Abstract: A process for the preparation of derivatives of halo-but-2-enoic acids and esters high in 2-ene content, several of which are novel. The esters and their derivatives are useful as promoters for the polymerization of ethylene or the copolymerization of ethylene with &agr;-olefins and, optionally, nonconjugated polyenes. The promoters can also be combined with transition metal compounds, e.g., vanadium, to form combination promoter-catalyst compounds.

Abstract: A polyolefin elastomer possessing a unique combination of properties, i.e., high molecular weight (Mw), high Mooney viscosity (ML1+4 at 125° C.), low polydispersity index (Mw/Mn) and low glass transition temperature (Tg), is obtained by a polymerization process employing a particular type of a metallocene catalyst. The polyolefin elastomer is useful for manufacturing a variety of products including rubber articles such as hoses, belts and moldings, polymer blends containing one or more other hydrocarbon polymers and lubricating oils in which the elastomer functions as a viscosity modifier. Also disclosed is a cocatalyst for activating the metallocene procatalyst employing a specific molar ratio of the components of the cocatalyst to the transition metal of the procatalyst.

Abstract: A process for the preparation of derivatives of halo-but-2-enoic acids and esters high in 2-ene content, several of which are novel. The esters and their derivatives are useful as promoters for the polymerization of ethylene or the copolymerization of ethylene with .alpha.-olefins and, optionally, nonconjugated polyenes. The promoters can also be combined with transition metal compounds, e.g., vanadium, to form combination promoter-catalyst compounds.

Abstract: 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; andR.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.