Diastereotopic Styrene Arrangement in the Heterosequences of Random Styrene‐Ethylene Copolymers

Random styrene‐ethylene copolymers have been synthesized by the hydrogenation of styrene‐butadiene copolymers. The samples were characterized by ¹³C NMR spectroscopy, X‐ray powder diffraction, thermal analysis, and Fourier transform IR (FTIR) spectroscopy. In the ¹³C NMR spectra, the resonance of the methylene carbon next to a methine bearing a phenyl group presents splitting due to its diastereotopic positions with respect to the phenyl substituents of the second and third inserted styrene units. A definitive assignment of the resonances of the SEES sequences (S = styrene, E = ethylene) was obtained by synthesis of a suitable model compound: 5,10‐diphenyl‐pentadecane. X‐ray powder diffraction and thermal analysis show that these samples are amorphous. This is probably due to the shortness of the ethylene and styrene sequences in the copolymers. DSC thermograms show a single glass transition, at a intermediate temperature, between the T_g values of polystyrene and polyethylene, depending on the styrene content in the chain. FTIR spectra indicate the presence of styrene sequences in an isotactic arrangement.