Note: Descriptions are shown in the official language in which they were submitted.
2 ~
CATALYST FOR POLYMERISATION
This invention relates to catalysts, more spe~ifi-
cally catalysts which are used in polymerisation reactions,
especially the polymerisation of organosiloxanes.
The polymerisation or copolymerisation of organo-
siloxanes has been known for some time and is a well known
step in the production of commercial siloxanes. Organo-
polysiloxanes have been prepared for example by contacting
low viscosity organosiloxanes, especially cyclic polysi-
loxanes, low viscosity siloxanols or a mixture thereof in
the presence of an acidic or basic catalyst. For example
organopolysiloxanes may be prepared by condensation of
organosiloxanes having reactive groups at terminal silicon
atoms, e.g. silicon-bonded hydroxyl groups, silicon-bonded
hydrocarbonoxy groups and mixtures of one or more of these.
Organopolysiloxanes may also be made by rearrangement of
linear and/or cyclic or~anosiloxanes. For each of the
polymerisation processes a range of catalysts have been
developed, some being more effective than others. Known
catalysts for such polymerisation reaction include
sulphuric acid, hydrochloric acia, Lewis acids, sodium
hydroxide, potassium hydroxide, tetra-methylammonium
hydroxide, tetrabutylphosphonium silanolate and amines.
A number of patent applications discloses phospho-
nitrile halide catalysts. G.B. Patent Specification
765 744 discloses that preferred phosphonitrile halides for
the polymerisation of liquid organosiloxanes having an
average degree of substitution of from 1.9 to 2.1 organic
groups attached to silicon per silicon atom are polymeric
chlorides represented by the formula (PNCl2)n, wherein n is
an integer of at least 3, most preferably 3 to 6. The
process is described as being especially valuable for the
2 ~
production of polymerised organosiloxanes to be used for
the manufacture of silicone rubber. G.B. Patent Specifi-
cation 910 513 discloses phosphonitrile halide catalysts
for use in a process for the manufacture of stabilised high
viscosity organopolysiloxane oils, which comprises
preparing a fluid mixture of the halides with a hydroxyl-
terminated diorganopolysiloxane and a triorganosilyl end-
blocked diorganopolysiloxane with a viscosity from 1 to
lO,OOOmmZ/s, followed by bringing the mixture in contact
with a stream of air at room temperature until the visco-
sity is stabilised and thereafter bringing the mixture in
contact with a stream of air at a temperature of from 100
to 200C until the viscosity is stabilised. In U.S.
specification 3,549,680 phosphonitrile halide catalysts are
employed in rearrangement reactions, e.g. a method of
preparing organohalogenosilicon compounds in which organo-
halogenosiloxane compounds containing at least one halogen
atom bonded to silicon per molecule and organosiloxanes
free from halogen substituents having a viscosity of less
than lOO,OOOmm2/s are mixed with the halides. E.P. Patent
Specification 319 978 describes chlorophosphonitrile
catalysts for use in a process for the preparation of
diorganopolysiloxanes containing a silicon-bonded hydroxyl
group in each of the terminal units in which a cyclic
diorganopolysiloxane and/or diorganochlorosilane hydrolysis
product is reacted with a diorganochlorosilane, followed by
the treatment with water or an aqueous solution and sepa-
rating the low boiling substituents and the aqueous phase
There is a continuing search for catalysts which will
have improved activity in the polymerisation of
organosiloxanes.
We have now found that if phosphonitrile catalysts
include certain Lewis acid-based parts an improved catalyst
for making organopolysiloxanes is obtained.
2~61~
According to the invention there is provided a
phosphonitrile halide catalyst for use in polymerising
organosiloxanes, having the general formula
[X(PX2=N)nPx3] [MX(v-t+l) t]
wherein X denotes a halide atom, M is an element having an
electronegativity of from 1.0 to 2.0 on Pauling's scale, R
is an alkyl group having up to 12 carbon atoms, n has a
value of from 1 to 6, v is the valence or oxidation state
of M and 0 < t < v.
Some phosphonitrile halide compounds which are useful
as a catalyst in the polymerisation of organosiloxanes have
been described in the literature, but their use as a
catalyst has hitherto not been known.
U.S. Specification 3,449,091 describes metal halide
modified phosphonitrile chloride polymeric compositions
which are useful as high temperature lubricants. The
disclosed materials have the general formula
[Cl[PC12=N]nPC13] [EX(v+l)] , wherein E is an element
having an electronegativity value of from 1.2 to 2 and
differs in electronegativity from the halogen portion of
the halide by a maximum of 2.5, X is a halogen, _ is the
valence of element E and n is from 1 to 10 inclusive.
