Building lamellae from blocks: The pathway followed in the formation of crystallites of syndiotactic polypropylene

AFM images of isothermally crystallized samples of syndiotactic polypropyle ne and poly(propene-co-octene) show that the lamellar crystallites are comp osed of blocks. Upon heating the granular structure vanishes. Observations support the view recently established by SAXS experiments that polymer crys tallization is a two-step process, with the block. formation near the growt h front as a first and their fusion into a lamella as a second step. it is proposed that the blocks. have the minimum size necessary to remain intrins ically stable. This could explain the observed invariability of the crystal thickness with changing co-unit content.