CA1067241A - Mouldable lactone polyester-urethane composition having low compression set and high modulus - Google Patents

Abstract

ABSTRACT
A thermoplastic polyester urethane molding composi-tion is disclosed having low compression set and high elastic modulus and which comprises the reaction product of a poly(epsilon-caprolactone)polymer, a hydroxy terminated polyol, an organic diisocyanate and a siloxane polymer.
More specifically, by adding the siloxane polymer and main-taining a mole ratio of isocyanate to isocyanak-reactable hydroxy grouping in the range of from about 1.05 to about 1.3 or higher, it is possible to produce an improved molding composition having allophanate cross-links. The allophanate linkage breaks down at molding temperatures and reforms upon cooling thereby allowing an easily moldable thermoplastic urethane polyester which, after molding, will maintain its shape and have characteristics of a thermoset material.
Additionally, the use of the siloxane polymer improves cer-tain physical properties of the reaction product such as tensile and modulus of elasticity.

Description

~067241 BACKGROUND OF THE INVENTION
Field of the Invention Thls lnvention relates to thermoplastlc polyester-urethane molding composltions having certaln advantageous molding and physical properties for use ln sealing mechanisms where low compression set and good physical properties are requlred.
Descrlption of the Prlor Art Ep~ilon-caprolactone is known to polymerize wlth a polyhydric alcohol or a glycol-type materhal to form a hydroxy terminated polyester which, when mixed along with a dlol chain extender and a diisocyanate of the organic type, can be used to form relatively long chain polyester-poly-urethane polymers. Such polymers are presently known in the industry to be useful in many applications including in~ectlon and compression molding.
Exemplary of art using caprolactones is U. S.
Patent 3,658,756 which discloses the use of a caprolactone hydrolyzate or alcoholizate which is reacted with a glycol to form a polyester material. Such polyester material is then reacted with an organic diisocyanate and a chain extender such as a glycol material to form a polyester-urethane material.
It is also known bo utilize excess ratios of diisocyanate to isocyanate-reactable hydroxyl groups in the ~ 2 ~ p~ f~
~ polyester-polyurethanes in order to form ~}h~ih~s~e cross-llnking bonds, More specifically, the excess isocyanates can react through the carbon atom of such isocyanate to the nltrogen atom in the urethane grouping in the polyester-

- 2 -q~

polyurethane thereby formlng the allophonate cros~-links.
B a//oph It has been found that such ~llophonate llnkages break down at relatively high temper~ture~ and re~orm upon coollng forming a materlal which ls thermosetting ln charac-ter. At the higher temperature the allophonate linkage can break or be severed allowing the material to possess more o~
the thermoplastic properties which enhance molding operations.
However, I have found that, ln addition to the above use o~ the epsllon-caprolactone with chaln extenders and dlisocyanates and the use of excess diisocyanate to produce Q//o h~n~tc nll ~ho~*c linkages, unexpected lmprovement in physlcal properties can rçsult when there is incorporated in the reactant mixture an organlc siloxane polymer. Such polymer provldes and also increa~e~ the physlcal properties o~ the molded product. In a specific instance such addition will lncrease tensile strength, elongation percentage and a 100 and 300% modulus elasticity properties.
SUMMARY OF THE INVENTION
The present invention can be summarlzed as a thermoplastic urethane having low compression set and high elastlc modulus comprising the reaction product of a poly-(epsllon-caprolactone) polymer, a hydroxy terminated chain extender, an organic diisocyanate and a siloxane polymer.
In a broad embodiment my invention relates to a thermoplastic urethane having low compression set and high elastic modulus comprising the reaction product of a poly(epsilon-caprolactone) polymer having the ~ollowing general rormula:

. ,~

~ ~067Z41 o ' . o ,. . ..
- H t O - (CH2)5 - C ~ O - R - 0 ~ C - (CH2)5 - 0-~ H
wherein R ls alkyl, alkenyl or aryl having ~rom one, two and slx carbon atoms respectively, to about 10 carbon atoms; a hydroxy terminated polyol; an organic dlisocyanate; and a sl10xane polymer having the followlng general ~ormula:

~ si - o - ~i - o Rl R
wherein Rl ls alkyl, alkenyl or aromatic; havlng a molar ratio o~ lsocyanate groups to isocyanate-reactable hydroxy group of from about 1.05 to about 1.3.
DETAILED DESCRIPTION OF THE INVENTION
The present improved composltion comprlses a thermoplastic polyester-polyurethane which has low compresslon -set and high elastic modulus comprising the reactlon product Or ~our materials o~ which three enter into chem1cal.re.ac-tlons to form a polyester-polyurethane compositlon having ._ 4//~k~,?at~
¦ ~ 20 ~ll~e~a~e cross-links. The ~ourth material ~s ansiloxane polymer not thought to enter into reaction wlth the other three components.
One o~ the reactants used to produce thermoplastic polye~ter-polyurethane is a poly(epsilon-caprolactone) polymer which is produced by the reaction of epsilon capro-lactone and glycol or polyhydric alcohol. Speci~lcally such reaction mechanism ls shown in the equation below:
,- ..
+ HOROH-H~O-(CH2)s-C~x O-R-O-~C-(CH2)s-O~y H

