High activity polyethylene catalysts

A catalyst for producing higher flow index linear low density polyethylene with relatively narrower molecular weight distributions is described. The catalyst is formed by treating silica having reactive OH groups with a dialkylmagnesium in a solvent for said dialkylmagnesium; then adding to said solvent a carbonyl containing compound to form an intermediate which is subsequently treated with a transition metal to form a catalyst precursor. The catalyst precursor is activated with triethylaluminum.

FIELD OF THE INVENTION 
The present invention relates to a method for copolymerizing ethylene and 
alpha-olefins, a catalyst for such a polymerization and a method for 
producing such a catalyst. A particular aspect of the present invention 
relates to a method for producing linear low density copolymers of 
ethylene, hereinafter referred to as "LLDPE". 
LLDPE resins possess properties which distinguish them from other 
polyethylene polymers such as homopolymers of polyethylene. Certain of 
these properties are described in the Anderson et al U.S. Pat. No. 
4,076,698. 
BACKGROUND OF THE INVENTION 
When the LLDPE resins are fabricated into injection-molded products, it is 
imperative to assure that such products are not susceptible to warping or 
shrinking. As is known to those skilled in the art, the degree of warping 
or shrinking can be predicted from the molecular weight distribution of 
the resins. Resins having a relatively narrow molecular weight 
distribution produce injection-molded products exhibiting a minimum amount 
of warping or shrinkage. Conversely, resins having a relatively broader 
molecular weight distribution produce injection-molded products more 
likely to undergo warping or shrinkage. 
One of the measures of the molecular weight distribution of the resin is 
melt flow ratio (MFR), which is the ratio of high melt flow index (HLMI or 
I.sub.21) to melt index (I.sub.2) for a given resin. The MFR value is 
believed to be an indication of the molecular weight distribution of the 
polymer, the higher the value, the broader the molecular weight 
distribution. Resins having relatively low MFR values, e.g., of about 20 
to about 50, have relatively narrow molecular weight distributions. 
Additionally, LLDPE resins having such relatively low MFR values produce 
films of better strength properties than resins with high MFR values. 
Flow index response is attributable to the catalyst system used in 
polymerization. 
The molecular weight of ethylene copolymers may be controlled in a known 
manner, e.g., by using hydrogen. With the catalysts produced according to 
the present invention, molecular weight may be suitably controlled with 
hydrogen when the polymerization is carried out at relatively low 
temperatures, e.g., from about 30.degree. to about 105.degree. C. This 
control of molecular weight may be evidenced by a measurable positive 
change in melt index (I.sub.2) of the polymer produced. 
Another important property of catalyst compositions for 
ethylene/alpha-olefin copolymerization is the ability thereof to 
effectively copolymerize ethylene with higher alpha-olefins, e.g., C.sub.3 
-C.sub.10 alpha-olefins, to produce resins having low densities. This 
property of the catalyst composition is referred to as "higher 
alpha-olefin incorporation property" and is usually measured by 
determining the amount of a higher alpha-olefin (e.g., 1-butene, 1-hexene 
or 1-octene) required in the polymerization process, e.g. fluid-bed 
reactor process, to produce a copolymer of ethylene and the higher 
alpha-olefin having a given density. The lesser is the amount of the 
higher alpha-olefin required to produce a resin of a given density, the 
higher are the production rates and, therefore, the lower is the cost of 
producing such a copolymer. A high value of an alpha-olefin incorporation 
factor is especially important in the gas-phase fluid bed process, because 
relatively high concentrations of higher alpha-olefins in the fluid-bed 
reactor may cause poor fluidization caused, e.g., by resin stickiness. 
Therefore, production rates must be significantly reduced to avoid such 
problems. Consequently, catalyst compositions with relatively high 
alpha-olefin incorporation factor values avoid these problems and are more 
desirable. 
Accordingly, it is important to provide a catalyst composition capable of 
producing ethylene copolymers having a relatively narrow molecular weight 
distribution (low MFR values) and low densities. 
