Note: Descriptions are shown in the official language in which they were submitted.
3 3 5 9 9 0
l LeA 25,762
A PROCESS FOR THE PRODUCTION OF POLYISOCYANATES
CONTAINING ISOCYANURATE GROUPS AND THEIR USE
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention is directed to a new
process for the production of polyisocyanates containing
isocyanurate groups by trimerizing a portion of the
isocyanate groups of hexamethylene diisocyanate
(referred to hereinafter as "HDI"), to the products
obtained by this process, and their use, optionally in
blocked form, as the isocyanate component in
polyisocyanate polyaddition products, preferably
polyurethane lacquers.
Description of the Prior Art
The use of quaternary ammonium hydroxides as
catalysts for the trimerization of isocyanate groups is
known and has been repeatedly described. Thus,
according to JP-PS 601,337 (US-PS 3,487,080), quaternary
ammonium hydroxides are used together with certain
co-catalysts. The examples primarily describe the
partial trimerization of aromatic diisocyanates.
However, the partial trimerization of HDI is described
in the examples.
The process according to EP-A 10,589 represents
a further development of the process according to the
Japanese patent specification cited above. According to
this prior publication, quaternary ammonium hydroxides
containing hydroxyalkyl substituents are used for the
trimerization of HDI. With these catalysts, HDI can be
trimerized in excellent fashion without cloudiness. The
disadvantage of this process is that the hydroxyalkyl
ammonium hydroxides are very difficult to produce in
colorless form and have to be used in relatively large
Mo3146 ~ foreign countries
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133~990
quantities of up to 0.6%. Accordingly, the end products
of the process, i.e. the isocyanurate polyisocyanates
freed from excess starting diisocyanate, may possibly
show a yellowish coloration.
EP-A 47,452 describes the production of mixed
trimers based on HDI and IPDI by a process wherein
starting diisocyanates which are not freed from carbon
dioxide are used, necessitating comparatively large
quantities of catalysts, as can be seen from the
10 examples.
Other known processes for the production of
isocyanurate polyisocyanates based on HDI are also
attended by serious disadvantages. Thus, GB-PS 920,080,
DE-OS 3,100,262, DE-OS 3,219,608 or DE-OS 3,240,613 for
15 example describe processes for the trimerization of HDI
using metal-containing catalysts and co-catalysts such
as phenols, alcohols or tertiary amines. The metal
compounds can only be removed from the end products by
very elaborate processes, if at all, and can signifi-
20 cantly affect subsequent applications and also thestability of the end products. In addition, the use of
co-catalysts containing active hydrogen atoms leads to
secondary reactions in which valuable isocyanate groups
are consumed. The same also applies to the process
25 according to EP-AS 155,559, wherein ammonium salts of
organic acids are used as catalysts in combination with
large amounts of alcoholic compounds.
In the processes according to EP-A 57,653,
EP-A 89,297 and EP-A 187,105, organosilicon catalysts
30 are used in comparatively large quantities. These
compounds also cannot be completely removed from the end
product and adversely affect its use.
Accordingly, an object of the present invention
is to provide a new process for the partial trimeriza-
35 tion of the isocyanate groups of HDI which combines thefollowing advantages:
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- The end products are substantially col~rless, i.e.,
have a color value (HAZEN) according to DIN 53,409
below 100.
- The end products are free from cloudiness and can be
dissolved without cloudiness in any of the standard
lacquer solvents.
- The end products contain no metal ions.
- The process can be carried out using minimal
quantities of catalysts without being dependent on
the use of large quantities of isocyanate-reactive
co-catalysts.
It has now surprisingly been found that this
object can be achieved according to the present
invention as described in detail hereinafter.
SUMMARY OF THE lNv~:NllON
The present invention is directed to a process
for the production of polyisocyanates containing
isocyanurate groups by trimerizing a portion of the
isocyanate groups of hexamethylene diisocyanate using
20 quaternary ammonium hydroxides as the trimerization
catalyst, terminating the trimerization reaction at the
desired degree of trimerization by adding a catalyst
poison and/or by thermally deactivating the catalyst and
removing unreacted hexamethylene diisocyanate to a
25 residual content of at most 0.2% by weight,
characterized in that
a) the hexamethylene diisocyanate used as starting
material is freed from carbon dioxide to a
residual content of less than 20 ppm (weight)
and
b) the catalyst is used in a quantity of less than
about 0.03~ by weight, based on the weight of
the hexamethylene diisocyanate used.
