Note: Descriptions are shown in the official language in which they were submitted.
This invention relates to a method of producing homo- and co-polymers
of 1,3-dienes carrying reactive silyl groups.
It is known to use carbon blacks of various specifications as components
of rubber mixes. It is also known that the carbon black is added, not so much
for reducing the cost of vulcanized objects made of this mix, but rather to
increase the overall level of properties for technical applications, more
particularly tensile strength, modulus of elasticity. hardness and resistance
to tearing and abrasion. Thus carbon black is to be regarded as an active or
reinforcing filler.
For various reasons, however, there are limits to the use of carbon
black in rubber mixes. On the one hand, it allows only black mixes to be
obtained, not coloured or white mixes. On the other hand, good quality carbon
b]acks have become so expensive, as compared with inexpensive mineral fillers
such as silicic acid (SiO2), kaolin, aluminum hydroxide and glass, that
increasing efforts are being made to replace carbon black with so-called light
fillers, not least because this substitution reduces the proportion of components
derived from crude oil which is subject to supply crises. Furthermore, the use
of highly active silicic acids is very effective in optimizing specific proper-
ties, for example notched-impact strength.
Although light mineral fillers of this kind have already been used,
this has mainly been for reasons of cost and at the expense of valuable
operational properties, e.g. heat dissipation, elasticity and permanent
compression set. The same problems arise in filling and reinforcing other
polymeric materials with mineral fillers, for example polyolefins or unsaturated
polyester resins.
It is known that these disadvantages can be at least partly overcome
by the use of so-called bonding agents. Generally speaking, these are substances
having a certain affinity for both the polymer and the filler, preferably
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e~pressing itself as an ability to react chemically with both substrates.
The group of organo-functional silanes has become particularly well
kno-in as bonding agents. They are of the general formula R-SiX3, ~Jhere X is
usually an alkoxy group and less frequently a halogen atom, and the organic
residue R is an alkyl or aryl group substituted by a functional group. Although
these compounds give satisfactory results as regards the properties o polymer-
filler combinations produced with their help, they have certain disadvantages
in application. For instance, various silanes in vulcanizable rubber-filler
mixes may be used at bes~ only for a certain type of cross-linking technique.
L0 In the case of mercapto-silanes, moreover, there is an odour problem and a
tendency on the part of mixes in which it is used towards premature vulcanization
(scorching). Furthermore, as compared with conventional components of rubber
mixes, organo-functional silanes are extremely costly and generally possess far
from negligable toxicity when inhaled and upon contact with the skin.
Furthermore there has been no lack of attempts to synthesize bonding
agents of this kind, having a similar effect, on a polymer base. For instance,
it is ~nown that natural rubber and styrene-butadiene rubber (SBR) can be hydro-silylated by heating with trichlorosilane to about 300C (United States Patent
2,475,122). Ilowever, this reaction produces uncontrollable decomposition of therubber into liquid decomposition products, as a result of which the reactive silyl
groups introduced are not distributed as desired in the chains of the decomposi-tion products.
Photochemically produced hydrosilylating of a liquid polybutadiene
obtained by anionic polymerization is described in United States Patent
2,952,576 wllicll relatcs to glass fibres coa~ed with this material for reinforcing
unsaturated polyestcr resins. Althougll there is no mention of the micro-
structure of the liquid polybutadienc used, it is possible to conclude, from
information regarding thc production thercof from sodium suspension and by
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,~
.
~6~
comparison with information contained in the relevant literature, that it
contains about 60 to 70% of vinyl groups, about 30 to 20% of trans-vinylene
groups, and only about 10% of cis-vinylene groups.
Catalysis of the hydro-silylat;on of polybutadienes with platinum
compounds is described in German OLS 16 20 934 and 17 20 527 as an intermediate
stage in the production of foam-stabilizers and laminating resins, but the said
OLS contain no teaching of the use of the reaction products in rubber-filler
mixes. Furthermore, as above, both cases relate to products having a high
vinyl-group content, whereas the remaining double bonds consist mainly of trans-
vinyl groups. Even at relatively low molecular weights, polybutadienes having
a micro-structure of this kind are highly viscous at room temperature, which
makes them unusually difficult to handle, meter and mix. The hydro-silylated
derivatives thereof have the same limitations.
