Abstract: The comparison of ¹³CNMR spect ra of phenyl C₁carbon reg ion of polystyrenes hav ing molecular weig hts from 10²to 10⁶was studied.The spectra were assig ned with The reference of st yrene pentamer hav ing propyl end groups and model compound 1, 3, 5 triphenylhexane.The triad distributions were obtained from spect raLInt egration of phenyl C₁ carbon regions.It is found that The sequence dist ributions are much dif ferent above and below a definite critical molecular weight.The sample with a molecular w eight less than 10³hasrrtriad percentage of ca.20%, w hile those with a molecular weight larger than 10³have rrtriad percentage from 30%to 40%.The effects of phenyl groups locat ed at end and ex ternal positions on spect ra are discussed quant it atively for lower molecular weight samples.The results are coincident with The kinetic studies of styrene oilgomerization, there The propag ation const ant wil covert to a asym ptote value after molecular weight reaches 10³.The polyst yrene samples used in this work were prepared by anionic polymerization of styrene initiated with n butyllithium and terminated with alcohoLIn benzene.

Key words: ¹³CNMR method, Polysty rene, Sequence distribution