TITLE

Polypropylene Composiϋon For Buried Structures

BACKGROUND

There is a substantial need for non-pressure pipe useful for the transport of rainwater and sewage away from residential and commercial properties Typically, pipes of this nature are buried underground and are made of clay or metal Each of these materials, though, is susceptible to the environment in which it resides Clay pipes, for example, often contain junctions that allow the infiltration of roots or other materials that may clog the pipe or otherwise damage the piping system over time Similarly, metal pipes are susceptible to corrosion

In recent years, these issues have been addressed to some extent via the adoption of pipes made of materials such as polyvinyl chloride and polyethylene (HDPE) Even more recently, non-pressure pipe manufacturers have been employing polypropylene as a substitute material See, e g , U S 6,933,347 which discloses a polypropylene pipe comprising an impact copolymer, U S 6,433,087 which also discloses a pipe compπsing an impact copolymer, and United States Patent Publication 2007/01 17932 whjch teaches a heterophasic polyolefin composition comprising an elastomeric polymer in combination with a crystalline polymer having a broad molecular weight distribution

The widespread adoption of polypropylene non-pressure pipes in the United States has, however, been slow Specifically, although polypropylene provides an affordable alternative to polyethylene, and is easily fused to provide essentially seamless pipes of variable length, the performance characteristics of the pipes produced from presently available resins have not been ideal Moreover, presently available polypropylene resins suitable for manufacturing pipe are difficult to process

For example, polypropylene pipes made from resins that are currently available may deform if buried too deeply, impeding the flow of the rain water or sewage being transported These failures are believed to be due, in part, to an industry wide focus on developing resins having specific flexural moduli and notch impact strengths These properties, though, do not accurately predict long term performance of buried polypropylene structures as both flexural moduli and notch impact strength relate only to short term performance Thus, what is needed is a resin exhibiting good long term performance for use in buried structures, particularly corrugated non-pressure pipe In particular, it has been found that what is needed is a resin exhibiting good long term creep performance, good creep rupture strength, and a good balance of stiffness and impact resistance The present disclosure provides such a resin

BRIEF SUMMARY OF THE INVENTION

The present disclosure is directed to a polypropylene impact copolymer having superior processabilily, stiffness-impact balance, and superior long-term creep properties for the solid polymer

In one embodiment the polypropylene composition comprises about 83 to about 95 weight percent of a xylene insoluble fraction comprising a xylene insoluble portion of a propylene pol> mer The propylene polymer can have an mmmm of from about 88 to about 95 percent, an Nm of from about 55 to about 102, a xylene solubles content of from about 1 to about 5 %, and a polydispersity index of 2 5 to 6 The polypropylene composition further includes about 5 to about 17 weight percent of a xylene soluble fraction comprising a xylene soluble portion of a copolymer of propylene and ethylene The xylene soluble fraction can have about 20 to about 55 weight percent ethylene The composition can have about I 3 to about 19 vseight percent total ethylene, a polydispersity index of from about 2 5 to about 4 5, and a 50-year creep strain of less than about 8% at 1000 psi at 23 ⁰ C without creep rupture

In a sub-embodiment, the propylene polymer can have an mmmm of about 93, an Nm of about 72, and a polydispersity index of about 3 5 The xylene soluble fraction can have about 36 to about 37 weight percent ethylene The composition can have about 6 to about 7 weight percent total ethylene, and a polydispersity index of about 3 3

In one sub-embodiment, the composition can include a nucleator

In another sub-embodiment, the composition can have a melt flow rate of less than about 20 g/10 mm In certain sub-embodiments, the melt flow can be less than about 1 g/10 mm

In certain sub-embodiments, the composition can have a 1 % secant flexular modulus of about 170,000 to about 230,000 psi

In certain sub-embodiments, the composition can have a 50-year creep modulus of at least about 24,000 psi at 23 ⁰ C and 500 psi

In another sub-embodiment, the composition can include at least one additive selected from the group consisting of a nucleator, an acid scavenger, an antioxidant, a clarifier, a long term heat agent, a processing aid, a pigment, a filler, polyethylene, an impact modifier, a compatabilizer, and a slip agent.

In another sub-embodiment, the composition can have a total energy during instrumented impact at -20 ⁰ C of at least about 20 foot pounds.

The present disclosure also provides mono- or multi-layer pipes, pipe fittings, pipe junctions, tubes, or hoses comprising a polypropylene composition. In one embodiment, the mono- or multi-layer pipes, pipe fittings, pipe junctions, tubes, or hoses, the polypropylene composition can comprise about 83 to about 95 weight percent of a xylene insoluble fraction comprising a xylene insoluble portion of a propylene polymer The propylene polymer can have an mmmm of from about 88 to about 95 percent, an Nm of from about 55 to about 102, a x> lene solubles content of from about 1 to about 5 %; and a polydispersily index of 2 5 to 6 The polypropylene composition further includes about 5 to about 1 7 weight percent of a xylene soluble fraction comprising a xylene soluble portion of a copolymer of propylene and ethylene The xylene soluble fraction can have about 20 to about 55 weight percent ethylene The composition can have about 1 3 to about 19 weight percent total ethylene, a

polydispersity index of from about 2 5 to about 4.5, and a 50-year creep strain of less than about 8% at 1000 psi at 23 ⁰ C without creep rupture.

