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Description  |
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This invention relates to the making of a novel sucrose polyether polyol
having a high functionality and relatively low hydroxyl number. Such
polyols are useful in preparing polyurethanes, especially polyurethane
foams. The high functionality of the sucrose polyol enables the making of
rigid polyurethane foams with excellent dimensional stability,
particularly low temperature stability.
BACKGROUND OF THE INVENTION
There is a large amount of art relating to the production of sucrose
polyols. The process most commonly employed is described in U.S. Pat. No.
3,085,085 where sucrose is dissolved in water with an oxyalkylation
catalyst such as potassium hydroxide. Alkylene oxide is added over a
period of time until the reaction product is a liquid. At this stage the
water is removed. The remaining alkylene oxide is then added until the
desired polyether polyol is obtained. This method of making sucrose
polyols has been found to be satisfactory for many purposes. However, the
water present during the initial alkoxylation will react to some extent
with the alkylene oxide to form bifunctional by-products. Because of the
low equivalent weight of water, even small amounts of water reacting under
these conditions will severely reduce the functionality of the resulting
polyol. High functionality of sucrose polyols is required to enhance the
dimensional stability of rigid polyurethane foams made with such polyols.
Severe problems arise when water cannot be used as a solvent for high
melting sucrose. Normally, solid polyols such as sucrose undergo partial
decomposition as they melt and these solid compounds are insoluble in any
oxyalkylation-resistant solvents. Prior art in this regard is discussed
e.g. in U.S. Pat. Nos. 3,190,927 and 3,345,557. In these patents a
solution is given as to how to get sucrose into a form in which it can be
alkoxylated. An adduct of the high melting polyol with 1 to 4 mols of an
alkylene oxide is disclosed as a suitable solvent for the full
alkoxylation process. The disadvantage of this process is that it must be
carried out in two stages. A similar process is disclosed in U.S. Pat. No.
3,357,970.
In U.S. Pat. No. 3,442,888 the sucrose is mixed with a substantial amount
of glycerol and an alkali metal hydroxide catalyst. These polyols,
however, also suffer from the fact that glycerol, with a functionality of
only three, must be used in large amounts. The products are inevitably low
functional sucrose polyols.
In U.S. Pat. No. 3,640,997 sucrose is mixed with specific amounts of low
functional ethylene diamine and a specific amount of an alkali metal
hydroxide catalyst. The patent specifically discloses a lower limit of 0.6
mols of ethylene diamine which can be used per mol of sucrose. Less than
this amount creates solubility problems. The sucrose cannot completely
react and will precipitate out of the polyol. The use of at least 0.6 mols
of EDA/mol of sucrose places an upper limit on the functionality of the
polyol produced. The highest functional polyol in the examples of the
patent is 5.6.
In U.S. Pat. No. 3,865,806, sucrose and a tertiary amine catalyst are
directly alkoxylated with a blend of ethylene oxide and vicinal alkylene
oxide having 3 to 4 carbon atoms. The patent requires the blending of
alkylene oxides and produces a relatively inactive polyol although high
functionality polyols are produced.
In U.S. Pat. No. 3,941,769, sucrose is added to an inert aromatic
hydrocarbon solvent such as toluene. Specific amounts of a short chained
polyol, monoamine or polyamine, a small quantity of water, and a small
amount of alkali metal hydroxide catalyst are added to the suspension
followed by alkoxylation. High functional polyols can be produced by this
method i.e. with a functionality of 7 or more. However, polyols with a
functionality of more than about 6.5 can only be obtained at the expense
of cutting the alkoxylation short, i.e., stopping the alkoxylation before
the OH number is reduced below about 400. Each polyol produced in the
reference which has an OH number below 400 also has a functionality of
significantly less than 6.5. Example 4 shows a polyol with a functionality
of 7.18 but a hydroxyl number of 519 and a viscosity of 400,000 cP.
Polyols with viscosities in such a range cannot be easily handled by
conventional foaming equipment. The viscosity can only be lowered as the
alkoxylation proceeds and the OH number is lowered. The functionality of
the resulting polyol would be significantly reduced as the alkoxylation
continues because more and more water will react, forming difunctional
polyols.
The object of the present invention is to provide a process for making a
high functional, low hydroxyl number (and low viscosity), amine
co-initiated sucrose-based polyether polyol.
DESCRIPTION OF THE INVENTION
The present invention is directed to the use of polyalkylene polyamines as
both catalyst and co-initiator in the alkoxylation of sucrose.
Polyalkylene polyamines are mentioned in U.S. Pat. No. 3,941,769 as
possible co-initiators. However, the patent mentions low molecular weight,
high valent alcohols and amino alcohols as preferred compounds to be used.
