Ethylene polymerization catalyst and catalyst system

An ethylene polymerization catalyst and a catalyst system which provides an ethylene copolymer which, when formed into a film, is characterized by the combination of high stiffness and impact strength. The ethylene polymerization catalyst is formed by contacting a support with an organosilicon compound. The so-treated support is thereupon contacted, in a second step, with a dialkylmagnesium compound or complex. In a third step, the product of the second step is contacted with an alcohol or silane compound. This product, in turn, in a fourth step, is contacted with a transition metal compound. Finally, in a fifth and concluding step, the product of the fourth step is contacted with a Group 13 metal-containing compound. The second and third, as well as the third and fourth contacting steps may be reversed.

FIELD OF THE INVENTION
 The present invention relates to an ethylene polymerization catalyst which
 is employed in the polymerization of an ethylene copolymer, and more
 particularly to an in-situ prepared ethylene copolymer resin which has
 unique melt elastic properties when the resin is in its reactor-made or
 pelletized forms. The melt elastic properties observed by the ethylene
 copolymer resin of the present invention are not found in ethylene
 copolymers known heretofore, and importantly provide enhanced-impact
 strength properties to films that are produced therefrom.
 The present invention is also directed to a polymerization catalyst.
 BACKGROUND OF THE INVENTION
 The successful development of linear low density polyethylene (LLDPE) has
 forever changed the character of the polyethylene industry. For over fifty
 years, low density polyethylene (LDPE) was produced at pressures ranging
 up to 345 MPa (50,000 psi) and temperatures of about 300.degree. C.
 Technology was then developed in subsequent years which was capable of
 operating at less than 2 MPa (300 psi) and near about 100.degree. C. This
 technologic development has rapidly established itself as a low cost route
 to producing LLDPE.
 LLDPE, which is typically made using a transition metal catalyst rather
 than a free-radical catalyst, as required for LDPE, is characterized by
 linear molecules having no long-chain branching; short-chain branching is
 instead present and is the primary determinant of resin density. The
 density of commercially available LLDPE typically ranges from 0.915-0.940
 g/cm.sup.3. Moreover, commercially available LLDPEs generally exhibit a
 crystallinity of from about 25-60 vol. %, and a melt index which can range
 from 0.01 g/10 min. to several hundred g/10 min.
 Many commercial LLDPEs are available which contain one or more comonomers
 such as propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene and
 mixtures thereof. The specific selection of a comonomer for LLDPE is based
 primarily on process compatibility, cost and product design.
 In today's polyethylene industry, LLDPEs are used in a wide variety of
 applications including film forming, injection molding, rotomolding, and
 wire and cable fabrication. A principal area for LLDPE copolymers is in
 film forming applications since such copolymers typically exhibit high
 dart impact, high Elmendorf tear, high tensile strength and high
 elongation, in both the machine direction (MD) and the transverse
 direction (TD), compared with counterpart LDPE resins.
 Examples of previous developmental trends in this field include U.S. Pat.
 Nos. 5,260,245; 5,336,652; and 5,561,091, all to Mink et al., which
 disclose LLDPE films that exhibit the above properties made from
 polymerizing ethylene and at least one comonomer in the presence of a
 polymerization cocatalyst and vastly distinct transition metal catalysts.
 Specifically, in the '245 patent the transition metal catalyst is formed
 by treating silica having reactive OH groups with a dialkylmagnesium
 compound in a solvent; adding to said solvent a carbonyl-containing
 compound and then treating with a transition metal compound.
 In the '652 patent, the transition metal catalyst is prepared by treating a
 support having a reduced surface OH content with an organomagnesium
 compound; treating the product with a silane compound having the formula
 R.sub.x.sup.1 SiR.sub.y.sup.2 wherein R.sup.1 is R.sub.w --O where R.sub.w
 is hydrocarbyl containing 1 to 10 carbon atoms; R.sup.2 is halogen,
 hydrocarbyl having 1 to 10 carbon atoms or hydrogen; x is 1, 2, 3 or 4 and
 y is 0, 1, 2 or 3 with the proviso that x+y=4, and a transition metal
 compound. In this reference, reduction of surface OH content of the silica
 is effectuated by heating or by treatment with an aluminum compound.
 The transition metal catalyst employed in the '091 patent is one that is
 obtained by contacting silica having reactive OH groups with a
 dialkylmagnesium compound in a solvent; adding a mixture of an alcohol and
 SiCl.sub.4 thereto with subsequent treatment with a transition metal
 catalyst.
 U.S. Pat. No. 4,335,016 to Dombro provides a supported olefin
 polymerization catalyst which is prepared by (1) forming a mixture of a
 calcined, finely divided porous support material and an alkyl magnesium
 compound; (2) heating the mixture for a time and at a temperature
 sufficient to react the support and the alkyl magnesium compound; (3)
 reacting, by heating, the product of (2) with a
 hydrocarbylhydrocarbyloxysilane compound; (4) reacting, by heating, the
 product of (3) with a titanium compound that contains a halide; or (5)
 reacting the product of (2) with the reaction product of a
 hydrocarbylhydrocarbyloxysilane compound and a titanium compound that
 contains a halide; and (6) activating the catalyst product of (4) or (5)
 with a cocatalyst comprising hydrogen or an alkyl lithium, alkyl
 magnesium, alkyl aluminum, alkyl aluminum halide or alkyl zinc.
 Crotty et al. "Properties of Superior Strength Hexene Film Resins", Antec,
 193, pp. 1210 describes the properties of superior strength hexene
 copolymer resins that are prepared by the Unipol process. These resins
 reportedly yield films with exceptional strength properties (impact and
 tear strength) that are significantly higher than the standard hexene
 products and even higher than achieved with commercially available octene
 copolymers. At the same time, the resins show little or no difference in
 processability from standard LLDPE.
 The actual physical structures of polymers and abundant changes to same
 under various conditions is difficult to measure precisely and is commonly
 done indirectly. Rheology is often used in this regard, being especially
 suited to study the physical changes of polymers. Specifically, rheology
 deals with the deformation and flow of a polymer. Data so generated is
 used to provide information regarding the processability and even
 structural characterizations of the polymer.
 One rheological method that is typically used is conventional, high shear
 modification wherein disentanglement of the polymer or copolymer chains
 occur. If a polymer or copolymer melt is sheared mechanically, the melt
 may be processed in a less elastic state or possibly less viscous state
 than the initial resin. Effects of shear modification are typically
 manifested by changes in die swell, die entrance pressure losses, normal
 stresses and flow defects such as sharkskin surfaces and melt fracture.
 Although shear modification has been observed in LDPE, wherein
 disentanglement of the long chain branching of the polymer can readily
 occur, there was contention as to whether LLDPE could be shear modified.
 The question was answered in an article by The, et al. entitled "Shear
 Modification of Linear Low Density Polyethylene", Plastics and Rubber
 Processing and Applications, Vol. 4, No. 2, pg. 157 (1984). In this
 article, LLDPE was shear modified by preshearing the LLDPE resin under
 high shear conditions (&gt;3.9 sec.sup.-1) in an extruder. This study
 indicated that shear modification of the LLDPE polymer causes
 disentanglement to occur in the extruder, and that the relatively,
 disentangled polymer can be restored to a more highly elastic, entangled
 state by subjecting the melt to annealing or dissolving the shear modified
 polymer in a solvent.
 Another rheological technique employed in the prior art to determine the
 physical characteristics of a polymer is to measure the polydispersity or
 melt elasticity, ER, of the polymer melt. This technique is described in
 an article by R. Shroff, et al. entitled "New Measures of Polydispersity
 from Rheological Data on Polymer Melts", J. Applied Polymer Science, Vol.
 57, pp. 1605-1626 (1995).
 Using this Theological technique (ER calculation), prior art ethylene
 copolymer resins, such as described in The, et al., exhibit conventional
 melt elastic behavior in both the unsheared pelletized and sheared
 pelletized states. In the unsheared state, the ER values of prior art
 ethylene copolymers remain substantially unchanged in going from the
 powder to pellet form. Moreover, no change in ER is observed in dissolving
 the pellet in an organic solvent.
 As to the shear modified forms, prior art polymers exhibit a decrease in
 melt elasticity upon shear modification of the pelletized form. This
 signifies that the entanglement density of the polymer decreases. Upon
 dissolution of the shear modified form in an organic solvent, an increase
 in melt elasticity is observed with prior art ethylene copolymers. This
 increase in melt elasticity signifies a reversion of the polymer back to
 an entangled state.
 In prior art ethylene copolymers, no polymeric networks, i.e. systems of
 interconnected macromolecular chains, are present. This is verified by the
 above melt elastic behavior of prior art ethylene copolymers. As is known
 to those skilled in the art, the presence of network structures in
 polymers often provides polymers having improved properties. It is
 emphasized that while network structures are common in
 styrene-butadiene-styrene (SBS) block copolymers--See F. Morrison, et al.,
 "Flow-Induced Structure and Rheology of a Triblock Copolymer", J. Appl.
 Polymer Sci., Vol. 33, 1585-1600 (1987)--they are not known in LLDPE
 resins, until the advent of the present invention.
