Polymerization catalyst and process

An olefin polymerization catalyst is provided comprising chromium oxide on a titanium-containing silica support having at least about 3 weight percent titanium in combination with an organoboron promoter. The titanium may be incorporated by coprecipitation with the silica gel or added anhydrously or nonanhydrously to the silica gel. The polymerization process comprises the contacting of olefin monomer with the titanium-containing chromium oxide catalyst in the presence of an organoboron promoter.

BACKGROUND OF THE INVENTION 
This invention relates to modified supported chromium oxide olefin 
polymerization catalysts. 
It further relates to a method of making ethylene polymers and copolymers. 
Supported chromium oxide catalysts have been used for many years in the 
polymerization of olefins. Ethylene can be polymerized by contacting the 
monomer with a silica-supported chromium oxide catalyst, the reaction 
being carried out in an inert liquid at temperatures below 130.degree. C. 
for producing solid polymer suspended in the liquid or at temperatures 
above 130.degree. C. for solution polymerization. The properties of the 
resulting polymer depend upon a number of factors, including the type of 
catalyst employed and its activation temperature, the reaction pressure, 
and the reaction temperature. It is generally known that titanium can be 
added to the supported chromium oxide catalyst to produce a polymer having 
an increased melt index. It is also generally known that certain 
substances called promoters or adjuvants can be used in combination with 
chromium oxide catalysts to modify the properties of the polymer. The use 
of chromium catalysts with certain organoboron promoters is known 
generally to broaden the molecular weight distribution and improve the 
environmental stress crack resistance of polymers made using these 
catalysts as well as to increase the catalyst productivity. 
Attempts have been made to obtain ethylene polymers having the high 
productivity and the improved environmental stress crack resistance 
imparted by organoboron promoters and the increased melt index potential 
obtained with chromium oxide-silica catalysts containing titanium. When 
commercial cogel catalysts containing 2.0 to 2.5 weight percent titanium 
were employed with triethylborane (TEB) as a promoter, the resulting 
polymers exhibited reduced density, which resulted in ethylene polymers 
which lacked the high stiffness desired for blow molding and injection 
molding applications. It is believed that the use of the organoboron 
compound with chromium oxide catalysts containing about 2.5 weight percent 
or less titanium results in the production of a small amount of 1-butene 
and 1-hexene from the ethylene monomer. These higher olefins are 
incorporated into the polymer chain, reducing the density by disrupting 
the linear polymer structure. In polymerization processes in which 
ethylene monomer is recycled to the reactor, the presence of these higher 
olefins may necessitate a fractionation step to separate the accumulated 
butene and hexene from the ethylene monomer. When ethylene is 
copolymerized with other monomers, the generation of higher olefins in the 
reactor complicates the process of maintaining the ethylenecomonomer ratio 
and thereby producing polymer having a predictable density. 
It is therefore an object of this invention to provide an improved chromium 
oxide polymerization catalyst. 
It is a further object to provide a process by which high-density ethylene 
polymers having a high melt index and good stress crack resistance are 
prepared in high yield. 
It is a further object of the invention to minimize the production of 
higher olefins during the polymerization process. 
SUMMARY OF THE INVENTION 
According to one embodiment of the invention, a polymerization catalyst is 
provided which comprises chromium oxide on a silica-titania support 
containing at least about 3 weight percent titanium in combination with an 
organoboron promoter. Further according to the invention, an ethylene 
polymer or copolymer is produced by contacting an ethylene monomer with an 
activated catalyst comprising silica-supported chromium oxide containing 
at least about 3 weight percent titanium in the presence of an organoboron 
promoter. The resulting polymer is produced in high yield and has a 
combination of properties including high shear response, good 
environmental stress crack resistance, and high density. 
DETAILED DESCRIPTION OF THE INVENTION 
The silica-containing substrates used in the invention catalyst are silica 
or silica-alumina gels. Such gels conventionally are prepared by mixing an 
acid such as sulfuric acid with an aqueous solution of an alkali metal 
silicate such as sodium silicate to produce an aqueous gel, or hydrogel. 
