PROCESS FOR THE METATHESIS OF FUNCTIONALIZED POLYMERS

METHODE POUR LA METATHESE DE POLYMERES FONCTIONNALISES

English Abstract

A low-molecular weight nitrite rubber having narrower molecular weight
distributions
than those known in the art can be prepared by olefin metathesis.

Claims

Claims
1. A process for the preparation of a nitrile rubber which comprises
subjecting a nitrile
rubber to metathesis in the presence of a co-olefin and a catalyst selected
from the
group consisting of Formula I, II and III:
<IMG>
wherein:
M is Os or Ru;
R and R1 are, independently, hydrogen or a hydrocarbon selected from the
group consisting of C2-C20 alkenyl, C2-C20 alkynyl, C1-C20 alkyl, aryl, C1-C20
carboxylate,
C1-C20 alkoxy, C2-C20 alkenyloxy, C2-C20 alkynyloxy, aryloxy, C2-C20
alkoxycarbonyl, C1-
C20 alkylthio, C1-C20 alkylsulfonyl and C1-C20 alkylsulfinyl;
X and X1 are independently selected anionic ligands; and
L and L1 are, independently, ligands selected from the group consisting of
phosphines, sulfonated phosphines, fluorinated phosphines, functionalized
phosphines
having up to three aminoalkyl-, ammoniumalkyl-, alkoxyalkyl-,
alkoxylcarbonylalkyl-,
hydrocycarbonylalkyl-, hydroxyalkyl- or ketoalkyl- groups, phosphites,
phosphinites,
phosphonites, phosphinamines, arsines, stibines, ethers, amines, amides,
imines,
sulfoxides, thioethers and pyridines; optionally, L and L1 can be linked to
one another to
from a bidentate neutral ligand wherein at least one of the above-mentioned
functional
groups is present;
11

<IMG>
wherein:
M1 is Os or Ru;
R2 and R3 are, independently, hydrogen or a hydrocarbon selected from the
group
consisting of C2-C20 alkenyl, C2-C20 alkynyl, C1-C20 alkyl, aryl, C1-C20
carboxylate, C1-C20
alkoxy, C2-C20 alkenyloxy, C2-C20 alkynyloxy, aryloxy, C2-C20 alkoxycarbonyl,
C1-C20
alkylthio, C1-C20 alkylsulfonyl and C1-C20 alkylsulfinyl;
X2 is selected from any anionic ligand; and
L2 is a neutral .pi.-bonded ligand, preferably but not limited to arene,
substituted
arene, heteroarene, independent of whether they are mono- or polycyclic;
L3 is a ligand selected from the group consisting of phosphines, sulfonated
phosphines, fluorinated phosphines, functionalized phosphines bearing up to
three
aminoalkyl-, ammoniumalkyl-, alkoxyalkyl-, alkoxylcarbonylalkyl-,
hydrocycarbonylalkyl-,
hydroxyalkyl- or ketoalkyl- groups, phosphites, phosphinites, phosphonites,
phosphinamines, arsines, stibenes, ethers, amines, amides, imines, sulfoxides,
thioethers and pyridines;
Y- is a non-coordinating anion;
n is an integer in the range of from 0 to 5;
<IMG>
12

