Homogeneous Copolymers of Ethylene-1-Octene

The relatively high intensity of the open-orthorhombic phase, at these high pressures, means that this phase cannot be attributed to crystallization of the hexyl branches at crystal surface alone - unlike in case of branched alkanes. However, similar to branched alkanes the fold surface incorporating hexyl branches must be a prominent factor in forming the open-orthorhombic 

On releasing pressure, multiple reflections obseiwed in the sample crystallized at elevated pressure and temperature merge into simple 110 and 200 reflections of the orthorhombic phase. The starting WAXD pattern looks similar to the very first diffraction pattern recorded at l.-J kbar, as shown in Fig. 15.16. If pressure is once again increased at room temperature, the (110) and (200) orthorhombic reflections split into two distinct reflections. The (110) reflection splits into two distinct dvalues, d = 4.19 A (open-orthorhombic phase) and d = 3.99 A (dense orthorhombic phase). The intensity of the dense-orthorhombic reflection d = 3.99 A) decreases with the appearance of the (100) monoclinic reflection [d = 4.48 A). 

FVom Fig. 15.16 it can be further confirmed that with the appearance of the monoclinic phase, the intensity of the open-orthorhombic reflection (d = 4.19 A) remains unchanged and the reflection does not shift with compression. Thus the volume and density of the open-orthorhombic unit cell is invariant with pressure, a feature unusual compared to the changes in volume and density of the dense-orthorhombic phase. These observations strongly suggest that the origin of the open-orthorhombic phase is crystalUzation of the interphase, where pressure facilitates organization process of the interphase to the extent that it could be detected by conventional X-rays. 

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