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Functionalized Polypropylene-Based Polymers
Field of Invention
[0001] Embodiments of the present invention relate to functionalized
propylene-based polymers and processes for making the same. More particularly,
embodiments of the present invention relate to functionalized propylene-diene
copolymers and 'processes for making the same via peroxide grafting
techniques.
Background
[0002] Polypropylene-based graft copolymers are useful as compatibilizers for
a variety of polymer blends containing polypropylene. Polypropylene-based
graft
copolymers can be used as a blend component as well as an adhesion promoter
between polyolefins and other substrates, including glass, metal, mineral
fillers,
polar polymers, and engineering plastics such as polyamides.
[0003] Functionalized polypropylene-based polymers can be produced by
peroxide grafting of polypropylene backbones. During peroxide grafting of a
polyolefin backbone, free radicals are produced. Such radicals not only
trigger a
grafting reaction onto a polyolefin backbone, but can also cause beta-scission
of
the backbone itself. The resulting molecular weight reduction becomes more
severe as the degree of grafting and severity of the process conditions
increases.
The beta-scission reaction is especially prevalent in the neighborhood of
tertiary
carbon atoms in the polyolefin backbone chain. The production of highly
functionalized propylene based backbones by peroxide grafting involves an
appreciable loss of molecular weight, viscosity, and melt strength.
[0004] For many years, polypropylene (PP) has also been functionalized with
maleic anhydride in presence of peroxide to produce maleic anhydride grafted
polypropylene, which is used as an adhesion promoter in glass and mineral
filled
polypropylene compounds as well as compatibilizer of polyamide polypropylene
blends. The grafted polypropylene-based polymers are also used in other
applications where adhesion onto metal or polar substrates (including polar
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polymers) is required. Lately, grafted polypropylene has also found
applications
as coupling agents in natural fibers filled PP compounds. During the grafting
process, macroradicals are generated and beta scission usually occurs before
the
reaction with maleic anhydride takes place. The result is that grafting levels
are
generally low and the resulting functionalized polypropylene has a low
molecular
weight. In order to obtain highly functionalized polypropylene-based polymers,
it
is necessary to increase the amount of peroxide which leads to further MW
reduction. It has also been recognized in prior literature (M. Lambla et al.
in
Makromol. Chem., Macromol. S n U., 75, 137 (1993)) that the grafting yield of
maleic anhydride is not a monotonic function of its initial concentration but
reaches a maximum before decreasing. The existence of the maximum is
associated with a limited solubility of maleic anhydride in the molten
polypropylene. It is believed that with increasing the maleic anhydride feed,
the
polypropylene/maleic anhydride/peroxide mixture changes from a semi-
homogeneous to a more heterogeneous system with maleic anhydride/peroxide
droplets dispersed in the molten polypropylene.
[00051 EP 777 693 discloses a maleated polypropylene having an acid number
greater than 4.5, a yellowness index color of no greater than 76, and a number
average molecular weight of at least 20,000. The acid number can be translated
into a wt % content of maleic anhydride. The number average molecular weight
can be converted in co-dependence with the Mw/Mn ratio into weight average
Mw which changes inversely to the MFR. While EP 777 693 aims to provide a
relatively high molecular weight and a high degree of grafting without undue
yellowing at the same time, the flexibility remains insufficient and
significant
molecular weight breakdown still takes place.
[00061 U.S. 5,670,595 relates to diene modified polymers to improve the melt
strength of polypropylenes, low draw-down ratios in extrusion coating, poor
bubble formation in extrusion foam materials, and relative weakness in large-
part
blow molding. The dienes are acyclic alpha-omega dienes. The starting polymer
contains less than 5 mol% of other unsaturated compounds such as ethylene,
butene-1 etc. customarily used for Random Propylene Copolymers (RCP) used
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generally as a heat seal layer on oriented polypropylene (OPP) film . Use of
the
invention described is alleged to limit the molecular weight reduction to less
than
20% when the graft ratio is 0.7 wt%. Contacting in solution and in the molten
condition are illustrated. The materials lack the flexibility and low glass
transition
temperature desirable to preserve good adhesion at low temperature and when
deformed by flexing or impact.
[0007] The grafting of a broad range of olefin based polymers is discussed in
U.S. 5,367,022. A high degree of grafting is suggested combined with low MFR
(i.e., high molecular weight) polymer backbones. The examples show that the
grafting still results in a polymer with an MFR well in excess of 100, which
has
inadequate melt strength and is unsuited for use in film extrusion if used as
the
predominant component of a composition. The homopolymers are crystalline,
have an elevated heat of fusion before grafting, and possess limited
flexibility.
[0008] U.S. 5,059,658 discloses a method of producing modified
polypropylene having a Mw from 50000 to 1000000 and a graft ratio of 0.1 to
lOwt% by graft-polymerizing a substantially crystalline propylene random
copolymer consisting essentially of propylene and a linear diene. Although, it
is
mentioned that the backbone can contain up to 5 mole % comonomer, there is no
discussion of the level of crystallinity or isotacticity of the polymer to be
grafted.
[0009] U.S. 5,763,088 reports olefin resin-based articles having gas barrier
properties consisting of a maleic anhydride grafted polypropylene. The
starting
backbone can include a propylene copolymer with a C2-C8 alpha-olefin have a
melting point between 80 C and 187 C and a degree of crystallinity of 20% or
more. The object of this invention has a crystallinity level and melting
points
outside these ranges.
[00010] WO 2002/36651 describes the grafting of propylene based elastomers
containing ethylene derived units to lower crystallinity. WO 2005/049670
discloses incorporating dienes into propylene-based elastomers but the
grafting of
such material themselves is not disclosed.
