A macro-azo initiator comprising a mixture, of oligomers obtained in one reaction, each oligomer having at least repeating units represented by the formula: ##STR9## wherein R.sup.1, R.sup.2, R.sup.3 and R.sup.4 are independently a hydrogenatom, a lower alkyl group or a cyano group; R is --(CH.sub.2).sub.q --, --COO(CH.sub.2).sub.q -- or --CONH(CH.sub.2).sub.q ; q is an integer of 1 to 6; and p is