Note: Descriptions are shown in the official language in which they were submitted.
2044696
PROCESS FOR THE PRODUCTION OF
ORGANOSILICON COMPOUNDS
This invention relates to the production of organo-
siloxanes and relates in particular to a process for the
condensation of organosilicon compounds having silicon-
bonded hydroxyl groups.
The production of organosiloxane polymers by the
polymerisation or copolymerisation of relatively low mole-
cular weight organosiloxanes is a well known step in the
manufacture of commercial silicones. Generally the poly-
merisation or copolymerisation is carried out by contacting
cyclic organosiloxanes or low molecular weight siloxanols,
or mixtures thereof, with an acidic or a basic catalyst.
Many substances which may be employed as catalysts have
been described in the literature and include sulphuric
acid, hydrochloric acid, Lewis acids, sodium hydroxide,
potassium hydroxide, tetramethylammonium hydroxide, tetra-
butylphosphonium silanolate, amines and others. However,
although such catalysts are effective in producing the
desired increase in molecular weight of the starting
materials, they have the disadvantage of causing scission
and rearrangement of the siloxane bonds. As a result of
such rearrangement the product often contains a significant
proportion of low molecular weight siloxanes. For many
applications, for example in the fabrication of silicone
elastomers, it is necessary to remove such low molecular
weight materials by devolatilisation in order to obtain a
satisfactory product. Rearrangement of the siloxane bonds
is also undesirable when the polymer is to contain a
planned distribution of two or more types of organic subs-
tituents, for example in the production of a polydimethyl-
siloxane containing a proportion of organofunctional, e.g.
aminoalkyl, substituents.
2044696
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Catalysts for promoting =SioH + =SioH and
-SioH + SioR, R = organic, without siloxane bond cleavage
have been disclosed in G.B. 895 091 and 918 823 and include
for example tetramethylguanidine 2-ethylcaproate and
n-hexylamine 2-ethylcaproate. However, many of such
catalysts are liquids, or are not suitable for use at high
temperatures, or are not readily removable from the
product. There has, therefore, been a continuing search
for substances which would be effective as catalysts for
the production of condensation products of organosiloxanols
but which would not cause molecular rearrangement and the
consequent presence of significant amounts of low molecular
weight species in the product. In particular the desired
catalysts should preferably be suitable for use in hetero-
geneous systems and remain active during use, thereby
enabling their recovery and re-use in batch processes or
their application in a continuous process.
We have now found that carbonates and certain
carboxylates of rubidium and caesium have the ability to
catalyse the condensation of organosilicon compounds. We
have further found that said rubidium and caesium compounds
can advantageously be employed in the production of organo-
silicon polymers having a relatively low content of low
molecular weight species.
Accordingly, the present invention provides a process
for the production of organosiloxanes which comprises
contacting (A) at least one organosilicon compound having
in the molecule at least one silanol group and wherein the
silicon-bonded organic substituents are selected from mono-
valent hydrocabon groups having from 1 to 14 carbon atoms
and monovalent substituted hydrocarbon groups having from 1
to 10 carbon atoms, the said substituted hydrocarbon groups
being non-acidic in character, and (B) one or more
204~696
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compounds selected from rubidium carbonate, caesium
carbonate and carboxylates of rubidium and caesium of the
general formula Q.CO.OM, wherein M represents Rb or Cs and
Q represents an alkyl group having from 1 to 6 carbon atoms
or an alkenyl group having from 2 to 5 carbon atoms.
The process of this invention may be applied in the
production of condensation products of any type of organo-
silicon compound having at least one silanol, that is
-SioH, group in the molecule. Thus, the organosilicon
compound may be an organosilane, organosiloxane or a
silcarbane or mixtures of the same type or of different
types of such organosilicon compounds. The silicon-bonded
organic substituents in the organosilicon compound may be
monovalent hydrocarbon groups having from 1 to 14 inclusive
carbon atoms, for example alkyl, aryl, aralkyl, alkaryl or
alkenyl groups, or they may be monovalent substituted
hydrocarbon groups having up to 10 carbon atoms and which
are non-acidic in character, that is groups not containing
acidic substituents such as carboxyl, sulphate and
sulphonic. Examples of operative non-acidic groups are
amino-substituted alkyl and aryl groups, mercaptoalkyl
groups, haloalkyl groups, cyanoalkyl groups and hydroxy
alkyl groups. Specific examples of the organic substi
tuents which may be present in the organosilicon compounds
employed in the process of this invention are methyl,
ethyl, propyl, hexyl, dodecyl, tetradecyl, phenyl, xylyl,
tolyl, phenylethyl, vinyl, allyl, hexenyl, -RNH2,
-RNHCH2CH2NH2, -RSH, -RBr, -RCl and -ROH wherein R repre-
sents a divalent organic group, preferably having less than
8 carbon atoms for example alkylene e.g. -(CH2)3- and
CH CHCH CH -, arylene e.g. C6H4
-(C6H3.CH3)-. For the majority of commercial applications
at least 50% of the total organic substituents in (A) will
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be methyl groups,any remaining substituents being selected
from phenyl and vinyl groups.