The patent does not use a polyalkylene polyamine in any example. The
patent does not lead to the discovery, which is the subject of this
invention, that high functional, low viscosity/low OH number sucrose based
polyether polyols can be produced.
The present invention, therefore, relates to a novel sucrose-based
polyether polyol and its method of preparation wherein alkylene oxides are
reacted with a mixture containing:
(A) 100 parts by weight of sucrose;
(B) up to 1.3 parts by weight of water;
(C) 4-50 parts by weight of a polyalkylene polyamine containing at least
three nitrogen atoms and at least four active hydrogen atoms attached to
the nitrogen atoms;
(D) from about 50-110 parts by weight of an aromatic hydrocarbon solvent.
The polyalkylene polyamine acts as both a co-initiator with the sucrose and
as a catalyst for the alkoxylation reaction. The polyamine also imparts to
the resulting polyol the characteristic of being an "active" polyol, i.e.,
short foaming times are experienced in the polyurethane foam forming
reaction. This can enable the foaming time to be shortened (all other
formulation components being the same) or enable the foam producer to
reduce the amount of catalyst used as compared with what would otherwise
be required to obtain similar foaming times with less active polyols.
It is preferred that the polyamine contain at least 5 active hydrogen atoms
attached to nitrogen atoms.
Typical polyalkylene polyamines can be represented by the following general
formula
##STR1##
wherein m and n are the same or different and are integers of from 2-20,
preferably 2 or 3, and
p is an integer of from 1-10, preferably 1-2
R is H or C.sub.1 -C.sub.18 alkyl (at least four and preferably at least
five of the R groups being H), preferably H or C.sub.1 -C.sub.4 alkyl.
Other polyalkylene polyamines are suitable such as those containing a
piperazine ring. Examples of such polyamines include diethylene triamine,
triethylene tetraamine, tetraethylene pentamine, etc., dipropylene
triamine and 1,4-bis (aminopropyl) piperazine. Most preferred is
diethylene triamine. These polyamines may be used in amounts ranging from
4 to 50 parts by weight based on 100 parts of sucrose, preferably 5-20
parts by weight.
The present process can be carried out with up to about 1.3 parts by weight
of water based on 100 parts of sucrose. At least trace amounts of water
seem to be necessary for the alkoxylation reaction. The precise reason for
this is not known but it is possible that the water has a catalytic effect
in helping to open the alkylene oxide ring and thus speed the alkoxylation
reaction. Trace amounts of water are normally found in commercial grades
of the reactants of the present process, particularly in the sucrose which
will readily absorb moisture from the air. So trace amounts are desirable
and need not be removed. As an upper limit on the amount of water desired
in the sucrose mixture, it must be kept in mind that even small amounts of
water have a significant effect on lowering the final functionality of the
resulting polyol. Thus, large amounts and certainly amounts in excess of
1.3 parts by weight of water are undesirable.
Any aromatic hydrocarbon solvent which is inert under the reaction
conditions and has a boiling point in the range of from about 80.degree.
to 180.degree. C. may be used. Such solvents include toluene, xylene,
benzene, chlorobenzenes, ethyl benzene, etc. Toluene is preferred. These
solvents may also be mixed with aliphatic solvents with comparable boiling
points. There is essentially no upper limit to the amount of solvent which
can be used. However, practically it is advisable to minimize the amount
used since it eventually has to be removed from the final product.
Sufficient solvent should be used to provide a slurrying media for the
sucrose. Generally from 50-110 parts by weight of solvent per 100 parts
sucrose should be used.
Suitable alkylene oxides include any of those known in the art. These
include ethylene oxide, 1,2-propylene oxide, 1,2-butylene oxide and
2,3-butylene oxide and the like. Preferred, however, are ethylene oxide
and propylene oxide, and most preferably in the sequence discussed below.
The amount of oxide used depends on the desired length of the chains from
the sucrose i.e. the desired OH number. In general, OH numbers of greater
than 550, preferably 400 are not desired because of their larger
viscosities. In principle, because of the small amounts of water used,
there is no theoretical lower limit for the OH number. The functionality
of the polyol should not substantially decrease as the alkoxylation
proceeds. In general, it is desired to use alkylene oxide in amounts
sufficient to give OH numbers in the range of from 300-550, preferably
300-400 and viscosities at 25.degree. C. of from 15,000 to 40,000 mPa.s,
preferably 20-30,000 mPa.s.
