Energetics polymer chains

NRA is a powerful method of obtaining concentration versus depth profiles of labelled polymer chains in films up to several microns thick with a spatial resolution of down to a few nanometres. This involves the detection of gamma rays produced by irradiation by energetic ions to induce a resonant nuclear reaction at various depths in the sample. In order to avoid permanent radioactivity in the specimen, the energy of the projectile is maintained at a relatively low value. Due to the large coulomb barrier around heavy nuclei, only light nuclei may be easily identified (atomic mass < 30). 

Looking at C2-symmetric catalysts, there exist in principle two different metallocene-olefin complexes (Fig. 4). Structure a is energetically favored because the methyl group of the propene is in trans-position relative to the (3-methyl structure of the polymer chain. Both methyl groups in structure b are in cis position to each... 

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