Ethylene hexagonal phase

A hexagonal phase is found at room temperature and atmospheric pressure in some ethylene-propylene copolymers containing a small amount of diene component [86,93]. 

In a similar manner, the ethylene-octene copolymer crystallized directly via the orthorhombic phase without the intervention of the anticipated hexagonal phase as would be anticipated in linear polyethylenes at these high pressures and temperatures (at approximately 3.8 kbar and around 200 °C). At 100 °C, see Fig. 15, the d values for (110) and (200) orthorhombic reflections are 4.08 A and 3.71 A. When the sample is cooled below 100 °C, a new reflection adjacent to the (110) orthorhombic peak appears at 80 °C. The position of the new reflection is found to be 4.19 A and so corresponds to a new phase. No change in the intensity of the existing (110) and (200) reflections is observed, however the intensity of the amorphous halo decreases, which suggests that the appearance of the new reflection (d = 4.19 A) is solely due to the crystallization of a noncrystalline component. On cooling further as the new reflection intensifies, the (110) and (200) orthorhombic reflections shift gradually. However, at 50 °C, the (100) monoclinic reflection appears with a concomitant decrease in the intensity of the (110) orthorhombic reflec-... 

It is to be noted that the reflection assigned to the new phase in butyl branched alkanes is relatively weak compared to the reflections observed for the new phase in ethylene-1-octene copolymer (5.2 mol %). As explained in this chapter, we attribute the new phase to the crystallization of transient layer (butyl branches and fold surface). Considering the anticipated tight folds for butyl branched alkanes, the amount of crystallizable entities in the branched alkanes would be much less than in the ethylene-1-octene copolymers where the loose folds are expected. We would like to mention that, considering the d-value and intensity of the pseudo-hexagonal phase in branched alkanes, this reflection may be referred to as open-orthorhombic phase. 

Fig. 8a-c. Micrographs of cross-linked poly(butadiene)-fo-poly(ethylene oxide) gels, templated in a cubic b hexagonal c lamellar phases. A dense packing of cylinders can be observed by TEM after cross-linking in the hexagonal phase. (Reproduced with permission from [74])... 

FIG. 4 Phase diagram of phytosterol with (a) 5 oxyethylene units (b) 10 oxy-ethylene units (c) 20 oxyethylene units (d) 30 oxyethylene units. LI, L2, L Lp, II, Nc, and HI indicate a micellar phase, a reversed micellar phase, a lamellar and a gel phase, a cubic phase, and a nematic and a hexagonal phase, respectively. Increasing hydrophilicity of the surfactant results in the formation of a remarkably temperature stable isotropic cubic and hexagonal phases. (From Ref. 15.)... 

The method has severe limitations for systems where gradients on near-atomic scale are important (as in the protein folding process or in bilayer membranes that contain only two molecules in a separated phase), but is extremely powerful for (co)polymer mixtures and solutions [147, 148, 149]. As an example Fig. 6 gives a snapshot in the process of self-organisation of a polypropylene oxide-ethylene oxide copolymer PL64 in aqueous solution on its way from a completely homogeneous initial distribution to a hexagonal structure. 

The cross-sectional area per chain in the hexagonal lattice of irradiated PE varies between 20.6 and 22.0 A. It is, thus, always greater than the cross-sectional area in the rotator phase in paraffins (19.5-20.0 A ), but on average somewhat smaller than that in constrained PE fibers above 7, /, (21.4-22.7 A ). An ethylene-propylene diene copolymer with approximately 64%, 32%, and 4% by weight of each component, respectively, was found to contain hexagonal crystals with a cross-sectional area per chain of 20.3 A". 

When layers of certain block copolymers of ethylene oxide and butylene oxide are contacted with water, there is an initial period when the position of the interface is proportional to tm, where m < 0.5 [32]. That is, initial swelling is not controlled by diffusion but instead by hydration and rearrangement of the long molecules to form the various phases. In the case of (EO)i6(BO)22 small-angle X-ray scattering did detect evidence of both reverse hexagonal and lamellar phases during this initial period, but it was not clear whether all the swollen block copolymer layer consisted of these phases or how the... 

Polyoxybenzoate is a stiff chain, lyotropic liquid crystalline material, as was discussed on the basis of its copolymers with ethylene terephthalate (see Sect. 5.1.4). The crystal structure of the homopolymer polyoxybenzoate was shown by Lieser 157) to have a high temperature phase III, described as liquid crystalline. X-ray and electron diffraction data on single crystals suggested that reversible conformational disorder is introduced, i.e. a condis crystal exists. Phase III, which is stable above about 560 K, has hexagonal symmetry and shows an 11 % lower density than the low temperature phases I and II. It is also possible to find sometimes the rotational disorder at low temperature in crystals grown during polymerization (CD-glass). 

The existence of a second class of complex phases, the modulated and perforated layer structures, has largely been explored by Bates and co-workers (Forster et al. 1994 Hamley et al. 1993, 1994 Khandpur et al. 1995 Schulz et al. 1996), who used SANS and TEM to investigate shear oriented structures. The thermally-induced phase transition from the lam to the hex phase in polyolefin diblocks was studied in detail by Hamley et al. (1993, 1994) using SANS, TEM and rheology. Intermediate hexagonal modulated lamellar (HML) and hexagonal perforated layer (HPL) structures were observed on heating PEP-PEE, PE-PEP and PE-PEE diblocks, where PEP is poly(ethylene-propylene), PEE is... 

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