CA1043939A - Flexible automobile exterior body parts produced from poly(oxypropylene) glycol based polyurethane elastomer - Google Patents
Flexible automobile exterior body parts produced from poly(oxypropylene) glycol based polyurethane elastomerInfo
- Publication number
- CA1043939A CA1043939A CA211,254A CA211254A CA1043939A CA 1043939 A CA1043939 A CA 1043939A CA 211254 A CA211254 A CA 211254A CA 1043939 A CA1043939 A CA 1043939A
- Authority
- CA
- Canada
- Prior art keywords
- poly
- elastomer
- molecular weight
- oxypropylene
- polyol
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
- C08G18/00—Polymeric products of isocyanates or isothiocyanates
- C08G18/06—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen
- C08G18/28—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen characterised by the compounds used containing active hydrogen
- C08G18/40—High-molecular-weight compounds
- C08G18/48—Polyethers
- C08G18/4833—Polyethers containing oxyethylene units
- C08G18/4837—Polyethers containing oxyethylene units and other oxyalkylene units
- C08G18/4841—Polyethers containing oxyethylene units and other oxyalkylene units containing oxyethylene end groups
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B62—LAND VEHICLES FOR TRAVELLING OTHERWISE THAN ON RAILS
- B62D—MOTOR VEHICLES; TRAILERS
- B62D29/00—Superstructures, understructures, or sub-units thereof, characterised by the material thereof
- B62D29/04—Superstructures, understructures, or sub-units thereof, characterised by the material thereof predominantly of synthetic material
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
- C08G18/00—Polymeric products of isocyanates or isothiocyanates
- C08G18/06—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen
- C08G18/08—Processes
- C08G18/10—Prepolymer processes involving reaction of isocyanates or isothiocyanates with compounds having active hydrogen in a first reaction step
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
- C08G2120/00—Compositions for reaction injection moulding processes
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10S264/00—Plastic and nonmetallic article shaping or treating: processes
- Y10S264/77—Processes of molding urethanes
Abstract
ABSTRACT OF THE INVENTION
Flexible automobile exterior body parts are molded from A polyurethane elastomer prepared from a reaction mixture comprising:
a) a polymeric diol selected from the group con-sisting of poly(oxypropylene) glycol and ethylene oxide "tipped" poly(oxypropylene) glycol of molecular weight of from about 1750 to about 2500;
b) methylenebis(4-phenylisocyanate);
c) 1,4-butanediol.
The invention also relates to this polyurethane elastomer.
Flexible automobile exterior body parts are molded from A polyurethane elastomer prepared from a reaction mixture comprising:
a) a polymeric diol selected from the group con-sisting of poly(oxypropylene) glycol and ethylene oxide "tipped" poly(oxypropylene) glycol of molecular weight of from about 1750 to about 2500;
b) methylenebis(4-phenylisocyanate);
c) 1,4-butanediol.
The invention also relates to this polyurethane elastomer.
Description
3~
~lexible exterior body parts ~`or automobiles, including parts associate~ with energy-absorbin~ bumper systems such as sight shields, fender extensions and full fascia ~ront and rear ends, require a material with a particular set of properties. The material must bc capable of ~lexing under impact and then returning to its original shape. Therefore, it must be elastomeric in nature. It must have strength as typified by high tensile strength and high tear strength.
In addition, there are two more stringent require-ments. It must be capable of withstanding dynamic impact at -20~ F. and it must be resistant to distortion at 250 F~
The latter requirement is imposed by t~rpical conditions under which painted pieces are dried.
One class of materials which has been used ~or this purpose is polyurethane elastomers. Polyuretha~e elastomers are "block" type polymers resulting from the reaction of a polymeric diol of molecular weight of from about 500 to 5000 with a diisocyanate and a low molecular weight difunctional compound commonly referred to as the "chain extender". The chain extender has a molecular weight below 500 and generally below 300.
The polymeric diol is recognized as the "soft"
segment of the elastomer, conferring elasticity and soft-ness to the polymer. Typically, this component has a molecular weight of about 1000 to 2000 and may be a poly-(alkylene ether) glycol such as poly(tetramethylene ether) glycol or poly(oxypropylene) glycol, a polyester diol, a polycaprolactone diol or polybutadiene diol.
The combination of the diisocyanate and the chain .. ~. . . .
.
1~)4~
extender comprises the h~rd' ~e~ment OI the elastomer, contributing rigidity and strength Typical diisocyfln~tes include 2,4-tolylene diisocyRnate and methylenebis(4-phenylisocyanate). The chain extenders are typically diamines or diols. T~pical diols which may be used are listed, for example, in U.S. Patents 3,233,025 (col 4, lines 20-26), 3,620,905 (col. 2, lines 53_5a) and 3,718,622 (col. 2, lines 10-18).
