Note: Descriptions are shown in the official language in which they were submitted.
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MA,LEATED POLYPROPYLENES
AND PROCESSES FOR THE PREPARATION THEREOF
CROSS REFERENCE TO RELATED APPLICATIONS
The present application is related to and claims the priority benefit of
United States
Provisional Patent Application No. 60/289,269, filed 05/06/2001, which is
assigned to the
assignee of the present invention and which is incorporated herein by
reference.
FIELD OF INVENTION
The present invention relates to maleated polypropylenes and to methods for
producing maleated polypropylenes. More specifically, the invention relates to
methods for
producing maleated polypropylenes having a relatively high percentage of bound
malefic
anhydride moieties, and the maleated polypropylenes obtained from such
methods.
BACKGROUND
Maleated polyolefins, and in particular maleated polypropylenes, are known in
the
art and find use in a wide range of applications. For example, maleated
polypropylenes are
useful for compatibilizing polymers, particularly polyolefins with various
polar substrates,
including polar polymers, mineral fillers, and the like. Such copolymers are
also known for
use in metal bonding adhesive compositions.
Many classes of techniques are know for grafting malefic anhydride to a
polymer
backbone. For example, solid state maleation is carried out below the melting
point of the
polymer and the reaction takes place on the exposed surface of the polymer. In
solvent based
grafting, the substrate polymer is dissolved in an appropriate solvent and the
grafting reaction
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takes place in solution. In melt grafting, malefic anhydride is grafted onto a
polypropylene
backbone by introducing malefic anhydride, or a precursor thereof, into a melt
of
polypropylene polymer, typically in the presence of a catalyst.
Applicants have found that the conditions which have heretofore typically been
used
for grafting malefic anhydride onto a polymer backbone, and particularly the
conditions which
typically occur in melt grafting, tend to result in an undesirably small
percentage of the malefic
anhydride being bound to the polymer backbone. More particularly, applicants
have
discovered that prior art methods, as disclosed for example in U.S. Patent
Nos. 3,642,722 -
Knowles et al and 4,506,056 - Gaylord, each of which is incorporated herein by
reference,
result in maleated polypropylene products wherein less than about 50% of the
malefic
anhydride in the product of the grafting reaction is bound to the
polypropylene backbone.
Applicants believe that the remainder of the malefic anhydride present in the
prior art grafting
reaction product is unreacted and/or oligomeric malefic anhydride, as
indicated by the
articlelwork of Scott M. Hacker, one of the co-inventors hereof, entitled "Not
All Maleated
Polyolefins Are Created Equai"which is attached as an addendum hereto.
Applicants have recognized not only the above-noted drawbacks of the prior
art, but
that these drawbacks result in a product with poor performance properties in
ceratin
applications. More particularly, applicants have noted that one important use
for maleated
polypropylene is as a compatibilizing agent, particularly for polar
substrates, fibers and filler.
Applicants appreciate that as the level of bound malefic anhydride increases,
the
compatibilizing properties of the product increase. While bound malefic
anhydride contributes
to the desirable properties of maleated polypropylenes, unreacted and
oligomeric malefic
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anhydrides present in the pxoduct tend to inhibit such properties. In fact,
unbound malefic
anhydride compounds remaining in maleated polypropylene products tend to act
as scavengers
and inhibit the compatibilization properties of the maleated polypropylene.
SUMMARY OF THE 1NVENTION
The present invention is directed to methods for advantageously producing
maleated
polypropylenes having a relatively high percentage of bound malefic anhydride,
based on the
total amount of malefic anhydride moieties present in the grafting reaction
product, and the
maleated polypropylenes produced therefrom. The methods of the present
invention
overcome the disadvantages of the prior art by facilitating the production of
maleated
polypropylenes wherein at least about 60%, and preferably at least about 75%
of the malefic
anhydride moieties in the grafting reaction product are bound to the
polypropylene. Unless
indicated otherwise herein, all percentages are intended to refer to weight
percent.
The improved process is characterized judiciously selecting the type and
nature of the
reactants used and adding malefic anhydride to the selected polypropylene, and
preferably
polypropylene melt, under time, temperature and pressure conditions effective
to graft at least
about 55 %, and even more preferably at least about 60 %, of malefic anhydride
to the polymer
backbone, said percentage being based on the total malefic anhydride moieties,
including
precursors thereto, present in the grafting reaction product.
