Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Process for producing aerogels or xerogels
Description
The present invention relates to a process for producing porous materials in
the form of
aerogels or xerogels, which comprises reaction of at least one polyfunctional
isocyanate
with an amine component comprising at least one polyfunctional substituted
aromatic
amine in the presence of a solvent and a catalyst, with the reaction being
carried out in
the absence of water.
The invention further relates to the aerogels and xerogels which can be
obtained in this
way and the use of the aerogels and xerogels as insulation material and in
vacuum
insulation panels.
Porous materials, for example polymer foams, having pores in the size range of
a few
microns or significantly below and a high porosity of at least 70% are
particularly good
thermal insulators on the basis of theoretical considerations.
Such porous materials having a small average pore diameter can be, for
example, in the
form of organic xerogels. In the literature, the term xerogel is not used
entirely uniformly.
In general, a xerogel is considered to be a porous material which has been
produced by a
sol-gel process, with the liquid phase having been removed from the gel by
drying below
the critical temperature and below the critical pressure of the liquid phase
("subcritical
conditions"). In contrast, the term aerogels generally refers to gels obtained
when the
removal of the liquid phase from the gel has been carried out under
supercritical
conditions.
In the sol-gel process, a sol based on a reactive organic gel precursor is
first produced
and the sol is then gelled by means of a crosslinking reaction to form a gel.
To obtain a
porous material, for example a xerogel, from the gel, the liquid has to be
removed. This
step will hereinafter be referred to as drying in the interests of simplicity.
WO-95/02009 discloses isocyanate-based xerogels which are particularly
suitable for
applications in the field of vacuum insulation. The publication also discloses
a sol-gel-
based process for producing the xerogels, in which known, inter alia aromatic,
polyisocyanates and an unreactive solvent are used. As further compounds
having active
hydrogen atoms, use is made of aliphatic or aromatic polyamines or polyols.
The
examples disclosed in the publication comprise ones in which a polyisocyanate
is reacted
with diaminodiethyltoluene. The xerogels disclosed generally have average pore
sizes in
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the region of 50 pm. In one example, mention is made of an average pore
diameter of
pm.
WO-2008/138978 discloses xerogels which comprise from 30 to 90% by weight of
at least
5 one polyfunctional isocyanate and from 10 to 70% by weight of at least
one polyfunctional
aromatic amine and have a volume average pore diameter of not more than 5
microns.
The unpublished EP-A 09178783.8 describes porous materials based on
polyfunctional
isocyanates and polyfunctional aromatic amines, where the amine component
comprises
10 polyfunctional substituted aromatic amines. The porous materials
described are produced
by reacting isocyanates with the desired amount of amine in a solvent which is
inert
toward the isocyanates. The formation of urea linkages occurs exclusively by
reaction of
the isocyanate groups with the amino groups used. The reaction proceeds
without
catalysis.
However, the materials properties, in particular the mechanical stability
and/or the
compressive strength and also the thermal conductivity, of the known porous
materials
based on polyurea are not satisfactory for all applications. In addition, the
formulations on
which the materials are based display shrinkage, with reduction of the
porosity and an
increase in the density, on drying. Furthermore, the gelling time, i.e. the
time required for
gelling of the starting compounds, is often too long. In addition, the average
pore size of
the known porous materials having a low density is often too high.
Particularly at
pressures above the vacuum range, e.g. in the range from 1 to 1000 mbar, a
smaller
average pore size is advantageous in terms of a favorable thermal
conductivity.
A particular problem associated with the formulations based on isocyanates and
amines
which are known from the prior art are mixing defects. Mixing defects occur as
a result of
the high reaction rate between isocyanates and amino groups, since the gelling
reaction
has already proceeded a long way before complete mixing. Mixing defects lead
to
aerogels or xerogels having heterogeneous and unsatisfactory materials
properties. A
concept for reducing the phenomenon of mixing defects is thus generally
desirable.
However, an excessively long gelling time, i.e. an excessively long time until
complete
gelling of the gel precursor has occurred, should be avoided.
It was therefore an object of the invention to avoid the abovementioned
disadvantages. In
particular, an aerogel or xerogel which does not have the abovementioned
disadvantages, or has them to a reduced extent, should be provided. The porous
materials in the form of aerogels or xerogels should, compared to the prior
art, have
improved thermal conductivity in vacuo. In addition, the aerogels and xerogels
should
have a low thermal conductivity even at pressures above the vacuum range, in
particular
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in a pressure range from about 1 mbar to about 100 mbar. This is desirable
since an
increase in pressure occurs over time in vacuum panels. A further object of
the present
invention was to provide a porous material having a low thermal conductivity
after
admission of air, i.e. in the region of 1000 mbar. Furthermore, the aerogel or
xerogel
should at the same time have a high porosity, a low density and a sufficiently
high
mechanical stability.
Finally, mixing defects and thus the heterogeneities in the structure and the
materials
properties of the porous materials formed in the reaction of the isocyanates
with the
amines should be avoided.
We have accordingly found the process of the invention and the aerogels and
xerogels
which can be obtained in this way.
The process of the invention for producing an aerogel or xerogel comprises
reacting the
following components (al) and (a2) in the absence of water and in the presence
of a
solvent and of at least one catalyst:
(al) at least one polyfunctional isocyanate,
(a2) at least one polyfunctional substituted aromatic amine (a2-s) having the
general
formula I
2 3
Q3 Q2'
Q Q'
R1
Qi Q1'
2
Q RQ
Q4 5 5' Q4'
(I),
where R1 and R2 can be identical or different and are each selected
independently from
among hydrogen and linear or branched alkyl groups having from 1 to 6 carbon
atoms
and all substituents 01 to Q5 and Q1' to Q5' are identical or different and
are each selected
independently from among hydrogen, a primary amino group and a linear or
branched
alkyl group having from Ito 12 carbon atoms, where the alkyl group can bear
further
functional groups, with the proviso that
- the compound having the general formula I comprises at least
two primary
amino groups, where at least one of Q1, Q3 and Q5 is a primary amino
group and at least one of Q1', Q3' and Q5' is a primary amino group, and
=
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_ Q2, Q4, Q2, and Q4' are selected so that the compound having
the general
formula I has at least one linear or branched alkyl group, which can bear
further functional groups, having from 1 to 12 carbon atoms in the a
position relative to at least one primary amino group bound to the
aromatic ring,
optionally at least one further polyfunctional aromatic amine (a2-u) which
differs from the
amines (a2-s) having the general formula I to form the aerogels or xerogels of
the
invention.
Preferred embodiments may be found in the claims and the description.