wherein
M2 is Mo or W
R4, R5 are, independently, hydrogen or a hydrocarbon selected from the group
consisting of C2-C20 alkenyl, C2-C20 alkynyl, C1-C20 alkyl, aryl, C1-C20
carboxylate, C1-C20
alkoxy, C2-C20 alkenyloxy, C2-C20 alkynyloxy, aryloxy, C2-C20 alkoxycarbonyl,
C1-C20
alkylthio, C1-C20 alkylsulfonyl and C1-C20 alkylsulfinyl;
R6 and R7 are independently selected from any unsubstituted or halo-
substituted
alkyl, aryl, aralkyl groups or silicon-containing analogs thereof.
2. A process according to claim 1 wherein the metathesis catalyst is a
compound of
Formula I.
3. A process according to claim 2 wherein L and L1 are trialkylphosphines, X
and X1
are chloride ions and M is ruthenium.
4. A process according to claim 1 wherein the ratio of catalyst to nitrile
rubber is in the
range of from about 0.005 to about 5.
5. A process according to claim 4 wherein the ratio of catalyst to nitrile
rubber is in the
range of from about 0.025 to about 1.
6. A process according to claim 5 wherein the ratio of catalyst to nitrile
rubber is in the
range of from about 0.1 to about 0.5.
7. A process according to claim 1 wherein the co-olefin is a C2 to C16 linear
or
branched olefin.
8. A process according to claim 7 wherein the co-olefin is selected from the
group
consisting of ethylene, isobutene, styrene and 1-hexene.
9. A process according to claim 8 wherein the co-olefin is ethylene.
10.A process according to claim 1 wherein, if the co-olefin is a liquid, the
amount
employed is in the range of from about 1 to about 50 weight %.
13

11.A process according to claim 10 wherein the amount of co-olefin employed is
in the
range of from about 10 to about 30 weight %.
12.A process according to claim 1 wherein, if the co-olefin is a gas, the
amount
employed is such that the resulting pressure in the reaction vessel is in the
range of
from about 3 to about 3600 psi
13.A process according to claim 12 wherein, if the co-olefin is a gas, the
amount
employed is such that the resulting pressure in the reaction vessel is in the
range of
from about 15 to about 1500 psi.
14.A process according to claim 13 wherein the amount of co-olefin employed is
in the
range of from about 75 to about 600 psi.
15.A process according to claim 1 wherein the process is carried out in an
inert solvent
selected from the group consisting of monochlorobenzene, dichloromethane,
benzene, toluene, tetrahydrofuran, methyl ethyl ketone and cyclohexane.
16.A process according to claim 15 wherein the solvent is monochlorobenzene.
17.A process according to claim 1 wherein the concentration of nitrile rubber
is in the
range of from about 1 to about 40%.
18.A process according to claim 17 wherein the concentration of nitrile rubber
is in the
range of from about 6 to about 15%.
19.A process according to claim 1 wherein the metathesis reaction is carried
out at a
temperature in the range of from about 20 to about 140°C.
20.A process according to claim 19 wherein the metathesis reaction is carried
out at a
temperature in the range of from about 60 to about 120°C.
14

Description

CA 02357470 2001-09-18
Process for the Metathesis of Functionalized Polymers
Field of the Invention.
The present invention relates to nitrite rubber polymers having lower
molecular
weights and narrower molecular weight distributions than those known in the
art.
Background of the Invention
Nitrite rubber (NBR), a co-polymer of a conjugated diene and an
unsaturated nitrite, is a specialty rubber which has very chemical resistance,
and
excellent oil resistance. Coupled with the high level of mechanical properties
of the
rubber (in particular the high resistance to abrasion) it is not surprising
that NBR has
found widespread use in the automotive (seals, hoses, bearing pads),
electrical (cable
sheathing), mechanical engineering (wheels, rollers) and footwear industries,
amongst
others.
Commercially available NBR is manufactured by emulsion polymerization. The
monomers are emulsified in water, a free radical-generating catalyst is added
and the
mixture is agitated whilst a constant temperature is maintained. After the
desired
degree of polymerization is reached, a shortstop and stabilizers are added to
the
reaction system causing termination of the polymerization process. Generally,
NBR
obtained by this process has a Mooney viscosity in the range of from about 30
to about
90, an Mw in the range of from about 250,000 to about 350,000, an Mn in the
range of
from about 80,000 to about 150,000 and a polydispersity index greater than
about 3.2.
In addition, so-called "liquid NBR" having a very low Mooney viscosity and a
low
molecular weight can be produced be adding the shortstop agent early in the
reaction
process. As in the case of regular NBR, the resulting liquid NBR has a
polydispersity
greater than 3Ø
Karl Ziegler's discovery of the high effectiveness of certain metal salts, in
combination with main group alkylating agents, to promote olefin
polymerization under
mild conditions has had a significant impact on chemical research and
production to
date. It was discovered early on that some "Ziegler-type" catalysts not only
promote the
proposed coordination-insertion mechanism but also effect an entirely
different
chemical process, that is the mutual exchange (or metathesis) reaction of
alkenes
1