 SUMMARY OF THE INVENTION
 The present invention provides an ethylene polymerization catalyst that
 yields an ethylene copolymer that exhibits unique melt elastic properties
 that are not present in ethylene copolymers known heretofore. The unique
 melt elastic properties that are exhibited by the inventive ethylene
 copolymer are believed to be manifested by the presence of a network
 structure in the copolymer resin. While not being bound by any theory, it
 is hypothesized that the network structure in the present ethylene
 copolymer is formed at least in part of a rubber phase believed present in
 the copolymer which serves to interconnect the hard and soft phases of the
 ethylene copolymer.
 The presence of a network structure in the ethylene copolymer resin of the
 present invention is verified by the fact that the copolymer resin
 exhibits a reactor-made-to-pellet ER increase which is reversible, i.e.
 reduced, upon rheometric low shear modification. The term "ER" is used
 herein to measure the elasticity or the polydispersity of the ethylene
 copolymer which is derived from rheological data on polymer melts, See the
 article to Shroff, et al. suDra. The term "reactor-made" is used herein to
 denote powder, slurry or solution forms of the polymer resin which are
 formed in a polymerization vessel prior to melt processing.
 In addition to exhibiting the above melt elastic behavior, the pelletized
 form of the ethylene copolymer of the present invention exhibits a
 decrease in melt elasticity when dissolved in an organic solvent such as
 xylene. The solution dissolution ER value is nearly the same as that of
 the original reactor-made material.
 Specifically, the ethylene copolymer resin of the present invention
 comprises ethylene, as the major component, and at least one C.sub.4-8
 comonomer with the proviso that the resin, when in pelletized form, has a
 reduction in melt elasticity (ER) of 10% or more, to a final ER value of
 3.0 or less upon rheometric low shear modification or solution
 dissolution. A 10-30% reduction in ER of the pelletized form of the
 inventive copolymer resin upon rheometric low shear modification or
 solution dissolution is typically observed. Moreover, the ethylene
 copolymer resin of the present invention, when in reactor-made form,
 exhibits a partially reversible increase of 10% or more in said ER when
 pelletizing the same.
 The term "rheometric low shear modification is used in the present
 invention to indicate that the modification occurs in a rheometer that is
 capable of operating at shear rates of less than 1.0 sec.sup.-1 for a time
 period of from about 10 to about 60 minutes. This term is thus
 distinguishable from high shear modification, as disclosed in The, et al.,
 supra, wherein the modification is typically carried out in an extruder,
 prior to being introduced into a rheometer, at shear rates of 3.9
 sec.sup.-1 and higher.
 The term "solution dissolution" is used herein to indicate that the
 pelletized form of the ethylene copolymer resin can be dissolved in an
 organic solvent such as xylene. The importance of this technique is that
 it allows a means for estimating the ER value of the original reactor-made
 material if the same is not available.
 In addition to exhibiting unique melt elastic properties, the ethylene
 copolymer resin of the present invention is further characterized as
 having a base polymer density of about 0.930 g/cm.sup.3 or less, a melt
 index of from about 0.01 g/10 min or greater and a rubber content of about
 15 vol. % or greater. Moreover, the rubber phase of the ethylene copolymer
 resin of the present invention contains from about 35 to about 65 alkyl
 branches per 1000 total carbon atoms.
 Another aspect of the present invention relates to a high-impact strength
 film that can be produced from the ethylene copolymer resin of the present
 invention. The term "high-impact strength" is used herein to denote an
 impact strength, as measured using a free-falling dart, of at least about
 300 g/mil or higher.
 As stated earlier, the polymerization catalyst of the present invention
 relates to a polymerization catalyst which is capable of producing
 ethylene copolymers having the unique melt elastic properties mentioned
 above. In one embodiment of the present invention, the ethylene
 polymerization catalyst is obtained by:
 (a) contacting a support material with an organosilicon compound to
 effectuate reduction of surface hydroxyl groups present on said support
 material;
 (b) contacting the modified support material with a dialkylmagnesium
 compound or complex;
 (c) contacting the product of (b) with an alcohol or a silane compound; and
 (d) contacting the product of (c) with a transition metal compound; and
 (e) contacting the product of (d) with a Group 13 metal-containing
 compound.
 In another embodiment of the present invention, the polymerization catalyst
 is obtained by:
 (a) contacting a support material with an organosilicon compound to
 effectuate reduction of surface hydroxyl groups present on said support
 material;
 (b) contacting the modified support material with a dialkylmagnesium
 compound or complex;
 (c) contacting the product of (b) with a transition metal compound;
 (d) contacting the product of (c) with an alcohol or a silane compound; and
 (e) contacting the product of (d) with a Group 13 metal-containing
 compound.
 In yet another embodiment, the catalyst of the present invention is
 obtained by:
 (a) contacting a support material with an organosilicon compound to
 effectuate reduction of surface hydroxyl groups present on said support
 material;
 (b) contacting the modified support material with an alcohol or a silane
 compound;
 (c) contacting the product of (b) with a dialkylmagnesium compound or
 complex;
 (d) contacting the product of (c) with a transition metal compound; and
 (e) contacting the product of (d) with a Group 13 metal-containing
 compound.
 A still further aspect of the present invention relates to an ethylene
 polymerization process wherein ethylene and at least one C.sub.4-8
 comonomer are copolymerized in the presence of one of the above-mentioned
 ethylene polymerization catalysts, a suitable cocatalyst capable of
 activating the ethylene polymerization catalyst and, optionally, a
 cocatalyst modifier. This polymerization process results in the production
 of the inventive ethylene copolymer resin having the unique melt elastic
 properties described hereinabove.

DETAILED DESCRIPTION OF THE INVENTION
 As stated above, the present invention provides an ethylene copolymer resin
 which exhibits enhanced film impact when formed into a film, and has
 unique melt elastic properties which, in part, signify the presence of a
 network structure in the ethylene copolymer resin of the present
 invention.
 The ethylene copolymer resin of the present invention is characterized as
 containing ethylene, as the major component, and at least one C.sub.4-8
 comonomer, as a minor component. In accordance with an embodiment of the
 present invention, it is highly preferred that 1-hexene be used as the
 comonomer. When 1-hexene is employed as the comonomer, the resin typically
 contains 95% or less ethylene and the remainder being 1-hexene.
 Another characteristic of the ethylene copolymer resin of the present
 invention is that it has a base copolymer density of about 0.930
 g/cm.sup.3 or below. The term "base polymer density" represents the
 density of the polymer resin before the addition of any additives or
 fillers which are commonly introduced upon processing. More preferably,
 the base polymer density of the ethylene copolymer resin of the present
 invention is about 0.925 g/cm.sup.3 or below. Most preferably, the base
 polymer density is about 0.922 g/cm.sup.3 or below. The above density
 ranges qualify the ethylene copolymer resin of the present invention as
 LLDPE.
 In addition to the above characteristics, the ethylene copolymer resin of
 the present invention also contains a network structure which is believed,
 but not entirely known, to be formed at least in part by a rubber phase
 known to be present in the inventive ethylene copolymer resin. The rubber
 phase is characterized as being an ethylene/comonomer rubber which is
 highly branched, i.e. it contains from about 35 to about 65 alkyl branches
 per 1000 total carbon atoms. The network structure is believed to
 interconnect the hard and soft phases of the inventive copolymer resin
 thereby partly providing the ethylene copolymer resin of the present
 invention with its unusual and totally unexpected melt elastic properties.
 In one embodiment of the present invention, the ethylene copolymer resin
 contains about 15 vol. % or greater of a rubber phase, as measured by a
 technique known as Scanning Electron Microscopy (SEM) which is described,
 for example, in an article to F. Mirabella, et al. entitled "Morphological
 Explanation of the Extraordinary Fracture Toughness of Linear Low Density
 Polyethylenes", J. Polymer Science: Part B: Polymer Physics, Vol. 26, No.
 9, August 1988, pp. 1995-2005. Specifically, the following procedure was
 employed in the present invention to determine the vol. % rubber in the
 copolymer resin: A compression-molded sample was microtomed at a specimen
 temperature of about -80.degree. C. in an LKB Ultratome V with Cryokit.
 The bulk specimen thus prepared was etched in n-heptane at 60.degree. C.
 for 20 minutes in a sonic bath, mounted onto a scanning electron
 microscope specimen stub, and sputter coated with approximately 200 .ANG.
 of gold. The specimen was then analyzed in an ISI-40 SEM. This procedure
 removes any rubbery, amorphous or low-crystallinity, in the resin from the
 specimen surface and leaves definable cavities where the material was
 originally located. Photomicrographs were statistically analyzed with a
 Ziess Videoplan Image Analyzer.
 In one embodiment of the present invention, the rubber particles present in
 the ethylene copolymer resin of the present invention have an average
 radius, R.sub.w of about 0.05 to about 0.25 micrometers. The interparticle
 distance of the rubber particles in the rubber phase is determined using
 the following equation:
 ##EQU1##
 where R.sub.w is the average particle radius and .phi. is the volume
 fraction (vol. % rubber/100), See S. Wu "Phase Structure and Adhesion in
 Polymer Blends: A Criterion for Rubber Toughening", Polymer, Vol. 26, pp.
 1855 (1985). In one embodiment of the present invention, the rubber
 particles typically have an interparticle distance of 0.20 micrometers or
 less.