Combinations of
preferred embodiments do not go outside the scope of the present invention.
Preferred
embodiments of the components used are described below.
The polyfunctional isocyanates (al) will hereinafter be referred to
collectively as
component (al). Analogously, the polyfunctional amines (a2) will hereinafter
be referred
to collectively as component (a2). It will be obvious to a person skilled in
the art that the
monomer components mentioned are present in reacted form in the porous
material.
For the purposes of the present invention, the functionality of a compound is
the number
of reactive groups per molecule. In the case of the monomer component (al),
the
functionality is the number of isocyanate groups per molecule. In the case of
the amino
groups of the monomer component (a2), the functionality is the number of
reactive amino
groups per molecule. A polyfunctional compound has a functionality of at least
2.
If mixtures of compounds having different functionalities are used as
component (al) or
(a2), the functionality of the components is in each case given by the number
average of
the functionality of the individual compounds. A polyfunctional compound
comprises at
least two of the abovementioned functional groups per molecule.
According to the invention, the reaction proceeds in the absence of water. A
person
skilled in the art will be aware that traces of water in the solvent cannot be
completely
ruled out. Small amounts of water do not influence the present invention.
Accordingly, the
expression "absence of water" means that the total amount of water based on
the total
weight of the components (al) and (a2) and water is below 0.1% by weight, in
particular
from 0 to 0.09% by weight, particularly preferably from 0 to 0.08% by weight.
Component (al)
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In the process of the invention, at least one polyfunctional isocyanate is
reacted as
component (al).
In the process of the invention, the amount of component (al) used is
preferably from 20
5 to 80% by weight, in particular from 25 to 75% by weight, particularly
preferably from 35
to 68% by weight, in each case based on the total weight of the components
(al) and
(a2), which is 100% by weight.
Possible polyfunctional isocyanates are aromatic, aliphatic, cycloaliphatic
and/or
araliphatic isocyanates. Such polyfunctional isocyanates are known per se or
can be
prepared by methods known per se. The polyfunctional isocyanates can also be
used, in
particular, as mixtures, so that the component (al) in this case comprises
various
polyfunctional isocyanates. Polyfunctional isocyanates which are possible as
monomer
building blocks (al) have two (hereinafter referred to as diisocyanates) or
more than two
isocyanate groups per molecule of the monomer component.
Particularly suitable polyfunctional isocyanates are diphenylmethane 2,2`-,
2,4'- and/or
4,4'-diisocyanate (MDI), naphthylene 1,5-diisocyanate (NDI), tolylene 2,4-
and/or
2,6-diisocyanate (TDI), 3,3'-dimethylbiphenyl diisocyanate, 1,2-diphenylethane
diisocyanate and/or p-phenylene diisocyanate (PPDI), trimethylene,
tetramethylene,
pentamethylene, hexamethylene, heptamethylene and/or octamethylene
diisocyanate, 2¨
methylpentamethylene 1,5-diisocyanate, 2-ethylbutylene 1,4-diisocyanate,
pentamethylene 1,5-diisocyanate, butylene 1,4-diisocyanate, 1-isocyanato-3,3,5-
trimethy1-5-isocyanatomethylcyclohexane (isophorone diisocyanate, IPDI), 1,4-
and/or
1,3-bis(isocyanatomethyl)cyclohexane (HXDI), cyclohexane 1,4-diisocyanate,
1-methylcyclohexane 2,4- and/or 2,6-diisocyanate and dicyclohexylmethane 4,4'-
, 2,4'-
and/or 2,2'-diisocyanate.
As polyfunctional isocyanates (al), preference is given to aromatic
isocyanates.
Particularly preferred polyfunctional isocyanates of the component (al) are
the following
embodiments:
i) polyfunctional isocyanates based on tolylene diisocyanate (TDI), in
particular
2,4-TDI or 2,6-TDI or mixtures of 2,4- and 2,6-TDI;
polyfunctional isocyanates based on diphenylmethane diisocyanate (MDI), in
particular 2,2'-MDI or 2,4`-MDI or 4,4'-MDI or oligomeric MDI, also referred
to as
polyphenylpolymethylene isocyanate, or mixtures of two or three of the
abovementioned diphenylmethane diisocyanates or crude MDI which is obtained in
the production of MDI or mixtures of at least one oligomer of MDI and at least
one
of the abovementioned low molecular weight MDI derivatives;
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iii) mixtures of at least one aromatic isocyanate according to embodiment
i) and at
least one aromatic isocyanate according to embodiment ii).
Oligomeric diphenylmethane diisocyanate is particularly preferred as
polyfunctional
isocyanate. Oligomeric diphenylmethane diisocyanate (hereinafter referred to
as
oligomeric MDI) is an oligomeric condensation product or a mixture of a
plurality of
oligomeric condensation products and thus a derivative/derivatives of
diphenylmethane
diisocyanate (MDI). The polyfunctional isocyanates can preferably also be made
up of
mixtures of monomeric aromatic diisocyanates and oligomeric MDI.
Oligomeric MDI comprises one or more condensation products of MDI which have a
plurality of rings and a functionality of more than 2, in particular 3 or 4 or
5. Oligomeric
MDI is known and is frequently referred to as polyphenylpolymethylene
isocyanate or as
polymeric MDI. Oligomeric MDI is usually made up of a mixture of MDI-based
isocyanates having various functionalities. Oligomeric MDI is usually used in
admixture
with monomeric MDI.
The (average) functionality of an isocyanate comprising oligomeric MDI can
vary in the
range from about 2.2 to about 5, in particular from 2.4 to 3.5, in particular
from 2.5 to 3.
Such a mixture of MDI-based polyfunctional isocyanates having various
functionalities is,
in particular, crude MDI which is obtained in the production of MDI.
Polyfunctional isocyanates or mixtures of a plurality of polyfunctional
isocyanates based
on MDI are known and are marketed, for example, by BASF Polyurethanes GmbH
under
the name LupranatO.
The functionality of the component (al) is preferably at least two, in
particular at least 2.2
and particularly preferably at least 2.5. The functionality of the component
(al) is
preferably from 2.2 to 4 and particularly preferably from 2.5 to 3.
The content of isocyanate groups in the component (al) is preferably from 5 to
10 mmol/g, in particular from 6 to 9 mmol/g, particularly preferably from 7 to
8.5 mmol/g.
A person skilled in the art will know that the content of isocyanate groups in
mmol/g and
the equivalent weight in g/equivalent have a reciprocal relationship. The
content of
isocyanate groups in mmol/g can be derived from the content in % by weight in
accordance with ASTM D-5155-96 A.
