Patent Description:
The bimodal polypropylene random copolymer of the present invention and the according articles are characterised by an improved resistance against γ-irradiation and hence especially suitable for application in the medical, pharmaceutical or diagnostic field.

Polypropylene can be produced based on two major groups of polymerization technologies, namely based on Ziegler-Natta catalysis or metallocene based catalysis.

Each of these technologies produces polymers, especially polypropylene grades with specific characteristics:
Polypropylene grades produced with metallocene based catalysts are known for a rather narrow molecular weight distribution and high randomness of comonomer insertion. Ziegler-Natta based polypropylene are known for a broader molecular weight distribution, and a better processability in subsequent conversion steps.

Said highly random comonomer insertion of metallocene based polypropylene however can cause disadvantages for mechanical properties of the final polymer: based on this highly random comonomer distribution, the metallocene based polypropylene grades tend to become much softer than Ziegler-Natta grades at a similar comonomer content, nevertheless providing lower impact behaviour. On the other hand side it is known and accepted that a high randomness of the comonomer incorporation may be helpful to provide polymers with a good γ-irradiation resistance.

Ziegler-Natta catalysts however are more prone to insert the comonomers less randomly, resulting in polymers with longer sequences of the same monomer in a row, but provide polymers with more balanced mechanical properties.

Polypropylene (PP) is one of the most used plastics for packaging applications. In a continuously increasing part of this market, the material is sterilized by either heat (steam), radiation (β / electrons or y) or chemicals (mostly ethylene oxide), which affects the mechanical and optical properties.

Among all these, the sterilization via γ-radiation is the most relevant method for sterilizing pharmaceutical, medical or diagnostic items.

It is well known, that radiation, mostly the effect of γ-rays, induce chain scission and degradation effects, resulting in a reduced melt viscosity and severe embrittlement. What makes this radical reaction so critical is the fact that it continues for long times after the actual sterilization process, making long-term studies necessary for studying the effects.

Various strategies have been published for a reduction of these effects:
Some focus on the use of "mobilizing agents" (paraffinic oils) and special stabilizer formulations. Others combine the polypropylene with specific polyethylene qualities or other polymers:
<CIT> discloses a high energy radiation resistant polypropylene composition. It consists essentially of substantially crystalline normally solid polypropylene having a narrow molecular weight distribution, and, dispersed therein at a concentration effective to increase substantially the high energy radiation resistance of the polypropylene, a synergistic mixture of: (<NUM>) a hindered amine component, (<NUM>) a hindered phenolic component, and (<NUM>) a phosphorous containing component, the weight ratios of component (<NUM>) to component (<NUM>) to component (<NUM>) being about <NUM>:(<NUM>-<NUM>):(<NUM>-<NUM>). Also disclosed are radiation sterilized articles in which at least part of the material of construction comprises the polypropylene composition.

<CIT> discloses the use of an amorphous polypropylene consisting of a homopolymer of propylene or a copolymer of propylene with one or more alpha -olefins with a propylene content of at least <NUM> mol. -%, having a melt enthalpy of at most <NUM> J/g and a melt flow index MI2 of <NUM>-<NUM>/<NUM>, as additive to improve the stability to ionizing radiation. The addition of amorphous material leads to high migration levels due to oligomers present in the amorphous material.

<CIT> describes gamma irradiation resistant propylene/ethylene copolymer compositions comprising: a propylene/ethylene copolymer comprising from about i) <NUM> to about <NUM> wt. % ethylene; ii) from about <NUM> ppm to about <NUM> ppm of one or more light stabilizers; iii) from about <NUM> ppm to about <NUM> ppm of one or more acid scavengers; iv) from about <NUM> ppm to about <NUM> ppm of aluminum, hydroxybis[<NUM>,<NUM>,<NUM>,<NUM> tetrakis (<NUM>,<NUM>-dimethyl(ethyl)-<NUM>-hydroxy-<NUM> dibenzo[d,g][<NUM>,<NUM>,<NUM>] dioxaphoshocin <NUM>-oxidato]; and v) a sufficient amount of one of more viscosity modifiers to break down the resulting polymer viscosity to a melt index from about <NUM> to about <NUM>/<NUM> minutes measured at about <NUM>° C.

Sterilization effects on polypropylene (Markus Gahleitner, et. 9th European PLACE Conference (<NUM>) Rome), describes changes in mechanical properties of various polypropylene homopolymers and random copolymers after irradiation at <NUM> kGy. These results give an indication of the mechanical properties for short periods after sterilization. However, these results do not give any indication on the long term behaviour of irradiated polymer samples.

Maximum Rate of Crystallization and Morphology of Random Propylene Ethylene Copolymers as a Function of Comonomer Content up to <NUM> mol% (<NPL>) describes propylene ethylene copolymers synthesized with metallocene catalysts in a range of ethylene up to <NUM> mol%. A <NUM>NMR triad distribution analysis lends support for a random distribution of the comonomer in the complete series. The polymers disclosed have a molecular weight distribution between <NUM> and <NUM>. Propylene number average sequence lengths are given for polymers having a comonomer content of <NUM> mol% or higher.

The article is not concerned with bimodal random copolymers, and does not disclose any information on comonomer distribution or randomness, in the sense of Koenig-B.

<CIT> discloses unimodal propylene random copolymers with <NUM> - <NUM> wt. -% of ethylene as comonomer, having improved resistance against γ-irradiation.

It discloses polymers with a specific comonomer distribution determined via a-TREF, produced with a Ziegler Natta catalyst.

