A process for the preparation of a propylene copolymer, preferably a heterophasic propylene copolymer, in a multistage polymerisation process in the presence of a single site catalyst, said process comprising: (I) in a slurry polymerisation step, polymerising propylene and optionally at least one C2-10 alpha olefin comonomer; and subsequently (II) in a gas polymerisation step polymerising propylene and optionally at least one C2-10 alpha olefin comonomer, in the presence of catalyst and polymer from step (I); (III) in a second gas polymerisation step, polymerising propylene and at least one C2-10 alpha olefin comonomer in the presence of the catalyst and polymer from step (II); wherein said catalyst comprises (i) a metallocene complex of a group (IV) metal, said metallocene comprising at least two cyclopentadienyl type ligands; (ii) a boron based cocatalyst; and (iii) an aluminoxane cocatalyst; said catalyst being in solid form, preferably in solid particulate form, and being free from an external carrier.

A slurry polymerization process comprising polymerizing monomers in a reactor comprising baffles, a first slurry feed line for returning cooled slurry from a cooler and optionally a second slurry feed line for transferring reactor slurry from a previous reactor of a cascade of polymerization reactors, wherein the baffle top, the first slurry feed line discharge end and the second slurry feed line end are located below the reactor liquid level.

Techniques are provided for polymerization. A polymerization method may include polymerizing a monomer in a polymerization reactor to produce a slurry comprising polyolefin particles and a diluent, flowing the slurry out of the polymerization reactor through an outlet of the polymerization reactor, receiving the slurry from the outlet into a slurry handling system, conveying a first mixture from the slurry handling system to a diluent and monomer recovery system, and injecting steam into the first mixture downstream of the slurry handling system using a steam injection system.

A polyethylene resin having a multimodal molecular weight distribution comprising at least two polyethylene fractions A and B, fraction A being substantially free of comonomer and having a lower weight average molecular weight and a higher density than fraction B, each fraction prepared in different reactors of two reactors connected in series in the presence of a Ziegler-Natta catalyst system, the polyethylene resin having a density of from 0.950 to 0.965 g/cm.sup.3 and a melt index MI2 of from 0.5 to 5 g/10 min.

A polyethylene resin having a multimodal molecular weight distribution comprising at least two polyethylene fractions A and B, fraction A being substantially free of comonomer and having a lower weight average molecular weight and a higher density than fraction B, each fraction prepared in different reactors of two reactors connected in series in the presence of a Ziegler-Natta catalyst system, the polyethylene resin having a density of from 0.950 to 0.965 g/cm.sup.3 and a melt index MI2 of from 0.5 to 5 g/10 min.

A system and method for polymerizing olefin in the presence of a chain transfer agent in a first reactor to form a first polyolefin, discharging from the first reactor a transfer slurry having the first polyolefin and the chain transfer agent, and processing the transfer slurry in a separator to remove chain transfer agent and to provide a fluff slurry having the first polyolefin and a lower content of chain transfer agent than in the transfer slurry. The system and method provide for feeding the fluff slurry to a second reactor, polymerizing olefin in the second reactor to form a second polyolefin, and discharging from the second reactor a slurry having the second polyolefin.