Propylene polymer

Abstract

A propylene copolymer (I) containing ≤ 3.0 wt% of hexene-1 and optionally ≤ 1.0 wt% of ethylene and having: (i) Tm in the range from 148 to 156°C and Tc ≥ 102°C; (ii) MFR ≤ 2.0 g / 10min; (iii) MWD ≥ 12, wherein the propylene copolymer (I) is obtainable by a process comprising: (a) polymerize propylene and hexene in a first gas-phase polymerization reactor to obtain a copolymer fraction (A) comprising a propylene-hexene copolymer; (b) transfer the copolymer fraction (A) obtained step (a) to a further gas-phase polymerization reactor and polymerize propylene, and optionally ethylene, in the presence of the copolymer fraction (A) to obtain a propylene copolymer (I) comprising the copolymer fraction (A) and a polymer fraction (B) obtained in step (b) comprising a propylene homopolymer or a propylene- ethylene copolymer, wherein the process is carried out in the presence of a Ziegler-Natta catalyst system.

Description

TITLEPROPYLENE POLYMERFIELD OF THE DISCLOSURE

[0001] The present disclosure relates to a propylene polymer, particularly to an ex-reactor propylene polymer, especially suitable for making pipes and containers, like expansion tanks and pipe cooling systems, or sheets.BACKGROUND OF THE DISCLOSURE

[0002] Plastic materials play a vital role in modern pipe systems, offering numerous advantages such as corrosion resistance, lightweight design, ease of installation, and costeffectiveness. However, several criticalities associated with plastic materials must be carefully considered to ensure the reliability and safety of pipe systems. Among these, long-term durability at operation temperature plays a pivotal role, particularly for pipes systems.

[0003] The resistance to creep deformation of the material must be accounted for during system design to prevent stress accumulation and potential system failure.

[0004] Expansion tanks are essential components of cooling systems, particularly in closed- loop systems, and must withstand severe thermal and pressure variations during their whole service life, like thermal cycling of the cooling fluid and pressure fluctuations as the coolant expands and contracts in response to changes in temperature.

[0005] Resistance to creep and fracture under stress is therefore a prerequisite also for materials to be used in expansion tanks applications.

[0006] Copolymers of propylene and hexene have proven to have satisfactory creep resistance. For instance, the patent EP 1759139B1 discloses a pipe system comprising a propylene / hexene-1 copolymer containing 0.5-5 wt% of polymerized hexene-derived units, said copolymer being produced in a gas-phase polymerization apparatus comprising two interconnected polymerization zones, a riser and a downcomer.

[0007] The patent application W02009 / 083500A1 discloses a plastic tank made of a propylene / hexene copolymer having xylene soluble fraction of less than 5 wt% and containing 0.5-5 wt% of polymerized units derived from hexene. Also in this case, the copolymer is obtainedin a gas-phase polymerization apparatus comprising two interconnected polymerization zones, like riser and downcomer.

[0008] In this context, the applicant unexpectedly found that by producing propylene / hexene copolymers, optionally containing a minor amount of polymerized units derived from ethylene, in at least two sequential gas-phase polymerization stages and in the presence of a Ziegler-Natta catalyst system, a propylene copolymer is obtained having improved creep resistance compared to known propylene / hexene- 1 copolymers, while retaining a balanced set of mechanical properties.SUMMARY OF THE DISCLOSURE

[0009] In a first aspect, the present disclosure refers to a propylene copolymer (I) containing up to and including 3.0% by weight of polymerized units derived from hexene and optionally up to and including 1.0% by weight of polymerized units derived from ethylene, based on the weight of the propylene copolymer (I), wherein the amounts of polymerized units derived from hexene and ethylene are determined by IR according to the method described in the experimental part, and wherein the propylene copolymer (I) has:

[0010] (i) a melting temperature (Tm) in the range from 148°C to 156 °C and a crystallization temperature (Tc) equal to or greater than 102 °C (ISO 11357-3:2018);

[0011] (ii) a melt flow rate (MFR) (ISO 1133-1 :2011, 230°C / 5 Kg) equal to or lower than 2.0 g / lOmin;

[0012] (iii) a molecular weight distribution (MWD) equal to or greater than 12, wherein the MWD is determined by GPC with method described in the experimental part,

[0013] and wherein the propylene copolymer (I) is obtainable by a process comprising:

[0014] (a) polymerize propylene and hexene in a first gas-phase polymerization reactor to obtain a copolymer fraction (A) comprising a propylene-hexene copolymer; and

[0015] (b) transfer the copolymer fraction (A) to a further gas-phase polymerization reactor and polymerize propylene, and optionally ethylene, in the presence of the copolymer fraction (A) to obtain a propylene copolymer (I) comprising the copolymer fraction (A) and a polymer fraction (B) obtained in step (b), said polymer fraction (B) comprising a propylene homopolymer or a propylene-ethylene copolymer,

[0016] wherein the process is carried out in the presence of a Ziegler-Natta catalyst system.

[0017] In a still further aspect, the present disclosure refers to a polymerization process to prepare a propylene copolymer (I) comprising the following steps:

[0018] (a) polymerize propylene and hexene in a first gas-phase polymerization reactor to obtain a copolymer fraction (A) comprising a propylene-hexene copolymer; and

[0019] (b) transfer the copolymer fraction (A) to a further gas-phase polymerization reactor and polymerize propylene, and optionally ethylene, in the presence of the copolymer fraction (A) to obtain a propylene copolymer (I) comprising the copolymer fraction (A) and a polymer fraction (B) obtained in step (b) comprising a propylene homopolymer or a propylene-ethylene copolymer,

[0020] wherein the process is carried out in the presence of a Ziegler-Natta catalyst system.

[0021] The present disclosure also refers to a polypropylene composition comprising at least at least 95% by weight of the propylene copolymer (I), based on the weight of the polypropylene composition.

[0022] In a further aspect, the present disclosure refers to an article, preferably a pipe, a container or a sheet, comprising the propylene copolymer (I) or the polypropylene composition of the present disclosure.

[0023] While multiple embodiments are disclosed, still other embodiments will become apparent to those skilled in the art from the following detailed description. As will be apparent, certain embodiments, as disclosed herein, are capable of modifications in various obvious aspects, all without departing from the spirit and scope of the claims as presented herein. Accordingly, the following detailed description is to be regarded as illustrative in nature and not restrictive.DESCRIPTION OF THE DRAWINGS

[0024] FIG. 1 provides a plot of the time to reach a minimum (10%) strain vs applied stress at 80°C for the propylene copolymer of example El compared to two commercial products.

[0025] FIG. 2 provides a plot of the time to reach a minimum (10%) strain vs applied stress at 80°C for the propylene copolymer of example E3 compared to one commercial product.DETAILED DESCRIPTION OF THE INVENTION

[0026] In the context of the present disclosure;

[0027] - the percentages are expressed by weight, unless otherwise specified;

[0028] - the total weight of a composition sums up to 100% by weight, unless otherwise specified;

[0029] - the term “comprising” referred to a polymer or to a polymer composition, mixture or blend should be construed to mean “comprising or consisting essentially of’;

[0030] - the term “consisting essentially of’ means that, in addition to those components which are mandatory, other components may also be present in the material, provided that the essential characteristics of the material are not materially affected by their presence. Examples of components that, when present in customary amounts, do not materially affect the characteristics of a polymer or of polymer compositions, mixtures or blends are catalyst residues, antistatic agents and processing aids;

[0031] - the term “homopolymer” is referred to a polymer deriving from the intentional polymerization of a single type of monomer;

[0032] - the term “copolymer” is referred to a polymer deriving from the intentional polymerization of two different comonomers, i.e. the term “copolymer” does not include terpolymers;

[0033] - the term “hexene” refers to hexene- 1 ;

[0034] - the term “pre-polymerization” refers to any preparatory chemical reaction or treatment carried out prior to the main polymerization reactions, like catalyst activation and partial polymerization of propylene monomers to form short chain polypropylene. The expression “polymerization reaction” does not include pre-polymerization, and the expression “polymerization reactor” does not include any pre-polymerization vessel.