It is therefore a primary object of the present invention to provide a high 
activity catalyst for the polymerization of alpha-olefins yielding 
products of a relatively narrow molecular weight distribution. 
It is an additional object of the present invention to provide a catalytic 
process for copolymerizing ethylene and alpha-olefins which yields LLDPE 
resins of a relatively narrow molecular weight distribution at high 
productivity. 
SUMMARY OF THE INVENTION 
A supported catalyst composition of this invention is prepared in a 
multi-step process. In the first step, a mixture of a solid, porous 
carrier and a non-polar liquid, specifically a solvent, is contacted with 
at least one organomagnesium compound of the formula 
EQU R.sub.m Mg R'.sub.n 
where R and R' are the same or different C.sub.2 -C.sub.12 alkyl groups, 
preferably C.sub.4 -C.sub.10 alkyl groups, more preferably C.sub.4 
-C.sub.8 alkyl groups, and most preferably both R and R' are butyl groups, 
and m and n are each 0, 1 or 2, providing that m+n=2. 
Subsequently, the mixture of the first step is contacted with at least one 
carbonyl compound. The carbonyl treated mixture is then contacted with at 
least one transition metal compound soluble in the non-polar solvent. The 
resulting mixture is subsequently contacted, for activation and activated 
catalyst production, with a trialkylaluminum. 
The resulting activated catalyst composition has substantially higher 
activity and thus exhibits relatively high productivity in the 
copolymerization of ethylene and alpha-olefins. The catalyst also produces 
polymers having a narrow molecular weight distribution. The molecular 
weight distribution is narrower than that of polymers produced with 
catalytic compositions free of the carbonyl compound. The catalyst also 
produces polymers having increased flow index; that is, the flow index is 
greater than that of polymers produced with catalytic compositions free of 
the carbonyl compound 
DETAILED DESCRIPTION 
In accordance with the present invention, a supported titanium compound is 
incorporated onto a suitable support by impregnating this support first 
with a reactive magnesium compound and utilizing this supported magnesium 
compound to react with a tetravalent titanium compound in a liquid medium. 
The unreacted titanium compound remains soluble in this liquid medium, 
while the reacted titanium species and the supported magnesium species are 
insoluble in this liquid medium. 
As used herein, the concept of supporting a material on a carrier is 
intended to connote the incorporation of material (e.g., magnesium 
compounds and/or titantium compounds) onto the carrier by physical or 
chemical means. Accordingly, supported material need not necessarily be 
chemically bound to the carrier. 
Catalysts produced according to the present invention may be described in 
terms of the manner in which they can be made. More particularly, these 
catalysts can be described in terms of the manner in which a suitable 
carrier may be treated in order to form such catalysts. 
Suitable carrier materials which may be treated include solid, porous 
carrier materials such as silica, alumina and combinations thereof Such 
carrier materials may be amorphous or crystalline in form. These carriers 
may be in the form of particles having a particle size of from about 0.1 
micron to about 250 microns, preferably from 10 to about 200 microns, and 
most preferably from about 10 to about 80 microns. Preferably, the carrier 
is in the form of spherical particles, e.g., spray dried silica. 
The carrier material is also porous. The internal porosity of these 
carriers may be larger than 0.2 cm.sup.3 /gm, e.g., larger than about 0.6 
cm.sup.3 /g. The specific surface area of these carriers is at least 3 
m.sup.2 /g, preferably at least about 50 m.sup.2 /g, and more preferably 
from, e.g., about 150 to about 1500 m.sup.2 /g. 
It is desirable to remove physically bound water from the carrier material 
prior to contacting this material with water-reactive magnesium compounds. 
This water removal may be accomplished by heating the carrier material to 
a temperature from about 100.degree. C. to an upper limit of temperature 
represented by the temperature at which sintering occurs. A suitable range 
of temperatures may, thus, be from about 100.degree. C. to about 
800.degree. C., e.g., from about 150.degree. C. to about 650.degree. C. 
