Note: Descriptions are shown in the official language in which they were submitted.
r~
Mo3542
LeA 27,611
THERMOPLASTIC POLYURETHANE-POLYUREA
ELAS~OMERS HAVING INCREASED HEAT RESISTANCE
BACKGROUND OF THE INVENTION
This invention relates to new aliphatic, light-stable
thermoplastic polyurethane-polyurea elastomers having increased
heat resistance and to a process for their production.
Thermoplastic polyurethane elastomers ("TPU's") are
known. For example, D. Dieterich in Methoden der Orqanischen
Chemie (Houben-Weyl), Vol. E 20, pages 1638-41; Thieme,
Stuttgart 1987. One disadvantage of TPU's is their moderate
heat resistance which, particularly in the case of flexible
types, is not far above 100C.
According to Kunststoffe, 68, (12), pages 819-825
(1978), the range of shear modulus curves for diol-extended
TPU's extends only to 130C and, although amine extension
increases the range to higher temperatures, the resultant
polyurethane can no longer be plasticized without thermal
damage. In general, therefore, NCO prepolymers are extended
with amines only in RIM technology. The moldings thus
produced, however, are not thermoplastic elastomers. Various
methods have been adopted with a view to increasing the heat
resistance of TPU's. According to German Offenlegungsschrift
3,329,775, the heat resistance of aromatic TPU's can be
increased, for example, by partly replacing the 4,4'-diiso-
2~ cyanatodiphenylmethane with 1,5-diisocyanatonaphthalene. The
same effect is obtained by partial urea linkage with water or
by addition of a diamine. See German Offenle~ungsschrift
2,423,764 and European Patent Application 21,323. In general,
however, such measures also increase the hardness of the
corresponding thermoplastic polyurethane, which is undesirable.
It is known from U.S. Patent 2,923,802 that
thermoplastic polyurethane elastomers can be obtained by
condensation of ~,~-chloroformates of long-chain polyether or
polyester diols in admixture with piperazine. Elastomers such
35376RH0675
, . . .. . . . . . . . .
,. .: , . , . . :
;
~ ~ r, ,~
as these, however, are no different from conventional TPU's in
their behavior under dynamic stress at high temperatures.
It is known from U.S. Patent 3,635,908 that TDI-
terminated prepolymers can be chain-extended with the
bis-carbonate of 2-methylpiperazine to form soft thermoplastic
polyurethane elastomers. U.S. Patent 3,655,627 describes
light-stable TPU's for which the hard segment is synthesized
from bis(4-isocyanato)cyclohexylmethane and isophoronediamine.
In view of the small hard segment component, these products are
soft and have tensile strengths of up to 41 N/mm2 for breaking
elongations of 412 to 630%. The products, however, show
unsatisfactory dynamic behavior upon exposure to heat.
It is known that the hard segments of a polyurethane
can be optimally aggregated only if the synthesis components of
the hard segment are both chemically and stereochemically
identical. Unless this synthetic principle is observed, the
products obtained have low melting points and poor thermal
stability. According to Rubber ChemistrY and TechnoloqY, Vol.
58, pages 985-996 (1985), for example, butanediol-extended
TPU's based on 4,4'-diisocyanatodicyclohexylmethane achieve
satisfactory thermal stability only if the trans-trans content
in the isomer mixture of the diisocyanate is high. In
accordance with this finding, British Patent 1,554,102
describes polyurethanes having a 4,4'-diisocyanatodicyclohexyl-
methane/butanediol hard segment for which the advantage for the
application described therein lies precisely in the synthesis
of the hard segment disturbed by the presence of an isomer
mixture of the isocyanate and, hence, in the low melting point
of the products.
Accordingly, it was not to be expected that
thermoplastic polyurethane/polyurea elastomers of remarkably
high thermal stability, despite their small hard segment
component, would be obtained when 4,4'-diisocyanatodicyclo-
hexylmethane is used as an isomer mixture. This mixture is
optionally diluted by addition of more aliphatic diisocyanates
Mo3542
: , ,. . ~
" , " - . ., - .
., .
., .
.:
i ~ , .
.,
-3-
and the nard segment is synthesized by chain extension with
p;perazine.
The hard segments thus produced are polyureas. The
melting points and aggregation of polyurea hard segments are
generally higher than those of the corresponding polyurethanes.
This, however, applies only to chain extension with diprimary
diamines because it is only then that the very strong
interchain interaction occurs via bifurcate hydrogen bridges.
See Coll. Polvm. Sci., 263, 335-341 (1985).