Conventional platinum catalysis of hydro-silylation is also described
in United States Patent 3,759,~69 in which polymers are claimed which have
molecular weights of between 500 and 50,000 and which contain at least 25% by
weight of the structure:
~ C~l2 - CH ~ ~"X
C112 - CH2 - Si--Y
Where pure polybutadiene is used as the base polymer, this corresponds
to the introduction of a reactive silyl group SiX3 at about each tenth monomer
group. All that can be gathered from the examples given in this prior pa~ent
is the hydro-silylating of a polybutadiene having an average molecular weight
of l,OOO and a vinyl group content of 90% of the total double bonds, with almost
100% saturation of all vinyl groups present. Mixtures of such products, and of
derivatives thereof obtained by subsequent reaction with low-molecular weight
polypropylene (molecular weight 5~000) or EPM rubber, are merely mentioned, with
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no information regarding their effectiveness. Furthermore, such very largely
saturated polybutadi0ne derivatives, and fillers containing them, are poorly
suited (solely by reason of their lack of double bonds) for bonding to a polymer
network resulting from sulphur or peroxide vulcanization.
German OLS 23 43 108 claims hydrosilylationofrubber polymers,
preferably containing at least 5 to 30% by weight of vinyl groups, and the use
thereof as a coupling agent in vulcanizing a vulcanizable rubber which contains
a pigment containing silicic acid. These are products which, because of their
high molecular weight, can be used only in solution.
In contrast to this, German AS 26 35 601 describes the use of hydro-
silylation products of special polybutadieneoils having molecular weights of
400 to 6,000 which, because of their micro-structure (10 to 60% of vinyl
groups, 1 to 15% of trans-vinylene groups and 25 to 85% of cis-vinylene groups),
have particularly low viscosity and are therefore easily handled undiluted.
However, hydro-silylation products have the disadvantage that the platinum
catalysts used in their production remain largely in the product and thus go
to waste;
Also known is the reaction of lithium-terminated "living polymers"
with an excess of a tetrahalo- or tetralkoxy-silane according to the process
described in United States Patent 3,244,664. This excess, which must be used
in order to avoid coupling and cross-linking reactions, is almost impossible
to separate and thus goes to waste during further processing.
Also known, from German OLS 30 10 113 are homo- or co-polymers of
1,3-dienes carrying reactive silyl groups, which contain 0.4 to 9% by weight
of combined silicon and which are obtained by reacting a metallated 1,3-diene
homo- or co-polymer having a molecular weight (Mn) of 400 to 8,000, with a
silicon compound of the general formula: 2
xl-si--Y
\ z
4-
,~
wherein xl signifies a halogen atom or an alkoxy group and x2 signifies a hydro-
lizable group, Y and Z may be the same as X2, but may also represent hy~rogen,
or an alkyl group with 1 to 8 carbon atoms, a cycloalkyl group with 5 to 12
carbon atoms, or an optionally substituted phenyl group, said reaction being
carried out at a temperature of O to 80C. The disadvantage of this is the
prior metallating of the low-molecular weight base polymer.
The addition of sulphydryl groups of a mercapto-silane, e.g. ~-mercapto-
propyltriethoxy-silane, to double bonds of an unsaturated polymer has been
described repeatedly (United States Patent 3,440,302~ German OLS 23 33 566 and
23 33 567), but it has the disadvantage of being a very expensive and evil-
smelling charging stock.
Also known are methods which, by using peroxide compounds (German OLS
21 52 295 and 21 52 286) and azo compounds rJ. Appl. Pol Sci 18. 3259 (1974)~
containing silyl groups as initiators, or disulphides containing silyl groups
(German OLS 21 42 596) as chain-transfer agents, lead to radical polymerization
into polymers with reactive silyl groups. Here again, the auxiliary agents used
to introduce the silyl groups are of difficult access~ extremely costly and
almost unobtainable commercially. Furthermore, at most only two reactive silyl
groups can be introduced in this way at the end of the polymer chain. Products
having a higher silicon content, which may be desired in order to produce
specific effects, e.g. increased automatic cross-linking~ cannot therefore be
produced in this way.
Although polyalkenamers containing silyl groups can be produced quite
easily by the use of silylolefins ~German Patent 21 57 405) and silylcycloolefins
~German AS 23 14 543) as regulators and (co-) monomers in the ring-opening
polymerization of cycloolefins, general use is limited here again by lack of
commercial availability of the reactants.
