The present invention relates to alpha -olefin/vinyl aromatic monomer interpolymers with characteristic signals in their carbon 13 NMR spectra. In particular, ethylene/styrene copolymers of the present invention have peaks in the carbon 13 NMR spectra which appear in the chemical shift range 43.70 - 44.25 ppm, preferably from 43.75 - 44.25 ppm and 38.0 - 38.5 ppm, said peaks being at least three times the peak to peak noise. The interpolymers are prepared by polymerizing the appropriate mixture of monomers in the presence of a catalyst such as racemic-(dimethylsilanediyl(2-methyl-4-phenylindenyl)) zirconium dichloride. The polymers of the present invention possess increased modulus as determined from both tensile stress/strain and dynamic mechanical data at comparable vinyl aromatic monomer levels.
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