Note: Descriptions are shown in the official language in which they were submitted.
G_~,AFTING OF MONOMERS ONTO
POLYOLEFINS IN PRESENCE OF ORGANIC PEROXIDES
The present invention relates to the grafting of
monomers onto polyolefins in the presence of organic
peroxides, in which the organic peroxide is on a carrier
polymer that, under the grafting conditions, undergoes
chain scission in preference to cross-linking in the
presence of organic peroxides.
Polymers of alpha-olefins in which the alpha-olefin
is a hydrocarbon are well known. Such polymers,
especially homopolymers of ethylene and copolymers of
ethylene with the higher C4°Clo alpha-olefins are used in
large volumes for a variety of end-uses. These polymers
are relatively non-polar, which is an important and
beneficial characteristic for many end-uses. However,
non-polar characteristics are also a disadvantage, for
instance with respect to adhesion between polar materials
and the polyolefins.
Properties of polyolefins may be modified by the
grafting of polar monomers onto the polyolefin. Melt
grafting processes are described in U.S. Patent 4 612 155
of R.A. Zelonka and C.S. Wong, which issued 1986
September 16. In particular, that patent describes a
grafting process in which polyolefin in particulate form
is fed to an extruder together with grafting agent and
organic peroxide, the latter being in the form of a
composition with a second polymer of lower melting point
and lower melt viscosity.
In melt grafting processes, it is necessary to
obtain adequate mixing of the grafting monomer and
organic peroxide in the polyolefin prior to significant
formation of radicals upon decomposition of the organic
peroxide. If the mixing is inadequate, there is a
tendency for the polyolefin and/or grafting monomer to
undergo cross-linking reactions which form localized
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cross-linked polymer that becomes apparent as gel, black
contaminant particles or other specks in the grafted
polymer in the extruder. Both gel and black contaminant
particles or other specks are unacceptable in any
significant level for many end-uses e.g. in films.
A grafting process that is less susceptible to gel
formation and speck formation has now been found.
Accordingly, the present invention provides a method
for the grafting of a monomer onto a polyolefin in the
presence of an organic peroxide, said polyolefin being a
polyolefin that, when molten, undergoes cross-linking in
the presence of the organic peroxide, said method
comprising:
(a) admixing in an extruder an admixture of (i)
said polyolefin, (ii) 25 to 6000 ppm, based on the weight
of the polyolefin, of an organic peroxide coated onto a
carrier polymer, the amount of organic peroxide coated
onto said carrier polymer being at least 0.2% by weight
of the carrier polymer, and (iii) up to 5%, by weight of
the polyolefin, of a grafting monomer capable of being
grafted onto the polyolefin in the presence of the
organic peroxide;
(b) heating the admixture to a temperature above
the melting point of both the polyolefin and the carrier
polymer under admixing conditions to effect grafting of
said grafting monomer onto the polyolefin, said carrier
polymer undergoing chain scission in preference to cross-
linking in the presence of the organic peroxide at said
temperature; and
(c) extruding grafted polyolefin from the extruder.
In a preferred embodiment of the method of the
present invention, the grafted polyolefin so extruded has
a lower level of gel and specks than if the carrier
polymer had been a polyolefin that does not undergo chain
scission in the presence of the organic peroxide. In
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particular, the grafted polyolefin has a lower level of
gel and specks than obtained when the polyolefin of step
(a)(i) is also used as the carrier polymer.
In another embodiment, the melting point of the
carrier polymer is higher than the melting point of the
polyolefin.
As used herein, it is understood that it may be
determined whether a polymer preferentially undergoes
chain scission or cross-linking in the presence of an
organic peroxide at the temperature of grafting by
extruding the polymer at the temperature of grafting in
the presence of the organic peroxide and determining
whether the molecular weight of the polymer increases or
decreases. As disclosed above, the temperature of
grafting is above the melting point of both the carrier
polymer and the polyolefin that is to be grafted.