 The ethylene copolymer resin of the present invention is further
 characterized as having a melt index of from about 0.01 g/10 min. or
 greater. More preferably, the ethylene copolymer resin of the present
 invention has a melt index of from about 0.5 to about 4.0 g/10 min.
 Although various of the above resin properties may be known in the art, the
 unique melt elastic properties defined hereinbelow are not. It is this
 characteristic of the inventive ethylene copolymer resin which
 distinguishes same from all previously known ethylene copolymers.
 Specifically, the ethylene copolymer resin of the present invention, when
 in reactor-made form, has a ER value of 0.9 or below, which undergoes an
 increase in ER when pelletizing the reactor-made material. That is, when
 the original reactor-made form, i.e. powder, solution or slurry, of the
 ethylene copolymer resin of the present invention is made into a pellet
 one observes a positive %ER shift. An increase from about 10 to about 80%
 in ER is typically observed when comparing the reactor-made material to
 the pellet. However, such an increase is reversible. That is, the pellet's
 ER value can be reduced upon rheometric low shear modification or solution
 dissolution. This characteristic is distinct from irreversible increase in
 ER observed, for example, due to polymer degradation (chain extension
 and/or long chain branching formation).
 In addition to the above melt elastic property, the ethylene copolymer
 resin of the present invention, when in pelletized form, exhibits a
 reduction in ER to values below 1.0 after subjecting the same to
 rheometric low shear modification or solution dissolution. A 10-30%
 reduction in ER of the pelletized form of the invention copolymer resin is
 typically observed. This reduction in ER of the pelletized sample under
 rheometric low shear modification or solution dissolution signifies that
 the ER shift observed is reversible.
 The following techniques were employed in the present invention to obtain
 Theological data of the ethylene copolymer resin of the present invention.
 I. Xylene Dissolution Experiments: 2 grams of polymer were dissolved into
 200 ml of xylene at 110.degree. C. for about 1 hr. The resultant solution
 was allowed to cool at room temperature. The xylene solvent was allowed to
 slowly evaporate (typically over a period of 4-5 days).
 The polymer sample was recovered and dried in vacuum at 60.degree. C. for
 about 72 hours. The dried sample was then pressed into 25 mm disks for
 Theological measurements as described hereinbelow.
 II. Sample Preparation for Rheological Measurements: Measurement of polymer
 melt Theological properties were carried out in a Rheometric ARES
 rheometer using 25 mm disk samples having a thickness of about 1.2 mm. The
 disk samples were prepared by pre-pressing (pellet or powder, as
 necessary) using a compression press and a brass 1.2 mm template with 1
 inch holes sandwiched between two 1/4 inch steel plates with a sheet of
 mylar film placed between the press template and steel plates. About 2-3
 wt. % antioxidant (50% BHT-50% Irganox 1010) was added during disk
 pressing for extra stabilization. The compression press was maintained at
 150.degree. C.
 For polymers exhibiting powder-to-pellet changes in rheology, it is
 imperative to minimize flow and mixing during sample preparation. For
 example, pressing disks out of a polymer powder and then re-melting and
 repressing the same disks may increase the measured ER.
 III. Rheological Measurements for ER Calculation: A standard practice for
 measuring,dynamic rheology data in the frequency sweep mode, as described
 in ASTM 4440-95a, was employed herein. A Rheometrics ARES rheometer was
 used, operating at 150.degree. C., in the parallel plate mode in a
 nitrogen environment (in order to minimize sample oxidation/degradation).
 The gap in the parallel plate geometry was typically 1.2-1.4 mm and the
 strain amplitude was 10-20%, preferably 10% strain amplitude was employed.
 The range of frequencies was 0.0251 to 398.1 rad/sec.
 As disclosed in Shroff, et al. supra and U.S. Pat. No. 5,534,472 (See Col.
 10, lines 20-30), ER is calculated from the storage modulus (G')and loss
 modulus (G") data, as follows: the nine lowest frequency points are used
 (5 points per frequency decade) and a linear equation is fitted by
 least-squares regression to log G' versus log G". ER is then calculated
 from the following equation:
EQU ER=(1.781.times.10.sup.-3)xG', at a value of G"=5000dyn/cm.sup.2.
 It is understandable to those skilled in the art that nonlinearity in the
 log G' versus log G" plot will result in different ER values depending on
 the range of the data employed, which in turns relates to the range in
 frequency data. The procedure followed was to extend the lower end of the
 frequency range so that the lowermost G" value was within the range of
 7.times.10.sup.3 -10.sup.4 dyn/cm.sup.2. Practically speaking, this
 requires a lowermost frequency of 0.0398 rad/sec for 1 MI LLDPEs and
 0.0251 rad/sec for 0.6 MI LLDPEs, at 150.degree. C.
 IV. Rheometric Shear Modification: A sample was placed in the AERS
 rheometer and a standard frequency sweep was performed. Then, a steady
 preshearing was applied by specifying the shear rate and time of
 pre-shearing. Typically, the shear rate was 0.1 sec.sup.-1 and the time
 was 20-60 minutes. Preshearing was applied by specifying the rotational
 speed of the moving plate in the Rheometrics ARES rheometer. A rotational
 speed of about 0.01 rad/sec will result in a shear rate of 0.1 sec.sup.-1
 for a 1.25 mm gap and 25 mm plates. At the end of preshearing, a standard
 frequency sweep was performed. Comparison of the rheometric data before
 and after rheometric shear modification and calculation/comparison of ER
 calculated from each, will show and quantify whether the polymer exhibits
 rheometric shear modifiability.
 The above provides a description of the ethylene copolymer resin of the
 present invention, the description that follows is directed to the
 polymerization catalyst, polymerization process and film. The ethylene
 copolymer resin of the present invention is prepared in-situ by
 polymerizing ethylene and at least one C.sub.4 -C.sub.8 comonomer in the
 presence of an ethylene polymerization catalyst, a cocatalyst, and an
 optional cocatalyst modifier, under ethylene polymerization conditions.
 Mechanical blends of ethylene and various comonomers and/or copolymers
 such as ethylene propylene rubber (EPR) fall outside the realm of the
 present invention since they are not prepared in-situ.
 In one embodiment, the ethylene polymerization catalyst of the present
 invention is preferably prepared by contacting a chemically treated
 support material with a dialkylmagnesium compound or complex, contacting
 the magnesium-containing support material with either an alcohol or a
 hydrocarbyloxyhydrocarbylsilane and thereafter with a transition metal
 compound. It is again emphasized that when an alcohol is used, a
 hydrocarbyl alkoxysilane cocatalyst modifier is required.
 Suitable support materials that may be employed in the present invention
 include: inorganic supports such as silica, alumina, aluminum phosphate,
 celite, magnesium oxide, iron oxide and organic supports including
 polymers and copolymers.
 A preferred support material is silica. When silica is employed as the
 support material, it preferably pure, however, the silica may contain
 minor amounts of other inorganic oxides. In general, the silica support
 comprises at least 90-95% by weight pure silica. In a preferred
 embodiment, the silica is at least 99% pure.
 The silica support utilized in the present invention has a surface area of
 from about 50 to about 500 m.sup.2 /g; a particle size of from about 10 to
 about 200 micrometers; and a pore volume of about 0.5 to about 3.0 cc/g as
 determined by standard B.E.T. measurements.
 Another particularly preferred support material is celite. Celite is a
 diatomaceous earth composition composed of approximately 4% alumina,
 approximately 90% silica and the remainder calcium oxide and other
 inorganic oxides. Celite, commercially available from Eagle-Picher
 Minerals, Inc., has a porosity of between about 50 to about 90 volume %; a
 pore volume of between about 2.4 to about 3.5 cc/g; and a surface area of
 between about 2 to about 100 m.sup.2 /g.
 The aluminum phosphate, when employed as the support, has a preferred pore
 volume of between about 0.7 to about 1.25 cc/g and a preferred surface
 area of about 200 to about 350 m2/g. To obtain these preferred physical
 characteristics, it is preferred that the aluminum phosphate be made more
 amorphous than pure aluminum phosphate. Thus, AlPO.sub.4 is synthesized
 with other agents such that the atomic ratio of phosphorus to aluminum be
 in the range of between about 0.70 and about 0.95. More preferably, this
 atomic ratio is in the range of between about 0.72 and about 0.85.
 The alumina employed for use as the support is characterized by a pore
 volume of between about 0.8 to about 3 cc/g and a surface area of about
 300 m.sup.2 /g to about 400 m.sup.2 /g.
 Prior to contact with the organomagnesium compound or complex, the support
 material is contacted with an organosilicon compound, such as disclosed in
 U.S. Pat. Nos. 4,374,753 and 4,530,913 both to Pullukat, et al., the
 contents of each being incorporated herein by reference, to reduce the
 number of surface hydroxyl groups. Typically, about 0.3 to about 1.2 mmol
 of OH groups remain after this chemical treatment step. It is noted that
 calcination alone or chemical treatment of a support material with an
 aluminum compound does not provide a polymerization catalyst which
 exhibits high activity and yield yet is capable of providing ethylene
 copolymers having all of the above mentioned characteristics.