In a sub-embodiment, the propylene polymer can have an mmmm of about 93, an Nm of about 72, and a polydispersity index of about 3 5 The xylene soluble fraction can have about 36 to about 37 weight percent ethylene The composition can have about 6 to about 7 weight percent total ethylene, and a polydispersity index of about 3 3

In one sub-embodiment, the composition can include a nucleator

In certain sub-embodiments, the composition can have a 1 % secant flexular modulus of about 1 70,000 to about 230,000 psi

In certain sub-embodiments, the composition can have a 50-year creep modulus of at least about 24,000 psi at 23 ⁰ C and 500 psi.

In another sub-embodiment, the composition can include at least one additive selected from the group consisting of a nucleator, an acid scavenger, an antioxidant, a clarifier, a long term heal agent, a processing aid, a pigment, a filler, polyethylene, an impact modifier, a compatabihzer, and a slip agent

In another sub-embodiment, the composition can have a tola] energy during instrumented impact at -20 ⁰ C of at least about 20 foot pounds

The present disclosure further provides a method for preparing a composition The composition can comprise about 83 to about 95 weight percent of a xylene insoluble fraction comprising a xylene insoluble portion of a propylene polymer The propylene polymer can have an mmmm of from about 88 to about 95 percent, an Nm of from about 55 to about 102, a xylene solubles content of from about 1 to about 5 %, and a polydispersity index of 2 5 to 6 The composition further includes about 5 to about 17 weight percent of a xylene soluble fraction comprising a xylene soluble portion of a copol> mer of propylene and ethylene The x> lene soluble fraction can have about 20 to about 55 weight percent ethylene The composition can have about 1 3 to about 19 weight percent total ethylene, a polydispersity index of from about 2 5 to about 4 5, and a 50-year creep strain of less than about 8% at 1000 psi at 23 ⁰ C without creep rupture

The method for preparing this polypropylene composition can comprise feeding propylene and hydrogen into a first stage including at least one homopol> meπzation reactor The method further includes polymerizing propylene in said first stage at a first temperature and pressure in the presence of a catalyst, cocatalyst, and an electron donor to produce a first product The method of preparation further includes transferring said first product, catalyst, cocatalyst, and electron donor to a second stage including at least one copolymerization reactor 1 he polymerization process further includes copolymeπzing propylene and ethylene at a second temperature and pressure in the presence of the first product to form said composition

In a sub-embodiment of the above descnbed method, the propylene polymer can have an mnimm of about 93, an Nm of about 72, and a polydispersity index of about 3 5 The xylene soluble fraction can have about 36 to about 37 weight percent ethylene, and the composition can have about 6 to about 7 weight percent total ethylene and a polydispersity index of about 3 3

In a further sub-embodiment of the above descnbed method, the method includes adding a nucleator In another sub-embodiment of the method, the first temperature can be about 75 ⁰ C, the first pressure can be about 42 kg/cm ² , the second temperature can be at least about 70 ⁰ C, and the second pressure can be at least about 9 kg/cm ²

In still another sub-embodiment, the method can include transferring the composition to an extruder, optionally adding an additive to the composition in the extruder, and extruding and pelletizing the compound and optional additive

The present disclosure further provides a polypropylene composition, compπsing about 83 to about 95 weight percent of a xylene insoluble fraction compπsing a xylene insoluble portion of a propylene polymer The propylene polymer can have an mmmm of from about 88 to less than about 96 peicent. an Nm of from about 103 to about 120, a xylene solubles content of from about 1 to about 5 %, and a polydispersily index of 2 5 to 6 The polypropylene composition further includes about 5 to about 17 weight percent of a xylene soluble fraction compπsing a xylene soluble portion of a copolymer of propylene and ethylene The xylene soluble fraction can have about 20 to about 55 weight percent ethylene The composition can further have about 1 3 to about 19 weight percent total ethylene, a pol>dιspersιty index of from about 2 5 to about 4 5, and a 50-year creep strain of less than about 8% at 1000 psi at 23 ⁰ C without creep rupture

In one sub-embodiment, the xylene insoluble fraction can have an mmmm of about 95, an Nm of about 1 12, and a polydispersity index of about 3 9 The xylene soluble fraction can have about 38 to about 39 weight percent ethylene The composition can have about 7 to about 8 weight percent total ethylene and a polydispersity index or about 3 8 to about 3 9

In another sub-embodiment, the composition can have a melt flow rate of less than about 20 g/10min

In still another sub-embodiment, the composition can have a melt flow of less than about I g/10 mm

In certain sub-embodiments, the composition can have a 1 % secant flexular modulus of about 170,000 to about 230,000 psi

In certain sub-embodiments, the composition can have a 50-year creep modulus of at least about 24,000 psi at 23 ⁰ C and 500 psi

In another sub-embodiment, the composition can include at least one additive selected from the group consisting of a nucleator, an acid scavenger, an antioxidant, a clarifier, a long term heat agent, a processing aid, a pigment, a filler, polyethylene, an impact modifier, a compatabihzer, and a slip agent

In another sub-embodiment, the composition can have a total energy during instrumented impact at -20 ⁰ C of at least about 20 foot pounds

In another sub-embodiment, the composition can have an intrinsic viscosity ratio of copolymer to propylene polymer of about 1 to about 1 8

As noted elsewhere herein, the present disclosure also provides mono- or multi-layer pipes, pipe fittings, pipe junctions, tubes, or hoses compπsing a polypropylene composition In one embodiment, the composition can comprise about 83 to about 95 weight percent of a x> lene insoluble fraction compπsing a xylene insoluble portion of a propylene polymer, said prop) lene pol> mer having an mmmm of from about 88 to less than about 96 percent, an Nm of from about 103 to about 120, a xylene solubles content of from about 1 to about 5 %, and a pol> dispersity index of 2 5 to 6 The composition can further comprise about 5 to about 17 weight percent of a xylene soluble fraction comprising a xylene soluble portion of a copolymer of propylene and ethylene, said xylene soluble fraction having about 20 to about