CA 02357470 2001-09-18
R~ R2 R~ R2
Cat! alyst
R R R R
Figure 1
Acyclic diene metathesis (or ADMET) is catalyzed by a great variety of
transition
metal complexes as well as non-metallic systems. Heterogeneous catalyst
systems
based on metal oxides, sulfides or metal salts were originally used for the
metathesis of
olefins. However, the limited stability (especially towards hetero-
substituents) and the
lack of selectivity resulting from the numerous active sites and side
reactions are major
drawbacks of the heterogeneous systems.
Homogeneous systems have also been devised and used to effect olefin
metathesis. These systems offer significant activity and control advantages
over the
heterogeneous catalyst systems. For example, certain Rhodium based complexes
are
effective catalysts for the metathesis of electron-rich olefins.
The discovery that certain metal-alkylidene complexes are capable of
catalyzing
the metathesis of olefins triggered the development of a new generation of
well-defined,
highly active, single-site catalysts. Amongst these, Bis-
(tricyclohexylphosphine)-
benzylidene ruthenium dichloride (commonly know as Grubb's catalyst) has been
widely used, due to its remarkable insensitivity to air and moisture and high
tolerance
towards various functional groups. Unlike the molybdenum-based metathesis
catalysts,
this ruthenium carbene catalyst is stable to acids, alcohols, aldehydes and
quaternary
amine salts and can be used in a variety of solvents (C6H6, CH2C12, THF, t-
BuOH). The
most commonly-used catalysts are based on Mo, W and Ru.
The use of transition-metal catalyzed alkene metathesis has since enjoyed
increasing attention as a synthetic method. Research efforts have been mainly
focused
on the synthesis of small molecules, but the application of olefin metathesis
to polymer
synthesis has allowed the preparation of new polymeric material with
unprecedented
properties (such as highly stereoregular poly-norbornadiene).
2

CA 02357470 2001-09-18
The utilization of olefin metathesis as a means to produce low molecular
weight
compounds from unsaturated elastomers has received growing interest. The
principle
for the molecular weight reduction of unsaturated polymers is shown in Figure
2. The
use of an appropriate catalyst allows the cross-metathesis of the unsaturation
of the
polymer with the co-olefin. The end result is the cleavage of the polymer
chain at the
unsaturation sites and the generation of polymer fragments having lower
molecular
weights. In addition, another effect of this process is the "homogenizing" of
the polymer
chain lengths, resulting in a reduction of the polydispersity. From an
application and
processing stand point, a narrow molecular weight distribution of the raw
polymer
results in improved physical properties of the vulcanized rubber, whilst the
lower
molecular weight provides good processing behavior.
/ /
//
Cat
/ /
Figure 2 Metathesis of Partially Unsaturated Polymer
The so-called "depolymerization" of copolymers of 1,3-butadiene with a variety
of
co-monomers (styrene, propene, divinylbenzene and ethylvinylbenzene,
acrylonitrile,
vinyltrimethylsilane and divinyldimethylsilane) in the presence of classical
Mo and W
catalyst system has been investigated. Similarly, the degradation of a nitrite
rubber
using WCIs and SnMe4 or PhC---CH co-catalyst was reported in 1988. However,
the
focus of such research was to produce only low molecular fragments which could
be
characterized by conventional chemical means and contains no teaching with
respect
to the preparation of low molecular weight nitrite rubber polymers.
Furthermore, such
processes are non-controlled and produce a wide range of products.
3