As used herein, the term "grafting reaction product" refers to maleated
polypropylene,
together with any unreacted components, by products and impurities, after the
grafting
reaction is deemed to be substantially completed, but before any subsequent
purification steps.
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As used herein, the term "polypropylene" refers to and includes homopolymers
of
polypropylene and aII forms of polypropylene copolymers, and in particular
polypropylene-
polyethylene copolymers, provided that at least about the majority of the
polymer is formed of
polypropylene moities on a mole percent basis. As used herein, the term
copolymer refers to
and includes terpolymers and the like. Preferably, the polyolefin reactant of
the present
invention is polypropylene homopolymer, or a copolymer of propylene and
ethylene wherein
the concentration by weight of ethylene is less than about 10%, and more
preferably less than
about 5%. As used herein, the term "maleated polypropylene" refers generally
to the reaction
product formed by grafting malefic anhydride, preferably by covalent bonding,
to the polymer
backbone of polypropylene. As is known in the art, therefore, such grafting
reaction products
in commercial applications generally comprise not only maleated polypropylene
but also as
unbound malefic anhydride and oligomeric malefic anhydride. The term "bound
malefic
anhydride" as used herein, refers generally to the moieties derived from
malefic anhydride
which are grafted to the polypropylene backbone according to the present
invention.
"Unbound malefic anhydride" refers generally to unreacted malefic anhydride or
oligomeric
anhydride present in the grafting reaction product. In embodiments in which
the reaction
takes place in the melt, the grafting reaction product is generally the melt
at the conclusion of
the grafting reaction step.
In certain preferred embodiments, the malefic anhydride is introduced to the
polypropylene, and preferably a polypropylene melt, at a rate that maintains
the concentration
of malefic anhydride in the reaction mixture (e.g., in the melt) at no greater
than about 120 %,
and even more preferably no greater than 100 %, of the solubility limit of the
malefic anhydride
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in the polypropylene at the reaction conditions.
Applicants have unexpectedly and counter intuitively discovered that grafting
malefic
anhydride to polypropylene in a reaction mixture wherein the amount of
unreacted malefic
anhydride in the mixture is maintained at a relatively low level is capable of
producing a
reaction product copolymer that either contains a very high level of bound
malefic anhydride
and/or contains a relatively low level of oligomeric malefic anhydride .
For embodiments in which the reactant comprises polypropylene-polyethylene
copolymer, applicants have also unexpectedly discovered that the amount of
malefic anhydride
which is bound in the grafting reaction is generally related to the amount of
polyethylene in the
copolymer. More particularly, it is generally preferred that the copolymer
comprise up to
about 10 mole % polyethylene, more preferably up to about 5 mole % of
polyethylene, and
even more preferably from about 0.5 mole% to about 3 mole% polyethylene.
Applicants have
discovered that polyethylene levels as described herein help to produce the
claimed high levels
of bound malefic anhydride without negatively efrecting the compatibalization
properties of the
reaction product.
The present invention therefore provides an improved graft malefic
anhydride/polypropylene copolymer product comprising polypropylene backbone,
bound
malefic anhydride and from about 0% to about 40% of unbound malefic anhydride
wherein at
least about 60 wt% of said malefic anhydride moieties, more preferably at
least about 65wt%
of said malefic anhydride moieties, and even more preferably at least about 70
% of said
moieties are bound malefic anhydride, based on the total malefic anhydride
moieties in the
reaction product. In especially preferred embodiments, at least about 75 % of
said moieties
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are bound malefic anhydride, based on the total malefic anhydride moieties in
the reaction
product.
DESCRIPTION OF PREFERRED EMBODIMENTS
One aspect of the present invention is directed to methods for producing
maleated
polypropylenes comprising reacting malefic anhydride, or a precursor thereof,
with
polypropylene in a reaction mixture. It is contemplated that various
particular process and
unit parameters can be adapted for use with the present reaction step, and a
wide range of
known methods and steps for combining and reacting malefic anhydride and
polypropylene in a
reaction mixture can be used according to the present invention. For example,
it is
contemplated that processes of the present invention may comprise one or more
of the classes
of reaction procedures known in the art, including: melt grafting, solid state
grafting, solution
grafting, and the like. However, present invention is preferably conducted by
melt grafting.
