Polyethylene Pipe Resin with High Resistance to Slow Crack Growth

Abstract

The present invention relates to a polyethylene composition comprising a base resin which comprises (A) a first ethylene homo- or copolymer fraction, and (B) a second ethylene-hexene-1 copolymer fraction, wherein fraction (A) has a lower molecular weight than fraction (B) and wherein fraction (B) is present in an amount of from 51.0 to 58.5 wt. %, preferably 52.0 to 57.5 wt. %, more preferably 53.0 to 57.0 wt. % based on the total weight of the base resin, wherein fraction (B) of the base resin has a content of units derived from hexene-1 from 0.80 to 1.45 mol %, preferably of from 0.82 to 1.35 mol % and more preferably of from 0.85 to 1.30 mol %, wherein the base resin has a number average molecular weight Mn of 8,500 g/mol or higher, and wherein the polyethylene composition has a melt flow rate MFRs from 0.10 to 0.30 g/10 min, preferably from 0.15 to 0.28, and still more preferably from 0.16 to 0.25 g/10 min, to a process for producing the polyethylene composition, to an article, especially a pipe comprising the polyethylene composition and to the use of the polyethylene composition for the production of an article, especially a pipe.

Claims

1. A polyethylene composition comprising a base resin which comprises (A) a first ethylene homo- or copolymer fraction, and (B) a second ethylene-hexene-1 copolymer fraction, wherein fraction (A) has a lower molecular weight than fraction (B) and wherein fraction (B) is present in an amount of from 51.0 to 58.5 wt. %, based on the total weight of the base resin, wherein fraction (B) of the base resin has a content of units derived from hexene-1 from 0.80 to 1.45 mol %, wherein the base resin has a number average molecular weight Mn of 8,500 g/mol or higher, and wherein the polyethylene composition has a melt flow rate MFR.sub.5 from 0.10 to 0.30 g/10 min.

2. Polyethylene composition according to claim 1 wherein the composition has a strain hardening modulus of 80 MPa or higher.

3. Polyethylene composition according to claim 1 wherein the base resin has a density of at least 945 kg/m.sup.3.

4. Polyethylene composition according to claim 1 wherein the base resin has a content of units derived from hexene-1 of 0.44 to 0.70 mol %.

5. Polyethylene composition according to claim 1 wherein the composition has a Charpy Impact Strength (CIS) at 23° C. of higher than 35 kJ/m.sup.2, or a Charpy Impact Strength (CIS) at 0° C. of higher than 22.5 kJ/m.sup.2, or a Charpy Impact Strength (CIS) at −20° C. of higher than 14.7 kJ/m.sup.2.

6. Polyethylene composition according to claim 1 wherein fraction (A) of the base resin has an MFR.sub.2 as measured in accordance with ISO 1133 of 150 to 600 g/10 min.

7. Polyethylene composition according to claim 2 wherein the polyethylene composition has a critical temperature Tc in the rapid crack propagation test of −10° C. or lower.

8. Polyethylene composition according to claim 1 wherein the composition further comprises carbon black.

9. Polyethylene composition according to claim 8 wherein fraction (B) of the base resin is present in the base resin in an amount of from 54 to 57 wt. %, based on the total weight of the base resin, or wherein the composition has a density of from 953 to 965 kg/m.sup.3, or wherein the base resin has a number average molecular weight of 9,000 g/mol or higher.

10. Polyethylene composition according to claim 1 wherein the composition does not comprise carbon black and the base resin has a total content of units derived from hexene-1 of 0.44 to 0.65 mol %.

11. Polyethylene composition according to claim 10 wherein fraction (B) of the base resin is present in the base resin in an amount of from 54 to 57 wt. %, based on the total weight of the base resin, or wherein the composition has a density of from 946 to 955 kg/m.sup.3, or wherein the base resin has a number average molecular weight Mn of 9,300 g/mol or higher.

12. A process for producing a polyethylene composition according to claim 10 wherein the base resin is produced in a multi-stage polymerization process in the presence of a Ziegler-Natta catalyst.