55 weight percent ethylene The can have about 1 3 to about 19 weight percent total ethylene, a polydispersity index of from about 2 5 to about 4 5, and a 50-year creep strain of less than about 8% at 1000 psi at 23 ⁰ C without creep rupture

In one sub-embodiment, the propylene polymer can have an mmmm of about 95, an Nm of about 1 12, and a polydispersily index of about 3 9 The xylene soluble fraction can have ubout 38 to about 39 weight percent ethylene The composition can have about 7 to about 8 weight percent total ethylene and a polydispersity index of about 3 8 to about 3 9

In a further sub-embodiment, the composition can have a 50-year creep modulus of at least about 24,000 psi at 23 ⁰ C and 500 psi

In another sub-embodiment, the composition can have a 1 % secant flexular modulus of about 170,000 to about 230,000 psi

In still another sub-embodiment, the polypropylene composition can further comprise at least one additive selected from the group consisting of a nucleator, an acid scavenger, an antioxidant, a clarifier, a long term heat agent, a processing aid, a pigment, a filler, polyethylene, an impact modifier, a compatabihzer, and a slip agent

In another sub-embodiment, the composition can have an intrinsic viscosity ratio of copolymer to homopolymer of about 1 to about 1 8

The present disclosure further includes a method for preparing a composition that can compπse about 83 to about 95 weight percent of a xylene insoluble fraction comprising a xylene insoluble portion of a propylene polymer, said propylene polymer having an mrnmm of from about 88 to less than about 96 percent, an Nm of from about 103 to about 120, a xylene solubles content of from about 1 to about 5 %, and a polydispersity index of 2 5 to 6 The composition can further comprise about 5 to about 17 weight percent of a xylene soluble fraction comprising a xylene soluble portion of a copolymer of propylene and ethylene, said xylene soluble fraction having about 20 to about 55 weight percent ethylene 1 he can have about 1 3 to about 19 weight percent total ethylene, a polydispersity index of from about 2 5 to about 4 5, and a 50-year creep strain of less than about 8% at 1000 psi at 23 ⁰ C without creep rupture The method includes feeding propylene and hydrogen into a first stage including at least one homopolymenzation reactor, polymerizing the propylene in the first stage at a first temperature and pressure in the presence of a catalyst, cocatalyst. and an electron donor to produce a first product, transferring the first product, catalyst, cocatalyst, and electron donor to a second stage including at least one copolymerization reactor, and copolymerizing propylene and ethylene at a second temperature and piessure in the presence of the first product

In one sub-embodiment, the propylene polymer can have an mmmm of about 95, an Nm of about 1 12, and a polydispersity index of about 3 9 The xylene soluble fraction can have about 38 to about 39 weight percent ethylene The composition can have about 7 to about 8 vseight percent total ethylene and a polydispersity index of about 3 8 to about 3 9

In another sub-embodiment, the composition can have an intrinsic viscosity ratio of copolymer to homopolymer of about 1 to about 1 8

In a further sub-embodiment, the first temperature can be about 75 ⁰ C. the first pressure can be about 42 kg/cm ² , the second temperature can be at least about 70 ⁰ C, and the second pressure can be at least about 9 kg/cm ²

Another method for making the composition described herein is also provided This method may include mixing a propylene polymer having an mmmm of from about 88 to about 95 percent, an Nm of from about 55 to about 102, a xylene solubles content of from about 1 to about 5 %, and a polydispersity index of 2 5 to 6, with an ethylene propylene copolymer The method may further include optionally adding an additive to the extruder The method also includes extruding and pelletizing the composition

The present disclosure further recites an article comprising any one of the composition as descnbed herein wherein the article is prepared via extrusion, injection molding, compression molding, blow molding, or thermoforming

The present disclosure further includes another method of prepaπng a composition disclosed herein This can include mixing a propylene polymer having an mmmm of from about 88 to about 96 percent, an Nm of from about 103 to about 120, a xylene solubles content of from about 1 to about 5 %, and a polydispersity index of 2 5 to 6, with an ethylene propylene copolymer, in an extruder to form said composition, optionally adding an additive to the extruder, and extruding and pelletizing the composition

DRAWINGS

For the purpose of illustrating the resin described herein, there are depicted in the drawings certain embodiments of the resin in various tables and graphs However, the resin descnbed herein is not limited to the precise arrangements and instrumentalities of the embodiments depicted in the drawings

figure 1 is a table of \ aπous compositional properties of representative polymers of the invention

Figure 2 is a table detailing the performance characteristics of various polymers of the invention as well as comparative examples

Figure 3 is a table detailing the performance characteristics of various polymers of the invention as well as comparative examples

Figure 4 is a table detailing the performance characteristics of various polymers of the invention as well as comparative examples

Figure 5 is a graph depicting the Creep Modulus of various compositions of the im ention and several comparative examples at 500 PSl

Figure 6 is a graph depicting the Creep Strain (%) of vaπous compositions of the invention and several comparative examples at 500 PSI

Figure 7 is a graph depicting the Creep Modulus of various compositions of the invention and several comparative examples at 1000 PSl figure 8 is a graph depicting the Creep Strain (%) of various compositions of the invention and several comparative examples at 500 PSI

