Morphology of polypropylene crystals. III. Lamellar crystals of thermally decomposed polypropylene

Morphology and crystal structure of solution-grown and melt-grown crystals of thermally decomposed polypropylene have been studied by electron microscopy and x-ray diffraction. By crystallization from dilute α-chloronaphthalene or carbitol solutions well-defined lamellar crystals about 100–150 A. in thickness are obtained from fractions (number-average molecular weights 1600–2100) of thermally decomposed crystalline polypropylene. The structure is monoclinic as crystallized from very dilute α-chloronaphthalene or carbitol solutions (0.02–0.005 wt.-%). However crystals of the triclinic as well as of the monoclinic forms are precipitated from carbitol solutions of higher concentrations (0.05-1 wt.-%). On the other hand, the separated triclinic form has been obtained from the melt. Crystals of both modifications have similar morphology. In addition, the chain molecules cannot be expected to fold, within the thickness of lamellae in crystals of either modification prepared from the low molecular weight fractions used in this study.