13. An article comprising the polyethylene composition according to claim 1.

14. The article according to claim 13 being a pipe or pipe fitting.

15. A method, comprising producing an article using the polyethylene composition of claim 1.

16. The polyethylene composition of claim 1, wherein fraction (B) is present in an amount of from 53.0 to 57.0 wt %.

17. The polyethylene composition of claim 1, wherein fraction (B) of the base resin has a content of units derived from hexene-1 from 0.85 to 1.30 mol %.

18. The polyethylene composition of claim 8, wherein the base resin has a total content of units derived from hexene-1 of 0.50 to 0.70 mol %.

19. The polyethylene composition of claim 8, wherein fraction (B) of the base resin has a content of units derived from hexene-1 from 0.9 to 1.45 mol %.

20. The polyethylene composition of claim 10, wherein the composition does not comprise carbon black and wherein fraction (B) of the base resin has a content of units derived from hexene-1 from 0.8 to 1.35 mol %.

Description

EXAMPLES

1) Polyethylene Compositions and Pipes Comprising Carbon Black

[0183] Polyethylene base resins and compositions according to the invention (IE1 to 1E8) and for comparison (CE1 to CE4) were produced using a Ziegler-Natta catalyst which was prepared according to Example 1 of EP 1 378 528 A1 (catalyst

[0184] A)

IE1

[0185] A loop reactor having a volume of 50 dm.sup.3 was operated at a temperature of 70° C. and a pressure of 57 bar. Into the reactor were fed ethylene, propane diluent and hydrogen. Also a solid polymerization catalyst component produced as described above was introduced into the reactor together with triethylaluminium cocatalyst so that the molar ratio of Al/Ti was about 15. The estimated production split was 2 wt. %.

[0186] A stream of slurry was continuously withdrawn and directed to a loop reactor having a volume of 150 dm.sup.3 and which was operated at a temperature of 95° C. and a pressure of 55 bar. Into the reactor were further fed additional ethylene, propane diluent and hydrogen so that the ethylene concentration in the fluid mixture was 3.4% by mole and the hydrogen to ethylene ratio was 415 mol/kmol. The estimated production split was 16 wt. %. The ethylene homopolymer withdrawn from the reactor had MFR.sub.2 of 657 g/10 min.

[0187] A stream of slurry from the reactor was withdrawn intermittently and directed into a loop reactor having a volume of 350 dm.sup.3 and which was operated at 95° C. temperature and 54 bar pressure. Into the reactor was further added a fresh propane, ethylene, and hydrogen so that the ethylene concentration in the fluid mixture was 3.3 mol-% and the molar ratio of hydrogen to ethylene was 345 mol/kmol. The ethylene homopolymer withdrawn from the reactor had MFR.sub.2 of 350 g/10 min. The estimated production split was 27 wt. %.

[0188] The slurry was withdrawn from the loop reactor intermittently and directed to a flash vessel operated at a temperature of 50° C. and a pressure of 3 bar. From there the polymer was directed to a fluidized bed gas phase reactor operated at a pressure of 20 bar and a temperature of 80° C. Additional ethylene and 1-hexene comonomer, nitrogen as inert gas and hydrogen were added so that the molar ratio of hydrogen to ethylene was 7 mol/kmol and the molar ratio of 1-hexene to ethylene was 59 mol/kmol. The estimated production split was 55 wt. %. The polymer had a melt flow rate MFR.sub.5 of 0.20 g/10 min and a density of 946.0 kg/m.sup.3.

1E2 to 1E8 and CE1 to CE4

[0189] The procedure of IE1 was repeated by changing reactor conditions as described in Table 1.

[0190] Polymerization conditions and properties of the produced base resins and polyethylene compositions of the inventive and comparative examples are shown in Tables 1 and 2, respectively.

[0191] The polymer powder of each of the samples IE1 to IE 8 and CE1 to CE4 was mixed under nitrogen atmosphere with 5.5% of carbon black master-batch (CB content 40%), 2500 ppm of antioxidants and 400 ppm Ca-stearate. Then it was compounded and extruded under nitrogen atmosphere to pellets by using a JSW CIMP90 twin screw extruder so that the SEI was about 180 kWh/ton and the melt temperature 250° C. to obtain the polyethylene compositions.