Figure 9 is a graph showing the correlation between ASTM D6992 (SlM Creep Rupture) and ΛSTM 2990 (Conventional Creep Rupture) using composition XlII

5 Figure I O is a graph showing representative profiles of instrumented impact energy at

-20 ⁰ C for composition XIII

Figure 1 1 is a graph showing representative profiles of instrumented impact energy at -20 ⁰ C for composition IX

Figure 12 is a graph showing representative profiles of instrumented impact energy at I O -29 ⁰ C for composition VIII

DE TAILED DESCRIPTION OF THE INVENTION

Definitions δc Abbreviations

1 5 In accordance with this detailed description, the following abbreviations and

definitions apply It must be noted that as used herein, the singular forms "a", "an", and "the" include plural referents unless the context clearly dictates otherwise Thus, for example, reference to "a resin" includes a plurality of such resins and reference to "the resin" includes reference to one or more resins and equivalents thereof known to those skilled in the art, and 0 so forth

As used herein the phrase "propylene polymer" refers to a propylene homopolymer or to an ethylene propylene random copolymer having, in certain embodiments, less than 1 5 weight percent ethylene, and in other embodiments, less than 1 weight percent ethylene In the context of an impact copolymer, the propylene polymer may be referred to as the 25 "matrix '

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art

Ranges are provided in various locations throughout this specification For any given range in the present specification, every whole integer therein is deemed to be part of that 30 range, as is every hundredth and thousandth of an integer, such that a range of from, for example, I to 2 includes at least 1 000, 1 001 , I 002, I 003, 1 004, 1 005, 1 006, 1 007, 1 008. I 009, I 010, 1 01 1 , etc through to 2, unless otherwise provided

It is generally accepted in the art that there is a direct correlation between the isotacticit) of the matrix of an impact copolymer and the stiffness of the total impact copolymer As a result, it is generally accepted that the higher the isotacticity of the matrix, the higher the stiffness in the total polymer It is also generally appreciated that a broad molecular weight distribution in the matrix portion of an impact copolymer, such as the propylene polymer portion of the impact copolymer, correlates to a polymer having enhanced stiffness Good long term creep resistance as measured by creep modulus, % creep strain, and creep rupture strength, are likewise generally believed to be associated with high stiffness Thus, a person of ordinary skill in the art attempting to design an impact copolymer with outstanding long term creep properties, would likely prepare an impact copolymer wherein the matrix of the impact copolymer has a high isotacticity and a broad molecular weight distribution

It has now been surprisingly discovered, though, that the matrix of a heterophasic impact copolymer used for non-pressure pipes does not need to be highly isotactic to achieve excellent long-term (50- 100 year) creep resistance In particular, the data provided herein demonstrates that an impact copolymer comprising a matrix having an "mmmm" of less than about 96 percent, and in certain embodiments, less than about 95 percent, can have outstanding long term creep resistance

The lact that an impact copolymer having a low or medium isotacticity matrix provides a iesin having excellent long-term creep performance is both counterintuitive and unexpected The unexpected nature of these results is made even more surprising by the fact that experimentation has shown that a matrix having a relatively narrow molecular weight distribution, which results in a less stiff resin, results in a product with excellent long term creep resistance, too

In addition to the above, the impact copolymer described herein has superior ductility at temperatures at least as low as -29 ⁰ C The combination of excellent long term creep resistance and outstanding cold temperature impact strength for the composition described herein is highly advantageous and desirable for use in buried structures, such as non-pressure pipe The Components of the Composition

The composition of the present invention is an impact copolymer An impact copolymer includes both a matπx and an ethylene propylene copolymer Particularly for in- reactor produced materials, the percent content of the matrix and ethylene propylene copolymer arc difficult to ascertain directly As a result of the difficulties associated with direct measurement, polymer chemists of ordinary skill in the art frequently report the weight percentages of the xylene insolubles and solubles content of an impact copolymer These values are easily measured and provide a rough approximation of the weight percent content of the matrix and ethylene propylene copolymer, respectively

For the composition described herein, the xylene insoluble fraction comprises, amongst other components, the xylene insoluble portion of the propylene polymer The xylene insoluble fraction makes up anywhere from about 83 to about 95 weight percent of the composition In certain embodiments, the xylene insoluble fraction makes up from about 84 to about 89 weight percent of the composition The weight percent of the xylene insoluble fraction in the composition can be determined by measuring the weight percent of the xylene solubles fraction of the composition, and subtracting the resulting value from 100 The weight percent of the xylene soluble fraction in the composition is measured by adding 2 g of the composition to 200 ml of o-xylene (stabilized with AO- 1010) in a flask equipped with a water cooled condenser The mixture is then heated to reflux (about 140 ⁰ C) under a nitrogen purge and allowed to stir for about 30 minutes Subsequently, the temperature is lowered to about 100 ⁰ C for about 30 minutes at w hich point the pol>mer is thoroughly dissolv ed in o-xylene

I he heat source is then removed and any condensate remaining in the condenser is allowed to drain into the flask (approximately 5 minutes) The condenser is removed and the flask is placed into a thermostatically controlled water bath maintained at 25 ⁰ C ± 0 5 ⁰ C for

I hour During this time, a precipitate forms

The flask is then removed from water bath and the flask's contents are filtered through a Whatman 1 14V (Qualitative Wet-Strengthened) filter paper The filtrate is collected and adjusted to the original starting volume of 200 ml After stirring, a 50 ml aliquot of the diluted filtrate is collected with a volumetric pipette The aliquot is subsequently transferred to a tared stainless steel beaker

