Comments on the possibility that the mesomorphic form of isotactic polypropylene is composed of small crystals of the β crystalline form

The hypothesis that the mesomorphic form of isotactic polypropylene is composed of an ensemble of very small crystals of the β crystalline form, already suggested many years ago and recently renewed on the basis of a possible interpretation of high resolution solid state n.m.r. data, is reinvestigated through a further analysis of the available X-ray data. A comparison of the Fourier transform analysis for various hexagonal models with the measured X-ray diffraction intensities leads to the conclusion that the mesomorphic form is not composed of small β-form crystals but of much more disordered bundles of chains. The main features of the short range structure of the bundles is discussed in the paper.