Abstract: A method for producing aqueous polymer dispersions by means of radically initiated emulsion polymerisation, in an aqueous medium, of vinyl ester and ethylene, in series-connected polymerisation reactors, wherein in a first discontinuous polymerisation phase at least some of the reactants are introduced into the first polymerisation reactor and the remainder is added in a metered fashion. The reactor is filled up to more than 90% by volume, and at least 90 wt % of the monomers are reacted; in a second continuous polymerisation phase, the reactants are continuously supplied to the first polymerisation reactor and product is continuously withdrawn, and the product is continuously transferred into a second polymerisation reactor, and in the second polymerisation reactor the polymerisation is continued until at least 98 wt % of the monomers used have reacted.

Abstract: An olefin polymerization reactor is provided with a first cylinder extending vertically; a first tapered cylindrical member placed in the first cylinder, having the inner diameter decreasing progressively downward, and having a gas inlet orifice at a bottom end thereof; a first liquid supplying part supplying a liquid so that the liquid may come into contact with an outer surface of the first tapered cylindrical member; and a gas supplying part supplying an olefin-containing gas through the gas inlet orifice into a first reaction region surrounded by an inner surface of the first tapered cylindrical member and an inner surface of the first cylinder above the first tapered cylindrical member, to form a spouted bed in the first reaction region.

Abstract: The present invention deals with polymer compositions suitable for making pipes. The compositions comprise a multimodal copolymer of ethylene and one or more alpha-olefins having from 4 to 10 carbon atoms wherein the multimodal ethylene copolymer has a density of from 924 to 935 kg/m3, a melt index MFR5 of from 0.5 to 6.0 g/10 min, a melt index MFR2 of from 0.1 to 2.0 g/10 min and a shear thinning index SHI2.7/210 of from 2 to 50.

Abstract: The present invention relates to a slurry process for preparing an ethylene polymer having a melt flow ratio F/P, according to ASTM 1238, of higher than 25, carried out in two or more stages of polymerization at temperatures in the range from 60 to 120° C., in which at least two of the said two or more polymerization stages are carried out under different concentration of a molecular weight regulator, said process being carried out in the presence of a catalyst system comprising the product obtained by contacting (A) a solid catalyst component comprising Ti, Mg, halogen, and having a porosity (PF), measured by the mercury method and due to pores with radius equal to, or lower than, 1 ?m of at least 0.3 cm3/g and a surface area determined by BET method, of lower than 100 m2/g, and (B) of an organoaluminum compound.

Abstract: The present invention relates to a process for the preparation of a propylene homo- or copolymer, comprising the following steps: (i) feeding propylene and hydrogen, and optionally one or more comonomers, to a reactor R1, wherein the hydrogen is fed to the reactor R1 in a periodically varying amount, (ii) preparing a first fraction of the propylene homo- or copolymer in the reactor R1 in the presence of a catalyst, (iii) transferring the first fraction to a reactor R2, and (iv) preparing a second fraction of the propylene homo- or copolymer in the reactor R2, wherein the melt flow rate MFR (2.16 kg, 230° C.) of the propylene homo- or copolymer is higher than the melt flow rate MFR (2.16 kg, 230° C.) of the first fraction.

Abstract: Process for the preparation of a multimodal polyolefin polymer at temperatures of from 40 to 150° C. and pressures of from 0.

Abstract: A propylene polymerization reaction apparatus and a production method of a propylene-based polymer are capable of producing a continuous multi-stage polymer in low cost, high productivity and stably, and significantly reducing generation amount of an off-specification product accompanying change of polymerization condition, in multi-stage continuous vapor phase polymerization method of a propylene-based polymer using a catalyst for olefin polymerization. A reaction apparatus for producing a propylene-based polymer by a multi-stage continuous vapor phase polymerization method is used. One or more reactor of a horizontal-type reactor having inside a stirring machine which rotates around a horizontal axis, and a continuous stirred tank reactor to be connected to the horizontal-type reactor are provided, and a production method of a propylene-based polymer using the same.

