[en] The authors study the activity of triphenylmehtylneodymium chlorides and the nature of the polymerization reaction of isoprene by the action of RNdC1₂ and obtain experimental data revealing the nature of the cis-regulating sites. A graph is presented which incicates that the activities of the triphenylmethylneodymium dichloride and triphenylneodymium sesquichloride complexes become equal relative to the isomerization of isoprene when the concentration of R /SUB 1.5/ NdCl /SUB 1.5/ is twice as great as that of RNdCl₂. This finding indicates that R₂NdCl in the presence of trialkylaluminum does not participate in the polymerization of these dienes. The IR spectra of the Ph₃CNdCl /SUB 2./ nTHF complex and the products of its reaction with (iC₄H₉)₃Al and piperylene were studied. Another study was carried out on the isoprene polymerization kinetics upon the action of the NdCl /SUB 2./ R₃Al /SUP ./ aC₅H₈ complex in hexane. A derease in the polymerization rate was found in going from hexane to toluene and then to o-xylene