The silicate is preferably added to the acid, and the reaction mixture is 
strongly agitated. The mixing temperature can range from about 1.degree. 
to 43.degree. C. The resulting hydrogel is approximately 3 to 12 weight 
percent SiO.sub.2 and has a pH in the range of about 3 to 9. The hydrogel 
is aged at a temperature of about 18.degree. to 98.degree. C. for a 
suitable time, generally more than one hour. Silica gels often have a 
minor portion, generally not exceeding 20 weight percent, of alumina or 
other metal oxides, and the support of the invention includes composite 
silica gels comprising silica and alumina, thoria, zirconia and like 
substances. 
The hydrogel is then washed with water and either an ammonium salt solution 
or a dilute acid to reduce the alkali metal content of the gel to less 
than about 0.1 weight percent. The ammonium salt solution is preferably 
one such as ammonium nitrate or an ammonium salt of an organic acid which 
volatizes upon subsequent calcination. 
The water in the hydrogel can be removed by a conventional method such as 
repeated washing with an organic compound soluble in water, azeotropic 
distillation in the presence of an organic compound, or heating by a 
method such as spray drying, vacuum oven drying, or air-oven drying at 
temperatures up to about 425.degree. C. If the hydrogel is dried by 
heating, it may be necessary to add an agent to the gel to prevent 
shrinkage of the pores. This pore-preserving agent can be incorporated in 
one of the ingredients used to make the silica hydrogel, but it is 
preferably incorporated into the hydrogel after the washing step to avoid 
loss of the agent during washing. The pore-preserving agent can be 
selected from a variety of substances such as oxygen-containing organic 
compounds selected from polyhydric alcohols, mono- and dialkyl ethers of 
ethylene glycol, and poly(alkylene)glycol; anionic, cationic and nonionic 
surfactants; organic silicon compounds such as triarylsilanols as 
disclosed in Ser. No. 914,258, filed June 9, 1978; and combinations of the 
oxygen-containing compounds with a normally liquid hydrocarbon such as 
n-heptane or kerosene and, optionally, a surfactant. An alternate group of 
pore-preserving agents includes certain inorganic and organic acids used 
at a specified level of pH. The hydrogel is contacted with the acid in an 
amount sufficient to impart to the mixture a pH ranging generally from 
about 0 to about 3.5, preferably about 2.2 or below. Suitable acids are 
those which are water soluble, sufficiently ionized to produce the pH 
level required in the hydrogel, and are not harmful to the silica or the 
polymerization. For the production of ethylene polymerization catalysts, 
suitable inorganic acids include, for example, hydrochloric acid, 
hydrobromic acid, hydroiodic acid, nitric acid, sulfamic acid, sulfuric 
acid, orthophosphoric acid and iodic acid. Suitable organic acids include, 
for example, acetic acid, formic acid, tartaric acid, citric acid, maleic 
acid, malic acid, malonic acid, succinic acid, gluconic acid, diglycolic 
acid, ascorbic acid, cyclopentane tetracarboxylic acid, and 
benzenesulfonic acid. In general, the organic acids having suitable water 
solubility, stability, acid strength, and nondeleterious action also have 
pK values of about 4.76 or less as disclosed in Lange's Handbook of 
Chemistry, 11th Edition (1973), Tables 5-7, 5-8. That is, their acid 
strength is equal to or greater than that of acetic acid. Acids such as 
sulfuric acid and hydrochloric acid are generally preferred because of 
their availability, cost, strength and effectiveness in the process. The 
nonionic surfactant is the presently preferred pore-preserving agent for 
reasons of economy and effectiveness. 
If used, the oxygen-containing pore preserving agent is present in an 
amount such that the weight ratio of the oxygen-containing compound to 
hydrogel ranges from about 5:1 to 0.5:1. When a normally liquid 
hydrocarbon is used with the oxygen-containing organic compound, the 
weight ratio of hydrocarbon to organic compound can range from about 0.5:1 
to 20:1. When a surfactant is used with the hydrocarbon/oxygen-containing 
organic compound, generally about 0.1 to 5 weight percent surfactant is 
used based on the weight of the hydrocarbon/oxygen-containing organic 
compound mixture. If a surfactant or an organic silicon compound is used 
as the silica pore structure preserving agent, the weight ratio of 
hydrogel to surfactant or organic silicon compound can range from about 
20:1 to 500:1, preferably about 40:1 to 100:1. Sufficient treatment time 
is allotted for the agent to occupy the pores of the gel, generally about 
30 seconds to 10 hours. The use of certain pore-preserving agents such as 
the oxygen-containing compounds is disclosed in U.S. Pat. No. 4,169,926, 
the disclosure of which is hereby incorporated by reference. The treated 
hydrogel is then dried to remove the liquids. The drying procedure 
produces a porous silica gel which is substantially free of water, or 
xerogel, which can then be used as a substrate for the other components of 
the catalyst system. 
