Poly butene epitaxial crystallization

Epitaxial Crystallization of Isotactic Poly(l-Butene), Form I. 26... 

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. 

Kopp S, Wittmann JC, Lotz B. Epitaxial crystallization and crystalline polymorphism of poly (1-butene), forms III and II. Polymer 1994 35 908-915. 

Epitaxy of Isotactic Poly (1-butene) Isotactic poly(1-butene) (iPBul) is an archetypical polymorphic polymer with three different structures that differ by the chain conformation, and thus by the unit-cell geometry and symmetry (cf Chapter 2).The three crystal phases could be obtained by epitaxial crystallization on appropriate substrates [48-50]. Most interesting among them are the epitaxy of Form I (trigonal unit cell, threefold helical conformation, racemic phase) and that of Form III (orthorhombic unit cell, fourfold helical geometry, chiral crystal phase). 

It should be pointed out here that the epitaxy caused by special crystallographic interaction provides another efficient way to control the crystal modification of semicrystalline polymers together with molecular chain orientation [83,88,139-142]. As examples, while the crystal structure of isotactic poly(l-butene) (iPB-1) is successfully controlled through using substrates with different crystal structures... 

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