Epitaxy of isotactic poly(1-butene): new substrates, impact and attempt at recognition of helix orientation in form I′ by AFM

Epitaxial crystallization of isotactic poly(1-butene) (iPBu) is performed on different substrates, which help expand the range of interactive substrates used in a previous study. All three crystal forms of iPBu1, which rest on different helix and unit-cell geometries and symmetries, have been produced by epitaxial crystallization. The different epitaxial interactions are discussed. Epitaxial crystallization of form I′ yields an exposed (110) contact plane. The films have true single crystal structure; they display electron diffraction patterns with sharp peaks, but also characteristic streaks due to the co-existence of up and down helices in the crystal structure (anticline helices). The streaks are modelled with a ‘Diffraction faulted’ program. Further, this same (110) contact face of Form I′ provides the potential to observe in direct space (i.e. by AFM) the up or down orientation of helices. Such a possibility would require differentiation by AFM of a methyl group from an ethyl group of the side chains. The AFM resolution reached in our investigation falls short of doing so, but the problematics could be adapted to other, more suitable polymers.