Silanol groups (Si-OH) may be present when the carrier is contacted with 
water-reactive magnesium compounds in accordance with the present 
invention. These Si-OH groups may be present at from about 0.5 to about 3 
mmoles of OH groups per gram of carrier, but a preferred range is from 
about 0.4 to about 1.5 mmoles of OH groups per gram of carrier. Excess OH 
groups present in the carrier may be removed by heating the carrier for a 
sufficient time at a sufficient temperature to accomplish the desired 
removal. More particularly, for example, a relatively small number of OH 
groups may be removed by sufficient heating at from about 150.degree. C. 
to about 250.degree. C., whereas a relatively large number of OH groups 
may be removed by sufficient heating at least 500.degree. or 800.degree. 
C., most especially, from about 550.degree. C. to about 650.degree. C. The 
duration of heating may be from 4 to 16 hours. In a most preferred 
embodiment, the carrier is silica which, prior to the use thereof in the 
first catalyst synthesis step, has been dehydrated by fluidizing it with 
nitrogen or air and heating at least about 600.degree. C. for about 16 
hours to achieve a surface hydroxyl group concentration of about 0.7 
millimoles per gram (mmol/gm). The surface hydroxyl concentration of 
silica may be determined according to J. B. Peri and A. L. Hensley, Jr., 
J. Phys. Chem., 72 (8), 2926 (1968). The silica of the most preferred 
embodiment is a high surface area, amorphous silica (surface area=300 
m.sup.2 /gm; pore volume of 1.65 cm.sup.3 /gm), and it is a material 
marketed under the tradenames of Davison 952 or Davison 955 by the Davison 
Chemical Division of W. R. Grace and Company. When silica which has been 
dehydrated by fluidizing with nitrogen or air and heating at about 
600.degree. C. for about 16 hours, the surface hydroxyl concentration is 
about 0.72 mmols/g. 
While heating is a preferred means of removing OH groups inherently present 
in a carrier such as silica, other removal means are also possible such as 
chemical means. For example, a desired proportion of OH groups may be 
reacted with a chemical agent such as a hydroxyl reactive aluminum 
compound, e.g., triethylaluminum. 
Other examples of suitable carrier materials are described in the Graff, 
U.S. Pat. No. 4,173,547. Note particularly the passage extending from 
column 3, line 62 to column 5, line 44 of this Graff patent. It is noted 
that internal porosity of carriers can be determined by a technique termed 
BET-technique, described by S. Brunauer, P. Emmett and E. Teller in 
Journal of the American Chemical Society, 60, pp. 209-319 (1938). Specific 
surface areas of carriers can also be measured in accordance with the 
above-mentioned BET-technique, with use of the standardized method as 
described in British Standards BS 4359, Volume 1, (1969). 
The carrier material is slurried in a non-polar solvent and the resulting 
slurry is contacted with at least one organomagnesium compound. The slurry 
of the carrier material in the solvent is prepared by introducing the 
carrier into the solvent, preferably while stirring, and heating the 
mixture to about 25.degree. to about 100.degree. C., preferably to about 
40.degree. to about 60.degree. C. The slurry is then contacted with the 
aforementioned organomagnesium compound, while the heating is continued at 
the aforementioned temperature. 
The organomagnesium compound has the empirical formula 
EQU R.sub.m Mg R'.sub.n 
where R and R' are the same or different C.sub.2 -C.sub.12 alkyl groups, 
preferably C.sub.4 -C.sub.10 alkyl groups, more preferably C.sub.4 
-C.sub.8 alkyl groups, and most preferably both R and R' are butyl groups, 
and m and n are each 0, 1 or 2, providing that m+n=2. 