Abstract: The present invention relates to a process for the gas-phase polymerisation of olefins in a fluidised bed reactor, which process comprises: a) passing a fluidising gas comprising one or more olefin monomers through a fluidised bed of polymer particles in the presence of a polymerisation catalyst, b) withdrawing a first gaseous stream comprising solid particles from the top of the reactor, c) passing the first gaseous stream to a gas/solids separator, separating solid particles therefrom, and forming a second gaseous stream comprising residual solid particles, d) passing at least a portion of the second gaseous stream to one or more heat exchangers to remove the heat of reaction, and e) recycling at least a portion of the cooled stream from step (d) as the fluidising gas in step (a), characterised in that the rate of fouling of the one or more heat exchangers is such that i) the increase in pressure drop across the heat exchangers is equivalent to less than 5% per year, and/or ii) the decrease in heat transfer

Abstract: An ethylenic polymer comprising amyl groups from about 0.1 to about 2.0 units per 1000 carbon atoms as determined by Nuclear Magnetic Resonance and both a peak melting temperature, Tm, in ° C., and a heat of fusion, Hf, in J/g, as determined by DSC Crystallinity, where the numerical values of Tm and Hf correspond to the relationship Tm?(0.2143*Hf)+79.643. An ethylenic polymer comprising at least one preparative TREF fraction that elutes at 95° C. or greater using a Preparative Temperature Rising Elution Fractionation method, where at least one preparative TREF fraction that elutes at 95° C. or greater has a gpcBR value greater than 0.05 and less than 5 as determined by gpcBR Branching Index by 3D-GPC, and where at least 5% of the ethylenic polymer elutes at a temperature of 95° C. or greater based upon the total weight of the ethylenic polymer.

Abstract: This invention is related to the preparation of polyethylene pipe resins suitable for transporting water containing chlorine.

Abstract: The present invention deals with polymer compositions suitable for making pipes. The compositions comprise a multimodal copolymer of ethylene and one or more alpha-olefins having from 4 to 10 carbon atoms wherein the multimodal ethylene copolymer has a density of from 924 to 960 kg/m3, a melt index MFR5 of from 0.5 to 6.0 g/10 min, a melt index MFR2 of from 0.1 to 2.0 g/10 min and a shear thinning index SHI2.7/210 of from 2 to 50. The compositions further have a level of volatile compounds of at most 100 ppm by weight and/or a homogeneity rating of at most 3.

Abstract: Process for heating a polymer-containing stream being transferred from a polymerization reactor to a separation zone or device, by passing the stream through at least two heaters operating in parallel, each heater having at least one transfer line for the stream and a heater for heating the transfer line. The average particle of the polymer is below 3 mm, the temperature of the polymer-containing stream at the outlet of all heaters is maintained above the dew point of the stream, and no heater has a volumetric flowrate of polymer-containing stream more than three times that of any other heater.

Abstract: The present invention provides a thermoplastic resin composition which comprises (A) a (meth)acrylic acid alkyl ester-based polymer forming a network-shaped disperse phase; and (B) an aromatic vinyl-cyanide vinyl based copolymer forming a continuous phase. The thermoplastic resin composition of the present invention can have an excellent low gloss characteristics while maintaining basic physical properties of a weather resistance, impact strength, thermal resistance, and delamination characteristics.

Abstract: The present application provides a process for polymerizing at least one olefin in the presence of a polymerization catalyst, including: (A) continuously introducing a first liquid with a transition metal compound, an organometallic compound, and a solvent and a second liquid into an emulsification stage, (B) continuously withdrawing the emulsion and directing it into a solidification stage to form a slurry with a solid polymerization catalyst component, (C) continuously recovering the solid polymerization catalyst component, (D) directing the solid polymerization catalyst component into a first prepolymerization stage with a monomer and a second liquid to form a slurry, (E) recovering a prepolymerized solid polymerization catalyst component, (F) continuously introducing the prepolymerized solid polymerization catalyst component into a second prepolymerization stage with an olefin monomer to form a prepolymerized catalyst, and (G) continuously withdrawing the prepolymerized catalyst and directing it into a su

Abstract: A method for feeding an antistatic compound to a polymerization reactor, the method comprising the steps of: a) dispersing, under mixing conditions, a catalyst powder and an antistatic compound in a liquid medium, so as to form a suspension of the catalyst powder and of the antistatic compound in the liquid medium; b) transferring the obtained suspension to a polymerization reactor.

Abstract: A method for the copolymerization of ethylene and a C3+ olefin copolymer in a loop reactor system and polymers formed therefrom are described herein.

