Polytetrafluoroethylene , disordered

Crystalline polymers characterized by disordered conformations of the chains are, for instance, polytetrafluoroethylene (PTFE), /ra .s-1,4-poly (1,3-butadiene), and cis-1,4-poly(isoprcnc). 

In this section information on possible condis states of the following macromolecules are reviewed polyethylene, polytetrafluoroethylene, poly(vinylidene fluoride), poly-chlorotrifluoroethylene, polypropylene, trans-1,4-polybutadiene, cis-l,4-poly(2-me-thylbutadiene), polyoxybenzoate, polyethylene terephthalate), nylon, poly(diethyl siloxane), and polyphosphazene. There is no reason to assume that this selection is complete. Station ni) has shown, for example, already in 1959 on a list of 29 macromolecules that longitudinal and lateral disorder may exist. Similarly, textbooks18> u2)... 

The thermal data on possible condis crystals are collected in Table 8. Substantial entropy gains are observed at the disordering transition, but variations are large, depending on the amount of conformational mobility gained. When compared to the total entropy of fusion, the listed entropies of disordering vary from 30 %, for polytetrafluoroethylene, to close to 100% for the polyphosphazenes. 

Marx, P. and Dole, M. Specific heat of synthetic high polymers. V. A. study of the order-disorder transition in polytetrafluoroethylene. J. Am. Chem. Soc. 17, 4771 (1955)... 

Marx and Dole and Miyake have presented descriptive models for the 19° C transition in terms of order-disorder theories. Studies of transitions at high pressure in polytetrafluoroethylene have been reported by Bridgman, Weir (1953), and Beecroft and Swenson. The phase diagram in Fig. 7 shows that in addition to the two crystalline phases which are separated by the 19° transition at atmospheric pressure there is a third modification at high pressures. The triple point has been... 

Clark ES, Muus LT (1962) Partial disordering and crystal transition in polytetrafluoroethylene. Z Kristallogr 117P 119... 

Crystalline polymers characterized by disordered conformations of the chains are, for instance, polytetrafluoroethylene [10-12,49-54], cis-l,4-poly (isoprene) [100-102] and trans-1,4-poly( 1,3-butadiene) [8,9,55-58]. In these cases, disorder does not destroy the crystallinity because of the similar shape of the various conformational units. The occmrence of cases of conformational isomorphism of the first kind demonstrates that a polymer chain can remain straight, as if it was constrained to run inside the walls of a tight cylinder, while its conformational freedom remains of the same order of magnitude as that in the melt. 

Conformationally disordered crystals (condis crystals) were discovered in the 1980 s. They show positional and orientational order, but are partially or fully conformationally mobile. The condis crystals complete the comparison of mesophases in Figs. 2.103 and 2.107. Linear, flexible molecules can show chain mobility that leaves the position and orientation of the molecule unchanged, but introduces large-amplitude conformational motion about the chain axis. Again, the symmetry of the molecule is in this case increased. Condis crystals have often a hexagonal, columnar crystal structure. Typical examples of condis crystals are the high-temperature phase of polyethylene, polytetrafluoroethylene, frawj-1,4-polybutadiene, and the low-temperature phases of soaps, lipids and other liquid-crystal forming, flexible molecules. 

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