In a preferred embodiment, the component (al) comprises at least one
polyfunctional
isocyanate selected from among diphenylmethane 4,4'-diisocyanate,
diphenylmethane
40. 2,4'-diisocyanate, diphenylmethane 2,2'-diisocyanate and oligomeric
diphenylmethane
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diisocyanate. In this preferred embodiment, the component (al) particularly
preferably
comprises oligomeric diphenylmethane diisocyanate and has a functionality of
at least
2.5.
The viscosity of the component (al) used can vary within a wide range. The
component
(al) preferably has a viscosity of from 100 to 3000 mPa.s, particularly
preferably from 200
to 2500 mPa.s.
Component (a2)
According to the invention, at least one polyfunctional substituted aromatic
amine (a2-s)
having the general formula I
3 2 '
Q3 Q2.
Q Q
R1
Qi Qv
R2
Q4
Q5 Q5' Q4'
(I),
where R1 and R2 can be identical or different and are each selected
independently from
among hydrogen and linear or branched alkyl groups having from 1 to 6 carbon
atoms
and all substituents Q1 to Q5 and Cr to Q5' are identical or different and are
each selected
independently from among hydrogen, a primary amino group and a linear or
branched
alkyl group having from 1 to 12 carbon atoms, where the alkyl group can bear
further
functional groups, with the proviso that
- the compound having the general formula I comprises at least
two primary
amino groups, where at least one of Q1, Q3 and Q5 is a primary amino
group and at least one of Q1', Q3' and Q5' is a primary amino group, and
_ Q2, Q4, Q2, and Q4' are selected so that the compound having
the general
formula I has at least one linear or branched alkyl group, which can
optionally bear further functional groups, having from 1 to 12 carbon
atoms in the a position relative to at least one primary amino group bound
to the aromatic ring, and
optionally at least one further polyfunctional aromatic amine (a2-u) which
differs from the
amines (a2-s) having the general formula I is/are reacted as component (a2).
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Component (a2) thus comprises polyfunctional aromatic amines, with the
polyfunctional
aromatic amines (a2-s) having the general formula I being a constituent.
For the purposes of the present invention, polyfunctional amines are amines
which have
at least two amino groups which are reactive toward isocyanates per molecule.
Here,
primary and secondary amino groups are reactive toward isocyanates, with the
reactivity
of primary amino groups generally being significantly higher than that of
secondary amino
groups.
The amount of component (a2) used is preferably from 20 to 80% by weight, in
particular
from 25 to 75% by weight, particularly preferably from 32 to 65% by weight, in
each case
based on the total weight of the components (al) and (a2), which is 100% by
weight.
According to the invention, R1 and R2 in the general formula I are identical
or different and
are each selected independently from among hydrogen, a primary amino group and
a
linear or branched alkyl group having from 1 to 6 carbon atoms. R, and R2 are
preferably
selected from among hydrogen and methyl. Particular preference is given to R,
= R2 = H.
Q2, Q4, Q2, and Q4' are preferably selected so that the substituted aromatic
amine (a2-s)
comprises at least two primary amino groups which each have one or two linear
or
branched alkyl groups having from 1 to 12 carbon atoms, which may bear further
functional groups, in the a position. If one or more of Q2, Q4, Q2, and Q4'
are selected so
that they correspond to linear or branched alkyl groups which have from 1 to
12 carbon
atoms and bear further functional groups, preference is given to amino groups
and/or
hydroxy groups and/or halogen atoms as such functional groups.
The alkyl groups as substituents Q in the general formula I are preferably
selected from
among methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl and tert-butyl.
The amines (a2-s) are preferably selected from the group consisting of
3,3',5,5'-tetraalky1-
4,4'-diaminodiphenylmethane, 3,3',5,5'-tetraalky1-2,2'-diaminodiphenylmethane
and
3,3',5,5'-tetraalky1-2,4'-diaminodiphenylmethane, where the alkyl groups in
the 3,3,5 and
5' positions can be identical or different and are each selected independently
from among
linear or branched alkyl groups which have from 1 to 12 carbon atoms and can
bear
further functional groups. The abovementioned alkyl groups are preferably
methyl, ethyl,
n-propyl, i-propyl, n-butyl, sec-butyl or t-butyl (in each case
unsubstituted).
In one embodiment, one, more than one or all hydrogen atoms of one or more
alkyl
groups of the substituents Q can have been replaced by halogen atoms, in
particular
chlorine. As an alternative, one, more than one or all hydrogen atoms of one
or more alkyl
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groups of the substituents Q can have been replaced by NH2 or OH. However, the
alkyl
groups in the general formula I are preferably made up of carbon and hydrogen.
In a particularly preferred embodiment, component (a2) comprises 3,3',5,5'-
tetraalky1-4,4'-
diaminodiphenylmethane, where the alkyl groups can be identical or different
and are
each selected independently from among linear or branched alkyl groups which
have
from 1 to 12 carbon atoms and can optionally bear functional groups. The
abovementioned alkyl groups are preferably selected from among untubstituted
alkyl
groups, in particular methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl
and tert-butyl,
particularly preferably methyl and ethyl. Very particular preference is given
to 3,3',5,5'-
tetraethyl-4,4'-diaminodiphenylmethane and/or 3,3',5,5'-tetramethy1-4,4'-
diaminodi-
phenylmethane.
The abovementioned polyfunctional amines of the type (a2-s) are known per se
to those
skilled in the art or can be prepared by known methods. One of the known
methods is the
reaction of aniline or derivatives of aniline with formaldehyde in the
presence of an acid
catalyst, in particular the reaction of 2,4- or 2,6-dialkylaniline.
The component (a2) can optionally also comprise further polyfunctional
aromatic amines
(a2-u) which differ from the amines of the structure (a2-s). The aromatic
amines (a2-u)
preferably have exclusively aromatically bound amino groups, but can also have
both
(cyclo)aliphatically and aromatically bound reactive amino groups.
Suitable polyfunctional aromatic amines (a2-u) are, in particular, isomers and
derivatives
of diaminodiphenylmethane. Isomers and derivatives of diaminodiphenylmethane
which
are preferred as constituents of component (a2) are, in particular, 4,4'-
diaminodiphenylmethane, 2,4'-diaminodiphenylmethane, 2,2'-
diaminodiphenylmethane
and oligomeric diaminodiphenylmethane.
Further suitable polyfunctional aromatic amines (a2-u) are, in particular,
isomers and
derivatives of toluenediamine. Isomers and derivatives of toluenediamine which
are
preferred as constituents of component (a2) are, in particular, toluene-2,4-
diamine and/or
toluene-2,6-diamine and diethyltoluenediamines, in particular 3,5-
diethyltoluene-2,4-
diamine and/or 3,5-diethyltoluene-2,6-diamine.
