Note: Descriptions are shown in the official language in which they were submitted.
- 1 - RD-15,201
IONIC~LLY CROSS-hINKED 'SIL'OX'~E POLYMERS
_
''BA~KGROUND OF THE 'INVENTI'ON
This invention relates to ionically cross-
linked siloxane polymers. More particularly, this
invention relates to ionically cross-linked zwitterionic
siloxane polymers having ionic corss-links at trifunctional
silicone atoms and a method of their production.
Zwitterions are ions which are both positively
and negatively charged. Common zwitterionic species are
the amino sulfonates, NH2 -R-S03 and the amino carbonates,
NH2 -R-COO ; wherein R is a divalent hydrocarbon radical
more particularly defined below. Zwitterionic species are
typically obtained from ionizing amino acids and the like;
however, siloxane polymers containing zwitterions have
been prepared by Litt and Matsuda, J. Polymer Science,
VolO 19, p. 1221 (1975) and by Graiver et al, J.Poly. Sci.,
Polymer,Chem. Ed., Vol. 17, p. 3559 (1975).
Litt and Matsuda disclose a process for
producing zwittionic silanes by reacting the trifunctional
aminoalkyl silanes, ~-aminopropyltriethoxysilane and
N-aminoethyl- ~-amino-propyltrimethoxy silane, with
~-propane sultone.
Graiver et al disclose that siloxane polymers
containing zwitterions can be obtained by treating an
amlnoalkyl siloxane with ~-propane sultone. The
aminoalkyl siloxanes are provided by copolymeriæing
a dimethoxy silane having an aminoalkyl radical with a
low molecular weight hydroxy-terminated polydimethylsiloxane
. j .... .. -.
~ RD-1S,201
and decamethyl-tetrasiloxane.
The zwitterions on the siloxane polymers provide
ionic cross-linking be-tween the siloxane polymers due to
the coulombic forces exerted by the ions. An example of
an ionic cross-link which may exist between two siloxane
polymer segments is illustrated in the following formula:
Siloxane polymer backbone Siloxane polymer backbone
Sl-R -NH2 -R-S03
~ S03-R- NH2-R'-Si-
wherein Rl is a divalent hydrocarbon radical of
from 1 to 20 carbon atoms and R is a divalent hydrocarbon
radical of from 2 to 20 carbon atoms.
These cross-links reduce the mobility of the
polymer segments and increases their stiffness. For
example, polydimethylsiloxane (DP = 500) are typically
liquid at room temperature, yet corresponding zwitterionic
polysiloxanes are solid rubbers at this temperature.
Introducing zwitterions to as few as 0.5~ of the silicone
atoms within a siloxane fluid will provide a solid
elastomeric material.
These elastomeric materials exhibit high
adhesion to glass and other substrates such as, for
example, wood, metal, polycarbonates, polystyrene,
po]yphenylene oxides and blends thereof, etc. The
elastomeric properties and adhesive properties of these
zwitterionic silo~anes ma~e them suitable for use as
adhesives, elastomeric adhesives, sealants, coatings,
injection moldable and compression moldable rubbers and
plastics, and various silicone based rubbers.
In the present state of the art, only
difunctional silanes are utilized to obtain zwitterionic
siloxane polymers having a degree of polymerization
- 3 - RD-15,201
sufficiently high to provide the useful elastomeric materlals
described above. Difunctional zwitterionic siloxanes are
either copolymerized with dimethyl siloxane oligomers or
difunctional aminoalkyl silanes are copolymerized with
dimethyl siloxane oligomers and subsequen-tly reacted with
~ propanesultone to obtain the zwitterionic species on
the siloxane polymers. It is difficult to prepare the
difunctional zwitterionic silanes and the difunctional
aminoalkyl silanes, which makes the production of
zwitterionic siloxane polymers expensive. It is deslrable
to utilize less costly precursors in the production of
zwitterionic siloxane polymers.
Trifunctional aminoalkyl silanes are more
readily available and less expensive than their
difunctional counterparts. However, copolymerization of
such trifunctional aminoalkyl silanes with dimethyl
siloxane by conventional methods has been difficult, if
not impossible, to achieve. Typically the trifunctional
aminoalkyl silane polymerizes with itself to form a
yellow precipitate and does not become incorpcrated
within the siloxane polymer.