[0035] In a first aspect, the present disclosure refers to a propylene copolymer (I) preferably containing, based on the weight of the propylene copolymer (I):

[0036] - up to and including 3.0% by weight, preferably from 0.1 to 2.5 % by weight, more preferably from 0.5 to 2.0 % by weight, of polymerized units derived from hexene, and

[0037] - optionally up to and including 1.0% by weight, preferably from 0.1 to 0.8 % by weight, of polymerized units derived from ethylene, wherein the amounts of polymerized units derived from propylene, hexene and optionally ethylene sums up to 100% by weight and wherein said amounts are determined by IR according to the method described in the experimental part.

[0038] The propylene copolymer (I) preferably has at least one, more preferably all, the following properties:

[0039] (i) a melting temperature (Tm) in the range from 150° to 154°C and / or a crystallization temperature (Tc) equal to or greater than 103 °C, more preferably in the range of from 103° to 109°C (ISO 11357-3:2018); and / or

[0040] (ii) a melt flow rate (MFR) (ISO 1133-1 :2011, 230°C / 5 Kg) equal to or lower than 1.7 g / lOmin, more preferably ranging from 0.8 to 1.5 g / lOmin, still more preferably from 1.1 to 1.3 g / lOmin; and / or

[0041] (iii) a molecular weight distribution (MWD) ranging from 13 to 22, wherein the MWD is determined by GPC with the method described in the experimental part.

[0042] Preferably, the melt flow rate of the propylene copolymer (I) measured in accordance with ISO 1133-1 :2011 at 230°C with a load of 2.16 Kg is equal to or lower than 0.5 g / lOmin.

[0043] Preferably, the isotactic pentad fraction (mmmm° / o) of the propylene copolymer (I) is equal to or greater than 97.0%, more preferably equal to or greater than 98.0%.

[0044] Preferably, the propylene copolymer (I) is not 0-nucleated, i.e. does not comprise a 0- nucleating agent and / or it is crystallized in the 0-modification for less than 50 %, like from 0.5 to 20%, as determined according to the method described in the experimental part.

[0045] Preferably, the propylene copolymer (I) also has at least one, more preferably all, the following properties:

[0046] (iv) a xylene soluble fraction at 25°C (XS) equal to or lower than 4.0% by weight, preferably in the range of from 1.0 to 3.5% by weight, more preferably from 1.8 to 3.0% by weight, based on the weight of the propylene copolymer (I), wherein the xylene soluble fraction is determined with the method described in the experimental part; and / or

[0047] (v) tensile modulus (ISO 527-1,-2, 48h) equal to or greater than 1100 MPa, preferably in the range of from 1150 to 1600 MPa, more preferably from 1200 to 1400 MPa; and / or

[0048] (vi) elongation at break (ISO 527-1,-2, 48h) equal to or greater than 490 MPa, preferably in the range of from 500 to 650 MPa; and / or

[0049] (vii) Charpy impact strength at 23°C (ISO 179-1:2010, Type 1, Edgewise, Notch A) in the range of from 10 to 20 KJ / m2, preferably from 13 to 18 KJ / m2

[0050] In a preferred embodiment, the propylene copolymer (I) is a propylene-hexene copolymer, i.e. the propylene copolymer (I) contains polymerized units derived only from propylene and hexene, and does not contain polymerized units derived from ethylene. The propylene-hexene copolymer has at least one, preferably all, the properties (i)-(vii) above.

[0051] The propylene copolymer (I) is endowed with a good balance of mechanical properties, in particular with improved creep resistance, if compared with propylene-hexene copolymers obtained by different polymerization processes.

[0052] Resistance to creep of the propylene copolymer (I) is evidenced by the comparatively high time-to-failure in a static creep test carried out according to the method described in the experimental part. Preferably, the propylene copolymer (I) shows a “time to 10% creep” equal to or greater than 5 hours at 80°C under a load of 10 MPa, preferably equal to or greater than 8 hours. In embodiments, the upper limit of the time to 10% creep is 15 hours.

[0053] In a preferred embodiment, the propylene copolymer (I) comprises or consists of:

[0054] - a copolymer fraction (A) comprising a propylene-hexene copolymer containing up to and including 4.0% by weight, preferably from 0.1 to 3.0 % by weight, more preferably from 0.5 to 2.0 % by weight, of polymerized units derived from hexene, based on the weight of the copolymer fraction (A), the copolymer fraction (A) having MFR(A) equal to or lower than 2.5 g / lOmin, preferably in the range of from 0.8 to 2.0 g / lOmin. (ISO 1133-1 :2011, 230°C / 5 Kg); and

[0055] - a polymer fraction (B) comprising a propylene homopolymer or a propylene-ethylene copolymer containing up to and including 3.0% by weight, preferably from 0.1 to 2.0 % by weight, of polymerized units derived from ethylene, based on the weight of the copolymer fraction (B).

[0056] In one embodiment the propylene copolymer (I) consists of a copolymer fraction (A) and of a polymer fraction (B) comprising or consisting of a propylene homopolymer.

[0057] More preferably, the propylene copolymer (I) comprises or consists of:

[0058] - from 70 to 95 % by weight of copolymer fraction (A), and

[0059] - from 5 to 30 % by weight of copolymer fraction (B),

[0060] based on the total weight of the propylene copolymer (I).

[0061] The copolymer fraction (A) is optionally obtained in one gas-phase polymerization reactor. In a preferred embodiment, the copolymer fraction (A) is obtained in two gas-phase polymerization reactors connected in series.

[0062] Accordingly, in one embodiment the copolymer fraction (A) comprises or consists of:

[0063] - a copolymer fraction (Al) comprising a propylene-hexene copolymer containing up to and including 4.0% by weight, preferably from 0.1 to 3.5 % by weight, more preferably from 0.5 to 2.0 % by weight, of polymerized units derived from hexene, based on the weight of thecopolymer fraction (Al) and having MFR(A1) equal to or lower than 2.5 g / lOmin, preferably ranging from 0.8 to 2.0 g / lOmin. (ISO 1133-1 :2011, 230°C / 5 Kg); and

[0064] - a copolymer fraction (A2) comprising a propylene-hexene copolymer containing up to and including 3.0% by weight, ppreferably from 0.1 to 2.5 % by weight, more preferably from 0.5 to 2.0 % by weight, of polymerized units derived from hexene, based on the weight of the copolymer fraction (A2), and having MFR(A2) equal to or lower than 2.5 g / lOmin, preferably ranging from 0.8 to 2.0 g / lOmin. (ISO 1133-1:2011, 230°C / 5 Kg),

[0065] wherein the propylene-hexene copolymer comprised in fraction (Al) is different from the propylene-hexene copolymer comprised in fraction (A2), like the propylene-hexene copolymer comprised in fraction (Al) has an hexene content different from the hexene content of the propylene-hexene copolymer comprised in fraction (A2) and / or the propylene-hexene copolymer comprised in fraction (Al) has MFR(A1) different from the melt flow rate MFR(A2) of the propylene-hexene copolymer comprised in fraction (A2).

