Crystallization in Thin Films of Isotactic Polypropylene

Abstract

Microstructure of spherulites of the monoclinic modification of isotactic polypropylene has been studied in thin films by transmission electron microscopy and electron diffraction. Centers of spherulites are found to consist invariably of complex arrays of intercrossing lamellae. Radiating from the central regions are frondlike growths which constitute the coarse arms that are visible by optical microscopy. Each of the fronds is composed of a cluster of ribbonlike leaders, each of which, in turn, is covered with dense arrays of lamellar branches. Electron diffraction shows that constituent lamellae of both central and frondlike regions are chain-folded single crystals. Diffraction from the central regions confirms a model proposed by Khoury in which parent and daughter branches intersect at an acute dihedral angle of 80° 40′. Morphological evidence suggests that the same branching relation is preserved in the fronds and indicates that branching is initiated on the thin (010) faces of the lamellae.