There is a constant need within the Health Care industry to have polymers at hand, which can be used for medical articles, withstand higher dosages of irradiation, provide good mechanical properties in the sense of good flexural and impact behaviour. Furthermore, they are supposed to retain the mechanical properties, especially impact behaviour at a higher level and for a longer time after irradiation had taken place.

So the present inventors have sought new propylene-random copolymers, developed in particular for the health care and medical market, which have good mechanical properties in the sense of good flexural and impact behaviour as well as improved resistance against γ-irradiation. This improvement should not be at the expense of any other properties of the polymer or any article formed. Thus, other mechanical properties, e.g. stiffness or low levels of fractions soluble in cold xylene (XCS), should be maintained.

It has been an objective for the present invention to provide a bimodal polypropylene random copolymer showing good mechanical properties in the sense of good flexural and impact behaviour as well as improved long term retention of mechanical properties after irradiation, especially improved long term retention of impact strength after irradiation.

The present inventors have sought for possibilities to modify the polymer structure of propylene-ethylene random copolymers in such a way, that the polymers provide good mechanical properties in the sense of good flexural and impact behaviour and improved long term retention of impact strength after irradiation.

Surprisingly the present inventors have identified a bimodal polypropylene random copolymer of propylene and <NUM> - <NUM> wt. -% of ethylene as comonomer as set forth in claim <NUM> comprising.

In a preferred embodiment, the bimodal polypropylene random copolymer relates to a bimodal polypropylene random copolymer of propylene and <NUM> - <NUM> wt. -% of ethylene as comonomer comprising.

In an alternatively preferred embodiment the invention relates to a bimodal polypropylene random copolymer of propylene and <NUM> - <NUM> wt. -% of ethylene as comonomer, comprising <NUM> - <NUM> wt. -% of a first polypropylene fraction being a propylene homopolymer,
<NUM> - <NUM> wt. -% of a second polypropylene fraction being a random copolymer of propylene and ethylene as comonomer, comprising <NUM> - <NUM> wt. -% of comonomer and <NUM> - <NUM> wt. -% of a soluble nucleating agent and optionally comprising <NUM> - <NUM> wt. -% of a fraction soluble in cold xylene (XCS).

In still a further alternative embodiment the invention relates to moulded articles comprising the bimodal polypropylene random copolymer and using them in applications intended for gamma-irradiation.

In still a further alternative embodiment the invention relates to the use of the bimodal polypropylene random copolymer for producing articles such as medical, pharmaceutical or diagnostic article or any such articles produced for gamma-irradiation applications.

In still a further alternative embodiment the invention relates to the use of soluble nucleating agents to improve the irradiation resistance or polypropylene copolymers.

The present invention discloses a bimodal polypropylene random copolymer.

The term "random copolymer" has to be preferably understood according to IUPAC (<NPL>).

Accordingly, it is preferred that the propylene copolymer does not contain elastomeric (co)polymers forming inclusions as a second phase for improving mechanical properties. A polymer containing elastomeric (co)polymers as insertions of a second phase would by contrast be called heterophasic and is preferably not part of the present invention. The presence of second phases or the so called inclusions are for instance visible by high resolution microscopy, like electron microscopy or atomic force microscopy, or by dynamic mechanical thermal analysis (DMTA). Specifically, in DMTA the presence of a multiphase structure can be identified by the presence of at least two distinct glass transition temperatures.

Accordingly, it is preferred that the propylene copolymer (R-PP) according to this invention has no glass transition temperature below -<NUM>, preferably below -<NUM>, more preferably below -<NUM>.

The bimodal polypropylene random copolymer of the present invention may have a melt flow rate MFR<NUM> (<NUM>) measured according to ISO <NUM> of in the range of <NUM> - <NUM>/<NUM>, preferably in the range of <NUM> to <NUM>/<NUM>, like the range of <NUM> to <NUM>/<NUM>.

The bimodal polypropylene random copolymer of the present invention comprises <NUM> - <NUM> wt. -% ethylene as comonomer. Preferably the comonomer content may be in the range of <NUM> - <NUM> wt. -%, such as <NUM> - <NUM> wt.

The bimodal polypropylene random copolymer of the present invention comprises low amounts of fractions soluble in cold xylene (XCS). The amount of XCS may be in the range of <NUM> - <NUM> wt. -%, preferably in the range of <NUM> - <NUM> wt. -%, like <NUM> - <NUM> wt.

The bimodal polypropylene random copolymer may have an average molecular weight (Mw) of <NUM> - <NUM>/mol, preferably in the range of <NUM> - <NUM>/mol, more preferably in the range of <NUM> - <NUM>/mol.

The bimodal polypropylene random copolymer may further have a molecular weight distribution (Mw/Mn) of in the range of <NUM> to <NUM>, like in the range of <NUM> to <NUM>.

The bimodal polypropylene random copolymer of the present invention may have at least two distinct melting temperatures, namely a first melting temperature (Tm1) and a second melting temperature (Tm2).

The first melting temperature (Tm1) may be at least <NUM> or higher, preferably in the range of <NUM> - <NUM>, more preferably in the range of <NUM> - <NUM>.

The second melting temperature by be at most <NUM> or below, preferably in the range of <NUM> - <NUM>, more preferably in the range of <NUM> - <NUM>.

It is understood that first melting temperature Tm1 indicates the higher melting temperature, whereas the second melting temperature Tm2 indicates the lower melting temperature.

The bimodal polypropylene random copolymer of the present invention may further be characterised by specific melt enthalpies (Hm) of the two melting peaks.