[0066] In one embodiment, the copolymers of fractions (Al) and (A2) have different hexene content and substantially the same MFR. In this embodiment, the hexene content of the propylene- hexene copolymer comprised in fraction (Al) is greater than the hexene content of the propylene- hexene copolymer comprised in fraction (A2) and the MFR(Al) of the propylene-hexene copolymer comprised in fraction (Al) is equal to the MFR(A2) of the propylene-hexene copolymer comprised in fraction (A2).

[0067] In a further embodiment, the copolymers of fractions (Al) and (A2) have substantially the same hexene content and a different MFR. In this embodiment the hexene content of the propylene-hexene copolymer comprised in fraction (Al) is equal to the hexene content of the propylene-hexene copolymer comprised in fraction (A2) and the MFR(A1) of the propylene- hexene copolymer comprised in fraction (Al) is greater than the MFR(A2) of the propylene- hexene copolymer comprised in fraction (A2).

[0068] In one embodiment, propylene copolymer (I) consists of a copolymer fraction (A) consisting of the copolymer fractions (Al) and (A2), and of the polymer fraction (B) comprising or consisting of a propylene homopolymer.

[0069] In copolymer fraction (A) the weight ratio of the copolymer fraction (Al) to the copolymer fraction (A2) preferably ranges from 3: 1 to 1:2, more preferably from 2:1 to 1:1.

[0070] The propylene copolymer (I) is obtained by a polymerization process carried out in at least two sequential gas-phase polymerization reactors.

[0071] In a further aspect the present disclosure refers to a polymerization process to prepare a propylene copolymer (I) comprising the following steps:

[0072] (a) polymerize propylene and hexene in a first gas-phase polymerization reactor to obtain a copolymer fraction (A) comprising a propylene-hexene copolymer;

[0073] (b) transfer the copolymer fraction (A) obtained step (a) to a further gas-phase polymerization reactor and polymerize propylene, and optionally ethylene, in the presence of the copolymer fraction (A) to obtain a propylene copolymer (I) comprising the copolymer fraction (A) and a polymer fraction (B) obtained in step (b), said polymer fraction (B) comprising a propylene homopolymer or a propylene-ethylene copolymer,

[0074] wherein the process is carried out in the presence of a Ziegler-Natta catalyst system.

[0075] The process of the present disclosure is therefore a multistage sequential polymerization process, in which each polymerization step following the first polymerization step is carried out in the presence of the polymer produced and the catalyst used in the immediately preceding polymerization step.

[0076] Preferably, in the polymerization process of the present disclosure

[0077] - the copolymer fraction (A) obtained in step (a) comprises a propylene-hexene copolymer containing up to and including 4.0% by weight, preferably from 0.1 to 3.0 % by weight, more preferably from 0.5 to 2.0 % by weight, of polymerized units derived from hexene, based on the weight of the copolymer fraction (A), and has melt flow rate equal to or lower than 2.5 g / 1 Omin, preferably ranging from 0.8 to 2.0 g / lOmin. (ISO 1133-1:2011, 230°C / 5 Kg), and

[0078] - the polymer fraction (B) obtained in step (b) comprises a propylene homopolymer or of a propylene-ethylene copolymer containing up to and including 3.0% by weight, preferably from 0.1 to 2.0 % by weight, of polymerized units derived from ethylene, based on the weight of the copolymer fraction (B).

[0079] In a preferred embodiment, step (a) of the polymerization process of the present disclosure comprises the following steps:

[0080] (al) polymerize propylene and hexene in a first gas-phase polymerization reactor to obtain a copolymer fraction (Al) comprising a propylene-hexene copolymer;

[0081] (a2) transfer the copolymer fraction (Al) to a further gas-phase polymerization reactor and polymerize propylene and hexene in the presence of the copolymer fraction (Al) to obtain a copolymer fraction (A) comprising the copolymer fraction (Al) and a copolymer fraction (A2), said copolymer fraction (A2) comprising a propylene-hexene copolymer obtained in step (a2),

[0082] wherein the propylene-hexene copolymer comprised in fraction (Al) is different from the propylene-hexene copolymer comprised in fraction (A2).

[0083] Preferably, the propylene-hexene copolymer comprised in fraction (Al) contains up to and including 4.0% by weight, preferably from 0.1 to 3.5 % by weight, more preferably from 0.5 to 2.0 % by weight, of polymerized units derived from hexene, based on the weight of the copolymer fraction (Al), and has MFR(A1) equal to or lower than 2.5 g / lOmin, preferably ranging from 0.8 to 2.0 g / lOmin. (ISO 1133-1:2011, 230°C / 5 Kg), and the propylene-hexene copolymer comprised in fraction (A2) contains up to and including 3.0% by weight, preferably from 0.1 to 2.5 % by weight, more preferably from 0.5 to 2.0 % by weight, of polymerized units derived from hexene, based on the weight of the copolymer fraction (A2), and has MFR(A2) equal to or lower than 2.5 g / lOmin, preferably ranging from 0.8 to 2.0 g / lOmin. (ISO 1133-1 :2011, 230°C / 5 Kg),

[0084] wherein the propylene-hexene copolymer comprised in fraction (Al) is different from the propylene-hexene copolymer comprised in fraction (A2).

[0085] Differences between the copolymers comprised in fractions (Al) and (A2) are preferably as described in the foregoing.

[0086] In a preferred embodiment, step (a2) comprises the following steps, carried out in the given order:

[0087] - discharging the copolymer fraction (Al) obtained in step (al) continuously or discontinuously from the first gas-phase polymerization reactor,

[0088] - transferring the copolymer fraction (Al) to one or more degassing units,

[0089] - degassing the copolymer fraction (Al) thereby at least partially removing unreacted monomers, and

[0090] - transfer the copolymer fraction (Al) to a further gas-phase polymerization reactor and polymerize propylene and hexene in the presence of the copolymer fraction (Al) to obtain a copolymer fraction (A) comprising the copolymer fraction (Al) and a copolymer fraction (A2), said copolymer fraction (A2) comprising a propylene-hexene copolymer obtained in step (a2).

[0091] The degassing step is carried out according to methods known in the art of olefin polymerization.

[0092] In a preferred embodiment, propylene is homopolymerized in step (b) of the polymerization process according to the present disclosure. In this preferred embodiment, the polymer fraction (B) obtained in step (b) comprises a propylene homopolymer.

[0093] Preferably, step (b) comprises the following steps, carried out in the given order:

[0094] - discharging the copolymer fraction (A) obtained in step (a) continuously or discontinuously from the gas-phase polymerization reactor,

[0095] - transferring the copolymer fraction (A) to one or more degassing units,

[0096] - degassing the copolymer fraction (A) thereby at least partially removing unreacted monomers, and

[0097] - transfer the copolymer fraction (A) to a further gas-phase polymerization reactor and polymerize propylene, and optionally ethylene, in the presence of the copolymer fraction (A) to obtain a propylene copolymer (I) comprising the copolymer fraction (A) and a polymer fraction (B) obtained in step (b), said copolymer fraction (B) comprising a propylene homopolymer or a propylene-ethylene copolymer.

[0098] In a particularly preferred embodiment, each polymerization reactor in which propylene and hexene are copolymerized, like reactors in which steps (a), or alternatively (al) and (a2), are carried out, is operated at an operating temperature independently selected from values equal to or lower than 80°C, preferably equal to or lower than 79°C, more preferably ranging from 65° to 78°C.

[0099] The polymerization temperature in the gas-phase reactor in which propylene is homopolymerized or optionally copolymerized with ethylene is preferably comprised in the range from 20°C to 100°C.

[0100] Each gas-phase polymerization reactor is preferably independently operated at a pressure in the range from 0.5 to 3.0 MPa.