Piperazine, on the other hand, is a disecondary
diamine. Consequently, when this compound is used, the number
of possible hydrogen bridges in the hard segment corresponds to
those of corresponding polyurethanes. Accordingly, it was not
to be expected that the higher heat resistance observed in
accordance with the invention would be caused by the polyurea
structure of the hard segments because no more hydrogen bridges
are present than in the polyurethane.
Accordingly, the problem addressed by the present
invention was to provide thermoplastic polyurethanes combining
relatively low hardness with excellent heat resistance.
SUMMARY OF THE INVENTION
The present invention relates to thermoplastic
polyurethane polyureas based on an aliphatic polyisocyanate, at
least one macrodiol, and a diamine chain-extending agent
prepared by a process comprising reacting
(a) 4,~'-diisocyanatodicyclohexylmethane,
(b) a cyclic secondary diamine, and
(c~ a macrodiol having a molecular weight greater than 400,
optionally in the presence of
(d) low molecular weight diols, chain regulators, and typical
auxil;arles and additives.
The diamine (b) is preferably a piperazine which may
optionally be substituted with one or more C1-C6 alkyl
(preferably one or two methyl groups). In a preferred
Mo3542
.
,
,.~ ,
embodiment, the thermoplastic contains partly recurring
structural units corresponding to formula I
~1
0 H O
-C-N- ~ -CH2- ~ -N-C-N\__~ N- (I)
wherein Rl and R2 are independently hydrogen or methyl
(preferably hydrogen), with the remainder of the thermoplastic,
of course, including urethane-based structural units formed by
reaction of the macrodiol hydroxyl groups with isocyanate
groups.
DETAILED DESCRIPTION OF TH~ INVENTION
4,4'-Diisocyanatodicyclohexylmethane is generally
prepared as an isomer mixture. The properties of the hard
segments are largely determined by the trans-trans isomer
content of the diisocyanate. It has been found that with a
very small trans-trans isomer content, the polyurethanes
obtained show unsatis~actory elastic properties and poor
thermal stability. In contrast, with a high trans-trans isomer
content, the thermoplastic products obtained cannot be
processed without decomposition.
According to the invention, therefore, preferred
polyurethanes are those according to the invention in which the
4,4'-diisocyanatodicyclohexylmethane used in the synthesis of
recurring structural units corresponding to formula I is an
isomer mixture containing about 10 to about 30% (preferably
20%~ of the trans-trans isomer, the remainder being cis-trans
and/or cis-cis isomers.
In a preferred embodiment, 4,4'-diisocyanatodicyclo-
hexylmethane is blended with other polyisocyanates. The
prepolymers thereby obtained are thinner liquids than those
obtained with the same molar quantity of
Mo3542
-
.
'
~ .
I
d d ~
-5-
4,4'-diisocyanatodicyclohexylmethane alone. It has been found
that such blending is possible without causing significant
adverse effects on the properties of the end products as long
as the content of 4,4'-diisocyanatodicyclohexylmethane does not
fall below 20%. Accordingly, the present invention preferably
relates to polyurethanes in which mixtures of 4,4'-diiso-
cyanatodicyclohexylmethane and other aliphatic diisocyanates
(preferably hexamethylene diisocyanate and isophorone diiso-
cyanate) are used for the synthesis of the hard segments, with
the proviso that these mixtures must contain between 20 and 90
mol-% (preferably between 40 and 80 mol-% and more preferably
between 60 and 70 mol-%) 4,4'-diisocyanatodicyclohexylmethane.
In a preferred embodiment, the thermoplastics
according to the invention contain at least 10% by weight of
the recurring units corresponding to formula I.
The polyurethanes according to the invention acquire
their spectrum of properties through the special synthesis of
their hard segments. These hard segments are produced by chain
extension with cyclic secondary diamines, especially with
p;perazine and its 2-monoalkyl or 2,5-d;alkyl derivatives,
unsubstituted piperazine being particularly preferred.
Suitable additional chain-extending agents are the
short-chain alcohols typically used in polyurethane chemistry,
which generally have an isocyanate functionality of two.
Examples of suitable such compounds include alcohols such as
ethylene glycol, 1,4 butanediol, 1,6-hexanediol, neopentyl
glycol, hydroquinone bis(2-hydroxyethyl ether), 1,4-cyclo-
hexanediol, diethylene glycol, and 4,4'-dihydroxydicyclohexyl-
methane.
~he soft segment macrodiols used in the synthesis of
the thermoplastic polyurethane-polyurea elastomers according to
the invention may be any of the preferably difunctional and,
optionally in small quantities of preferably up to 10%,
trifunctional polyols known in the art. Suitable such polyols
include polyesters, polylactones, polyethers, polythioethers,
Mo3542
- . ,
~, .