- I l - The beaker is placed into a steam bath and the solvent contained in the aliquot is evaporated The beaker is then placed in a vacuum oven for 1 hr at 80 ⁰ C to ensure that any remaining solvent is fully evaporated Finally, the beaker is removed from the vacuum oven, allowed to cool to room temperature under ambient conditions for 1 hour, and then weighed The weight of the contents of the flask are determined by subtracting the weight of the tared beaker from the measured weight of beaker with the dried soluble fraction The weight percent xylene soluble fraction (%XS) of the composition can thus be calculated as follows o _{/ KC i} nn• I ^ ^eι 8 ^nl °f Solid Sample Contained in 4lιquot \ ( Total Volume of xylene Used To Dissolve Sample |

\_ Starling Sample Weigh] J \ Volume of Aliquot ) Thus, using a 2g sample of composition, 200ml of solvent for the initial dissolution, and a

50ml aliquot, as in the above described example, the % XS = 100*( Weight of Solid Sample Contained in Alιquot/2g)*(200ml/50ml) or 200* Weight of Solid Sample Contained in Aliquot The Propylene Polymer

The xylene insoluble fraction of the composition descπbed herein comprises, amongst other components, the xylene insoluble portion of the propylene polymer

Regardless of the method used to prepare the composition descπbed herein, the properties of the propylene polymer may be measured directly by sampling propylene polymer from a given reactor prior to blending the propylene polymer with an ethylene propylene copolymer

The propylene polymer can exhibit an mmmm (meso pentad) content of from about 88 to less than about 96 percent In certain embodiments, the mmmm can be from about 89 to less than about 95 percent Percent meso pentad content is measured by ¹³ C NMR according to Macromolecules, volume 6, no 6, 1973, p 925-926 Without wishing to be bound to any particular theory, it is believed that this relatively low isotacticity, in combination with the various other properties described herein, results in a polymer having desirable long teπn creep properties

In certain embodiments, the mmmm can be about 92 to less than about 96 percent In one embodiment, mmmm content can be about 92 percent In another embodiment, mmmm content can be about 92 8 percent In another embodiment, mmmm content can be about 92 86 percent In yet another embodiment, mmmm can be about 95 percent In another embodiment, mmmm content can be about 95 3 percent In still another embodiment, mmmm content can be 95 33 percent

The propylene polymer can have an average Nm [meso sequence (run) length] of about 55 to about 120 Nm can be measured using ¹³ C NMR according to the following equation

Nm=2(mm/mr)+l as described in the Bovey, F Chain Structure and Conformation of Macromolecules, New Yoik Academic Press. 1982, p 55, wherein "mm" is the molar fraction of isotactic triads and "mr" is the molar fraction of heterotactic (meso-racemic) tπads

In one embodiment, Nm may be about 55 to about 102 In another embodiment, Nm may be about 103 to about 120 In one embodiment, Nm can be about 72 In another embodiment, Nm can be about 72 I In another embodiment, Nm can be about 1 12 In another embodiment, Nm can be about 1 12 2

The propylene polymer can be further characterized by a xylene soluble and a xylene insoluble fraction The weight percent of the xylene soluble fraction of the propylene polymer can be measured according to methodology described above for measurement of the weight percent of the xylene soluble fraction of the composition The xylene soluble fraction of the propylene polymer can be from about 1% to about 5% Accordingly, the xylene insoluble fraction of the propylene polymer of the composition can be from about 95% to about 99%

The propylene polymer can be further characterized by an intrinsic viscosity of from about 2 5 to about 6 dl/g Hie intrinsic viscosity of the propylene polymer can be measured in tetralin at 135 ⁰ C using a Desreux-Bischoff dilution viscometer (Ubbelohde-type) on a 1 g/L solution of the propylene polymer In one embodiment, the intrinsic viscosity of the propylene polymer can be about 3 dl/g In another embodiment, the intrinsic viscosity of the propylene polymer can be about 3 4 dl/g In another embodiment, the intrinsic viscosity of the propylene polymer can be about 3 44 dl/g In another embodiment the intrinsic viscosity of the propylene polymer can be about 3 5 to about 4 dl/g

The propylene polymer can be further characterized by a polydispersity index of from about 2 5 to about 6 Polydispersity can be measured according to the crossover modulus method The crossover modulus method is described in Zeichner, G R , et al, Proc Of the 2 ^nd World Congress of Chemical Engineering, Montreal, Canada, 1981 , as well as in equation 6 as presented in Shroff, R , et al , Applied Polymer Sciences, VoI 57, 1605-1626, 1995 For the propylene polymer, the polydispersity index is measured via frequency sweep oscillatory shear data at 200 ⁰ C This data is generated using an ARES (TA Instruments) controlled strain rheometer using 25 mm parallel plates with a frequency range from 0 1 to 500 rad/s

In instances where the melt flow rate of the propylene polymer is greater than about 40 g/10 nun, polydispersity index cannot be determined by the crossover modulus method due to instrument limitations Thus, for propylene polymers with melt flows greater than about 40 g/10 mm, the modulus separation technique described by H J Yoo in 'MWD Determination of Ultra High MFR Polypropylene by Melt Rhcology", Advances in Polymer l echnology, VoI 13, 201 -205, 1994 should be used instead

Without wishing to be bound to any particular theory, it is believed that this range of narrow molecular weight distributions, in combination with the other properties described herein, surprisingly results in a composition having enhanced creep properties In certain embodiments, the polydispersity index of the propylene polymer is from about 3 to about 4 In one embodiment, the polydispersity index can be about 3 5 In another embodiment, the polydispersity index can be about 3 9