The present invention is based on the discovery
of an effective method for copolymerizing the less expensive
trifunctional aminoalkyl silanes or trifunctional
zwitterionic silanes with siloxane oligomers to provide
aminoalkyl siloxane polymer intermediates and zwitterionic
siloxane polymers, respectively. Only a small quanti-ty
of the trifunctional aminoalkyl silanes and trifunctional
zwitterionic silanes homo polymerize in this process,
which permits a greater proportion to be incorporated
within the copolymer produced.
SUMMARY OF THE I_VENTI~ON
This invention provides zwitterionic siloxane
polymers having at least about 0.5~ of the silicon atoms
chemically combined in accordance with the formula
- 4 - RD-15,201
R -Si(~)3
and aminoalkyl siloxane polymer intermedia-tes having at
least 0.5~ of the silicon atoms chemically combined in
accordance with the formula
R -Si(~)3
wherein Ra is an aminoalkyl radical, Rx is a radical
selected from the group consisting of aminoalkyl sulfona-tes
and aminoalkyl carbonates and ~ is a siloxane segmen-t
selected from the group consisting of siloxane radicals
or a link to the siloxane polymer chain.
Methods for producing these zwitterionic siloxane
polymers and aminoalkyl siloxane polymer intermediates are
also provided, wherein trifunctional silanes having amino-
alkyl radicals r or zwitterions are copolymerized with a
hydroxy-terminated siloxane oligomer in -the presence of a
catalytic quantity of acid and solvent~
O~JECT OF THE INVENTION
An object of the present invention is to provide
aminoalkyl siloxane polymer intermediates and zwitterionic
siloxane polymers by utilizing trifllnctional silanes.
Another object of the present invention is to
provide a method of incorporating a significant quantity
of trifunctional aminoalkyl silane or -trifunctional
zwitterionic silane into a siloxane polymer.
Another object of the present invention is to
provide zwitterionic siloxane rubbers which obtain their
ridigity ~rom both covalent and ionic cross-links.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
-
The zwitterionic siloxane polymers and amino-
alkyl siloxane polymer intermediates provided by this
invention have a siloxane polymer backbone. These siloxane
polymers typically have repeating units of a general
formula selected from the group consisting of
-(R2 SiO)m- and -(R"SiO2)m-
- 5 - RD-15,201
wherein R" is a monovalent radical selected from the
group consisting of hydrogen, alkyl radicals from 1 to
10 carbon atoms and aryl radicals 1 to 20 carbon atoms,
including alkylaryl radicals, and m is an integer from 1
to abou-t 2000. The zwitterions or aminoalkyl radicals
replace the monovalent radical R" on the silicone a-toms.
Examples of the siloxane polymer backbones where the
zwitterions and aminoalkyl radicals are absent include,
polydimethylsiloxane, polydimethyl-co-diphenylsiloxane,
poly(methyl phenyl siloxane), etc. At least about 0.5%
of the silicon atoms have the monovalent radical R"
replaced with a zwitterion in the zwitterionic siloxane
polymers of this invention. These silicone atoms are
chemically combined in accordance with the formula
RX-Si(~)3
wherein R is a zwitterion and ~ is either a siloxane
radical or a link to the siloxane polymer chain.
~dditional zwitterions may be bound to silicone atoms
having a different chemical structure than tha-t of
formula I.