 Suitable organosilicon compounds that can be employed in the present
 invention to treat the support material are those having one of the
 following formulas: (R.sub.3.sup.4 Si).sub.2 NH, R.sub.3.sup.4
 Si(OR.sup.4), R.sub.3.sup.4 SiX.sup.4 and (R.sub.3.sup.4 Si).sub.2 O
 wherein R.sup.4 is alkyl or aryl, preferably each containing 1 to 20
 carbon atoms, and X.sup.4 is a halogen. Specific examples of such
 organosilicon compounds are hexaalkyl disilazane, trialkylsilyl ethoxide
 and alkyl chlorosilanes. Of these, hexaalkyl disilazanes are particularly
 useful in this application, with hexamethyl disilazane, i.e. HMDS, being
 highly preferred.
 After chemically treating the support material with an organosilicon
 compound, the chemically modified support is optionally dried by calcining
 the same in an inert atmosphere at a temperature of at least 50.degree. C.
 More specifically, the calcining step is carried out at a temperature of
 from about 150.degree. to about 650.degree. C. in nitrogen or argon. The
 chemically treated support may optionally be dried by vacuum.
 The chemically treated support material is then slurried in a hydrocarbon
 solvent, e.g. heptane or hexane, and thereafter treated with a
 dialkylmagnesium compound or complex having one of the following formulas:
EQU R.sub.2 Mg;
 or
EQU (R.sub.2.sup.1 Mg).cndot.nAlR.sub.3.sup.1
 wherein R and R.sup.1 are the same or different and each is independently
 an alkyl containing from 1 to 12 carbon atoms and n is from 0.5 to 10. Of
 the compounds that satisfy the above formula, dibutylmagnesium sold by FMC
 Corporation, butylethylmagnesium and a complex of dibutylmagnesium and
 triethylaluminum sold by Akzo Chemicals under the tradename MAGALA are
 highly preferred.
 The amount of organomagnesium compound or complex added to the chemically
 treated support material is from about 0.01 to about 10 mmole per gram
 support material. More preferably, the amount of organomagnesium compound
 or complex added in making the ethylene polymerization catalyst of the
 present invention is from about 0.5 to about 1 mmole per gram support
 material.
 The contact between the organomagnesium compound or complex and treated
 support material usually occurs at a temperature range of between about
 15.degree. to about 120.degree. C. for a time period of from about 5 to
 about 180 minutes. Preferably, this contact occurs at a temperature of
 from about 20.degree. to about 40.degree. C. for a time period of from
 about 30 to about 60 minutes.
 To this contact product is added either an alcohol or a silane compound.
 When an alcohol is employed, aliphatic or aromatic alcohols containing
 from 1 to 12 carbon atoms can be employed. For a complete description of
 this embodiment of the present invention, applicants refer to U.S. Pat.
 No. 4,374,753 to Pullukat, et al. which was previously incorporated herein
 by reference. In a preferred embodiment of the present invention, the
 alcohol is an aliphatic alcohol containing 1 to 5 carbon atoms. Of these
 preferred alcohols, n-butanol, i.e. butyl alcohol, is most preferred. The
 amount of alcohol added to the organomagnesium-containing support reaction
 mixture is from about 0.1 to about 10 mmole per gram support material.
 More preferably, the concentration range of added alcohol is from about
 0.4 to about 1.0 mmole per gram support material.
 The silane compound that can be employed in the present invention has the
 following formula:
EQU (R.sup.2 O).sub.n Si (R.sup.3).sub.4-n
 wherein R.sup.2 and R.sup.3 may be the same or different and are C.sub.1
 -C.sub.20 alkyl, cycloalkyl, aryl, alkaryl or aralkyl radicals, and n is
 from 1 to 4. Suitable compounds include: ethoxytrimethylsilane,
 diethoxydimethylsilane, triethoxymethylsilane, tetraethoxysilane (TEOS),
 diisopropyldimethoxysilane (DIPS), tetrabutoxysilane (TBOS),
 methoxytriphenylsilane, methyltriethoxysilane (MTEOS) and
 phenoxytrimethylsilane. Of these compounds, it is preferred to employ TEOS
 or TBOS as the hydrocarbyloxyhydrocarbylsilane.
 The silane compound is added in an amount of from about 0.05 to about 10
 mmole per gram support, with from about 0.1 to about 1 mmole per gram
 support being highly preferred.
 The contact step between the organomagnesium-containing support contact
 reaction mixture and the alcohol or silane compound usually occurs at a
 temperature range of from about 15.degree. to about 120.degree. C. for a
 time period of from about 5 to about 180 minutes. More preferably, this
 contact occurs at a temperature of from about 20.degree. to about
 40.degree. C. for a time period of from about 30 to about 60 minutes.
 The above contact product is then contacted with at least one transition
 metal compound belonging to Groups IVB and/or VB of the Periodic Table of
 Elements. The transition metal compounds belonging to Group IVB of the
 Periodic Table of Elements have the structure formula M'x.sub.p (OR')
 wherein M' is titanium or zirconium; R' is aryl, alkyl, aralkyl,
 cycloalkyl or alkylsilyl; X is a halogen; p is 0 or an integer from 1 to
 4; and q is 0 or an integer from 1 to 4; with the proviso that the sum of
 p and q is 4. It is especially preferred that M' be titanium.
 In a preferred embodiment, the titanium-containing compound is one wherein
 p is an integer from 2 to 4 and q is 0 or an integer 1 or 2. Suitable
 titanium compounds within the contemplation of this embodiment are
 titanium tetrachloride, titanium tetrabromide, methoxytitanium
 trichloride, ethoxytitanium trichloride, diethoxytitanium dichloride and
 the like.
 Still, more preferably, the titanium-containing compound is defined by p
 being 4, q being 0, and X is chlorine or bromine. Thus, the titanium
 compound is most preferably titanium tetrachloride or titanium
 tetrabromide. Of these two titanium compounds, titanium tetrachloride is
 most preferred.
 Suitable transition metal compounds belonging to Group VB are compounds
 that have the structural formula M"(OR").sub.x (O).sub.y (X.sup.2).sub.z
 wherein M" is a metal of Group VB of the Periodic Table of Elements, R" is
 a hydrocarbyl having from 1 to 18 carbon atoms; X.sup.2 is halogen; x is 0
 or an integer from 1 to 5; y is 0 or 1; and z=(5-x-2y) or 4 or 3 when x=0,
 y=0. It is especially preferred that MN' be vanadium.
 Suitable vanadium compounds encompassed by the above formula include:
 vanadium oxyhalides, vanadium alkoxides, vanadium carboxylates, vanadium
 halides and mixtures thereof. It is especially preferred that the
 vanadium-containing compound be vanadium tributyloxy, triisobutyl
 vanadate, vanadium tetrachloride and the like.
 This contact between the transition metal-containing compound and the
 modified organomagnesium-containing support contact product occurs at a
 temperature from about 15.degree. to about 120.degree. C. More preferably,
 the temperature of this contacting step is from about 20.degree. to about
 40.degree. C. The time employed for contacting with the transition
 metal-containing compound is at least about 5 minutes. Most preferably,
 the time of this contacting step is from about 30 to about 60 minutes.
 The concentration range of transition metal-containing compound employed in
 the present invention is from about 0.1 to about 10 mmole transition metal
 compound per gram support. More preferably, the concentration of
 transition metal compound used in this contacting step is from about 0.5
 to about 1.0 mmole transition metal compound per gram support.
 In another preferred embodiment the ethylene polymerization catalyst of the
 present invention is prepared by the above described steps but includes,
 as a concluding contacting step, contact with a Group 13 metal-containing
 compound. Preferably, the Group 13 metal-containing compound has the
 structural formula MR.sup.4 R.sup.5 R.sup.6, where M is a Group 13 metal;
 and R.sup.4, R.sup.5, and R.sup.6 are the same or different and are
 C.sub.1 -C.sub.20 hydrocarbyl or halogen, with the proviso that at least
 one of R.sup.4, R.sup.5, and R.sup.6 is C.sub.1 -C.sub.20 hydrocarbyl.
 More preferably, M is aluminum or boron; and R.sup.4, R.sup.5 and R.sup.6
 are the same or different and are C.sub.1 -C.sub.20 alkyl, C.sub.5
 -C.sub.20 cycloalkyl, C.sub.6 -C.sub.18 aryl C.sub.7 -C.sub.20 aralkyl,
 C.sub.7 -C.sub.20 alkaryl, chlorine or bromine, with the proviso that at
 least one of R.sup.4, R.sup.5 and R.sup.6 is not chlorine or bromine.
 Still more preferably, R.sup.4, R.sup.5, and R.sup.6 are the same or
 different and are C.sub.l -C.sub.10. alkyl, chlorine or bromine with the
 proviso that at least one of R.sup.4, R.sup.5, and R.sup.6 is C.sub.1
 -C.sub.10 alkyl.
 Even still more preferable, R.sup.4, R.sup.5 and R.sup.6 are the same or
 different and are C.sub.1 -C.sub.6 alkyl or chlorine, with the proviso
 that at least one of R.sup.4, R.sup.5 and R.sup.6 is C.sub.1 -C.sub.6
 alkyl.
 Yet even still more preferably, R.sup.4, R.sup.5 and R.sup.6 are the same
 or different and are C.sub.2 -C.sub.4 alkyl or chlorine with the proviso
 that at least one of R.sup.4, R.sup.5 and R.sup.6 is C.sub.2 -C.sub.4
 alkyl.
