Note: Descriptions are shown in the official language in which they were submitted.
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Mo3449
LeA 27,126
POLYURETHANE ELASTOMERS OF LOW HARDNESS
BACKGROUND OF THE INVENTION
This invention relates to polyurethane elastomers of
low hardness, to a process for their preparation, and to their
5 use.
The hardness values obtainable with polyurethane
elastomers prepared according to known methods are in the range
of about 80 Shore A to 75 Shore D and thus cover a range from
typical rubber elastomers (20 to 80 Shore A) to rigid synthetic
resins (greater than 55 Shore D).
Hardness is determined mainly by the proportion of
the hard phase formed by the isocyanate and chain lengthening
agent. At values below 80 Shore A, properties are markedly
deteriorated. If the proportion of hard phase is reduced while
15 the polydiol content is kept constant, the dimensional
- stability under heat deteriorates because of the partial
miscibility of the hard phase with the polydiol component. If
the hard phase component is reduced due to an increase in the
mGlecular weight of the polydiol component, the flexibility of
20 the product in the cold deteriorates because of the increasing
tendency to crystallization of the polydiols with increasing
molecular weight. See also Becker/Braun, Kunststoffhandbuch,
Volume 7, Polyurethane, page 36, Carl Hanser Verlag, Munich,
Vienna, 1983.
2s Matrix materials of great hardness are disclosed in
German Offenlegungsschrift 3,513,980. These materials are
obtainable by the reaction of isocyanates, phenolic chain
lengthening agents, and soft segment formers based on dimerized
and/or trimerized fatty acids. The use of a dimeric fatty acid
3~ polyol with a high trimer content in a polyurethane lacquer
which has improved resistance to chemicals is described in U.S.
Patent 3,349,049. The introduction of small proportions of
dimeric fatty acid polyols is described in European Application
35376RH0609 . .
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156,665 (corresponding to U.S. Patent 4,602 079). The
proportion of dimeric fatty acid is at most 35% by weight. The
use of higher proportions of predominantly dimeric fatty acid
is not obvious since it is known that large proportions of
polydiols having a predominantly aliphatic character, such as
OH-terminated polybutadiene or its hydrogenated form, give rise
to materials that have only moderate mechanical properties
("strength") caused by poor miscibility with the hard phase.
Houben-Weyl, Handbuch der organischen Chemie, Volume E20, pages
o 1569 and 1599.
Isocyanate-modified polyesters based on a glycol and
a polymeric fatty acid are disclosed in U.S. Patent 3,264,236.
Soft polyurethane elastomers having high dimensional
stability under heat, excellent flexibility in the cold, and
high elasticity have not, however, been previously known in the
art.
It is an object of the present invention to provide
soft, highly elastic polyurethane elastomers having high
dimensional stability under heat and excellent flexibility in
the cold.
SUMMARY OF THE INVENTION
This invention relates to thermoplastic polyurethanes
that are at least substantially linear in structure prepared by
a process comprising reacting
(aJ organic polyisocyanates;
(b) at least one polyester derivative having at least two
isocyanate reactive hydrogen atoms, wherein said polyester
derivative is a polyester of an ~ dicarboxylic acid
containing a total of at least 16 carbon atoms and a
non-vicinal diol, in an amount such that the proportion of
the ~,~-dicarboxylic acid is greater than 35% by weight
based on the total quantity of thermoplastic polyurethane;
and
(c) chain lengthening agents having no phenolic OH groups.
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Catalysts, other known addltives, and other
isocyanate-reactive compounds having a molecular weight greater
than 400 may optionally be included in the preparation of the
thermoplastic polyurethanes of the invention.
This invention further relates to a process for the
preparation of thermoplastic polyurethanes having a
substantially linear structure by the reaction of the organic
polyisocyanates (a) with the polyester derivatives (b) and the
chain lengthening agents (c).
Yet another object of this invention is the use of
the thermoplastic polyurethanes according to the invention for
medical purposes.
DETAILED DESCRIPTION OF THE INVENTION
In a preferred embodiment, the thermoplastic
polyurethanes according to the invention have a hardness of
less than about 80 Shore A, preferably less than 75 Shore A.