Exemplified E elements include Zn, Al, B, Ti, Sn, Sb, Th
and Fe. Although several of the described compounds may be
useful as catalysts for the polymerisation of organo-
siloxanes, not all are effective and some compounds are
more preferred than others. Nothing in the art indicates
the usefulness of some of these compounds as catalysts and
nothing indicates which of these compounds would be useful
as catalysts for the polymerisation of organosiloxanes.
Catalysts according to the invention have a cationic
phosphonitrile part and an anionic part which has been
derived from a Lewis acid. The phosphonitrile part is a
2~Qt,~
linear oligomeric or polymeric phosphonitrile halide having
the general formula [X(PX2=N)nPX3]+ wherein n denotes an
integer having a value of from 1 to 6. It is preferred
that the halogen X is a chlorine atom. Phosphonitrile
halide cationic parts with a value for n which is higher
than 6 are less suitable as catalysts. Most preferred are
the phosphonitrile halide parts in which the value of n is
from 2 to 4. It is sometimes difficult to separate the
polymeric phosphonitrile halides having different _ values
and mixtures are often used. It is particularly preferred
that the amount of phosphonitrile halide polymer, in which
_ has a value of 2, is as high as possible as this gives
the most active catalyst. Particularly preferred is a
catalyst which exclusively consists of compounds according
to the invention in which the value of n is 2.
The anionic part of the catalyst is derived from a
Lewis acid and has the formula [MX(V t+l)Rt] . Although it
is preferred that the value of t is zero alkyl groups may
be included. Preferably the Lewis acid based anion
contains a halide X which is the same as the halide of the
phosphonitrile cationic part, i.e. most preferably a
chlorine. The element M of the Lewis acid part is an
electropositive element having an electronegativity value
according to Pauling's scale of from 1 to 2, preferably
from 1.2 to l.9, most preferably 1.5 to 1.9. Suitable
elements are found in Groups Ib, IIa, IIb, IIIa, IVa, IVb,
Va, Vb, VIb, VIIb and VIII of the Periodic Table. They
include Al, B, Be, Mg, Sb and Si. It is preferred that the
difference in electronegative value between the phosphorus
atom of the phosphonitrile part of the catalyst and the M
element is as large as possible within the preferred range,
giving improved catalytic activity when this value is
larger. The presence of the anionic Lewis acid based part
2~1g~
in the catalyst improves the catalytic activity of the
catalyst in the polymerisation reaction of organosiloxanes.
It also tends to make the catalyst more stable in itself,
thus preventing it from cyclisation and from polymerisation
with other phosphonitrile compounds, even at higher tempe-
ratures.
A particularly suitable compound is the one where the
Lewis acid derived portion is based on antimony, especially
SbCl3 or SbCl5. An example of such suitable catalyst has
the formula [Cl3P=N-(PCl2=N)s-PCl3] [SbC16] , wherein s has
a value from 1 to 4. Another suitable compound is the one
where the Lewis acid derived portion is based on aluminium.
Phosphonitrile halide catalysts according to the
invention may be made by reacting a phosphorus pentahalide,
an ammonium halide and a Lewis acid. Preferably they are
made by reacting in the presence of an aromatic hydrocarbon
or more preferably of a chlorinated aliphatic or aromatic
hydrocarbon, e.g. toluene, sym-tetrachloroethane or 1,2,4-
trichlorobenzene, as inert solvent, the phosphorus penta-
halide, e.g. phosphorus pentachloride, the ammonium halide,
e.g. ammonium chloride and the selected Lewis acid.
Suitable Lewis acids are those which are based on an
electropositive element M having an electronegativity value
according to Pauling's scale of from 1 to 2. Examples of
suitable Lewis acids are SbCl3, SbCl5, AlCl3, SiCl4, MgCl2,
BCl3 and BF3. The reaction may be carried out at a tempe-
rature between 100 and 220~C followed by separating the
reaction products from the solids and the volatile compo-
nents, thus isolating the liquid reaction product. Attemperatures below 100C the reaction does not occur or is
so slow as not to be economically feasible. Mere mixtures
of the reagents do not give satisfactory polymerisation
rates. Temperatures above 220C may be used provided that
2 ~ U ~
pressure is applied to maintain the solvent in the system;
however, temperatures above 220C are not generally
recommended because of the tendency of the products to
darken at elevated tempera- tures. Preferred temperature
range is the refluxing temperature of the inert solvent
used in the reaction, for example 120 to 160C. The
reagents may be added in any order although it is preferred
that no Lewis acid is added before a suitable solvent has
been introduced in the reaction vessel. The reagents may
be contacted for any period of time but preferably a period
which may vary from 2 to lO hours. It is preferred to
continue the reaction for a period in excess of 6 hours.
