Forces also intrachain

The Youngs modulus of poly(ethylene glycol) was also calculated from the intrachain force field [Matsuura and Miya wa (1968)]. The calculated value of =0.0132 mdyne/A [Matsuura and Miyazawa (1969c)] agrees clo ly with the experimental value of =0.010 mdyne/A [Sakurada, Ito, and Nakamae (1966)]. 

Frequency-dispersion curves are useful for analysing infrared and Raman spectra of polymer chains of Gnite length where chain vibrations associated with various phase different are observed. From the frequency-dispersion curves, the frequency distribution of the optical branches may be calculated, for studying the contributions of chain vibrations to heat capacities and the zero-point energy. The intrachain force field is also used in treating the elastic modulus along the chain axis, for comparison with the experimental data. 

For polymer chains in a crystal lattice, however, acoustic vibrations of polymer chains are subject to interchain interactions, yielding the crystal vibrations of the acoustic and optical branches. Accordingly, for vibrational analyses of neutron-scattering spedra in the low-frequency region, it is required to treat the normal vibrations of the crystal, on the basis of the interchain force field as well as the intrachain force field. Treatments of crystal vibrations are also necessary for the theoretical study of specific heat, zero-point energy and temperature factor of x-ray diffraction. 

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