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[00011] Apart from changes in the polymer backbone to be grafted and the
grafting process, it has also been proposed to counteract any reduction in the
molecular weight as a result of peroxide grafting by blending the propylene
based
polymer with a polyethylene which has a countervailing tendency of increasing
its
molecular weight as the result of a peroxide grafting process. If large
amounts of
polyethylene are used melt processability and compatibility with polypropylene
substrates can be negatively affected. Similarly higher molecular weight
ungrafted
propylene and or ethylene based polymers can be added to a grafted polymer
with
a degraded molecular weight to restore the overall melt strength to a
sufficient
level. In practice, thus far, grafted propylene based polymer compositions for
applications such as CTR have been made, in spite of the absence of high
molecular weight grafted propylene based polymer materials, by blending low
viscosity functionalized propylene based polymers with high molecular weight
un-functionalized propylene based polymers, or by the use of electron donating
agents during grafting such as DMF.or styrene to reduce chain scissioning. See
Gaylord, N.G., Mishra, M.K., J. Polym. Sci. B21, 23 (1983) and (styrene use) :
Hu, G.H. Flat, J-J, Lambla, M , Makromol. Chem., Macromol. Symp. 75, 137
(1993).
[00012] The effectiveness of the former compositions is however reduced by
reduction- of the grafting level and broadening of the molecular weight
distribution. The use of these latter chemicals generates safety issues on
typical
reactive extrusion processes in their handling and feeding to the reaction
device.
They also require more extensive venting in order to minimize their residual
level
in the final functionalized polymer. These residuals can also be seen as
contaminations which prevent the final polymer to be used in certain
applications
such as those requiring food contact classification.
[00013] There is a need, therefore, for a grafted polymer which combines a
high content of propylene derived units for improved compatibility with
propylene
based materials as well as a high degree of grafting to improve adhesion.
There is
also a need for a grafted propylene-based polymer with sufficient flexibility
to
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maintain adhesion under local deformation at the same time as a sufficiently
high
viscosity to give a melt strength needed for extrusion.
Summary of the Invention
[00014] A process for preparing a functionalized propylene-based polymer is
provided. In at least one specific embodiment, the process includes contacting
a
propylene-based polymer backbone comprising propylene derived units, one or
more dienes with a free-radical initiator and at least one ethylenically
unsaturated
carboxylic acid or acid derivative, such as maleic anhydride, the backbone
having
a triad tacticity of from 50 to 99 % and a heat of fusion of less than 80 J/g.
The at
least one ethylenically unsaturated carboxylic acid or acid derivative is
reacted
with the backbone in the presence of the free-radical initiator under
conditions at
which free radicals are generated to graft the backbone and provide a grafted
propylene copolymer, the grafted propylene-based polymer comprising from
about 0.5 wt% to about 10 wt% of an unsaturated moiety derived from the one or
more dienes incorporated into the backbone. The grafted propylene copolymer is
pelletized to provide a pelletized propylene copolymer, wherein the pelletized
propylene copolymer has a MFR ratio from about 0.01 to about 15.
[000151 In at least one other specific embodiment, the process includes
contacting a propylene-based polymer backbone comprising propylene derived
units, one or more alpha olefins, and one or more dienes with a free-radical
initiator and at least one ethylenically unsaturated carboxylic acid or acid
derivative, such as maleic anhydride, the backbone having a triad tacticity of
from
50 to 99% and a heat of fusion of less than 80 J/g. The at least one
ethylenically
unsaturated carboxylic acid or acid derivative is reacted with the backbone in
the
presence of the free-radical initiator under conditions at which free radicals
are
generated to graft the backbone and provide a grafted propylene copolymer, the
grafted propylene-based polymer comprising from about 0.5 wt% to about 10 wt%
of an unsaturated moiety derived from the one or more dienes incorporated into
the backbone. The grafted propylene copolymer is pelletized to provide a
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pelletized propylene copolymer, wherein the pelletized propylene copolymer has
a
MFR ratio from about 0.01 to about 15.
[00016] Also disclosed is a functionalized polymer comprising a propylene-
based polymer backbone comprising one or more dienes, the backbone having an
MFR (1.2 kg @ 190 C) of from 0.1 g/10 min to 15 g/10 min, a content of at
least
one ethylenically unsaturated carboxylic acid or acid derivative derived units
from
about 1 wt% to about 3 wt%, a triad tacticity from about 50% to about 99 %;
and
a heat of fusion of less than 80 J/g. Also disclosed is a maleated polymer
comprising a propylene-based polymer backbone comprising one or more alpha
olefins and one or more dienes, the backbone having an MFR (1.2 kg @ 190 C) of
from about 0.1 to about 6 g/10 min; a content of maleic anhydride derived
units
from about 1 wt% to about 3 wt%; a triad tacticity of from about 50% to about
99
%; and a heat of fusion of less than 80 J/g.
Detailed Description of Invention
[000171 In one or more embodiments, a propylene-based polymer is grafted
(functionalized) with at least one ethylenically unsaturated carboxylic acid
or acid
derivative, preferably in a single stage in the presence of a peroxide
initiator.
Many embodiments are discussed herein describing maleic anhydride as the
preferred grafting monomer. Such embodiments may include an ethylenically
unsaturated carboxylic acid or acid derivative other than the preferred maleic
anhydride. The propylene-based polymer can be a propylene-a-olefin-diene
terpolymer or propylene-diene copolymer. For simplicity and ease of
description,
the propylene-a-olefin-diene terpolymers or propylene-diene copolymers
described herein will be simply referred to as a "propylene-based polymer."
The
terms functionalized and grafted are used interchangeably herein.