In a first, particularly preferred embodiment, component (a2) consists
exclusively of
polyfunctional aromatic amines of the type (a2-s). In a second preferred
embodiment,
component (a2) comprises polyfunctional aromatic amines of the types (a2-s)
and (a2-u).
In the latter, second preferred embodiment, the component (a2) preferably
comprises at
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least one polyfunctional aromatic amine (a2-u), of which at least one is
selected from
among isomers and derivatives of diaminodiphenylmethane (MDA).
In the second preferred embodiment, component (a2) correspondingly
particularly
5 preferably comprises at least one polyfunctional aromatic amine (a2-u)
selected from
among 4,4'-diaminodiphenylmethane, 2,4'-diaminodiphenylmethane, 2,2'-diamino-
diphenylmethane and oligomeric diaminodiphenylmethane.
Oligomeric diaminodiphenylmethane comprises one or more methylene-bridged
10 condensation products of aniline and formaldehyde having a plurality of
rings. Oligomeric
MDA comprises at least one oligomer, but in general a plurality of oligomers,
of MDA
having a functionality of more than 2, in particular 3 or 4 or 5. Oligomeric
MDA is known
or can be prepared by methods known per se. Oligomeric MDA is usually used in
the
form of mixtures with monomeric MDA.
The (average) functionality of a polyfunctional amine (a2-u) comprising
oligomeric MDA
can vary in the range from about 2.3 to about 5, in particular from 2.3 to 3.5
and in
particular from 2.3 to 3. One such mixture of MDA-based polyfunctional amines
having
differing functionalities is, in particular, crude MDA which is formed, in
particular, as
intermediate in the condensation of aniline with formaldehyde, usually
catalyzed by
hydrochloric acid, in the production of crude MDI.
In the abovementioned preferred second embodiment, particular preference is
given to
the component (a2) comprising oligomeric diaminodiphenylmethane as compound
(a2-u)
and having an overall functionality of at least 2.1.
The proportion of amines of type (a2-s) having the general formula I based on
the total
weight of all polyfunctional amines of the component (a2), which thus add up
to a total of
100% by weight, is preferably from 10 to 100% by weight, in particular from 30
to 100%
by weight, very particularly preferably from 50 to 100% by weight, in
particular from 80 to
100% by weight.
The proportion of polyfunctional aromatic amines (a2-u) which differ from the
amines of
type (a2-s) based on the total weight of all polyfunctional amines of the
component (a2) is
preferably from 0 to 90% by weight, in particular from 0 to 70% by weight,
particularly
preferably from 0 to 50% by weight, in particular from 0 to 20% by weight.
In the present invention, the calculated use ratio (equivalence ratio) n
NCO/namme can vary
over a wide range and in particular be from 1.01 to 5. The equivalence ratio
mentioned is
particularly preferably from 1.1 to 3, in particular from 1.1 to 2. An excess
of nNco over
=
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namine leads, in this embodiment, to lower shrinkage of the porous material,
in particular
xerogel, in the removal of the solvent and as a result of synergistic
interaction with the
catalyst to an improved network structure and to improved final properties of
the resulting
porous material.
In the present invention, the abovementioned components (al) and (a2) are
preferably
used in the following ratio, in each case based on the total weight of the
components (al)
and (a2), which is 100% by weight: from 20 to 80% by weight, in particular
from 25 to
75% by weight, particularly preferably from 35 to 68% by weight, of the
component (al),
from 20 to 80% by weight, in particular from 25 to 75% by weight, particularly
preferably
from 32 to 65% by weight, of the component (a2).
The components (al) and (a2) will hereinafter be referred to collectively as
organic gel
precursor (A).
Catalyst
The process of the invention is preferably carried out in the presence of at
least one
catalyst as component.
Possible catalysts are in principle all catalysts known to those skilled in
the art which
accelerate the trimerization of isocyanates (known as trimerization catalysts)
and/or the
reaction of isocyanates with aromatically bound amino groups (known as gelling
catalysts).
The corresponding catalysts are known per se and have different relative
activities in
respect of the abovementioned reactions. Depending on the relative activity,
they can
thus be assigned to one or more of the abovementioned types. Furthermore, it
will be
known to a person skilled in the art that reactions other than those mentioned
above can
also occur.
Corresponding catalysts can be characterized, inter alia, according to their
catalytic
activity, as is known, for example, from Polyurethane, 3rd edition, G. Oertel,
Hanser
Verlag, Munich, 1993, page 104-110.
Preferred catalysts have a significant activity in respect of trimerization.
This favorably
influences the homogeneity of the network structure, resulting in particularly
advantageous mechanical properties.
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12
The catalysts can be able to be incorporated as a monomer building block
(incorporatable
catalyst) or not be able to be incorporated, with preference being given to
catalysts which
cannot be incorporated.
The component is advantageously used in the smallest effective amount.
Preference is
given to employing amounts of from 0.01 to 5 parts by weight, in particular
from 0.1 to
3 parts by weight, particularly preferably from 0.2 to 2.5 parts by weight, of
the catalyst or
catalysts (referred to as component (a4) below) based on a total of 100 parts
by weight of
the components (al) and (a2).
Catalysts preferred as component (a4) are selected from the group consisting
of primary,
secondary and tertiary amines, triazine derivatives, organic metal compounds,
metal
chelates, quaternary ammonium salts, ammonium hydroxides and also alkali metal
and
alkaline earth metal hydroxides, alkoxides and carboxylates.
Suitable catalysts are in particular strong bases, for example quaternary
ammonium
hydroxides such as tetraalkylammonium hydroxides having from 1 to 4 carbon
atoms in
the alkyl radical and benzyltrimethylammonium hydroxide, alkali metal
hydroxides such
as potassium or sodium hydroxide and alkali metal alkoxides such as sodium
methoxide,
potassium and sodium ethoxide and potassium isopropoxide.
Further suitable catalysts are, in particular, alkali metal salts of
carboxylic acids, e.g.
potassium formate, sodium acetate, potassium acetate, potassium 2-
ethylhexanoate,
potassium adipate and sodium benzoate, alkali metal salts of long-chain fatty
acids
having from 10 to 20 carbon atoms and optionally lateral OH groups.
Further suitable catalysts are, in particular, N-hydroxyalkyl quaternary
ammonium
carboxylates, e.g. trimethylhydroxypropylammonium formate.