~ 1067Z~
where x and y can vary depending on the ratio of the reactants and R can be alkylJ alkenyl, aryl or other slmilar type - materlal. In a pre~erable lnstance the R is alkyl havln~ a reasonably low molecular weight.
Poly(epsilon-c~prolactone) can be purchased ~rom the Union Carblae Corporatlon, Chemical and Plastics Divlslon.
They gene~ally are referred to under the registered trademark of "NIAX" polyols and have product identi~lc~tlons such as D-510, D-520, D-540 and D-560. The average molecular we~ght and other physlcal properties Or such polyols can vary de-pen~ing upon method o~ productlon, the ratio of the reactants etc. Speclflcally the D-510 polyol has an average molecular welght of 530, the D-520 polyol has a molecular welght of about 830, the D-540 polyol has a molecular welght o~ about 1,250 while the D-560 polyol ha~ a molecular weight of approximately 2,000.
Another or the reactants used to produce polyester-polyurethane is a hydroxy termlnated polyol, more typically referred to as a chain extender. Such materials can react with the epsilon caprol~ctone which has been reacted wlth a glycol or dihydric alcohol to ~orm a polyester-polyurethane polymer. Speci~ically, the hydroxy terminated polyols such a~ lower alkyl glycols, for example, ethylene glycol, 1,4 butane diol, di-ethylene glycol, propylene glycol or the like are preferred. It is especlally preferred that the hydroxy terminated polyols h~ve no pendant hydroxyl groupings present wlthln the chaln other than those at the termlnal or end por-tlons of the polyol to prevent cross-linking between the polyester-polyurethane chalns through such pendant hydroxy i067~41 grouplngs. It is preferred that 1,4 butane diol be utilized - as the chain extender.
me third reactant utilized to produce the above polyester-polyurethane polymer is a suitable organic diisocyanate selected ~rom 2,4 toluene diisocyanate, 2,6 toluene dilsocyanate, 1,5 naphthalene diisocyanate, 1,4 di-ethyl benzil beta-diisocyanate~ 4,4 diphenyl methane diisocyanate, toluene diisocyanates or other similar type aromatic, aliphatic or cyclo aliphatic diisocyanates.
- 10 The ratio of isocyanate to hydroxyl groups in the reactlon mixture should be from about 1.05:1 to about 1.3:1 or greater. In a preferred instance, the ratio of isocyanate groups to isocyanate-reactable hydroxy groups should vary withln the range of from about 1.05:1 to ~bout 1.15:1.
Such ratios of the diisocyanate to the hydroxyl groups are . c~//o~
preferred in order to cause formation of the all~pholiate cross-linking mechanism. Such-mechanism is shown in the equation below and is thought to take place at the ni~rogen atom of the urethane segment of the polyester-polyurethane polymer.
O

{- ~ - 0 - C - N - R
C = O
NH
R
NH
C= O

O

In the above equation the vertical cross-linking member is referred to as allophanate linkage.
The allophanate breaks down at molding temperatures forming a diisocyanate material and reforms upon cooling.
Accordingly, by utilizing a controlled excess quantity of diisocyanate it is possible to produce a material which, at high molding temperatures, is essentially thermoplastic (sub-stantially no cross-linking occuring between the polyester-polyurethane chains). After cooling the allophanate linkage reforms causing cross-linking to take place between the long polyester-polyurethane chains giving the molded product advantages over comparable polyester-polyurethane materials which do not contain the allophanate linkage.
The fourth component of the claimed composition is a siloxane polymer which is generally represented by the recurring structural formula as shown below:
R
[ si - O
R

wherein R is generally an alkyl of low molecular weight. The~
siloxane polymer as shown above is not thought to enter into a chemical reaction with the other three components of the present composition. In some instances the R grouping above may be aryl or alkenyl or combinations of alkyl, aryl or alkenyl. It may also be partially or totally substituted with halogens or similar materials.
The siloxane polymer improves the tensile and elon-gation properties of the molded product. Such improvement in properties is unexpected since the siloxane polymer is not 1067~