[0192] Comparative Examples CE5 and CE6 are commercially available black polyethylene compositions Eltex TUB 121N6000 and Eltex TUB 121N9000, respectively.

TABLE-US-00001 TABLE 1 Example IE1 IE2 IE3 IE4 IE5 IE6 IE7 IE8 CE1 CE2 CE3 CE4 Catalyst A A A A A A A A A A A A Prepoly. reactor Temp. (° C.) 70 70 70 70 70 70 70 70 70 70 70 70 Press. (kPa) 5771 5765 5752 5760 5770 5715 5755 5760 5590 5602 5593 5604 Split (wt. %) 2 2 2 2 2 2 2 2 2 2 2 2 First loop reactor Temp. (° C.) 95 95 95 95 95 95 95 95 95 95 95 95 Press. (kPa) 5536 5533 5542 5535 5540 5535 5530 5540 5424 5400 5412 5406 C2 conc. (mol %) 3.4 3.7 4.6 4.1 4.0 3.9 3.9 3.9 5.3 5.0 6.3 5.5 H2/C2 ratio (mol/kmol) 415 376 394 405 390 380 380 385 331 362 330 373 Split (wt. %) 16 16 16 16 16 16 16 16 13 11 11 12 MFR2 (g/10 min) 657 168 128 310 280 260 260 260 160 192 208 284 Second loop reactor Temp. (° C.) 95 95 95 95 95 95 95 95 95 95 95 95 Press. (kPa) 5393 5392 5392 5390 5390 5394 5391 5391 5390 5391 5389 5390 C2 conc. (mol %) 3.3 3.7 3.6 3.6 3.7 3.7 3.6 3.6 4.0 3.8 4.0 3.9 H2/C2 ratio (mol/kmol) 345 322 392 395 375 370 365 365 366 368 371 374 Split (wt. %) 27 26 27 27 27 27 27 27 28 29 26 26 MFR2 (g/10 min) 350 256 272 400 300 290 280 280 380 280 360 331 Gas phase reactor Temp. (° C.) 80 80 80 80 80 80 80 80 85 85 85 85 Press. (kPa) 2002 2000 2000 2000 2002 2002 2000 2000 2000 2000 2000 2000 H2/C2 ratio (mol/kmol) 7 7 7 8 7 6 5 5 13 16 3 21 C6/C2 ratio (mol/kmol) 59 57 53 61 59 62 61 60 35 35 59 59 Split (wt. %) 55 56 55 55 55 55 55 55 57 58 61 60

