Abstract: The invention relates to a process for the production of polyurethanes, in particular of polyurethane elastomers under use of diols and diisocyanates as well as optionally chain extenders, comprising the improvement of using diols or optionally chain extenders having at least one terminal group of the formula ##STR1## wherein X is a straight or branched alkylene group with 2 to 12 C-atoms. The diols or chain extenders are mainly polymers or oligomers of ethylenically unsaturated monomers and preferably have a hydroxyl functionality in the proximity of 2, preferably of 1,9 to 2,1.The invention further relates to a process for the radical polymerization, comprising the improvement of polymerizing ethylenically unsaturated monomers in the presence of azo-bis-N,N'-isobutyric acid hydroxyalkyl amides of the general formula ##STR2## wherein X is a straight or branched alkylene group with 2 to 12 C-atoms.