The reaction may be carried out in the presence of an alkali metal
hydroxide as catalyst, preferably sodium or potassium hydroxide, most
preferably potassium hydroxide. This is particularly true of the later
stages of the reaction. The hydroxide is normally used in the form of an
approximately 50% aqueous solution. The amount of hydroxide used can vary
anywhere from 0.1-1.0 parts by weight per 100 parts by sucrose. Equivalent
amounts of other hydroxides would be used. The hydroxide must be
neutralized at the end of the reaction. The water added when the hydroxide
is added may be immediately distilled if it is felt that there is too much
water in the batch. The basic catalyst cannot be used at the beginning of
high functional, sucrose-based polyol reactions because hydroxide addition
to the slurry causes the sucrose to agglomerate into unstirrable and
unreactive clumps. The hydroxide is therefore only added after partial
alkylation preferably when all the sucrose has dissolved.
The most advantageous method of carrying out the reaction is to add the
water, if desired, and the solvent to the reactor at ambient temperature
and then add the sucrose at once with stirring. The mixture is then heated
to approximately 60.degree.-100.degree. C., preferably about 80.degree. so
that the polyalkylene polyamine will not cake when it is charged to the
sucrose slurry. The polyalkylene polyamine is then charged to the reactor.
A nitrogen pressure of anywhere from about 15 psig to 200 psig, preferably
25 to 140 psig, and most preferably about 2 atmospheres, is then built up
in the reactor.
The reaction of the alkylene oxide is done under typical conditions for
making polyether polyols, i.e. at a temperature of from about 70.degree.
C. to 160.degree. C., preferably 80.degree. C. to 120.degree. C.
A preferred embodiment of the invention is to add anywhere from about 5 to
15% of the alkylene oxides used as ethylene oxide at the beginning of the
alkoxylation. The alkoxylation is then completed with propylene oxide.
This initial ethylene oxide charge tends to preserve both the strength and
duration of the catalytic activity of the polyalkylene polyamine. This is
apparently due to the fact that the nitrogen atoms of the polyamine are
not severely hindered with ethylene oxide addition as they would be with
propylene oxide and other higher molecular weight oxides. Thus, it is best
to add at least as much ethylene oxide as is necessary to react with all
the active hydrogen atoms attached to the nitrogen atoms of the
polyalkylene polyamine prior to the use of other alkylene oxides.
While it is possible to avoid the use of alkali metal hydroxide catalysts
altogether, the reaction tends to slow at its later stages even with the
polyalkylene polyamines. However, the reaction is quite fast in the early
stages up to the time all the sucrose in the reaction vessel has
dissolved. All the sucrose tends to dissolve when from about 50-65% of the
total oxide has been added. At this point, there is no problem at all in
adding a hydroxide catalyst to the reaction batch. No clumping occurs once
the sucrose is completely dissolved. Therefore, it is another preferred
embodiment of the invention to add an alkali metal hydroxide to the batch
at this point in the reaction sequence in order to speed the reaction to
its completion at the desired OH number. As previously mentioned, the
batch can be dewatered at this point, if desired, to keep the water
content low.
When the alkylene oxide addition is complete the polymer is neutralized in
known manner, e.g. by dilute mineral acid addition. The remaining water
and hydrocarbon solvent are distilled off i.e. at higher temperatures,
under vacuum. The salts produced by the neutralization are removed by
filtration by known methods.
The polyalkylene polyamine catalyst/co-initiator provides a means for
catalyzing the alkoxylation reaction in its early stages. The
catalyst/co-initiator is highly functional. This means that more can be
added on a molar basis than lower functional co-initiators such as
triethanolamine and ethylene diamine to obtain the same final polyol
functionality. The higher amine content aids in the speed of the
alkoxylation reaction and also in enhancing the activity of the final
polyol.
The present invention, thus enables the making of a high functional,
moderate viscosity and hydroxyl number sucrose based polyether polyol. The
problems inherent with the use of sucrose are obviated, i.e. the fact that
it takes a large amount of co-initiator to get the sluggish reaction off
the ground, a sluggishness which cannot be obviated with the use of alkali
metal hydroxide catalyst because it causes clumping in the sucrose slurry.
The polyols produced by the above described process are useful as starting
components in the preparation of polyurethanes, particularly rigid
polyurethane foams which have good dimensional stability, particularly at
low temperatures.
The present polyols also have excellent activity when used as a polyol in a
polyurethane foaming reaction. When compared to foaming reactions with a
typical polyol and a given amount of catalyst, foaming reactions using the
polyols prepared by the present process exhibit significantly reduced
gellation and tack-free times.
Means for making rigid and other polyurethane foams from polyisocyanates,
polyether polyols, catalysts, water and/or other blowing agents e.g.
Freon, stabilizers and other additives are well known.
EXAMPLES
EXAMPLE 1
A polyether polyol was prepared using the following components (given in
parts by weight).