Titanation of the silica can be effected using a variety of methods. The 
titanated catalyst must contain at least about 3 weight percent titanium 
based on the weight of the catalyst (not including the organoboron 
component) after calcining. All or part of the titanium can be supplied by 
coprecipitation of silica and titania. In the coprecipitation method, a 
titanium compound such as a titanium halide, nitrate, sulfate, oxalate, or 
alkyl titanate, for example, is incorporated with the acid or the silicate 
in an amount such that the amount of titanium present as titanium dioxide 
in the final calcined catalyst is at least about 3 weight percent. The 
amount of titanium in the calcined catalyst will generally be about 3 
weight percent to about 10 weight percent, preferably within the range of 
about 3.0 to 4.0 weight percent. The coprecipitation of titania with 
silica is disclosed in U.S. Pat. No. 3,887,494, the disclosure of which is 
hereby incorporated by reference. 
Titanation of the catalyst support can alternatively be effected by 
impregnation of the hydrogel or xerogel before or after incorporation of 
the chromium component of the catalyst system. For example, an aqueous 
solution of a hydrolysis-resistant titanium compound can be incorporated 
into a silica hydrogel and dried by conventional techniques, preferably 
after incorporation of a pore-preserving agent as discussed above. 
Suitable hydrolysis-resistant compounds include certain titanium chelates, 
particularly alkanolamine titanates such as triethanolamine titanate, 
which is available commercially as Tyzor-TE.sup.(R). 
Titanation of the silica support can also be accomplished by adding a 
titanium compound to the silica xerogel, usually with heat to vaporize the 
solvent and cause titanium to be deposited on the support. Suitable 
titanium compounds for impregnation of the silica xerogel include the 
hydrolysis-resistant titanium chelates discussed above; titanium 
hydrocarbyloxides containing from 1 to about 12 carbon atoms per 
hydrocarbon group such as titanium alkoxides including titanium 
tetramethoxide, titanium tetraethoxide, titanium tetraisopropoxide, 
titanium tetradodecyloxide, titanium tetracyclohexyloxide, titanium 
tetraphenoxide; and titanium tetrahalides. Water-sensitive compounds such 
as titanium tetraisopropoxide are applied neat or dissolved in a 
nonaqueous solvent such as n-hexane. Water-tolerant compounds such as 
triethanolamine titanate can be applied in an aqueous or non-aqueous 
solvent. To incorporate the titanium into the support, the xerogel can be 
slurried with a nonaqueous solution or slurry of the titanium compound 
while heating the mixture moderately at temperatures up to about 
150.degree. C. to remove the solvent or diluent, and then activating as 
described below. The invention also includes catalysts in which a 
silica-titania gel containing less than 3 weight percent titanium is 
impregnated with a titanium compound to bring the total amount of titanium 
to a level of at least about 3 weight percent. 
The presently preferred method of titanation of the support is to add a 
titanium compound, preferably neat titanium tetraisopropoxide, to a silica 
xerogel in a fluidized bed prior to activation of the catalyst. The 
xerogel preferably contains chromium incorporated into the silica hydrogel 
as an aqueous solution of chromium acetate or chromium oxide prior to 
drying the hydrogel. The gel is placed in an activator, fluidized with dry 
nitrogen gas, and heated to about 100.degree. to 200.degree. C. for about 
2 hours. The titanium compound is added slowly to the fluidized catalyst 
while purging with dry nitrogen at the elevated temperature. The treated 
catalyst can then be activated by heating at about 400.degree. to about 
1000.degree. C. in dry air as described below. 
The chromium component of the catalyst comprises about 0.001 to about 10 
weight percent chromium, preferably about 0.1 to about 5 weight percent, 
based on the weight of the calcined catalyst. The chromium component can 
be coprecipitated with the silica or the silicatitania or added by means 
of an nonaqueous solution of a chromium compound such as tertiary butyl 
chromate to the xerogel, but it is preferably introduced by incorporating 
an aqueous solution of a watersoluble chromium compound into the hydrogel 
after washing the hydrogel to remove alkali metal ions. Suitable chromium 
compounds include chromium acetate, chromium nitrate, chromium sulfate, 
chromium trioxide, ammonium chromate or any other chromium compound which 
can be converted to chromium oxide by calcination, with at least part of 
the chromium being converted to the hexavalent state. As used herein, the 
term "chromium oxide", as used to describe the chromium compound present 
in the catalyst after calcining, includes fixed surface chromates formed 
by the reaction of chromium oxide and silica, as discussed in Hogan, J. 
