Mesophase transition,

The condis crystal forming polymer is poly(4,4 -phthaloimidobenzoyl-dodecamethyleneoxycarbonyl) (PEIM-12) with the following repeating unit  

Combining Eqs. (26) and (27) and substituting the phase angle, H, corrected for instrument changes, as outlined below, then results in 

The phase angle g is derived from the phase shifts — S of the sample temperature Ts and the temperature difference A. The phase lags are measured relative to the phase of the reference. In order to find the lag due to the sample only, one must subtract e — So, the interpolated value measured for the reversible baseline  

During the derivation that led to Eq. (11) [31], it was also found that  

These relationships allow the evaluation of Eq. (28) by finding (s — S) for the transition range of interest and subtraction of the appropriate reversible 

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The number of examples of Uquid crystalline systems is limited. A simple discotic system, hexapentyloxytriphenylene (17) (Fig. 4), has been studied for its hole mobUity (24). These molecules show a crystalline to mesophase transition at 69°C and a mesophase to isotropic phase transition at 122°C (25). 

No coherent threadline could be maintained and the extmdate flew off the windup as short, brittle, crystalline lengths. Not until many years later did other workers show that this polymer on cooling exhibits a mesophase transition directly from the isotropic melt to a smectic A phase. Good sources of information on Hquid crystals and Hquid crystal polymers are available (212—216). 

Wunderlich, B. and Grebowicz,J. Thermotropic Mesophases and Mesophase Transitions of Linear, Flecible Macromolecules. Vol. 60/61, pp. 1 —60. 

Wunderlich, B. and Baur, H. Heat Capacities of Linear High Polymers. Vol. 7, pp. 151-368. Wunderlich, B. and Grebowicz, J. Thermotropic Mesophases and Mesophase Transitions of Linear, Flexible Macromolecules. Vol. 60/61, pp. 1-60. 

Most solid materials produce isotropic liquids directly upon melting. However, in some cases one or more intermediate phases are formed (called mesophases), where the material retains some ordered structure but already shows the mobility characteristic of a liquid. These materials are liquid crystal (LCs)(or mesogens) of the thermotropic type, and can display several transitions between phases at different temperatures crystal-crystal transition (between solid phases), melting point (solid to first mesophase transition), mesophase-mesophase transition (when several mesophases exist), and clearing point (last mesophase to isotropic liquid transition) [1]. Often the transitions are observed both upon heating and on cooling (enantiotropic transitions), but sometimes they appear only upon cooling (monotropic transitions). 

The members of Class II in Table 1 present very small enthalpies of the mesophase-liquid transition [ AHml < 0.5 kJ/(mol of chain bonds)], suggesting that their mesophase is hardly stabilized by specific interatomic interactions. By contrast, we point out that in all cases the crystal-mesophase transition has a significant enthalpy value, mostly AHqm > 1 kJ/(mol of chain bonds). Consistent with their relatively flexible character, the polymers listed in the Tables have their glass transition below ambient temperature. 

The LC nature of diols la-lg was demonstrated by DSC (Fig. 1). Two first order transitions were observed. The lower transition temperature appeared to be the crystalline-mesophase transition (T, ), and the higher transition temperature the mesophase-isotropic transition (T ). Other transitions were not evident in the DSC. The thermal data revealed an odd-even spacer effect for Tj . 

Mesophase that is thermodynamically stable over a definite temperature or pressure range. Note The range of thermal stability of an enantiotropic mesophase is limited by the melting point and the clearing point of an LC compound or by any two successive mesophase transitions. 

Thermotropic Mesophases and Mesophase Transitions of Linear, Flexible Macromolecules... 

The crystal-mesophase transitions at Td are first order transitions. In the case of plastic crystals, they show usually the major heat of transition. In the condis crystals the magnitude of the transitions depends on the number of bonds which gain con-... 

The kinetics of the mesophase transitions can be discussed by comparison with the crystallization-melting and the vitrification-devitrification transitions of the three limiting phases of Fig. 2. Except for the crystallization kinetics, the literature on the kinetics of phase transitions is limited. For the mesophases, information is scarce. 

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