AbstractThe use of dipropylene glycol in the polyaddition of 2,2′‐azobis(2‐cyanopropanol) (ACP) with hexamethylene diisocyanate results in soluble polyurethane‐type macroazo initiators (PUMAI) in high yields. By adjusting the amount of ACP used, the number‐average molecular weight of the polyurethane segments was adjusted in the range from 2000 to 6000 at an azo content in the PUMAI's of 0,18 to 0,5 mmol/g‐polymer (determined by UV). 13C NMR spectroscopy of the PUMAI's showed that no significant decomposition of azo groups occurred during polyaddition. At 80°C the PUMAI's initiated effectively the radical solution polymerization of vinyl monomers. As supposed from extraction results and the polymerization mechanism, block copolymers are formed. The whole process seems to be adequate for industrial applications.