Abstract: Provided are ethylene copolymers with excellent impact resistance. More specifically, provided are ethylene copolymers satisfying certain correlation between the falling dart impact strength (F) or high rate impact resistant breakage energy (E) and Vicat softening point. The ethylene copolymers with improved impact properties are applicable to film, injection, compound, sheet, roto, pipe or blow molding.

Abstract: Ethylene-based interpolymers, e.g., ethylene-acrylic acid copolymers, are made by a process comprising the steps of: A. Injecting a first feed comprising a chain transfer agent system (CTA system) and ethylene into a first autoclave reactor zone to produce a first zone reaction product, the CTA system of the first reactor zone having a transfer activity Z1; and B. (1) Transferring at least part of the first zone reaction product to a second reactor zone selected from a second autoclave reactor zone or a tubular reactor zone, and (2) at least one of transferring or freshly injecting a feed comprising a CTA system into the second reactor zone to produce a second zone reaction product, the CTA system of the second reactor zone having a transfer activity of Z2; and with the proviso that the ratio of Z1:Z2 is greater than 1. The comonomer comprises at least one carboxylic acid group or an anhydride group.

Abstract: This present invention provides devices for the parallelization of the formation of droplets in a multiple droplet generator integrating two or more parallel flow-focusing devices (FFDs) with either identical, or different, geometries. In the parallel identical FFDs, emulsification generates droplets with a narrow (below 4%) polydispersity despite weak coupling between the identical flow-focusing devices. Formation of droplets in the integrated droplet generator comprising FFDs with different dimensions of the microchannels occurs with strong coupling between the FFDs and produces droplets with varying sizes and size distributions. For such devices the regime in which emulsification produces droplets with varying dimensions and a narrow size distribution have been identified. The results of this work can be used in scaling up the production of droplets and in the simultaneous production of droplets and particles with different dimensions.

Abstract: The present invention deals with polymer compositions suitable for making pipes. The compositions comprise a multimodal copolymer of ethylene and one or more alpha-olefins having from 4 to 10 carbon atoms wherein the multimodal ethylene copolymer has a density of from 937 to 950 kg/m3, a melt index MFR5 of from 0.3 to 3.0 g/10 min, a melt index MFR2 of from 0.1 to 2.0 g/10 min and a shear thinning index SHI2.7/210 of from 2 to 30.

Abstract: A method for continuously producing a thermoplastic resin from a conjugated diene includes: primarily polymerizing a conjugated diene monomer with an aromatic vinyl monomer in a first solvent in a first reactor, and feeding a hydroxyl group-containing polymerization inhibitor and a polar hydrocarbon to the first reactor to prepare a rubber solution; and adding an aromatic vinyl monomer and a monomer copolymerizable with the aromatic vinyl monomer to the rubber solution, and subjecting the mixture to secondary polymerization in a second solvent of the same kind as the first solvent in a second reactor. The method can provide a thermoplastic resin that can have excellent color and low gloss characteristics.

Abstract: A gas-phase polymerization reactor having interconnected polymerization zones comprising:—a riser through which the polymer particles flow upwards under fast fluidization conditions or transport conditions—a dowcomer through which the polymer particles flow downward in a densified form under the action of gravity, the bottom of said downcomer being connected to the lower region of said riser by means of a transport section, said transport section being designed as a bend descending from the downcomer to the riser.

Abstract: A polyester production process employing an esterification system that utilizes a horizontally elongated esterification vessel as an esterification reactor and/or a vapor-liquid disengagement vessel.

Abstract: A process for preparing a polyethylene in a multi-stage process is described. The process comprises pre-treating a Ziegler catalyst in a first stage in the presence of a 1-olefin/ethylene mixture or a 1-olefin to produce a LLDPE or VLDPE, which have the characteristics of a polymer prepared with a single-site catalyst, e.g. high levels of short-chain branching that are uniformly distributed. The contents of the first stage are then transferred to a second stage where an ethylene or an ethylene/1-olefin mixture is polymerized in the presence of the pre-treated catalyst to form a polyethylene with good processability.

Abstract: Process for the preparation of a polyolefin polymer by continuously polymerizing one or more olefin monomers in suspension at temperatures of from 40° C. to 120° C. and pressures of from 0.1 to 10 MPa in the presence of a polymerization catalyst in at least one polymerization reactor, comprising a) withdrawing a suspension of solid polyolefin particles in a suspension medium from the polymerization reactor, wherein the suspension has a temperature of from 65° C. to 120° C.; b) feeding the suspension withdrawn from the polymerization reactor to a moderating vessel; c) keeping the suspension in the moderating vessel at a temperature of from 60° C. to 85° C. for a time sufficiently long that the mean residence time of the suspension in the moderating vessel is at least 5 min; d) withdrawing suspension from the moderating vessel; e) cooling the suspension withdrawn from the moderating vessel to a temperature of from 20° C. to 55° C.