 Among the preferred compounds within the contemplation of the Group 13
 metal-containing compounds are triethylborane, diethylaluminum chloride,
 ethylaluminum dichloride and ethylaluminum sesquichloride. The last named
 compound is a preformulated compound obtained by combining diethylaluminum
 chloride and ethylaluminum dichloride.
 The step of contacting the Group 13 metal-containing compound with the
 supported product of the earlier steps involves providing the Group 13
 metal-containing compound in an amount of between about 0.05 mmole and
 about 50 mmole per gram of support. More preferably, between about 0.1
 mmole and about 30 mmole of the Group 13 metal-containing compound is
 added per gram of support.
 The contacting step between the Group 13 metal-containing compound and the
 supported product of the earlier steps occurs at a temperature in the
 range of between about 15.degree. C. and about 120.degree. C. over a
 period of between about 5 minutes and about 3 hours. More preferably, this
 contacting step occurs at a temperature of between about 20.degree. C. and
 about 40.degree. C. over a period of between about 30 minutes and about 1
 hour.
 It should be noted that the above order of addition represents one
 embodiment for preparing the polymerization catalyst of the present
 invention. It is also within the contemplation of the present invention to
 change the order of addition so that the alcohol or silane compound is
 added after contact with the transition metal-containing compound. In that
 embodiment of the present invention, the reaction sequence would be
 It should be appreciated that all the treatment steps in the formation of
 the ethylene polymerization catalyst of this invention, the contact of
 support with the organomagnesium compound or complex, the alcohol or
 silane, the transition metal compound and the Group 13 metal-containing
 compound, involve contact between a solid, a support material, and a
 liquid. This is because each of the compounds that are contacted with the
 support material are liquids, or are soluble in an inert hydrocarbon
 solvent under the conditions employed by the present process. As such, no
 ball-milling or other solid mixing is required. Ball-milling is an
 expensive and difficult operation typically used in the formation of
 polymerization catalysts of the prior art. Those skilled in the art are
 aware, in the case where a hydrocarbon is employed, that the solvent may
 be allowed to remain with the reaction mass or can be removed by
 decantation, filtration, evaporation, or the like.
 The cocatalysts employed by the present invention in activating the
 ethylene polymerization catalyst are conventional aluminum-containing
 compounds well known in the art. The aluminum-containing, cocatalysts are
 preferably alkylaluminum-containing compounds. Alkylaluminum-containing
 compounds suitable for the present process include trialkylaluminum,
 alkylaluminum halide, alkylaluminum hydride, aluminoxane (either cyclic or
 linear) or mixtures thereof. More preferably, the cocatalyst is a
 trialkylaluminum compound. Of the trialkylaluminum compounds,
 triethylaluminum (TEAL) is particularly preferred.
 The molar ratio of aluminum-containing cocatalyst to transition metal in
 the solid catalyst is from about 0.01 to about 500. More preferably, the
 molar ratio of cocatalyst to transition metal in said solid catalyst is
 from about 10 to about 120.
 The cocatalyst modifiers that may be optionally employed by the present
 invention are hydrocarbyl alkoxysilanes. It is again emphasized that when
 an alcohol is employed in preparing the polymerization catalyst the
 cocatalyst modifier is not optional. Rather it is required in that
 embodiment of the present invention. Preferred hydrocarbyl alkoxysilanes
 include: hydrocarbyl trialkoxysilanes, dihydrocarbyl dialkoxysilanes and
 trihydrocarbyl alkoxysilanes. Of the hydrocarbyl trialkoxysilanes,
 diisopropyldimethoxysilane (DIPS) is highly preferred.
 When a cocatalyst modifier is employed, the molar ratio of said cocatalyst
 modifier to transition metal in said solid catalyst is from about 0.01 to
 about 100. More preferably, the molar ratio of cocatalyst modifier to
 transition metal in said solid catalyst employed is from about 0.1 to
 about 10.
 The polymerization process can be conducted in either the gas phase
 (stirred or fluidized bed) or solution phase. When gas phase
 polymerization is employed, a single or multiple reactor connected in
 parallel or series may be employed. The conditions of gas phase
 polymerization employed in the present invention include any that have
 heretofore been utilized. Examples of suitable conditions for operating in
 the gas phase that can be employed herein are disclosed, for example, in
 U.S. Pat. No. 5,258,345 to Kissin, et al., the contents of which are being
 incorporated herein by reference.
 When solution polymerization is employed, the polymerization is carried out
 in a liquid organic medium in which the solid ethylene polymerization
 catalyst is suspended using any slurry polymerization conditions
 heretofore utilized. A pressure sufficient to maintain the organic diluent
 and at least a portion of the comonomer in the liquid phase is maintained.
 Examples of typical operating conditions for slurry polymerization that
 can be employed herein are described in EPO 848 021 A2, the contents of
 which are being incorporated herein by reference.
 The above ethylene polymerization catalyst and polymerization process
 provide the ethylene copolymer resin having the above-described unique
 melt elastic properties. Hence, the ethylene copolymer resin has all of
 the properties mentioned hereinabove which include having a density of
 0.930 cc/g or lower and having a network structure. Moreover, the ethylene
 copolymer resin exhibits the unique melt elastic properties mentioned
 hereinabove. Such melt elastic properties distinguish the inventive
 copolymer resin from any commercially known copolymer since the same do
 not exhibit the above-mentioned melt elastic properties.
 Another aspect of the present invention relates to a high-impact strength
 film that can be produced from the ethylene copolymer resin of the present
 invention. Specifically, the high-impact strength film is formed from the
 pellet of the ethylene copolymer resin of the present invention, and it
 exhibits improvement in film properties and/or processability.
 Specifically, the film of the present invention exhibits a dart impact
 strength of greater than about 300 g/mil and a MD tear of greater than
 about 300 g/mil. In one embodiment of the present invention, the film has
 a dart impact strength greater than about 350 g/mil and a modulus of
 elasticity of from about 20 to about 35 Ksi.
 The film is formed in the present invention using a single layer blown film
 extrusion line which operates under the following conditions:
 1 mil, 2.5 Blow-up-ratio, 150 lb/hr, 8 inch die, 100 mil die gap, dual lip
 air ring, 16 inch frostline height, 420.degree. F. melt temperature, 3.5
 inch extruder with a barrier screw and a Maddock mixing section.
 The resin and film properties are determined using standard ASTM
 procedures. Specifically, the following ASTM procedures are used in the
 present invention:

Melt Index D-1238
 Density D-2389
 Film Impact/Free Falling Dart D-1709
 MD-Tear D-1922
 Modulus of Elasticity, 1% D-882
 secant
 The following examples are given to illustrate the scope of this invention.
 Because these examples are given for illustrative purposes only, the
 present invention should not be limited thereto.
 The catalysts were prepared in a three-neck round bottom flask with a
 paddle type stirrer. All glassware was oven dried and assembled hot under
 a nitrogen purge. The left and right joints were fitted, respectively,
 with a nitrogen source and a vent to a mineral oil bubbler. The vent was
 also used to add the ingredients and to remove the finished catalyst. The
 glassware was purged 1 hr. prior to starting the catalyst synthesis.
 Typically, 4 to 8 grams of HMDS treated silica was added to the flask
 followed by about 8 ml of heptane/gram of silica and the slurry was
 stirred at about 160 rpm. The appropriate amount of dialkyl magnesium in
 heptane was added by syringe. After 30 minutes, the appropriate amount of
 silane in heptane was added. After 30 minutes, the appropriate amount of
 TiCl.sub.4 in heptane was added. After 30 minutes the heptane was
 distilled off with a sweep of N.sub.2 at 100.degree. C.
 Catalysts 1-12 were prepared on Davison 948 silica and dried at 100.degree.
 C.
 Catalysts 1-9, 11 and 12 were prepared with dibutylmagnesium (DBM).
 Catalysts 1-6, 10-13, were prepared with Si(OEt).sub.4 (TEOS).
 Catalysts 7 and 8 prepared with MeSi(OEt).sub.3 (MTEOS).
 Catalyst 9 prepared with (isopropyl).sub.2 Si(OME).sub.2 (DIPS).
 Catalysts 10, 13, and 14 were prepared with butylethylmagnesium (BEM).
 Catalyst 11 addition order was Si(OEt).sub.4, dibutylmagnesium, and
 TiCl.sub.4.
 Catalysts 13 and 14 were prepared on Davison XPO silica and dried at
 85.degree. C.
 Catalyst 14 prepared with Si(OBu) 4 (TBOS).