Suitable non-polar solvents are materials in which all of the reactants 
used herein, e.g., the organomagnesium compound, the transition metal 
compound, and the carbonyl compound are at least partially soluble and 
which are liquid at reaction temperatures. Preferred non-polar solvents 
are alkanes, such as isopentane, hexane, n-heptane, octane, nonane, and 
decane, although a variety of other materials including cycloalkanes, such 
as cyclohexane, aromatics, such as benzene and ethylbenzene, may also be 
employed. The most preferred non-polar solvents are isopentane, hexane, or 
heptane. Prior to use, the non-polar solvent should be purified, such as 
by percolation through silica gel and/or molecular sieves, to remove 
traces of water, oxygen, polar compounds, and other materials capable of 
adversely affecting catalyst activity. 
In the most preferred embodiment of the synthesis of this catalyst it is 
important to add only such an amount of the organomagnesium compound that 
will be deposited--physically or chemically--onto the support since any 
excess of the organomagnesium compound in the solution may react with 
other synthesis chemicals and precipitate outside of the support. The 
carrier drying temperature affects the number of sites on the carrier 
available for the organomagnesium compound--the higher the drying 
temperature the lower the number of sites. Thus, the exact molar ratio of 
the organomagnesium compound to the hydroxyl groups will vary and must be 
determined on a case-by-case basis to assure that only so much of the 
organomagnesium compound is added to the solution as will be deposited 
onto the support without leaving any excess of the organomagnesium 
compound in the solution. Thus, the molar ratios given below are intended 
only as an approximate guideline and the exact amount of the 
organomagnesium compound in this embodiment must be controlled by the 
functional limitation discussed above, i.e., it must not be greater than 
that which can be deposited onto the support. If greater than that amount 
is added to the solvent, the excess may react with the reagents added 
subsequently, thereby forming a precipitate outside of the support which 
is detrimental in the synthesis of our catalyst and must be avoided. The 
amount of the organomagnesium compound which is not greater than that 
deposited onto the support can be determined in any conventional manner, 
e.g., by adding the organomagnesium compound to the slurry of the carrier 
in the solvent, while stirring the slurry, until the organomagnesium 
compoundion is detected in the solvent. 
For example, for the silica carrier heated at about 600.degree. C., the 
amount of the organomagnesium compound added to the slurry is such that 
the molar ratio of Mg to the hydroxyl groups (OH) in the solid carrier is 
about 1:1 to about 4:1, preferably about 1.1:1 to about 2.8:1, more 
preferably about 1.2:1 to about 1.8:1 and most preferably about 1.4:1. 
It is also possible to add such an amount of the organomagesium compound 
which is in excess of that which will be deposited onto the support, and 
then remove, e.g., by filtration and washing, the organomagnesium compound 
not deposited onto the carrier. However, this alternative is less 
desirable than the most preferred embodiment described above. 
Preferably, the carrier should be impregnated such that the pores of same 
contain the reactive solid magnesium compound. A preferred means of 
accomplishing this result is by incorporating a porous carrier in a liquid 
medium containing dissolved organomagnesium compound and allowing 
magnesium to become impregnated into the pores of the carrier by a 
reaction of the organomagnesium compound. Evaporation of the non-polar 
solvent which is a non-Lewis base liquid from this step would obtain a 
carrier, containing magnesium, in the form of a dry, free-flowing powder. 
The amount of magnesium compound which is impregnated onto the carrier 
should be sufficient to react with the carbonyl compound and then the 
tetravalent titanium compound in order to incorporate a catalytically 
effective amount of titanium on the carrier in the manner set forth herein 
below. When a liquid containing an organomagnesium compound is contacted 
with a carrier the amount of magnesium in this liquid in terms of mmoles 
may be essentially the same as that stated above with respect to that 
which is impregnated onto the carrier. 