It is understood that the melt enthalpy of the first melting peak (Hm1) is associated with the higher melting temperature (Tm1), whereas the melt enthalpy of the second melting peak (Hm2) is associated with the lower melting temperature (Tm2).

In particular, the bimodal polypropylene random copolymer may be characterised by specific values for the melt enthalpies and especially by a specific ratio of the melt enthalpies of the two melting peaks.

Preferably, the bimodal polypropylene random copolymer of the present invention has a melt enthalpy Hm1 of at most <NUM> J/g, preferably in the range of <NUM> - <NUM> J/g, more preferably in the range of <NUM> - <NUM> J/g.

It is equally preferred, that the melt enthalpy Hm2 of the bimodal polypropylene random copolymer may be at least <NUM> J/g, preferably in the range of <NUM> - <NUM>, like <NUM> - <NUM> J/g.

The ratio of the second to the first melt enthalpy (Hm2/Hm1) may be at least <NUM>, preferably in the range of <NUM> to <NUM>, more preferably in the range of <NUM> to <NUM>, like even more preferably in the range of <NUM> to <NUM> or in the range of <NUM> to <NUM>.

Preferably, the nucleated bimodal polypropylene random copolymer of the present invention has a Hm2 of at least <NUM> J/g and a ratio of Hm2/Hm1 of at least <NUM> or more.

Preferably, the propylene copolymer according to this invention has been produced in the presence of a metallocene catalyst. The catalyst influences in particular the microstructure of the polymer. In particular, polypropylenes prepared by using a metallocene catalyst provide a different microstructure compared to polypropylenes prepared by using Ziegler-Natta (ZN) catalysts. The most significant difference is the presence of regio-defects in metallocene-made polypropylenes. These regio-defects can be of three different types, namely <NUM>,<NUM>-erythro (<NUM>,<NUM> e), <NUM>,<NUM>-threo (<NUM>,<NUM> t) and <NUM>,<NUM> defects.

A detailed description of the structure and mechanism of formation of regio-defects in polypropylene can be found in Chemical Reviews <NUM>,<NUM>(<NUM>), pages <NUM>-<NUM>.

The bimodal polypropylene random copolymer of the present invention is further characterised by its way of comonomer insertion, especially by the normated amount of < >-triads as determined via NMR.

The bimodal polypropylene random copolymer of the present invention may have a normated amount of <PEP>-triads of at most <NUM> % or lower, such as <NUM> - <NUM> %, preferably <NUM> - <NUM> %.

The bimodal polypropylene random copolymer of the present invention may be characterised by a specific randomness of the comonomer insertion, defined by a Koenig B value of at least <NUM> or higher, preferably in the range of <NUM> - <NUM>, like <NUM> - <NUM>, or <NUM> - <NUM>. The person skilled is well aware, that the Koenig B describes the randomness of the comonomer insertion of the polymer as a whole and does not take into consideration any specific comonomer distribution depending on molecular weight or the like, which are usually determined via a-TREF.

The bimodal polypropylene random copolymer of the present invention comprises at least two polypropylene fractions, preferably a first and a second polypropylene fraction, which may differ in view of the viscosity, their comonomer content or both.

It is preferred, that the bimodal polypropylene random copolymer of the present invention is bimodal in view of its comonomer content.

Accordingly, it is preferred, that the first polypropylene fraction differs from the second polypropylene fraction in view of its comonomer content. Preferably, the comonomer content of the second polypropylene fraction is higher than the comonomer content of the first polypropylene fraction.

It is further preferred, that the bimodal polypropylene random copolymer comprises, more preferably consists of, two polypropylene fractions and additionally a soluble nucleating agent or any further commonly used additive, such as antioxidants, acid scavengers, UV-stabilisers or lubricants up to <NUM> wt. Preferably the additive content (without soluble nucleating agents) is below <NUM> wt. -%, like below <NUM> wt.

The bimodal polypropylene random copolymer comprises.

In a particular preferred first embodiment, the bimodal polypropylene random copolymer comprises.

and has a total comonomer content of <NUM> - <NUM> wt. -%, preferably <NUM> - <NUM> wt. -% and optionally <NUM> - <NUM> wt. -%, like <NUM> - <NUM> wt. of a fraction soluble in cold xylene (XCS).

In one alternatively preferred second embodiment the bimodal polypropylene random copolymer comprises.

wherein the bimodal polypropylene random copolymer is characterised by a total comonomer content of <NUM> - <NUM> wt. -%, preferably <NUM> - <NUM> wt. -% and optionally by <NUM> - <NUM> wt. -%, such as <NUM> - <NUM> wt. -% of a fraction soluble in cold xylene (XCS).

The bimodal polypropylene random copolymer comprises:.

The melt flow rate (MFR <NUM>/<NUM>) according to ISO <NUM> of the first polypropylene fraction may be in the range of <NUM> - <NUM>/<NUM>, preferably in the range of <NUM> to <NUM>/<NUM>, like the range of <NUM> - <NUM>/<NUM>.

The first polypropylene fraction may be a random copolymer of propylene and ethylene or a propylene homopolymer.

The comonomer content of the first polypropylene fraction differs from the second polypropylene fraction. The first polypropylene fraction may comprise less comonomer than the second polypropylene fraction or none at all.

The comonomer content of the first polypropylene fraction may be in the range of <NUM> - <NUM> wt. -%, preferably in the range of <NUM> - <NUM> wt. -%, such as <NUM> - <NUM> wt.

In an equally preferred embodiment the comonomer content of the first polypropylene fraction is <NUM> wt.