880 pts Toluene
135 pts Diethylene triamine
12 pts Water
1414 pts Sucrose
445 pts Ethylene oxide
2226 pts Propylene oxide
66 pts Potassium hydroxide (45% solution in water)
1780 pts Propylene oxide
The toluene solvent, water and sucrose were added to the reaction vessel
with vigorous stirring. This mixture was heated to about 80.degree. C. and
the reaction vessel then evacuated of air and replaced with a nitrogen
atmosphere. The diethylene triamine was then added to the reaction mixture
and a nitrogen pressure of 30 psig placed on the reactor. The reaction
mixture was heated to about 105.degree. C. and the ethylene oxide charge
begun. The oxide was added at a rate such that the batch temperature
remained in the 100.degree.-120.degree. C. range without significant
external heating or cooling. Following the ethylene oxide addition, the
initial propylene oxide charge was begun. Upon its completion, there was
no visible undissolved sucrose. At this point, the KOH was added followed
by an azeotropic distillation of water and toluene. The remaining
propylene oxide was then added under the same conditions mentioned above.
The product was treated with water in an amount of about 10% of the batch
weight. Sufficient aqueous sulfuric acid to neutralize the potassium
hydroxide was then added. The batch was then dewatered to about 1% water.
A filtering agent was then added and further dewatering down to 0.1%
water. The product was then filtered.
The product had the following properties:
OH functionality: 6.7
OH number: 361
Acid number: 0.09
Ph: 9.7
H.sub.2 O: 0.03%
Viscosity: 23,600 mPa.sec.
Color (Gardner): 12
% polypropylene glycol: 1.2%
EXAMPLE 2
The following formulations were hand mixed and allowed to freely foam.
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A B C D
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Polyol from Example 1
-- 100.0 -- 100.0
Polyol A.sup.1 100.0 -- -- --
Voranol 370.sup.2 -- -- 100.0
--
Water 1.0 1.0 1.0 --
DC - 193.sup.3 1.5 1.5 1.5 1.5
Dabco R - 8020.sup.4
1.5 1.5 1.5 2.0
R-11-B.sup.5 35.0 35.0 35.0 30.0
Density (kg/m.sup.3)
23.8 23.5 23.5 --
% closed cells 80.6 83.9 76.1 --
Dimensional Stability (% Vol. Change)
70.degree. C./100% R.H.
1 day 11.0 12.1 10.1 --
7 days 14.7 9.6 8.7 --
14 days 14.3 9.4 7.2 --
28 days 13.6 7.8 6.5 --
100.degree. C./Amb. R.H.
1 day 1.6 2.4 2.1 --
7 days 6.4 9.3 5.6 --
14 days 6.6 11.5 5.2 --
28 days 7.5 12.8 4.2 --
-30.degree. C./Amb. R.H.
1 day -0.6 0.2 -0.1 --
7 days -0.7 -0.2 -0.4 --
14 days -0.3 -0.4 -0.3 --
28 days -1.0 -1.1 0.0 --
Reactivity
Mix Time.sup.6 (Sec.) 10 10 10 --
Cream Time.sup.7 (Sec.)
35 20 25 27
Gel Time.sup.8 (Sec.) 150 75 125 61
Tack Free Time.sup.9 (Sec.)
215 100 175 72
Rise Time.sup.10 (Sec.)
310 140 220 --
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.sup.1 Polyol A is a sucrose-based polyether with a hydroxyl number of 380
available from Mobay Chemical Corp.
.sup.2 Voranol 370 is a high functional (>6.5) sucrose polyol, believed to
be prepared with triethyl amine co-initiator and a mixed EO/PO block
according to U.S. Pat. No. 3,865,806, having an OH number of about 350 and
available from Dow Chemical.
.sup.3 DC-193 is a polysiloxane surfactant foam Dow-Corning for use in
rigid foams.
.sup.4 Dabco R-8020 is an amine catalyst from Air Products Corp.
.sup.5 R-11-B is monofluorotrichloro methane blowing agent.
.sup.6 Mix Time: the duration of mixing after the isocyanate is added to
the resin blend.
.sup.7 Cream Time: the elapsed time from the start of mix time until the
time at which a change in color of the mixed liquid from brown to creamy
tan is noted.
.sup.8 Gel Time: the elapsed time from the start of mix time until the time
at which a 1/8" diameter applicator stick inserted 2" into the rising
foams, pulls with it a 6" long "string" when it is quickly removed from
the foam.
.sup.9 Tack Free Time: the elapsed time from the start of mix time until
the time at which a clean dry tongue depressor lightly touched to the foam
surface can be removed without pulling off the foam surface.
.sup.10 Rise Time: the elapsed time from the start of mix time until the
time at which no additional visible foam rise can be observed.
As can be seen from the comparisons, the gel, tack-free and rise times for
the foams produced with the polyol of the present invention are
significantly lower than those foams using a conventional sucrose-based
polyol and another high-functional sucrose polyol (Voranol 370).
Foam D was only tested for reactivity.
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