Sabine Graff

Single crystals of γ phase isotactic polypropylene: combined diffraction and morphological support for a structure with non-parallel chains

Abstract Single crystals of the unusual γ phase of isotactic polypropylene have been produced by thin film growth. Their examination by selected area electron diffraction using a tilting stage enables the exploration of nearly the full reciprocal space of this crystal modification. The results fully support and provide an absolute test for a crystal structure proposed recently by Bruckner and Meille characterized by the coexistence in the unit cell of two sets of 31 helices with non-parallel axes. The structural relationship between α and γ phases makes it possible to determine the left- or right-handed chirality of all helices in the single crystals. The surface structure is investigated by the polymer decoration technique, and occasional α growth on γ crystals is described and analysed.

Hetero-arm star copolymers with potentially ionogenic branches

Abstract Hetero-arm star copolymers—i.e. star polymers the cores of which carry branches of two different kinds—have been made by a three-step anionic process. The polystyrene (PS) precursor was made first, and used to initiate the polymerization of a small amount of divinylbenzene. The cores of the resulting star polymers still contain the active sites and can therefore be used to initiate the polymerization of another suitable monomer. tert.Butyl acrylate (t.BuA) was shown by Teyssie to polymerize anionically without transfer or termination, provided lithium chloride is present. An attempt was made to have poly(t.BuA) branches grow from the “living” cores of the PS star molecules. A detailed characterization of the resulting samples was performed, to establish whether these hetero-arm star copolymers exhibit the expected structure. The method can be considered quite reliable, and leads to star polymers with branches that are potentially ionogenic.

Electrodeposition of lithium phthalocyanine thin films: Part I. Structure and morphology

A new thin film synthesis route based on the electrochemical oxidation of PcLi 2 and deposition of lithium phthalocyanine (PcLi) onto indium tin oxide (ITO) substrate is demonstrated. The effects on the thin film morphology of various parameters such as the electrolysis time, the nature of the solvent, and the oxidation potential are investigated. The thin film growth is studied via x-ray diffraction, potential step experiments, and ex situ scanning electron microscopy. Various morphologies of the x -form thin films are observed for different electrolysis times and solvents. Thin films grown in acetonitrile of thickness above 1 μm consist in unidirectionally oriented needle-shaped crystallites.