The first polypropylene fraction of the bimodal polypropylene random copolymer may have an average molecular weight (Mw) of <NUM> - <NUM>/mol, preferably in the range of <NUM> - <NUM>/mol, more preferably in the range of <NUM> - <NUM>/mol.

The first polypropylene fraction of the bimodal polypropylene random copolymer may further have a molecular weight distribution (Mw/Mn) of in the range of <NUM> to <NUM>, like in the range of <NUM> to <NUM>.

Preferably the weight ratio between first polypropylene fraction and the second polypropylene fraction is <NUM>/<NUM> to <NUM>/<NUM>, more preferably <NUM>/<NUM> to <NUM>/<NUM>, like <NUM>/<NUM> to <NUM>/<NUM> or <NUM>/<NUM> to <NUM>/<NUM>.

The second polypropylene fraction may have a melt flow rate (MFR <NUM>/<NUM>) in a similar range as the first polypropylene fraction. Hence it may be in the range of <NUM> - <NUM>/<NUM>, preferably in the range of <NUM> to <NUM>/<NUM>, like the range of <NUM> - <NUM>/<NUM>.

The melt flow rate (MFR <NUM>/<NUM>) of the second polypropylene fraction may also differ from the melt flow rate (MFR <NUM>/<NUM>) of the first polypropylene fraction.

The second polypropylene fraction of the bimodal polypropylene random copolymer may have an average molecular weight (Mw) of <NUM> - <NUM>/mol, preferably in the range of <NUM> - <NUM>/mol, more preferably in the range of <NUM> - <NUM>/mol.

The second polypropylene fraction of the bimodal polypropylene random copolymer may further have a molecular weight distribution (Mw/Mn) of in the range of <NUM> to <NUM>, like in the range of <NUM> to <NUM>.

The second polypropylene fraction is characterised by a higher comonomer content that the first polypropylene fraction. Preferably, the comonomer content of the second polypropylene fraction may be in the range of <NUM> - <NUM> wt. -%, like preferably <NUM> - <NUM> wt.

Furthermore it is preferred, that the comonomer content of the second polypropylene fraction, Co(<NUM>), and the comonomer content of the final bimodal polypropylene random copolymer, Co(tot), fulfil together the inequation (I a), preferably (I b), more preferably (I c). Co(<NUM>) is the comonomer content [wt. -%] of the second polypropylene fraction, Co(tot) is the comonomer content [wt. -%] of the second polypropylene fraction. <MAT> <MAT> <MAT>.

The bimodal polypropylene random copolymer comprises <NUM> - <NUM> wt. -% of a soluble nucleating agent. Preferably, the soluble nucleating is present in ranges of <NUM> - <NUM> wt. -%, such as <NUM> - <NUM> wt. -% or <NUM> - <NUM> wt.

Soluble nucleating or clarifying agents comprise substances listed below:
e.g. di(alkylbenzylidene)sorbitols as <NUM>,<NUM>:<NUM>,<NUM>- dibenzylidene sorbitol, <NUM>,<NUM>:<NUM>,<NUM>-di(<NUM>-methylbenzylidene) sorbitol, <NUM>,<NUM>:<NUM>,<NUM>-di(<NUM>- ethylbenzylidene) sorbitol and <NUM>,<NUM>:<NUM>,<NUM>-Bis(<NUM>,<NUM>-dimethylbenzylidene) sorbitol, as well as nonitol derivatives, e.g. <NUM>,<NUM>,<NUM>-trideoxy-<NUM>,<NUM>;<NUM>,<NUM>-bis-O-[(<NUM>-propylphenyl)methylene] nonitol, and benzene-trisamides like substituted <NUM>,<NUM>,<NUM>-benzenetrisamides as N,N',N"-tris-tert-butyl-<NUM>,<NUM>,<NUM>- benzenetricarboxamide, N,N',N"-tris-cyclohexyl-<NUM>,<NUM>,<NUM>-benzene-tricarboxamide and N-[<NUM>,<NUM>-bis-(<NUM>,<NUM>-dimethyl-propionylamino)-phenyl]-<NUM>,<NUM>-dimethyl-propionamide.

<NUM>,<NUM>:<NUM>,<NUM>-di(<NUM>-methylbenzylidene) sorbitol, <NUM>,<NUM>:<NUM>,<NUM>-Bis(<NUM>,<NUM>-dimethylbenzylidene) sorbitol and N-[<NUM>,<NUM>-bis-(<NUM>,<NUM>-dimethyl-propionylamino)-phenyl]-<NUM>,<NUM>-dimethyl-propionamide are equally preferred.

Sorbitol based nucleating agents and nonitol based nucleating agents are particularly preferred.

The bimodal polypropylene random copolymer of the present invention may have a Flexural Modulus determined according to ISO <NUM> of at least <NUM> MPa, such as in the range of <NUM> - <NUM> MPa.

Preferably, the Flexural Modulus may be in the range of <NUM> MPa to <NUM> MPa, like <NUM> MPa to 1500MPa, or from <NUM> to <NUM> MPa.

The Notched impact strength (NIS) is determined according to ISO179/1eA +<NUM> and may be at least <NUM> kJ/m<NUM>. It may be in the range of <NUM> to <NUM> kJ/m<NUM>, such as in the range of <NUM> to <NUM> kJ/m<NUM>, like in the range of <NUM> to <NUM> kJ/m<NUM>.

The bimodal polypropylene random copolymer of the present invention is characterised by a low Haze on <NUM> injection moulded plaques according to ASTM D1003. Said Haze values determined on <NUM> injection moulded plaques is denominated as Haze<NUM>.

