Trigonal packing frustrated structures

The crystal structiue of the p form of iPP was only recently described despite the fact that this phase has been known to exist for 40 years. The structure consists of sections of three isochiral helices packed in a trigonal cell. One of the three helices is embedded in a crystallographic environment which is different from the other two, i.e. the structure is frustrated [5]. AFM studies of the (110) plane confirmed this frustrated character. In addition, it seems that in epitaxy the chains in the contact plane of polymer crystals (grown on dicyclohexylterephthalamide) expose rows of 2, 2 and 1 methyl groups. 

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