It is preferred to react the reagents till a fair amount of
the phosphonitrile halides produced are oligomers with more
than 2 units. This can be observed easily as phospho-
nitrile halide dimers are not soluble in the solvents. If
the remaining reaction product contains dimers, it is
preferred that these dimers are separated and refluxed in a
solvent in order to be transformed into higher oligomers,
preferably in the presence of traces of ammonium halide.
Preferably the reaction conditions are adapted to provide a
high level of linear trimers and tetramers. The yield of
linear phosphonitrile halides versus cyclic phosphonitrile
halides can be increased by using a stoichiometric excess
of phosphorus halide, which is the preferred method. In
such preferred method from 0.1 to 1 mole, more preferably
0.3 to 0.6 mole of the selected Lewis acid is provided for
each mole of phosphorus pentahalide.
Representative chlorinated aliphatic or aromatic
hydrocarbons that are inert solvents and can be used in the
present invention include symmetric tetrachloroethane,
monochlorobenzene, o-dichlorobenzene and 1,2,4-trichloro-
benzene. The amount of chlorinated hydrocarbon used as
20S~
solvent seems not to be critical provided a sufficient
amount is used to dissolve at least a portion of the solid
reactants, i.e. phosphorus pentahalide and ammonium halide.
Of course the reaction rate improves substantially when a
significant portion of the solid reactants is in solution.
The use of large quantities of solvent, however, is not
recommended because of the necessity of subsequent removal
of the solvent from the reaction product. The manner of
recovering the desired modified phosphonitrile halide
polymeric composition is not critical. If any solid
material is present in the reaction mixture it may be
removed by any conventional method, e.g. hot filtration,
decantation, centrifugation etc. The volatile materials
e.g. the solvent, may be also removed by conventional
methods, e.g. distillation. A preferred method of
recovering the catalyst includes the removal of the
reaction solvent and the addition of a solvent in which
only the most preferred compounds are soluble, e.g.
dichloromethane. Other compounds can then be filtered off.
The catalyst according to the invention can be conveniently
stored in solvent, preferably under a blan~et of nitrogen.
The invention accordingly also includes catalyst composi-
tions which comprise a catalyst according to the invention.
The other parts of the composition may include a solvent, a
carrier, a support and some unreacted materials which were
used for making the catalyst. It is also possible that
some compounds according to formula (1) are present but
wherein the value of n is O or larger than 6. Preferably
the amount of such compounds is kept to a minimum.
Concentrations of the catalyst in such compositions may
range from 1 to 50~ by weight. Preferably from 5 to 20% as
this facilitates its use in polymerisation processes.
2~ Q~
The catalysts of the invention are useful for the
polymerisation of organosiloxanes. The invention
accordingly also provides the use of phosphonitrile halide
catalyst of formula (1), as defined above, in the process
of polymerising organosiloxanes. They are particularly
useful as condensation catalysts but are also suitable as
rearrangement catalysts. Thus they will be useful for a
process of making organopolysiloxanes having units of the
general formula Rlasio4 a (2) wherein Rl denotes a hydrogen
atom, a hydrocarbon group having from 1 to 18 carbon atoms,
a substituted hydrocarbon group having from 1 to 18 carbon
atoms or a hydrocarbonoxy group having up to 18 carbon
atoms and a has on average a value of from 1.8 to 2.2.
substituents may be alkyl, e.g. methyl, ethyl, propyl,
isobutyl, hexyl, dodecyl or octadecyl, alkenyl, e.g. vinyl,
allyl, butenyl, hexenyl or decenyl, alkynyl, e.g.
propargyl, aryl, e.g. phenyl, aralkyl, e.g. benzyl,
alkaryl, e.g. tolyl or xylyl, alkoxy, e.g. methoxy, ethoxy
or butoxy, aryloxy, e.g. phenoxy, substituted groups, e.g.