The steps of the present invention may be conducted on a continuous basis, on
a batch
basis, or on a combination of both. Those of skill in the art will, in view of
the teachings
contained herein, be able to adopt the present invention to any of these modes
of operation
without undue experimentation.
The amount of malefic anhydride which is bound in the reaction step of the
present
invention can be affected by numerous reaction parameters, including the
nature of the
polypropylene as described above, and applicants believe that it is highly
advantageous to
control one or more of the relevant parameters in accordance with teachings of
the present
invention in order to achieve a high level of bound malefic anhydride and/or
low levels of
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unreacted and oligomeric malefic anhydride. In general, the grafting reaction
step of the
present invention can be conducted under any combination of particular
grafting reaction
conditions, provided that the reaction of polypropylene with malefic anhydride
is favored
relative the reaction of malefic anhydride with itself or with other
components in the reaction
mixture, such as malefic anhydride oligomers.
One preferred mechanism for obtaining a reaction mixture in which the
polypropylene/maleic anhydride grafting reaction is highly favored is to
maintain the
concentration of unreacted malefic anhydride in the reaction mixture at
relatively low levels
compared to those levels used in prior art processes. Although applicants do
not wish to be
bound by or to any theory of operation, it is believed that the unexpectedly
higher percentages
of bound malefic anhydride found in the preferred products of the present
method are
achieved, at least in part, because malefic anhydride has a limited solubility
in polypropylene,
an in particular in a polypropylene polymer melt. Thus, use of a low
concentration of malefic
anhydride results in less phase separation in the reaction mixture between the
malefic
anhydride, or the precursors thereof and polypropylene. Thus, the use of
malefic anhydride
concentrations that are not substantially greater than the solubility limit of
the polymer has two
distinct beneficial results. First it results in a very high percentage of the
malefic anhydride
being in the same phase as and in intimate contact with the polymer molecules,
which is
favorable for the anhydride/polymer reaction. Second, the present invention
minimizes the
amount of unreacted malefic anhydride exposed to conditions which favor
anhydride/anhydride
reaction, as would occur with the malefic anhydride that exists in a phase
separate from the
polymer phase. Lower phase separation therefore allows for binding of a higher
percentage of
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the malefic anhydride introduced to the polymer melt. Furthermore, the
initially formed, lightly
maleated product is believed to help solubilize any additional malefic
anhydride reactant that is
subsequently introduced to the polymer melt in preferred embodiments of the
present
invention.
According to certain preferred embodiments, especially those which involve the
production of graft polypropylene copolymers having viscosity of from about
200 cps at 190C
to about 2000 cps at 190C, the methods of the present invention comprise
reacting malefic
anhydride with polypropylene under conditions effective to maintain the
concentration of
unreacted malefic anhydride in the reaction mixture at less than about 2.S %,
more preferably
less than about 2 %, and even more preferably less than about 1 %, during a
substantial
portion, and preferably during at least about 7S%, of the grafting step. In
ceratin
embodiments, this grafting reaction step comprises adding malefic anhydride to
a reaction
mixture comprising polypropylene, and preferably a polypropylene melt, under
conditions
elective to maintain the concentration of malefic anhydride in the reaction
mixture at less than
about 2.5, more preferably less than about 2 %, and even more preferably less
than about 1
weight percent during a substantial portion, and preferably during at least
about 75% of the
adding step.
As used herein, the term "substantial portion" with respect to the reaction
step and
adding step refers to any portion or portions of the grafting reaction in
which, in the
aggregate, at least 50% of the malefic anhydride-polypropylene bonds are
formed.
For particular embodiments in which the reaction is batch reaction, it is
preferred that
the malefic anhydride is added to the reaction mixture at rate of less than
about 0.045 pounds
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of malefic anhydride or precursor thereof ("MA") per pound of polypropylene
("PP") per hour
of grafting reaction conditions (MA/PP/hr), and even more preferably less than
about 0.040
MA/PPl hr.
In addition, applicants have discovered that the molecular weight of the
polypropylene
used in the maleation process, as well as the malefic anhydride content of the
maleated
polypropylene, typically characterized by the saponification number of the
final product, ai~ect
the percent of bound malefic anhydride found in the final product. As used
herein, the term
saponification number ("SAP") refers to the measure of the amount of
saponifiable matter
present, including bound single unit malefic anhydride, bound oligomeric
malefic anhydride,
unreacted malefic anhydride, unbound oligomeric malefic anhydride, and other
hydrolyzable
moieties, in the. maleated polypropylene. The SAP is generally calculated as
the number of
milligrams of potassium hydroxide required to hydrolyze one gram of sample (mg
KOHIg).