Finally, German OLS 30 03 893 and 30 28 839 disclose homo- or co-
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polymers of 1,3-dienes containing reactive silyl groups, which contain 0.4 to
12% by weight of combined silicon and are obtained by reacting slightly more or
less than 1% of their 1,3-diene homo- or co-polymer, contai~in~ aliphatic double
bonds in conjugation, having a molecular weight (Mn) of 400 to 6,000, with a
silicon compound of the general formula:
/x
R-Si \ Y
wherein R is an unsaturated aliphatic hydrocarbon residue with 2 to 20 carbon
atoms and X is a hydroly~able group, Y and Z may be the same as X independently
of each other, or represent hydrogen~ an alkyl group with l to 8 carbon atoms,
a cycloalkyl group with 5 to 12 carbon atoms, or an optionally substituted
phenyl group, the reaction being carried out at a temperature of 190 to 300C.
Now, it was the purpose of the present invention to develop a method
for producing homo- and co-polymers of 1,3-dienes of narrow molecular weight
distribution and containing silyl groups, which will make it possible to start
with easily accessible and inexpensive polymer materials which may be used in
their commercial forms immediately after polymerization, to avoid losing valuable
noble metals, to eliminate costly metallating, to use simplified processing
conditions, to vary the content of reactive silyl groups within wide limits,
and to obtain uniform distribution of silyl groups throughout the chains of the
base polymers.
Accordingly the invention provides a method for producing a homo- or
co-polymer of a 1,3-diene carrying reactive silyl groups, with 0.4 to 12% by
weight of combined silicon, which method comprises reacting a 1,3-diene homo-
or co-polymer having a molecular weight (Mn) of 400 to 8~000 with a silicon
compound of the general formula:
/x
H-Si~Y (I)
wherein X is a hydrolyzable residue, Y and Z may be the same as X independently
of each other, or may represent hydrogen, an alkyl group with 1 to 8 carbon atoms,
a cycloalkyl group with 5 to 12 carbon atoms, or an optionally substituted phenyl
group the reaction being carried out at a temperature of 150 to 300C under an
inert gas.
Thus initial reactants for the method according to the invention are
1,3-diene homo- and co-polymers with molecular weights (Mn) of 400 to 8,000
(measured with the assistance of gel-permeation chromatography) and silicon
compounds of the general formula I.
Within the scope of this invention, homo- and co-polymers of 1,3-dienes
are intended to include homopolymers of e.g. butadiene-(1,3), isoprene, 2,3-
dimethyl butadiene and piperylene, copolymers of these 1,3-dienes with each
other and copolymers of these 1,3-dienes with vinyl-substituted aromatic
compounds, for example styrene, ~-methylstyrene, vinyl toluene, and divinyl
ben~ene.
For the method according to the invention3 preference is given to
polybutadienes with molecular weights ~Mn) of 600 to 3,000. The micro-
structure of the dienes in the homo- and co-polymers, and in the reaction
productsJ is not critical. Commonly used are homo- and co-polymers with the
following distribution of double bonds:
0 to 60% of vinyl groups
1 to 50% of trans-vinyl groups
lO to 85% of cis-vinyl groups.
In addition to this, up to 40% of alicyclic structures may be
present. Furthermore, a part of the isolated double bonds may have been
converted, with the aid o an isomerizing catalyst, into conjugated double
bonds by a method known to the state o-f the art ~German OLS 29 24 548~ 29 24 577
and 29 24 598).
Products of this kind may be produced by many methods known to the
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state of the art (e.g. German Patent 11 86 631, German AS 12 12 302, German
Patent 12 92 853, ~erman OLS 23 61 782 and German OLS 23 42 885).
According to the invention, the reactive silyl groups arc introduced
by reaction of a silicon compound o~ the general formula I with a 1,3-diene
homo- or co-polymer. In formula I, X stands for a hydrolyzable residue, e.g.
halogen, preerably chlorin0 and bromine; alkoxy, preferably with up to 4
carbon atoms; aroxy, preferably with 6 to 12 carbon atoms; carboxylate, prefer-
ably with up to 8 carbon atoms; ketoximate, preferably with up to 6 carbon atoms
in the keto-group; or amide, preferably with up to 12 carbon atoms. Y and Z
may be the same as X, but may also be hydrogen, an alkyl group with 1 to 8
carbon atoms, a cycloalkyl group with 5 to 12 carbon atoms, or an optionally
substituted phenyl group.