In the aminoalkyl siloxane polymer intermediates
produced by this invention, at least about 0.5% of the
silicon atoms have the monovalent radical R" replaced with
an aminoalkyl radica]. These silicon atoms are chemically
combined in accordance with the formula
R -Si(~)3 II
wherein Ra is an aminoalkyl radical and ~ is as defined
above. The ~witterions, RX, that may appear on the
silicone atoms of formula I, are aminoalkyl sulfonates
and aminoalkyl carbonates. Suitable aminoalkyl sulfonates
and aminoalkyl carbonates/ are those of the formulas
R'-NH ~~ R SO ~ and -R'-NH2 -R-COO
respectively,
wherein R' is a divalent hydrocarbon radical of
from 1-20 carbon atoms and R is a divalent hydrocarbon
radical of from 2-20 carbon atoms. These divalent
- ~ - RD-15,201
hydrocarbon radicals include alkyl radicals, aromatic
radicals, alkylaryl radicals, and substituted derivatives
thereof. The preferred zwitterions are -the aminoalkyl
sulfonate radicals of the formula
-(R -TH )n~~ IH2
R3 R3 III
_
SO3 SO3
wherein Rl and R2 are selected from a group consisting of
diva]ent alkylene radicals of from l-lO carbon atoms and
divalent aromatic radicals of from 6-20 carbon atoms,
including alkylaryl radicals; R3 is selected from a group
consisting of divalent alkylene radicals of from 3 to ~
carbon atoms and divalent aromatic radicals of from 6-20
carbon atoms, including alkylaryl radicals; and n is an
integer in the range of 0 to 5.
The preferred aminoalkyl radicals that appear
on the aminoalkyl siloxane intermediates are of the
formula
-(Rl-NH)n-R -NH2 IV
wherein Rl, R2 and n are as previously defined.
The silicon atoms of formulas I and II are of
a tertiary structure, i.e., the silicon atom is bonded
to three siloxane segments. These siloxane segments, ~,
are either siloxane radicals or a link to the siloxane
polymer chain. The siloxane radicals are distinguished
from the siloxane polymer chain only by their length,
the siloxane radi~als being the shortest siloxane segment
bonded to the tertiary silicone atom. Where the two
shortest segments are of equal length, all of the siloxane
segments are considered a part of the siloxane polymer chain.
Both the siloxane radicals and the siloxane polymer chains
are of the formu].a
- 7 - RD 15,201
( 2 )m / V
wherein R" is a monovalenk radical select:ed from the group
consisting of alkyl radicals of from 1 to 10 carbon atoms
and aryl radicals of from 6 to 20 carbon atoms, including
alkyl aryl radicals; m is an integer of from 1 to about
2jO00 and R"' is selected from a group consisting of alkyl
radicals of from 1 to 10 carbon atoms, the hydroxy radical,
tertiary silicon atoms of the formulas
RX-Si-O- , and R -si-o-
and secondary silicon atoms of the formulas
RX-si-o- , and Ra-Si_o_
R" ~'
wherein RX, Ra, R" are as defined above and ~' is the
hydroxy and alkyl terminated siloxane polymer segments
defined by ~.
The preferred zwitterionic siloxane polymers
provided by this invention are those wherein the zwitterion,
R , is of the ~ormula -CH2-CH2-CH2-NH -CH2-CH2-NH2
,CH2 C, H2
C,H2 C,H2
C,H2_ C,H2_
SO3 SO3
and the siloxane radicals and the siloxane polymer chain
are of the formula CH3
R"'-(Si-O)m- VI
CH3
wherein R"' is limited to the methyl radical and the
tertiary silicon atoms of the formula defined above having
only the zwitterionic radical, RX, and m is an integer
having an avexage value between 30 and 200. The actual
values for m may range from about 1 to about 2000 in the
preferred zwitterionic siloxane polymers.
_ 8 - RD-15,201
The preferred aminoalkyl siloxane polymer
intermediates are those wherein Ra is of the formula
-CH2-CE12 -CH2 -NH-CH2-CH2-NH2
and the siloxane radicals and the siloxane polymer chain
are of the structure shown in formula VI with R"' heing
limited to the methyl radical and the tertary silicon atoms
of the formula defined above having only the aminoalkyl
radical, Ra, and m is an integer having an average value
between 30 and 200.
It is preferable to maintain the number of
zwitterions and aminoalkyl radicals bound to the silicon
atoms of the siloxane polymer backbones below about 10%.
Where the number exceeds this proportion, the zwitterionic
siloxane polymers produced become highly cross-linked and
excessively rigid. However, siloxane polymers having more
than 10% of their silicon atoms chemically bonded to
zwitterions or aminoalkyl radicals are within the scope
of this invention, providing the siloxane polymer has at
least about 0.5% of the silicon atoms of formula I or II.