Although applicable to any type of organosilicon
compound having at least one silanol group the process of
this invention is particularly useful for the production of
higher molecular weight organosiloxane polymers from lower
molecular weight hydroxylated species. For example, during
the production of organosiloxanes by the hydrolysis of the
corresponding organochlorosilanes there is obtained a
mixture of low molecular weight organosiloxanes having two
or more silanol groups per molecule. The process of this
invention may be employed to increase the molecular weight
of such organosiloxanes where the production of high
proportions of volatile siloxanes may be undesirable.
According to a preferred embodiment of this invention the
organosilicon compounds (A) are silanol-terminated polydi-
organosiloxanes, that is substantially linear organo-
siloxane polymers or oligomers having a hydroxyl group
attached to each terminal silicon atom. Such polydiorgano-
siloxanes include those which can be represented by the
average general formula
R' R'
HO - Si os i OH
R' R' n
wherein each R' represents the hereinabove defined organic
substituents and n is an integer, preferably from 1 to
about 100. As hereinbefore stated, commercially the R'
substituents are normally predominantly methyl,with any
remaining R' substituents being selected from vinyl and
phenyl.
If desired the condensation products may be end-
stopped with triorganosiloxy units. One method of
effecting such end-stopping comprises incorporating in the
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reaction mixture a triorganosilane, for example a
triorganoalkoxysilane, which is reactive with the
condensation product. Such a reaction may be effected
in the presence of a suitable catalyst, for example
- barium or strontium hydroxide as described in Canadian
Patent Application No. 2,009,276 of S.B. Rees and S.
Westall, published August 9, 1990. However, a more
preferred method of producing end-stopped
polydiorganosiloxanes employing the process of this
invention comprises employing as the organosilicon
compound (A) both (i) at lease one polydiorganosiloxane
- having a hydroxyl group attached to each terminal
silicon atom, and (ii) a polydiorganosiloxane terminated
with a hydroxyl group at one end and a triorganosiloxy
group at the other.
The catalyst substance (B) is a carbonate or
carboxylate of rubidium or caesium. In the general formula
of the carboxylates Q may be for example methyl, ethyl,
propyl, hexyl, vinyl or allyl. Specific examples of
catalyst (B) are rubidium carbonate, caesium carbonate,
rubidium acetate, caesium propionate, caesium butyrate and
rubidium acrylate. The particle size of the catalyst
substance is not critical. Generally, the smaller the
particles the greater is the catalytic surface available.
However, very fine particle size powders may be more
difficult to remove from the condensation product.
The process of this invention involves contacting the
organosilicon compound (A) with the catalyst (B) at a
temperature at which the desired rate of molecular weight
increase occurs. The temperatures employed may vary within
wide limits,for example from about 30~C to about 200~C.
Reaction at the lower temperatures is, however, normally
too slow for commercial purposes and the process is prefer-
ably carried out at temperatures within the range from
about 700C to 150~C. It is also preferred to accelerate
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the removal of water formed during the condensation reac-
tion by carrying out the process under reduced pressure,
that is, at a pressure less than normal atmospheric and
most preferably less than about 0.5 bar (0.5 x 105 Pa).
One method of carrying out the process is by means of a
batch procedure. For example, the catalyst may be
dispersed in the organosilicon compound and the mixture
raised to the required temperature. Alternatively, the
organosilicon compound may be preheated prior to the
addition of the catalyst. Advantageously the mixture is
agitated during the reaction period to maintain the
catalyst in suspension. Sufficient catalyst is employed to
achieve the desired rate of condensation having regard to
the nature and geometry of the processing equipment, tempe-
rature and other factors. From considerations of speed of
reaction and economy of operation we prefer to employ from
about 0.001 to about 5~ by weight of the catalyst based on
the weight of the organosilicon compound. Termination of
the condensation reaction, if desired, may be achieved for
example by lowering the temperature of the mixture, and/or
raising the reaction pressure to atmospheric and/or by
separation or neutralisation of the catalyst.
Because of their heterogeneous nature the catalysts
(B) are particularly adapted for use in processes involving
manufacture on a continuous, rather than a batch, basis.
Properly employed such so-called 'continuous processes'
avoid the delays and costs common to batch processing, for
example those involved in the charging and discharging of
the reaction vessel and separation of the catalyst material
from the product. Thus, for example, the process of this
invention may be advantageously employed for the continuous
production of higher molecular weight siloxane polymers
from lower molecular weight hydroxyl-containing species.