[0101] The molecular weight of the polymers is regulated by feeding a molecular weight regulator, like hydrogen, into polymerization reactor.

[0102] In a preferred embodiment, the hydrogen / propylene (H2 / C3) ratio in step (a) is in the range of from 0.001 to 0.005 mol / mol, preferably in the range of from 0.0015 to 0.004 mol / mol.

[0103] The amounts of polymer fractions (A), (Al), (A2) and (B) correspond to the split between the polymerization steps. Hence, from 70 to 95% by weight of the propylene copolymer (I), corresponding to polymer fraction (A), is preferably produced in polymerization steps (a), or in step (al)+(a2), and from 5 to 30% by weight of the propylene copolymer (I), corresponding to polymer fraction (B), is produced in step (b).

[0104] Gas-phase reactors suitable to produce the propylene copolymer (I) are any mechanically mixed or fluidized bed reactor of the type known in the art for the polymerization of olefins, fluidized bed type reactors being particularly preferred.

[0105] The polymerization process of the instant disclosure is carried out in the presence of a Ziegler-Natta catalyst system. It is preferred that the fresh Ziegler-Natta catalyst system, optionally pre-polymerized, is fed only to the gas-phase reactor in which step (a) or step (al) is carried out. Accordingly, each copolymer fractions transferred to a subsequent gas-phase polymerization reactor is comprised in a polymerization mixture including a still active Ziegler-Natta catalyst system.

[0106] In one embodiment, the polymerization process further comprises a prepolymerization step (aO) comprising or consisting of pre-polymerize propylene in liquid phase in the presence of a Ziegler-Natta catalyst system to obtain a pre-polymerization mixture comprising a pre-polymerized Ziegler-Natta catalyst system, and transfer the pre-polymerization mixture to the gas-phase polymerization reactor in which step (a) is carried out.

[0107] The pre-polymerization reactor is of smaller size compared to the gas-phase polymerization reactors in which steps (a) and (b) are conducted. The reaction volume of the pre- polymerization reactor can be, for example, between 0.001 % and 10 % of the reaction volume of the first gas-phase reactor. In said pre-polymerization reactor, the pre-polymerization of propylene is performed in liquid phase, either in bulk or slurry, producing a propylene polymer, preferably a propylene homopolymer. In embodiments, the pre-polymerization is carried out in a loop or in a continuously stirred tank reactor using liquid monomer or a hydrocarbon solvent as liquid medium. The amount of hydrocarbon solvent is preferably lower than 40% by weight, more preferably lower than 20% by weight, based on the weight of the pre-polymerization mixture. In a particularly preferred embodiment, the pre-polymerization step (aO) is carried out in bulk using liquid propylene as liquid medium, in the absence of any hydrocarbon solvent.

[0108] The operating temperature in the pre-polymerization reactor is in the range of 5° to 60 °C, preferably in the range of 10° to 50 °C, more preferably in the range of 15° to 35 °C.

[0109] The pressure in the pre-polymerization reactor is not critical and it is preferably in the range of 2 to 10 MPa, preferably in the range of 3 to 7 MPa.

[0110] The average residence time in pre-polymerization step (aO) is preferably in the range of from 2 to 40 min., more preferably from 10 to 25 min.

[0111] In the pre-polymerization step (aO) from 60 to 800 g of polymer are preferably produced per gram of solid catalyst component, more preferably from 150 to 500 g.

[0112] Hydrogen is optionally added in the pre-polymerization reactor in order to control the molecular weight and the melt flow rate of the propylene polymer produced in the pre- polymerization reactor.

[0113] In one embodiment, the polymerization process consists of steps (aO), (al), (a2) and (b).

[0114] The propylene copolymer (I) is obtained by polymerizing the relevant monomers in the presence of a Ziegler-Natta catalyst systems comprising:

[0115] (1) a solid catalyst component comprising a magnesium halide support on which a Ti compound having at least a Ti-halogen bond is present, and a stereoregulating internal donor;

[0116] (2) a cocatalyst preferably selected from Aluminum alkyl compounds; and

[0117] (3) optionally, but preferably, a further electron-donor compound (external donor).

[0118] The solid catalyst component (1) preferably comprises TiCh in an amount securing the presence of from 0.5 to 10% by weight of Ti with respect to the total weight of the solid catalyst component (1).

[0119] The solid catalyst component (1) comprises at least one stereoregulating internal electron donor compound selected from mono or bidentate organic Lewis bases, more preferably selected from esters, ketones, amines, amides, carbamates, carbonates, ethers, nitriles, alkoxysilanes and combinations thereof.

[0120] Suitable donors are the esters of phthalic acids such as those described in EP45977A2 and EP395083 A2, in particular di-isobutyl phthalate, di-n- butyl phthalate, di-n-octyl phthalate, diphenyl phthalate, benzylbutyl phthalate and combinations thereof.

[0121] Esters of aliphatic acids can also be selected from esters of malonic acids such as those described in WO98 / 056830, WO98 / 056833, WO98 / 056834, esters of glutaric acids such as those disclosed in WOOO / 55215, and esters of succinic acids such as those disclosed WOOO / 63261.

[0122] Particular type of diesters are those deriving from esterification of aliphatic or aromatic diols such as those described in W02010 / 078494 and USP 7,388,061.

[0123] In one embodiment, the internal donor is selected from 1,3 -di ethers such as those described in EP361493, EP728769 and W002 / 100904.

[0124] Specific mixtures of internal donors, in particular of aliphatic or aromatic mono or dicarboxylic acid esters and 1,3-diethers as disclosed in W02007 / 147864, WO2007 / 147865 and WO2012 / 139897 can be used as internal donor.

[0125] Preferred magnesium halide support is magnesium dihalide.

[0126] The amount of internal donor that remains fixed on the solid catalyst component (1) is 1 to 20% by moles, preferably 5 to 20% by moles, with respect to the magnesium dihalide.

[0127] A preferred molar ratio Mg / Ti is comprised in the range of from 35:1 to 2: 1.

[0128] The final amount of the electron donor compound is such that its molar ratio with respect to the Ti atoms ranges from 0.01: 1 to 2: 1, preferably from 0.05:1 to 1.5: 1.

[0129] The preparation of catalyst component (1) according to a general method is described for example in US4,220,554, EP344755, EP728769A1 and WO2012 / 139897A1.

[0130] In a preferred embodiment, the solid catalyst component (1) comprises a magnesium halide as described in the foregoing, a titanium compound having at least a Ti-halogen bond as described in the foregoing and at least two electron donor compounds one of which is selected from1.3-diethers and the other is selected from succinates, said catalyst component being characterized by the fact that the molar ratio ID / Ti is from 0.30 to 0.90, preferably from 0.45 to 0.75, where ID is the total molar amount of succinate and 1,3 -diether, the molar ratio of the 1,3 -diether donor to the succinate donor is equal to or greater than 0.60, preferably from 0.80 to 2, and the porosity due to pore with radius equal to or less than 1 micron of the said solid catalyst component, determined by mercury method, is at least 0.30 cm3 / g.

[0131] In a further preferred embodiment, the solid catalyst component (1) comprises diethyl2.3-diisopropylsuccinate and 9,9-bis(methoxymethyl)fluorene as internal electron donors, in total amount and proportions described above.

[0132] The solid catalyst component (1) of the preferred embodiment is described in WO2012 / 139897A1, which is herein incorporated by reference.

[0133] The catalyst system preferably comprises an Al-containing cocatalyst (2) selected from Al-trialkyls, preferably selected from the group consisting of Al-triethyl, Al-triisobutyl and Al-tri- n-butyl. The Al / Ti weight ratio in the catalyst system is from 1 to 1000, preferably from 20 to 800.