The additional zwitterions or aminoalkyl radicals may be
bonded eithex to tertiary silicon atoms or secondary
silicon atoms of the formulas within the scope of R"'
defined above.
The zwitterionic siloxane polymers of this
invention typically exhibit a degree of polymerization up
to about 2000 with a molecular weight approaching 150/000.
The average degree of polymerization is approximately 1500
with an average molecular weight of about 105,000. The
zwitterionic siloxane polymers of this invention may be
produced by two different processes. The first process
co-polymerizes trifunctional zwit-terionic silanes with
hydroxy-endcapped silo~ane oligomers. The second process
utilizes the aminoalkyl siloxane polymer intermediates
of this invention which are obtained by co-polymerizing a
trifunctional aminoalkyl silane with a hydroxy-endcapped
~p
- 9 - RD-15,201
siloxane oligomer. The aminoalkyl siloxane polymer
intermediate is then treated with an oryanosultone of
the formula O
o
or an organolactone o the formula
o
g ¦ VIII
\O
wherein Z is a divalent hydrocarbon species selected from
the group consisting of alkalene radicals of from 3 to 4
carbon atoms and aryl radicals of from 6 to 20 carbon atoms,
including arylalkyl~radicals. Treatment of the aminoalkyl
siloxane precursor wit~ the organosultone or organolactone
provides the zwitterionic species.
The same gro~p of hydroxy endcapped siloxane
oligomers may be utilized in both syntheses. These
hydroxy-endcapped siloxane oligomers are typically of the
formula
H-(R"2si)m-H Ho-(R''sio2)m-H/H
wherein each R" is as defined above and m is an integer
of from 1 to about 2~00. Suitable hydroxy-endcapped
siloxane oligomers aIso include branched chained siloxane
oligomers that contain tertiary silicon atoms. Other
suitable siloxane oligomers are those which already
contain ~witterionic or aminoalkyl radicals. These
oligomers may be obtained from a process known to the
art or by the process provided by this invention. The
preferred hydroxy-endcapped siloxane oligomers are the
'` :,
_10 _ RD-15,201
dimethyl siloxanes having a degree of polymerization of
from 3 to about ~00. Other suitable si]oxane oligomers
include polydimethyldiphenyl s.iloxanes and poly(me-thyl
phenyl) siloxanes.
In the second process, where the zwitterionic
siloxane po~ymers are obtained by first producing -the
aminoalkyl siloxane polymer intermediates, a trifunctional
aminoalkyl silane is copolymerized with the hydroxy
terminated siloxane oligomer to obtain the intermediate.
Suitable trifuncti.onal aminoalkyl silanes are those of
the formula
Ra-Si(ORb)3
hwerein each Rb is independently selected from the group
consisting of alkyl radicals of from 1 to 20 carbon atoms
and aryl radicals of from 6 to 20 carbon atoms and Ra is
as defined above. The preferred trifunctional aminoalkyl
silanes are those wherein each Rb is a methyl radical.
The most preferred trifunctional aminoalkyl silanes
include N-aminoethyl~ ~-aminopropyl trimethoxysilane and
N-aminopropyl trimethoxysilane. Other suitable trifunctional
aminoal]syl silanes include
N-aminoethyl- ~-aminopropyl triethoxysilane,
N-aminoethyl-~ -aminobutyl-trimethoxysilane,
2-aminoethyl-trimethoxysilane,
2-aminoethyl-triethoxysilane,
3-aminopropyl-triethoxysilane,
3-aminopropyl-tributoxysilane, etc.
The trifunctional zwitterionic silanes utilized
in the first process for producin~ the z~itterionic siloxane
polymers of this in~ention are derived from the trifunctional
aminoalkyl silanes described above. These trifunctional
zwitterionic silanes can be described by the formula
R ~Si(ORb~3 V
wherein Rx and Rb are as defined above. As with the
trifunctional aminoalkyl silanes, the preferred
trifunc-tional zwitterionic silanes are those wherein
_ 11 _ RD-15,201
each Rb is a methyl radical. The most preferred
trifunctional zwitterionic silanes include N-(3-propane-
sulfonate)- ~-aminopropyl-trimethoxysilane and N-(N-(3-
propane sulfonate~aminoethyl) (3-propane-sulfonate)-~ -
aminopropyl trimethoxy silane.
