Intramolecular chain segment

For this kind of cooperative processes, it is characteristic that the formation of the nucleus is thermodynamically more difficult than for further propagation steps (positive cooperativity). This implies that the elementary transition step of an individual chain segment (tripeptide unit) is influenced by the state of adjacent segments through intramolecular interactions. 

A low melting entropy is experienced if the intramolecular motions of the polymer are hindered, for example, the free rotation of chain segments. This is preferentially be done by stiffening of the polymer chain. Table 2.12 shows a selection of building blocks for temperature-resistant polymers. 

The autocorrelation function (Fig. 2) shows clearly that a representative chain segment embracing about 5-7 CH2-units should be sufficiently long to describe the intramolecular interference modulation in the WAXS-pattern of a PE-melt completely up to distances of approx. 30 A. 

In the case of the PE melt, the largest part of the configuration entropy is included in the variety of chain conformations. In our model of the PE melt, these chain conformations cause the diameter of the correlation cylinders in which the chain segments are embedded to fluctuate. This leads necessarily to distance fluctuations of next neighbor segments because of steric hindrance of the local segment exclusion volume. Therefore, the inter- and intramolecular distance correlations cannot be discussed independently. 

The effects of this transition on the WAXS pattern have been investigated in detail by Clark and Muus [27,28]. The local rotation of chain segments around the helix axis smears out the hkl-reflections along the layer lines leaving only the equatorial hkO-reflections and the intramolecular helix reflections near the meridian (Fig. 22). 

To find the anisotropy of the whole molecule in molecular coordinates h, the value of cos d should be averaged over all chain elements and all its conformations corresponding to a given value of h. To solve this problem Kuhn and Griin ) have considered the statistics of the intramolecular orientational distribution of segments with respect to h in a freely jointed chain and have shown that for the most probable distribution the value of cos d averaged over all chain segments can be expressed as a unique function of the h/L ratio... 

Just as the equilibrium conformational properties of macromolecules, the theory of which has been developed in well-known classical works by Kuhn, Flory, Volken-stein and others the kinetic properties of polymer chains can be determined by two main mechanisms of intramolecular mobility. First, it is the discrete rotational isomeric (rotameric) mechanism of mobility caused by the jump of small-chain segments (kinetic units) from certain energically stable allowed conformers into others is4-i6S) gg ond it is the continuous mechanism of motion deter-... 

The close agreement between frequencies of Nylon-6 and n-heptane was interpreted as indicating that the motions of the five Hg units in nylon are similar to those of the five H2 units in solid n-heptane. It was pointed out that this is reasonable, as it has been shown that the inter-molecular forces have negligible effect on the intramolecular motions of n-paraffins and that, in Nylon-6, the packing of the chain segments is... 

Intramolecular excimer and exciplex formation has been used to study the structure and mobility of chain segments in poly-chromic systems. A review of the results of these studies can be found in ref. 9. 

Of course, LCPs are not static Iwt dynamical systems. The most important molecular motions, expected for these systems, are shown in Fig. 4. One can distinguish at least three different motional modes. The intramolecular motions consist of local internal reorientations such as tram-gmu isomerization or ring flips [6,10]. The intermolecular motion is the motion of several chain segments or the molecule as a whole. Two basic motional modes are distinguished, namely rotation about the long molecular axis and reorioitation of this axis, respectively [10]. 

The weaker dependence is completely unexpected and contradicts the common view that hydrodynamic friction force drives CST and chain fracture. Nguyen and Kausch [108] ascribed (10) to the intramolecular friction (so-called internal viscosity ) between chain segments in the coiled part in FTF. Unlike the internal viscosity depends on strain rate and could reach much higher values than... 

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