[00018] The propylene-based polymer when functionalized, exhibits a higher
grafting level than one skilled in the art would expect, and can include
isotactic
sequences long enough to engender crystallinity. The propylene-based polymer
contains a single hydrocarbon phase unlike the polymers of the prior art of
the
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same composition, grafting level and tacticity (so called grafted reactor
copolymers and impact copolymers) which typically consist of at least two
distinct phases. In addition, the propylene-based polymer preferably is very
flexible as determined by its flexural modulus (< 350 MPa), has high
elongation
under a unidimensional tensile load of greater than 800%, and has a level of
crystallinity much lower than expected from the prior art for their
composition and
tacticity of the propylene residues. The functionality level of the propylene-
based
polymer is greater than that for similarly grafted propylene homopolymers, and
the functionality level of the propylene-based polymer increases with the
increase
in the level of the maleic anhydride feed. The level of the maleic anhydride
feed
can be as much as 5 wt%. Furthermore, the higher incorporation of functional
groups is accomplished without a lower degree of molecular weight loss as in
the
case of propylene homopolymers.
Polymer Component
[00019) In at least one specific embodiment, the propylene-based polymer can
be prepared by polymerizing propylene with one or more dienes. In at least one
other specific embodiment, the propylene-based polymer can be prepared by
polymerizing propylene with ethylene and/or at least one C4-C20 aolefin, or a
combination of ethylene and at least one C4-C20 a-olefin and one or more
dienes.
The one or more dienes can be conjugated or non-conjugated. Preferably, the
one
or more dienes are non-conjugated.
[00020) The comonomers can be linear or branched. Preferred linear
comonomers include ethylene or C4 to C8 a-olefins, more preferably ethylene,
1-butene, 1-hexene, and 1-octene, even more preferably ethylene or 1-butene.
Preferred branched comonomers include 4-methyl-l-pentene, 3-methyl-l-pentene,
and 3,5,5-trimethyl-l-hexene. In one or more embodiments, the comonomer can
include styrene.
[000211 Illustrative dienes can include but are not limited to 5-ethylidene-2-
norbornene (ENB); 1,4-hexadiene; 5-methylene-2-norbomene (MNB); 1,6-
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octadiene; 5-methyl-1,4-hexadiene; 3,7-dimethyl-1,6-octadiene; 1,3-
cyclopentadiene; 1,4-cyclohexadiene; vinyl norbornene (VNB);
dicyclopendadiene (DCPD), and combinations thereof. Preferably, the diene is 5-
ethylidene-2-norbomene (ENB).
Preferred methods for producing the propylene-based polymers are
found in U.S. Patent Application Publication 20040236042 and U.S. Patent
6,881,800..
Pyridine amine complexes, such as those described in W003/040201
are also useful to produce the propylene-based polymers useful herein. The
catalyst can involve a fluxional complex, which undergoes periodic intra-
molecular re-arrangement so as to provide the desired interruption of
stereoregularity as in U.S. 6,559,262. The catalyst can be a stereorigid
complex
with mixed influence on propylene insertion, see Rieger EP1070087. The
catalyst
described in EP1614699 could also be used for the production of backbones
suitable for the invention.
The propylene-based polymer can have an average propylene content
on a weight percent basis of from about 60 wt % to about 99.7 wt %, more
preferably from about 60 wt% to about 99.5 wt%, more preferably from about. 60
wt% to about 97 wt%, more preferably from about 60 wt% to about 95 wt% based
on the weight of the polymer. In one embodiment, the balance comprises diene.
In another embodiment, the balance comprises one or more dienes and one or
more of the at-olefins described previously. Other preferred ranges are from
about
80 wt % to about 95 wt% propylene, more preferably from about 83 wt % to about
95 wt% propylene, more preferably from about 84 wt % to about 95 wt%
propylene, and more preferably from about 84 wt % to about 94 wt% propylene
based on the weight of the polymer. The balance of the propylene based polymer
comprises a diene and optionally, one or more alpha olefins. In some
embodiments, the alpha-olefin is butene, hexene or octene. In other
embodiments,
two alpha-olefins are present, preferably ethylene and one of butene, hexene
or
octene.
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[000251 Preferably, the propylene-based polymer comprises about 0.3 wt% to
about 24 wt%, of a non-conjugated diene based on the weight of the polymer,
more preferably from about 0.5 wt% to about 12 wt %, more preferably about 0.6
wt% to about 8 wt %, and more preferably about 0.7 wt% to about 5 wt%. In
other embodiments, the diene content ranges from about 0.3 wt% to about 10
wt%, more preferably from about 0.3 to about 5 wt%, more preferably from about
0.3 wt% to about 4 wt%, preferably from about 0.3 wt% to about 3.5 wt%,
preferably from about 0.3 wt% to about 3.0 wt%, and preferably from about 0.3
wt% to about 2.5 wt% based on the weight of the polymer. In a preferred
embodiment, the propylene-based polymer comprises ENB in an amount of from
about 0.5 to about 4 wt%.
[00026] In other embodiments, the propylene-based polymer preferably
comprises propylene and diene in one or more of the ranges described above
with
the balance comprising one or more C2 and/or C4-C20 olefins. In general, this
will
amount to the propylene-based polymer preferably comprising from about 5 to
about 40 wt% of one or more C2 and/or C4-C20 olefins based the weight of the
polymer. When C2 and/or a C4-C20 olefins are present the combined amounts of
these olefins in the polymer is preferably at least about 5 wt% and falling
within
the ranges described herein. Other preferred ranges for the one or more a-
olefins
include from about 5 wt% to about 35 wt%, more preferably from about 5 wt% to
about 30 wt%, more preferably from about 5 wt% to about 25 wt%, more
preferably from about 5 wt% to about 20 wt%, more preferably from about 5 to
about 17 wt% and more preferably from about 5 wt% to about 16 wt%.