The process of the present invention involves
feeding to an extruder an admixture of a polyolefin,
organic peroxide coated onto a carrier polymer and a
grafting monomer. The polyolefin may be a homopolymer of
ethylene or copolymer of ethylene or propylene, including
copolymers with the higher alpha-olefins e.g. C4-Coo alpha-
olefins, examples of which are butane-1, 4-methyl
pentane-1, hexane-1 and octane-1. In addition, the
polyolefin may be a copolymer of ethylene with one or
more other ethylenically-unsaturated monomers that are
polar in nature e.g. vinyl esters of carboxylic acids,
vinyl halides and unsaturated carboxylic acids or esters
thereof. Specific examples include copolymers of
ethylene with at least one of acrylic acid, methacrylic
acid, carbon monoxide, methyl acrylate, butyl acrylate,
methyl hydrogen maleate and vinyl acetate. In addition,
the polyolefin may be an ionomer e.g. a sodium, zinc or
aluminum ionomer of an acid copolymer formed from
ethylene and an ethylenically unsaturated carboxylic
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-
acid. Examples of the above polymers are available from
Du Pont Canada Inc. or E.I. du Pont de Nemours and
Company under the trade marks Sclair~, Elvax~, Nucrel~ or
Surlyn~, depending on the particular polymer.
The organic peroxide used in the process of the
present invention has a half-life at 150°C of from about
one minute to about 120 minutes. The organic peroxide,
which as used herein includes hydroperoxides, may for
example be a peroxy ester, peroxy ketal, bis (tent.-alkyl
peroxy alkyl) benzene, dicumyl peroxide or acetylenic
diperoxy compound. Other organic peroxides are known to
those skilled in the art, including t-butyl hydroperoxide
and di-t-butyl peroxide. Preferred organic peroxides are
2,5-dimethyl-2,5-di(t-butyl peroxy) hexane and 2,5-
dimethyl-2,5-di(t-butyl peroxy)hexyne-3 which are E
available under the trade marks Lupersol 101 and 130,
respectively, from Elf Atochem. The organic peroxide is
coated onto a polymer in an amount of at least 0.2% by
weight, which may result in absorption into the polymer,
such that the polymer acts as a carrier for the organic
peroxide. The carrier polymer is a polymer that, under
the grafting conditions, undergoes chain scission in
preference to cross-linking in the presence of an organic
peroxide. In preferred embodiments, the carrier polymer
also has a melting point that is higher than the melting
point of the polyolefin, although the melting point of
the carrier polymer should not be unreasonably higher
because both the polyolefin and carrier polymer need to
become molten during the extrusion process, without
excessive heating especially excessive heating of the
polyolefin or carrier polymer above its melting point.
Examples of the carrier polymer are polypropylene,
copolymers of propylene with ethylene or other C,-Clo
alpha-olefin, poly-1-butene, copolymers of 1-butene with
minor amounts of ethylene or other C3-Clo alpha-olefin,
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~~ ~ '~i
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polystyrene, and block copolymers of styrene with a C4-C8
diene.
The,grafting monomer may be ethylenically
unsaturated carboxylic acids and ethylenically
unsaturated carboxylic acid anhydrides, including
derivatives of such acids, and mixtures thereof, and
vinyl trialkoxy silanes. Examples of the acids and
anhydrides, which may be mono, di- or polycarboxylic
acids, are acrylic acid, methacrylic acid, malefic acid,
l0 fumaric acid, itaconic acid, crotonic acid, itaconic
anhydride, malefic anhydride and substituted malefic
anhydride e.g. dimethyl malefic anhydride or citraconic
anhydride, nadir anhydride, nadir methyl anhydride and
tetrahydro phthalic anhydride. Examples of derivatives
of the unsaturated acids are salts, imides, amides and
esters e.g. mono- and disodium maleate, acrylamide,
maleimide, glycidyl methacrylate and diethyl fumarate.
Examples of the vinyl trialkoxy silanes are vinyl
trimethoxy silane and vinyl triethoxy silane.
The amount of organic peroxide will depend in
particular on the characteristics of the polyolefin and
of the grafting monomer but will be in the range of 25-
6000 ppm, especially 100-3000 ppm, and particularly in
the range of 500-2000 ppm, based on the amount of
polyolefin in the admixture fed to the extruder.
