Mesophases temperatures

Ib-lg, 2a-2g, and 3a-3g were crosslinked with HMMM at 150°. Cure temperature was within the mesophase temperature range for Ib-lg. Enamel formation of la was not feasible because of poor miscibility. The properties of the enamels are summarized in Table 11. 

Comparison of the data shown in Figure 10 with d values from the diffraction pattern in Figure 11 indicate (Figure 11a) that the mesomorphous component (a narrow reflex), d, is independent of poly(decamethylcyclohexasiloxane) chain tacticity. Hence, irrespective of trans-tactic polymer abi-lity to crystallization, the mesophase temperature range changes insignificantly. At lower tempera-ture of -73°C only, a bending on the temperature dependence curve, d(T), of the mesophase peak occurs. 

As a result of their low Tg values and lack of crystallinity, many of these polymers showed liquid crystallinity at room temperature. The liquid crystalline mesophases of the monomers were identified as nematic but the polymeric mesophases were not identified, although they possessed a very broad thermal stability between their Tg and their clearing transitions. A mesophase temperature stability of up to 170 °C was observed for the polymers with bicyclohexane central mesogenic units. These polymers showed decreases in Tg and Tj with increased spacer lengths. 

Another point to be noted is the fact that the mesophase temperature ranges, i.e., ATlq= Ti - Tm, are broader for the random copolyesters than for the ordered sequence ones. This phenomenon is particularly evident when a copolyester is composed of linear and nonlinear units, as shown for the copolymers of Equations 20 and 22. 

Rourke has recently demonstrated [72] that di-cyclopalladated Schiff base complexes, with -diketones of various chain-length as co-ligands, 39, were mesomorphic. They showed nematic phases, with a decrease in the clearing points as m was raised (melting points were reduced, when compared to complexes 39 with m-1, by around 100 °C), although at the expense of a large mesophase temperature range,... 

It was found that copolymerization lowers the crystal-mesophase transition temperature and increases the mesophase temperature range. This effect becomes progressively more pronounced as the difference in length of the flexible spacers increases. In addition, spacers of comparable length but different parity are not compliant with the steric-packing requirements of the crystalline solid state, thus decreasing the crystallization propensity of the copolymer with respect to the corresponding homopolymers. However, the nematic and smectic mesophases can accommodate different... 

The widest columnar mesophase temperature ranges were obtained for the bis-[l,3-di-(substi-tuted-phenyl)-/3-diketonate] metal complexes bearing ten and twelve chains ((55) R = H or OC H2 +i). The ten-chain copper, palladium, and oxovanadium(IV) complexes ((55) M = Cu, Pd, VO R = H, = 6, 8, 10, 12, 14) were all mesomorphic and the enantiotropic mesophases were identified by optical texture and variable-temperature X-ray diffraction as columnar phases (Table 34). The copper and palladium complexes displayed a Coh phase for short chain length ( = 6, 8 for M = Cu = 6, 8, 10 for M = Pd), which transformed to a Coin phase as the chain length was increased. Surprisingly, no direct Cok-to-Colh phase transition was observed within the same compound, but weakly first-order Cok-to-Cok and Colh-to-Colh phase transitions were found for compounds with intermediate chain lengths. In contrast, the vanadyl complexes exhibited only one Coh mesophase. Infrared studies indicated that the VO complexes possessed a linear V=0—V=0 linear polymeric chain structure in the crystal phase, while no... 

C, without apparent decomposition. Complexation to CuCl of isonitrile ligands based on phenyl benzoates considerably enhanced the mesophase stability, with mesophase temperatures well in excess of 200 °C and without decomposition. 

This type of material often has quite high solid-mesophase temperatures and is insoluble in most organic solvents. These types of polymers are usually nematic, reasonably thermally stable and have Tg temperatures above 0°C. de Gennes has predicted that for type polymers smectic phases should be obtained if the flexible segments are of equal length allowing lamellar organization. 

The scattering patterns of monodomain liquid crystalline polymers represent those from oriented liquid crystalline polymers. Such orientation can be achieved either in the solid state by quenching the oriented polymers or in the melt state by shearing the melt at the mesophase temperatures. Under a force field, such as a tensile force, shear force, or magnetic field, all the domains are aligned in the direction of the external field so that the polydomain liquid crystalline polymers can effectively become monodomain liquid crystalline polymers. For oriented main-chain liquid crystalline polymers, the scattering on the equator is due to interchain correlation and the scatterings on meridian raised from intrachain correlation. 

Quite often, room-temperature X-ray scattering data are used to characterize packing structures of mesophases by assuming that the mesophase structures can be frozen when the polymers are cooled down from mesophase temperatures to room temperature. However, liquid crystalline polymers normally crystallize at room temperature. The X-ray scatterings from liquid crystalline polymers at... 

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