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 alpha and beta crystal modifications (alphaiPP and betaiPP). A derivation of the frustrated crystal structure of betaiPP is presented. The existence of two beta --> alpha growth transitions, at both low and high crystallization temperatures is so far unique in polymer science. The optical properties of the so-called mixed alpha 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 alphaiPP. Possible structural origins of reduced lamellar branching are considered, namely the tapering of lamellae and surface roughness.