An essential component in the production of the catalyst composition of the 
invention is a carbonyl compound, which is added as a component to the 
catalyst or catalyst precursor preparation. The carbonyl compound is of 
the formula 
##STR1## 
wherein R is phenyl or alkyl of 1 to 12 carbon atoms and R' is Cl--, alkyl 
of 1 to 6 carbon atoms or --OR" wherein R" is phenyl alkyl of 1 to 8 
carbon atoms. The compound is added in an amount effective to decrease the 
molecular weight distribution of the copolymer or in amounts effective to 
increase catalyst activity. Generally the amount of this compound is such 
that the molar ratio of carbonyl compound to Mg ranges from 0.40 to 1.40. 
The slurry of the carrier material containing the organomagnesium species 
in the solvent is maintained at temperatures of about 40.degree. to about 
60.degree. C., for introduction of the carbonyl compound. The carbonyl 
compound is introduced after organomagnesium incorporation and preferably 
before transition metal incorporation into the catalyst. The amount of the 
carbonyl compound added to the slurry is such that the molar ratio of 
carbonyl to Mg on the solid carrier is about 0.40 to about 1.40. 
The slurry is then contacted with at least one transition metal compound 
soluble in the non-polar solvent. This synthesis step is conducted at 
about 25.degree. to about 65.degree. C., preferably at about 30.degree. to 
about 60.degree. C., and most preferably at about 45.degree. to about 
55.degree. C. In a preferred embodiment, the amount of the transition 
metal compound added is not greater than that which can be deposited onto 
the carrier. The exact molar ratio of Mg to the transition metal and of 
the transition metal to the hydroxyl groups of the carrier will therefore 
vary (depending, e.g., on the carrier drying temperature) and must be 
determined on a case-by-case basis. For example, for the silica carrier 
heated at about 200.degree. to about 850.degree. C., the amount of the 
transition metal compound is such that the molar ratio of the transition 
metal, derived from the transition metal compound, to the hydroxyl groups 
of the carrier is about 1 to about 2.0, preferably about 1.3 to about 2.0. 
The amount of the transition metal compound is also such that the molar 
ratio of Mg to the transition metal is about 0.5 to about 3, preferably 
about 1 to about 2. These molar ratios appear to produce a catalyst 
composition which produces resins having relatively low MFR values of 
about 20 to about 35. As is known to those skilled in the art, such resins 
can be utilized to produce high strength films or injection molding 
products which are resistant to warping and shrinking. 
Suitable transition metal compounds used herein are compounds of metals of 
Groups IVA, VA, VIA or VIII of the Periodic Chart of the Elements, as 
published by the Fisher Scientific Company, Catalog No. 5-702-10, 1978 
providing that such compounds are soluble in the non-polar solvents. 
Non-limiting examples of such compounds are titanium halides, e.g., 
titanium tetrachloride, titanium alkoxides (e.g., where the alkoxide 
moiety contains an alkyl radical of 1 to 6 carbon atoms, or mixtures 
thereof, and vanadium halides (vanadium tetrachloride), vanadium 
oxytrichloride, and vanadium alkoxides. The preferred transition metal 
compounds are titanium compounds, preferably tetravalent titanium 
compounds. The most preferred titanium compound is titanium tetrachloride. 
Mixtures of such transition metal compounds may also be used and generally 
no restrictions are imposed on the transition metal compounds which may be 
included. Any transition metal compound that may be used alone may also be 
used in conjunction with other transition metal compounds. 
The reaction of the transition metal compound, such as the tetravalent 
titanium compound, in the liquid medium conveniently takes place by 
slurrying the solid carrier containing the reactive magnesium species in a 
solution of the tetravalent titanium compound and heating the reaction 
medium to a suitable reaction temperature, e.g., to the reflux temperature 
of the solvent at standard atmospheric pressure. Thus, the reaction may 
take place under reflux conditions. Preferred solvents for the tetravalent 
titanium compound are heptane or hexane or isopentane. 