[0134] In a preferred embodiment, the catalyst system comprises a further electron donor compound (3) (external electron donor) selected among silicon compounds, ethers, like cyclopolyenic 1,3 -di ethers, esters, amines, heterocyclic compounds, particularly 2, 2,6,6- tetramethylpiperidine, and ketones.

[0135] Preferred silicon compounds are selected among methylcyclohexyldimethoxysilane (C-donor), dicyclopentyldimethoxysilane (D-donor) and mixtures thereof.

[0136] In a preferred embodiment of the process according to the present disclosure, the catalyst is a Ziegler-Natta catalyst system as described EP728769, i.e. wherein the internal and / or the external donor is selected from cyclopolyenic 1,3-diethers wherein the carbon atom in position 2 belongs to a cyclic or polycyclic structure containing two or three unsaturations.

[0137] In a preferred embodiment of the process according to the present disclosure, the catalyst is a Ziegler-Natta catalyst system is as described in WO2012 / 139 / 897A1, wherein the solid catalyst component comprises at least two electron donor compounds one of which is selected from 1,3-diethers and the other one is selected from succinates.

[0138] In the process according to the present disclosure, the polymerization reaction terminates at the end of step (b) and the polymer mixture obtained in step (b) is not circulated back to step (a). The propylene polymer (I) is therefore discharged from the gas-phase polymerization reactor at completion of step (b), and preferably transferred to a finishing section.

[0139] Accordingly, in a preferred embodiment the process of the present disclosure comprises a step (c) which is discharge the propylene copolymer (I) from the gas-phase reactor, and optionally, but preferably, transfer the propylene copolymer (I) to a finishing section to obtain a finished propylene copolymer (I).

[0140] The finishing section preferably comprises:

[0141] - a polymer degassing unit, like a degassing vessel or an extruder under vacuum, to remove volatiles, like unreacted monomers and carrier gas, from the polymer; and optionally, but preferably

[0142] - an extruder or a pelletizer downstream of the polymer degassing unit, to convert the polymer into manageable pellets. The extruder or pelletizer comprises a cutting section, a cooling system to solidify the polymer pellets and optionally a dryer to remove cooling liquid from the pellets.

[0143] In a less preferred embodiment, the finishing section does not comprise the extruder, and a propylene copolymer (I) in powder form is obtained in step (c).

[0144] In a further aspect, the present disclosure refers to a polypropylene composition comprising or consisting of:

[0145] - at least 95% by weight, preferably from 96 to 99.9% by weight, of the propylene copolymer (I), and

[0146] - up to 5% by weight, preferably from 0.1 to 4% by weight, more preferably 0.5 to 3% by weight, of an additive,

[0147] wherein the amounts of the propylene copolymer (I) and of the additive are based on the weight of the polypropylene composition.

[0148] The additive is preferably selected from the type commonly used in the polymer field. In a more preferred embodiment, the additive is selected from the group consisting of antioxidants, light stabilizers, slipping agents, acid scavengers, melt stabilizers, pigments, colorants, and combinations thereof.

[0149] The additive is added to the propylene copolymer (I) either directly, like neat, or preferably as masterbatch, i.e. pre-dispersed in a polymer carrier, preferably a polypropylene carrier. In the latter case, the amount of additive in the polypropylene composition includes the amount of the polymer carrier.

[0150] The polypropylene composition is obtained by mixing the propylene copolymer (I) and the additive at a temperature at which the propylene copolymer (I) is at least partially molten, like in conventional extruder.

[0151] The propylene copolymer (I) and / or the polypropylene composition described above are optionally used in blend with further components, e.g. different plastic materials and / or fillers, to obtain polymer compositions having a different set of properties, like stiffer or softer.

[0152] The propylene copolymer (I) and the articles obtained therefrom are endowed with a good balance of mechanical properties, in combination with good creep resistance.

[0153] It is therefore a further aspect of the present disclosure an article comprising the propylene copolymer (I) or the polypropylene composition described above, said article being preferably selected from pipes, containers, like tanks, and sheets.

[0154] Articles according to the present disclosure are obtained by processes well known in the art for plastic shaping, like injection molding, blow molding, compression molding and extrusion.

[0155] EXPERIMENTAL PART

[0156] The following examples are illustrative only, and are not intended to limit the scope of the disclosure in any manner whatsoever.

[0157] The following methods are used to determine the properties indicated in the description, claims and examples.

[0158] Hexene and ethylene content: determined by IR using Fourier Transform Infrared Spectrometer (FTIR). The spectrum of a pressed film of the polymer is recorded in absorbance vs. wavenumbers (cm ). The following measurements are used to calculate C2 and C6 content:

[0159] - area (At) of the combination absorption bands between 4482 and 3950 cm'1which is used for spectrometric normalization of film thickness;

[0160] - a linear baseline is subtracted in the 790 - 660 cm'1range and the remaining constant offset is eliminated;

[0161] - the C2 and C6 contents are obtained by applying a Partial Least Square (PLS1) multivariate regression to the 790 - 660 cm'1range.

[0162] The method is calibrated by using polymer standards based on 13C NMR analyses. Atmospheric CO2 absorbs at 669 cm'1. The optical bench should be properly purged.

[0163] Sample preparation: using a hydraulic press, a thick sheet is obtained by pressing about 1g of sample between two aluminum foils. A small portion is cut from this sheet to mold a film. Recommended film thickness: 0.02-0.05 cm. Pressing temperature: 180 ± 10°C, applying ca. 10kg / cm2pressure for about one minute. Release the pressure, remove from the press and cool the sample to 25 °C.

[0164] Collect the IR spectrum of the sample vs. an air background. To avoid fringes, the sample is placed in a goniometric sample holder set to 56° degree and an infrared KRS-5 wired polarizer (set to 0° degree) is put across the IR beam before the sample holder.

[0165] Purge time: 3 minutes minimum (till CO2 peak disappears)

[0166] Collect time: 1 minutes minimum (64 scans)

[0167] Apodization: Happ-Genzel

[0168] Resolution: 4 cm'1

[0169] Pentad fraction: determined via13C NMR. Spectra are acquired on a Bruker AV-600 spectrometer equipped with cryoprobe, operating at 160.91 MHz in Fourier transformation mode at 120°C. The peak of the Ppp carbon (nomenclature according to C. J. Carman, R. A. Harrington and C. E. Wilkes, Macromolecules, 10, 3, 536 (1977)) is used as internal reference at 21.8 ppm. The samples are dissolved in l,l,2,2-tetrachloroethane-d2, added with 0.1 mg / ml of Irganox 1010 as antioxidant at 120°C with a 8 % wt / v concentration. Each spectrum is acquired with a 90° pulse, 15 seconds of delay between pulses and CPD to removeJH-13C coupling. 512 transients were stored in 32K data points using a spectral window of 9000 Hz. The assignments of the methyl region deriving from propylene units is made according to Resconi et al. [('hem. Rev. 2000, 100, 4, 1253-1346], The pentad fraction (mmmm%) is calculates as follow:100 X 41 / ( 41 + A2) wherein, Al is the area between 22.2 ppm and 21.6 ppm and A2 is the area between 21.6 ppm and 19.7 ppm.

[0170] Melt Flow Rate: Determined according to the method ISO 1133-1 :2011 at 230°C with5 Kg load unless otherwise specified.

[0171] Melting and crystallization temperatures: determined by DSC according to the method ISO 11357-3:2018 with a scanning rate of 20°C / min in cooling and heating, on a sample weighting 5-7 mg, under nitrogen flow. Instrument calibration made with Indium.

