical rotation values obtained for each of the pairs of diastereomers were also very similar, and consistent with the known fact that the contribution to optical rotation from the butenolide moiety dominates that from a pseudosymmetrical... 

The extensive literature on low molar mass liquid crystals demonstrates that specific mesogens (specific chemical structures) tend to form specific mesophases, which vary somewhat with the length of the flexible substituent. We therefore expect that the type of mesogen, including the terminal substituent(s) and the length of the spacer should be the primary factors determining the specific mesophase(s) exhibited by a given SCLCP. The nature of the polymer... 

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