Poly. Sci. A-1, 8, 2637-2652 (1970). The chromium compound is employed in 
an amount so as to provide the desired weight percent chromium in the 
final catalyst. 
The catalyst is activated by calcining at a temperature within the range of 
about 400.degree. to 1000.degree. C. in a dry atmosphere containing 
oxygen, usually dry air, for a time of about 10 minutes to 20 hours or 
longer. The activation can follow titanation of the catalyst in the 
activator, as described above, by heating the fluidized catalyst sample to 
about 316.degree. C., substituting dry air for the nitrogen atmosphere 
present during titanation, raising the temperature to at least about 
400.degree. C., and calcining the fluidized catalyst at this elevated 
temperature for the chosen activation time. The catalysts of the invention 
can also be activated for polymerization by a method involving sequential 
calcining in a nonoxidizing atmosphere such as carbon monoxide and an 
oxygen-containing atmosphere such as dry air, as disclosed in U.S. Pat. 
No. 4,151,122, the disclosure of which is hereby incorporated by 
reference. Following activation, the catalyst is stored in a dry 
atmosphere until used. 
The organoboron compounds used as promoters with the silicatitania chromium 
oxide catalyst of the invention can be expressed as BR.sub.3, wherein each 
R is selected independently from hydrogen, alkyl, cycloalkyl and aryl, at 
least one R in each compound being a hydrocarbon radical having from 1 to 
12 carbon atoms, with the total number of carbon atoms not exceeding 30 in 
each compound. Examples of suitable boron promoters include 
trimethylborane, triethylborane, tri-n-dodecylborane, tricyclohexylborane, 
tri(2-methylcyclopentyl)borane, triphenylborane, tribenzylborane, 
tri(2-ethylphenyl)borane, methyldiethylborane, and like compounds. Boron 
compounds such as diborane which form the organoboron compound in situ on 
contact with the olefin monomer(s) are also suitable. The trialkylboranes 
are presently preferred because of their availability. The amount of boron 
compound used is generally within the range of about 0.3 to about 15 
weight percent preferably about 0.5 to about 13 weight percent, based on 
the weight of the calcined catalyst fed to the reactor. In a continuous 
particle form process using a loop reactor, for example, it is convenient 
to introduce the organoboron compound as a separate stream into the 
reactor, either continuously or in pulses, as a dilute solution in an 
inert hydrocarbon, e.g., 0.1 weight percent in isobutane. The 
concentration of the organoboron compound can also be expressed in parts 
per million based on the diluent used in the polymerization reactor. The 
weight percent ranges given above correspond to a range of about 0.1 to 
about 12 ppm organoboron compound, based on the amount of diluent charged 
per hour in a continuous particle form process using a loop reactor. 
The catalyst of the invention is suitable for the production of normally 
solid ethylene homopolymer and copolymers, preferably in a particle-form 
process. Ethylene can be copolymerized with one or more aliphatic 
mono-1-olefins containing from 3 to about 10 carbon atoms and/or a 
conjugated diolefin containing from 4 to about 12 carbon atoms. In such 
polymers the ethylene content generally ranges from about 90 to about 99.9 
mole percent. Examples of the polymers which can be produced include 
polyethylene, ethylene/1-butene copolymers, ethylene/1-hexene copolymers, 
ethylene/1,3-butadiene copolymers, ethylene/propylene copolymers and 
ethylene/propylene/1,3-butadiene terpolymers. The polymers can be 
fabricated by conventional plastics processes such as blow molding and 
injection molding into various useful articles such as film, bottles, 
fibers, and pipes. 
Polymerization according to the process of the invention can be conducted 
batchwise in a stirred reactor or continuously in a loop reactor or series 
of reactors. The monomer(s) can be polymerized by contact with the 
invention catalyst systems under particle form, solution or gas phase 
conditions at temperatures ranging from about 20.degree. to 200.degree. C. 
and pressures from about atmospheric to about 6.9 MPa (1000 psia) or 
higher. 