[0172] Molecular weight distribution (Mw / Mn): the determination of the means Mn and Mw, and Mw / Mn is carried out using a PolymerChar GPC-IR apparatus, equipped with a column set of four PLgel Olexis mixed-gel (Polymer Laboratories) and an IR5 infrared detector (PolymerChar). Dimension of the columns: 300x7.5 mm; particle size of stationary phase: 13 microns. The mobile phase used is 1 -2-4-trichlorobenzene (TCB), and its flow rate is kept at 1.0 ml / min. All the measurements are carried out at 150°C. Solution concentrations are 0.15 g / dl in TCB. 0.1 g / 1 of 2,6-diterbuthyl-p-chresole are added to prevent degradation. For GPC calculation, a universal calibration curve is obtained using 12 polystyrene (PS) standard samples supplied by Polymer Laboratories (peak molecular weights ranging from 266-12200000). A third order polynomial fit is used for interpolating the experimental data and obtaining the calibration curve. Data acquisitionand processing is done using Empower (Waters). The Mark-Houwink eqauation is used to determine the molecular weight distribution and the average molecular weights. The K and a values for homopolymers are: KPS = 1.21 1 O'4dl / g and a=0.706 for polystyrene, Kpp=1.90xl0'4dl / g and a=0.725 for polypropylene, KPE=4.06X 10'4dl / g and a=0.725 for polyethylene and KPH=1.78 X 10'4dl / g and a=0.725 for poly- 1 -hexene. For propylene copolymers, it is assumed that the comonomer distribution is constant in the whole range of molecular weights and the K value of the Mark-Houwink equation is estimated using a linear combination:

[0173] Kco= XpKpp + XjKpj

[0174] wherein Kco is the constant of the copolymer, Kpp is the constant for polypropylene, Kpi is the constant for polyethylene or poly- 1 -hexene depending on the comonomer. Xp and Xi are relative amounts of propylene and of comonomer (ethylene or hexene- 1) in the polymer and Xp+Xi=l. The Mark-Houwink exponent a=0.725 is used for all copolymers.

[0175] Solubility in xylene at 25°C: 2.5 g of polymer sample and 250 ml of xylene are introduced in a glass flask equipped with a refrigerator and a magnetic stirrer. The temperature is raised in 30 minutes up to 135°C. The obtained clear solution is kept under reflux and stirring for further 30 minutes. The solution is cooled in two stages. In the first stage, the temperature is lowered to 100°C in air for 10 to 15 minute under stirring. In the second stage, the flask is transferred to a thermostatically controlled water bath at 25°C for 30 minutes. The temperature is lowered to 25°C without stirring during the first 20 minutes and maintained at 25°C with stirring for the last 10 minutes. The formed solid is filtered on quick filtering paper (eg. Whatman filtering paper grade 4 or 541). 100 ml of the filtered solution (SI) is poured in a previously weighed aluminum container, which is heated to 140°C on a heating plate under nitrogen flow, to remove the solvent by evaporation. The container is then kept on an oven at 80°C under vacuum until constant weight is reached. The amount of polymer soluble in xylene at 25 °C is then calculated. XS(I) and XSA values are experimentally determined. The fraction of component (B) soluble in xylene at 25°C (XSB) can be calculated from the formula:XS = W(A)X(XSA) + W(B) X(XSB) wherein W(A) and W(B) are the relative amounts of components (A) and (B), respectively, and W(A)+ W(B)=1.

[0176] Tensile properties: determined according to ISO 527-1,-2:2019 on injection molded specimens test specimens (80 x 10 x 4 mm) obtained according to the method ISO 19069-2:2016.

[0177] Impact resistance: Charpy impact strength - Notched (ISO 179-1 :2010 at 23°C, Type 1, Edgewise, Notch A) on injection molded specimens test specimens (80 x 10 x 4 mm) obtained according to the method ISO 19069-2:2016.

[0178] Shrinkage: measured on injection molded specimens test specimens (200x100x2.5mm) obtained according to the method ISO 19069-2:2016 (Meld temperature: 250°C; mold temperature: 40°C; injection time: 4sec; hold time: 6 sec; cooling time 20 sec; Cavity pressure: 145bar). The specimens are conditioned for 48h at a temperature of 23±2°C before testing. The dimensions of the specimens are measured with a micrometer and compared to the dimensions of the reference metallic plaque having the same dimensions of the mould. The shrinkage is calculated as mean value over 10 measures using the formula:Ci = (100 X(DR-DS)) / DR whereinCi is the shrinkage in one selected direction (longitudinal or transverse, i.e. parallel or perpendicular to the flow);DR is the dimension of the reference metallic plaque in the selected direction; and DS is the dimension of the sample in the selected direction.

[0179] 0-phase in polypropylene: determined by X-Ray Diffraction (XRPD), with a diffractometer that uses the Cu-Kai radiation with fixed slits and able to collect spectra between diffraction angle 20 = 5° and 20 = 35° with step of 0.1° every 6 seconds). Sample preparation (diskettes of ca. 1.5 mm of thickness and 25 mm of diameter) by compression molding. The diskettes are prepared by using frames inserted into the plates of the molding press. Set the platen press temperature at 200°C ± 5°C. Select a quantity of materials sufficient to fill the frame. Place an aluminum foil under the frame and put the material into the holes of the frame. Place a second aluminum foil on the top of the frame to embed the frame containing the polymer. Place the embedded frame into the press platens, without any appreciable applied pressure, and keep for 10 minutes. Apply a pressure to the platens of ca. 10 Kg / cm2for few second to eliminate air bubbles. Repeat this operation for 3 times. Release the press and put the embedded frame under running water. Once it reaches room temperature, extract a diskette and place it into XRPD sample holder. Set the XRPD instrument in order to collect the XRPD spectrum of the sample from diffraction angle 20 = 5° to 20 = 35° with step of 0.1° by using counting time of 6 seconds and collect the XRPD spectrum of the sample. The diffraction peaks used for the calculation of 0 phase index arethose present at diffraction angles 20 =14.1°, 20 =16.9°, 20 =18.5°and 20 =16.1°, indexed as reflections (110)al, (040)a2 and (130)a3 of polypropylene a phase and reflection (300)01 of polypropylene 0 phase, respectively. The heights of the diffraction peaks indexed as (110), (040) and (130) of polypropylene a phase and of the diffraction peak indexed as (300) of polypropylene 0 phase are calculated from the spectrum. The 0 phase index, i.e. the relative amount of polypropylene in 0 phase in the crystalline portion of the sample, is calculated using the following formula: 100

[0180] where hal ha2 ha3 h01 are the heights of the diffraction peaks assigned to polypropylene in a and 0 phase, respectively.

[0181] Uniaxial tensile creep test: specimens were cut by low-speed machining from injection molded plaques (250x150x2.5mm, film gated on the short side) perpendicular to the direction of the injection flow. Main molding conditions were: melt temperature 240°C, mold temperature 50°C, injection time 3 sec, packing time 20 sec, packing pressure packing pressure corresponding to 70-80% of maximum pressure during filling. Specimens had the same profile and thickness of the ISO R527 type IB tensile bars. Specimens were fixed vertically at one end in a support inside a conditioning oven able to keep the temperature at the specified value (80°C), and a weight was hanged at the other end, generating the required stress in the specimen. Elongation of the specimen during the test was measured by means of a clip-on extensometer having an initial span of 50mm. Time to reach a given strain value (10%) was recorded as a function of the applied stress and plotted. Data were fitted by a logarithmic trendline.