Organic metal compounds as, in particular, gelling catalysts are known per se
to those
skilled in the art and are likewise suitable as catalysts (a4). Organic tin
compounds such
as tin 2-ethylhexanoate and dibutyltin dilaurate are preferred as constituents
of
component (a4).
Tertiary amines are known per se to those skilled in the art as gelling
catalysts and as
trimerization catalysts. Tertiary amines are particularly preferred as
catalysts (a4).
Preferred tertiary amines are, in particular, N,N-dimethylbenzylamine, N,N'-
dimethyl-
piperazine, N,N-dimethylcyclohexylamine, N,N',N"-tris(dialkylaminoalkyl)-s-
hexahydro-
triazines, such as N,N',N"-tris(dimethylaminopropy1)-s-hexahydrotriazine,
tris(dimethylaminomethyl)phenol, bis(2-dimethylaminoethyl) ether, N,N,N,N,N-
CA 02816739 2013-05-02
13
pentamethyldiethylenetriamine, methylimidazole, dimethylbenzylamine, 1,6-diaza-
bicyclo[5.4.0]undec-7-ene, triethylamine, triethylenediamine (IUPAC: 1,4-diaza-
bicyclo[2.2.2]octane), dimethylaminoethanolamine, dimethylaminopropylamine,
N,N-dimethylaminoethoxyethanol, N,N,N-trimethylaminoethylethanolamine,
triethanolamine, diethanolamine, triisopropanolannine and diisopropanolamine.
Catalysts which are particularly preferred as component (a4) are selected from
the group
consisting of N,N-dimethylcyclohexylamine, bis(2-dimethylaminoethyl) ether,
N,N,N,N,N-
pentamethyldiethylenetriamine, methylimidazole, dimethylbenzylamine,
1,6-diazabicyclo[5.4.0]undec-7-ene, tris(dimethylaminopropy1)-s-
hexahydrotriazine,
triethylamine, tris(dimethylaminomethyl)phenol, triethylenediamine
(diazabicyclo[2.2.2]octane), dimethylaminoethanolamine,
dimethylaminopropylamine,
N,N-dimethylaminoethoxyethanol, N,N,N-trimethylaminoethylethanolamine,
triethanolamine, diethanolamine, triisopropanolamine, diisopropanolamine,
metal
acetylacetonates, ammonium ethylhexanoates and metal ethylhexanoates.
The use of the catalysts which are preferred for the purposes of the present
invention
leads to aerogels and xerogels having smaller average pore diameters and
improved
mechanical properties, in particular improved compressive strength. In
addition, the
gelling time is reduced by use of the catalysts (a4), i.e. the gelling
reaction is accelerated,
without other properties being adversely affected.
Solvent
According to the present invention, the reaction takes place in the presence
of a solvent.
For the purposes of the present invention, the term solvent comprises liquid
diluents, i.e.
both solvents in the narrower sense and also dispersion media. The mixture
can, in
particular, be a true solution, a colloidal solution or a dispersion, e.g. an
emulsion or
suspension. The mixture is preferably a true solution. The solvent is a
compound which is
liquid under the conditions of step (a), preferably an organic solvent.
The solvent can in principle be an organic compound or a mixture of a
plurality of
compounds, with the solvent being liquid under the temperature and pressure
conditions
under which the mixture is provided in step (a) (dissolution conditions for
short). The
composition of the solvent is selected so that it is able to dissolve or
disperse, preferably
dissolve, the organic gel precursor. Preferred solvents are those which are a
solvent for
the organic gel precursor (A), i.e. ones which dissolve the organic gel
precursor (A)
completely under the reaction conditions.
CA 02816739 2013-05-02
14
The reaction product of the reaction in the presence of the solvent is
initially a gel, i.e. a
viscoelastic chemical network which is swollen by the solvent. A solvent which
is a good
swelling agent for the network formed in step (b) generally leads to a network
having fine
pores and a small average pore diameter, while a solvent which is a poor
swelling agent
for the gel resulting from step (b) generally leads to a coarse-pored network
having a
large average pore diameter.
The choice of the solvent thus influences the desired pore size distribution
and the
desired porosity. The choice of the solvent is also generally made in such a
way that
precipitation or flocculation due to formation of a precipitated reaction
product does not
occur to a significant extent during or after step (b) of the process of the
invention.
When a suitable solvent is chosen, the proportion of precipitated reaction
product is
usually less than I Vo by weight, based on the total weight of the mixture.
The amount of
precipitated product formed in a particular solvent can be determined
gravimetrically by
filtering the reaction mixture through a suitable filter before the gelling
point.
Possible solvents are the solvents known from the prior art for isocyanate-
based
polymers. Preferred solvents are those which are a solvent for the components
(al) and
(a2), i.e. solvents which dissolve the constituents of the components (al) and
(a2)
virtually completely under the reaction conditions. The solvent is preferably
inert, i.e.
unreactive, toward component (al).
Possible solvents are, for example, ketones, aldehydes, alkyl alkanoates,
amides such as
formamide and N-methylpyrollidone, sulfoxides such as dimethyl sulfoxide,
aliphatic and
cycloaliphatic halogenated hydrocarbons, halogenated aromatic compounds and
fluorine-
containing ethers. Mixtures of two or more of the abovementioned compounds are
likewise possible.
Further possibilities as solvent are acetals, in particular diethoxymethane,
dimethoxymethane and 1,3-dioxolane.
Dialkyl ethers and cyclic ethers are likewise suitable as solvents. Preferred
dialkyl ethers
are, in particular, those having from 2 to 6 carbon atoms, in particular
methyl ethyl ether,
diethyl ether, methyl propyl ether, methyl isopropyl ether, propyl ethyl
ether, ethyl
isopropyl ether, dipropyl ether, propyl isopropyl ether, diisopropyl ether,
methyl butyl
ether, methyl isobutyl ether, methyl t-butyl ether, ethyl n-butyl ether, ethyl
isobutyl ether
and ethyl t-butyl ether. Preferred cyclic ethers are, in particular,
tetrahydrofuran, dioxane
and tetrahydropyran.