A table detailing the properties of exemplary propylene polymers useful for the preparation of the impact copolymer described herein can be found in Table 1 Composition I is a comparative sample Each of samples 1-V]] is a propylene homopolymer

Table 1

In order to form an impact copolymer having the advantageous properties described herein, the above described propylene polymer is blended with an ethylene-propylene copolymer The blending may take place via melt-blending in an extruder, however, more preferably, the propylene polymer and ethylene-propylene copolymer are blended via an ιn- reactor process

The properties of the ethylene propylene copolymer, particularly for reactor blends, cannot be measured directly As a result, the properties of the xylene solubles fraction of the composition which comprises, amongst other components, the xylene soluble portion of the ethylene propylene copolymer, are reported herein The xylene soluble fraction of the composition can comprise anywhere from about 5 to about 17 weight percent of the composition In certain embodiments, however, the xylene soluble fraction can comprise from 8 to 13 weight percent of the composition The weight percentage of the xylene solubles fraction in the composition may be measured according to the method described pres iousl)

The xylene solubles fraction of the composition can contain about 20 to about 55 weight percent ethylene as measured by ¹³ C NMR In certain embodiments, however, the xylene solubles fraction of the composition may only contain about 32 to about 39 weight percent ethylene In one embodiment, the ethylene content of the xylene solubles fraction of the composition can be about 36 weight percent In another embodiment, the ethylene content can be about 36 7 weight percent In another embodiment, the ethylene content in the xylene solubles fraction of the composition can be about 38 weight percent In still another embodiment, the ethylene content can be about 38 7 weight percent

The intrinsic viscosity of the xylene soluble fraction of the composition (β) can be from about 2 to about 7 In certain embodiments, β is from about 3 to about 5 Properties of the Composition of the Invention

In one embodiment, the composition can have about 1 3 to about 19 weight percent total ethylene In another embodiment, the composition can have about 3 to about 10 weight percent total ethy lene In an alternative embodiment, the total ethylene may be about 6 to about 8 weight percent total ethylene In one embodiment, the composition can have about 6 5 weight percent total ethylene In another embodiment, the composition can have about

7 4 weight percent total ethylene Total ethylene content may be measured by FTIR according to ASTM D5576

The composition of the invention can be further characterized by an intrinsic viscosity ratio of the xylene soluble fraction of the composition to the xylene insoluble fraction of the composition of about 1 to about I 8 In other embodiments, the ratio may be about 1 to about

1 5 In a further embodiment, the ratio may be about I 15 to 1 25 In certain embodiments, the intrinsic viscosity ratio of the xylene soluble fraction to the xylene insoluble fraction can be about 1 2 In another embodiment, the intrinsic viscosity ratio of the xylene soluble fraction to the xylene insoluble fraction may be about 1 5

The intrinsic viscosity ratio of the xylene soluble fraction of the composition ("β") to the xylene insoluble fraction of the composition ('"α") may be calculated according to the following formula

β/α = ([η/α] - [A/l 00])/[B/100]

wherein "η" is the intrinsic viscosity of the composition, "A" is the weight percent of the x> lenc insoluble fraction of the composition and; "B" is the weight percent of the xylene soluble fraction of the composition The intrinsic viscosity of the composition (η) and the xylene soluble fraction of the composition (β) are measured in tetralin at 14O ⁰ C using a Desreux-Bischoff dilution viscometer (Ubbelohde-type) viscometer on solutions with 1 5 g/l of polymer as described in US Patent 6,933,347

The composition can be further characterized by a polydispersity index of from about

2 5 to about 4 5 In one embodiment, the polydispersity index can be about 3 3 In another embodiment, the polydispersity index can be about 3 8 In yet another embodiment, the polydispersity index can be about 3 9 Polydispersity may be measured according to the crossover modulus method described elsewhere herein

The composition of the invention can have a percent crystallinity of at least 50 as measured by annealed differential scanning caloπmetry (DSC) according to ASTM D3414

Following the general ASTM specification, films were pressed from pellets or powder at 200 ⁰ C for 3 min These films were subsequently run in TA Q200 Robotics DSC with a refrigerated cooling system In the DSC, polymer is melted at 200 ⁰ C and equilibrated for 5 minutes The sample is then cooled to O ⁰ C at a rate of 10°C/min while recording the re- crystallization exotherm (cooling curve) Once cool, the sample is then heated to 200 ⁰ C at a rate of 1 5°C/mιn to record the melting endotherms The percent crystallinity is determined by integrating the area under the re-crystallization peak on the cooling curve and dividing by 165 J/g

In one embodiment, the percent crystallinity of the total polymer can be about 51 In another embodiment, the percent crystallinity of the total polymer can be about 51 5 In still another embodiment, the percent crystallinity of the total polymer can be about 51 6 In another embodiment, the percent crystallinity of the total polymer is about 54 In another embodiment, the percent crystallinity of the total polymer can be about 54 5 In yet another embodiment, the percent crystallinity of the total polymer can be about 54 8

The composition of the invention can be further characterized by a melting temperature ("T _mc n") of at least about 163 ⁰ C (DSC) In one embodiment, the T _mc ι, is about 163 9 ⁰ C Ln another embodiment, the X ₀ , _e u is about 164 5 ⁰ C

