The metastable phase of isotactic polypropylene (βiPP) is crystallized epitaxially on two specific nucleating agents:  γ-quinacridone and dicyclohexylterephthalamide (DCHT). The resulting thin films are investigated by electron microscopy and atomic force microscopy. Epitaxial crystallization yields a biaxially oriented sample of βiPP, an orientation which cannot be achieved by mechanical means due to the β → α phase transformation on stretching. Electron diffraction indicates that the βiPP (110) plane is the contact face involved in both epitaxies. AFM investigation with methyl group resolution reveals a lateral periodicity of 19 Å in that (110) contact face, which corresponds to the distance between three chains and is a trademark indicator of the frustrated packing of βiPP. AFM further indicates some variability of the surface pattern, suggesting that two different frustrated structures may coexist in the surface layer; this, in turn, suggests some type of surface reconstruction. Structural requirements that efficient βiPP nucleating agents must meet are analyzed.

The morphology of syndiotactic polypropylene (sPP) containing >99 % racemic diads has been investigated following controlled crystallization from the melt in thin films. At high growth temperatures, large rectangular single crystals are obtained with preferred growth along the crystallographic 6-axis, while at lower temperatures these branch out to yield dendritic, axialitic, and eventually spherulitic aggregates. These crystals exhibit two very unusual properties: transverse fractures and ripples. Both are quasi-periodic, the fractures with a spacing of 3-7 jam and the ripples generally 1 /um or less. The fractures are ubiquitous in samples crystallized both at low and high undercooling and are expected to have severe negative consequences on the mechanical properties and uses of syndiotactic polypropylene. We associate formation of these transverse cracks with an approximate order-of-magnitude greater thermal expansion (and contraction) along the crystallographic 6-axis vs the a-axis, which we have documented using variable-temperature X-ray diffractometry. This technique also demonstrated that samples quickly cooled to ambient undergo a heatinginduced crystallographic transformation to the fully antichiral packing (cell III) that begins at ca. 40 °C below the melting point. Using surface decoration with evaporated polyethylene, we found that the (200) sectors have much more uniform amorphous-surface structure than the (020) sectors and that their folding is oriented along the preferred crystal-growth direction (6-axis).

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