The present invention is also directed to the
35 polyisocyanates containing isocyanurate groups obtained
Mo3146 - 3 -
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by this process and to their use, optionally blocked by
blocking agents for isocyanate groups, as the isocyanate
component for the production of polyisocyanate
polyaddition products.
DETAILED DESCRIPTION OF THE INVENTION
The use of HDI which is substantially free from
carbon dioxide as the starting material is crucially
important to the present invention. The HDI used in
accordance with the invention has a carbon dioxide
10 content of less than 20 ppm (weight), preferably less
than 10 ppm (weight) and more preferably less than 5 ppm
(weight).
Technical HDI purified by distillation, which
has previously been used for the production of poly-
15 isocyanates containing isocyanurate groups, containsconsiderable quantities (approximately 20 ppm to 100 ppm
by weight) of carbon dioxide. Carbon dioxide can enter
the HDI during the production process, for example
during the phosgenation of carbonic acid salts of
20 hexamethylenediamine. It can be taken up from the air
during storage and can be formed by chemical reaction of
the NCO groups, for example by forming carbodiimide
groups or by reaction with moisture. HDI freshly
purified by vacuum distillation contains, for example,
25 40 ppm carbon dioxide after 24 hours in a sealed
container. HDI stored for a period of about 6 months
can contain up to 0.6~ by weight carbon dioxide if the
container is opened during the period of storage.
Carbon dioxide can be removed from HDI by
30 blowing ultra-pure nitrogen or a noble gas, for example
argon, for example at a temperature of about 0 to 70C,
through HDI. Although it is possible to apply a higher
temperature, this does not afford any significant
advantages. Carbon dioxide may also be removed by
35 distillation in a stream of nitrogen or noble gas. The
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method by which the carbon dioxide is removed is not
crucial to the process according to the invention.
However, substantially complete removal of carbon
dioxide is generally not possible merely by
distillation.
Quaternary ammonium hydroxides are used as
catalyst in the process according to the invention.
Basically, it is possible to use any quaternary ammonium
hydroxides of the type previously recommended as
trimerization catalysts for isocyanate groups. Suitable
quaternary ammonium hydroxides include those according
to US-PS 3,487,080 at column 2, lines 10 to 38 or
according to EP-A 10,589 at page 6, line 5 to page 8,
line 10 (U.S. Patent 4,324,879). Also suitable are
compounds corresponding to the formula
R~ OH
I
wherein _ ~ _
R is an alkyl radical containing 1 to 20, preferably 1
to 4 carbon atoms, an araliphatic hydrocarbon
radical containing 7 to 10, preferably 7 carbon
atoms or a saturated cycloaliphatic hydrocarbon
radical containing 4 to 10, preferably 5 to 6 carbon
atoms.
Preferred catalysts include compounds
corresponding to the formula
R
12 oHe
Rl-N-R3
R4
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wherein
Rl, R2 and R3 may be the same or different and represent
alkyl radicals containing 1 to 18 carbon atoms,
preferably 1 to 4 carbon atoms, more preferably
methyl groups and
R4 is a benzyl, 2-hydroxyethyl, 2-hydroxypropyl or
2-hydroxybutyl radical.
Particularly preferred catalysts include
N,N,N-trimethyl-N-benzylammonium hydroxide and
10 N,N,N-trimethyl-N-(2-hydroxypropyl)-ammonium hydroxide.
The quaternary ammonium hydroxides to be used
in accordance with the invention and their production
are known. They are commercially available either in
the form of colorless substances or solutions or as
15 already stated, only as brightly colored solutions.
This natural color of the catalysts is often a
disadvantage in the processes corresponding to the prior
art cited above for the production of isocyanurate
polyisocyanates based on HDI, because in these known
20 processes the catalysts have to be used in comparatively
large quantities. By contrast, in the process according
to the invention, the natural color of the catalysts is
not an important factor because the catalyst is only
used in extremely low concentrations.