Typical suitable silanes ara, for example: trichlorosilane,
trimethoxysilane, triethoxysilane, tripropoxysilane, tribromosilane, methyl-
dichlorosilane, methyldibromosilane, methyldiiodosilane, methylditnethoxysilane,
methyldiethoxysilane, methylmethoxychlorosilane, ethyldipropoxysilane, phenyl-
dibutoxysilane and methoxyethoxychlorosilane. Special preference is given to
the use of trichlorosilane.
Possible conversion of the halo-silyl groups, introduced with halide-
containing silanes, preferably chlorosilyl groups into other reactive silyl
groups may be carried out, for example, during processing, e.g. by the addition
preferably of alcohols, trialkylorthoformates, epoxides or sodium acetate, by
reactions known to the state of the art. However, this conversion may be
omitted if the liquid hydro-silylation product is applied, advantageously
directly, to a mineral filler, and if care is taken to eliminate the hydrogen
halide released during this reaction in the preferred case hydrogen chloride,
which in this case occurs dry and no~ as a solution in alcohol or alkyl chloride,
and may thus be re-use~.
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The addition reaction between the 1,3-diene homo- or co-polymer and
the silicon compound of general formula I is carried out by heating the reactants
to a temperature of 150 to 300C, preferably 200 to 280C, under an inert gas,
the amount of silane used being generally up to a ten-fold molar excess.
Dependent upon the reaction temperature used, reaction times are from 1 to 12
hours, preferably from 3 to 6 hours.
An elevated pressure is required for the addition only if the
vapour-pressure of the added silane amounts to greater than 1 bar at the reaction
temperature selected. The addition of silane to the 1,3-diene homo- or co-
polymer may also be carried out in the presence of an organic solvent.
The particularly low viscosity of the usable 1,3-diene homo- or co-
polymers facilitates not only the execution of the addi-tion reaction, since
this may thus be carried out generally without the addition of an otherwise
necessary solvent, but also the processing and handling of the addition products.
This not only renders the production method less costly, but also reduces
pollution, since no solvents are used which must subsequently be released into
the sewers or the atmosphere.
The processing of homo- and co-polymers of 1,3-dienes, carrying
reactive silyl groups, is carried out (if it is even necessary) by removing
unreacted silane in a vacuum.
The desired content of combined silicon~ namely from 0.~ to 12,
preferably from 1 to 5%, by weight, and the amount of silane added, and there-
fore -the average number of reactive silyl groups present in the addition
product, may be adjusted by the amount of silane employed, and is governed
mainly by the particular purpose for which the addition product is to be used.
For instance, an increase in the reactive silyl group content increases the
reactivity of the addition products and their tendency to form a network of
increased cross-linking density by polycondensation of the silanol groups
arising after hydrolysis. These
~,
_g_
properties may be valuable, for example in a series of applications of the
homo- and co-polymers of 1,3~dienes carrying reactive silyl groups according
to the invention, e.g. in connection with adhesives and insulating and sealing
compounds.
~ lowever, the addition compounds produced according to the invention
are used mainly as bonding agents in the production of mixtures of polymers,
preferably rubbers, mineral fillers and possibly other additives. In this
connection, they may be added either before the mixture is produced, in
substance or in solution, to the mineral filler, or they may be added to the
mixture as it is being produced.
The following are examples of particularly suitable mineral fillers:
silicic acids (SiO2) and silicates (such as kaolin, talcum, asbestos, mica,
glass fibres, glass balls, synthetic Ca-, Mg- and Al-silicates, Portland cement
and blast-furnace slag), aluminum hydroxide and oxides (hydrate) and iron
(hydr)oxide(s).
It is possible to use all conventional types of rubber which can be
vulcanized with peroxides or sulphur, for example natural rubber, synthetic
polyisoprene, polybutadiene, styrene-butadiene copolymers, poly-alkenamers
(such as polypentenamers, polyoctenamers or polydodecenamers), ethylene-
propylene copolymers (EPM), ethylene-propylene-diene-terpolymers (EPDM),
isobutylene-isoprene copolymers (butyl rubber) and butadiene-acrylonitrile
copolymers.