Amount
 Catalyst Amount of Mg of Si Amount of TiCl.sub.4
 1 .65 DBM .16 TEOS .65
 2 .65 DBM .16 TEOS .65
 3 .90 DBM .23 TEOS .90
 4 .90 DBM .10 TEOS .90
 5 .40 DBM .10 TEOS .40
 6 .65 DBM .16 TEOS .65
 7 .70 DBM .40 MTEOS 1.0
 8 1.0 DBM 1.0 MTEOS 1.0
 9 .50 DBM .12 DIPS .50
 10 .50 BEM .12 TEOS .50
 11 .50 DBM .12 TEOS .50
 12 .50 DBM .12 TEOS .50
 13 .50 BEM .12 TEOS .50
 14 .50 BEM .12 TEOS .50
 Bench Scale Polymerization
 The reactor used was a 3.3 liter vessel with a helical agitator,
 thermocouple, and a valve for removing the resultant polymer. The jacket
 contained water which was recirculated for temperature control at
 82.degree. C. 1.5 ml of 25% triethylaluminum in heptane was added by
 syringe to the seed bed. The catalyst was added to the polymer bed through
 a polyethylene tube. The agitator was started and 163 psi of N.sub.2 was
 added to the reactor. Next, 18.9 psi of hydrogen was added to the reactor;
 and thereafter 80 ml of hexene was added to the reactor. Ethylene was then
 added to give 300 psi reactor pressure. A mixture of 12 wt % hexene in
 ethylene was fed into the reactor to maintain 300 psi on the reactor. When
 the total ethylene feed reached about 400 grams, the ethylene feed was
 stopped and the reactor was cooled and vented. About 448 grams of polymer
 was drained out of the reactor and the polymerization was repeated three
 more times to remove the original seed bed. The fourth batch of polymer
 that was drained from the reactor was submitted for testing.
 For inventive catalysts 1-6 (see Table 1) it can be seen that the inventive
 catalysts show good activity, good comonomer response, good bulk density
 and produce polyethylene narrow molecular weight distributions.
 Bench Scale Slurry Polymerizations with Hexene:
 Polymerizations were carried out in a 1 gallon Autoclave Engineering.RTM.
 reactor at 80.degree. C. and 300 psi. After purging the reactor with
 nitrogen, 400 ml of hexene was added and hydrogen was added as a 250 psi
 pressure differential from a 300 cc vessel. About 0.7 liter of isobutane
 was added and the stirrer was started. Ethylene was added to give a total
 reactor pressure of 260 psi. 1.92 ml of 1.56 M triethylaluminum in heptane
 was flushed into the reactor with about 200 ml of isobutane. After 1
 minute, the catalyst was flushed into the reactor with 200 ml of isobutane
 to give a total isobutane volume of 1.1 liters. Ethylene was allowed to
 feed into the reactor to maintain 300 psi. The reaction was terminated by
 stopping the ethylene feed and venting the reactor. Reactivities were
 calculated based on grams polymer recovered in one hour/grams of catalyst
 weight. Melt index (MI, grams/10 minutes) and high load melt index (HLMI,
 grams/10 minutes) measurements were made using ASTM method D1238-86.
 Comparison of catalysts 7, 8, 9 and 12 (see Table 1) show that several
 other alkoxy silane compounds can be used in the inventive catalysts.
 TEOS, MTEOS and DIPS show narrow molecular weight distributions.
 Comparison of catalysts 11 and 12 show that the addition order is
 unimportant and both catalysts show good reactivity and narrow molecular
 weight distributions. Comparison of catalysts 10 and 12 show that the
 exact dialkylmagnesium compound is unimportant and both catalysts using
 different magnesium compounds show good reactivity and narrow molecular
 weight distributions.
 Bench-scale Slurry Polymerizations with Butene:
 Polymerizations were carried out in a 1 gallon Autoclave Engineering.RTM.
 reactor at 75.degree. C. and 335 psi. After purging the reactor with
 nitrogen, 200 ml of butene was added and hydrogen was added as a 200 psi
 pressure differential from a 300 cc vessel. About 1.0 liter of isobutane
 was added and the stirrer was started. Ethylene was added to give a total
 reactor pressure of 300 psi. 1.92 ml of 1.56 M triethylaluminum in heptane
 was flushed into the reactor with about 150 ml of isobutane. After 1
 minute, the catalyst was flushed into the reactor with 150 ml of isobutane
 to give a total isobutane volume of 1.3 liters. Ethylene was allowed to
 feed into the reactor to maintain 335 psi. The reaction was terminated by
 stopping the ethylene feed and venting the reactor. Reactivities were
 calculated based on grams polymer recovered in one hour/grams of catalyst
 weight. Melt index (MI, grams/10 minutes.) and high load melt index (HLMI,
 grams/10 minutes) measurements were made using ASTM method D1238-86.
 Comparison of catalysts 13 and 14 show that TBOS works equally well as
 TEOS. In addition, catalysts 13 and 14 also show that the amount of HMDS
 used to treat the silica can be reduced from 20 to 12 wt % and the type of
 silica can be varied from 948 to XPO.
 Dombro Catalyst Synthesis (CE1):
 704.degree. C. dried 948 silica/0.65 mM BEM/0.16 mM Si(OEt).sub.4 /0.65 mM
 TiCl.sub.4
 About 20 grams of Davison 948 silica was placed in a 1 inch diameter quartz
 glass tube equipped with a glass frit. The silica was fluidized with a
 stream of N.sub.2 and placed in a vertical tube furnace. The silica was
 heated to 704.degree. C. over 6 hours, held at 704.degree. C. for 6 hours,
 and cooled to room temperature over 6 hours.
 The catalyst was prepared in a three-neck round bottom flask with a
 paddle-type stirrer. All glassware was oven dried and assembled hot under
 a nitrogen purge. The left and right joints were fitted, respectively,
 with a nitrogen source and a vent to a mineral oil bubbler. The vent was
 also used to add the ingredients and to remove the finished catalyst. The
 glassware was purged for about 1 hr. prior to starting the catalyst
 synthesis. 4.805 grams of the 948 silica was added to the flask followed
 by about 40 ml of heptane and the slurry was stirred at about 160 rpm.
 4.73 ml of a 0.66 M butylethylmagnesium (BEMg) in heptane was added by
 syringe. After 30 minutes, 0.77 ml of a 1.0 M solution of Si(OEt).sub.4 in
 heptane was added. After 30 minutes, 3.12 ml of a 1.0 M solution of
 TiCl.sub.4 in heptane was added. After 30 minutes, the heptane was
 distilled off with a sweep of N.sub.2 at 100.degree. C.
 Mink Catalyst Synthesis (CE2):
 948 silica/3.67 mM TEA/0.7 mM BEM/0.17 mM Si(OEt).sub.4 /0.7 mM TiCl.sub.4
 The method used for treating silica with triethylaluminum is described by
 A. Noshay and F. J. Karol in "Transition Metal Catalyzed Polymerizations
 Ziegler-Natta and Metathesis Polymerizations" Cambridge University Press,
 New York, N.Y., edited by R. P. Quirk, 1988, pp. 396-416.
 The catalyst was prepared in a three-neck round bottom flask with a
 paddle-type stirrer. All glassware was oven dried and assembled hot under
 a nitrogen purge. The left and right joints were fitted, respectively,
 with a nitrogen source and a vent to a mineral oil bubbler. The vent was
 also used to add the ingredients and to remove the finished catalyst. The
 glassware was purged for about 1 hr. prior to starting the catalyst
 synthesis. 10.236 grams of Davison 948 silica was added. The flask was
 purged for 30 minutes and about 80 ml of heptane was added. The slurry was
 stirred at about 160 rpm. 24.1 ml of a 1.56 M triethylaluminum solution in
 heptane was added. After 30 minutes, the slurry was warmed to 40.degree.
 C. 10.86 ml of a 0.66 M butylethylmagnesium in heptane was added. After 30
 minutes, 1.74 ml of a 1.0 M solution of Si(OEt).sub.4 in heptane was
 added. After 30 minutes, 7.16 ml of a 1.0 M solution of TiCl.sub.4 in
 heptane was added. After 30 minutes the temperature was increased to
 55.degree. C. and the heptane was distilled off with a sweep of N.sub.2.
 CE1 (Dombro) and CE2 (Mink) showed lower H.sub.2 response, lower reactivity
 and lower polymer bulk density than the inventive catalysts 1 and 2. CE1
 showed lower comonomer response, CE2 produced a density similar to
 catalysts 1 and 2 but produced a polymer with a broader molecular weight
 distribution than catalysts 1 and 2.
 II. Scale-up catalysts--Inventive catalyst 15:
 HMDS 948/0.65 mM BEM/0.16 mM Si(OEt).sub.4 /0.65 mM TiCl.sub.4
 A steel reactor was purged for 6 hrs with N.sub.2. HMDS Davison 948 silica
 that was dried at 150.degree. C. was added and the stirrer was started at
 100 rpm. 5 lbs. of heptane/lb. of silica was added and the slurry was
 stirred for 30 minutes. The appropriate amount of butylethylmagnesium (10%
 in heptane) was added and the slurry was stirred for 30 minutes. The
 appropriate amount of Si(OEt).sub.4 (5% in heptane) was added and the
 slurry was stirred for 30 minutes. The appropriate amount of TiCl.sub.4
 (10% in heptane) was added and the slurry was stirred for 30 minutes. The
 catalyst was dried at 99.degree. C. with a sweep of N.sub.2.