-6-
polyester amides, polycarbonates, and polyacetals typically
used in polyurethane chemistry and known in the art; vinyl
polymers (for example, polybutadiene diols); polyhydroxyl
compounds already containing urethane or urea groups; and
optionally modified natural polyols and other compounds
containing Zerewitinoff-active groups capable of reacting with
isocyanates, such as amino, carboxyl, or thiol groups. These
compounds are described in detail, for example, in German
Offenlegungsschriften 2,302,564, 2,423,764, 2,549,372,
2,402,804, 2,920,501, and 2,457,387.
Preferred polyols according to the invention are
substantially difunctional hydroxyl-containing polyesters of
diols and adipic acid, hydroxyl polycarbonates, hydroxyl
caprolactones, hydroxyl polytetrahydrofurans, or hydroxy-
polyethers based on polyethylene oxide and/or polypropylene
oxide, as well as corresponding mixed ethers of such
components.
These polycls have average molecular weights of about
550 to about lO,OOO and preferably 1,000 to 4,000. Polyols
having molecular weights of 1,500 to 2,500 are particularly
preferred.
The monofunctional alcohols, amines, and aliphatic
isocyanates typically used in polyurethane chemistry and known
in the art may be used as chain regulators in quantities of
f 25 0.05 to 5 mol-%, based on the soft segment polyol. However, it
ha~ proved to be particularly favorable to use monofunctional
ethylene oxide-propylene oxide mixed polyethers having
molecular weights of about 2,000 as the chain regulators.
These chain regulators also reduce the viscosity of the
prepolymers and thus favorably affect their processability.
Accordingly, ~he present invention particularly relates to
polyurethanes according to the invention in which mono-
functional ethylene ox;de/propylene oxide polyethers having a
molecular weight of 400 to 4,000 (preferably 1,000 to 2,000)
Mo3542
~ "
r ,~,, ,1 r-,
-7-
are used as chain regulators in quantities of about 0.05 to
about 5 mol-%, based on the macrodiol or mixture used.
Further auxiliaries and additives are understood to
be the known catalysts used in polyurethane chemistry, such as,
5 for example, tin(II) octoate, dibutyltin dilaurate, titanium
tetrabutylate, iron(II) acetylacetonate, diazabicyclooctane,
and N,N-tetramethyl ethylenediamine. Other additives include
fillers and reinforcing materials, such as glass fibers, carbon
fibers, TiO2, diatomaceous earth, aromatic polyamides, liquid
10 crystal ("LC") polyesters, even in ground form, quartz powder,
and polyureas, as well as inorganic or organic dyes or
pigments. Such additives are insoluble in the hydrocarbon
phase and are advantageously incorporated in the macropolyols
used before carrying out direct synthesis of the polyurethane
15 powder.
Several methods for preparing the polyurethane
polyureas according to the invention can be used. In the
preferred methods, an NCO prepolymer is prepared by the
reaction of the 4,4'-diisocyanatodicyclohexylmethane (or
20 diisocyanate mixtures) with the macrodiol component. The
prepolymer is then chain-extended with the cyclic secondary
diamine to form the polyurethane polyurea. Suitable methods
for preparing the polyurethane polyureas according to the
invention include synthesis in known manner in solution using
25 polyurethane solvents, the solution processes described in
German Offenlegungsschrift 2,644,434 being particularly
suitable. The product may be subsequently separated from the
solvent (mixture) in an evaporation screw. Synthesis of the
polymer, however, may also be carried out in heterogeneous
30 phase using emulsifiers for the NCO prepolymer, with the
product accumulating in powder form. Such processes using a
hydrocarbon carrier phase are known and are described, for
example, in German Offenlegungsschriften 2,556,945, 2,559,769,
and 2,442,085 and U.S. Patents 4,032, 516 and 3,787,525. The
emulsifiers which are the subject of German Offenleyungs-
Mo3542
',
., , ~
,
.
schriften 3,928,150 and 3,928,149 and the synthesis processesdescribed therein are used with particular advantage for this
synthesis.
Suitable such emulsifiers include substantially
l;near, surface-active copolymers that can be obtained by
copolymerization of
(A) a partial reaction product of (A)(l) (meth)acrylic acid or
a derivative thereof and (A)(2) a macromolecular compound
substituted with at least two functional groups selected
from OH and NH2, the functional groups which are not
reacted with (A)(l) being irreversibly blocked
with
(B) a urethane of (B)(1) a long-chain alkyl isocyanate and
(B)~2) a hydroxyalkyl (meth)acrylate.