The amount of monomer will depend in particular on
the reactivity of the monomer and the level of grafting
that is to be achieved. For example, if the monomer is
malefic anhydride, the amount of monomer may be as high as
about 5% by weight of the polyolefin, especially 0.1-3%
by weight and particularly in the range of 0.2-2% by
weight. With other monomers, different amounts may be
preferred.
In preferred embodiments of the invention, the
temperature of the extruder, the half-life of the organic
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peroxide at the extrusion temperature, the relative
melting points of the polyolefin and carrier polymer, the
rate of chain scission of the carrier polymer at the
extrusion temperature, the melt viscosities of the
polyolefin and the carrier polymer, especially during
chain scission, are all balanced to obtain uniform
distribution of the grafting monomer in the melt
sufficiently prior to decomposition of the organic
peroxide at significant rates in order to optimize the
uniformity of the grafted polyolefin, including minimal
formation of gel or black contaminants or specks. Such
an ability to optimize the process will depend on many
factors, including the particular extruder being used.
While additives may be incorporated into the
polyolefin or carrier polymer prior to feeding the
admixture to the extruder, it will be appreciated by
persons skilled in the art that some additives have
detrimental effects on the grafting process, and for that
reason should not be used in the process of the present
invention.
The components of the admixture may be fed to the
extruder in a number of ways. For example, the
polyolefin may be fed to the extruder and heated to a
molten condition. The organic peroxide, on carrier
polymer, and grafting monomer may then be fed directly
into the molten polyolefin, using the same or different
ports in the extruder. Alternatively, one or more of the
organic peroxide and grafting monomer may be fed to the
extruder simultaneously with the polyolefin, especially
the organic peroxide. The extruder should have gaod
mixing characteristics, with twin screw extruders being
the preferred type of extruder but other extruders with
good mixing characteristics may be used.
The process of the present invention may be used to
produce compositions of monomer grafted onto polyolefins
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CA 02134462 2004-02-10
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with lower levels of gel and black contaminants,
especially in comparison with the corresponding grafting
process in the absence of use of a carrier of the type
described herein. The grafted polyolefin obtained by the
process will normally be in the form of pellets or other
comminuted shapes, but is not restricted thereto. The
grafted polyolefins may be used as such or as blends with
other polymers, especially in the form of adhesive
compositions for use with polymers or metals, in co-
extrusion of multi-layer structures, in coating
compositions, as compatibilizers in filled compositions
and to improve the dyeability and printability of
polymers.
The present invention is illustrated by the
following examples.
example I
This example illustrates the degree of film
contamination formed in grafted polyolefins made using
peroxide carrier resins which are not part of the present
invention i.e. each of polymers (i), (ii) and (iii) in
Table I below, undergo cross-linking in preference to
chain scission in the presence of organic peroxide under
the grafting conditions.
The grafting extruder used in this example was an
intermeshing co-rotating twin-screw extruder with a
barrel having a ratio of length:diameter of 38:1. The
temperature was set at 235°C.
An admixture was formed in the extruder from a base
polyolefin, viz. an ethylene/vinyl acetate copolymer,
organic peroxide and malefic anhydride.
The organic peroxide, viz. Lupersol 10~M was coated
onto a carrier polymer. The polyolefin and organic
peroxide were each fed, as an admixture, to the extruder
in pellet form, and the malefic anhydride was fed directly
into the first zone of the extruder. The polymer was
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_ g _
extruded from the extruder into water in the form of a
strand and palletized.
The grafted polyolefin was fed subsequently to a 1.9
cm diameter single screw extruder operating at 180°C and
extruded into a film having a width of 8 cm.
Gels and black contaminant particles or other specks
in a sample of the film were counted and normalized to
the weight of sample being assessed. In this example and
in the examples that follow, the measured gel and speck
level of the grafted polyolefin has been compared to the
gel and speck level of the base polyolefin extruded
through the same equipment in the absence of both organic
peroxide and grafting monomer. The grafted polyolefin
has been assigned a Gel Index based upon this comparison
according to the formula: I
Gel Index = 5 x LOGIO (NGC~~y-~)---------__)
2 0 ( NGCb", p~,obti. )
where NGC = normalized gel count.