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When carrying out the process of this invention in a
continuous mode contact between the catalyst material and
the organosilicon compound may be achieved by passing the
organosilicon compound over or through a bed containing the
catalyst material. When employing viscous reactants or
products it may be necessary to adjust the porosity of the
bed by granulation of the catalyst or other means. We have
found that a particularly suitable form of bed for conti-
nuous operation can be obtained by depositing the catalyst
substance in or on a particulate solid material, for
example silica, which is substantially inert under the
process conditions and which has a particle size appro-
priate to the desired porosity of the bed.
The condensation products produced by the process of
this invention may be employed in any of the variety of
applications known for the corresponding products made by
prior art procedures. For example they may be used for
treating textiles to render them water repellent and impart
softness, as components of paper coating compositions, as
heat transfer liquids and in the production of adhesives
and sealing materials.
The following Examples illustrate the invention.
ExamPle 1
2g of rubidium carbonate Rb2CO3 was added to 100g of a
linear ~,~ silanol terminated polydimethylsiloxane having
an average molecular weight of 3,300 and silanol content of
1.1% by weight (as OH). The mixture was agitated and
heated to 100~C at a pressure of 100mm.Hg (13.3 kPa).
After two hours the mixture was cooled and filtered. The
filtrate was a siloxane polymer having an average molecular
weight of 53,800 and silanol content 0.064% by weight (as
OH). The non-volatile content of the product polymer
(measured by weight loss in a forced draught oven at 150~C
.
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for 3 hours on a lg sample) was 98.6% by weight. The
starting polymer had a corresponding non-volatile content
of 97.5% indicating that no additional volatile cyclo-
siloxanes were formed during the polymerisation process.
ExamPle 2
The procedure of Example 1 was followed but substi-
tuting caesium carbonate Cs2CO3.2H2O for the rubidium salt.
All other conditions were identical. The product polymer
had an average molecular weight of 96,300, a silanol
content of 0.03S% by weight (as OH) and a non-volatile
content of 98.5% by weight.
ExamPle 3
The procedure of Example 1 was repeated except that
rubidium acetate RbOCCH3 and cesium acetate CsOCCH3
O O
respectively were substituted for the rubidium carbonate.
The results were as follows:
Starting PolYmer Product Pol,ymer
SioH% SiOH% Non-Volatile
Mn w/w_ Mn w/w_ Content
RbOAc 3,300 1.1 10,330 0.32 98.2
CsOAc 3,300 1.1 26,030 0.13 98.3
Example 4
250ml of "Harshaw"* A1-0104T neutral alumina, 3mm
pellets were slurried overnight with a solution of 150g of
Cs2CO3 in 100ml of distilled water. The saturated pellets
were drained and oven-dried to constant weight. The
pellets had a calculated Cs2CO3 content of 25.6% by weight.
A 100 x 2.5cm ID glass column was packed along its
total length with the treated pellets and fixed vertically.
The column was wrapped with electrical heating tape and
heated to a temperature of 130~C. A product receiving
flask was fitted to the bottom of the column and the system
* Trademark
~044696
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was evacuated to 50mm Hg (6.67 kPa) pressure. A polydi-
methylsiloxane of average molecular weight 3,300 was heated
to 120 to 130~C and fed into the upper opening of the glass
column at a rate sufficient to allow the feed to trickle
over the packing without flooding. A countercurrent dry
nitrogen flow of 0.5 cu ft/hour was also employed to aid in
the removal of water formed by condensation. After one
pass through the column the viscosity of the polydimethyl-
siloxane had increased and the silanol content had fallen
as follows:
SampleTotal OH H2O SioHViscosity
ppm _ ~e_ EE__cS at 25~C
Feedstock15100 1181 13919 87.0
Product 6700 103 65971700.0
Gpc analysis of the polymer product showed no
evidence of siloxane bond rearrangement, e.g. the presence
of dimethyl cyclics.
Example 5
lg of caesium carbonate was added to 200g of a linear
methylvinylpolysiloxane fluid with terminal silanol
functionality _ _
CIH3
HO - SiO - H
CH=CH2 n -6 2
having a viscosity at 25~C of 54.7 cS (54.7 x 10 m /s)-
The mixture was heated to 100~C under a reduced pressure of
40mbar (4 x 103 Pa) with constant agitation. After 2 hours
the mixture was cooled. The cooled product had a viscosity
of 156,667 cS (157 x 10 3 m2/s) 25~C.
When the experiment was repeated using lg of caesium
acetate in place of the carbonate and identical reaction
conditions, the viscosity of the methylvinylsiloxane fluid
increased from 54.7 cS at 25~C to 24,343 cS (24.3 x 10
m /s).
