17:15 Uhr
Brandeis University, Waltham, Massachusetts, USA
Chain Ends at Polymer Crystallite Surfaces
Abstract:
The principle of avoidance of density anomalies in semicrystalline polymers predicts that chains will preferably end at the crystallite surface. For polyethylene, polyoxymethylene, and (partially) poly(e-caprolactone), this prediction has been confirmed by NMR experiments that probe the chain-end conformation, immobilization, localization at the crystallite surface, and clustering in the surface layer, by means of conformation-dependent chemical shifts, absence of significant motional narrowing, 1H spin diffusion and 13C spin exchange, respectively. Chain-end diffusion is also restricted.