CA 02357470 2001-09-18
The catalytic depolymerization of 1,4-polybutadiene in the presence of
substituted olefins or ethylene (as chain transfer agents) in the presence of
well-defined
Grubb's or Schrock's catalysts is also possible. The use of Molybdenum or
Tungsten
compounds of the general structural formula {M(=NR,)(OR2)2(=CHR); M = Mo, W}
to
produce low molecular weight polymers or oligomers from gelled polymers
containing
internal unsaturation along the polymer backbone was claimed in US 5,446,102.
Again,
however, the process disclosed is non-controlled, and there is no teaching
with respect
to the preparation of low molecular weight nitrite rubber polymers.
Summar~r of the Invention
We have now discovered that a low molecular weight nitrite rubber having
narrower molecular weight distributions than those known in the art can be
prepared by
olefin metathesis. Rubbers having a narrow molecular weight distribution have
certain
advantages over those having a broad molecular weight distribution, one of
these being
that they have improved physical properties, resulting, for example, in better
processability of the rubber.
Thus, one aspect of the disclosed invention is a nitrite rubber having a
molecular
weight (MW) in the range of from about 25,000 to about 200,000, a Mooney
viscosity
(ML 1+4 100) of less than about 25, and a MWD (or polydispersity index) of
less than
about 2.5.
Description of the Invention
As used throughout this specification, the term "nitrite rubber" is intended
to have
a broad meaning and is meant to encompass a copolymer of a conjugated diene
and
an unsaturated nitrite.
The conjugated diene may be a C4 Cs conjugated diene. Non-limiting examples
of suitable such conjugated dienes may be selected from the group comprising
butadiene, isoprene, piperylene, 2,3-dimethyl butadiene and mixtures thereof.
The
preferred C4 C6 conjugated diene may be selected from the group comprising
butadiene, isoprene and mixtures thereof. The most preferred C4 C6 conjugated
diene
is butadiene.
4

CA 02357470 2001-09-18
The unsaturated nitrite may be a C3 C5 a,~3-unsaturated nitrite. Non-limiting
examples of suitable such C3 C5 a,~-unsaturated nitrites may be selected from
the
group comprising acrylonitrile, methacrylonitrile, ethacrylonitrile and
mixtures thereof.
The most preferred C3 C5 a,~3-unsaturated nitrite is acrylonitrile.
Preferably, the copolymer comprises from about 40 to about 85 weight percent
of the copolymer of bound conjugated diene and from about 15 to about 60
weight
percent of the copolymer of bound unsaturated nitrite. More preferably, the
copolymer
comprises from about 60 to about 75 weight percent of the copolymer of bound
conjugated diene and from about 25 to about 40 weight percent of the copolymer
of
bound unsaturated nitrite. Most preferably, the copolymer comprises from about
60 to
about 70 weight percent of the copolymer of bound conjugated diene and from
about
30 to about 40 weight percent of the copolymer of bound unsaturated nitrite.
Optionally, the copolymer may further comprise a bound unsaturated carboxylic
acid. Non-limiting examples of suitable such bound unsaturated carboxylic
acids may
be selected from the group comprising fumaric acid, malefic acid, acrylic
acid,
methacrylic acid and mixtures thereof. The bound unsaturated carboxylic acid
may be
present in an amount of from about 1 to about 10 weight percent of the
copolymer, with
this amount displacing a corresponding amount of the conjugated diolefin.
Further, a third monomer may be used in production of the nitrite polymer.
Preferably, the third monomer is an unsaturated mono- or di-carboxylic acid or
derivative thereof (e.g., esters, amides and the like).
The metathesis reaction can be catalysed by compounds of formula I, II or III;
as
shown below
L
X' I R
/ M C'
X1 ( R1
L1
Formula I
5