It may be desirable to hydrolyze a portion of
the alkoxy or aryloxy groups on the silanes prior to
copolymerization in accordance with the process described
in Canadian Application Serial No. , filed
, Florence et al. Hydrolysis of all
the functional groups produces a highly relative species
which encourages polymerization within itself and may not
be desirable. However, hydrolysis of only a portion of
the functional groups will not inhibit the copolymerization
with the siloxane oligomers completely and permits the pro-
duction of zwitterionic siloxane polymers of a high
molecular weight.
To produce the zwitterionic siloxane polymers
of this invention the ratio of trifunctional silane to
siloxane oligomer must be sufficiently large to
incorporate zwitterions on at least 0.5 percent of the
silicone atoms within the polymers produced. Therefore,
the actual ratios are dependent on the size o~ the
siloxane oligomer or oligomers that are utilized. The
process described herein is also capable of producing
zwitterionic siloxane polymers and aminoal~yl siloxane
polymer intermediates, having less than .05 percent of
the silicone atoms of che formulas I and II, respectively.
The same steps and procedures are utilized when
copolymerizing the siloxane oligomers with the trifunctional
zwitterionic silanes and the trifunctional aminoalkyl
silanes. Copolymeriza~ion is accomplished by reacting a
mixture of the starting materials in the presence of an
acid catalyst at a temperature within the range oE about
25C to about 100C. It is preferable to let -the reac-tion
continue for about 0.5 to 5 hours.
- 12 - RD-15,201
The rate of reaction is dependent on temperature.
The magnitude of the reaction temperature is limited by
the degradation of the starting materials. The most
preferred reaction -temperature falls in the range of about
40C to abou-t 90C. Copolymerization takes place almost
immediately upon addi-ton of the acid catalyst. The
reaction approaches completeness within the preferred time
range. It may be desirable to place the reaction mixture
under a nitrogen a~mosphere to prevent oxidation of the
silanes. Alternatively, the reaction can be run under
vacuum or another inert atmosphere.
Suitable acid catalysts include the carboxylic
acids such as, acetic acid, formic acid, trifloroacetic
acid, steric acid, trichloroacetic acid, benzoic acid,
phenylacetic acid~ 2-chlorobutanoic acid, 3-chlorobutanoic
acid, dichloroacetic acid, 4-chlorobutanoic acid,
5 chlorobutanoic acid, etc. Other acids such as hydrogen
chloride, hydrogen bromide, hydrogen iodide, hydrogen
fluoride, perchloric, chloric, chlorous, hypochlorous,
p-toluene sulfonic, bromic, carbonic, phosphoric,
hypophosphorous, phosphorous, etc. are also suitable.
Quantities of acid sufficient to catalyze the
reaction typically fall within the range of about 0.1 to 2
weight percent. However, smaller quantities can be
expected to provide catalysis of -this reaction and are
deemed to be equivalent to those within the range defined
above. Larger ~uantities will also provide catalysts,
but do not provide any improvement in results.
Silanes other than trifunctional silanes, such
as the difunctional silanes, may be present in the reaction
medium. Introducing difunctional zwitterionic or amino-
alkyl silanes may be d~sired to increase the number of
ionic cross-links without increasing the branched chains
of the zwitterionic siloxane polymers produced. Although
these difunctional silanes compete for the siloxane
oligomers, they do not exclude the trifunctional zwitterionic
- 13 - RD-15,201
silanes or aminoalkyl silanes.
Upon copolymerization of the starting materials,
a chain stopper may be introduced into the reaction medium
to remove the hydroxy-endcaps. Any siloxane oligomer
having trialkyl substituted silicone atoms as end groups
may be utilized as a chain stopper. Examples of such
chain stoppers include~ hexamethyl disiloxane, octamethyl
trisiloxane, decamethyl tetrasiloxane, hexamethyl
disilizane, etc. The quantity of chain stopper preferably
provides a molar ratio of siloxane oligomer to chain
stopper of about 1000 to 1. Suitable molar ratiGs provide
values for the range of about 100 to 1500. However, -the
use of a chain stopper is unnecessary to produce either
the aminoalkyl siloxane polymers or the zwitterionic
siloxane polymers and may not be desired.