trifluoropropyl, chloropropyl or chlorophenyl. Preferably
at least 80~ of all Rl groups are alkyl or aryl groups,
more preferably methyl groups. Most preferably substan-
tially all Rl groups are alkyl or aryl groups, especially
methyl groups. The organopolysiloxanes are preferably
those in which the value of a is 2 for practically all
units, except for the endblocking units, and the siloxanes
are substantially linear polymers of the general formula
R2[R'2S io ] ps iR'2R2 (3)
wherein Rl is as defined above, R2 is a group Rl or a
hydroxyl group and ~ is an integer. It is, however, also
possible that small amounts of units wherein the value of a
denotes 0 or 1 are present. Polymers with such units in
20~Q~3~
-- 10 --
the chain would have a small amount of branching present.Preferably R2 denotes a hydroxyl group or an alkyl or aryl
group, e.g methyl or phenyl. The viscosity or the organo-
polysiloxanes which may be produced by the process using acatalyst according to the present invention may be in the
range of from 1000 to many millions mm2/s, depending on the
reaction conditions and raw materials used in the method of
the invention. Suitable organosiloxanes for use as
reagents in a polymerisation process in which the catalysts
of the invention are used include polydiorganosiloxanes
having terminal hydroxydiorganosiloxane units, e.g.
hydroxyldimethyl siloxane endblocked polydimethylsiloxanes,
hydroxyldimethyl siloxane endblocked polydimethyl poly-
methylphenyl siloxane copolymers, triorganosiloxaneendblocked polydimethylsiloxanes, e.g. trimethylsiloxane
endblocked polydimethylsiloxanes and cyclic polydiorgano-
siloxanes, e.g. polydimethylcyclosiloxanes.
The catalysts of the invention may be used at a
concentration of from 1 to 500ppm by weight based on the
total weight of the organosiloxanes used as reagents in a
polymerisation process. Preferably from 5 to 150ppm by
weight are used, most preferably from 5 to 50ppm. The
amount of catalyst used in the method of the invention may
be reduced when the temperature at which the organosilicon
compounds and the catalyst are contacted is increased. The
method of the invention may conveniently be carried out at
room temperature. The temperature may also be as high as
250C. Preferably, however, the temperature range is from
20 to 150C, most preferably from 50 to 120C.
Catalysts according to the invention may be neutra-
lised at the end of the polymerisation reaction in order to
stabilise the reaction product, e.g. in respect of its
viscosity. The neutralisation may be done at any stage of
20~0~v
the polymerisation process, e.g. as soon as the desired
viscosity of the organopolysiloxanes is reached. Neutrali-
sation agents for the catalysts are alkaline materials,
preferably lightly alkaline materials. Examples of suit-
able neutralisation agents are diethylamine, propylamine,
ammonia and hexamethyldisilazane.
There now follow a number of examples which illus-
trate the invention and its usefulness. Parts and percent-
ages are by weight unless otherwise mentioned.
Example 1
2 parts of NH4Cl, 5 parts of PC15 and 1 part of AlC13were mixed together and stirred under a nitrogen blanket at
180~C for 3 hours in 1,1,2,2, tetrachloroethane as solvent.
A white solid was obtained which was soluble in dichloro-
methane but insoluble in diethyl ether. The reaction
product has the average formula
[PC13=N-PC12=N-PC13] [AlC14] -
Example 2
0.12 mole of PC15, 0.0~ mole of NH4Cl and 0.04 mole
of SbC15 were allowed to react together in 60ml of sym-
tetrachloroethane at its refluxing temperature of 147C for
3.5 hours. After the reaction the solution was filtered to
remove insoluble compounds followed by removal of the
solvent under reduced pressure. A bright yellow liquid was
obtained which slowly crystallised upon cooling. The
resulting catalyst was analysed by NMR (nuclear magnetic
resonance) spectroscopy. It was found to be a 50/50
mixture of [PC13=N-PC12=N-PC13] [SbC16] and
[PC13=N-(PC12=N)2-PC13] [SbC16] while no [PC16] anion was
observed.
Example 3
The preparation method of Example 2 was repeated
except that instead of SbC15 SbC13 was used. The resulting
2 0 ~
- 12 -
catalyst was a 50/50 mixture of
[PC13=N-PC12=N-pC13] [SbC14] and
[PC13=N-(PC12=N)2-PC13] [SbC14] -
Example 4
The procedure of Example 2 was followed except that
after 3 hours the compounds of the formula
[PC13=N-PC13] [SbC16] which were insoluble in dichloro-
methane were separated. A part (A) was retained and the
rest was refluxed in sym-tetrachloroethane to yield a pure
compound (B) of the formula
[PC13=N-(PC12=N)2-PC13] [SbC16] .