[000271 The propylene-based polymer can have a weight average molecular
weight (Mw) of 5,000,000 or less, a number average molecular weight (Mn) of
about 3,000,000 or less, a z-average molecular weight (Mz) of about 10,000,000
or less, and a g' index of 0.95 or greater measured at the weight average
molecular
weight (Mw) of the polymer using isotactic polypropylene as the baseline, all
of
which can be determined by size exclusion chromatography, e.g., 3D SEC, also
referred to as GPC-3D as described herein.
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In a preferred embodiment, the propylene-based polymer can have a
Mw of about 5,000 to about 5,000,000 g/mole, more preferably a Mw of about
10,000 to about 1,000,000, more preferably a Mw of about 20,000 to about
500,000, more preferably a Mw of about 50,000 to about 400,000, wherein Mw is
determined as described herein.
In a preferred embodiment, the propylene-based polymer can have a
.Mn of about 2,500 to about 2,500,000 g/mole, more preferably a Mn of about
5,000 to about 500,000, more preferably a Mn of about 10,000 to about 250,000,
more preferably a Mn of about 25,000 to about 200,000, wherein Mn is
determined as described herein.
In a preferred embodiment, the propylene-based polymer can have a
Mz of about 10,000 to about 7,000,000 g/mole, more preferably a Mz of about
50,000 to about 1,000,000, more preferably a Mz of about 80,000 to about
700,000, more preferably a Mz of about 100,000 to about 500,000, wherein Mz is
determined as described herein.
The molecular weight distribution index (MWD--(Mw/Mn)),
sometimes referred to as a "polydispersity index" (PDI), of the propylene
based
polymer can be about 1.5 to 40. In an embodiment the MWD can have an upper
limit of 40, or 20, or 10, or 5, or 4.5, and a lower limit of 1.5, or 1.8, or
2Ø In a
preferred embodiment, the MWD of the propylene-based polymer is about 1.8 to 5
and most preferably about 1.8 to 3. Techniques for determining the molecular
weight (Mn and Mw) and molecular weight distribution (MWD) can be found in
U.S. Pat. No. 4,540,753 (Cozewith, Ju and Verstrate) and references cited
therein, in Macromolecules, 1988, volume 21, p 3360 (Verstrate et al.),
and references cited therein, and in accordance with the procedures
disclosed in U.S. Patent No. 6,525,157, column 5, lines 1-44.
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[00032] In a preferred embodiment, the propylene-based polymer can have a g'
index value of 0.95 or greater, preferably at least 0.98, with at least 0.99
being
more preferred, wherein g' is measured at the Mw of the polymer using the
intrinsic viscosity of isotactic polypropylene as the baseline. For use
herein, the
g' index is defined as:
g 77b
771
where T1b is the intrinsic viscosity of the propylene-based polymer and
711 is the intrinsic viscosity of a linear polymer of the same viscosity-
averaged
molecular weight (Mv) as the propylene-based polymer. rl1= KMv, K and a were
measured values for linear polymers and should be obtained on the same
instrument as the one used for the g' index measurement.
[000331. In a preferred embodiment, the propylene-based polymer can have a
crystallization temperature (Tc) measured with differential scanning
calorimetry
(DSC) of about 200 C or less, more preferably, 150 C or less, with 140 C or
less
being more preferred.
[00034] In a preferred embodiment, the propylene-based polymer can have a
density of about 0.85 g/cm3 to about 0.92 g/cm3, more preferably, about 0.87
g/cm3 to 0.90 g/cm3, more preferably about 0.88 g/cm3 to about 0.89 g/cm3 at
room temperature as measured per the ASTM D-1505 test method.
[00035] In a preferred embodiment, the propylene-based polymer can have a
melt flow rate (MFR, 2.16 kg weight @ 230 C), equal to or greater than 0.2
g/10
min as measured according to the ASTM D-1238(A) test method as modified
(described below). Preferably, the MFR (2.16 kg @ 230 C) is from about 0.5
g/10
min to about 200 g/10 min and more preferably from about 1 g/10 min to about
100 g/10 min. In an embodiment, the propylene-based polymer has an MFR of
0.5 g/10 min to 200 g/10 min, especially from 2 g/10 min to 30 g/10 min, more
preferably from 5 g/10 min to 30 g/10 min, more preferably 10 g/10 min to 30
g/10 min or more especially 10 g/10 min to about 25 g/10 min.
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[00036] In an alternative procedure, the test is conducted in an identical
fashion
except using 1.2 kg at a temperature of 190 C, also referred to as the Melt
Flow
Rate (MFR (1.2 kg @ 190 C). In some embodiments wherein the propylene-
based polymer is a propylene-alpha olefin diene copolymer, the propylene-based
polymer preferably has a Melt Flow Rate (1.2 kg @ 190 C) according to ASTM
D-1238 (A) of less than 15 g/10 min, more preferably 12 g/10 min or less, more
preferably 10 g/10 min or less, more preferably 8 g/10 min or less, and even
more
preferably about 6 g/10 min or less.
[00037] The grafted polymer preferably has a MFR ratio (MFR (1.2 kg @
190 C) of grafted polymer to the MFR (1.2 kg @ 190 C) of the starting polymer
backbone) of from about 0.01 to about 10, more preferably from about 1 to
about
and more preferably from about 1 to about 5, and more preferably from about 1
to about 4 and more preferably from about 1 to about 3. A higher ratio is
representative of polymers giving high levels of chain scission whereas the
polymers of the invention have low MFR ratio indicating low Mw change during
the grafting process.
[00038] In one or more embodiments, the grafted propylene polymer has a
shear thinning ratio greater than 15, more preferably >_ 20, more preferably
>_ 25,
more preferably >_ 30, more preferably >_ 40 and more preferably >_ 50.
[00039] The propylene-based polymer can have a Mooney viscosity ML
(1+4)@125 C, as determined according to ASTM D1646, of less than 100, more
preferably less than 75, even more preferably less than 60, most preferably
less
than 30.