Fig. 1 is a graphic depiction of the percent bound malefic anhydride plotted
against the SAP of
a low molecular weight polypropylene and a high molecular weight
polypropylene. As
illustrated in Fig.1, generally, the percent bound malefic anhydride decreases
as the SAP
increases. In addition, as the molecular weight of the polypropylene
increases, the percent
bound decreases. It is believed such variables are controlled in accordance
with the present
invention to produce useful maleated polypropylenes having high a percent of
bound malefic
anhydride. More particularly, it is preferred to select the molecular weight
of the
polypropylene reactant and the SAP of the reactant to achieve bound malefic
anhydride in
accordance with the present invention. For embodiments which utilize high
molecular weight
polypropylene, as the term is used by skilled artisans, it is preferred that
the high molecular
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weight polypropylene has a SAP of no greater than about 70, more preferably no
greater than
about 75 and even more preferably no greater than 80. For embodiments which
utilize low
molecular weight polypropylene, as the term is used by skilled artisans, it is
preferred that the
polypropylene has a SAP of no greater than about 100, more preferably no
greater than about
120 and even more preferably no greater than 150.
Any commercial grade of malefic anhydride, or a precursor thereof such as
malefic acid
(which is converted to malefic anhydride under many commonly used grafting
reaction
conditions) is suitable for use in the present invention. Examples of suitable
malefic anhydrides
include those that are is commercially available, for example, though Monsanto
Company (St.
Louis , NO) as Malefic Anhydride, and Huntsman Petrochemical Corporation
(Chesterfield,
MO) as Manbri Malefic Anhydride.
Polypropylenes suitable for use in the present invention include those
polypropylenes
commercially available, for example, through Honeywell (Morristown, N~ under
the trade
name ACX1089.
Any suitable amounts of malefic anhydride and polypropylene can be used in the
method of the present invention. In certain preferred embodiments, the weight
ratio of
polypropylene to malefic anhydride used in the present method is from about
5:1 to about 40:1.
More preferably the weight ratio is from about 5:1 to about 25:1, and even
more preferably is
from about 10:1 to about 20:1.
In certain preferred embodiments of the present invention, the reacting step
further
comprises reacting the malefic anhydride with the polypropylene in the
presence of a catalyst.
Any of a wide range of catalysts can be used in the present invention.
Suitable catalysts
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include, for example, free radical forming agents known in the art and
include, for example,
dialkyl peroxides, tertiary butyl hydroperoxide, cumene hydroperoxide, p-
menthane peroxide,
p-menthane hydroperoxide or axo compounds, such as azobis (isobutyronitrile),
or irradiation
sources. The preferred free radical sources are the peroxides with the butyl
peroxides being
more preferred. The most preferred peroxide, due to availability and suitable
good results
obtained thereby, is ditertiary butyl peroxide (di-t-butyl peroxide). These
compounds are
commercially available through, for example, Elf Atochem as Lupersol 101 or Di-
t-Butyl
Peroxide, and Akzo Nobel Chemicals Inc. as Trigonox B.
The amount of peroxide or free radical agent used is generally quite low,
being of the
order of about 0.01 to about 5 wt % based on the starting material, preferably
about O. l to
about 3 wt % with about 0.75 to about 1.25 wt % being most preferred. Amounts
much
above 5 wt % are not needed for good properties whereas amounts below about
0.01 wt
provide reactions that are too slow and incomplete.
Like the polycarboxylic compound feed, it is highly preferable that the free
radical
initiator be added to the reaction mass slowly. The free radical initiator is
added to the
reaction at a rate of preferably about 0.01 to about 3 wt % of the starting
material per hour,
more preferably about 0.1 to about 1 wt % of the starting material per hour,
and even more
preferably about 0.3 wt % of the starting material per hour.
According to certain embodiments, the catalysts are added to the reaction
mixture of
the present invention. The catalyst can be added simultaneously and/or
separately in relation
to the malefic anhydride. In preferred embodiments, the malefic anhydride and
catalyst are
added to the reaction mixture substantially simultaneously in a temporal sense
but separately in
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the sense location at which they are added to the reaction mixture. In other
words, it is
preferred that malefic anhydride and catalyst are added to the reaction
mixture in overlapping
time periods but through different nozzles or inlet ports which introduce the
catalysts at a
place that is displaced from the location of the malefic anhydride
introduction.
