A novel epitaxy of isotactic polypropylene (alpha phase) on PTFE and organic substrates

Isotactic polypropylene in its a modification (alpha iPP) crystallises epit axially on polytetrafluoroethylene (PTFE) and several hemiacids or salts of substituted benzoic acids via a novel contact plane, namely (110): so far, the only known contact plane involved in alpha iPP homo- and hetero-epitax ies was (010). In spite of its complicated architecture (alternation of ant ichiral helices with different azimuthal settings), the (110)(alpha iPP) co ntact plane displays well defined, if not prominent, rows of methyl side ch ains parallel to the crystallographic (112) direction (at 57 degrees to the c-axis) and approximate to 5.5 Angstrom apart. The matching contact planes of the substrates display linear gratings made of rows of e.g. chlorine at oms or PTFE chains with similar approximate to 5.5 Angstrom inter-row or in terchain distances. Various morphologies are observed in iPP thin films cry stallised at different cooling rates in the presence of PTFE; they can be a nalysed in terms of a succession and interplay of successive epitaxies: ini tial alpha iPP/PTFE heteroepitaxy, followed by alpha iPP/alpha iPP and gamm a iPP/alpha iPP homoepitaxies. (C) 1999 Published by Elsevier Science Ltd. All rights reserved.