[00040] In a preferred embodiment, the propylene-based polymer can have a
heat of fusion (Hf) determined according to the DSC procedure described later,
which is greater than or equal to about 0.5 Joules per gram (J/g), and is
Sabout 80
J/g, preferably <about 70 J/g, more preferably <about 60 J/g, more preferably
_<
about 50 J/g, more preferably _<about 35 J/g. Also preferably, the propylene-
based polymer has a heat of fusion that is greater than or equal to about 1
J/g,
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preferably greater than or equal to about 5 J/g. In another embodiment, the
propylene-based polymer can have a heat of fusion (Hf), which is from about
0.5
J/g to about 70 J/g, preferably from about 1 J/g to about 70 J/g, more
preferably
from about 0.5 J/g to about 35 J/g. Preferred propylene-based polymers and
compositions can be characterized in terms of both their melting points (Tm)
and
heats of fusion, which properties can be influenced by the presence of
comonomers or steric irregularities that hinder the formation of crystallites
by the
polymer chains. In one or more embodiments, the heat of fusion ranges from a
lower limit of 1.0 J/g, or 1.5 J/g, or 3.0 J/g, or 4.0 J/g, or 6.0 J/g, or 7.0
J/g, to an
upper limit of 30 J/g, or 35 J/g, or 40 J/g, or 50 J/g, or 60 J/g or 70 J/g,
or 80 J/g.
[000411 The crystallinity of the propylene-based polymer can also be expressed
in terms of percentage of crystallinity (i.e. % crystallinity). In a preferred
embodiment, the propylene-based polymer has a % crystallinity of from 0.5 % to
40%, preferably 1% to 30%, more preferably 5% to 25% wherein % crystallinity
is determined according to the DSC procedure described above. In another
embodiment, the propylene-based polymer preferably has a crystallinity of less
than 40%, preferably about 0.25% to about 25%, more preferably from about
0.5% to about 22%, and most preferably from about 0.5% to about 20%. As
disclosed above, the thermal energy for the highest order of polypropylene is
estimated at 189 J/g (i.e., 100% crystallinity is equal to 189 J/g.).
[00042] In addition to this level of crystallinity, the propylene-based
polymer
preferably has a single broad melting transition. However, the propylene-based
polymer can show secondary melting peaks adjacent to the principal peak, but
for
purposes herein, such secondary melting peaks are considered together as a
single
melting point, with the highest of these peaks being considered the melting
point
of the propylene-based polymer.
[00043] The propylene-based polymer preferably has a melting point of equal
to or less than 100 C, preferably less than 90 C, preferably less than 80 C,
more
preferably less than or equal to 75 C, preferably from about 25 C to about 80
C,
preferably about 25 C to about 75 C, more preferably about 30 C to about 65 C.
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The propylene-based polymer can have a triad tacticity of three
propylene units, as measured by 13C NMR of 75% or greater, 80% or greater, 82%
or greater, 85% or greater, or 90% or greater. Preferred ranges include from
about
50 to about 99 %, more preferably from about 60 to about 99%, more preferably
from about 75 to about 99% and more preferably from about 80 to about 99%; and
in other embodiments from about 60 to about 97%. Triad tacticity is determined
by the methods described in U.S. Patent Application Publication 20040236042.
In one or more embodiments above or elsewhere herein, the propylene-
based polymer can be a blend of discrete random propylene-based polymers.
Such blends can include ethylene-based polymers and propylene-based polymers,
or at least one of each such ethylene-based polymers and propylene-based
polymers. The number of propylene-based polymers can be three or less, more
preferably two or less.
In one or more embodiments above or elsewhere herein, the propylene-
based polymer can include a blend of two propylene-based-polymers differing in
the olefin content, the diene content, or both.
In a preferred embodiment, the propylene-based polymer can include a
propylene based elastomeric polymer produced by random polymerization
processes leading to polymers having randomly distributed irregularities in
stereoregular propylene propagation. This is in contrast to block copolymers
in
which constituent parts of the same polymer chains are separately and
sequentially
polymerized.
In another embodiment, the propylene-based polymers can include
copolymers prepared according to the procedures in WO 02/36651. Likewise, the
propylene-based polymer can include polymers consistent with those described
in WO
03/040201, WO 03/040202, WO 03/040095, WO 03/040233, and/or WO 03/040442.
Additionally, the propylene-based polymer can include polymers consistent with
those described in EP 1233 191, and U.S. 6,525,157, along with
CA 02647562 2010-06-02
suitable propylene homo- and copolymers described in U.S. 6,770,713 and U.S.
Patent Application Publication 2005/215964. The propylene-based polymer can
also include one or more polymers consistent with those described in EP 1 614
699
or EP 1 017 729.
The Grafting Monomer
The grafting monomer is at least one ethylenically unsaturated
carboxylic acid or acid derivative, such as an acid anhydride, ester, salt,
amide,
imide, acrylates or the like. Such monomers include but are not necessary
limited
to the following: acrylic acid, methacrylic acid, maleic acid, fumaric acid,
itaconic
acid, citraconic acid, mesaconic acid, maleic anhydride, 4-methyl cyclohexene-
1,2- dicarboxylic acid anhydride, bicyclo(2.2.2)octene-2,3-dicarboxylic acid
anhydride, 1,2,3,4,5,8,9,10-octahydronaphthalene-2,3-dicarboxylic acid
anhydride, 2-oxa-1,3-diketospiro(4.4)nonene, bicyclo(2.2.1)heptene-2,3-
dicarboxylic acid anhydride, maleopimaric acid, tetrahydrophtalic anhydride,
norbomene-2,3-dicarboxylic acid anhydride, nadic anhydride, methyl nadic
anhydride, himic anhydride, methyl himic anhydride, and x-
methylbicyclo(2.2.1)heptene-2,3- dicarboxylic acid anhydride. Other suitable
grafting monomers include methyl acrylate and higher alkyl acrylates, methyl
methacrylate and higher alkyl methacrylates, acrylic acid, methacrylic acid,
hydroxy-methyl methacrylate, hydroxyl-ethyl methacrylate and higher hydroxy-
alkyl methacrylates and glycidyl methacrylate.
