he effect of CH2 = CH - CH2X (X=Cl

Br and I ) on polymerization activity and molecular weight of polymer has been studied in molybdenum catalyst system for 1

2-- polymerization of butadiene. The functions of CH2=CH -- CH2Br among three kind of allyl--halogen are the best for the catalytic activity and the regulation of molecular weight of 1

2-- polybutadiene from Mn= 3. 5 × 105 to 17. 5×105. From the data obtained by 13C--nmr and UV spectra of CH2= CH -- CH2X and butadiene molecules as well as parameters of polymerization activity and kynetics it was proposed that a frequency mechanism which was under the control of the molecular weight of polymer existed in the reac-tions between complexing reaction and discomplexing reaction

i.e.