IsoSm* phase

As seen in Figure 5.IB, the polymer forms a layered structure below the transition point, showing a well-developed system of SAXS peaks. Moreover, the ORD measurements (see Figure 5.2) exhibit drastic growth of the optic rotation in the IsoSm phase towards shorter wavelengths, in contrast to the proper isotropic melt of the same polymer above the transition point, suggesting some helix-like superstructural ordering in the mesophase with a pitch below 300 nm. That hypothesis was further supported with CD, dielectric spectroscopy, and UV-vis spectroscopy data. " Tlie critical importance of chirality for the formation of the IsoSm phase is also confirmed by... 

We should state that our suggested model is not completely justified yet, but it remains the only one that can explain the whole ensemble of properties observed for the isotropic smectic phase of P8 M and related polymers. Keeping that in mind, we will refer hereafter to the mesophase as the isoSm phase, which most probably has the uitrashort pitch TGB A structure. 

It should be noted that the Iso —> IsoSm phase transition on cooling is thermodynamically controlled for the former two series but kinetically controlled for the KM series. As an example. Figure 5.7A presents DSC data from KMll, As seen from the figure, the second DSC scan from the polymer sample shows no transition peaks, but glass transition inflexion only the... 

On the other hand, as mentioned in Section 5.3, theTri s-isomcr also absorbs within band C, especially in the condensed state of the copolymer, so that illumination with blue-green light creates not a pure trans fAm but a new steady-state proportion of both isomers. Moreover, UV irradiation of the Sm A film of SK8 has been reported to transform it back to the IsoSm phase. Therefore, the ds-isomers seem to be preferred for the formation of the TGB A phase. 

P8 M is not the only polymer forming the isotropic smectic phase. To date, we have observed formation of that phase for a half-dozen chiral polymethacrylates and polysiloxanes. Table 5.1 summarizes the chemical structure and phase behavior of synthesized side-chain homopolymers, which carry chirally substituted side chains derived from asymmetric esters of terephthalic acid and hydroquinone. Such a structure with alternating orientation of carboxylic link groups seems to favour the formation of the IsoSm phase, whereas isomeric derivatives of p-hydroxybenzoic acid, where all carboxylic links have the same orientation, form only conventional Sm A and Sm C phases. Molar mass of all the synthesized homo- and copoly(meth)acrylates is within the range of 1 to 2-10 g mol the poiysilox-anes have the average degree of polymerization, p 35. 

It is worth noticing that the combination of properties of the Iso,Sm phase can hardly be explained in terms of known LC phases. The ultrashort pitch TGB-like structure suggested in reference 64 still remains the only structural model that can explain the observed lack of birefringence in the IsoSm phase. 

FIG. 5.S Range of compositions fevoring the formation of the isoSm phase for chiral azo dye side-chain copolymers. 

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