Maleic anhydride is a preferred grafting monomer. As used herein, the
term "grafting" denotes covalent bonding of the grafting monomer to a polymer
chain of the polymeric composition. In some embodiments, the grafted propylene
based polymer comprises from about 0.5 to about 10 wt% ethylenically
unsaturated carboxylic acid or acid derivative, more preferably from about 0.5
to
about 6 wt%, more preferably from about 0.5 to about 3 wt%; in other
embodiments from about 1 to about 6 wt%, more preferably from about 1 to about
3 wt%. In a preferred embodiment wherein the graft monomer is maleic
anhydride, the maleic anhydride concentration in the grafted polymer is
preferably
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16
in the range of about 1 to about 6 wt. %, preferably at least about 0.5 wt. %
and
highly preferably about 1.5 wt. %.
Preparing Grafted Propylene-based Polymers
[000511 The grafted polymeric products can be prepared in solution, in a
fluidized bed reactor, or by melt grafting as desired. A particularly
preferred
grafted product can be conveniently prepared by melt blending the ungrafted
polymeric composition, in the substantial absence of a solvent, with the free
radical generating catalyst, such as a peroxide catalyst, in the presence of
the
grafting monomer in a shear-imparting reactor, such as an extruder reactor.
Single
screw but preferably twin screw extruder reactors such as co-rotating
intermeshing
extruder or counter-rotating non-intermeshing extruders but also co-kneaders
such
as those sold by Buss are especially preferred.
[000521 The preferred sequence of events used for the grafting reaction
consists
of melting the polymeric composition, adding and dispersing the grafting
monomer, introducing the peroxide and venting the unreacted monomer and by-
products resulting from the peroxide decomposition. Other sequences can
include
feeding "the monomers and the peroxide pre-dissolved in a solvent.
[000531 The monomer is typically introduced to the reactor at a rate of about
0.01 to about 10 wt. % of the total of the polymeric composition and monomer,
and preferably at about 1 to about 5 wt. % based on the total reaction mixture
weight. The grafting reaction is carried at a temperature selected to minimize
or
avoid rapid vaporization and consequent losses of the peroxide and monomer and
to have residence times about 6 to 7 times the half life time of the peroxide.
A
temperature profile where the temperature of the polymer melts increases
gradually through the length of the reactor up to a maximum in the grafting
reaction zone of the reactor, and then decreases toward the reactor output is
preferred. Temperature attenuation in the last sections of the extruder is
desirable
for product pelletizing purposes.
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17
[00054] In order to optimize the consistency of feeding, the peroxide is
usually
dissolved at concentrations ranging from 10 to 50 wt% in a mineral oil whereas
the polymer and the grafting monomer are fed neat. Illustrative catalysts
include
but are not limited to: diacyl peroxides such as benzoyl peroxide;
peroxyesters
such as tert-butyl peroxy benzoate, tert-butylperoxy acetate, 00-tert-butyl-0-
(2-
ethylhexyl)monoperoxy carbonate; peroxyketals such as n-butyl-4,4-di-(tert-
butyl
peroxy) valerate; and dialkyl peroxides such as 1,1-bis(tertbutylperoxy)
cyclohexane, 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane, 2,2-
bis(tert-
butylperoxy)butane, dicumylperoxide, tert-butylcumylperoxide, Di-(2-tert-
butylperoxy-isopropyl-(2))benzene, di-tert-butylperoxide (DTBP), 2,5-dimethyl-
2,5-di(tert-butylperoxy)-hexane, 2,5-dimethyl-2,5-di(tert-butylperoxy)-
hexyne,
3,3,5,7,7-pentamethyl 1,2,4-trioxepane; and the like.
[00055] In a preferred embodiment, the polymer backbone is reacted with the at
least one ethylenically unsaturated carboxylic acid or acid derivative in a
continuous melt extruder with at least 0.2 wt% of the at least one
ethylenically
unsaturated carboxylic acid or acid derivative and at least 0.001 wt% of the
peroxide initiator.
[00056] Styrene and derivatives thereof such as paramethyl styrene, or other
higher alkyl substituted styrenes such as t-butyl styrene can be used as a
charge
transfer agent in presence of maleic anhydride to inhibit chain scissioning.
This
allows further minimization of the beta scission reaction and the production
of a
higher molecular weight grafted polymer (MFR=1.5).
Properties of Grafted Polymeric Products
[00057] MFR (1.2 kg @ 190 C) of ungrafted polymer backbone and grafted
polymer was measured according to a modified ASTM D-1238(A) at 190 C, 1.2
kg weight. The ASTM D-1238(A) was modified as follows: Preheating of the
polymer in the barrel was performed for 4 minutes instead of 7 minutes
according
to ASTM D-1238(A). Wherever ASTM D-1238(A) is mentioned in the
application, it is meant modified ASTM D-1238(A) as described in this
paragraph.
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[00058] The MFR ratio was obtained by dividing the MFR of the grafted
polymer by the MFR of the starting backbone as described earlier.
[00059] The shear thinning ratio was calculated by dividing low shear rate
viscosity by high shear rate viscosity. The low shear and high shear
viscosities
were measured by a sweep of frequencies from 0.31 to 201.06 radiant/sec at
100 C on a dynamic analyzer, such as a Rubber Processing Analyzer RPA 2000
from Alpha Technologies Co. The low shear viscosity was the viscosity at 0.31
rad/sec, and the high shear viscosity was the viscosity at 201.06 rad/sec.
