The sequence structure of butyllithium catalyzed SBS block copolymers polymerized by two-step feed method has been studied. The results were shown below:(1)The aromatic proton resonance of non-block styrene of SBS does not show a single peak but consists of two peaks in 250 MHz NMR spectra. By using ethyl benzene as a model compound

the phenyl resonance peak of non-block styrene of butadiene-styrene was assigned.(2)If the non-block styrene and 1

2-butadiene contents are both below 10%

their low glass transition temperatures Tg are all below -69℃ obtained from dynamic me-chanical temperature spectra.