Using these surface-active copolymers, polyurethane
powders may be directly produced in finely divided form by
reaction of polyisocyanates and isocyanate-reactive compounds
in a carrier phase.
By virtue of the low reactivity of the NCO-terminated
prepolymers to water, the chain-extending reaction may be
carried out in water as the continuous phase. Urea chain
extension by hydrolysis of the NCO groups takes place to only a
limited extent, if at all. Processes such as these are also
known and are described, for example, in U.S. Patent 3~655,627
and in German Offenlegungsschri~t 2,906,159. In general,
surfactants must also be added in these processes to enable
them to be carried out safely.
As discussed above, polyurethanes according to the
invention may be synthesized both in hydrocarbons and in water
as the continuous phase. The polyurethanes accumulate in
powder form and are isolated, for example, by filtration.
However, this powder synthesis ;n water as the continuous phase
is particularly easy to carry out when polyurethane polyureas
are prepared using monofunctional ethylene oxide/propylene
oxide polyethers having a molecular weight of about 400 to
Mo3542
- . .......... . .
:' ~ i ~ ,.
.
~5.~ 'J. 3 5 ~ ~ "
_9_
about 4,000 (preferably 1,000 to 2,000) in quantities of 0.05
to 5 mol-%, based on the macrodiol or mixture used. In the
production of these polyurethanes in powder form in an aqueous
carrier phase, surfactants need not be added. As a result, the
steps that would otherwise be necessary for removing these
substances from the product are not needed.
Accordingly, the present invention also relates to a
process for the production of polyurethanes in powder form,
wherein the chain-extending agent is initially introduced in
water, the prepolymer is stirred into the aqueous carrier
phase, and the chain-extending reaction is completed
(optionally at elevated temperature).
The polyurethanes according to the invention may be
processed to molded articles by conventional methods, for
example, by injection molding or press molding. By virtue of
their powder form, the polyurethanes may be used with
particular advantage for the production of elastic, flexible
skins and coatings by sintering.
Preferred polyurethanes are prepared using about 1.7
to about (preferably 1.8 to 2.2) mol of diisocyanate (mixture)
per mol of macrodiol, optionally in admixture with low
molecular weight diols having a molecular weight in the range
from 62 to 400.
The polyurethanes according to the invention are soft
products having Shore A hardnesses of about 60 to about 80,
coupled with good elastic behavior and high heat resistance.
These properties are achieved by a surprisingly small hard
segment content when compared with MDI-butanediol types.
The special hard segment synthesis of the TPU's, by
which soft products having a heat resistance of greater than
about 130C are obtained~ is a key feature of the invention.
The following examples further illustrate details for
the preparation of the compounds of this invention. The
invention, which is set forth in the foregoing disclosure, is
not to be limited either in spirit or scope by these examples.
Mo3542
,
,. `
Those skilled in the art will readily understand that known
variations of the conditions and processes of the following
preparative procedures can be used to prepare these compounds.
Unless otherwise noted~ all temperatures are degrees Celsius
and all percentages are percentages by weight.
EXAMPLES
Example 1
Hexanediol polycarbonate (OH value 56, functionality
2) (90 9) was introduced into a 2-liter three-necked flask
equipped with a stirrer and reflux condenser and dehydrated for
2 hours at 120C/14 mbar. Commercial 4,4'-diisocyanatodicyclo-
hexylmethane containing 20% trans-trans isomer (20.0~ 9) was
then added and the mixture was stirred at 110 to 120C. After
2 hours, the prepolymer had an NCO content of 2.36%. The
prepolymer was diluted with 155 ml of toluene. A solution of
2.7 9 of piperazine in 230 ml of 1:1 toluene/isopropyl alcohol
was rapidly added dropwise to the resultant solution with
stirring at 60C until the product was NCO-free (IR control~.
A 1.5-ml portion of the chain-extending solution remained
unused. Because of viscosity, the mixture was diluted with 535
ml of the 1:1 toluene/isopropyl alcohol mixture. Films were
cast from the solution and, after evaporation of the solvent,
were reduced in si~e, dried, and press-molded under a pressure
of 100 bar at 180C to form 1-mm thick test specimens.
Mo3542
.~ ~ : , . . .
.
,. . - .
-
~ ,, .
,~ ,
-~ .
