Main-chain orientation relaxation

The different available expressions for the OACF (Table 1) were compared to the data. As for solutions, the non-polymer models (rotational diffusion or restricted rotation (RR)) gives a poor fit. This is shown in Fig. 9 where the best fit OACF for the RR model is compared with the experimental data ( = 62.7 °C). Thus, the very specific character of main-chain orientation relaxation is as apparent in melt polymers as it was in solution. 

In polymer systems such a mutually independent dipole orientation is inapplicable because dipole orientation is highly correlated. The very essence of a pd3mer chain generally renders independent orientation of a main chain dipole component impos-rible and frequently, coupling between side chain and main chain modes are involved. For a rigid chain polymer in solution, dipole orientation requires rotatory diffusion of a macromolecule as a whole, and no component due to local modes is involved, but this situation is the exception. Flexible polymers permit polarization by local mode motions as well as rotatory diffusion as illustrated in Fig. 5. Equation (5) is also inapplicable for polymers because of dispersity in molecular weight, since if the relaxation involves molecular wel t dependent modes there will be a tead of relax-... 

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