TABLE-US-00002 TABLE 2 Example IE1 IE2 IE3 IE4 IE5 IE6 IE7 Base resin properties Density [kg/m.sup.3] 946.0 946.0 946.6 945.0 946.0 945.0 945.0 Polyethylene composition properties MFR.sub.5 [g/10 min] 0.21 0.21 0.21 0.29 0.26 0.22 0.21 MFR.sub.21 [g/10 min] 6.16 6.06 6.73 8.95 8.39 7.49 7.52 FRR.sub.21/5 29.3 28.9 32.0 30.9 32.3 34.0 35.8 Mn [kg/mol] 10.4 10.2 9.97 9.06 9.35 9.78 9.74 Mw [kg/mol] 260 264 260 240.5 246.5 274.0 265.5 Mz [kg/mol] 1,290 1,290 1,310 1,325 1,360 1,575 1,520 Mw/Mn 25.0 25.9 26.1 26.6 26.4 28.0 27.3 C6 total [mol %] 0.64 0.64 0.60 0.65 0.66 0.64 0.62 C6 in HMW fraction [mol %] 1.16 1.17 1.09 1.18 1.20 1.16 1.13 Eta.sub.747 [kPa*s] 401.1 424.3 465.9 405.4 453.7 698.2 684.4 SH modulus [MPa] 91.3 94.1 94.1 90.4 96.0 99.2 98.7 Density [kg/m.sup.3] 956.9 956.5 958.0 957.9 957.3 957.0 957.2 SPTR (12.0 MPa/20° C.) [h] 282 273 373 345 253 204 241 Tc [° C.] −18.5 −18.6 −18.6 −12.9 −12.0 −15.7 −17.3 CIS (23° C.) [kJ/m.sup.2] 49.2 50.5 45.5 35.4 37.1 41.9 42.1 CIS (0° C.) [kJ/m.sup.2] 36.0 36.4 33.7 CIS (−20° C.) [kJ/m.sup.2] 22.1 22.9 22.2 14.8 15.6 18.7 18.6 PLT+, 32 mm pipes [h] 2350 2227 3432 4578 PLT+, 110 mm pipes [h] 3363 4330 3652 ACT [h] 3646 3712 4347 4661 Example IE8 CE1 CE2 CE3 CE4 CE5 CE6 Base resin properties Density [kg/m.sup.3] 946.0 948.9 948.4 942.5 945.5 NA NA Polyethylene composition properties MFR.sub.5 [g/10 min] 0.23 0.31 0.31 0.21 0.62 0.28 0.22 MFR.sub.21 [g/10 min] 7.93 8.04 7.74 6.18 12.88 7.9 7.5 FRR.sub.21/5 34.5 25.9 25.0 29.4 20.8 28.2 34.1 Mn [kg/mol] 9.69 9.5 9.42 9.72 9.81 7.98 9.23 Mw [kg/mol] 265.5 230.5 228.5 257.5 192.5 217.5 240 Mz [kg/mol] 1,525 1,150 1,100 1,295 909.5 1,070 1,245 Mw/Mn 27.4 24.3 24.3 26.5 19.6 27.3 26.0 C6 total [mol %] 0.58 0.48 0.44 0.88 0.76 0.46 0.46 C6 in HMW fraction [mol %] 1.05 0.83 0.77 1.47 1.26 Eta.sub.747 [kPa*s] 590.2 253.2 248.3 426.3 101.9 265.6 828.1 SH modulus [MPa] 94 64.7 65.3 111 65.1 81.9 87.3 Density [kg/m.sup.3] 957.8 959.0 960.6 955.6 955.7 960.0 959.4 SPTR (12.0 MPa/20° C.) [h] 241 614 431 87 79 Tc [° C.] −13.6 −13.6 −13.7 −18.5 −6.4 −4.1 CIS (23° C.) [kJ/m.sup.2] 37.6 30.4 30.8 55.7 32.2 28.2 35.8 CIS (0° C.) [kJ/m.sup.2] 22.5 22.1 41.5 21.7 17.6 22.4 CIS (−20° C.) [kJ/m.sup.2] 16.8 11.3 14.3 24.6 10.0 9.4 14.6 PLT+, 32 mm pipes [h] 1936 PLT+, 110 mm pipes [h] ACT [h] 3234

[0193] 1E1 to IE8 demonstrate the combination of excellent slow crack growth resistance (as demonstrated by the strain hardening modulus) together with very good impact resistance and good rapid crack propagation resistance (low critical temperature), while also meeting the requirements of PE100 standard. Furthermore, the compositions of 1E4 to 1E8 also show excellent behaviour in the accelerated point loading test and in the ACT test.

[0194] This advantageous combination of properties is achieved by the relatively high Mn of the composition, the specific amount of hexene-1 in the high molecular weight fraction, the specific amount (weight fraction) of the high molecular weight fraction, the MFR in the defined range and the specific comonomer used (hexene-1).

[0195] Comparative Examples 1 to 6 demonstrate that deviation from the proposed polymer structure yield inferior combination of the aforementioned polymer properties. CE1 and CE2 contain 0.83 and 0.77 mol %, respectively, of hexene-1 in the high Mw fraction, resulting in the immediate reduction of the strain hardening modulus (used as the measure of slow crack growth resistance). On the other side, CE3 contains 1.47 mol % of hexene-1 in the high Mw fraction, i.e. more comonomer than the inventive examples. This results in higher strain hardening modulus but this material fails to meet the requirement of PE100 standard, which is, i.a., to withstand 100 hours in the short term pressure resistance testing at 12.0 MPa and 20° C.

