Isolated chain conformations

Figure 3. Isolated chain conformations of cellulose predicted by MM2(85) (left) and PS79 (middle). The conformation on the right is that of the crystal structure of cellulose I (3). Hydrogen bonds are shown by dashed lines.

The different chain conformations observed in different polymorphic forms of a polymer are generally associated to nearly equivalent minima in the conformational energy maps, calculated for isolated chain models [2, 3],... 

Principle of Minimum Internal Conformational Energy. The conformation of a polymer chain in a crystal approaches one of the minima of the internal conformational energy, which would be taken by an isolated chain subjected to the restrictions imposed by the equivalence principle. 

We will obtain for the conformation free energy of isolated chain into m-ball... 

We conclude that a) all degrees of freedom should be unconstrained (including those related to the shape of the sugar rings)/ b) the packing forces can significantly influence the conformation even of a polymer main chain and c) a suitable potential set (with all atoms), used in total energy minimization, can account for these effects. With these considerations in mind, we attempted to model the crystal structures of DeS and an isolated chain of Hep. 

The Isolated Chain and the Crystalline Form of DeS. The molecular conformation given by Mitra et al. (1 ) for the tetragonal structure of DeS was used as the starting point for building all helical models of the isolated polyanion, assuming the tetrasaccharide I-N-I-N to be... 

The proton NMR shifts of diad, triad, and tetrad protons in an isolated chain of PP are calculated, taking into account its configurations and conformations using Pople s approximation. The agreement between the observed and calculated results, however, is insufficient with respect to the large difference between syn and anti protons and the order of tetrad protons. Here, a priori probabilities of specified conformations necessary to the estimation of the chemical shifts are calculated using Flory s matrix method. 

The above analysis was based upon a consideration of deviations from Gaussian behaviour of isolated chains. In reality we are concerned with network chains. This introduces a restriction on the conformational... 

---