 Dombro Catalyst Synthesis (CE3):
 700 dried 948/0.65 mM BEM/0.16 mM Si(OEt).sub.4 /0.65 mM TiCl.sub.4
 A 5 gallon steel reactor was purged for 6 hrs with N.sub.2. 2 lbs. of
 700.degree. C. dried Davison 948 silica was added and the stirrer was
 started at 100 rpm. 10 lbs. of heptane was added and the slurry was
 stirred for 30 minutes. 1.43 lbs. of butylethylmagnesium (10% in heptane)
 was added and the slurry was stirred for 30 minutes. 1.33 lbs. of
 Si(OEt).sub.4 (5% in heptane) was added and the slurry was stirred for 30
 minutes. 2.47 lbs. of TiCl.sub.4 (10% in heptane) was added and the slurry
 was stirred for 30 minutes. The catalyst was dried at 99.degree. C. with a
 sweep of N.sub.2. A second preparation of this catalyst was made following
 the same procedure called CE3-2.
 Mink Catalyst Synthesis (CE4):
 948 silica/3.67 mM TEA/0.7 mM BEM/0.17 mM Si(OEt).sub.4 /0.7 mM TiCl.sub.4
 Glassware was oven dried and purged with N.sub.2 for 1 hour. 250 g undried
 948 silica was charged to a 3 liter round bottom reaction flask. The flask
 was purged with N.sub.2 for 1 hour with stirring at about 100 rpm and 500
 ml hexane was added. 582 ml of 25% triethylaluminum in heptane was added.
 After 30 minutes, the slurry was heated to 40.degree. C. 275 ml of
 butylethylmagnesium (10% in
 TABLE 1
 Bulk
 Catalyst MI MIR density Reactivity ER density
 1 .80 29.6 .9219 2234 .86 .422
 2 .75 29.6 .9202 1937 1.0 .422
 3 .65 31.8 .9206 2979 .90 .423
 4 .89 32.6 .9218 2606 1.0 .376
 5 .56 33.4 .9168 1493 1.0 .386
 6 .75 33.6 .9164 2139 .98 .396
 7 .70 27.0 -- 682 -- --
 8 .40 27.5 .9366 295 -- --
 9 .70 24.0 .9365 1762 .73 --
 10 1.19 27.2 -- 1144 -- --
 11 1.78 27.3 -- 2480 .77 --
 12 1.19 25.2 -- 1058 .83 --
 13 .57 25.3 .9221 1751 .72 --
 14 .55 25.2 .9274 1777 -- --
 CE1 .38 29.7 .9251 558 1.0 .332
 CE2 .34 28.2 .9220 266 .92 .325
 heptane) was added. After 30 minutes, 9.5 ml of Si(OEt).sub.4 was added.
 After 30 minutes, 19.5 ml of TiCl.sub.4 was added. After 30 minutes, the
 slurry was heated to 55.degree. C. and the catalyst was dried with a
 stream of N.sub.2. A total of three batches of this catalyst was prepared
 and blended together for testing.
 Gas-phase Fluidized Bed Polymerizations:
 Gas-Phase polymerizations were carried out as described in U.S. Pat. Nos.
 4,001,382 and 4,302,566.
 The reaction temperature used was 180.degree. F. with a fluidized velocity
 of 1.7 ft/sec. The ethylene, hydrogen and hexene concentrations were
 adjusted to produce a target polymer with a 0.915 g/cc density and a 1.0
 melt index.
 TABLE 2
 Produc- Mole % Mole % Mole %
 Catalyst tivity MI density ER ethylene hydrogen hexene
 15 6100 1.16 .915 .71 28.3 5.8 5.8
 CE3 1900 1.35 .925 1.24 28.0 5.4 6.8
 CE3-2 1100 1.11 .926 -- 27.0 5.8 7.0
 CE4 300 .80 .926 1.29 28.0 5.4 6.8
 Inventive catalyst 15 showed good catalyst activity and good comonomer
 response as well as narrow molecular weight distribution. CE3 (Dombro) and
 CE4 (Mink) catalysts had poor catalyst productivity and such poor density
 response that the target products could not be produced. A new batch of
 CE3 (Dombro) catalyst was made to verify the results from the first batch.
 Once again hexene response and catalyst productivity were very poor.
 EXAMPLE 2
 In this example, the melt elastic properties of the ethylene copolymer
 resin of the present invention were compared with prior art ethylene
 copolymers. Both the powder and pelletized forms were investigated. Other
 pertinent physical data are also reported herein and compared to
 commercial ethylene copolymer resins.
 In this example, all the resins were prepared using a gas-phase fluidized
 bed polymerization process like the one described in Example 1. Resins 1-4
 and 10-11 represent prior art or commercial resins; whereas resins 5-9
 represent resins of the present invention.
 Resins 1 and 4 were prepared from a standard polymerization catalyst using
 a gas phase process; resins 2 and 3 were prepared using a conventional
 catalyst such as described in U.S. Pat. No. 4,374,753 to Pullukat, et al.
 and resins 10-11 are commercially available high performance hexene LLDPE
 resins.
 Resins 5-6, which represent the present invention, were prepared from a
 catalyst system which contained silica/MAGALA/butanol/TiCl.sub.4 as the
 solid catalyst component and DIPS as a cocatalyst modifier.
 Resins 7-9, which also represent the present invention, were prepared using
 a catalyst similar to catalyst 10 of Example 1.
 The properties of each resin determined using the techniques defined
 hereinabove are reported in Table 3 and are graphically illustrated in
 FIGS. 1-6.
 As shown in FIGS. 1-4, the resins of the present invention typically have
 higher impact, more rubber phase and smaller interparticle rubber distance
 than prior art resins. of significance is that the ethylene copolymer
 resins of the present invention, resins 5-9, exhibited the unique melt
 elastic properties mentioned above, whereas prior art resins 1-4 and 10-11
 did not exhibit the unique melt elastic properties. Specifically, as shown
 in FIG. 5, the powder form of resins 5-9 all have ER values of 0.9 or
 below which undergo an increase in ER when pelletizing the powder.
 Unlike the resins of the present invention, prior art resins 1-4 and 10-11
 do not exhibit the same. Instead, when an increase in ER value from powder
 to pellet is observed, prior art powders had an initial ER value of
 greater than 0.8 (i.e. ER&gt;0.8, if % ER shift was greater than 0), or when
 the prior art powder ER is 0.8 or below, the prior art resins did not
 exhibit an increase in ER in going from the powder to the pellet, (i.e. %
 ER shift=0, if ER is 0.8 or less).
 In addition to the above melt elastic properties, the inventive resins
 exhibited the melt elastic properties shown in FIG. 6. Specifically, the
 pelletized forms of resins 5-9 exhibited a 10-30% reduction in ER to
 values below 1.0 after rheometric low shear modification.
 In contrast thereto, prior art pelletized samples had ER&gt;1.0, if % ER shift
 reduction was less than 0, or they had % ER shift reduction=0, if ER was
 is less than 1.0.
 Another important property of the resins of the present invention is that
 an increase in ER is observed in going from the powder to the pellet. This
 increase is almost completely reversible when the pellet is dissolved in
 xylene (See, Table 4). In the case of prior art resins, the ER values
 remained unchanged when going from pellet to solution dissolved pellet.
 TABLE 3
 LIST OF RESIN AND FILM DATA
 ER-After
 Melt Film % Rubber ER, ER, ER- Shear
 ER-Shear MD-Tear, Modulus,
 Resin Index Density Impact (SEM) Powder pellet Shift, %
 modification Mod., % g/mil Ksi
 1 1.0 0.918 188 .+-. 15 2.7 .+-. 0.7 0.82 0.82 N/A 0.82
 0.0 335 .+-. 40 29.0 .+-. 1.0
 2 0.7 0.9163 266 .+-. 28 9.3 .+-. 5.1 1.0 1.3 30 1.18
 -9 245 .+-. 7 31.0 .+-. 1.0
 3 0.7 0.9146 356 .+-. 13 12.5 .+-. 2.0 1.06 1.54 45
 1.12 -27 265 .+-. 7 30.0 .+-. 0.7
 4 0.9 0.915 336 .+-. 6 5.0 .+-. 1.5 0.86 1.26 47 1.10
 -13 320 .+-. 14 28.0 .+-. 0.9
 5 1.0 0.917 355 .+-. 56 18.7 .+-. 1.0 0.68 1.2 76
 0.25 -21 339 .+-. 8 28.0 .+-. 1.0
 6 0.75 0.9155 590 .+-. 85 23.1 .+-. 3.6 0.67 1.1 64
 0.76 -31 366 .+-. 17 27.6 .+-. 1.1
 7 1.0 0.919 196 .+-. 9 5.1 .+-. 0.5 0.76 0.84 11 0.76
 -10 340 32.2 .+-. 1.0
 8 1.0 0.917 331 .+-. 8 8.9 .+-. 1.8 0.76 0.98 29 0.80
 -18 355 .+-. 7 28.8 .+-. 0.7
 9 1.0 0.915 602 .+-. 40 19.8 .+-. 2.0 0.76 1.14 50
 0.82 -28 380 .+-. 14 25.6 .+-. 0.2
 10 0.95 0.917 476 .+-. 35 3.0 .+-. 1.0 N/A 0.68 N/A 0.68
 0.0 420 .+-. 34 26.8 .+-. 1.1
 11 1.1 0.917 462 .+-. 88 N/A N/A 0.61 N/A 0.61
 0.0 429 .+-. 31 25.7 .+-. 1.1
 1. All films made under same conditions: 1 mil, 2.5 Blow-Up-Ratio, 150
 lb/hr, 8" die, 100 mil die gap, dual lip air ring, 16" frostline height,
 420.degree. F. melt temperature, 3.5" extruder with a barrier screw and a
 Maddock mixing section.