The various reaction parameters are subject to a wide variety of 
possibilities, suitable selection of such parameters being well within the 
skill of those having ordinary skill in the art. However, for example, the 
volume of tetravalent titanium solution to treated carrier initially 
slurried in the solution may be from about 0.1 to about 10 ml per gram of 
such carrier. The concentration of the tetravalent titanium solution may 
be, for example, from about 0.1 to about 9 Molar. The amount of 
tetravalent titanium in solution may be, e.g., in excess of the molar 
amount of organomagnesium earlier used to treat the carrier. More 
particularly, for example, the molar ratio of tetravalent titanium to 
organomagnesium may be from about 0.3 to about 2, more particularly from 
about 0.7 to about 1.4. Unreacted titanium compounds may be removed by 
suitable separation techniques such as decantation, filtration and 
washing. 
The supported catalyst precursor formed from components described above is 
then activated with suitable activators. Suitable activators include 
organometallic compounds. Preferably, the activators are trialkylaluminum 
compounds. More preferably, the activator is triethylaluminum. 
The catalyst precursor may be activated in situ by adding the activator and 
catalyst precursor separately to the polymerization medium. It is also 
possible to combine the catalyst precursor and activator before 
introduction into the polymerization medium, e.g., for up to about 2 hours 
at a temperature from about -40.degree. to about 80.degree. C. 
A suitable activating amount of the activator may be used. The number of 
moles of activator per gram atom of titanium in the catalyst may be, e.g., 
from about 1 to about 100 and is preferably greater than about 5. 
Alpha-olefins may be polymerized with the catalysts prepared according to 
aspects of the present invention by any suitable process. Such processes 
include polymerizations carried out in suspension, in solution or in the 
gas phase. Gas phase polymerizations are preferred such as those taking 
place in stirred bed reactors and, especially, fluidized bed reactors. 
The molecular weight of the polymer may be controlled in a known manner, 
preferably by using hydrogen. With the catalysts produced according to the 
present invention, molecular weight may be suitably controlled with 
hydrogen when the polymerization is carried out at relatively low 
temperatures, e.g., from about 30.degree. to about 105.degree. C. 
The catalysts prepared according to the present invention are highly active 
and may have an activity of at least from about 2,000 to about 8,000 in 
terms of grams of polymer produced per hour per gram of catalyst per 100 
psi of ethylene pressure. 
The catalysts prepared according to the present invention are particularly 
useful for the production of LLDPE resins. Such LLDPE resins may have a 
density of 0.94 g/cc or less, preferably 0.930 or less or even 0.925 g/cc 
or less. In accordance with certain aspects of the present invention, it 
is possible to achieve densities of less than 0.915 g/cc and even 0.900 
g/cc. 
Advantageous properties of LLDPE resins are described in the Anderson et 
al. U.S. Pat. No. 4,076,698. These resins may be copolymers of ethylene 
with one or more C.sub.3 -C.sub.10 alpha-olefins. Thus, copolymers having 
two monomeric units are possible as well as terpolymers having three 
monomeric units. Particular examples of such polymers include 
ethylene/1-butene copolymers, ethylene/1-hexene copolymers, 
ethylene/4-methyl-1-pentene copolymers, ethylene/1-butene/1-hexene 
terpolymers, ethylene/propylene/1-hexene terpolymers and 
ethylene/propylene/1-butene terpolymers. 
The molecular weight distribution of the polymers prepared in the presence 
of the catalysts of the present invention, as expressed by the MFR values, 
varies from about 20 to 35, preferably about 25-29, for LLDPE products 
having a density of about 0.900 to about 0.940 g/cc, and an I.sub.2 (melt 
index) of about 0.1 to about 100. As is known to those skilled in the art, 
such MFR values are indicative of a relatively narrow molecular weight 
distribution of the polymer. As is also known to those skilled in the art, 
such MFR values are indicative of polymers especially suitable for 
injection molding applications since polymers having such MFR values 
exhibit relatively low amounts of warpage and shrinkage on cooling of the 
injection molded products. The relatively low MFR values of the polymers 
prepared with the catalysts of this invention also indicate that these 
resins are suitable for the preparation of various film products since 
such films are likely to have excellent strength properties. 