CA 02357470 2001-09-18
wherein:
M is Os or Ru;
R and R' are, independently, hydrogen or a hydrocarbon selected from the
group consisting of CZ C2o alkenyl, CZ C2o alkynyl, C,-C2o alkyl, aryl, C,-C2o
carboxylate,
C,-C2o alkoxy, C2 C2o alkenyloxy, C2 C2o alkynyloxy, aryloxy, C2 C2o
alkoxycarbonyl, C,-
C2o alkylthio, C,-C2o alkylsulfonyl and C,-C2o alkylsulfinyl;
X and X' are independently selected anionic ligands; and
L and L' are, independently, ligands selected from the group consisting of
phosphines, sulfonated phosphines, fluorinated phosphines, functionalized
phosphines
having up to three aminoalkyl-, ammoniumalkyl-, alkoxyalkyl-,
alkoxylcarbonylalkyl-,
hydrocycarbonylalkyl-, hydroxyalkyl- or ketoalkyl- groups, phosphites,
phosphinites,
phosphonites, phosphinamines, arsines, stibines, ethers, amines, amides,
imines,
sulfoxides, thioethers and pyridines; optionally, L and L' can be linked to
one another to
from a bidentate neutral ligand wherein at least one of the above-mentioned
functional
groups is present.
0
LZ R2
M~ C C C
x2~~ n
L3 Rs
Formula II
wherein:
M' is Os or Ru;
R2 and R3 are, independently, hydrogen or a hydrocarbon selected from the
group
consisting of C2 C2o alkenyl, CZ C2o alkynyl, C,-C2o alkyl, aryl, C,-C2o
carboxylate, C,-C2o
alkoxy, C2 C2o alkenyloxy, C2 C2o alkynyloxy, aryloxy, C2 C2o alkoxycarbonyl,
C,-C2o
alkylthio, C,-C2o alkylsulfonyl and C,-C2o alkylsulfinyl;
X2 is selected from any anionic ligand; and
L2 is a neutral ~-bonded ligand, preferably but not limited to arene,
substituted
arene, heteroarene, independent of whether they are mono- or polycyclic;
L3 is a ligand selected from the group consisting of phosphines, sulfonated
phosphines, fluorinated phosphines, functionalized phosphines bearing up to
three
6

CA 02357470 2001-09-18
aminoalkyl-, ammoniumalkyl-, alkoxyalkyl-, alkoxylcarbonylalkyl-,
hydrocycarbonylalkyl-,
hydroxyalkyl- or ketoalkyl- groups, phosphites, phosphinites, phosphonites,
phosphinamines, arsines, stibenes, ethers, amines, amides, imines, sulfoxides,
thioethers and pyridines;
Y~ is a non-coordinating anion;
n is an integer in the range of from 0 to 5;
OR'2 a
I R
OR' -M2 C
z
R5
N
R6
Formula III
wherein
M2 is Mo or W
R4, R5 are, independently, hydrogen or a hydrocarbon selected from the group
consisting of C2 C2o alkenyl, C2 C2o alkynyl, C,-C2o alkyl, aryl, C,-C2o
carboxylate, C,-C2o
alkoxy, C2 C2o alkenyloxy, C2-C2o alkynyloxy, aryloxy, CZ C2o alkoxycarbonyl,
C,-C2o
alkylthio, C,-C2o alkylsulfonyl and C,-C2o alkylsulfinyl;
Rs and R' are independently selected from any unsubstituted or halo-
substituted
alkyl, aryl, aralkyl groups or silicon-containing analogs thereof.
Catalysts of Formula I are preferred. More preferably, catalysts of Formula I
wherein L and L' are trialkylphosphines, X and X' are chloride ions and M is
Ruthenium
are preferred.
The amount of catalyst employed in the metathesis reaction will depend upon
the nature and activity of the catalyst in question. Typically, the ratio of
catalyst to NBR
is in the range of from about 0.005 to about 5, preferably in the range of
from about
0.025 to about 1 and, more preferably, in the range of from about 0.1 to about
0.5.
7

