New (Macro)molecular Facets of an Old Problem: What Controls the Morphology of Semicrystalline Polymer

In defending his “macromolecular hypothesis,” Staudinger realized early on the relevance long chain molecules being able to crystallize. Since then, a variety of theories has been set up to explain the salient features of the semicrystalline morphology found for bulk high polymers, yet most of them do not consider explicitly the effect of intracrystalline chain dynamics and entanglements in the amorphous phase on the resulting lamellar morphology.

In an encompassing study [1-4] relying on a multi-method approach comprising NMR spectroscopy, SAXS, DSC, optical microscopy and rheology applied to various different polymers in a wide range of MW and timescales of intracrystalline chain dynamics, we have worked out a systematic picture. The talk stresses the use of different NMR methods, which are used to probe the timescale of intra­crystalline chain motion and the entangle­ment density in the amorphous phase [1-3]. We find that (i) in crystal-fixed polymers, such as PCL, the thickness of the amor­phous phase and thus the crystallinity is controlled by entanglements in the amorphous phase, thus excluding a “reeling-in” process [1,4]. (ii) Comparing PCL with the crystal-mobile PEO [2] and POM [3], we find that in the latter cases the amorphous phase has a significantly better-defined thickness, which is attributed to a thickening process that occurs during primary growth of the lamellae and is controlled by the ratio of the timescales of intracrystalline dynamics and crystal growth.