[0196] CE4 has 1.26 mol % of hexene-1 in the high Mw fraction, i.e. more comonomer in the high Mw fraction than the comparative examples, but at the same time it has lower strain hardening modulus due to a higher melt flow rate, and also the critical temperature Tc, indicating the rapid crack propagation resistance behaviour, is inferior.

[0197] Comparative examples Eltex TUB 121 N6000 and Eltex TUB 121 N9000, while having high strain hardening modulus values, which, however, are still lower than those of the inventive examples, demonstrate lower Charpy impact strength. For Eltex TUB 121N6000 also the inferior sagging resistance (as measured by the eta.sub.747 value) and the inferior rapid crack propagation as measured by the critical temperature T.sub.cr (only −4.1° C.) needs to be noted.

2) Polyethylene Composition not Comprising Carbon Black

[0198] Polyethylene base resins and compositions according to the invention (1E9 to 1E12) and for comparison (CE7 to CE10) were either produced using a Ziegler-Natta catalyst which was prepared according to Example 1 of EP 1 378 528 A1 (catalyst A), or using a similar catalyst B which was prepared as follows:

Complex Preparation

[0199] 87 kg of toluene was added into the reactor. Then 45.5 kg Bomag A (Butyloctyl magnesium) in heptane was also added in the reactor. 161 kg 99.8% 2-ethyl-1-hexanol was then introduced into the reactor at a flow rate of 24-40 kg/h. The molar ratio between BOMAG-A and 2-ethyl-1-hexanol was 1:1.83.

Solid Catalyst Component Preparation

[0200] 330 kg silica (calcined silica, Sylopol® 2100) and pentane (0.12 kg/kg carrier) were charged into a catalyst preparation reactor. Then EADC (Ethylaluminium dichloride) (2.66 mol/kg silica) was added into the reactor at a temperature below 40° C. during two hours and mixing was continued for one hour. The temperature during mixing was 40-50° C. Then Mg complex prepared as described above was added (2.56 mol Mg/kg silica) at 50° C. during two hours and mixing was continued at 40-.50° C. for one hour. 0.84 kg pentane/kg silica was added into the reactor and the slurry was stirred for 4 hours at the temperature of 40-50° C. . Finally, TiCl.sub.4 (1.47 mol/kg silica) was added during at least 1 hour at 55° C. to the reactor. The slurry was stirred at 50−60° C. for five hours. The catalyst was then dried by purging with nitrogen.

[0201] Molar composition of the ready catalyst is: Al/Mg/Ti=1.5/1.4/0.8 (mol/kg silica).

1E9

[0202] A loop reactor having a volume of 50 dm.sup.3 was operated at a temperature of 70° C. and a pressure of 57 bar. Into the reactor were fed ethylene, propane diluent and hydrogen. Also a solid polymerization catalyst component B produced as described above was introduced into the reactor together with triethylaluminium cocatalyst so that the molar ratio of Al/Ti was about 15. The estimated production split was 2 wt. %.

[0203] A stream of slurry was continuously withdrawn and directed to a loop reactor having a volume of 150 dm.sup.3 and which was operated at a temperature of 95° C. and a pressure of 55 bar. Into the reactor were further fed additional ethylene, propane diluent and hydrogen so that the ethylene concentration in the fluid mixture was 3.9% by mole and the hydrogen to ethylene ratio was 390 mol/kmol. The estimated production split was 16 wt. %. The ethylene homopolymer withdrawn from the reactor had MFR.sub.2 of 280 g/10 min.

[0204] A stream of slurry from the reactor was withdrawn intermittently and directed into a loop reactor having a volume of 350 dm.sup.3 and which was operated at 95° C. temperature and 52 bar pressure. Into the reactor was further added a fresh propane, ethylene, and hydrogen so that the ethylene concentration in the fluid mixture was 3.7 mol-% and the molar ratio of hydrogen to ethylene was 370 mol/kmol. The ethylene homopolymer withdrawn from the reactor had MFR.sub.2 of 282 g/10 min. The estimated production split was 27 wt. %.

