in Figure 2 we present dielectric loss spectra for N = 13-314 at 245 K, a temperature at which segmental and normal modes are simultaneously visible in the accessible frequency window. The data are normalized with respect to the peak height of the segmental mode but not scaled as far as their peak frequency is concerned. This means that the average time scale of the segmental dynamics is practically unaffected by the length of the chain. The normal mode appears only as a weak feature close to the segmental peak at N = 13, then separates more from the later as the chain length is successively increased, and finally evolves into a clearly discernible feature for larger N

Figure 2. Dielectric loss spectra recorded at T=245 K for a wide range of chain lengths are represented by the symbols. The amplitudes of the data are normalized with respect to the maximum of the R-peak. The dashed lines reflect a peak corresponding to a single relaxation time N. The solid lines are calculations based on N using eq 3. They describe the normal mode contributions very well for molecular weights for which entanglement effects do not occur.

PLZ, explain the above for polypropylene glycol