Compounds of the formula: ##STR1## wherein n is 1, 2, 3, or 4; X.sup.1 and X.sup.2 are each, independently, chlorine or bromine; A is O or S; R.sup.1 is hydrogen or C.sub.1 -C.sub.16 alkyl; R.sup.2 is C.sub.1 -C.sub.16 alkyl, C.sub.6 -C.sub.16 aryl, C.sub.1 -C.sub.4 alkylidene, or CH.sub.2 OR.sup.5 ; R.sup.3 is hydrogen, chlorine, bromine, or OR.sup.6 ; R.sup.4 is C.sub.1 -C.sub.16 alkyl, C.sub.7 -C.sub.16 aralkyl, C.sub.2 -C.sub.16 alkenyl, or C.sub.6 -C.sub.18 aryl; R.sup.5 is hydrogen, C.sub.1 -C.sub.16 alkyl, C.sub.7 -C.sub.16 aralkyl, C.sub.2 -C.sub.16 alkenyl, or C.sub.6 -C.sub.18 aryl; and R.sup.6 is hydrogen or C.sub.1 -C.sub.16 alkyl. These compounds by themselves and in combination with certain halo-but-2-enoic acids and esters are useful as catalyst promoters in ethylene polymerization processes.
Promoters are described for vanadium-based catalysts used in the (co)polymerization of olefins and, in particular, in the production of ethylene/propylene (EPR) or ethylene/propylene/diene (EPDM) elastomeric copolymers. The promoters of the present invention belong to the group of compounds having general formula I: ##STR00001## wherein: "X" represents a (--CO--) carbonyl or (--SO.sub.2--) sulfonyl group; "n" is 0 or 1; R' is an alkyl or alkylaryl group having from 1 to 20 carbon atoms; R''=R', H.