CA 02357470 2001-09-18
The metathesis reaction is carried out in the presence of a co-olefin. The co-
olefin may be a hydrocarbon or it may be functionalised, with the caveat that
it should
not inactivate the metathesis catalyst or otherwise interfere with the
reaction. Preferred
olefins include, but are not limited to, C2 to C,6 linear or branched olefins
such as
ethylene, isobutene, styrene or 1-hexene. Where the co-olefin is a liquid
(such as 1-
hexene), the amount of co-olefin employed is in the range of from about 1 to
about 50
weight %; preferably in the range of from about 10 to about 30 weight %. Where
the
co-olefin is a gas (such as ethylene) the amount of co-olefin employed is such
that it
results in a pressure in the reaction vessel in the range of from about 3 to
about 3600
psi, preferably in the range of from about 15 to about 1500 psi and, more
preferably, in
the range of from about 75 to about 600 psi.
The metathesis reaction can be carried out in any suitable solvent which does
not inactivate the catalyst or otherwise interfere with the reaction.
Preferred solvents
include, but are not limited to, dichloromethane, benzene, toluene,
tetrahydrofuran,
methyl ethyl ketone, cylcohexane and the like. The most preferred solvent is
monochlorobenzene (MCB). In certain cases the co-olefin can itself act as a
solvent
(for example, 1-hexene), in which case no other solvent is necessary.
The concentration of NBR in the reaction mixture is not critical but,
obviously,
should be such that the reaction is not hampered if the mixture is too viscous
to be
stirred efficiently, for example. Preferably, the concentration of NBR is in
the range of
from about 1 to about 40%, most preferably in the range of from about 6 to
about 15%.
The metathesis reaction is carried out at a temperature in the range of from
about 20 to about 140°C; preferably in the range of from about 60 to
about 120°C.
The reaction time will depend upon a number of factors, including cement
concentration, amount of catalyst used and the temperature at which the
reaction is
performed. The metathesis is complete within the first two hours under typical
conditions. The progress of the metathesis reaction may be monitored by
standard
analytical techniques, for example using GPC or solution viscosity .
The Mooney viscosity of the rubber was determined using ASTM test D1646.
8

CA 02357470 2001-09-18
For a typical product the Mn is about 30,000 (compared to about 85,000 for the
starting polymer) whilst the Mw is about 55,000 (compared to 300,000 for the
starting
polymer. As can be seen from Table 1, however, higher molecular weights (Mw)
can
also be obtained by manipulation of the experimental conditions (for example
by
lowering the catalyst loading). As expected, the molecular weight distribution
falls from
about 3.5 for the starting NMB feedstock to about 2.0 for the metathesized
product.
This is consistent with a more homogeneous range of polymer chain lengths and
molecular weights.
A summary of the polymer properties for selected samples is shown in Table 1.
The GPC results show up to a fivefold reduction in Mw and a narrowing of the
polydispersity index to about 2Ø
Table 1 Summary of Polymer Properties
MN MW MZ PDI Mooney Viscosity
(ML 1+4 @ 100)
Starting NBR 85000 296000 9390003.50 35
(Perbunan)
Experiment 1 27000 54000 92000 2.00 2.5
Experiment 2 27000 53000 89000 1.98 -
Experiment 3 32000 66000 1170002.06 -
Experiment 4 67000 134000 2530002.00 -
Experimental Details
Bis(tricyclohexylphosphine)benzylidene ruthenium dichloride (Grubb's
metathesis catalyst), 1-hexene and monochlorobenzene (MCB) were purchased from
Alfa, Aldrich Chemicals, and PPG respectively and used as received. Perbunan
was
obtained from Bayer Inc. .
The metathesis reactions were carried out in a Parr high-pressure reactor
under
the following conditions:
Cement Concentration 6 or 15%
9

CA 02357470 2001-09-18
Co-Olefin Ethylene or 1-Hexene
Co-Olefin Concentration Variable
Agitator Speed 600 rpm
Reactor Temperature Variable
Catalyst Loading Variable
Solvent Monochlorobenzene
Substrate Perbunan NT 3435 T
Perbunan NT 3429 T
In a typical lab experiment, 200g of rubber was dissolved in 1133g of MCB (15%
solid). The cement was then charged to the reactor and degassed 3 times with
C2H4
(100 psi) under full agitation. The reactor was heated to desired temperature
and 60mL
of a monochlorobenzene solution containing Grubb's catalyst was added to the
reactor.
The temperature was maintained constant for the duration of the reaction. A
cooling
coil connected to a temperature controller and a thermal sensor was used to
regulate
the temperature. The progress of the reaction was monitored using solution
viscosity
measurements for the 6% cements. At higher cement concentration, the reaction
was
assumed to be complete after 18 hours.