CA 02816739 2013-05-02
Aldehydes and/or ketones are preferred as solvents. Aldehydes or ketones
suitable as
solvents are, in particular, those corresponding to the general formula R2-
(C0)-R1, where
R1 and R2 are each hydrogen or an alkyl group having 1, 2, 3 or 4 carbon
atoms. Suitable
aldehydes or ketones are, in particular, acetaldehyde, propionaldehyde, n-
butyraldehyde,
5 isobutyraldehyde, 2-ethylbutyraldehyde, valeraldehyde, isopentaldehyde, 2-
methylpentaldehyde, 2-ethylhexaldehyde, acrolein, methacrolein,
crotonaldehyde,
furfural, acrolein dimer, methacrolein dimer, 1,2,3,6-tetrahydrobenzaldehyde,
6-methy1-3-
cyclohexenaldehyde, cyanoacetaldehyde, ethyl glyoxylate, benzaldehyde,
acetone,
methyl isobutyl ketone, diethyl ketone, methyl ethyl ketone, methyl isobutyl
ketone,
10 .. methyl n-butyl ketone, ethyl isopropyl ketone, 2-acetylfuran, 2-methoxy-
4-methylpentan-
2-one, cyclohexanone and acetophenone. The abovementioned aldehydes and
ketones
can also be used in the form of mixtures. Ketones and aldehydes having alkyl
groups
having up to 3 carbon atoms per substituent are particularly preferred as
solvents. Very
particular preference is given to ketones of the general formula R1(CO)R2,
where R1 and
15 R2 are selected independently from among alkyl groups having from 1 to 3
carbon atoms.
In a first preferred embodiment, the ketone is acetone. In a further preferred
embodiment,
at least one of the two substituents R1 and/or R2 comprises an alkyl group
having at least
2 carbon atoms, in particular methyl ethyl ketones. Use of the abovementioned
particularly preferred ketones in combination with the process of the
invention gives
aerogels and xerogels having a particularly small average pore diameter.
Without
applying restriction, it is presumed that the pore structure of the gel being
formed is
particularly fine-pored because of the greater affinity of the abovementioned
particularly
preferred ketones.
In many cases, particularly suitable solvents are obtained by using two or
more
completely miscible compounds selected from the abovementioned solvents in the
form
of a mixture.
To obtain a sufficiently stable gel which does not shrink too much during
drying in step (c)
in step (b), the proportion of the components (al) and (a2) based on the total
weight of
the components (al) and (a2) and the solvent, which is 100% by weight, must
generally
be not less than 5% by weight. The proportion of the components (al) and (a2)
based on
the total weight of the components (al) and (a2) and the solvent, which is
100% by
weight, is preferably at least 6% by weight, particularly preferably at least
8% by weight,
in particular at least 10% by weight.
On the other hand, the concentration of the components (al) and (a2) in the
mixture
provided must not be too high since otherwise no porous material having
favorable
properties is obtained. In general, the proportion of the components (al) and
(a2) based
on the total weight of the components (al) and (a2) and the solvent, which is
100% by
CA 02816739 2013-05-02
16
weight, is not more than 40% by weight. The proportion of the components (al)
and (a2)
based on the total weight of the components (al) and (a2) and the solvent,
which is 100%
by weight, is preferably not more than 35% by weight, particularly preferably
not more
than 25% by weight, in particular not more than 20% by weight.
The total proportion by weight of the components (al) and (a2) based on the
total weight
of the components (al) and (a2) and the solvent, which is 100% by weight, is
preferably
from 8 to 25% by weight, in particular from 10 to 20% by weight, particularly
preferably
from 12 to 18% by weight. Adherence to the amount of the starting materials in
the range
mentioned leads to aerogels and xerogels having a particularly advantageous
pore
structure, low thermal conductivity and low shrinking during drying.
Before the reaction, it is necessary to mix the components used, in particular
to mix them
homogeneously. The rate of mixing should be high relative to the rate of the
reaction in
order to avoid mixing defects. Appropriate mixing methods are known per se to
those
skilled in the art.
Preferred process for producing the aerogels and xerogels
In a preferred embodiment, the process of the invention comprises at least the
following
steps:
(a) provision of the components (al) and (a2) the catalyst, and the
solvent as
described above,
(b) reaction of the components (al) and (a2) in the presence of the solvent
and the
catalyst to form a gel and
(c) drying of the gel obtained in the preceding step.
Preferred embodiments of steps (a) to (c) will be described in detail below.
Step (a)
According to the invention, the components (al) and (a2) and the solvent are
provided in
step (a).
The components (al) and (a2) are preferably provided separately from one
another, each
in a suitable partial amount of the solvent. The separate provision makes it
possible for
the gelling reaction to be optimally monitored or controlled before and during
mixing.
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17
The mixture or mixtures provided in step (a) can also comprise customary
auxiliaries
known to those skilled in the art as further constituents. Mention may be made
by way of
example of surface-active substances, flame retardants, nucleating agents,
oxidation
stabilizers, lubricants and mold release agents, dyes and pigments,
stabilizers, e.g.
against hydrolysis, light, heat or discoloration, inorganic and/or organic
fillers, reinforcing
materials and biocides.
Further information regarding the abovementioned auxiliaries and additives may
be found
in the specialist literature, e.g. in Plastics Additive Handbook, 5th edition,
H. Zweifel, ed.
Hanser Publishers, Munich, 2001.
The catalyst can in principle be added to one of the two components before
mixing or to
the resulting mixture. The catalyst is preferably added to the solvent in the
presence of
the component (a2).
Step (b)
According to the invention, the reaction of the components (al) and (a2) takes
place in
the presence of the solvent to form a gel in step (b). To carry out the
reaction, a
homogeneous mixture of the components provided in step (a) firstly has to be
produced.
The mixing of the components provided in step (a) can be carried out in a
conventional
way. A stirrer or another mixing device is preferably used here in order to
achieve good
and rapid mixing. The time required for producing the homogeneous mixture
should be
short in relation to the time during which the gelling reaction leads to at
least partial
formation of a gel, in order to avoid mixing defects. The other mixing
conditions are
generally not critical; for example, mixing can be carried out at from 0 to
100 C and from
0.1 to 10 bar (absolute), in particular at, for example, room temperature and
atmospheric
pressure. After a homogeneous mixture has been produced, the mixing apparatus
is
preferably switched off.
The gelling reaction is a polyaddition reaction, in particular a polyaddition
of isocyanate
groups and amino groups.
For the purposes of the present invention, a gel is a crosslinked system based
on a
polymer which is present in contact with a liquid (known as Solvogel or
Lyogel, or with
water as liquid: aquagel or hydrogel). Here, the polymer phase forms a
continuous three-
dimensional network.
,
18
In step (b) of the process of the invention, the gel is usually formed by
allowing to rest, e.g.
by simply allowing the container, reaction vessel or reactor in which the
mixture is present
(hereinafter referred to as gelling apparatus) to stand. The mixture is
preferably no longer
stirred or mixed during gelling (gel formation) because this could hinder
formation of the gel.
It has been found to be advantageous to cover the mixture during gelling or to
close the
gelling apparatus.