These thermoplastic polyurethanes are substantially linear and
preferably have a volume flow index ("MVI") of at least 0.3
cm3/10 min (preferably at least 1 cm3/10 min), as determined at
l9O-C with a testing force of 10 kp (DIN 53735; ISO 1132).
Preferred polyester derivatives (b) are polyesters,
polyester carbonates, polyetheresters, and polyetherester
carbonates containing terminal OH or NH2 groups. Particularly
preferred polyesters (b) have an acid number below about 2 and
a hydroxyl number of from about 11 to about 170.
Preferred ~ dicarboxylic acids used to prepare the
polyester derivatives (b) include dimeric fatty acids obtained
by reductive dimerization of unsaturated aliphatic
monocarboxylic acids, preferably monocarboxylic acids having
about 8 to about 22 carbon atoms and most preferably oleic
acids. The trimer content formed in the reaction is no more
than about 5% by weight based on the dimeric fatty acid,
preferably no more than 1.5% by weight.
The polyester derivatives (b) to be used according to
the invention may be obtained in known manner by condensation
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of ~ dicarboxylic acids with non-vicinal diols, optionally
with the addition of diaryl or dialkyl carbonates or phosgene.
The OH end groups obtained in the reaction may optionally be
replaced by NH2 groups.
~he polyester derivatives to be used according to the
invention may contain other aliphatic dicarboxylic acids in
addition to the dimeric acids (for example, glutaric acid,
adipic acid, suberic acid, azelaic acid, sebacic acid, dodecane
diacid, or mixtures thereof), but pure dimeric acid is
o preferably used. Examples of non-vicinal diols suitable for
the condensation reaction include ethylene glycol, 1,3- and
1,2-propanediol, di-, tri-, tetra-, and octa-ethylene glycol,
dipropylene glycol, tripropylene glycol, 1,4-butanediol, 1,3-
and 1,5-pentanediol, 2,2-dimethyl-1,3-propanediol,
1,6-hexanediol, and higher, optionally branched, aliphatic
diols. The molecular weights of components (b) may be from
about 700 to about 10,000.
The organic polyisocyanates (a) include those used in
previously known processes and are described e.g. in
20 . Kunststoff-handbuch, Volume VII, Polyurethane, Hanser Verlag,
Munich, 1983, or in Houben-Weyl, Makromolekulare Stoffe, Volume
E20. Aromatic or aliphatic diisocyanates, especially bis(iso-
cyanatophenyl)methane, are preferably used. Other diiso-
cyanates, however, may also be used, including aliphatic
diisocyanates such as tetra- or hexamethylene diisocyanate,
trimethylhexamethylene diisocyanate; cycloaliphatic diiso-
cyanates such as cyclohexyl diisocyanate, isophorone diiso-
cyanate or dicyclohexylmethane diisocyanate; or aromatic diiso-
cyanates such as benzene diisocyanate, toluene diisocyanate,
dichlorodiphenylmethane diisocyanate, dimethyldiphenylmethane
diisocyanate, or dibenzyldiisocyanate.
The chain lengthening agents (c) are preferably
bifunctional polyols such as ethylene glycol, propylene glycol,
1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,4-cyclo-
hexanedimethanol, hydroquinone-bis(2-hydroxyethyl) ether, and
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1,5-bis(2-hydroxyethoxy)naphthalene. The preferred ch~in
lengthening agents have a molecular weight of from about 32 to
about 399~ preferably from 62 to 220.
In one particularly preferred embodiment~ polyiso-
cyanate (a~ is an isocyanate based on diphenylmethane and the
chain lengthening agent (c) is butanediol.
In another preferred embodiment, components (a), (b),
and (c) are substantially bifunctional and from about 0.9 to
about 1.2 equivalents of isocyanate-reactive compounds are used
per isocyanate equivalent.
Known catalysts, such as organic or inorganic tin
compounds, amines, or alkali metal compounds, are optionally
used for the preparation of polyurethanes. Other additives,
such as blowing agents, stabilizers, emulsifiers, dyes,
pigments, and fillers may also be used in known manner.