The LLDPE resins produced in accordance with the present invention 
preferably contain at least about 80 percent by weight of ethylene units. 
Most preferably, the LLDPE resins of the invention contain at least 2 
weight percent, for example from 2 to 20 weight percent of an alpha 
olefin. 
A particularly desirable method for producing LLDPE resins, according to 
the present invention, is in a fluid bed reactor. Such a reactor and means 
for operating same is described in the Levine et al U.S. Pat. No. 
4,011,382 or the Karol et al U.S. Pat. No. 4,302,566, each of which is 
relied upon and incorporated by reference herein. The activity of the 
catalyst produced in accordance with the present invention is sufficient 
to produce an LLDPE resin such as an ethylene/1-hexene copolymer, e.g., 
having a density of less than 0.940 g/cc, in such a fluid bed reactor. 
In order to achieve the desired density ranges in the copolymers it is 
necessary to copolymerize enough of the alpha-olefin comonomers with 
ethylene to achieve a level of 1 to 5 mol percent of the comonomer in the 
copolymer. The amount of the comonomer needed to achieve this result will 
depend on the particular comonomer(s) employed. 
In accordance with the invention, it has unexpectedly been found that using 
a gas phase catalytic polymerization reaction, 1-hexene can be 
incorporated into an ethylene-based copolymer chain with high efficiency. 
In other words, a relatively small concentration of 1-hexene monomer in 
the gas phase reactor can lead to a relatively large incorporation of 
1-hexene into the copolymer. Thus, 1-hexene can be incorporated into an 
ethylene-base copolymer chain in a gas phase reactor in amounts up to 15 
percent by weight, preferably 4 to 12 percent by weight, to produce an 
LLDPE resin having a density of less than 0.940 g/cc. 
It is essential to operate the fluid bed reactor at a temperature below the 
sintering temperature of the polymer particles. For the production of 
ethylene copolymers in the process of the present invention an operating 
temperature of about 30.degree. to 115.degree. C. is preferred, and a 
temperature of about 75.degree. to 95.degree. C. is most preferred. 
Temperatures of about 75.degree. to 90.degree. C. are used to prepare 
products having a density of about 0.91 to 0.92, and temperatures of about 
80.degree. to 100.degree. C. are used to prepare products having a density 
of about 0.92 to 0.94, and temperatures of about 90.degree. to 115.degree. 
C. are used to prepare products having a density of about 0.94 to 0.96. 
The fluid bed reactor is operated at pressures of up to about 1000 psi, and 
is preferably operated at a pressure of from about 150 to 350 psi. 
Films having especially desirable properties may be formed with the 
above-mentioned ethylene/1-hexene copolymers prepared with the catalysts 
of the present invention by a variety of techniques. For example, 
desirable blown films as well as slot cast films may be formed. 
Blown films formed from ethylene/1-hexene copolymers having a density from 
0.916 to 0.928 g/cc may have especially desirable properties for bag 
manufacture. For example, such blown films may be fabricated into trash 
bags. A particular example of a blown film formed from an 
ethylene/1-hexene copolymer having a density of 0.927 and an I.sub.2 of 1 
(ASTM D-1238, condition E), which is, in turn, formed in a gas phase, 
fluid bed reactor with a catalyst according to the present invention, is a 
blown film having an improved dart impact strength, enhanced Elmendorf 
tear strength in the machine direction of the film (MD) and higher tensile 
strength. 
Slot cast films formed from LLDPE ethylene/1-hexene copolymers having a 
density of from about 0.916 to about 0.92 may have especially desirable 
properties as pallet stretch wrap. A particular example of a slot cast 
film formed from an ethylene/1-hexene copolymer having a density of about 
0.92 and an I.sub.2 of 1.7 (ASTM D-1238, condition E), which is, in turn, 
formed in a gas phase, fluid bed reactor with a catalyst according to the 
present invention, is a slot cast film having a thickness of 1 mil, an 
improved MD tensile strength and a very high Elmendorf tear strength in 
the traverse direction of the film. 