The bimodal polypropylene random copolymer of the present invention may have a Haze<NUM> of at most <NUM> %, such as <NUM> - <NUM> %, like <NUM> - <NUM> %, such as <NUM> - <NUM> %.

In a preferred embodiment, the bimodal polypropylene random copolymer of the present invention is characterised by.

The bimodal polypropylene random copolymer of the present invention is characterised by good retention of the mechanical properties, especially a good retention of the impact behaviour after long time after irradiation.

The person skilled is aware, that the radical reaction induced by irradiation continues for long times after the actual sterilization process had taken place and been finished. To simulate and accelerate the long term behaviour after said irradiation had occurred, irradiated samples are exposed to elevated temperatures (i.e. <NUM>). The mechanical properties, especially impact behaviour (Notched Impact Strength, NIS), are tested on said heat aged, irradiated specimen.

The bimodal polypropylene random copolymer of the present invention is characterised by a good retention of the impact behaviour, in particular by a good Retained Notched Impact Strength after Radiation rNIS(rad; days), wherein "rad" indicates the irradiation dosage in kGy and "days" indicate the consecutive exposure of the irradiated samples in days at <NUM>.

Retained Notched Impact Strength (rNIS(rad; days), ) is determined according to the formula: <MAT> wherein:.

Again, "rad" indicates the irradiation dosage in kGy and "days" indicate the consecutive exposure of the irradiated samples in days at <NUM>.

Both γNIS(rad; days) and NIS(<NUM>; days)) are determined according to Charpy ISO <NUM>/1eA +<NUM>.

Retained Notched Impact Strength after Radiation rNIS(rad; days) is determined by putting into relation the (γNIS(rad; days)) to the NIS(<NUM>; days) of the same, heat-aged but non-irradiated material.

The bimodal polypropylene random copolymers of the present invention are characterised by a retained notched impact strength rNIS(<NUM>, <NUM>) of at least <NUM> %, or at <NUM> %.

It has been observed that the impact behaviour, namely the notched impact strength (NIS) after irradiation of the present bimodal polypropylene random copolymer has exceeded the values of the neat, untreated samples, resulting in retained NIS values of above <NUM> %. Further worth mentioning is the fact, that the Yellowness index (YI) of all inventive and comparative examples has increased during the irradiation to comparable levels. This is a clear indication, that the polymer did undergo degradation caused by irradiation. The more remarkable is the fact, that the retained impact strength of the bimodal polypropylene random copolymer of the present invention improved to values of above <NUM> %.

The bimodal polypropylene random copolymers of the present invention are characterised by a retained notched impact strength rNIS(rad; days) of at least <NUM> %, wherein.

The bimodal polypropylene random copolymer according to the invention is preferably obtainable by a single-site catalyst, more preferably being obtainable by a metallocene catalyst.

The metallocene catalyst is preferably according to the following formula (I).

Preferably R<NUM> and R<NUM>' are H or a linear or branched C1-C4-alkyl group or a OR group, wherein R is a C1-C3-alkyl group;.

The single-site metallocene complex, especially the complexes defined by the formula (I) specified in the present invention, used for manufacture bimodal polypropylene random copolymer are symmetrical or asymmetrical. For asymmetrical complexes that means that the two indenyl ligands forming the metallocene complex are different, that is, each indenyl ligand bears a set of substituents that are either chemically different, or located in different positions with respect to the other indenyl ligand. More precisely, they are chiral, racemic bridged bis-indenyl metallocene complexes. Whilst the complexes of the invention may be in their syn-configuration, ideally they are in their anti-configuration. For the purpose of this invention, racemic-anti means that the two indenyl ligands are oriented in opposite directions with respect to the cyclopentadienyl-metalcyclopentadienyl plane, while racemic-syn means that the two indenyl ligands are oriented in the same direction with respect to the cyclopentadienyl-metal-cyclopentadienyl plane, as shown in the Figure below.

Formula (I) is intended to cover both, syn- and anti-configurations. By nature of their chemistry, both anti and syn enantiomer pairs are formed during the synthesis of the complexes. However, by using the ligands of this invention, separation of the preferred anti-isomers from the syn-isomers is straightforward.

It is preferred that the metallocene complexes of the invention are employed as the racemic antiisomer. Ideally therefore at least <NUM>% mol, such as at least <NUM>% mol, especially at least <NUM>% mol of the metallocene catalyst is in the racemic anti-isomeric form. In a preferred embodiment at least one of the phenyl groups is substituted with at least one of R<NUM> or R<NUM>', thus n can be <NUM> only for one of the ligands and not for both. If n is <NUM>, then R<NUM> and R<NUM>' are preferably on position <NUM> (para) of the phenyl ring and if n is <NUM> then R<NUM> and R<NUM>' are preferably on positions <NUM> and <NUM> of the phenyl ring. Different combinations for R<NUM> and R<NUM>' are possible. Preferably both phenyl rings are substituted by R<NUM> and R<NUM>', whereby n can be the same or can be different for the two phenyl rings and is <NUM> or <NUM>.

More preferably in the catalyst according to formula (I) M is Zr,.

In one variant both of R<NUM> and R<NUM> as well as R<NUM>' and R<NUM>' together form an unsubstituted <NUM>-<NUM>, preferably <NUM>-<NUM> membered ring condensed to the benzene ring of the indenyl moiety and, optionally and preferably, R<NUM> and R<NUM>' each is a C1 to C4 alkyl group, more preferably methyl group.

More preferably both of R<NUM> and R<NUM> as well as R<NUM>' and R<NUM>' form an unsubstituted <NUM> membered ring condensed to the benzene ring of the indenyl moiety and optionally and preferably, R<NUM> and R<NUM>' each is a methyl group.

