On the crystallization of gamma-isotactic polypropylene: A high pressure study

The non-parallel chain structure determined for gamma-phase isotactic polypropylene (gamma-iPP) is confirmed by Rietveld analysis for highly isotactic high molecular mass iPP crystallized at 200 MPa. The new refinement shows that: i) stereoregularity or crystallization pressure do not significantly influence the lattice dimensions; ii) defect inclusion in gamma-iPP crystals is unlikely. The alpha and gamma forms have nearly identical bulk internal energy and density, but alpha-iPP should be normally kinetically favored over gamma-iPP which may in turn predominate due to its greater ability to host defects at the crystalline-amorphous interface.