Other Flexible Carbon-Backbone Macromolecules

Besides the eight well documented condis phases of flexible, carbon-backbone macro-molecules described in Sects. 4.1 to 4.5, ttere is evidence of an even larger abxmdance of condis crystals as stable phase, intermediate in crystallization, and possibly also on large scale deformation. In this section some indication of the existence of condis phases for aliphatic nylons, polyallene and pofy[(S)-3-methyl-pentene-1] will be reviewed. Lateral and longitudinal disorder was noted much earlier for a larger series of polymers but little is known about the dynamic nature, i.e. if these macromolecules must be considered CD glasses or if they are stable condis crystals at any temperature. 

Nylon 6, nylon 11, and nylon 12 have been reported to grow as extended chain crystals when crystallized at pressures of up to 800 MPA 250-252) qjj the needed 

Another interesting case of conformational disorder is provided hy isotactic poly[ (S)-3-methy pentene-l ] (P3MP1) 

In this case the skle-groups may take-on statistical disorder with respect to rotation of the terminal —CH—CH3. The two minimum-eneigy conformational isomers of different side-group orientation seem to have only small energy differences when parked in their tetrahedral crystal (space group I4j) The backbone helix is always 

PolydialkyMoxanes represent a group of flexible macionK te iiles that have not only interesting low and high temperature materials p-operties (silicones), but they may also show special electronic properties. The simplest member of the hcanologous series is polydimethylsiloxane. It exhibits no condis pha% ami s ms to have normal thermodynamic properties On samples of crystallinity varying 

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Long flexible pol3nners have a large number of Internal degrees of freedom. The typical primary structure of such molecules Is a linear chain of atoms (often carbon) connected by chemical bonds ("backbone"). Usually, every other backbone atom carries a side group. By rotation about the bonds In the backbone the molecule changes Its shape, and since there are many of these bonds In a polymer. a wide spectrum of conformations Is available. The rotation is hindered by the side groups, so that some of these conformations may be rather unfavourable. In some macromolecules (for instance proteins) sequences of preferred bond orientations show up as helical or folded sections In the molecules (secondary structure). 

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