Abstract: A process for producing polymer particles in a gas phase polymerization reaction using a group 4 metal complex containing delocalized &pgr;-electrons and optionally a flow aid.

Abstract: A process for the polymerization of propylene or a mixture comprising propylene and one or more alpha-olefins and, optionally, one or more diolefins comprising contacting the propylene or the mixture of olefins in at least one reaction zone, under polymerization conditions, with a catalyst system comprising (i) a solid catalyst precursor, which includes magnesium; titanium; a halogen which is chlorine, bromine, or iodine, or mixtures thereof; and a mono- or polycarboxylic acid ester; (ii) a hydrocarbylaluminum cocatalyst; and (iii) a mixture of selectivity control agents comprising a mono- or polycarboxylic acid ester and a silicon compound containing at least one silicon-oxygen-carbon linkage with the proviso that (a) the atomic ratio of aluminum to titanium is in the range of about 5 to about 300; and (b) the molar ratio of the ester to silicon compound in the mixture of selectivity control agents is at least about 1.5:1.

Abstract: A process for terminating or retarding the rate of polymerization of propylene or a mixture comprising propylene and one or more other olefin monomers, in a gas phase reactor, in the presence of a catalyst system comprising (i) a solid catalyst precursor composition which includes magnesium, titanium, halogen, and carboxylic acid ester; (ii) hydrocarbyl aluminum cocatalyst; and (iii) a silicon compound containing at least one silicon-oxygen-carbon linkage, which comprises introducing a phthalate compound at a rate and in a sufficient quantity to substantially retard or terminate the said polymerization reaction.