Abstract: A sulfonic acid-functionalized vinyl alcohol copolymer is provided which is characterized by a substantial absence of compositional drift. The copolymer is produced by polymerization in two continuously-fed reaction zones such that the ratio of sulfonic acid-containing comonomer fed to the first reaction zone to the sulfonic acid-containing comonomer fed to the second reaction zone is within the range of about 55:45 to about 80:20. The resin is characterized by a resistance to irreversible dehydration upon exposure to harsh chemicals and by retention of hydroxide functionality upon aging. A resin composition comprising a copolymer lacking compositional drift is also provided for preparation of an oil and grease barrier coating, an oxidation resistant water soluble package, or a battery separator.

Abstract: Polymerization process comprising the steps of: (a) reacting an aqueous suspension comprising initiator, vinyl chloride, and optionally one or more co-monomers in a continuous stirred tank reactor; and (b) further reacting the resulting suspension in at least one second reactor; wherein the conversion level of vinyl chloride in the continuous stirred tank reactor of step (a) is from 10 to 60 wt %.

Abstract: The present invention provides an ethylene-based polymer composition characterized by a Comonomer Distribution Constant in the range of from greater than 45 to less than 400, wherein the composition has less than 120 total unsaturation unit/1,000,000C, and method of producing the same.

Abstract: This invention is related to the preparation of polyethylene pipe resins suitable for transporting hot and cold water containing chlorine dioxide.

Abstract: A process for producing an olefin-based polymer in a polymerization reactor including a fluidized bed, a disengaging section and a neck connecting the bed and disengaging section, at least one monomer, in the gas phase, in the presence of at least one catalyst containing at least two transition metals, one of the at least two transition metals being Ti, at least one cocatalyst, a composition having at least one compound selected from formula (I), and/or at least one compound selected from formula (II): (R1CO2)2AlOH (I), (R2)xN(R3OH)y (II); wherein R1 is a hydrocarbon radical containing from 13 to 25 carbons; R2 is a hydrocarbon radical containing from 14 to 26 carbons; R3 is a hydrocarbon radical containing from 1 to 4 carbons; and x+y=3, and x has a value of 1 or 2; and wherein the reactor is operated in a condensed mode and the average height of the fluidized bed is maintained above the neck of the polymerization reactor is provided. The reaction product of the process is also provided.

Abstract: Provided are ethylene copolymers with excellent impact resistance. More specifically, provided are ethylene copolymers satisfying certain correlation between the falling dart impact strength (F) or high rate impact resistant breakage energy (E) and Vicat softening point. The ethylene copolymers with improved impact properties are applicable to film, injection, compound, sheet, roto, pipe or blow molding.

Abstract: A process for polymerizing ethylene to produce an ethylene-based polymer including contacting ethylene with a Ziegler-Natta procatalyst, an alkylaluminum cocatalyst and a self limiting agent selected from the group of aliphatic, cycloaliphatic, substituted cycloaliphatic or aromatic esters, anhydrides and amides such that the self limiting agent reduces polymerization rates to no greater than 40% of the polymerization rate in the absence of the self limiting agent at temperatures equal to or greater than 120° C. is provided.

Abstract: Methods and systems for preparing catalyst, such as chromium catalysts, are provided. The valence of at least a portion of the catalyst sent to an activator is changed from Cr(III) to Cr(VI). The catalyst is prepared or activated continuously using a fluidization bed catalyst activator.

Abstract: Catalysts are activated in a dual reactor solution process by adding substoichiometric and superstoichiometric amounts of an ionic activator to an organometallic polymerization catalyst in a first and second reactor respectively. The new activation method allows one to alter process conditions in a favorably way with minimum impact to process economics. The new activation method also provides polymers which give films having improved optical properties.

