Provided herein are polyethylene compositions with unimodal molecular weight distribution exhibiting an excellent balance of physical properties. The polyethylene compositions may have density of 0.935 to 0.975 g/cm.sup.3 and Melt Index (I.sub.2.16) of 0.1 to 1 g/10 min. Polyethylene compositions of certain embodiments may exhibit environmental stress crack resistance (ESCR, 10% Igepal, ASTM D1693 Cond. B) within the range from 45 to 80 hours, and/or (ESCR, 100% igepal, ASTM D1693 Cond. B) within the range from 70 to 250 hours. Such ESCR outperforms other unimodal resins of similar melt index and density, approaching ESCR performance of more expensive and complex resins with bimodal molecular weight distribution. The polyethylene compositions of certain embodiments may have two distinct crystalline fractions as shown by temperature rising elution fractionation (TREF).

A supported catalyst system is based on a transition metal carbene including the moiety M1=CR*).sub.2, wherein M.sup.1 is the transition metal and R* is hydrogen or a C.sub.1-C.sub.8 hydrocarbyl. The catalyst system can be supported on a metal oxide support such as silica or the catalyst can be self-supporting. Methods of making the catalyst system can involve precursors based on and/or reacted with aluminum alkyls, halides, and/or alkoxides. Methods of polymerizing cyclic olefins with the catalyst system can obtain polyalkenamers, cyclic olefin polymers, cyclic olefin copolymers, and other metathesis reaction products. The supported catalyst and/or monomer can be recovered and recycled to the polymerization reactor.

The invention relates to a solid catalyst system comprising a first chromium compound, a second chromium compound, a reaction product of an alkyl aluminium compound and a nitrogen containing compound and a silicon oxide support, wherein the first chromium compound is chromium trioxide or a compound convertible to chromium trioxide, the second chromium compound is a slilylchromate compound and the nitrogen containing compound is a cycloalkylamine compound having the general formula: R.sup.3—NH.sub.2, wherein R.sup.3 is selected from C3-C8 cycloalkyl groups.

The invention relates to a solid catalyst system comprising a first chromium compound, a second chromium compound, a reaction product of an alkyl aluminium compound and a nitrogen containing compound and a silicon oxide support, wherein the first chromium compound is chromium trioxide or a compound convertible to chromium trioxide, the second chromium compound is a slilylchromate compound and the nitrogen containing compound is a cycloalkylamine compound having the general formula: R.sup.3—NH.sub.2, wherein R.sup.3 is selected from C3-C8 cycloalkyl groups.

The invention relates to a solid catalyst system comprising a first chromium compound, a second chromium compound, a reaction product of an alkyl aluminium compound and a nitrogen containing compound and a silicon oxide support, wherein the first chromium compound is chromium trioxide or a compound convertible to chromium trioxide, the second chromium compound is a slilylchromate compound and the nitrogen containing compound is a cycloalkylamine compound having the general formula: R.sup.3—NH.sub.2, wherein R.sup.3 is selected from C3-C8 cycloalkyl groups.

A bimodal polymer composition comprising a lower molecular weight homopolymer and a higher molecular weight copolymer wherein the bimodal polymer composition has a density of from about 0.930 gram per cubic centimeter (g/cc) to about 0.970 g/cc, a ratio of high load melt index:melt index of from about 10 to about 150 and an Environmental Stress Crack Resistance (ESCR) of from about 25 hours to about 300 hours when measured in accordance with ASTM D1693 or ASTM D2561. A chromium-catalyzed polymer composition comprising (i) a lower molecular weight homopolymer and (ii) a higher molecular weight copolymer, wherein the bimodal polymer composition has an Environmental Stress Crack Resistance (ESCR) of from about 25 hours to about 300 hours when measured in accordance with ASTM D1693 or ASTM D2561.

A bimodal polymer composition comprising a lower molecular weight homopolymer and a higher molecular weight copolymer wherein the bimodal polymer composition has a density of from about 0.930 gram per cubic centimeter (g/cc) to about 0.970 g/cc, a ratio of high load melt index:melt index of from about 10 to about 150 and an Environmental Stress Crack Resistance (ESCR) of from about 25 hours to about 300 hours when measured in accordance with ASTM D1693 or ASTM D2561. A chromium-catalyzed polymer composition comprising (i) a lower molecular weight homopolymer and (ii) a higher molecular weight copolymer, wherein the bimodal polymer composition has an Environmental Stress Crack Resistance (ESCR) of from about 25 hours to about 300 hours when measured in accordance with ASTM D1693 or ASTM D2561.

The invention relates to a solid catalyst system comprising a chromium compound, a metal compound, an aluminium compound and a silicon oxide support, wherein the silicon oxide support has an average particle diameter in the range between ≥20 and ≤50 μm, a pore volume in the range between ≥1.7 ml/g and ≤3 ml/g, and a surface area in the range between ≥400 m.sup.2/g and ≤800 m.sup.2/g, and wherein the aluminium alkoxide compound has the formula
R.sub.1—Al—OR.sub.2
wherein R.sub.1 is selected from (C.sub.1-C.sub.8) alkyl groups and OR.sub.2 is selected from (C.sub.1-C.sub.8) alkoxyl groups.

The invention relates to a solid catalyst system comprising a chromium compound, a metal compound, an aluminium compound and a silicon oxide support, wherein the silicon oxide support has an average particle diameter in the range between ≥20 and ≤50 μm, a pore volume in the range between ≥1.7 ml/g and ≤3 ml/g, and a surface area in the range between ≥400 m.sup.2/g and ≤800 m.sup.2/g, and wherein the aluminium alkoxide compound has the formula
R.sub.1—Al—OR.sub.2
wherein R.sub.1 is selected from (C.sub.1-C.sub.8) alkyl groups and OR.sub.2 is selected from (C.sub.1-C.sub.8) alkoxyl groups.

The invention relates to a solid catalyst system comprising a chromium compound, a metal compound, an aluminium compound and a silicon oxide support, wherein the silicon oxide support has an average particle diameter in the range between ≥20 and ≤50 μm, a pore volume in the range between ≥1.7 ml/g and ≤3 ml/g, and a surface area in the range between ≥400 m.sup.2/g and ≤800 m.sup.2/g, and wherein the aluminium alkoxide compound has the formula
R.sub.1—Al—OR.sub.2
wherein R.sub.1 is selected from (C.sub.1-C.sub.8) alkyl groups and OR.sub.2 is selected from (C.sub.1-C.sub.8) alkoxyl groups.