It is preferred to conduct the polymerization under particle form 
conditions to obtain the polymer in the form of discrete, solid particles 
suspended in the reaction medium. This can be accomplished by conducting 
the polymerization in the presence of a dry inert hydrocarbon diluent such 
as isobutane, n-heptane, methylcyclohexane, or benzene at a reactor 
temperature within the range of about 60.degree. to about 110.degree. C. 
and a reactor pressure of about 1.7 to about 4.1 MPa (250 to 600 psia). 
The polymer can be recovered, treated with CO.sub.2 or H.sub.2 O, for 
example, to deactivate residual catalyst, stabilized with an antioxidant 
such as butylated hydroxy toluene (BHT), and dried by conventional methods 
to obtain the final product. Hydrogen can be used in the reactor as known 
in the art to provide some control of the molecular weight of the polymer.

EXAMPLE I 
Catalyst Titanation and Activation 
Catalysts prepared in three different ways were used in the example 
polymerization runs. Catalysts A in Table I were cogel catalysts prepared 
by coprecipitation of an aqueous sodium silicate solution with sulfuric 
acid containing sufficient titanyl sulfate to obtain a series of catalysts 
(after activation) containing about 2 to about 2.5 weight percent titanium 
as the dioxide. The hydrogel cogels were impregnated with sufficient 
aqueous chromium trioxide to provide about 1 weight percent chromium on 
the final activated catalysts and were dried by azeotropic distillation 
with ethyl acetate. These chromium oxide cogel catalysts are commercially 
available materials. 
Catalyst B is a catalyst containing about 1 weight percent chromium, the 
remainder being silica and about 0.1 weight percent alumina. The catalyst 
is prepared by spray-drying a silica hydrogel having about 20 weight 
percent solids and containing an aqueous solution of chromium acetate 
sufficient to give 1 weight percent chromium in the final dried catalyst. 
Catalyst C is similar to catalyst B, except the silica hydrogel was spray 
dried in the presence of 3 weight percent Siponic.sup.(R) F-300 
(polyoxyethylated (30) t-octylphenol), a liquid nonionic surfactant sold 
by Alcolac Inc., Baltimore, Md. 
Two titanation methods were used in titanating the above catalysts. In 
method I, the catalyst sample was placed in an activator 7.62 cm in 
diameter, and titanium in the form of neat titanium tetraisopropoxide was 
slowly added to the fluidized catalyst sample while purging with dry 
nitrogen at 300.degree. F. (149.degree. C.). The treated catalyst was then 
heated to 600.degree. F. (316.degree. C.), dry air was then substituted 
for the nitrogen, the temperature was raised to the activation temperature 
shown in Table I, and calcining at that temperature was continued for 6 
hours using a superficial air velocity of about 0.16 ft./sec. (4.9 
cm/sec). Following activation, the recovered catalyst was stored in a dry 
atmosphere until ready for use. 
In titanation method II, dry samples of catalyst B were slurried with an 
aqueous solution of a commercially available triethanolamine titanate (du 
Pont's Tyzor-TE) sufficient to supply the calculated amount of titanium, 
based on the weight of the calcined catalyst. The slurry was dried and the 
product activated as previously described by calcining in air at an 
elevated temperature. 
EXAMPLE II 
Ethylene Polymerization 
Ethylene was polymerized in a continuous process in an 87-liter pipe loop 
reactor using samples of the catalysts of Example I. Isobutane was used as 
the diluent, and an operating pressure of about 3.65 MPa was maintained. 
Catalyst as a slurry in dry isobutane was intermittently charged to the 
reactor as required in 0.2 mL increments at the rate of about 10 to 30 
additions per hour. Ethylene, isobutane, comonomer, if used, and a 0.1 
weight percent solution of triethylborane in isobutane were supplied to 
the reactor as required. Reactor effluent was intermittently discharged 
and passed to a chamber where volatiles were flashed off. The polymer was 
recovered and dried to determine catalyst productivity. Polymer samples 
were stabilized with a conventional antioxidant system, and the polymer 
melt index (ASTM D 1238-65T, condition E), high load melt index (ASTM D 
1238-65T, condition F), and density (ASTM D 1505-68) were determined. 