In another variant it is also possible that at both ligands R<NUM> and R<NUM> as well as R<NUM>' and R<NUM>' are hydrogen.

Still a further possibility is that only one of the ligands is unsubstituted in position <NUM> and <NUM>. In other words, either R<NUM> and R<NUM> or R<NUM>' and R<NUM>' are hydrogen.

The term "sequential polymerization process" indicates that the bimodal polypropylene random copolymer is produced in at least two reactors, preferably in two reactors, connected in series.

Accordingly, the present process comprises at least a first reactor (R1) and a second reactor (R2). The term "polymerization reactor" shall indicate that the main polymerization takes place. Thus, in case the process consists of two polymerization reactors, this definition does not exclude the option that the overall process comprises for instance a pre-polymerization step in a pre-polymerization reactor. The term "consist of" is only a closing formulation in view of the main polymerization reactors. The first reactor (R1) is preferably a slurry reactor (SR) and can be any continuous or simple stirred batch tank reactor or loop reactor operating in bulk or slurry. Bulk means a polymerization in a reaction medium that comprises of at least <NUM> % (w/w) monomer. According to the present invention the slurry reactor (SR) is preferably a (bulk) loop reactor (LR).

The second reactor (R2) is preferably a gas phase reactor (GPR). Such gas phase reactor (GPR) can be any mechanically mixed or fluid bed reactor. For example the gas phase reactor (GPR) can be a mechanically agitated fluid bed reactor with gas velocities of at least <NUM>/sec. Thus it is appreciated that the gas phase reactor is a fluidized bed type reactor, optionally with a mechanical stirrer.

Thus in a preferred embodiment the first reactor (R1) is a slurry reactor (SR), like a loop reactor (LR), whereas the second reactor (R2) is a gas phase reactor (GPR). Accordingly for the instant process two polymerization reactors, namely a slurry reactor (SR), like a loop reactor (LR), and a gas phase reactor (GPR) are connected in series. If needed prior to the slurry reactor (SR) a pre-polymerization reactor is placed. Preferably in the first reactor (R1) the first polypropylene fraction of the bimodal polypropylene random copolymer is produced, whereas in the second rector (R2) the second polypropylene fraction is produced.

A preferred multistage process is a "loop-gas phase"-process, such as developed by Borealis A/S, Denmark (known as BORSTAR® technology) described e.g. in patent literature, such as in <CIT>, <CIT> <CIT>, <CIT>, <CIT>, <CIT> or in <CIT>.

A further suitable slurry-gas phase process is the Spheripol® process of Basell described e.g.in figure <NUM> of the paper by <NPL>.

The bimodal polypropylene random copolymer of the present invention is especially suitable for producing moulded article, like injection moulded articles, for various applications, which are intended for sterilization.

The bimodal polypropylene random copolymer of the present invention is especially suitable for articles for medical or diagnostic applications intended for sterilization via gamma-radiation, such as syringes, connectors, pouches, tubes, peripheral venous catheter, butterfly winged infusion sets, protective caps or protective covers, etc..

Such moulded articles may comprise at least <NUM> wt. -%, like at least <NUM> wt. -%, more preferably at least <NUM> wt. -%, yet more preferably at least <NUM> wt. -%, still more preferably consisting of the bimodal polypropylene random copolymer of the present invention as defined herein.

Further the present invention is also directed to the use of the bimodal polypropylene random copolymer as defined herein for producing moulded articles, particularly injection moulded articles.

The present invention is also directed to the use of the bimodal polypropylene random copolymer as defined herein for producing medical applications intended for sterilization via gamma-radiation, such as syringes, connectors, pouches, tubes, peripheral venous catheter, butterfly winged infusion sets, protective caps or protective covers, etc..

The present invention encompasses the use of soluble nucleating agents for improving the resistance against γ-irradiation.

Soluble nucleating agents are particularly beneficial to improve the γ-irradiation resistance of propylene polymers, like polypropylene random copolymers, such as bimodal polypropylene random copolymer.

Soluble nucleating agents are particularly beneficial to improve the retained notched impact strength (rNIS) after irradiation.

Soluble nucleating agents can be used to achieve values for retained notched impact strength (rNIS) after irradiation at <NUM> or <NUM> kGy of <NUM> % or above.

In particular, soluble nucleating agents can be used to achieve values for retained notched impact strength rNIS(rad; days) of at least <NUM> %, wherein.

The present invention will now be described in further detail by the examples provided below:.

The melt flow rate (MFR) is determined according to ISO <NUM> and is indicated in g/<NUM>. The MFR is an indication of the flowability, and hence the processability, of the polymer. The higher the melt flow rate, the lower the viscosity of the polymer. The MFR<NUM> of polypropylene is determined at a temperature of <NUM> and a load of <NUM>.

The MFR of the second fraction, produced in the second reactor is determined according to <MAT>.

Wherin MFR (BPR) denominates the MFR of the bimodal polypropylene random copolymer, w(F1) and w(F2) denominate the weight fractions of the first polypropylene fraction and second polypropylene fraction respectivlely.

MFR(F1) denominates the MFR of the first polypropylene fraction produced in the first reactor.

Xylene Cold Soluble fraction at room temperature (XCS, wt. -%) is determined at <NUM> according to ISO <NUM>; <NUM>th edition; <NUM>-<NUM>-<NUM>.

The flexural modulus was determined in <NUM>-point-bending at <NUM> according to ISO <NUM> on 80x10x4 mm<NUM> test bars injection moulded in line with EN ISO <NUM>-<NUM>.