While polyurethane elastomers as a class have excellent tear strength and tensile strength and can be designed to the required modulus and elongation, not all polyurethane elastomers can meet the two requirements of low temperature impact resistance and resistance to heat distortion. In fact, a polyurethane elastomer b~sed on poly(oxypropylene) glycol as the polymeric diol and 1,4-butanediol as the chain extender has not yet been used ~or flexible automobile body parts because of the previous def~ciencies of such an elastomer in these two areas. It is generally recognized (N. E. Rustad and R. G. Krawiec, Rubber Age, Nov. 1973, pp. 45-49) that elastomers based on poly(oxypropylene) glycols have poorer low temperature properties than those based on poly(tetramethyleneether) glycol, another polyol used in polyurethane elastomers but higher in cost. One known way to improve the low temperature properties is to increase the molecul~r weight of the polyol while keeping the mol ratios of ingredients constant.
Unfortunately, while the low temperature properties are indeed improved, the hardness and rigidity are normally lowered markedly. See Table II, page 47 of the Rustad et al. article.
J
I have now discovered that~ by the use o~ a unique set o~ formulation variables, it is possible to design a poly(oxypropylene) ~]ycol based elastomer suitable for ~utomobile flexible e~terior body parts.
Such a material can be prepared ~rom a polyol of approxi-mately 1750 to 2500 molecular weight, methylenebis(4-phenylisocyanate) and 1,4-butanediol, the molar ratio of butanediol to polyol being about 3.0:1 to about 9.0:1.
It was most unexpected to be able to make hard elastomers with the necessary high and low temperature properties - from poly(oxypropylene) glycol.
While the specific formulation ~or a poly(oxy-propylene) glycol based elastomer necessary to achieve the proper combination of properties has not been described previously, there has appeared a paper describing a similar concept applied to flexible automobile body parts using elastomers based on polycaprolactone diol as the polyol This paper, by F. E. Critchfield, J. V. Koleske and C. G.
Seefried, Jr., was presented at the Automobile Engineering Meeting o~ the Society of Automotive Engineers in Detroit, Michigan during the week of May 14-18, 1973. Summarizing their data on the polycaprolactone diol based elastomers, the authors stated "~or automotive elastomer applications, the thermoplastic polyurethanes based on an approximately 2000 Mn diol are more desirable since they show less modulus-temperature dependence in the use region." They also concluded: "Apparently at similar hard segment con-centrations, the molecular weight Or the urethane polymer soft segment has a greater effect on the temperature dependence of physical properties than the molecular length _ 3 _ 10~
of the hard se~ent seqllences." The~ ~ttributed th~
unique properties of these matelials to l~e the l~e~ult o~`
incompatibility on a microscopic scale between the hard and soft segments. In turn, "Incompatibillty quite probably is due to the molecular weight of the soft segment being high enough to be immiscible in a thermodynamic sense with the hard segment."
EXPOSITION OF THE INVENTION
Completely independently of the paper last mentioned above, I have found that polyurethane elastomers suitable for the preparation of flexible automobile exterior body parts may be obtained from the reaction o~ a mixture comprising:
a) a polymeric diol selected Prom the group consisting ~ poly(oxypropylene) glycol and ethylene oxicle "tipped"
poly(oxypropylene) glycol Or molecular weight ~rom about 1750 to about 2500 (preferably about 2000);
b) methylenebis(4~phenylisocyanate);
c) 1,4-butanediol.
Suitable elastomers are those which have a hardness of about 40 to 55 Shore D, preferably 45 to 50 Shore D.
They should have an elongation greater than 300~, an ultimate tenslle strength o~ about 3000 psi or greater and a Die C
tear strength of 500 pli or greater.
Painted parts made from these elastomers must remain intact under a 5 MPH impact at -20 F. To simulate the dynamic conditions involved in a 5 MPH impact at -20 F., a drop impact test system was developed. The unit consists basically of a vertical guide tube, a drop weight of appropriate design and associated instrumentation.
10~3~3~
Polymers to be evaluated were molded into 2" x 6" x o.o8" specimens, which were conditioned in an environmental chamber to -20 F. and then fitted into ~wo slots 3 inches apart so that the s~mple formed an inverted "U" with a total flexed height of 2 inches. The sample was impacted at its center line with a force of 50 ft. lbs., the weight traveling at 5 MPH at impact.
Drop height above the top of the sample was 38 inches.
The drop weight is an 18 inch long cylinder weighing 16 lbs, It is 2.5 inches in diameter for 16.5 inches of its length and then tapers to a blunt end, which is the striking surface.