[0182] Examples El and E2

[0183] The propylene copolymers of examples El and E2 were prepared in three fluidized bed gas-phase reactors connected in series, wherein the growing polymer is discharged from the upstream to the downstream reactor via gas lock devices that allow keeping the wanted gas composition in each reactor.

[0184] A Ziegler-Natta catalyst systems was used comprising a titanium solid catalyst component prepared according to example 4 of WO2012 / 139897A1.

[0185] The solid catalyst component was contacted with TEAL and dicyclopentyl dimethoxy silane in a pre-contacting vessel. In a pre-polymerization loop reactor the thus obtained catalystsystem was contacted with a liquid stream of propylene and propane to obtain a pre-polymerized active catalyst. The slurry containing the pre-polymerized active catalyst was continuously and constantly fed to the first fluidized bed gas-phase reactor, to which hydrogen (used as molecular weight regulator), propylene and hexene were also fed, all in gaseous phase.

[0186] The propylene copolymer fraction containing the still active catalyst coming from the first reactor is transferred in a continuous flow into the second fluidized bed gas phase reactor, after having been purged of unreacted monomers. Quantitatively constant flows of propylene, hexene and hydrogen, all in the gas state, were fed to the second reactor to obtain further propylene copolymer fraction.

[0187] The polymerization mixture obtained in the second fluidized bed gas-phase reactor, comprising the propylene copolymer fraction produced in the first fluidized bed gas-phase reactor and the propylene copolymer fraction produced in the second fluidized bed gas-phase reactor, together with the still active catalyst system, is transferred in a continuous flow to the third gas phase reactor, after having been purged of unreacted monomers. Quantitatively constant gaseous flows of propylene and hydrogen were also fed to the third reactor to obtain a third polymer fraction. Pre-polymerization and polymerization conditions are illustrated in Table 1, together with data measured on the polymer exiting each gas-phase polymerization reactor.

[0188] The propylene copolymer was discharged from the third gas phase reactor and sent to the finishing section, where it was extruded into pellets and additivated with (based on the final composition) 0.1 wt% of calcium stearate, 0.15 wt% Hostanox SE-10 by Clariant, 0.25 wt% of Irgafos 168 by BASF, 0.05 wt% of Irganox 1790 by BASF and 0.15 wt% of distearyl thiodipropionate.

[0189] The hexene content and the MFR of fraction (A2) produced in the GPR2 were calculated using the following formulas:

[0190] wherein

[0191] C6(GPR1) and C6(GPR2) are the amounts of hexene measured on the copolymer exiting GPR1 and GPR2 respectively;

[0192] MFR(GPR1) and MFR(GPR2) are the melt flow rates measured on the copolymer exiting respectively GPR1 and GPR2;

[0193] TV(GPPl) = split(GPRl) / (split(GPRl') + sp / it(GP7?2)); and

[0194] W(GPR2) = split GPR2) / (split(GPRl) + split GPR2y)),

[0195] wherein the splits correspond to the amount of polymer produced in the respective reactor, referred to the total amount of polymer produced in three reactors. Calculated values are reported in Table 2, together with test results obtained on the pelletized polymers.

[0196] It was determined that the polymer of example El contained 8% of 0-phase.

[0197] Example E3

[0198] To prepare the propylene copolymer of example E3, a Ziegler-Natta catalyst systems was used comprising a titanium solid catalyst component prepared according to example 5 of EP728769A1.

[0199] The solid catalyst component was contacted with TEAL and dicyclopentyl dimethoxy silane in a pre-contacting vessel, and the catalyst system was fed to a pre-polymerization loop reactor. Pre-polymerization and polymerization were conducted as described in examples E1-E2, with the difference that in the third fluidized bed gas-phase reactor a gaseous stream of ethylene was fed and a propylene-ethylene copolymer fraction was obtained. Pre-polymerization and polymerization conditions are illustrated in Table 1, together with data measured on the polymer exiting each gas-phase polymerization reactor.

[0200] The propylene copolymer was discharged from the third gas phase reactor and sent to the finishing section, where it was extruded into pellets and additivated with the same additive package used in examples El and E2.

[0201] The hexene content and the MFR of fraction (A2) were calculated as for Example 1. The ethylene content of fraction (B) obtained in GPR3 was calculated with the formulaC2(tot) C2(B) = 100 * ' split(GPR3)

[0202] wherein C2(tot) is the total amount of ethylene determined on the polymer exiting the third gas-phase reactor and the split is the amount of polymer produced in the third gas-phase reactor, referred to the total amount of polymer produced in three reactors.

[0203] Calculated values are reported in Table 2, together with test results obtained on the pelletized polymers.Table 1Table 2

[0204] The propylene copolymer of examples El tested for creep resistance according to the method described above. Data generated on the copolymer of example El are compared to those obtained on Hostalen PP HP1886 and Hostalen PP Hl 850, both marketed by LyondellBasell foruse in automotive expansion tanks. Fig. 1 is a plot (logarithmic trendline) of the “time to reach 10% strain” vs. applied stress measured at a temperature of 80°C.

[0205] The propylene copolymer of example El has a better performance in terms of “time to failure”, i.e. given an applied stress it takes more time to reach 10% strain compared to commercial products having similar properties.

[0206] Also the copolymer obtained in example E3 was tested for creep resistance according to the same method and in the same conditions (80°C). Fig. 2 plots the result and the logarithmic regression line of the “time to reach 10% strain” vs. applied stress for the copolymer of example E3 and for Hostalen PP Hl 850.

[0207] The propylene copolymer of example E3 has an improved resistance to strain, i.e. it takes longer to the copolymer of example E3 to reach a strain of 10% at low stress values, like below 10 MPa.

Claims

CLAIMSWhat is claimed is:

1. A propylene copolymer (I) containing up to and including 3.0% by weight of polymerized units derived from hexene and optionally up to and including 1.0% by weight of polymerized units derived from ethylene, based on the weight of the propylene copolymer (I), wherein the propylene copolymer (I) has:(i) a melting temperature (Tm) in the range from 148° to 156°C and a crystallization temperature (Tc) equal to or greater than 102 °C (ISO 11357-3:2018);(ii) a melt flow rate (MFR) (ISO 1133-1:2011, 230°C / 5 Kg) equal to or lower than 2.0 g / lOmin;(iii) a molecular weight distribution (MWD) equal to or greater than 12, wherein the MWD is determined by GPC with method described in the experimental part, wherein the propylene copolymer (I) is obtainable by a process comprising:(a) polymerize propylene and hexene in a first gas-phase polymerization reactor to obtain a copolymer fraction (A) comprising a propylene-hexene copolymer; and(b) transfer the copolymer fraction (A) to a further gas-phase polymerization reactor and polymerize propylene, and optionally ethylene, in the presence of the copolymer fraction (A) to obtain a propylene copolymer (I) comprising the copolymer fraction (A) and a polymer fraction (B) obtained in step (b), said polymer fraction (B) comprising a propylene homopolymer or a propylene-ethylene copolymer, wherein the process is carried out in the presence of a Ziegler-Natta catalyst system.

2. The propylene copolymer (I) according to claim 1 containing from 0.1 to 2.5 % by weight, preferably from 0.5 to 2.0 % by weight, of polymerized units derived from hexene and optionally from 0.1 to 0.8 % by weight of polymerized units derived from ethylene.

3. The propylene copolymer (I) according to claim 1 or 2 having at least one, preferably all, the following properties:(i) a melting temperature (Tm) in the range from 150°C to 154°C and / or a crystallization temperature equal to or greater than 103 °C, preferably in the range from 103 °C to 109°C (ISO 11357-3:2018); and / or(ii) a MFR (ISO 1133-1 :2011, 230°C / 5 Kg) equal to or lower than 1.7 g / lOmin, preferably ranging from 0.8 to 1.5 g / lOmin, more preferably from 1.1 to 1.3 g / lOmin; and / or(iii) a MWD ranging from 13 to 22, wherein the MWD is determined by GPC with the method described in the experimental part.