~)7 ;': - r~
The product had the following properties:
Hardness (Shore A) 74
Melting point (Kofler, from 240C
film, 5 mins. dwell time)
Modulus (100%) 4.43 N/mm2
Modulus (300%) 10.52 N/mm2
Ultimate tensile stress 21.9 N/mm2
Elongation at break 631%
Softening point under static load 198C
(Penetration method: I mm
diameter bar, load 0.2N; test
specimen thickness 1 mm)
ExamPle 2
A mixture of 45 9 of hexanediol polycarbonate (OH
value 56, functionality 2~ and 45 9 of hexanediol/neopentyl
glycol polyadipate (OH value 56, functionality 2) was
dehydrated as in Example 1 and then prepolymerized with a
mixture of 13.36 of 4,4'-diisocyanatodicyclohexylmethane and
5.56 g of isophorone diisocyanate to an NCO content of 2.42%.
The prepolymer was dissolved in 600 ml of toluene and
chain-extended as in Example 1 with 2.7 g of piperazine in 225
ml of 2:1 toluene/isopropyl alcohol. A 10-ml portion of the
chain-extending solution remained unused. After dilution with
400 ml of 2:1 toluene/isopropyl alcohol, films ~ere cast as in
Example I and press-molded to test specimens.
The product had the following properties:
Hardness (Shore A) 70
Melting point (Kofler) 230C
Ultimate tensile stress 34.7 N/mm2
30 Elongation at break 1100%
Softening point under static load 138C
Example 3
Ethylene glycol polyadipate (~H value 56,
functionality 2) (9 kg) was dehydrated for 2 hours at 120C/40
mbar in a 150-liter reactor equipped with an anchor stirrer,
Mo3542
,
,
.
:
., ~
-12-
reflux condenser, and addition funnel. A mixture of 1.572 kg
of 4,4'-diisocyanatodicyclohexylmethane (trans-trans content of
20%) and 666 9 of isophorone diisocyanate was introduced and
the mixture was prepolymerized at 110C. After 30 minutes, the
NCO content had fallen to 3.36%. The prepolymer was dissolved
in 15.5 L of toluene and chain-extended at 60C with a solution
of 3~7 9 piperazine in 23 L of 1:1 toluene/isopropyl alcohol.
Because of viscosity, the solution was diluted with another
53.5 L of the 1:1 toluene/isopropyl alcohol solvent mixture.
The product was freed from the solvent in an evaporation screw,
granulated, dried, and injection-molded to test specimens.
The product had the following properties:
Hardness (Shore A) 73
Melting point (Kofler) 230C
15 Ultimate tensile stress 21.7 N/mm2
Elongation at break llCO%
Softening point under static load 159C
Example 4
A mixture of 75.735 9 of a hexanediol/neopentyl
glycol polyadipate (OH value 66, functionality 2) and 1.0125 9
of a butanol-started ethylene oxide/propylene oxide mixed
polyether having an average molecular weight of 2250 was
dehydrated and prepolymerized with a mixture of 6.5934 9 of
isophorone diisocyanate and 18.1566 g of 4,4'-diisocyanato-
dicyclohexylmethane at 110C to an NCO content of 4.27%. Thehot (100C) prepolymer was added dropwise over a period of 15
minutes to a rapidly stirred sulution of 403856 g of piperazine
in 439.5 g water. To complete the reaction, the suspension of
the resultant powder was stirred for 12 hours at 80~C. The
powder was f;ltered under suction and dried, giving a
quantitative yield of a material having a melting point of
2307C (Kofler)
Test specimens (1 mm thickness) were prepared from
the powder by press molding at 180~C ~200 bar). The product
had the following properties:
Mo3542
"
.
' . :
13 2 s
Hardness (Shore A) 74
Modulus (300%) 7 N/mm2
Modulus (600%) 21 N/mm2
Ultimate tensile stress 25 N/mm2
5 Elongation at break 600%
Storage modulus G (from Plateau up to 140C
torsion measurement)
Example 5
As in Example 4, 89.1 g of an ethylene glycol
polyadipate (OH value 56, functionality 2) and 1.0125 9 of the
sàme butanol-started ethylene oxide/propylene oxide mixed
polyethPr were dehydrated and prepolymerized with a mixture a
6.5934 9 of isophorone diisocyanate and 18.1566 g of 4,4'-
diisocyanatodicyclohexylmethane to an NCO content of 3.95%.
The hot prepolymer was added dropwise over a period of 15
minutes to a rapidly stirred solution of 4.3856 9 of piperazine
in 439.5 g of water. The reaction mixture was then stirred as
in Example 4 and the powder was separated off, dried, and
processed to test specimens. The yield was quantitative.
The product had the following properties:
Hardness (Shore A) 73
Melting point (Kofler) 220C
Modulus (300%) 7.5 N/mm2
Modulus (600%) 24 N/mm2
Ultimate tensile stress 33 N/mm
Elongation at break 760%
Storage modulus G (from Plateau up to lSOC
torsion measurement)
Mo3542
.
,