[0205] The slurry was withdrawn from the loop reactor intermittently and directed to a flash vessel operated at a temperature of 50° C. and a pressure of 3 bar. From there the polymer was directed to a fluidized bed gas phase reactor operated at a pressure of 20 bar and a temperature of 85° C. Additional ethylene and 1-hexene comonomer, nitrogen as inert gas and hydrogen were added so that the molar ratio of hydrogen to ethylene was 7 mol/kmol and the molar ratio of 1-hexene to ethylene was 46 mol/kmol. The estimated production split was 55 wt. %. The polymer had a melt flow rate MFR.sub.5 of 0.21 g/10 min and a density of 946.6 kg/m.sup.3.

1E10 to 1E12 and CE7 to CE10

[0206] The procedure of IE9 was repeated by changing catalyst and reactor condition as described in Table 3.

[0207] Polymerization conditions and properties of the produced base resins and polyethylene compositions of the inventive and comparative examples are shown in Tables 3 and 4, respectively.

[0208] Compounding of the polyethylene composition was done in the following ways:

CE7

[0209] The polymer powder was mixed under nitrogen atmosphere with 3000 ppm of antioxidants, 3000 ppm UV-stabiliser and 400 ppm Ca-stearate. Then it was compounded and extruded under nitrogen atmosphere to pellets by using a JSW CIMP90 twin screw extruder so that the SEI was about 180 kWh/ton and the melt temperature 250° C.

IE9 and CE8

[0210] The polymer powder was mixed under nitrogen atmosphere with 3000 ppm of antioxidants, 2000 ppm UV-stabiliser and 400 ppm Ca-stearate. Then it was compounded and extruded under nitrogen atmosphere to pellets by using a JSW CIMP90 twin screw extruder so that the SEI was about 180 kWh/ton and the melt temperature 250° C.

1E10, IE10a and CE9

[0211] The polymer powder was mixed under nitrogen atmosphere with 1% of orange colour master-batch (pigment orange 72 (2%) and pigment brown 24 (40%) on LDPE carrier), 3000 ppm of antioxidants, 2000 ppm UV-stabiliser and 400 ppm Ca-stearate. Then it was compounded and extruded under nitrogen atmosphere to pellets by using a JSW CIMP90 twin screw extruder so that the SEI was about 180 kWh/ton and the melt temperature 250° C.

1E11, 1E12 and CE10

[0212] The polymer powder was mixed under nitrogen atmosphere with 1.9% of blue colour master-batch (pigment blue 29 (4%), pigment blue 15:4 (5%) and pigment white 6 (1%) on LDPE carrier), 3000 ppm of antioxidants, 2000 ppm UV-stabiliser and 400 ppm Ca-stearate. Then it was compounded and extruded under nitrogen atmosphere to pellets by using a JSW CIMP90 twin screw extruder so that the SEI was about 180 kWh/ton and the melt temperature 250° C.

TABLE-US-00003 TABLE 3 Example IE9 IE10 IE10a IE11 IE12 CE7 CE8 CE9 CE10 Catalyst A A A A A B A A A Prepoly. reactor Temp. (° C.) 70 70 70 70 70 70 70 70 70 Press. (kPa) 5725 5725 5740 5760 5755 5791 5715 5755 5760 Split (wt. %) 2 2 2 2 2 2 2 2 2 First loop reactor Temp. (° C.) 95 95 95 95 95 95 95 95 95 Press. (kPa) 5530 5530 5550 5540 5535 5590 5535 5530 5540 C2 conc. (mol %) 3.9 3.9 3.8 3.9 3.8 4.6 3.8 3.9 3.9 H2/C2 ratio (mol/kmol) 390 385 400 385 385 303 385 385 385 Split (wt. %) 16 16 16 16 16 23 16 16 16 MFR2 (g/10 min) 280 270 290 272 270 304 280 280 260 Second loop reactor Temp. (° C.) 95 95 95 95 95 95 95 95 95 Press. (kPa) 5395 5395 5400 5391 5390 5198 5394 5391 5391 C2 conc. (mol %) 3.7 3.7 3.6 3.6 3.6 2.6 3.7 3.6 3.6 H2/C2 ratio (mol/kmol) 370 370 380 365 365 446 380 375 375 Split (wt. %) 27 27 27 27 27 24 27 27 27 MFR2 (g/10 min) 282 280 292 273 275 420 310 300 300 Gas phase reactor Temp. (° C.) 80 80 80 80 80 85 80 80 80 Press. (kPa) 2002 2002 2000 2000 2001 2000 2002 2000 2000 H2/C2 ratio (mol/kmol) 7 7 7 7 7 10 11 11 11 C6/C2 ratio (mol/kmol) 46 47 49 46 45 40 36 35 36 Split (wt. %) 55 55 55 55 55 51 55 55 55