~hen copolymerization provides the aminoalkyl
siloxane polymer intermediate to obtain a zwitterionic
siloxane polymer, it is necessary to convert -the
aminoalkyl radicals to the corresponding zwitterion.
Typically an organic solvent is added to solublize the
aminoalkyl siloxane polymers. Suitable solvents include,
toluene, benzene, tetrahydrofuran, etc. The reaction
mixture is then dried to remove a substantial portion of
~ater along with any alcohol produced by the polymerization
reaction and allowed to cool to room temperature. An
organo-sultone or organo-lactone is added to the reaction
mixture while under a nitrogen atmosphere. Zwi-tterionic
species begin to form immediately. After a period of
about 10 to 20 hours, substantially all the aminoalkyl
radicals are converted to zwitterions. The organic solven-t
is then removed from the reaction mixture to allow -the
ionic cross-links to form and obtain the zwitterionic
siloxane rubber. Suitable organosultones and organo-
lactones utilized to produce the zwitterionic species
are those o~ formulas VII and VIII. The preferred
organosultone is ~-propane sultone and the preEerred
- 14 - RD-15~201
is ~ propiolactone. The preferred quantity of the
organosultone or organolactone utilized is about 1 molar
equivalent to the number of amino groups which appear
on the aminoalkylslloxane polymer intermediate.
The following examples are provided to illustrate
the process comprising this invention. I~hese examples are
not provided with the intent to limit the scope of this
invention -to their contents.
Example 1
To a 250 milliliter round bottom flask with
mechanical stirrer were added N-(2-aminoethyl)-3-amino-
propyl-trimethoxysilane (1.50 grams, 6.76 millimoles) and
a hydroxy-terminated polydimethyl siloxane fluid (50 grams;
MW about 15000; DP about 200) under a nitrogen atmosphere.
Acetic acid (10 drops) was added and the conten-ts of the
flask were heatecl to 55C with an external oil both.
After 1.5 hours the flask contained a milky white oil
of a much higher viscosity than the starting mixture.
Hexamethyldisilizane (1.5 grams) was added and stirring
continued at 55C for an additional 0.5 hours. Toluene
(450 grams) was added, the flask was equipped with a
distillation head and the oil bath temperature was raised
to 130C. Approximately 150 grams of distillate was
collected, the toluene served to remove any water or
methanol produced by the siloxane condensation reactions.
The remaining toluene solution was allowed to cool to 23C
and ~-propane sultone (3.0 grams, 13.5 millimoles) was
added in one portion as a solution in 60 grams of dry
toluene. The solution was stirred at 23C for 16 hours.
Removal of the toluene by heating in vacuo tllOC, 0-05
millimeters, 1.5 hours) produced a white, translucent,
elastomeric, siloxane rubber.
Examp'l'e'2
This example demonstrates a co-polymerization
process that is known to the art. To a 250 ml round
bottom flask with mecllanical stirrer were added ~-amino-
- 15 - ~D-15,201
ethylaminopropyltrimethoxysilane (6 parts), octamethyl-
tetrasiloxane (100 parts) and decamethyl-tetrasiloxane
(0.84 part). A powdered potassium hydroxide catalyst
(0.4 parts) was utilized instead of an acid catalyst
as utilized in Example 1. The mixture was stirred and
heated to 160 under a nitrogen atmosphere. At about
140C the mixture increased in viscosity and a copious
amount of white precipitate was observed. After 18 hours
at 160C, the mix-ture was cooled to ambient temperature,
diluted with toluene (150 par-ts), stirred for 1 hour, and
the solids removed by a vacuum filtration. A yellow oil
was obtained by concentrating the solution on a rotary
- evaporator and further drying under vacuum (0.1 torr,
75C, 2 hours). Analysis of the oil by infrared
spectroscopy indicated a low level of nitrogen incorporation
in the polyme~ (N-H stretch at 340 centimeters ).
Infrared analysis of the solid indicated that most of the
amine was within the precipitate.
Although the above examples have shown an
embodiment of the present invention, further modiEications
are possible by those skilled in the art without departing
from the scope and spirit of this invention.