The results for Runs 1-4 are reported in Table
I. Run 1 was a control run in which neither organic
peroxide nor grafting monomer was used. In each of Runs
2-4, the amount of malefic anhydride fed to the extruder
was 1.6% and the amount of organic peroxide fed was 1600
ppm, each based upon the total weight of the base
polyolefin plus carrier polymer.
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Base Carrier % Monomer Gel
Run No. Polyolefin Polymer Grafted Index
1 A none - 0
2 A i 1.5 4
3 A ii 1.5 6
4 A iii 1.3 5
Note: Polyolefin A - ethylene/vinyl acetate
copolymer, containing 9% of
vinyl acetate and having a
melt index of 7 dg/min
Polymer i ~ Polyolefin A
Polymer ii - ethylene/vinyl acetate
copolymer, containing 18% of
vinyl acetate and having a
melt index of 150 dg/min
Polymer iii = ethylene/butene linear low
density copolymer
(polyethylene) havin~ a
density of 0.93 g/cm and a
melt index of 73 dg/min
As used in this example, melt index was
measured according to the procedure of ASTM D-1238 at
190°C and using a 21608 weight.
These runs demonstrate that grafting of
polyolefin A using carrier polymers which undergo
crosslinking in the presence of organic peroxides results
in a grafted product having a significantly increased
level of gels and specks.
Exaigple II
The procedure of Example.I was repeated, using
different carrier polymers which illustrate an embodiment
of the present invention i.e. using carrier polymers that
undergo chain scission in preference to cross-linking in
the presence of an organic peroxide.
In each of the runs in this example, the amount
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of maleic anhydride fed to the extruder was 1.4% and the
amount of organic peroxide fed was 1200 ppm, each based
upon the total weight of the base polyolefin plus carrier
polymer. The organic peroxide employed in these runs was
Lupersol 101.
Table II
Base Carrier % Monomer Gel
Run No. Polyolefin Polymer Grafted Index
5 A iii 0.9 5
6 A iv 1.0 2
7 A v 1.1 1
Note Polymer iv - propylene/ethylene copolymer
having a DSC melting point of
129°C and a melt flow index o~
5 dg/min.
Polymer v = propylene/ethylene copolymer
having a DSC melting point of
135°C and a melt flow index of
6.8 dg/min.
The melt index of polymers (iv) and (v) was
measured using the procedure of ASTM D-1238 at 230°C and
with a 2160g weight. Run 5 is a comparative run, using a
polymer of Example I.
These runs demonstrate that grafting of
polyolefin A using carrier polymers which undergo
scissioning in the presence of organic peroxides results
in a grafted product having a significantly reduced level
of gels and specks.
Example IIT
The procedure of Example II was repeated, using
a different base polyolefin.
In each of the runs in this example, the amount
of malefic anhydride fed to the extruder was 1.5% and the
amount of organic peroxide fed was 1600 ppm, each based
upon the total weight of the base polyolefin plus carrier
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polymer. The organic peroxide employed in these runs was
Lupersol 101.
Table III
Base Carrier % Monomer Gel
Run No. Polyolefin Polymer Grafted Index
s B vi 1.1 8
9 B iv 1.2 2
B vii 1.3 0
10 11 B viii 1.3 -2
Note Polyolefin B - ethylene/vinylacetate
copolymer, containing 28% of
Vinyl acetate and having a
melt index of 6 dg/min.
Polymer Vi - Polyolefin B
Polymer vii ~ propylene/ethylene copolymer
having a DSC melting point ofd
135°C and a melt flow index of
4.6 dg/min.
Polymer viii - propylene/ethylene copolymer
having a DSC melting point of
143°C and a melt flow index of
5 dg/min.
The melt index of Polymer B was measured at
190°C and the malt indices of polymers (vii) and (viii)
were measured at 230°C.
