Interchain packing effect

Scheme 2 shows a cross-sectional representation of a two-stranded a-helical coiled coil of 35 residues per polypeptide chain. The design of this idealized coiled coil incorporated the factors that maximize coiled-coil stability, for example, the hydrophobicity and packing effects in the hydrophobic core, intrachain electrostatic attractions, helical propensity contribution s[2324 from residues outside of the hydrophobic interface, and interchain electrostatic interactions.125 ... 

An aspect ratio T=a/V1/3 has been introduced [213], characterizing an effective stiffness of the chain and reflecting an interchain packing ability. The real more linear (low x) olefinic copolymers are described as the more stiff chains (with large T and a), while the more branched polyolefines (high x) as the more flexible blend components (with small r and a). 

The model athermal blend is defined [59,62] as the hypothetical limit of vanishing interchain attractive potentials relative to the thermal energy, i.e., Pvmm-W = 0- For this situation the atomic site-site Percus-Yevick closure approximation of Eq. (2.7) is employed where the subscripts now refer to the spedes type. The constant volume athermal blend is of theoretical interest since it isolates the purely entropic packing effects. However, as emphasized by several workers [2,62,63,67], the athermal reference blend is not an adequate model of any real phase separating system. Its primary importance is as a reference system for the theories of thermally-induced phase separation discussed in Sect 8. 

In theoretical modeling, it was assumed that single-polymer chains are not interacting with each other, as in the gas phase. To make the models and calculations more realistic, however, three-dimensional packing effects in solid-state systems should be taken into account, and this can play an important role in the desired properties of conjugated polymers. Usually, the three-dimensional packing effects enhance the interchain interaction, giving rise to a complex set of vibrational modes. This eventually... 

The effective method for increasing thermal oxidation stability of polymers is control of the physical structure [7], The additive effect on the physical structure of PI film was studied with the help of X-ray structural analysis. The film possesses mesomorphous regularity, of which the presence of an intrachain order in the absence of interchain packing regulation is typical. As shown on the diffraction pattern, such structure manifests itself by a single narrow peak of the intrachain order (5-6 deg) and wide amorphous halo (Figure 19). Diffraction patterns show high intrachain orderliness of the stabilized sample. This difference is... 

Introduction of bulky lateral substituents on monomer units to increase interchain distance and prevent close packing in polymer crystal. The use of unsymmetrically substituted monomers, resulting in a random distribution of head-to-head and head-to-tail structures in polymer chains, further helps in disrupting regularity. Some examples of substituent effects are given in Table 2.16. 

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