Special Polymer Melt Phase Distributions

It is also important that there be strong enough interphase forces that the products so produced mechanically hold together. This usually requires miscibility or some method of interphase adhesion. Compatibilizing agents such as described in sections 6.5 to 6.7 maybe used in this regard. 

---

The Raman spectrum of a polymer is sensitive to the chain conformation since the latter determines the vibrational properties. One expects characteristic differences between a crystalline sequence with a unique regular helical conformation and the wide distribution of different conformations typical for a melt. Figure 5.16 displays spectra measured for polyethylene, in part (a) the spectrum of a crystal, measured for a specially prepared sample of extended chain polyethylene with a crystallinity close to 100%, and in part (b) the spectrum of the melt. The third spectrum (part (c)) was obtained for a partially crystalline sample. The spectrum of the crystal shows sharp bands because restrictive selection rules apply in order to be Raman active, all monomers have to move in-phase. This contrasts with the disordered liquid state, where in the absence of a structural symmetry, selection rules are relaxed and the Raman bands are broadened. On first view, the spectrum of the semicrystalline sample looks like a superposition of the elementary spectra (a) and (b) however. 

---