In the process according to the invention, the
catalyst is used in a quantity of less than 0.03% by
weight, preferably in a quantity of less than O.OlZ by
weight and more preferably in a quantity of from 0.0005
to 0.005% by weight, based on the HDI used. The
30 particular optimal quantity of catalyst depends on the
type of quaternary ammonium compound used and may
readily be determined by a preliminary test. When
N,N,N-trimethyl-N-benzyl ammonium hydroxide is used, it
is sufficient to use particularly small quantities.
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In contrast to the process according to JP-PS
601,337, co-catalysts, especially isocyanate-reactive
co-catalysts, are not necessary and may be omitted in
the process according to the invention. In particular,
5 there is no need to use relatively large quantities of
compounds containing isocyanate-reactive groups such as
phenols, oximes and, in particular, methanol. Secondary
reactions between a portion of the isocyanate groups of
HDI and the isocyanate-reactive groups are avoided.
10 Valuable isocyanate groups are not consumed and the
formation of cloudiness attributable to these secondary
products may be prevented.
Accordingly, the trimerization process
according to the invention may also be carried out very
15 effectively when no urethane groups are formed during
the catalysis process. However, since many of the
catalysts used in the process according to the invention
are dissolved in solvents containing hydroxyl groups or
themselves carry hydroxy groups, the formation of
20 urethane groups in the process according to the
invention is not ruled out. It is particularly
preferred to use solvents which do not contain any
isocyanate-reactive groups for the catalysts. The
catalyst may also be used in solvent-free form.
When hydroxyl group-containing solvents are
used, it is preferred to use those which do not form
solid reaction products with HDI at room temperature and
which reduce the functionality of the end products as
little as possible. Hydroxyl group-containing solvents
30 such as these include 2-ethylhexane-1,3-diol and
2-ethylhexanol. Examples of suitable solvents with no
isocyanate-reactive groups include dimethylformamide,
dimethylacetamide, dimethylsulfoxide and acetonitrile.
Due to the extremely small quantities of
35 catalyst, dosing and incorporation of the pure,
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undiluted catalyst, although possible, is not easy,
particularly when the process is carried out
continuously on an industrial scale. Accordingly, it is
preferred to use heavily diluted catalyst solutions.
5 Concentrations below 5% by weight, preferably below 1%
by weight are particularly suitable. To prepare
catalyst solutions such as these, it is often advisable
to remove solvents present in the catalysts such as
methanol by mild distillation after the addition of a
10 suitable solvent of the type mentioned by way of the
example above.
The trimerization reaction is preferably
carried out in the absence of a solvent (apart from the
solvent for the catalyst), although this does not rule
15 out the use of standard lacquer solvents during the
trimerization reaction. Examples include esters such as
butyl acetate or ethoxyethylacetate; ketones such as
methylisobutylketone or methylethylketone; hydrocarbons
such as xylene; and mixtures of such solvents. However,
20 since unreacted HDI is removed after the trimerization
reaction, the use of such solvents during the
trimerization reaction results in unnecessary additional
expense.
To carry out the trimerization reaction, the
25 catalyst is added to HDI which has been substantially
freed from carbon dioxide. The catalyst may be added in
increments during the trimerization reaction. The
trimerization reaction is generally carried out at a
temperature of about 0 to 100C, preferably about 20 to
30 80C and is terminated at a degree of trimerization of
about 10 to 40Z, preferably about 20 to 30Z. By "degree
of trimerization" is meant the percentage of isocyanate
groups present in the starting diisocyanate which react
during the trimerization reaction.
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To terminate the trimerization reaction, a
suitable catalyst poison is generally added to the
reaction mixture. Suitable catalyst poisons include
inorganic acids such as hydrochloric acid, phosphorous
5 acid or phosphoric acid; sulfonic acids or derivatives
thereof such as methanesulfonic acid, p-toluenesulfonic
acid or p-toluenesulfonic acid methyl or ethyl ester;
and perfluorinated sulfonic acids such as
nonafluorobutanesulfonic acid. Particularly suitable
10 deactivators, i.e. catalyst poisons, include acidic
esters of phosphorous acid or phosphoric acid such as
dibutylphosphite, dibutylphosphate or
di-(2-ethylhexyl)-phosphate, which are preferably used
in the form of a dilute solution in HDI. The
15 deactivators are generally added to the reaction mixture
in a quantity at least equivalent to the catalyst.