The Charpy notched impact strength (NIS) was measured according to ISO <NUM>1eA at +<NUM>, using injection moulded bar test specimens of 80x10x4 mm<NUM> prepared in accordance with EN ISO <NUM>-<NUM>.

γNIS(rad; days) denominates Notched impact strength (NIS) determined after irradiation and heat exposure at <NUM>, wherein "rad" denominates the irradiation (<NUM> kGy) and "days" denominates the duration of heat exposure at <NUM> in circulating air of the irradiated sample in days.

Accordingly NIS(<NUM>; days) denominates the notched impact strength determined samples that underwent heat exposure at <NUM> for the given days in circulating air without preceding irradiation.

Retained Notched Impact Strength after Radiation rNIS(rad; days) is determined by putting into relation the notched impact strength of an irradiated and heat aged sample (γNIS(rad; days)) to the NIS(<NUM>; days) of the same, heat-aged but non-irradiated material: <MAT>.

Based on the values given below, the retained Impact Strength after Radiation rNIS(<NUM>;<NUM>) for IE1 after <NUM> kGy and <NUM> days would be:<MAT>.

Injection moulded test specimen of 80x10x4 mm<NUM> prepared in accordance with EN ISO <NUM>-<NUM> were exposed to gamma irradiation at <NUM> and <NUM> kGy using a <NUM>CO γ-ray source. Consecutively the samples were aged at <NUM> in a circulating air oven up to <NUM> days as indicated below.

Once the desired time was reached, the samples were taken out from the oven and aged at <NUM> for <NUM> hours before the impact test according to Charpy ISO <NUM>/1eA+<NUM> was performed.

Yellowness Index was determined according to ASTM E <NUM>.

Haze determined according to ASTM D1003-<NUM> on 60x60x1 mm<NUM> plaques injection moulded in line with EN ISO <NUM>-<NUM>. Haze<NUM> denominates a haze value determined on <NUM> thick plaques.

Throughout the patent the term Tc or (Tcr) is understood as Peak temperature of crystallization as determined by DSC at a cooling rate of <NUM>/min.

Quantitative nuclear-magnetic resonance (NMR) spectroscopy was used to quantify the comonomer content of the polymers, comonomer dyad sequence distribution and sequence order parameter quantification.

Quantitative <NUM>C{<NUM>H} NMR spectra were recorded in the solution-state using a Bruker Avance III <NUM> NMR spectrometer operating at <NUM> and <NUM> for <NUM>H and <NUM>C respectively. All spectra were recorded using a <NUM>C optimised <NUM> extended temperature probehead at <NUM> using nitrogen gas for all pneumatics. Approximately <NUM> of material was dissolved in <NUM> of <NUM>,<NUM>-tetrachloroethane-d<NUM> (TCE-d<NUM>) along with chromium-(III)-acetylacetonate (Cr(acac)<NUM>) resulting in a <NUM> solution of relaxation agent in solvent (Singh, G. , Kothari, A. , Gupta, V. , Polymer Testing <NUM><NUM> (<NUM>), <NUM>). To ensure a homogenous solution, after initial sample preparation in a heat block, the NMR tube was further heated in a rotatory oven for at least <NUM> hour. Upon insertion into the magnet the tube was spun at <NUM>. This setup was chosen primarily for the high resolution and quantitatively needed for accurate ethylene content quantification. Standard single-pulse excitation was employed without NOE, using an optimised tip angle, <NUM> recycle delay and a bi-level WALTZ16 decoupling scheme (<NPL>; <NPL>). A total of <NUM> (<NUM>) transients were acquired per spectra.

Quantitative <NUM>C{<NUM>H} NMR spectra were processed, integrated and relevant quantitative properties determined from the integrals using proprietary computer programs. All chemical shifts were indirectly referenced to the central methylene group of the ethylene block (EEE) at <NUM> ppm using the chemical shift of the solvent. This approach allowed comparable referencing even when this structural unit was not present. Characteristic signals corresponding to the incorporation of ethylene were observed (<NPL>) and the comonomer fractions calculated as the fraction of ethylene and propylene in the polymer with respect to all monomer in the polymer: <MAT> <MAT>.

The mole percent comonomer incorporation was calculated from the mole fraction:<MAT>.

Comonomer sequence distribution was quantified at the dyad level using the characteristic signals corresponding to the incorporation of ethylene into propylene-ethylene copolymers (<NPL>). Integrals of respective sites were taken individually, the regions of integration described in the article of Wang et. were not applied for dyad sequence quantification.

It should be noted that due to overlapping of the signals of Tβδ and Syy, the compensation equations were applied for integration range of these signals using the sites Sβδ and Sγδ: <MAT> <MAT>.

With characteristic signals corresponding to regio defects observed (<NPL>; <NPL>; <NPL>) the correction for the influence of the regio defects on comonomer contents was required.

In case of <NUM>,<NUM>-erythro mis-insertions presence the signal from ninth carbon (S21e9) of this microstructure element (<NPL>) was chosen for compensation.

In case of <NUM>,<NUM> regeioirregular propene units in structure with one successive ethylene units presence, the signal from Tγγ ( <NPL>; <NPL>) was chosen for compensation.

The constitutive equations were: <MAT> <MAT> <MAT>.

Note that for simplicity the two indistinguishable reversible PE and EP dyads are termed EP i.e. EP = PE + EP. The mole fraction of each dyad was determined through normalisation to the sum of all dyads. <MAT> <MAT> <MAT> <MAT>.