[00060] The ethylene comonomer content was measured by Fourier Transform
Infrared Spectroscopy (FTIR). This method produces an ethylene content based
on the weight of the propylene and ethylene in the polymer. When the polymer
comprises a diene, the diene content can be measured as indicated below, and
the
overall ethylene content based on the weight of the polymer, including all
monomers, can be determined.
[00061] The amount of diene present can be inferred by the quantitative
measure of the amount of the pendant free olefin present in the polymer after
polymerization. Several procedures such as iodine number and the determination
of the olefin content by 1H or 13C nuclear magnetic resonance (NMR) have been
established. In embodiments described herein where the diene was ENB, the
amount of diene was measured according to ASTM D3900.
[00062] Maleic anhydride (MA) content was measured by FTIR. A thin
polymer film is pressed from 2-3 pellets at 165 C. When the film is used as
such,
the maleic anhydride content is reported as before oven. The film is than
placed in
a vacuum oven at 105 C for 1 h and placed in the FTIR; the measured maleic
anhydride content is reported as after oven. The peak height of the anhydride
absorption band at 1790 cm -1 and of the acid absorption band (from anhydride
hydrolysis in air) at 1712 cml was compared with a band at 4324 cm -1 serving
as a
standard. The total percentage of maleic anhydride (%MA) was then calculated
by the formula:
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%MA = a + k(A1790 + A1712)/A4324,
where "a" and "k" are constants determined by internal calibration with
internal
standards and having values 0.078 and 0.127, respectively.
[00063] The maleic anhydride content of the grafted propylene-based polymers
used as the standards was determined according to following procedure. A
sample of grafted polymer was first purified from residual monomer by complete
solubilization in xylene followed by re-precipitation in acetone. This
precipitated
polymer was then dried in a vacuum oven at 200 C for 2 hours in order to
convert
all maleic acid into anhydride. 0.5 to 1 grams of re-precipitated polymer was
dissolved in 150 mL of toluene. The solution was heated at toluene reflux for
1
hour and 5 drops of a 1% bromothymol blue solution in MeOH were added. The
solution was titrated with a solution of 0.1 N tetrabutyl ammonium hydroxide
in
methanol (color change from yellow to blue). The amount of the tetrabutyl
ammonium hydroxide solution used to neutralize the anhydride during the
titration
was directly proportional to the amount of grafted maleic anhydride present in
the
polymer.
[00064] Differential Scanning Calorimetry procedure: About 0.5 grams of
polymer was weighed out and pressed to a thickness of -15-20 mils ('-381-508
microns) at -'140 C-150 C, using a "DSC mold" and Mylar as a backing sheet.
The pressed pad was allowed to cool to ambient temperature by hanging in air
(the
Mylar is not removed). The pressed pad was annealed at room temperature (23-
25 C) for - 8 days. At the end of this period, a -15-20 mg disc was removed
from
the pressed pad using a punch die and placed in a 10 microliter aluminum
sample
pan. The sample was placed in a Differential Scanning Calorimeter (Perkin
Elmer
Pyris 1 Thermal Analysis System) and cooled to about -100 C. The sample was
heated at 10 C/min to attain a final temperature of about 165 C. The thermal
output, recorded as the area under the melting peak of the sample, was a
measure
of the heat of fusion and expressed in Joules per gram of polymer and
automatically calculated by the Perkin Elmer System. The melting point was
recorded as the temperature of the greatest heat absorption within the range
of
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melting of the sample relative to a baseline measurement for the increasing
heat
capacity of the polymer as a function of temperature.
Examples
[000651 The foregoing discussion can be further described with reference to
the
following non-limiting examples. In the tables below, the designation "Mn"
means not measured.
[000661 Polymers 1 and 2 are propylene ethylene copolymers that do not
contain a diene, i.e. comparative polymers. Polymer 1 was a propylene-ethylene
polymer commercially available from ExxonMobil Chemical Company as
VistamaxxTM 6100. Polymer 2 was a propylene-ethylene polymer commercially
available from ExxonMobil Chemical Company as VistamaxxTM 3000
[00067] Polymers 3-6 are propylene ethylene copolymers containing from 2
wt% to 4 wt% of ENB (i.e., a propylene-based polymer as described).
Polymerization was conducted as follows. In a 27 liter continuous flow stirred
tank reactor equipped with dual pitched blade turbine agitators, 83 kg of dry
hexane, 24 kg of propylene, 1.5 to 2.0 kg of ethylene, 0.6 to 1.4 kg of 5-
ethylidene-2-norbornene (ENB) were added per hour. The reactor was agitated at
700 rpm during the course of the reaction and was maintained liquid full at
about
1600 psi pressure (gauge) so that all regions in the polymerization zone had
the
same composition during the entire course of the polymerization. A catalyst
solution in toluene of 1.5610-3 grams of dimethylsilylindenyl dimethyl hafnium
and 2.42 x 10"3 grams of dimethylanilinium tetrakis (heptafluoronaphthyl)
borate
was added at a rate of 6.35 ml/min to initiate the polymerization. An
additional
solution of tri-n-octyl aluminum (TNOA) was added to remove extraneous
moisture during the polymerization. The polymerization was conducted at 58 to
60 C in an adiabatic reactor. The feed was cooled to between -3 to 3 C. The
polymerization was efficient and led to the formation of about 8 to 11 kg of
polymer per hour. The polymers were recovered by three stage removal of the
solvent, first by removing about 70% of the solvent using a lower critical
solution
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21
process as described in W00234795A1, and then removing the remaining solvent
in a flash pot followed by further devolatilization in a LIST devolatization
extruder. The polymers were recovered as pellets. The polymers analysis
results
are shown in Table 2. The catalyst feed in Table 1 contains from 5 to 17.32 x
10-4
mol/liter of the catalysts in toluene, and the activator feed contains and
approximately from 4.9 to 9.3 x 10-4 mol/liter of the activator in toluene.
