AbstractA mechanism is proposed for the polymerization of aliphatic diazo compounds catalyzed by boren trifluoride and similar boron derivatives which satisfactorily accounts for the observed kinetic and molecular weight results. The final polymer molecule is shown to be a baron alkyl of the type . Such molecules are catalysts for the polymerization of fresh diazo compounds and in this manner it has been possible to prepare block copolymers of the typeThe mechanism of polymerization is shown to be similar to the polymerization of ethylene catalyed by aluminum alkyls and possibly to the Ziegler‐type polymerization of α‐ole