Gelling is known per se to a person skilled in the art and is described, for
example, in
WO-2009/027310 on page 21, line 19 to page 23, line 13.
Step (c)
According to the invention, the gel obtained in the previous step is dried in
step (c).
Drying under supercritical conditions is in principle possible, preferably
after replacement of
the solvent by CO2 or other solvents suitable for the purposes of
supercritical drying. Such
drying is known per se to a person skilled in the art. Supercritical
conditions characterize a
temperature and a pressure at which the fluid phase to be removed is present
in the
supercritical state. In this way, shrinkage of the gel body on removal of the
solvent can be
reduced.
However, in view of the simple process conditions, preference is given to
drying the gels
obtained by conversion of the liquid comprised in the gel into the gaseous
state at a
temperature and a pressure below the critical temperature and the critical
pressure of the
liquid comprised in the gel.
The drying of the gel obtained is preferably carried out by converting the
solvent into the
gaseous state at a temperature and a pressure below the critical temperature
and the critical
pressure of the solvent. Accordingly, drying is preferably carried out by
removing the solvent
which was present in the reaction without prior replacement by a further
solvent.
Such methods are likewise known to those skilled in the art and are described
in
WO-2009/027310 on page 26, line 22 to page 28, line 36.
Properties of the aerogels and xerogels and use ,
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CA 02816739 2013-05-02
19
The present invention further provides the aerogels and xerogels which can be
obtained
by the process of the invention.
Xerogels are preferred as porous materials for the purposes of the present
invention, i.e.
the porous material which can be obtained according to the invention is
preferably a
xerogel.
For the purposes of the present invention, a xerogel is a porous material
which has a
porosity of at least 70% by volume and a volume average pore diameter of not
more than
50 microns and has been produced by a sol-gel process, with the liquid phase
having
been removed from the gel by drying below the critical temperature and below
the critical
pressure of the liquid phase ("subcritical conditions").
The average pore diameter is determined by means of mercury intrusion in
accordance
with DIN 66133 and for the purposes of the present invention is essentially a
volume
average. The mercury intrusion method in accordance with DIN 66133 is a
porosimetric
method and is carried out in a porosimeter. Here, mercury is pressed into a
sample of the
porous material. Small pores require a higher pressure in order to be filled
with the
mercury than do large pores, and a pore size distribution and the volume
average pore
diameter can be determined from the corresponding pressure volume graph.
The volume average pore diameter of the porous material is preferably not more
than
4 microns. The volume average pore diameter of the porous material is
particularly
preferably not more than 3 microns, very particularly preferably not more than
2 microns
and in particular not more than 1 microns.
Although a very small pore size combined with a high porosity is desirable
from the point
of view of a low thermal conductivity, from the point of view of production
and to obtain a
sufficiently mechanically stable aerogel or xerogel, there is a practical
lower limit to the
volume average pore diameter. In general, the volume average pore diameter is
at least
100 nm, preferably at least 150 nm. In many cases, the volume average pore
diameter is
at least 200 nm, in particular at least 300 nm.
The aerogel or xerogel which can be obtained according to the invention
preferably has a
porosity of at least 70% by volume, in particular from 70 to 99% by volume,
particularly
preferably at least 80% by volume, very particularly preferably at least 85%
by volume, in
particular from 85 to 95% by volume. The porosity in % by volume means that
the
specified proportion of the total volume of the aerogel or xerogel comprises
pores.
Although a very high porosity is usually desirable from the point of view of a
minimal
CA 02816739 2013-05-02
thermal conductivity, an upper limit is imposed on the porosity by the
mechanical
properties and the processability of the aerogel or xerogel.
The components (al) and (a2) are present in reactive (polymer) form in the
aerogel or
5 xerogel which can be obtained according to the invention. Owing to the
composition
according to the invention, the monomer building blocks (al) and (a2) are
predominantly
bound via urea linkages and/or via isocyanurate linkages in the porous
material, with the
isocyanurate groups being formed by trimerization of isocyanate groups of the
monomer
building blocks (al). If the porous material comprises further components,
further possible
10 linkages are, for example, urethane groups formed by reaction of
isocyanate groups with
alcohols or phenols.
The components (al) and (a2) are preferably linked to an extent of at least 50
mol% by
urea groups -NH-CO-NH- and/or via isocyanurate linkages in the porous
material. The
15 components (al) and (a2) are preferably linked to an extent of from 50
to 100 mol% by
urea groups and/or via isocyanurate linkages in the porous material, in
particular from 60
to 100 mol%, very particularly preferably from 70 to 100 mol%, in particular
from 80 to
100 mol%, for example from 90 to 100 mol%.
20 The balance to 100 mol% are present as further linkages, with such
further linkages being
known per se to a person skilled in the art from the field of isocyanate
polymers.
Examples which may be mentioned are ester, urea, biuret, allophanate,
carbodiimide,
isocyanurate, uretdione and/or urethane groups.
The determination of the mol% of the linkages of the monomer building blocks
in the
porous material is carried out by means of NMR spectroscopy (nuclear magnetic
resonance) in the solid or in the swollen state. Suitable methods of
determination are
known to those skilled in the art.
The density of the porous material which can be obtained according to the
invention is
usually from 20 to 600 g/I, preferably from 50 to 500 g/I and particularly
preferably from 70
to 200 g/I.
The process of the invention gives a coherent porous material and not only a
polymer
powder or particles. Here, the three-dimensional shape of the resulting porous
material is
determined by the shape of the gel which is in turn determined by the shape of
the gelling
apparatus. Thus, for example, a cylindrical gelling vessel usually gives an
approximately
cylindrical gel which can then be dried to give a porous material having a
cylindrical
shape. However, it is in principle also possible to produce a powder, for
example by
milling the porous material.
CA 02816739 2013-05-02
21
The aerogels and xerogels which can be obtained according to the invention
have a low
thermal conductivity, a high porosity and a low density combined with high
mechanical
stability. In addition, the porous materials have a small average pore size.
The
combination of the abovementioned properties allows the materials to be used
as
insulation material in the field of thermal insulation, in particular for
applications in the
vacuum sector where a very low thickness of vacuum panels is preferred, for
example in
refrigeration appliances or in buildings. Thus, the use in vacuum insulation
panels, in
particular as core material for vacuum insulation panels, is preferred. In
addition, use of
the aerogels and xerogels of the invention as insulation material is
preferred.
