Catalyst system for polymerization of olefins

#The invention relates to a catalyst system for polymerization of olefins. The invention also relates to a process for polymerization of olefins using the catalyst system and to the polyolefin prepared by the process.

#Polymerization of olefins is usually carried out in the presence of a catalyst system containing a Ziegler-Natta type procatalyst carrying internal electron donor(s), an organo aluminium cocatalyst and an external electron donor. Depending upon the kind of internal electron donor used, the polymerization catalyst systems could either be (a) a monoester based catalyst system or (b) a diester based catalyst system.

#Monoester based catalyst systems use monoester of aromatic carboxylic acids as internal electron donors. When a monoester based catalyst system is used, the polypropylene productivity is usually low to moderate and polymers having relatively high polydispersity are formed. However, the extent of kinetic control achieved for the polymerization reaction, using such catalyst systems, is high, thus avoiding run away reactions leading to chunk formation. In most cases, monoester based catalyst systems provide polymerization reactions that are self extinguishing in nature i.e polymerization activity reduces with increasing temperature of the reaction.

#Accordingly, the invention provides a catalyst system for polymerization of olefins, the catalyst system comprising a mixture of external electron donors, the mixture comprising para isopropoxy ethyl benzoate, an alkoxy silane and a nitrogen based compound.

#In one embodiment, the invention provides a catalyst system for polymerization of olefins, the catalyst system comprising a titanium-containing procatalyst carrying internal electron donor(s), an organoaluminium cocatalyst and a mixture of external electron donors, the mixture comprising a carboxylic acid ester or derivatives thereof, an alkoxy silane and a nitrogen based compound.

#In another embodiment, the invention provides a catalyst system for polymerization of olefins, the catalyst system comprising a titanium-containing procatalyst carrying internal electron donor(s), an organoaluminium cocatalyst and a mixture of external electron donors, the mixture comprising a carboxylic acid ester or derivatives thereof, an alkoxy silane and a nitrogen based compound, wherein the carboxylic acid ester is present in 70 to 85% by mole, the silane is present in 10 to 20% by mole and the nitrogen based compound is present in 0.5 to 10% by mole of the mixture.