Run 8 is a comparative run, which employed an
ethylene/Vinyl acetate copolymer as the carrier polymer.
It exhibited a large degree of gel contamination since
this carrier polymer undergoes crosslinking predominantly
under these conditions in the presence of organic
peroxide. Runs 9-11 each employed a polypropylene
copolymer carrier and exhibit Very much lower levels of
gel because the carrier polymers undergo scissioning
predominantly under these conditions.
Example IV
The procedure of Example I was repeated, using
additional different carrier polymers which further
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, ~I~i~~~'
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illustrate of the present invention.
embodiments
In each of
the runs in
this example,
the amount
of malefic to the extruder was 1.5% and
anhydride the
fed
amount of organic
peroxide fed
was 1600 ppm
(except 2200
ppm in runs 13 and each based upon the total weight
17),
of the base polyolefinplus carrier polymer. The organic
peroxide
employed
in these
runs
was
Lupersol
101.
Table IV
Base Carrier % Monomer Gel
Run No. Polyolefin Polymer Grafted Index
12 A vii 1.1 0
13 A ix 0.8 0
14 A x 1.1 0
15 A xi 1.1 8
16 B iv 1.1 1
17 B ix 0.7 -1
is B xii 1.0 3
19 B xi 1.2 8
Note: Polymer ix - styrene homopolymer having
a
melt flow index of 9 dg/min.
Polymer x - butene/ethylene copolymer
having a density of 0.895
g/cm3 and a melt flow index
of
4.0 dg/min.
Polymer xi - ethylene/propylene elastomer
having a Mooney viscosity
(100C, 1+8) Of 33
Polymer xii - styrene-ethylene/butene-
styrene block copolymer having
a melt flow index of 65
dg/min.
Melt Index of polymers (ix) and (xii) was
measured at 200°C and a weight of 5000 g, whereas that
for polymer (x) was measured at 230°C and a weight of
2160 g.
Runs 12-14 and 16-18 all exhibit reduced levels
of film contaminants when compared respectively with
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- 13 -
comparative Runs 15 and 19 which employed a carrier
polymer for the organic peroxide which was outside the
scope of the invention.
exam llZe V
The procedure of Example II was repeated, using
a different base polyolefin.
In each of the runs in this example, the amount
of malefic anhydride fed to the extruder was 1.5% and the
amount of organic peroxide fed was 1500 ppm, each based
upon the weight of the base polyolefin plus carrier
polymer. The organic peroxide employed in these runs was
Lupersol 101.
Table V
Base Carrier % Monomer Gel
Run No. Polyolefin Polymer Grafted Index
C xiii 1.4 4
21 C iV 1.5 -1
20 Note: Polyolefin C ~ ethylene/methyl acrylate
copolymer, containing 21% of
methyl acrylate and having a
melt index of 2 dg/min.
Polymer xiii - ethylene/methyl acrylate
copolymer, containing 20% of
methyl acrylate and having a
melt index of 5 dg/min.
Melt index was measured at 190°C using a weight
of 21608. Run 20 is a comparative example.
This example again shows the reduction in gel
count that is obtainable.
Example VI
The procedure of Example II was repeated, using
a different base polyolefin.
In each of the runs in this example, the amount
of malefic anhydride fed to the extruder was 1.1% and the
amount of organic peroxide fed was 570 ppm, each based
upon the weight of the base polyolefin plus carrier
DC-0272 - 13 -
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- 14 -
polymer. The organic peroxide employed in these runs was
Lupersol 101. The carrier polymers were as defined
previously.
Table V
Base Carrier % Monomer Gel
Run No. Polyolefin Polymer Grafted Index
22 D iii 0.7 7
23 D vii 0.7 4
Note: Polyolefin - ethylene/butene-1
D linear
low
density copolymer having
a
density of 0.92 g/cm' and
a
melt index
of 12 dg/min.
Melt index
was measured
at 190C
using a
weight
of 21608. Run 22 is comparativeexample.
a
This exampleagain showsthe reduction in
gel
count that
is obtainable.
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