Example S
The procedure of Example 2 was followed except that
the reaction was continued for 8 hours. The resulting
catalyst mixture was 35% [PC13=N-PC12=N-PC13] [SbC16] and
[ 13 N (PC12=N)2-PC13] [SbC16] .
Example 6
When 150ppm of the catalyst of Example 1 were added
to 1500g of dimethylsilanol endblocked polydimethyl
siloxane having a viscosity of 1oomm2/s, and the mixture
stirred at a reduced pressure of 20 mbar for 15 minutes at
room temperature (18C), a very high viscosity polydi-
methylsiloxane was obtained.
Example 7
The catalysts of Examples 2 and 3 were used in the
polymerisation of hydroxyl endblocked polydimethylsiloxanes
and were compared with a prior art catalyst prepared by the
reaction of 0.4mole of PC15 and 2 mole of NH4Cl, resulting
in a mixture of 75% [PC13=N-PC12=N-PC13] [PC16] and 25%
[PC13=N-(PC12=N)2-PC13] [PC16~ . 3 batches of 1500g of
dimethylsilanol endblocked polydimethylsiloxane having a
viscosity at 25C of lOOmm2/s were dried under reduced
pressure for 10 minutes to remove all traces of water.
2 0 ~
- 13 -
12ppm of the catalyst of Example 2, 12ppm of the catalyst
of Example 3 and 24ppm of the prior art catalyst were added
respectively to the first, second and third batch of poly-
dimethylsiloxane under stirring. The first batch reached aviscosity of 200,000mm2/s after only 23 minutes, of which
the first 20 were an induction period. The second batch
had an induction period of 18 minutes and reached a visco-
sity of 200,000mm2/s after 21 minutes, while the third
batch had an induction period of 30 minutes and did not
reach a viscosity of 200,000mm2/s until after 35 minutes.
Example 8
This example shows the improved heat stability of
polymers which are prepared by using catalysts according to
the invention which are neutralised with amines. The
results are compared with stability of polymers prepared
with traditional polymerisation catalyst KOH neutralised
with CO2. 4 batches of polydimethylsiloxanes were
prepared. Batches 1 and 2 used 35ppm of the catalyst
prepared in Example 2 at room temperature whilst batches 3
and 4 used KOH as a catalyst. Batches 1 and 2 were
neutralised with diethylamine upon reaching a viscosity of
41000 and 14000mm2/s respectively. Batches 3 and 4 were
neutralised with CO2 after having reached a viscosity of
40800 and 14200mm2/s respectively. All batches were then
stored at 160C for a period of up to 122 hours and the
viscosity was measured. As can be seen in the Table below
the viscosity of Batches 1 and 2 was much more stable than
that of Batches 3 and 4.
2~1Qg~
TABLE
Viscosity in mm2/s
Time Batch 1 Batch 2Batch 3Batch 4
(hours)
0 41,000 14,00040,800 14,200
22 51,500 - 80,000 25,500
29.5 - - 99,000 30,700
51,500 - 300,000 73,500
- 20,000500,000 122,000
122 63,500
Example 9
40kg of dimethylsilanol endblocked polydimethyl
siloxane was mixed with 50ppm of the catalyst of Example 2
and the mixture was reacted at a temperature of 80C for 5
minutes, at which time 60ppm of diethylamine was added to
neutralise the catalyst. A viscosity of 300,000mm2/s was
obtained.
Example 10
Part A of Example 4 was tested as condensation
catalyst by mixing it in with dimethylsilanol endblocked
polydimethyl siloxane, but showed no catalytic activity
even when the mixture was heated.
Example 11
Part B of Example 4 and the catalyst of Example 5
were each mixed in with 40g of dimethylsilanol endblocked
polydimethyl siloxane at a concentration of 12ppm and the
mixture was reacted at 50C and a pressure of 20 mbar. The
reaction went faster with the Catalyst of Example 5,
showing that the presence of a compound of the formula
[PCl3=N-PCl2=N-PCl3] [SbC16] improves the catalytic
activity of the catalyst.
2 ~
- 15 -
Example 12
40g of octamethylcyclotetrasiloxane was loaded to a
flask together with 120ppm of the catalyst of Example 5.
After 4 hours of reaction at 140C at atmospheric pressure,
almost 50% of the cyclic siloxane was polymerised into
longer chain polydimethylsiloxanes, showing that the
catalyst of the invention is also an active rearrangement
catalyst.