The thermoplastic polyurethanes according to the
invention may be prepared by various methods. In one preferred
embodiment, the polyurethane thermoplast is prepared by the
band or screw process. See Becker/Braun, Kunststoff-Handbuch,
Volume 7, Polyurethane, Chapter 8.2.1, pages 428 et seq, Carl
Hanser Verlag, Munich, Vienna, 1983. A double screw kneading
machine is used in a preferred embodiment.
The polyurethane-forming components may be introduced
into the extruder at one feed point or at several feed points.
The components may be introduced into the screw machine either
separately or as a pre-mix. See German Offenlegungsschrift
2,842,806. In a particularly preferred process, a prepolymer
is first formed from isocyanate (a) and polyester derivative
(b) and the chain lengthening agent is then added to the
30 prepolymer.
Apart from the low hardness and high elasticity
compared with polyurethane elastomers prepared without dimeric
fatty acids or with only small proportions of dimeric fatty
acids, the polyurethane elastomers according to the invention
35 are also distinguished by their good compatibility with body
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tissues and blood, which is due to the reduced surface tension,
and their great durability when in contact with body fluids.
The elastomers of the invention are therefore particularly
suitable for the manufacture of medical equipment such as blood
bags, catheters, pacemaker leads, and artificial blood vessels
or tubes to be inserted intravenously. Pharmacologically
valuable substances may be incorporated in the materials, in
particular anti-coagulants such as heparin, immunosuppressive
drugs, antibiotics, or other known pharmacologically active
o ingredients described, for example, in Polymer Science and
Technology, Volume 34, "Polymers in Medicine IIn, Plenum Press,
New York, 1983.
The following examples further illustrate details for
the preparation of the compositions 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.
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
20 - compositions. Unless otherwise noted, all temperatures are
degrees Celsius and all percentages are percentages by weight.
EXAMPLES
General Method of Preparation: Polyester component
(b) (having compositions as described below) (0.~5 mole) was
reacted with the total quantity of bis(4-isocyanatophenyl)-
methane ("MDI~) (or other polyisocyanate, if indicated) at
100-C to form a prepolymer. The quantity of chain lengthening
agent (c) equivalent to the remaining NCO groups was added to
the melt at 110 C and the mi~ture was briefly degassed, poured
into a mold, and tempered at llO-C for 8 hours. Plates 1 or 2
mm in thickness were produced by compression molding at 200-C
for determination of mechanical properties.
Comparison examples were prepared using a polyester
diol of adipic acid and butanediol (OH number of 49.7) instead
of component (b).
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The low hardness of the polyurethanes according to
the invention is evident from the following Examples.
~xamPle 1
The procedure described above was carried out using
5 butanedio~ as the chain lengthening agent (c) and as component
(b) a polyester having an OH number of 49.2 prepared from (1)
hydrogenated dimeric fatty acid with acid number 197 (trimer
content 1% and monomer content 0.1%) and (2) butanediol. The
dimeric fatty acid had been obtained by dimerization of fatty
acids and contains 36 carbon atoms (CAS Registry Number
68783-41-5, iodide value of 7).
The data listed in the following Table show that the
thermoplastic polyurethanes obtained were surprisingly soft, in
view of the percentage content of hard segment.
g MDI g Butane- Polyester X Hard Hardness
diol OH number segment Shore A Shore D
37.5 9 49.2 28.92 80 28
13.5 49.2 35.71 85 30
62.5 18 50.7 41.32 89 39
22.5 50.7 46.88 92 44
Similar properties were obtained using as component
~b) a similar polyester having an OH number of 50.7.
When an adipic acid polyester having an OH number of
49.7 is used instead of the polyester derivative to be used
according to the invention, the product obtained with the same
proportion of hard segment is less soft.