The process of the present invention may further comprise the use of other
additives in
the reaction mixture andlor in the final product. In general, any additive
which does not
substantially hinder the formation of a product of the present invention may
be used in suitable
amounts. Examples of suitable additives include: comonomers, such as, styrene,
chain transfer
agents, stabilizers, and the like.
The reaction of the present invention may be carried out under any suitable
reaction
conditions. In general, it is preferred that the polypropylene comprise a
polypropylene melt.
Accordingly, it is generally preferred that the temperature of reaction be
above the melt
temperature of the polypropylene, but preferably no greater than about 200
° C. The
temperature is dependent upon the particular polypropylene, free radical
initiators/catalyst and
other parameters that impact the grafting reaction rate. At temperatures much
below about
150°C, many of the preferred starting materials will not be in the
molten form and therefore
will not adequately react with the malefic anhydride. However, at temperatures
above about
200°C, the ease of emulsification and melt viscosity of the resulting
emulsible polyolefin wax
is not as high as preferred. Therefore, reaction temperature is generally
preferably between
about 150 and about 200°C, and preferably between about 180 and about
190°C.
The reaction pressure depends, among other things, upon the reaction
temperature
and desired rate of reaction. Generally, the reaction is conducted under a
pressures preferably
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from about 0 to about 50 psig, more preferably from about 5 to about 30 psig,
and even more
preferably from about 10 to about 20 psig. Reactions conducted at or around
atmospheric
pressure avoid expensive high pressure equipment.
Generally, the grafting reaction of the present invention is conducted such
that at least
about 60wt% of malefic anhydride, based on total weight of malefic anhydride
in the grafting
reaction product, is bound to the polymer backbone. Preferably, the reaction
is conducted
such that at least 70wt% malefic anhydride is bound, and even more preferably
at least 80wt%
is bound.
EXAMPLES
Comparative Example
This example illustrates the production of a maleated propylene in accordance
with the
prior art as represented by U.S. Patent No. 3,642,722.
High molecular weight polypropylene having an inherent viscosity of 1.5 is fed
to a
thermal degradation unit for an average contact time of 30 minutes. The
thermal degrader is
operated at a temperature of 370C with the agitator operated at a speed of
such that all of the
thermal energy for degradation is supplied by the friction of mixing. The
degraded
polypropylene wax has a melt viscosity of about 800 centipoise measured at
190C. This
material is passed along with 5 percent by weight of malefic anhydride and
0.25 percent by
weight of ditertiary butyl peroxide to a thermal agitated reactor maintained
at about 2000 to
produce a reaction product mixture, and even after standard techniques for
separating
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unreacted malefic hydride from the reaction mixture, had a concentration of
bound malefic
anhydride of less than about 50%.
Example 1
To a clean, dry reactor, purged with nitrogen, is charged 89 parts by weight
(pbw) of
polypropylene (Hiwax NPO55). The polypropylene is heated to melt, agitation of
the
polypropylene is started, and the temperature is then adjusted to 185-
187°C. The nitrogen is
stopped and to the reactor is charged with 9 pbw of malefic anhydride at a
rate of 0.034 lbs
malefic anhydride/lbs polypropylene/hr and 2 pbw of a peroxide mixture
comprising 1 pbw
Lupersol and 1 pbw Parol 100 at a rate of 0.008 lbs/lbs polypropylene/hr.
Introduction of the
malefic anhydride and the catalyst begin substantially simultaneously but
using displaced
reactor inlet nozzles.
After the peroxide mixture is completely added (which occurs 15 minutes after
the malefic
anhydride' addition is completed) the reaction mixture is stirred for an
additional 10 minutes.
Standard techniques are used in an effort to remove unreacted malefic
anhydride. More
particularly, a vacuum of 25" Hg is applied to the grafting reaction product
and periodic
samples are removed and tested for unreacted malefic anhydride. The vacuum is
removed and
the reaction mixture is cooled to 170°C, and the grafting reaction
product mixture after the
standard vacuum purification comprises greater than 70%, and more preferably
greater than
about 80%, and even more preferably greater than 85% bound malefic anhydride.
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