4. The propylene copolymer (I) according to any one of claims from 1 to 3 having at least one, preferably all, the following properties:(iv) xylene soluble fraction at 25 °C (XS) equal to or lower than 4.0% by weight, preferably ranging from 1.0 to 3.5% by weight, more preferably from 1.8 to 3.0% by weight, based on the weight of the propylene copolymer (I), wherein the xylene soluble fraction is determined with the method described in the experimental part; and / or(v) tensile modulus (ISO 527-1,-2, 48h) equal to or greater than 1100 MPa, preferably in the range from 1150 to 1600 MPa, more preferably from 1200 to 1400 MPa; and / or(vi) elongation at break (ISO 527-1,-2, 48h) equal to or greater than 490%, preferably in the range from 500 to 650%; and / or(vii) Charpy impact strength at 23°C (ISO 179-1:2010, Type 1, Edgewise, Notch A) in the range of from 10 to 20 KJ / m2, preferably from 13 to 18 KJ / m2.

5. The propylene copolymer (I) according to any one of claims from 1 to 4 being a propylenehexene copolymer.

6. The propylene copolymer (I) according to any one of claims from 1 to 4 comprising:- a copolymer fraction (A) comprising a propylene-hexene copolymer containing up to and including 4.0% by weight, preferably from 0.1 to 3.0 % by weight, more preferably from 0.5 to 2.0 % by weight, of polymerized units derived from hexene, based on the weight of the copolymer fraction (A), the copolymer fraction (A) having MFR(A) equal to or lower than 2.5 g / lOmin, preferably in the range of from 0.8 to 2.0 g / lOmin. (ISO 1133-1:2011, 230°C / 5 Kg); and- a polymer fraction (B) comprising a propylene homopolymer or a propylene-ethylene copolymer containing up to and including 3.0% by weight, preferably from 0.1 to 2.0 % byweight, of polymerized units derived from ethylene, based on the weight of the copolymer fraction (B).

7. The propylene copolymer (I) according to claim 6, wherein the copolymer fraction (A) comprises:- a copolymer fraction (Al) comprising a propylene-hexene copolymer containing up to and including 4.0% by weight, preferably from 0.1 to 3.5 % by weight, more preferably from 0.5 to 2.0 % by weight, of polymerized units derived from hexene, based on the weight of the copolymer fraction (Al) and having MFR(Al) equal to or lower than 2.5 g / lOmin, preferably ranging from 0.8 to 2.0 g / lOmin. (ISO 1133-1 :2011, 230°C / 5 Kg); and- a copolymer fraction (A2) comprising a propylene-hexene copolymer containing up to and including 3.0% by weight, ppreferably from 0.1 to 2.5 % by weight, more preferably from 0.5 to 2.0 % by weight, of polymerized units derived from hexene, based on the weight of the copolymer fraction (A2), and having MFR(A2) equal to or lower than 2.5 g / lOmin, preferably ranging from 0.8 to 2.0 g / lOmin. (ISO 1133-1 :2011, 230°C / 5 Kg), wherein the propylene-hexene copolymer comprised in fraction (Al) is different from the propylene-hexene copolymer comprised in fraction (A2).

8. The propylene copolymer (I) according to claim 7, wherein the weight ratio of the copolymer fraction (Al) to the copolymer fraction (A2) ranges from 3:1 to 1 :2, preferably from 2: 1 to 1: 1.

9. The propylene copolymer (I) according to any one of claims from 6 to 8, wherein the polymer fraction (B) comprises a propylene homopolymer.

10. The propylene copolymer (I) according to any one of claims from 6 to 9 comprising from 70 to 95 % by weight of copolymer fraction (A), and from 5 to 30 % by weight of copolymer fraction (B), based on the total weight of the propylene copolymer (I).

11. Process to prepare the propylene copolymer (I) according to any one of claims from 1 to 10, comprising the steps:(a) polymerize propylene and hexene in a first gas-phase polymerization reactor to obtain a copolymer fraction (A) comprising a propylene-hexene copolymer;(b) transfer the copolymer fraction (A) obtained step (a) to a further gas-phase polymerization reactor and polymerize propylene, and optionally ethylene, in the presence of the copolymer fraction (A) to obtain a propylene copolymer (I) comprising the copolymer fraction (A) and a polymer fraction (B) obtained in step (b), said copolymer fraction (B) comprising a propylene homopolymer or a propylene-ethylene copolymer, wherein the process is carried out in the presence of a Ziegler-Natta catalyst system.

12. The process according to claim 11, wherein:- the copolymer fraction (A) obtained in step (a) comprises a propylene-hexene copolymer containing up to and including 4.0% by weight, preferably from 0.1 to 3.0 % by weight, more preferably from 0.5 to 2.0 % by weight, of polymerized units derived from hexene, based on the weight of the copolymer fraction (A), and has melt flow rate equal to or lower than 2.5 g / lOmin, preferably ranging from 0.8 to 2.0 g / lOmin. (ISO 1133-1:2011, 230°C / 5 Kg), and- the polymer fraction (B) obtained in step (b) comprises a propylene homopolymer or of a propylene-ethylene copolymer containing up to and including 3.0% by weight, preferably from 0.1 to 2.0 % by weight, of polymerized units derived from ethylene, based on the weight of the copolymer fraction (B).

13. The process according to claim 11 or 12, wherein step (a) comprises the steps:(al) polymerize propylene and hexene in a first gas-phase polymerization reactor to obtain a copolymer fraction (Al) comprising a propylene-hexene copolymer; and(a2) transfer the copolymer fraction (Al) to a further gas-phase polymerization reactor and polymerize propylene and hexene in the presence of the copolymer fraction (Al) to obtain a copolymer fraction (A) comprising the copolymer fraction (Al) and a copolymer fraction (A2), said copolymer fraction (A2) comprising a propylene-hexene copolymer obtained in step (a2), wherein the propylene-hexene copolymer comprised in fraction (Al) is different from the propylene-hexene copolymer comprised in fraction (A2).

14. The process according to any one of claims from 11 to 13, wherein in step (b) propylene is homopolymerized.

15. The process according to any one of claims from 11 to 14, wherein each polymerization reactor in which propylene and hexene- 1 are copolymerized is operated at an operating temperature selected from values equal to or lower than 80°C, preferably equal to or lower than 79°C, more preferably ranging from 65° to 78°C.

16. The process according to any one of claims from 11 to 15 wherein from 70 to 95% by weight of the propylene copolymer (I), corresponding to polymer fraction (A), is produced in polymerization steps (a) and from 5 to 30% by weight of the propylene copolymer (I), corresponding to polymer fraction (B), is produced in step (b).

17. A polypropylene composition comprising:- at least 95% by weight, preferably from 96 to 99.9% by weight, of the propylene copolymer (I) according to any one of claims from 1 to 10, and- up to 5% by weight, preferably from 0.1 to 4% by weight, of an additive.

18. The polypropylene composition according to claim 17, wherein the additive is selected from the group consisting of anti-oxidants, light stabilizers, slipping agents, acid scavengers, melt stabilizers, pigments, colorants, and combinations thereof.

19. An article comprising the propylene copolymer (I) according to any one of claims from 1 to 10 or the polypropylene composition according to claim 17 or 18.

20. Article according to claim 16 selected from pipes, containers and sheets.

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