However, since the catalysts can partly decompose during
the trimerization reaction, the addition of a
sub-equivalent quantity of the deactivator is often
20 sufficient. On the other hand, to guarantee safe
termination of the reaction, it is often also advisable
to use a larger than equivalent quantity, for example
twice the equivalent quantity of deactivator.
Accordingly, it is preferred to use deactivators
25 (catalyst poisons) in up to twice the equivalent
quantity, based on the quantity of catalyst used. When
thermally labile catalysts, for example quaternary
ammonium hydroxides containing hydroxyalkyl substituents
at the nitrogen, are used, it is often unnecessary to
30 add a catalyst poison. When these catalysts are used,
it is often sufficient to terminate the reaction by
brief heating of the reaction mixture to temperatures
above 100C (thermal decomposition, i.e. deactivation of
the catalyst).
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After deactivation, excess HDI is removed in a
suitable manner such as extraction (for example using
n-hexane as extractant) or, preferably, thin-layer
distillation in a vacuum, to a residual HDI content of
5 at most 0.2% by weight, preferably less than O.lZ by
weight.
The end products of the process according to
the invention are colorless liquids having a color value
(HAZEN) according to DIN 53,409 below 100, preferably
10 below 50, an isocyanate content of about 10 to 24% by
weight and a viscosity at 23C of about 500 to
10,000 mPa.s.
Since only very small quantities of catalyst
are used in the process according to the invention, the
15 quantity of deactivator, i.e. the catalyst poison, can
also be kept correspondingly small, with the result that
the end products of the process according to the
invention contain only very small quantities of
secondary products formed from catalyst and catalyst
20 poison which remain in solution and do not affect the
subsequent use of the products. Even when the process
is carried out using HDI, which has not been purified
beforehand in the usual way by distillation to remove
traces of chlorine-containing compounds via weakly basic
25 compounds such as metal oxides or sodium hydrogen
carbonate, clear and colorless end products are
obtained. By virtue of their low viscosity, the end
products of the process according to the invention are
suitable for the production of polyisocyanate
30 polyaddition products by reaction with compounds
containing at least two isocyanate-reactive groups and
are particularly suitable for the production of
solventless or low-solvent two-component polyurethane
lacquers.
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When the end products of the process according
to the invention are used in accordance with the
invention, they may be blocked by blocking agents for
isocyanate groups. Suitable blocking agents include the
compounds mentioned by way of example in EP-A 10,589,
5 page 15, lines 14 to 26 (U.S. Patent 4,324,879).
The end products of the process according to the
invention are used for the production of high-quality
two-component polyurethane lacquers, preferably in
combination with known polyhydroxy polyesters,
polyhydroxy polyethers and, in particular, polyhydroxy
polyacrylates. In addition to the relatively high
molecular weight polyhydroxyl compounds mentioned, the
lacquers may also contain low molecular weight,
preferably aliphatic polyols. Combinations of the end
products of the process according to the invention with
polyhydroxyl polyacrylates represent particularly
valuable two-component binders for high-quality car
repair lacquers which have outstanding weather
20resistance.
Polyamines, particularly in blocked form as
polyketimines or oxazolidines, may also be used as
reactants for the end products of the process according
to the invention. The quantitative ratios in which the
25optionally blocked polyisocyanates according to the
invention and the isocyanate-reactive compounds mentioned
are reacted in the production of polyisocyanate
polyaddition products lacquers are selected such that for
every (optionally blocked) isocyanate group, there are
30about 0.8 to 3, p~eferably about 0.9 to 1.8 hydroxyl,
amino and/or carboxyl groups.
To accelerate the hardening process, it is
possible to use the known catalysts from isocyanate
chemistry, for example tertiary amines such as
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triethylamine, pyridine, methyl pyridine, benzyldi-
methylamine, N,N-dimethylaminocyclohexane, N-methyl
piperidine, pentamethyl diethylenetriamine, N,N'-endo-
ethylene piperazine or N,N'-dimethyl piperazine; and
5 metal salts such as iron(III) chloride, zinc chloride,
zinc(II) ethylcaproate, tin(II)-2-ethylcaproate,
dibutyltin(IV) dilaurate or molybdenum glycolate.
