Crystal structure chain direction repeat

The poly(ethylene terephthakte) analyzed was about 75% cr5retalline. The cr tal structure is triclinic with the moleculEu chains in an almost planar conformation. The poly(ethylene sebacate) was about 57% crystalline with a nomoclinic crystal structure with the molecular chains also in a planar conformation, in fact quite similar to the polyethylene crystal structure. The two repeating units, however, do not cocrystallize since the repeating unit lengths in the chain direction do not match. The copolymers thus show only poly(ethylene terephthalate) crystallinity. The 80/20 copolymer was about 22% crystalline, while the 60/40 copolymer was about 15% cr5retalline. 

Wollastonite is calciiun sihcate with a triclinic crystal system (P21). It has infinite-chain structure, with three tetrahedra per unit cell arranged parallel to y, this repeat unit consists of a pair of tetrahedra joined apex to apex as in the [Si07] group, alternating with a single tetrahedron with one edge parallel to the chain direction. Steady-state luminescence of wollastonite has been previously studied and luminescence of Mn, Fe and supposedly Cr has been proposed (Min ko et al. 1978). 

A series of salts M] 75[Pt(CN)4]T.5H20 (where M is K, Rb or Cs) has been reported but only the K salt has been studied in detail. The DPO for this salt is 0.25 and, therefore, the PD will have a repeat distance of eight dpt—pt and this would be expected to lead to a crystal structure with an eight-fold superlattice repeat distance. Structural studies have shown that above about 294 K the unit cell contains four fPt(CN)4]175- ions with a zig-zag Pt atom chain.58 Below 294 K a phase transition occurs to give a new unit cell with a repeat distance in the Pt atom chain direction which... 

Epitaxial crystallization of helical polymers may involve three different features of the polymer chain or lattice. These are (a) the interchain distance (as for stretched out polymers), (b) the chain axis repeat distance, and (c) the interstrand distance - the distance between the exterior paths of two successive turns of the helix. The two former periodicities are normal and parallel to the chain axis direction, and are therefore not usually sensitive to the chirality of the helix (unless the substrate topography is asymmetric and favors a given helical hand). However, the interstrand distance is oblique to the helix axis (it is normal to the orientation of the outer chain path) and therefore has different, symmetric orientations relative to the helix axis for left-handed and right-handed helices (Fig. 2). In other words, epitaxies that involve the interstrand distances are discriminative with respect to helix chirality. This discrimination becomes visible if the crystal structure is based on whole layers of isochiral helices. Such a situation does indeed exist for isotactic poly(l-butene), Form I, that will be considered soon. 

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