The following Examples illustrate reactants and parameters which may be 
used in accordance with aspects of the present invention.

EXAMPLES 
EXAMPLE A - PREATION OF CATALYST PRECURSOR 
All manipulations were conducted under a nitrogen atmosphere by using 
standard Schlenk techniques. Into a 200 ml Schlenk flask was placed 7.0 
grams of Davison grade 955 silica, which was previously dried under a 
nitrogen purge at 600.degree. C. for about 16 hours. Hexane (90 ml) was 
added to the silica. Dibutylmagnesium (7.0 mmol) was added to the stirred 
slurry at 50.degree.-55.degree. C. and stirring was continued for one 
hour. A carbonyl compound (9.2 mmol) was added to the slurry 
(50.degree.-55.degree. C.) and stirring was continued for one hour. 
TiCl.sub.4 (7.0 mmol) was added to the reaction medium 
(50.degree.-55.degree. C.) and stirring was continued for an additional 
hour. Hexane was then removed by distillation with a nitrogen purge at 
50.degree.-55.degree. C. Yield varied from 8.5-9.5 grams depending on the 
carbonyl compound employed. Weight percent of Ti in the catalyst precursor 
varied from 2.56 to 3.62 depending on the carbonyl reagent. 
EXAMPLE B - POLYMERIZATION 
Ethylene/1-hexene copolymers were prepared with the catalyst precursors of 
Example A and triethylaluminum. A typical example is shown below. 
Polymerization 
A 1.6 liter stainless steel autoclave under a slow nitrogen purge at 
50.degree. C. was filled with 750 ml dry hexane and 30 ml of dry 1-hexene, 
and 3.0 mmol of triethylaluminum (TEAL) was added. The reactor was closed, 
the stirring was increased to 900 rpm, and the internal temperature was 
increased to 85.degree. C. The internal pressure was raised 12 psi with 
hydrogen. Ethylene was introduced to maintain the pressure at about 120 
psi. The internal temperature was decreased to 80.degree. C., 40 mg of 
catalyst precursor was introduced into the reactor with ethylene 
over-pressure, and the internal temperature was increased and held at 
85.degree. C. The polymerization was continued for 60 minutes, and then 
the ethylene supply was stopped and the reactor was allowed to cool to 
room temperature. The polyethylene was collected and air dried. 
Catalyst productivities, polymer flow indexes and MFR values are given in 
TABLE A below. Catalyst productivities are given in units of gram of 
polymer/gram of catalyst-h-100 psi ethylene. The catalyst precursors were 
prepared according to the sequence below and activated with TEAL. 
##STR2## 
TABLE A 
______________________________________ 
Carbonyl Compound 
Productivity 
Flow Index MFR 
______________________________________ 
None (Control) 
590 2.4 70.1 
ethyl benzoate 
2890 12.9 29.9 
2-pentanone 2940 17.1 27.6 
propiophenone 
3030 10.8 30.5 
benzoyl chloride 
3490 10.5 27.0 
propionyl chloride 
3440 8.7 27.2 
acetyl chloride 
3130 7.0 26.1 
______________________________________ 
The data show that carbonyl-based catalysts are much more active compared 
to the control catalyst and produce a polymer product which exhibits a 
much narrower molecular weight distribution. Also, the carbonyl-based 
catalysts have a higher flow index response compared to that of the 
control catalyst. 
Thus it is apparent that there has been provided, in accordance with the 
invention, a catalyst that fully satisfies the objects, aims, and 
advantages set forth above. While the invention has been described in 
conjunction with specific embodiments thereof, it is evident that many 
alternatives, modifications, and variations will be apparent to those 
skilled in the art in light of the foregoing description. Accordingly, it 
is intended to embrace all such alternatives, modifications, and 
variations as fall within the spirit and broad scope of the appended 
claims.