Example 2
A thermoplastic polyurethane was prepared as
described in Example 1 except that the polyester (b) was a
polyester having an OH number 37. The resultant thermoplastic
polyurethane had the following properties:
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% Hard segment: 23.5
Shore A hardness: 72
Tensile strength: 17 MPa
Melting point of hard segment: 150C
Brittleness point: -40C
Example 3
A thermoplastic polyurethane was prepared as
described in Example 1 except that the polyester (b) was a
polyester having an OH number 28 prepared from the dimeric
fatty acid from Example 1 and neopentyl glycol. The resultant
thermoplastic polyurethane had the following properties:
% Hard segment: 19
Shore A hardness: 61
Tensile strength: 12 MPa
Melting point of hard segment: 145C
Brittleness point: -40C
Thermoplastic polyurethanes having the degree of
softness shown in Examples 2 and 3 are not obtained when
conventional polyols are used. A polyurethane prepared from
20 the comparison polyester of Example 1 and containing a hard
segment proportion of 20.8% by weight had a Shore A hardness of
94.
Example 4
A polyester having an OH number of 34.8 prepared from
25 the dimeric acid from Example 1 and ethylene glycol was used as
component (b). The resultant polyurethane had a hard segment
content of 22.4% and a Shore A hardness of 60.
Example 5
A polyester having an OH number of 27.0 prepared from
30 the dimeric acid from Example I and hexanediol was allowed to
react with hexamethylene diisocyanate instead of bis(4-iso-
cyanatophenyl)methane with the aid of butanediol as chain
lengthening agent. The resultant product had a hard segment
content of 14.2% and a Shore A hardness of 66.
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Example 6
Example 5 was repeated but using 1,4-bis(2-hydroxy-
ethoxy)benzene instead of butanediol as chain lengthening
agent. The resultant polyurethane had a hard segment content
of 13% and a Shore A hardness of 76.
Example 7
A polyether ester haYing an OH number of 34.7
prepared from the dimeric acid from Example I and diethylene
glycol was used as component tb). The resultant polyurethane
o had a hard segment content of 22.4% and Shore A hardness of 68.
Example 8
A polyester having an OH number of 20 prepared from
the dimeric acid from Example I and hexanediol was used as
component (b). The resultant polyurethane had a hard segment
content of 14.2% and Shore A hardness of 53.
Example 9
A thermoplastic polyurethane was prepared as
described in Example 1 except that the polyester derivative (b)
had an OH number of 45.7. The resultant thermoplastic
polyurethane had a hard segment content of 27.5%. The
interfacial tension of this polyurethane with water was 24.6
mN/m.
Conventional thermoplastic polyurethanes have a
higher interfacial tension and are therefore less suitable for
2S medical implants.
Examp,le~ 10
A polyester prepared from the dimeric fatty acid of
Example 1 and hexanediol (OH number 30) was used. In addition,
bis(4-isocyanatocyclohexyl)methane was used instead of MDI. As
chain lengthening agent, butanediol was used. The following
results were obtained for the resultant polyurethane:
% Hard segment: 31
Shore A hardness: 71
% Elongation 500
Tensile strength: 2~.7 MPa
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The elastomer obtained was transparent.
Example 11
Polyurethanes were prepared as in Example 10 except
for using MDI as the polyisocyanate and different percentages
5 by weight of the hard segment (as indicated). The resultant
polyurethanes had the following properties:
ExamDle 11a Example 11b
% Hard segmen~: 25.8 16.1
Shore A hardness: 65 34
% Elongation 744 822
Tensile strength: 17 MPa 12 MPa
Tear resistance (DIN 53,515)25 KN/m20 KN/m
% Compression set (24 h,
70C; DIN 53,517) 45 52
ExamDle 12
Example 11 was repeated using a hard segment
percentage by weight of 18.3. The resultant polyurethane
(compound 12a) had the following properties:
Shore A hardness: 59
20 . % Elongation 830
Tensile strength: 13 MPa
As a comparison, a polyurethane elastomer (compound
12b) hav;ng a hard segment percentage of 29% was prepared by
the general method described above from the polyesterdiol of
25 adipic acid (described in Example 1).
The permanent elongation of polyurethanes 12a and 12b
were measured. The results are entered into the following
Table:
12a 12b 12a 12b 12a 12b 12a 12b
% Elongation100 100150 150 200 200 250 250
Permanent elongation 7 12 12 20 21 48 30 78
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