Both
feeds are introduced into the polymerization reactor after an initial
premixing for
about 60 seconds at the rates indicated below.
TABLE 1
Ethylene Propylene Catalyst Activator Hexane Reactor
Feed Feed ENB Concentrate Concentration feed Temperature
Sample # kg/hr) (k hr (k hr (xlO-4 moll x10-4 mol/1 (k /hr) ( C)
Polymer 3 2.10 24.39 0.65 5.05 4.90 81.85 69.5
Polymer 4 1.65 24.39 0.69 7.58 4.90 83.25 63.3
Pol r5 1.10 24.41 0.65 9.52 9.25 83.63 61.4
Polymer 6 1.24 24.38 1.41 17.32 5.60 83.59 60.2
Table 2
Polymer C2 ENB MFR Tm Heat of Triad MFR
(wt%) (wt%) (1.2 kg @ ( C) fusion tacticity (230 C @
190 C) (J/g) (%) 2.16 kg) (g/10
(g/10 min) min)
1 12 1.5 67 29 90 rim
2 16 0.7 49 5 91 run
3 16.3 2.0 0.9 48 9 nm 3.6
4 13.4 2.0 0.8 59 24 Mn 3.8
9.4 1.95 1.2 Mn rim 95 4.4
6 9.8 4.0 0.9 nm nm 96 5.8
AC2 (ethylene) content based on combined amount of propylene and ethylene
BENS content determined by ASTM D-3900 and based on weight of polymer
1000681 The polymers were grafted on a non-intermeshing counter-rotating
twin screw extruder (30 cm, L/D = 48) under the following conditions: 97.5 to
98.5 weight % of polymer, 0.5 or 2.5 weight % of Crystalman TM Maleic
Anhydride were fed at 7 kg/h feed rate to the hopper of the extruder and 0.5
weight % of a 10 % solution of LuperoxTM 101 dissolved in MarcolTM 52 oil were
added to the second barrel. The screw speed was set at 125 rpm and following
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22
temperature profile was used: 180 C, 190 C, 190 C, 190 C with the die at 180
C.
Excess reagents as well as peroxide decomposition products were removed with
vacuum prior to polymer recovery.
[000691 Table 3 shows polymers 3-6 (those containing diene) when reacted
with high amounts of peroxide and maleic anhydride gave functionalized
polymers having a low MFR (i.e., high molecular weight, or a low MFR ratio
between MFR of the functionalized (grafted) polymer and the originally used
backbone, which indicates a small viscosity change during the grafting. Under
the
same conditions, the polymers 1 and 2 without diene lead to a higher MFR and
higher MFR ratio as well as a lower shear thinning ratio.
Table 3
1 2
3 4 5 6
Example (Comparative) (Comparative)
Polymer 1 97.0
Polymer 2 97.0
Polymer 3 97.0
Polymer 4 97.0
Polymer 5 97.0
Polymer 6 97.0
MA % added 2.5 2.5 2.5 2.5 2.5 2.5
Luperox 130 0.5 0.5 0.5 0.5 0.5 0.5
MA wt% before oven 1.4 1.5 1.7 1.6 1.7 1.8
MA wt% after oven 1.3 1.5 1.6 1.6 1.7 1.7
MFR of grafted polymer (1.2 kg 46 34 1.3 1.5 3.8 0.1
190 C
MFR ratio 31 48 1.4 1.9 4.2 0.04
shear thinning Ratio 11 11 71 59 urn 111
[00070] The propylene-based polymer backbones containing dienes permit the
use of increased amounts of peroxide and maleic anhydride for a given final
MFR
of the functionalized polymer as shown in Table 4 below. Under the same
conditions, the comparative polymers, polymer 1 and 2, provided much higher
MFR and MFR ratio.
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23
Table 4 7 Example Co arative (Comparative) C9 (Comparative 10 11 12 13 14 15
Polymer 2 98.95 98.85 97.0
Polymer 5 98.95 98.85 97.0
Polymer 6 98.95 98.85 97.0
MA% 1.0 1.0 2.5 1.0 1.0 2.5 1.0 1.0 2.5
added
Luperox 130 0.05 0.15 0.5 0.05 0.15 0.5 0.05 0.15 0.5
MA wt% 0.5 0.7 1.5 0.6 0.7 1.7 0.6 0.8 1.6
before oven
MA wt% 0.5 0.6 1.5 0.6 0.7 1.6 0.6 0.7 1.6
after oven
MFR of 8 16 34 2.4 2.4 1.3 2.1 2.0 1.5
grafted
polymer (1.2
kg (a) 190
MFR ratio 11 22 48 2.6 2.6 1.4 2.6 2.4 1.9
shear 14 nm 11 38 nm 71 nm nm 59
thinning
Ratio
Various terms as used herein are defined. To the extent a term used in
a claim is not defined, it should be given the broadest definition persons in
the
pertinent art have given that term as reflected in at least one printed
publication or
issued patent. Furthermore, certain embodiments and features have been
described using a set of numerical upper limits and a set of numerical lower
limits.
It should be appreciated that ranges from any lower limit to any upper limit
are
contemplated unless otherwise indicated. Certain lower limits, upper limits
and
ranges appear in one or more claims below. All numerical values are "about" or
"approximately" the indicated value, and take into account experimental error
and
variations that would be expected by a person having ordinary skill in the
art.
While the foregoing is directed to embodiments of the present invention, other
and
further embodiments of the invention can be devised without departing from the
basic scope thereof, and the scope thereof is determined by the claims that
follow.