Abstract: The invention relates to a polyethylene composition with a bimodal molecular weight distribution and articles made therefrom, such as high topload blow moldings and transmission and distribution pipes. The composition comprises a low-molecular-weight (LMW) ethylene homopolymer component and a homogeneous, high-molecular-weight (HMW) ethylene interpolymer component, wherein the LMW component is characterized as having a molecular weight distribution, MWDL, of less than about 8. The composition is characterized as having a bimodal molecular weight distribution, and a ductile-brittle transition temperature, Tdb, of less than ?20° C. In some embodiments, the HMW component is characterized by a reverse comonomer distribution.

Abstract: A process for the gas-phase copolymerization of: (a) propylene, (b) at least one C4-C8 ?-olefin, and (c) optionally ethylene, the process being carried out in a reactor having two interconnected polymerization zones, wherein the growing polymer particles flow through the first of said polymerization zones (riser) under fast fluidization conditions, leave said riser and enter the second of said polymerization zones (downcomer) through which they flow downward in a densified form, leave said downcomer and are reintroduced into said riser, thus establishing a circulation of polymer between the riser and the downcomer, the gas mixture present in the riser being at least partially prevented from entering the downcomer by introducing into the upper part of said downcomer a liquid barrier having a composition different from the gaseous mixture present in the riser and comprising at least one C4-C8 ?-olefin in a total amount of from 0.1% to 35% by mol.

Abstract: A process for producing water-absorbing polymer particles, comprising polymerization, drying, comminution, classification and recycling of the undersize obtained in the classification, wherein the recycled undersize is coated with a reducing agent and/or inorganic particles.

Abstract: Provided are methods of producing polymers with broadened molecular weight and/or composition distribution in a continuous homogeneous polymerization system utilizing reactor temperature gradients, reactor polymer concentration gradients, monomer concentration gradients, catalyst concentration gradients, and combinations thereof in the polymerization reactor. Such methods are particularly suitable when utilizing metallocene catalysts and other single-site catalysts, which generally produce polymers with narrow molecular weight and composition distribution.

Abstract: A process is disclosed for producing a multi-modal linear low density polyethylene in at least two staged reactors connected in series, comprising (i) polymerizing in a first slurry phase stage ethylene monomers with a Ziegler-Natta polymerization catalyst system to obtain a first polyethylene fraction component (A); and (ii) polymerizing in a second gas or slurry phase stage ethylene monomers with a Ziegler-Natta polymerization catalyst system to obtain a second polyethylene fraction component (B). The Ziegler-Natta polymerization catalyst system comprises: 1) a solid procatalyst formed by contacting at least: a) a Mg-alcoholate complex of formula (I) b) an aluminum compound of formula (II); and c) a vanadium compound and a titanium compound having a molar ratio (V:Ti) from 10:90 to 90:10; and 2) one or more organometallic cocatalvsts of formula (III). The linear low density polyethylene shows an improved comonomer composition distribution Formulas (I), (II), and (III) are described herein.

Abstract: The present invention relates to a polymerization reactor for continuous polymerization, the reactor being constructed in two stages and comprising a prepolymerization stage which is configured as a stirred vessel or as a loop-type bubble column and also a main polymerization stage which is configured as a tubular reactor. Furthermore, the present invention relates to a method for the production of biodegradable polyester, in particular polylactide, the reactor according to the invention being used. Likewise, the invention relates to a polymerization device which comprises further components in addition to the polymerization reactor.

Abstract: The present invention relates to a polymer composition, comprising (i) a polypropylene homopolymer, (ii) a polypropylene random copolymer, prepared by copolymerization of propylene with an olefin comonomer and having an amount of olefin comonomer units of 0.2 to 5 wt %, and (iii) an elastomeric copolymer of propylene and at least one olefin comonomer, the polymer composition having a tensile modulus, determined according to ISO 527-2/1B at 1 mm/min. and 23° C., of at least 1200 MPa.

Abstract: A semi-continuous process and system thereof, for the synthesis of a narrow particle size distribution Zeigler Natta procatalyst for use in the manufacture of polyolefins. The process comprises: (a) mixing a reaction mixture containing a titanium compound; (b) charging a first reactor with said reaction mixture; (c) removing excess reactants from said first reactor as a filtrate; (d) feeding said filtrate to at least one further reactor; and continuously removing excess reactants from said at least further reactor.

Abstract: The invention is an improved apparatus for continuously stirring polymer particles in reactive gas-filled polymerization reactors incorporating contiguous paddle stations on a coaxial drive shaft wherein the drive shaft is driven by a hydraulic motor.