Moreover, other polymers may also be reinforced with mineral fillers,
for example polyethylene, polypropylene, polybutylene, polyvinyl-chloride,
ethylene-vinylacetate copolymers, polystyrene, if necessary with the addition
of radical formers, such as dicumyl-peroxide, with the aid of polymer bonding
agents produced by the method according to the invention.
It is also possible to graft homo- and co~polymers of 1,3-dienes,
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carrying silyl groups, to all of the above elastomers and thermoplastic polymers
by radical reaction. This imparts to the reaction products the ability to be
cross-linked by water, optionally with the addition of catalysts such as those
used in silanol condensation, for example di-n-butyl-tin-dilaurate and stannous
octoate.
Among the additives which may be added to mixtures of polymers, pre-
ferably rubbers~ mineral fillers and bonding agent according to the invention,
if necessary, are, in particular, vulcanizing agents and plasticizers.
The main vulcanizing agents to be considered are sulphur, in
combination with kno~n vulcanizing accelerators, with the addition of zinc
oxide and higher fatty acids such as stearic acid. Equally successful cross-
linking agents are peroxides or special sulphur donors such as N,N'-morpholine
disulphide or special thiurams.
Known refinery products may be mentioned as plasticizers, for example
oils with predominantly aromatic, naphthenic or paraffinic components. It is
to be understood that all known anti-aging agents may also be addecl.
The products obtained by the method according to the invention may
also be used as additives for improving the properties of adhesives, cements,
sealing and surfacing compounds, as means for dispersing pigments, for hydro-
phobing substrates such as paper, textiles, wood, cardboard and building
materials, and for soil-compaction.
Unless otherwise indicated, all percentages are by weight, even in
the following Examples which illustrate the present invention.
The ability to be cross-linked by water is determined in order to
check the incorporation of silicon, found by analysis, into polybutadiene oil.
To this end, 2.0 g of the product is dissolved in 40 ml of hexane, 1.0 ml of
a 5% solution of dibutyl-tin-dilaurate in hexane is added, and ~he solution is
poured onto water in a dish ~surface 600 cm2~. After standing for 24 hours
at room tempera~ure, a solid polymer film is formed, the portion thereof which
is insoluble in toluene at room temperature (25C) (the gel content) being
determined after dryillg.
_ample 1
225 g of polybu~adiene oil (Mn 1,500; viscosity at 20C 750 mPa s;
78% cis-1,4~, 21% trans-1,4- and 1% vinyl structure) were charged, in a counter-
flow of nitrogen, together with 75 g of SiHC13, into a 0.5 litre autoclave.
The autoclave was closed and the mixture was brought to a temperature of 235 C,
with stirring, and held for 7~ hours at that temperature. After heating, the
pressure in the autoclave rose to about 20 bar. The contents of the auto-
clave were then cooled, discharged under a protective gas (N2), and any
unreacted SiHC13 was removed over a period of 2 hours at 100C/l mbar.
The oil remaining after vacuum treatment contained 4.3% of silicon
(-- 82.8% of the addition). The viscosity had increased to 52,000 mPa s. The
cross-linking tes-t revealed 100% gel.
Examples 2 to 7.
The polybutadiene oil in Example 1 was again used. The polybutadiene
oil: SiHC13 ratio amounted to 2 : 1. Different times and temperatures were
selected from the addition reaction, as indicated in the following Table 1.
Table l
Example T t Si Reaction GelViscosity at 20 C
[ C] ~h] [%] [%][%] [mPa s]
_ _ _ I
2 200 1 2.1 30.8 88 2,200
3 225 3 2.0 29.0 88 2,100
4 225 5 3.3 47.8 100 3,700
225 7.5 3.7 53.5 100 4,500
6 240 0.5 2.0 29.0 95 11,000
7 240 1 5.6 81.0 94 25,000
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'7
The column "Reaction" was calculated from the ratio of used to added silane.
Example 8.
225 g of the polybutadiene oil of Examples 2 to 7 were reacted in
an autoclave for 5 hours at 250C with 75 g of SiH(OCH3)3. After the removal
of unreacted silane in vacuo under the conditions described in Example 1, there
remained an oil containing 0.6% of Si ~10.43% of the addition). The product
had a viscosity of 28,500 mPa s at 20C. The gel content after the cross-
linking test was 48%.
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