Sequence order parameter, χ as it is defined by Koenig (<NPL>) (or "Koenig B-value" as it is named in <CIT>), yields information about whether the distribution of the structures is random, i.e. can be described by Bernoullian statistics, and whether it tends towards an alternating or block distribution. This parameter can be determined by the formula: <MAT>.

The catalyst for the bimodal polypropylene random copolymer was rac-anti-Me<NUM>Si(<NUM>-Me-<NUM>-(p-tBuPh)-Ind)(<NUM>-Me-<NUM>-Ph-<NUM>-OMe-<NUM>-tBu-Ind)ZrCl<NUM> prepared as described in <CIT>.

Inside the glovebox, <NUM>µL of a dry and degassed mixture of perfluoroalkylethyl acrylate ester were mixed in a septum vial with <NUM> of a 30wt-% solution of MAO in toluene and left to react overnight. The following day, <NUM> of the metallocene of the invention rac-anti-Me<NUM>Si(<NUM>-Me-<NUM>-(p-tBuPh)-Ind)(<NUM>-Me-<NUM>-Ph-<NUM>-OMe-<NUM>-tBu-Ind)ZrCl<NUM> (<NUM> mmol, <NUM> equivalent) were dissolved with <NUM> of the MAO solution in another septum bottle and left to stir inside the glovebox. After <NUM> minutes, the <NUM> of the MAO-metallocene solution and <NUM> of the perfluoroalkylethyl acrylate ester mixture in MAO solution were successively added into a <NUM> emulsification glass reactor containing <NUM> of hexadecafluoro-<NUM>,<NUM>-dimethylcyclohexane kept at -<NUM> and equipped with an overhead stirrer (stirring speed = <NUM> rpm). Total amount of MAO is <NUM> (<NUM> equivalents). A red emulsion formed immediately (measured emulsion stability = <NUM> seconds) and was stirred during <NUM> minutes at <NUM> / 600rpm. Then the emulsion was transferred via a <NUM>/<NUM> teflon tube to <NUM> of hot hexadecafluoro-<NUM>,<NUM>-dimethylcyclohexane heated to <NUM>, and stirred at 600rpm until the transfer is completed. The speed was reduced to <NUM> rpm. After <NUM> minutes stirring, the oil bath was removed and the stirrer turned off. The catalyst was left to settle up on top of the hexadecafluoro-<NUM>,<NUM>-dimethylcyclohexane and after <NUM> minutes the solvent was siphoned off. The remaining red catalyst was dried during <NUM> hours at <NUM> over an argon flow. <NUM> of a red free flowing powder was obtained.

The polymerization of P1 and P2 was performed in a Borstar PP pilot plant unit with liquid phase prepolymerization unit, bulk loop reactor and one gas phase reactors in series. Table <NUM> summarizes the polymerization data.

The person skilled is aware, that the polymer fraction produced in GPR1 is produced in the presence of the preceding polymer fraction produced in the loop and accordingly cannot be analysed as such. Hence, it is clear that the properties C2 in GPR1 and MFR in GPR1 have been calculated based on the available figures for the material coming from the loop reactor and the values as determined on the final polymer.

All the polymers of the inventive examples IE1 to IE4 and were stabilised with <NUM> ppm Tinuvin <NUM>, <NUM> ppm Irgafos <NUM> (both supplied by BASF and others), <NUM> ppm Calcium-stearate.

As regards the soluble nucleating agents:.

All mentioned nucleating agents are commercially available by Milliken.

Comparative example CE <NUM> is the commercial grade RF830MO of Borealis AG, Austria, having an MFR of <NUM>/<NUM>, a total ethylene content of <NUM> wt. -% and an XCS content of <NUM> wt. CE1 comprises a <NUM> ppm of a soluble nucleating agent.

CE1 was produced in the presence of a Ziegler Natta catalyst system having an internal donor as disclosed in <CIT>, <CIT> and <CIT>.

For comparative example CE2 the base polymer P2 and has been nucleated by blending it with <NUM> wt. -% of the commercial grade BC918CF of Borealis AG, Austria and visbroken, resulting in a composition having an MFR of <NUM>/<NUM>, an ethylene content of <NUM> wt. -% and an XCS of <NUM> wt.

CE2 further comprised <NUM> ppm of synthetic hydrotalcite MAHC, <NUM> Arenox DL (supplied by Reagens) and <NUM> ppm Irgafos <NUM> (supplied by BASF).

BC918CF is a heterophasic copolymer having an MFR of <NUM>/<NUM>, an elastomer content equivalent to an XCS of <NUM> wt. -% and a total ethylene content of <NUM> wt. -%, comprising <NUM> ppm of a polymeric nucleating agent.

The data clearly show, that the bimodal polypropylene random copolymer of the present invention has improved resistance against γ-irradiation. The data further show, that the bimodal polypropylene random copolymer has improved long term retention of mechanical properties after irradiation, especially improved long term retention of impact strength after irradiation.

Claim 1:
Bimodal polypropylene random copolymer of propylene and <NUM> - <NUM> wt.-% of ethylene as comonomer comprising
a) <NUM> - <NUM> wt.-% of a first polypropylene fraction being a propylene homopolymer or a random copolymer of propylene and ethylene as comonomer comprising up to <NUM> wt.-% of comonomer,
b) <NUM> - <NUM> wt.-% of a second polypropylene fraction being a random copolymer of propylene and ethylene as comonomer comprising <NUM> - <NUM> wt.-% of comonomer,
c) <NUM> - <NUM> wt.-% of a soluble nucleating agent and being characterised by
d) normated <PEP>-triads of at most <NUM> % as determined by NMR.