Polyethylene composition and process for producing same

A particulate polyethylene composition which is prepared by polymerizing ethylene and an optional olefin having at least three carbon atoms in the presence of a macromonomer, wherein the macromonomer is an ethylene polymer having a terminal vinyl group, prepared by polymerizing ethylene, or an ethylene copolymer having a terminal vinyl group, prepared by copolymerizing ethylene and an olefin having at least three carbon atoms, and

• the macromonomer is characterized by having:
• (A) a number average molecular weight (Mn) in the range of 9,000 to 50,000, and
• (B) a ratio (Mw/Mn) of weight average molecular weight (Mw) to number average molecular weight (Mn), in the range of 2 to 5;
• (Q) a frequency of long chain branches of smaller than 0.01 per 1,000 carbon atoms, and
• (R) a frequency of short chain branches of smaller than 0.01 per 1,000 carbon atoms;
• and the polyethylene composition is characterized by comprising:
• (C) based on the weight of the polyethylene composition, 1% to 99% by weight of branched polyethylene which is a copolymer derived from ethylene, the macromonomer and an optional olefin having at least three carbon atoms, and 1% to 99% by weight of the macromonomer, and
• the polyethylene composition is further characterized by having:
• (D) a density in the range of 0.890 g/cm3 to 0.980 g/cm3,
• (E) a weight average molecular weight (Mw) in the range of 30,000 to 10,000,000,
• (F) a ratio (Mw/Mn) of weight average molecular weight (Mw) to number average molecular weight (Mn), in the range of 2 to 30,
• (G) a frequency of long chain branches at least 0.01 but smaller than 0.1 per 1,000 carbon atoms, and
• (H) a shrinking factor (g′ value) as determined by a combination of gel permeation chromatography (GPC) and on-line intrinsic viscosity measurements, in the range of at least 0.1 but smaller than 0.9, and
• (P) a powder bulk density in the range of 0.15 g/cm3 to 0.50 g/cm3, and satisfying the following relationship (3):
• (M) MS190>22×MFR−0.88 (3)
• wherein MS190 is a melt strength (MS) (mN) as measured at a temperature of 190° C., and MFR is a melt flow rate (g/10 min.) as measured under a load of 2.16 kg and at a temperature of 190° C., and further satisfying the following relationship (27):
• (M′) MS160>110−110×log(MFR) (27)
• wherein MS160 is a melt strength (MS) (mN) as measured at a temperature of 160° C., and MFR is a melt flow rate (g/10 min.) as measured under a load of 2.16 kg and at a temperature of 190° C.