DIRECT EVIDENCE OF STAR STRUCTURE FROM NUCLEAR-MAGNETIC-RESONANCE SPECTROSCOPY

Until now the characterization of a star-like structure has been based on an indirect method, i.e. the comparison of the molecular weight of the star polymer and its linear precursor. By preparing well-defined and narrow-molecular-weight-distribution polybutadiene and polyisopren e stars with up to four arms - using anionic polymerization techniques and the appropriate chlorosilane - and by characterising them by mean s of H-1 and C-13 NMR spectroscopy, the key point of the star, which i s the core next to the silicon atom, was observed.