Furthermore, uses at pressures of from 1 to 100 mbar and in particular from 10
to
100 mbar are possible because of the low thermal conductivity of the aerogels
and
xerogels which can be obtained according to the invention. The property
profile of the
aerogels and xerogels which can be obtained according to the invention opens
up, in
particular, uses in which a long life of the vacuum panels is desired and in
which the
thermal conductivity remains low after many years even in the even of a
pressure
increase of about 2 mbar per year, for example at a pressure of 100 mbar. The
aerogels
and xerogels which can be obtained according to the invention have
advantageous
thermal properties and also advantageous materials properties such as simple
processability and high mechanical stability, for example low brittleness.
Examples
The density p of the porous gel in the unit g/ml was calculated according to
the formula p
= m / (er2)*h, where m is the mass of the porous gel, r is the radius (half
diameter) of the
porous gel and h is the height of the porous gel.
The porosity in the unit % by volume was calculated according to the formula P
= (V, / (V,
+ Vs)) * 100% by volume, where P is the porosity, V, is the specific volume of
the porous
gel in ml/g and is calculated according to V, = 1 / p. Vs is the specific
volume in ml/g of the
test specimen. The value 1 / Vs = 1.38 g/mlwas used as specific volume. This
value can
be determined by He pycnometry.
The average pore diameter was determined by means of mercury intrusion in
accordance
with DIN 66133 and is a volume average.
The lambda value was determined by the dynamic hot wire method. Here, a wire
which
simultaneously serves as heating element and temperature sensor is embedded in
the
sample. The wire is heated at a constant electric power. Further details of
this
CA 02816739 2013-05-02
22
measurement method may be found, for example, in H.-P. Ebert et al., High
Temp. - High
Press., 1993, 25, 391-402.
The following compounds were used:
Component al:
Oligomeric MDI (Lupranat M200) having an NCO content of 30.9 g per 100 g in
accordance with ASTM D-5155-96 A, a functionality in the region of three and a
viscosity
of 2100 mPa.s at 25 C in accordance with DIN 53018 (hereinafter "compound
M200").
Oligomeric MDI (LupranatO M20) having an NCO content of 31.5 g per 100 g in
accordance with ASTM D-5155-96 A, a functionality in the region of three and a
viscosity
of 210 mPa.s at 25 C in accordance with DIN 53018 (hereinafter "compound
M20").
Component a2:
3,3',5,5'-Tetraethyl-4,4'-diaminodiphenylmethane (hereinafter "MDEA")
3,3',5,5'-Tetramethy1-4,4'-diaminodiphenylmethane (hereinafter "M DMA")
4,4'-Diaminodiphenylmethane (hereinafter "MDA").
Catalysts:
Lupragen N600, N,N',N"-tris(dimethylaminopropyI)-s-hexahydrotriazine
(hereinafter
"compound N600")
Example 1
1.8 g of the compound M200 were dissolved while stirring at 20 C in 10.5 g of
acetone in
a glass beaker. 1.6 g of MDEA (a2-1) and 0.1 g of compound N600 were dissolved
in
11 g of acetone in a second glass beaker. The two solutions from step (a) were
mixed.
This gave a clear, low-viscosity mixture. The mixture was allowed to stand at
room
temperature for 24 hours to effect curing. The gel was subsequently taken from
the glass
beaker and the liquid (acetone) was removed by drying at 20 C for 7 days.
The material obtained had a bimodal pore size distribution having pore
diameters in the
range from 0.4 pim to 2 m. The porosity was 83% by volume with a
corresponding
density of 185 g/I.
Example 2
CA 02816739 2013-05-02
23
1.8 g of the compound M200 were dissolved while stirring at 20 C in 10.5 g of
acetone in
a glass beaker. 1.6 g of MDEA (a2-1) and 0.2 g of compound N600 were dissolved
in
10.8 g of acetone in a second glass beaker. The two solutions from step (a)
were mixed.
This gave a clear, low-viscosity mixture. The mixture was allowed to stand at
room
temperature for 24 hours to effect curing. The gel was subsequently taken from
the glass
beaker and the liquid (acetone) was removed by drying at 20 C for 7 days.
The material obtained had a bimodal pore size distribution having pore
diameters in the
range from 0.3 jm to 2 1.1m. The porosity was 83% by volume with a
corresponding
density of 190 WI.
Example C3:
1.6 g of the compound M200 were dissolved while stirring at 20 C in 10.5 g of
acetone in
a glass beaker. 1.6 g of MDEA were dissolved in 11 g of acetone in a second
glass
beaker. The two solutions from step (a) were mixed. This gave a clear, low-
viscosity
mixture. The mixture was allowed to stand at room temperature for 24 hours to
effect
curing. The gel was subsequently taken from the glass beaker and the liquid
(acetone)
was removed by drying at 20 C for 7 days.
The material obtained had an average pore diameter of 4 p.m. The porosity was
89% by
volume with a corresponding density of 135 gil.
Example C4:
1.9 g of the compound M200 were dissolved while stirring at 20 C in 10.5 g of
acetone in
a glass beaker. 1.3 g of MDA were dissolved in 11 g of acetone in a second
glass beaker.
The two solutions from step (a) were mixed. This gave a clear, low-viscosity
mixture. The
mixture was allowed to stand at room temperature for 24 hours to effect
curing. The gel
was subsequently taken from the glass beaker and the liquid (acetone) was
removed by
drying at 20 C for 7 days.
The material obtained had an average pore diameter of 2.9 pim. The porosity
was 87% by
volume with a corresponding density of 170 g/I.
Example 5
1.8 g of the compound M20 were dissolved while stirring at 20 C in 12 g of
ethyl acetate
in a glass beaker. 1.6 g of MDMA (a2-2) and 0.1 g of compound N600 were
dissolved in
CA 02816739 2013-05-02
24
12.5 g of ethyl acetate in a second glass beaker. The two solutions from step
(a) were
mixed. This gave a clear, low-viscosity mixture. The mixture was allowed to
stand at room
temperature for 24 hours to effect curing. The gel monolith was subsequently
taken from
the glass beaker and dried in an autoclave by solvent extraction with
supercritical CO2
(described below).
Solvent extraction with supercritical CO2: the gel monolith was transferred to
an autoclave
having a capacity of 250 ml. The autoclave was filled with >99% acetone so
that the gel
monolith was completely covered by acetone and subsequently closed. The
monolith was
dried in a stream of CO2 for 24 hours. The pressure (in the drying system) was
in the
range from 115 to 120 bar; the temperature was 40 C. At the end, the pressure
in the
system was reduced in a controlled manner to atmospheric pressure over a
period of
about 45 minutes at a temperature of 40 C. The autoclave was opened and the
porous
material obtained was taken out.
The porous material obtained had a density of 136 The lambda value was
19.8 mW/m*K (pressure: 1 bar).