The composition of the invention can be further characterized by its melt flow For example, for the preparation of non-pressure pipes, which are typically prepared via extrusion, the melt flow of the composition of the invention should be less than about 2, more preferably less than I g/10 minutes, but greater than about 0 I g/10 minutes In certain embodiments, the melt flow of the composition is between about 0 25 and 0 45 g/10 minutes In other embodiments, the melt flow of the composition may be about 0 3 g/10 min or about 0 4 g/10 minutes The melt flow of the composition of the invention may, however, exceed 2 but be less than about 20 g/l 0 mm At these higher melt flows, the composition can be useful for injection molding, thermoforming, or blow molding The melt flow of the composition can be measured per ASTM 1238 using a load of 2 16 kg at 230 ⁰ C

In certain embodiments of the invention, the composition is nucleated with a nucleating agent such as Sodium 2,2'-methylene bis-(4,6-dι-tcrt-butyl phenyl)phosphate Other nucleating agents that can be used in a composition of the invention include, but are not limited to, talc, sodium benzoate, 2,2'-Methylenebis-(2,6-dilert-butylphenyl)phosphate

(lithium salt), Aluminum hydroxybis[2,4 _> 8, 10-tetrakis( 1 , 1 -dimethylethyl)-6-hydroλy- 12-H- dibenzo[d,g][ l ,3,2]dioxaphosphocin 6-oxidato], dibenzilidene sorbitol, norutol 1 ,2,3- tπdeoxy-4,6 5,7-bis-O-((4-propylphenyl)methylene], Cιs-endo-bicyclo[2 2 l ]heptane-2,3- dicarboxylic acid (disodium salt), l Λ,2S'-cyclohexanedicarboxylic acid (calcium salt), zinc stcaratc, pigments that act as nucleators, aromatic carboxylic acids, calcium carbonate, pimelic acid, calcium hydroxide, stearic acid, organic phosphates, and mixtures thereof In certain embodiments, fillers may be used in combination with, or instead of, nucleating agents Examples of fillers include, but are not limited to, talc, micro-talc, glass, and nano-composites In certain instances, fillers may act as nucleators

Performance Characteristics

The resin described herein can have the performance characteristics disclosed in Figures 2 3 and 4 In particular, the composition can have a 1 % secant flexural modulus of at least about 160 to about 250 kpsi In another embodiment, the flexural modulus can be about 1 70 to about 230 kpsi Secant flexural modulus is measured according to ASTM

D790 The Izod impact strength of the composition of the invention (according to ASTM D256) at room temperature can be 100% non-break At -4 ⁰ C, the Izod impact strength can be about 2 to about 6 ft-lb/ιn with partial breakage observed At -20 ⁰ C, the Izod impact strength can be about 1 to about 1 7 ft-lb/in, with complete breakage observed

The yield stress of the composition, as measured according to ASTM D638, can be about 4000 to about 4500 psi In certain embodiments, the yield stress of the composiϋon can be about 4200 to about 4270 psi The percent strain at the yield point can be from about 1 1 to about 13 percent In certain embodiments, the percent strain at the yield point can be from about 1 1 5 to about 12 5 percent In still other embodiments, the percent strain at the yield point can be from about 1 1 7 to about 12 1 percent

The tangent tensile modulus of the composition can be about 170 kpsi to about 220

- 1 ! kpsi In certain embodiments, the tangent tensile modulus of the composition can be about 180 kpsi to about 230 kpsi

Long Term Creep

Long term creep properties can be measured using the Step Isothermal Method

("SIM ') according to ASTM D6992 in the tensile mode of deformation using injection molded "Type 1 " specimens Type 1 specimens used for all SIM data measurements were prepared according to ASTM D4001 procedures All data resulting from the various SIM creep studies was normalized to a reference temperature of 23 ⁰ C using the time-temperature superposition principle as descπbed in ASTM D6992 Using these protocols, the creep- iesistancc of the composition can be evaluated at 50 and 100 years All SIM data was validated with AST M D2990, a conventional tensile creep-rupture measurement technique figure 9 shows the correlation between SIM (ASTM 6992) and conventional creep rupture method (ASTM D2990) for composition XlU as descπbed herein

The 50 year creep modulus according to the SlM method at 500 psi can be at least about 24 kpsi In certain embodiments, the 50 year creep modulus at 500 psi can be at least about 29 kpsi In still other embodiments, the 50 year creep modulus at 500 psi can be at least about 34 kpsi

The 50 year creep strain at 500 psi according to ASTM D6992 can be from about 1 to about 2 I % In certain embodiments, the 50 year creep strain can be about 1 5 to about 1 7

% In yet other embodiments, the 50 year creep strain can be about 1 52 to about 1 72 %

The 50 year creep strain at 1000 psi, also according to D6992, can be less than about 8 % In another embodiment, the 50 year creep strain at 1000 psi can be less than about 7 % In another embodiment, the 50 year creep strain at 1000 psi can be less than about 5 %

The 50 year creep rupture strength can be at least about 1000 psi

Instrumented Impact

Instrumented impact properties were measured according to ASTM D3763, using circular impact disks with a diameter of 4" and a thickness of 0 125" The disks were produced via injection molding according to ASTM D4001 A striker mass of 22 49 kg was used Impact height was 0 3888 m and the impact velocity was 2 76 m/s Using the above described parameters, the total energy of the instrumented impact at -20 ⁰ C can be at least about 20 foot pounds In other embodiments, the instrumented impact at -20 ⁰ C can be at least about 20 to about 45 foot-pounds In other embodiments, the total energy at -20 ⁰ C can be at least about 24 to about 40 foot-pounds In still other

embodiments, the total energy at -20 ⁰ C can be at least about 30 to about 40 foot-pounds