Abstract: An ethylene-based polymer composition has been discovered and is characterized by a Comonomer Distribution Constant greater than about 45. The new ethylene-based polymer compositions are useful for making many articles, especially including films. The polymers are made using a metal complex of a polyvalent aryloxyether.

Abstract: The invention relates to a continuous polymerization process for preparing a random ethylene interpolymer which comprises: (A) polymerizing ethylene, and an ?-olefin comonomer selected from propylene and/or 1-butene, and mixtures thereof, under continuous random polymerization conditions in the presence of single site catalyst system employing an ionic activator having cyclic ligands shielding a central charge bearing atom, at a temperature of 140° C. to 250° C. at a conversion of ethylene of 80 to 99% and a comonomer conversion of from at least 20%; and (B) devolatilizing the polymer to provide an ethylene copolymer having a density of from 0.85 to 0.92 g/cm3, an MI of from 0.01 to 100 g/10 min and an I21/I2 of from 30 to 400.

Abstract: The present invention relates to a process for improving the polymerization of ethylene and one or more optional co-monomer(s) in a polymerization loop reactor characterized in that said process comprises the step of controlling the hydrogen/monomer ratio along the path of the reactor by multiple, spatially separated, feeding of hydrogen along the path of the loop reactor. In particular, the invention provides a process for controlling, and preferably narrowing, the molecular weight distribution of the produced polymer particles. In another aspect, the invention relates to a polymerization loop reactor suitable for the polymerization process of ethylene and an optional olefin co-monomer, wherein the molecular weight distribution of the produced ethylene polymer can be controlled.

Abstract: The invention relates to a reactor system and process for the catalytic polymerization of olefin monomer and optionally comonomer(s), having one or more inlets for olefin monomer, catalyst, optionally for comonomer, chain growth controllers or chain transfer agents, and/or inert gas, an outlet for gas and an outlet for polymerized particles. The reactor system has at least one fluidized bed unit and at least one moving bed unit, wherein the fluidized bed unit has means for maintaining a fluidized bed in the fluidized bed unit and wherein the moving bed unit is provided with an inlet and an outlet which are connected to the fluidized bed unit, wherein the outlet of the moving bed unit is provided with means for displacing metered quantities of polymerized particles from the moving bed unit into the fluidized bed unit, and to the use of such reactor system.

Abstract: A process for the gas-phase polymerization of one or more alpha-olefins in the presence of a polymerization catalyst, the process comprising: at least a polymerization step wherein the polymer particles flow downward in densified form under the action of gravity so as to form a densified polymer bed; metering an anti-fouling agent in said polymerization step by means of at least N feeding lines placed at different heights of said densified polymer bed, N being the integer number satisfying the equation N?(1+0.08·H), where H is the height (expressed in meters) of the polymer bed.

Abstract: A method for producing aqueous polymer dispersions by means of radically initiated emulsion polymerisation, in an aqueous medium, of vinyl ester and ethylene, in series-connected polymerisation reactors, wherein in a first discontinuous polymerisation phase at least some of the reactants are introduced into the first polymerisation reactor and the remainder is added in a metered fashion. The reactor is filled up to more than 90% by volume, and at least 90 wt % of the monomers are reacted; in a second continuous polymerisation phase, the reactants are continuously supplied to the first polymerisation reactor and product is continuously withdrawn, and the product is continuously transferred into a second polymerisation reactor, and in the second polymerisation reactor the polymerisation is continued until at least 98 wt % of the monomers used have reacted.

Abstract: An apparatus defined as a set of loop reactors suitable for the polymerization process of a monomer, preferably ethylene and optionally an olefin co-monomer, comprising for each of said reactors: a plurality of interconnected pipes P defining a flow path for a polymer slurry, said slurry consisting essentially of ethylene, optionally a co-monomer, a polymerization catalyst, liquid diluent and solid olefin polymer particles, means for feeding monomer, optionally a co-monomer, diluent and optionally hydrogen in the reactor, means for feeding a polymerization catalyst in the reactor, a pump suitable for maintaining the polymer slurry in circulation in such reactor, one or more settling legs connected to the pipes P of such reactor for settling of polymer slurry, one or more control valves connected to the outlet of such settling legs, and one or more flash lines for discharging settled polymer slurry out of the reactor characterized in that each of said loop reactors comprises a three-or-more-way valve defini