.
thought to enter into a chemlcal reaction with the other three components and accordlngly would be expected to degrade the phy~ical properties of the produced polyester-polyurethane material.
Depending upon the physical properties required for the molded compositlon, pure reactants or mixtures thereof may be used to produce the claimed composition.
In preparing the polyester-polyurethane polymer claimed herein~ the poly(epsilon-caprolactone~ polymer should be present as from abou~ 7.5 to about 13 mole percent o~ the total reactants. Of course, this value will vary depending upon the particular poly(epsilon-caprolactone) polymer utllized but, when using approximately 50-50 mole o~ NIAX
polyolæ D-560 and D-540, it is pre~erred that roughly 10.5-mole percent of the reactants be these two components.
- The hydroxy terminated polyol can be present any-where fro~ about 33 to about 41 mole percent of the reactants.
Such hydroxy termlnated polyols, commonly referred to as chain extenders, preferably vary from around 35 to about 39 or even more pre~erably around ~7 mole percent of the total moles of reactantsO
The diisocyanate of the organic type can vary anywhere ~rom about 48 to about 57 mole percent of the total moles of the reactants and pre~erably should be somewhere around 52 mole percent of the total moles of reactants. It i~ preferable to regulate elther the quantitie~ of the poly(epsilon-caprolac-tone) polymer, the hydroxy terminated polyol or the organic dilsocyanate in order to maintain a ratio of isocyanate groups to the isocyanate-reactable hydroxy groups of 106724~ -anywhere ~rom about 1.05:1 to about 1.3:1. An even more preferable range-of such ratios can be from about 1.05:1 to about 1.15:1.
The siloxane polymer as described above should be present anywhere from a few tenths o~-a weight part per hundred to as many as 1 part per hundred by weight o~ the total reabtants.
In produclng the reactlons product of the above components various procedures can be utilized.
In a preferable instance the poly(epsilon-capro-lactone) polymer can be heated at about 100C and degassed to remove dissolved gases and water vapors therefrom. Similarly, the hydroxy termlnated polyols such as 1~4 butane diol can be degassed either at the elevated temperature or at room temperature. The poly(epsilon-caprolactone) polymer can be heated to about 150C and the required amount of the hydroxy termlnated polyol can therea~ter be added to the mixture.
The material can be mixed for a few minutes and then a pre-weighed quantity o~ the organic diisocyanide can be added and mixed very vigorously. mereafter the mixture can be cast into a mold, cured ~or approximately 3 to 3 1/~ hours at 300F and therea~ter granulated. The granulated polymer can then be processed by thermoplastic processing equipment.
Other methods o~ producing such polymers can be used.
me ~ollowing examples are presented to lllustrate the specl~ic embodiments Or ~he compositions of this invention and should not be utillzed to unduly restrict the scope of - the claims.
_ g _ ~

EXAMPLE
In this example two polymeric reactant products were produced using substantially identical processing condi-tions except that one of the compositions produced (composi-tion B) had added to it approximately 0.5 parts per hundred by weight of Dow Corning siloxane polymer DC 200 (trademark), generally referred to as dimethyl siloxane polymeric material.
The reaction procedures were as follows: Polyol D-560 and D-540 were heated at 100C and degassed for one hour at 5 mm of mercury. The 1,4 butane diol was degassed at room temperature for one hour. The mixture of D-560 and D-540 NIAX polyols were then heated to approximately 140 to 150C
and the required amount of the hydroxy terminated polyol (1,4 butane diol) was added to the polyol mixtures and mixed very thoroughly for 5 minutes. The predetermined quantity of diphenylmethane diisocyanate was then added and the ma-terial was mixed very vigorously and thereafter cast into a mold. The material was cured for approximately 3 to 3 1/2 hours at 300F then granulated.
Injection molded samples of the granulated polymeric materials produced above were then used to make test bars which were tested for various properties such as hardness, tensile strength, elongation and tensile modulus at 100 and 300% modulus.
The table below illustrates the differing proper-ties for composition A and composition B produced as de-scribed above.

'A7 -lo-.. . .

.:
COMPONENT COMPOSITIONS, MOLE %
A B
Polyol D-560 ~ ~.3 ~ ~.3 Polyol D-540 4.2 4.2 1,4 Butane diol 37.0 37.o 1,4' Diphenylmethane diisocyanate 52.4 52.1~
Siloxane polymer - 0.5 (by wt.) ~OTAL 100.0 100.0 PHYSICAL PROPERTIES A B

Hardness (Shore A) 93 ~ 92 Tensile (ASTM 41~), psi 6010 ~3 100% modulus, psi 1520 1830 300~ modulus, psi 3240 3930 Elongation, ~ 440 475 Rebound (ASTM D-2632) 30 28 Compresslon Set (ASTM D-1238 method B, 70 hrs. at 158F)29 30

Claims (4)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:
1. A plastic molding composition exhibiting thermo-plastic properties at molding temperatures and thermo-set properties at room temperature which comprises A. The reaction product of:

1. from about 7.5 to about 13 mol percent of a poly(epsilon-caprolactone) polymer having the general formula:

wherein R is alkyl, alkenyl aryl having from one to 10 carbon atoms, where x and y can vary depending on the ratio of the reactants.
2. from about 33 to about 41 mol percent of a lower alkyl glycol, and 3. from about 48 to about 57 mol percent of an organic diisocyanate;
and having a molar ratio of isocyanate groups to isocyanate reactable hydroxy groups of from about 1.05 to 1.15; and B. from about 0.3 to about 1.0 parts per 100 parts by weight of said reaction product of a siloxane polymer having the following general formula:

wherein R1 is alkyl, alkenyl or aromatic.

2. Composition according to Claim 1 wherein said lower alkyl glycol comprises: HO(CH2)4OH.

3. Composition according to Claim 1 wherein said organic diisocyanate comprises 4,4-diphenylmethane diisocyanate.

4. Composition according to Claim 1 wherein R1 is methyl.