In blocked form the products according to the
invention in combination with polyhydroxyl compounds are
10 used in particular for the production of stoving
lacquers which can be hardened at temperatures of about
80 to 180C (depending on the blocking agent used) to
form high-quality lacquer coatings.
To prepare ready-to-use lacquers the optionally
15 blocked polyisocyanate, the polyfunctional reactant,
optionally an isocyanate polyaddition catalyst and known
additives (such as pigments, dyes, fillers and levelling
agents) are thoroughly mixed with one another and
homogenized in a standard mixing unit, such as a sand
20 mill, either with or without solvents and diluents.
The paints and coating compositions may be
applied to the article to be coated either in solution,
from the melt or in solid form by standard methods such
as spread coating, roll coating, casting, spray coating,
25 fluidized bed coating or electrostatic powder spraying.
The lacquers containing the polyisocyanates
according to the invention produce films which adhere
surprisingly well to metal substrates and which are
particularly resistant to light, color stable under heat
30 and highly abrasion-resistant. In addition, they are
distinguished by extreme hardness, elasticity, high
resistance to chemicals, high gloss, excellent weather
resistance and good pigmentability.
In the following examples, percentages are
35 percentages by weight unless otherwise indicated.
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EXAMPLES
EXAMPLE 1 (Preparation of catalyst solution I)
600 g 2-ethylhexane-1,3-diol were added to and
stirred with 1000 g of a commercial, colorless 40~
5 solution of N,N,N-trimethyl-N-benzylammonium hydroxide
in methanol. The methanol was then removed with
thorough stirring in a water jet pump vacuum at 30 to
40C. The 40~ stock solution was adjusted with
additional 2-ethylhexane-1,3-diol to a catalyst
10 concentration of about 0.5Z.
EXAMPLE 2 (Preparation of catalyst solution II)
The procedure was as in Example 1, except that
dimethylformamide was used instead of 2-ethylhexane-
1,3-diol to replace methanol and for further dilution.
15 A 0.5% catalyst solution in dimethylformamide was
obtained.
EXAMPLE 3 (Preparation of catalyst solution III)
60 g 2-ethylhexanol were added to 100 g of a
70~ solution in methanol of N,N,N-trimethyl-N-(2-
20 hydroxypropyl)-ammonium hydroxide (prepared by the
reaction of trimethylamine with propylene oxide in
methanol) and the methanol was subsequently removed in a
water jet pump vacuum. The solution was then adjusted
with additional 2-ethylhexanol to a catalyst
25 concentration of 4~. The solution was brown in color.
EXAMPLE 4 (According to the invention)
In a stirred reactor 3200 g HDI were degassed
for about 10 minutes at about 20C by applying a vacuum
(50 mbar) and stirring vigorously. The gas space of the
30 apparatus was then filled with pure nitrogen. A stream
of pure, dry nitrogen was then vigorously passed through
the liquid for about 1 hour at around 25C. Prior to
treatment the HDI had a CO2 content of 44 ppm; the CO2
content was reduced to 2 ppm after the described
35 treatment. More nitrogen was passed through the
reaction mixture for the remainder of the reaction.
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32 g (0.96 mmol of base) of catalyst solution
(I) were then added dropwise over a period of 15 to 30
minutes, followed by heating for 30 minutes to 60C.
Since the reaction was now slightly exothermic, the
5 contents of the reactor were kept at 60 to 65C by
cooling. The reaction abated after about 0.5 h, at
which time the NCO content of the crude product measured
42Z. The crude product was then stirred for about 1 h
at 60C until an NCO content of 38Z was reached. The
10 reaction was then terminated by the addition of 0.32 g
of a 25Z solution of dibutylphosphate (0.38 mmol) in
HDI, followed by stirring for 15 minutes. The liquid
was then allowed to cool to ambient temperature and
excess HDI was removed by thin-layer distillation.
1382 g of a clear, light polyisocyanate
characterized by the following data were obtained:
Viscosity: 1800 mPa.s/23C
Color value (HAZEN) according to DIN 53,409: 20
NCO content: 22.3%
20 Free HDI content: 0.05Z
Dilutability with xylene: was diluted without
cloudiness to below a solids
content of lOZ
EXAMPLE 5 (Comparison Example)
The procedure was as in Example 4. 3200 g HDI
were introduced into an apparatus which was then
degassed by applying a vacuum and filled with nitrogen.
