Steps in the formation of the partially crystalline state

Time- and temperature-dependent SAXS studies carried out on s-polypropylene , various s-poly(propene-co-octene)s, two poly(ethyleneco-octene)s and poly (-caprolactone) indicate that the transition from the entangled melt to the partially crystalline state occurs generally in two steps. At first, an in itial form of lower order builds up which then becomes stabilized to end in the final state with lamellar morphology. AFM observations suggest that th e initial structure is composed of crystal blocks in planar assemblies, whi ch then fuse into a homogeneous lamella. The edge length of the blocks in c hain direction determines also the lamellar thickness. The size of the bloc ks corresponds to the minimum necessary to be stable. The crystallinities a fter isothermal crystallization processes remain invariant over larger temp erature ranges, thus demonstrating that the potential of the entangled melt to form crystals is a well-defined property. (C) 2000 Elsevier Science Ltd . All rights reserved.