Molecular Aspects of Structure and Morphology of Isotactic Polypropylene

Several aspects of the structure, morphology, growth transitions, and optical properties of isotactic polypropylene (iPP) are considered; we deal mostly with its two more classical α and β crystal modifications (αiPP and βiPP). A derivation of the frustrated crystal structure of βiPP is presented. The existence of two growth transitions, at both low and high crystallization temperatures is so far unique in polymer science. The optical properties of the so-called “mixed” α phase spherulites are known to depend on the crystal orientations of radial (parent) and tangential (daughter) lamellae and the absence of short-range averaging of cell orientations in αiPP. Possible structural origins of reduced lamellar branching are considered, namely the tapering of lamellae and surface roughness.