 2. All resin and film testing performed per standard ASTM procedures:
 D-1238 (Melt Index), D-2839 (Density), D-1709 (Film Impact/Free Falling
 Dart Drop), D-1922 (Tear) and D-882 (Modulus of Elasticity, 1% secant).
 3. % Rubber determined by Scanning Electron Microscopy (SEM) on etched
 sections microtomed from melt-pressed pellets.
 4. Rheometric shear modification performed as described herein for 60
 minutes.
 TABLE 4
 Effect of Xylene Dissolution on ER
 Resin 1 Resin 11 Resin 9
 Powder ER 0.82 N/A 0.76
 Pellet ER 0.82 0.59 1.14
 ER of Xylene 0.85 0.59 0.84
 Dissolved
 Pellet
 EXAMPLE 3
 Ethylene polymerization catalysts were prepared according to the embodiment
 which includes a Group 13 metal-containing compound concluding contacting
 step. Eight catalysts, denoted as Catalysts 15-22, were prepared. All
 eight catalysts were prepared utilizing a Davison.RTM. 948 silica treated
 with HMDS in accordance with the procedure enumerated in Example 1. The
 so-treated silica supports were thereupon contacted with
 butylethylmagnesium (0.65 mmoles per gram silica); tetraethoxysilane (0.16
 mmoles per gram silica); and titanium tetrachloride (0.65 mmoles per gram
 silica) in accordance with the method described in Example 1. The
 distinction in the eight catalysts involved the inclusion of a Group 13
 metal-containing compounds contacting concluding step or the absence of
 that step.
 Each supported catalyst, after contact with titanium tetrachloride, was
 contacted with the appropriate amount of a Group 13 metal-containing
 compound in a heptane slurry at a temperature of 25.degree. C. over a
 period of 30 minutes, in those examples where that step was conducted. A
 summary of the catalysts so synthesized appear below in Table 5.
 TABLE 5
 Gp 13 Metal Compd, mmol/gm.
 Catalyst No. silica
 15.sup.1 Triethylborane, 1.3
 16.sup.1 None
 17.sup.2 Triethylborane, 1.3
 18.sup.2 None
 19.sup.3 Diethylaluminum chloride, 0.65
 20.sup.3 Ethylaluminum dichloride, 0.65
 21.sup.3 Triethylborane, 1.3
 22.sup.3 None
 .sup.1 Catalysts 15 and 16 were identical but for the inclusion of the
 triethylborane contacting step in the formation of Catalyst 15.
 .sup.2 Catalysts 17 and 18 were identical but for the inclusion of the
 triethylborane contacting step in the formation of Catalyst 18.
 .sup.3 Catalysts 19-22 were identical but for inclusion of the differing
 Group 13 metal-containing compound contacting steps in the formation of
 Catalysts 19-21.
 EXAMPLE 4
 Catalysts 15-22, synthesized in accordance with Example 3, were employed in
 gas phase polymerization reactions. Each of these polymerization reactions
 were conducted in a 3.3 liter vessel equipped with a helical agitator, a
 thermocouple and a valve for removing product polymer. The reactor was
 water jacketed in which the water was recirculated at a temperature of
 82.2.degree. C. Triethylamine (25 wt. % solution in heptane, 1 ml) was
 added to the reactor by syringe to a seed polymeric bed. Catalyst was
 added to the seed bed through a polyethylene tube. The agitator was
 activated and nitrogen gas (175 psi) was added. Thereupon, hydrogen gas
 (19.0 psi) and n-hexene (46 ml) were added to the reactor. Ethylene gas
 was added to bring the total pressure up to 300 psi. A mixture of 11.8 wt.
 % n-hexene in ethylene was fed into the reactor until the total ethylene
 feed into the reactor reached 300 grams at which time the
 n-hexene-ethylene feed was discontinued. The reactor was cooled and
 vented. About 335 gms. of polymeric product was removed from the reactor
 and the polymerization was repeated 3 times to remove the original
 polymeric seed bed. The fourth polymeric batch removed from the reactor is
 reported as the results of the polymerization.
 The product ethylene-hexene copolymers were analyzed to determine their
 melt elasticities in accordance with the procedure provided in the
 aforementioned ASTM Test Procedure 4440-95a. The melt elasticity shift,
 determined by subjecting the polymeric melt to high shear, by passing the
 polymeric melt through an extruder, was next determined. In addition, the
 density of the polymer was determined in accordance with ASTM Test
 Procedure D-2389.
 These examples, including the molar concentration of the hexene-1
 comonomer, are summarized in Table 6.
 TABLE 6
 Hexene in Polymer
 Catalyst Copolymer, Density,
 No. mole % g/cm.sup.3 ER (Powder) ER Pellet ER, Shift, %
 15 3.73 0.919 0.88 1.29 46
 16 3.53 0.918 0.83 1.03 24
 17 3.50 0.918 0.81 1.35 67
 18 3.30 0.919 0.83 1.05 26
 19 4.10 0.918 0.95 1.49 57
 20 3.97 0.918 1.07 1.67 56
 21 4.00 0.918 0.90 1.35 50
 22 3.80 0.917 0.83 1.07 29
 DISCUSSION OF RESULTS OF EXAMPLE 4
 The results of Example 4 emphasize the advantages obtained by utilizing the
 catalyst of the present invention in the polymerization of linear low
 density polyethylene. In that a major application of linear low density
 polyethylene is its use as a film, a major problem associated with the
 production of a successful LLDPE film, as in the case of all polymeric
 films, is significantly alleviated. That is, two desirable physical
 properties of any film, stiffness and impact strength, are difficult to
 optimize since an increase in one of these properties usually results in a
 decrease in the other.
 Film stiffness, a property directly proportional to polymeric density, is
 desirably as high as possible. However, as is well known in the art, the
 greater the stiffness, the lesser is the impact strength of the film. The
 above suggested relationship that the greater the ER shift of a polymer,
 the greater the impact strength of a polymeric film formed from the
 polymer, however, can overcome this detriment.
 It is useful to observe that the data bears out the proposition that
 polymeric ER shift is proportional to impact strength of a film formed of
 that polymer. Attention is directed to the data included in Table 3.
 Therein, Resins 3 and 4 have substantially the same density. As such, they
 have equal stiffness. They also share an almost identical ER shift
 percentage. As such, it is not surprising that the well established
 relationship that films of the same polymer having the same stiffness have
 the same impact strength is borne out by the film impact data wherein the
 impact strength of Resins 3 and 4 are substantially the same.
 Another comparison taken from Table 3 further confirms this proposition.
 Resins 2 and 6 also have substantially the same density. However, the ER
 shift of Resin 6 is more than twice that of Resin 2. As established by the
 comparison between Resins 3 and 4, in the absence of a variation in ER
 shift, the two films should have substantially the same impact strength.
 However, the more than twice ER shift percentage of Resin 6 suggests that
 that resin has a higher impact strength compared to Resin 2. Indeed, this
 prediction, based on ER shift, is confirmed by the data. The impact
 strength of the film formed of Resin 6 is approximately twice that of the
 film made from Resin 2.
 The comparison between two identical linear low density polyethylenes, e.g.
 ethylene-hexene copolymers, polymerized in the gas phase by identical
 ethylene polymerization catalysts but for the inclusion of the Group 13
 metal compound contacting step, illustrate this advance. Catalyst 15,
 which included a final triethylborane contacting step in its formation,
 although possessing a substantially identical density, and thus a
 substantially identical stiffness, produced an ER shift double that
 obtained by Catalyst 16, the otherwise identical catalyst but for the
 inclusion of this inventive step. As such, Catalyst 15, within the scope
 of the present invention, produced a linear low density polyethylene
 having a higher impact strength than Catalyst 16, albeit the two catalyst
 possessed equivalent stiffness.
 The same result was observed in the comparison between Catalyst 17, within
 the scope of the present invention, and Catalyst 18, which differed from
 Catalyst 17 only insofar as its synthesis did not include the Group 13
 metal compound contacting step.
 Catalysts 19-22 each produced LLDPE polymers having substantially identical
 densities. Thus, films formed from these polymers possessed substantially
 identical stiffness. However, the lowest melt elasticity shift was
 obtained by the LLDPE polymerized in the presence of Catalyst 22 which
 included no terminating Group 13 metal compound contacting step in its
 synthesis. Catalysts 19, 20 and 21 were synthesized with the inclusion of
 a concluding contacting step with three different preferred Group 13 metal
 compounds. In each case the ER shift of the polymers produced by these
 catalysts was significantly higher than the ER shift of the polymer
 produced in the polymerization catalyzed by Catalyst 22 which did not
 include a Group 13 metal-containing compound contacting step. As such,
 they produced films having significantly higher impact strength.
 The above embodiments and examples are given to illustrate the scope and
 spirit of the present invention. These embodiments and examples will make
 apparent, to those skilled in the art, other embodiments and examples.
 These other embodiments and examples are within the scope of the present
 invention; therefore, the instant application should be limited only by
 the appended claims.