The instrumented impact energy at maximum load at -20 ⁰ C can be at least about 20 foot-pounds In other embodiments, the instrumented impact energy at maximum load at -20 ⁰ C can be at least about 21 foot-pounds In still other embodiments, the instrumented impact energy at maximum load at -20 ⁰ C can be at least about 22 foot-pounds Representative profiles of instrumented impact energy at maximum load at -20 ⁰ C for samples XIII, IX, and

VIII are shown in figures 10, 1 1 , and 12 respectively These figures show that the compounds of the invention retain their ductility, even at low temperature

For instrumented impact at room temperature, the composition descπbed herein can have a total energy of at least about 28 foot-pounds The maximum load at room temperature can be at least about 550 foot-pounds In other embodiments, the maximum load at room temperature can be at least about 560 foot-pounds In other embodiments, the maximum load at room temperature may be at least about 575 foot-pounds

The energy at maximum load at room temperature may be at least about 15 footpounds In other embodiments, the energy at maximum load at room temperature may be at least about 15 5 foot-pounds In yet another embodiment, the energy at maximum load at room temperature may be at least about 15 9 foot pounds

Method of Making

The composition of the invention may be prepared according to procedures known in the art More specifically, the composition of the invention may be prepared in a sequential polymerization process wherein a propylene polymer is prepared first, followed by the preparation of copolymer The composition descπbed herein can be prepared using a Ziegler-Natta catalyst, a co-catalyst such as triethylaluminum ("TEA"), and an electron donor such as dicyclopentyldimethoxysilane ("DPCMS"), cyclohexylmethyldimethoxysilane ("CMDMS"), diisopropyldimethoxysilane ("DIPDMS"), or other election donor known in the art The catalyst system is introduced at the beginning of the polymerization of the propylene polymer and is transferred with the product propylene polymer to the

copolymenzalion reactor where it serves to catalyze the gas phase copolymeπzation of propylene and ethylene

The propylene polymer may be prepared using at least one reactor or may be prepared using a plurality of parallel reactors or reactors in series Preferably, the

homopolymeπzation process utilizes one or two liquid filled loop reactors in series Despite a preference for liquid filled loop reactors, the propylene polymer may also be prepared in a gas-phase reactor

Once formation of the propylene polymer is complete, resulting in either a homopolymer or ethylene propylene random copolymer having less than 1 5 weight percent ethylene, the resultant powder is passed through a degassing vessel so that excess propylene and other gasses may be removed from the fresh resin After degassing, the propylene polymer is passed to one or more gas phase reactors wherein propylene is copolymeπzed with ethylene in the presence of the propylene polymer previously produced and the catalyst transferred therewith

Propylene polymer crystallinity and isotacticity can be controlled by the ratio of co- catalyst to electron donor The appropπate ratio of co-catalyst to electron donor is dependent upon the catalyst and donor selected It is within the skill of the ordinarily skilled artisan to determine the appropπate ratio to arrive at a product having the presently described properties

The amount of hydrogen necessary to prepare the homopolymer component of the invention is dependent in large measure on the donor and catalyst system used It is within the skill of the ordinar> skilled artisan to select the appropriate quantity of hydrogen for a given catalyst/donor system to prepare a propylene polymer having the combination of properties disclosed herein without undue experimentation

For copolymeπzation, the gas phase composition of the reaclor(s) are maintained such that the ratio of the mols of ethylene in the gas phase to the total mols of ethylene and propylene is held constant In certain embodiments, this ratio can be maintained at from about 0 3 to about 0 55 In other embodiments, this ratio can be maintained at about 0 45 In still other embodiments, the ratio of the mols of ethylene in the gas phase to the total mols of ethylene and propylene can be maintained at 0 43 In order to maintain the desired molar ratio, monomer feeds of propylene and ethylene are adjusted as appropπate

Hydrogen can be added in the gas phase reactors) to control the molecular weight of the copolymer The atmospheric composition of the gas phase is maintained such that the ratio of hydrogen to ethylene (mol/mol) is held constant In certain embodiments, the ratio of hydrogen to ethylene is maintained at about 0 001 to about 0 03 In other embodiments, the ration of hydrogen to ethylene is maintained at 0 01 to about 0 03 In one embodiment, the ratio is about 0 01 In another embodiment, the ratio is about 0 025 In a further

embodiment, the ratio is about 0 001 5 Exemplary reactor conditions are described in Table 2

Table 2

Upon completion of the polymerization process, the polymer powder produced according to the above described procedure can be fed into an extruder When an extruder is employed, typically, a twin screw extruder is preferred in order to obtain the best melt mixing and dispersion Despite the preference for a twin-screw extruder, other extruders known in the art, such as a single screw extruder, may be used to achieve the desired melt mixing

Additives including, but not limited to, antioxidants, acid scavengers, nucleators, antistatics, long term heat agents, slip agents, pigments, processing aids, fillers, polyethylene, impact modifiers, compatabilizers, as well as combinations of any of the aforementioned additives, may be added to the extruder to prepare compositions having specific properties The extruded polymer strands are subsequently pelletized

The disclosures of each and every patent, patent application, and publication cited herein arc hereby incorporated herein by reference in their entirety

While this invention has been disclosed with reference to specific embodiments, it is apparent that other embodiments and vaπations of this invention may be devised by others skilled in the art without departing from the true spirit and scope of the invention The appended claims are intended to be construed to include all such embodiments and equivalent vaπations