TABLE-US-00004 TABLE 4 Example IE9 IE10 IE10a IE11 IE12 CE7 CE8 CE9 CE10 Base resin properties Density [kg/m.sup.3] 946.6 946.6 946.5 946.7 946.7 950.3 949.0 949.0 949.0 Polyethylene composition properties MFR.sub.5 [g/10 min] 0.21 0.2 0.25 0.21 0.22 0.29 0.22 0.22 0.22 MFR.sub.21 [g/10 min] 6.04 6.7 7.9 5.89 6.25 10.4 6.19 6.61 6.28 FRR.sub.21/5 28.8 33.5 31.6 28.0 28.4 35.9 28.1 30.0 28.5 Mn [kg/mol] 9.2 8.7 9.4 9.0 10.3 9.39 9.10 9.64 Mw [kg/mol] 275.0 247 270.5 260.5 228.0 271.5 267.0 258.5 Mz [kg/mol] 1,490 1,235 1,470 1,455 1,225 1,455 1,350 1,360 Mw/Mn 30 28.3 28.9 28.9 22.1 28.9 29.3 26.8 C6 [mol %] total 0.53 0.61 0.52 0.53 0.38 0.38 0.35 0.39 C6 in HMW 0.96 1.11 0.95 0.96 0.75 0.69 0.64 0.71 fraction [mol %] Eta.sub.747 [kPa*s] 391.0 320.8 373.3 407.1 382.3 399.8 387.3 393.5 377.2 SH modulus [MPa] 95 84 88 88 86 73.0 72 73.1 69 Density kg/m.sup.3] 948.0 951 950 948.8 949.2 950.5 950.8 954.3 951.2 SPTR (12.0 137 169 413 771 322 1,036 7115 804 MPa/20° C.) [h] SPTR (5.8 50 120 MPa/80° C.) [h] SPTR (5.4 660 1636 MPa/80° C.) [h] Tc [° C.] −19.8 −14.7 CIS (23° C.) [kJ/m.sup.2] 43.7 41.8 40.7 40.5 CIS (−20° C.) [kJ/m.sup.2] 20.1 22.3 21 20 PLT+, 32 mm pipe 2329 1036 1179 582 949 [h] PLT+, 110 mm 4083 pipes [h] ACT [h] 3773 >2680 2046 4467 4174 2905 2639 1807 1777 NPT [h] >6800 >5300 >7000 7054 7978 3294

[0213] 1E9 to 1E12 demonstrate the combination of excellent slow crack growth resistance (as demonstrated by the strain hardening modulus), while also meeting the requirements of PE100 standard.

[0214] This advantageous combination of properties is achieved by the relatively high Mn of the composition, the specific amount of hexene-1 in the high molecular weight fraction, the specific amount (weight fraction) of the high molecular weight fraction, the MFR in the defined range and the specific comonomer used (hexene-1). Comparative Examples 7 to 10 demonstrate that deviation from the proposed polymer structure yield inferior combination of the aforementioned molecular design. CE7 to CE10 contain from 0.64 to 0.75 mol % of hexene-1 in the high Mw fraction, resulting in the immediate reduction of the strain hardening modulus (used as the measure of slow crack growth resistance) as well as ACT and NPT results.