Thereafter, however, no nitrogen, was blown through, so
that as a result nitrogen was not introduced into the
30 liquid but only passed over. The CO2 content of the HDI
was only negligibly reduced by this measure to 38 ppm.
32 g of catalyst solution (I) were then added
as described in Example 1, followed by heating to 60C.
No reaction was observed and there was hardly any
35 reduction in the NCO content. An additional 32 g of
Mo3146 - 14 -
133~9YO
catalyst solution were added after 4 h at 60C; the
reaction still did not start. After an additional 64 g
of catalyst was added, a reaction began and was
terminated at an NCO content of 38.2Z by the addition of
5 1.58 g of a 25Z solution of dibutylphosphate. After
cooling to 25C, the solution was in the form of a
cloudy liquid which gradually precipitated a white
deposit. After removal of free HDI by thin-layer
distillation, a cloudy yellow product having an NCO
10 content of 21.4% was obtained. The clouding did not
disappear after dilution with butyl acetate. Dilution
with xylene intensified the clouding. The product was
unsuitable for use in high-quality PUR lacquers.
EXAMPLE 6 (According to the invention)
In a stirred reactor, 798 g of freshly
distilled hexamethylene diisocyanate were vigorously
stirred in a vacuum (<50 mbar) for 30 minutes at 20C.
The gas space of the apparatus was then filled with
highly pure nitrogen. The carbon dioxide content of the
20 HDI was 44 ppm. A stream of pure, dry nitrogen was then
vigorously passed through the liquid for 1 hour at 30 to
40C. Re-determination of the CO2 revealed a content of
2 ppm.
Throughout the reaction, dry nitrogen was
25 passed through the reaction mixture. To initiate the
trimerization reaction, 12 g catalyst solution II were
added dropwise over a period of about 30 minutes,
followed by slow heating to 70C. The reaction was
exothermic and was sustained for 1 hour at about 75C
30 without any further supply of heat. Another 12 g of
catalyst solution were then added. The reaction mixture
was then left to react for another 30 minutes with
thorough stirring. The reaction was terminated at an
NCO content of 42.4Z by the addition of 0.6 g
35 (equivalent ratio of catalyst to terminator = approx.
Mo3146 - 15 -
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1:1) of a 25% solution of dibutylphosphate in HDI.
After 15 minutes, the reaction mixture was subjected to
thin-layer distillation at 130C to separate solvent and
HDI. 230 g of a polyisocyanate characterized by the
5 following data were obtained:
Viscosity: 2200 mPa.s/23C
NCO content: 22.0%
Free HDI content: 0.09%
Color value: 30 (DIN 53,409)
10 EXAMPLE 7 (According to the invention)
The procedure was as in Example 6. The
reaction was terminated at an NCO content of 38.0Z.
After termination of the reaction and after thin-layer
distillation at 120C, 350 g of a product having the
15 following characteristic data were obtained:
Viscosity: 3000 mPa.s/23C
NCO content: 21.7%
Color value: 40 (DIN 53,409)
Free HDI content: 0.1%
20 EXAMPLES 8-12 (According to the invention)
The procedure was as described in Example 1,
i.e. C02 was removed from the HDI with a vigorous stream
of nitrogen at 40 to 50C. The other conditions of the
polymerization reaction are shown in Table 1. The
25 catalyst was deactivated with dibutylphosphate with one
exception (Example 10). Table 1 also sets forth the NCO
content of the reaction mixture at which termination of
the polymerization reaction was initiated. Table 2 sets
forth the characteristic data of the end product after
30 removal of excess HDI.
Mo3146 - 16 -
1335930
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Mo3146 - 17 -
1335990
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Mo3146 - 18 -
133599~
Although the invention has been described in
detail in the foregoing for the purpose of illustration,
it is to be understood that such detail is solely for
that purpose and that variations can be made therein by
5 those skilled in the art without departing from the
spirit and scope of the invention except as it may be
limited by the claims.
Mo3146 - 19 -
