THIS INVENTION RELATED TO THE INTERPOLYMERIZATION OF OLEFINICALLY-UNSATURATED HYDROCARBONS BY MEANS OF ZIEGLER CATALYSTS. MORE PARTICULARLY, THIS INVENTIN RELATES TO A METHOD OF PREPARING NON-RUBBERY INTERPOLYMERS OF A MONOOLEFIN MONMER HAVING A SINGLE COPLYMERIZABLE ETHYLENIC GROUP, SAID INTERPOLYMER HAVING AN ESSENTIALLY SATURATED CARBON ATOM IN THE POLYMER MOLECULE AND CONTAINING SUFFICIENT ETHYLENICALLY-UNSATURATED GROUPS IN THE POLYMER MOLECULE TO PERMIT SUBSTANTIAL CURING OF FILMS THEREOF BY OXIDATIVE MECHANISM, EMPLOYING A ZIEGLER CATALYST IN A BATCH PROCESS IN WHICH THE CATALYST IS INCREMENTALLY ADDED.