The terminal structures of poly-l

3-pemadiene chains obtained by rare earth catalyst have been investigated with C-13 NMR method and effect of polymerization temperature on micros-tructure of the polymer has been studied. According to the experimental results it was supposed that the terminal active growing chain of the polymer would be anti- and syn-π-allyl formed in the "head-tail" and "tail-head" addition of the monomer. Therefore

there are four configurations of π-allylic terminal in the stereoregular polymerization of 1

3-pentadiene. When the polymerization temperature was reduced

the content of cis-poly-1

3-pentadiene increased. It is explained by the isomerization between the anti- and syn-π-allyl. The process forming trans-1

2 unit in the polymer was described.