The nature of the catalysts used, reactor conditions and results obtained 
are presented in Table I. 
TABLE I 
__________________________________________________________________________ 
Catalyst Reactor Conditions 
Catalyst 
Total Res. 
Productivity 
Polymer Properties 
Run 
Catalyst 
Titanation 
Ti Activ. 
TEB Wt. % 
Temp. 
Time 
g polymer/g 
HLMI Density 
(Fluff) 
No. 
No. Method 
Wt. % 
Temp. .degree.C. 
ppm 1-Hexene 
.degree.C. 
Hrs Catalyst 
(MI) g/cc Remarks 
__________________________________________________________________________ 
1 A coprec. 
2.5 704 9.6 2.7 92.9 
1.29 
5200 (0.14) 
0.951 
control 
2 A coprec. 
2.5 704 7.3 0 102.7 
1.27 
6700 (0.15) 
.954 control 
3 A coprec. 
2.0 704 4.1 0 104.6 
1.57 
6300 (0.17) 
.954 control 
4 A coprec. 
2.2 704 0 0 109.8 
1.69 
6300 (0.70) 
.961 control 
5 A I.sup.(a) 
3.0 677 3.4 0 99.4 
1.28 
7400 10.2 .961 invention 
6 B none 0 760 0 0 108.4 
1.27 
3900 (0.64).sup.(b) 
.966 control 
7 B none 0 760 0 0 107.2 
1.01 
2700 (0.73) 
.964 control 
8 B none 0 760 4.3 0 104.6 
1.27 
7100 11.5 .955 control 
9 B none 0 649 8.0 0 101.8 
1.28 
5600 9.1 .956 control 
10 B I 3.0 677 4.2 0 98.7 
1.27 
8200 8.8 .963 invention 
11 B I 3.0 816 3.1 0 97.2 
1.26 
5000 9.3 .961 invention 
12 B I 3.0 593 3.2 0 102.2 
1.28 
6700 8.4 .962 invention 
13 B II 3.0 677 4.3 0 98.3 
1.27 
6400 5.8 .961 invention 
14 B II 3.0 677 4.1 6.3 91.1 
1.25 
4800 10.2 .950 invention 
15 B II 3.0 677 4.1 0 101.1 
1.27 
6700 9.9 .962 invention 
16 C I 3.0 677 4.4 0 98.6 
1.27 
6700 15.5 963 invention 
17 C I 3.0 816 0 0 108.9 
1.26 
2200 (3.1) 
.963 control 
18 C I 4.0 649 4.1 0 100.2 
1.27 
7100 10.5 .963 invention 
__________________________________________________________________________ 
.sup.(a) Initial Ti level is 2 wt. %. 
.sup.(b) Properties determined from pelletized resin in run 6. 
The data outlined in the table show that ethylene polymers can be prepared 
in high yields using a chromium oxide-silica catalyst having at least 
about 3 weight percent titanium with a triethylborane promoter without the 
reduction in polymer density which generally results from using a TEB 
promoter with a catalyst having less titanium. The improvement is realized 
with catalysts containing at least about 3 weight percent titanium 
regardless of whether the titanium was incorporated in a single step or 
incorporated by coprecipitation and subsequent addition of an amount 
needed to bring the total titanium to at least about 3 weight percent, as 
an invention Run 5. The use of the invention catalyst permits the 
production of ethylene homopolymer having the desired density of at least 
about 0.960 g/cc without the necessity of hexane removal by thermal 
fractionation. 
Control Runs 2 and 3 show the results of polymerizations conducted using 
cogel catalysts containing less than 3 weight percent titanium with TEB in 
the reactor. The density of the resulting polymer, 0.954 g/cc, suggests 
that ethylene homopolymer was not being formed, since homopolymer 
densities are generally at least about 0.96 g/cc. Comparisons of Runs 2 
and 3 with Run 4 in which no TEB was used, and Run 7 (no TEB, density of 
0.964) and Run 8 (4.3 ppm TEB, density of 0.955) and Run 9 (8.0 ppm TEB, 
density of 0.956) show that the addition of TEB tends to depress polymer 
density while generally increasing catalyst productivity. The use of TEB 
in combination with at least 3 weight percent titanium permitted the 
recovery of polymers having densities above 0.960 g/cc. Invention Run 14 
shows that ethylene/1-hexene copolymers can be prepared with the invention 
catalyst.