Polymers with inadequate low temperature impact resistance invariably fractured in this test. This test correlates well with the automobile manufacturer's testlng where full size parts are made and mounted on a car or a portion o~ a car. After cooling to -2~ F., the full size part is hit with a pendul~um weight which is traveling at 5 MPH.
Parts made from these elastomers must also with-stand paint oven temperatures of 250 ~. without objection-able shrinkage or distortion. To evaluate materials for heat distortion characteristics, a sag resistance test (Heat Test O'S) was developed The apparatus consists of a jig to hold a 2" x 6" x o.o8" injection molded sample in a horizontal plane. The sample is mounted with 4 inches suspended beyond the edge of the cla~p. The jig with the sample is then placed in an oven pre-heated at 250 F.
for 1/2 hour. The amount of sag is the difference in height ~rom the end of the sa~nple to a horizontal plane before and , ,. - . ,, ., - - - . - . .
- lQ4~'3 after exposure to heat. Experience with a material that was acceptable to automobile manufacturers has shown that polyurethane elastomers with a sag less than 2.0 inches by this test will perform satisfactorily ~n paint bake ovens used to cure painted large autQmotive parts.
To demonstrate the ef~ect of the polyol molecular weight on the required properties, two elastomers were prepared at a hardness of about 40 Shore D. One elastomer was prepared with a 1000 molecular weight polyol, the second from a 2000 molecular weight polyol. Both polyols were poly(oxypropylene) glycols "tipped" with ethylene oxide. The ethylene oxide content was about 10% by weight, with about 50% of the polyol hydroxyl groups being primary.
These materials are described in Example 1. It is shown that the elastomer based on the 1000 molecular weight polyol failed the low temperature impact test while the material based on the 2000 molecular weight polymer passed the test.
In a similar manner, two elastomers were prepared at a hardness o~ 45 Shore D and injection molded as described in Example 2. The polymer based on the 1000 molecular weight polyol failed the low temperature impact and heat distortion tests, while the polymer based on the 2000 molecular weight polyol passed both tests.
A 50 Shore D elastomer meetlng the required properties is described in Example 3.
- An elastomer based on an untipped poly(oxypropylene) glycol of 2000 molecular weight is described in Example 4.
While the preferred molecular weight of the polyol is about 2000, it is recognized that the molecular weight ~.
-~o~
may be somewhat below or above this fi~ure ancl still ~ive acceptable elastomers. The lower limit of acceptable molecular weight is 1750, with an elastomer prepared ~rom 1500 molecular weight polyol being not completely acceptable with respect to low temperature lmpact (Example 5).
Similarly, the upper limit of acceptable molecular weight is 2500, l'olymer based on 3000 molecular weight polyol has lowered physical properties (Example 6). This is believed to be due to separation of soft and hard phases early enough in the polymerization to immobilize reactive end groups and thereby inhibit chain extension.
The molar ratio of chain extender to polyol which may be used depends on the molecular weight o~ the polyol.
It ranges from 3.0:1 ~or a 1750 molecular weight polyol to 9.0:1 for a 2500 molecular weight ~olyol. The pre~erred molar ratio of chaln extender to polyol for a 2000 molecular weight polyol ranges ~rom 3.5:1 to 5.0:1, ~ith 4.0:1 - 4,5:1 being preferred. The NCO/OH ratio used to prepared the elastomer may range from 0.95 to 1.2, with 1.00 to 1.05 being preferred.
- Although the elastomer may be prepared by a "one shot" technique in which the polyol, chain extender and isocyanate are reacted together in one step, this me-thod is not preferred because of separation of the reacting mass into incompatible phases resulting from the difference in reactivity between the polyol and the chain extender.
Although this may be overcome to a large extent by the careful choice of a catalyst, it is preferred to prepare the elastomer by the prepolymer process in which the polyol is first reacted with the diisocyanate and subsequently reacted with -the chain extender in a separate step. A
., .
- .. ~.: . ;:
lQ~
catalyst ~ay Ol~ may not ~e used as desired. Some exc~mples Ol uselul ca~al~sts are N-methyl-~orpholine, N-ethyl-morpholine, tliethyl amine, trie-thylene ~iamine I (Dabco), N,N'-bis(2-l~d~o~ylprop~1)-2-methyl pipera~ine, ¦ dimetl~l ethanol amine, tertiary amino alcohols, tertiar~
I ester amines, stannous octoate~ dibut~l tin dilaurnte and ¦ the like.
"Tipping" of poly(oxypropylene) glycol with ethylene oxide provides the glycol with primary hydroxyl end groups. These "tipped" diols provide greater reactivity with diisocyanates when such is desired. This technique is described in "Advances in Urethane Science and Techno-logy", by K.C. Frisch and S.L. Reegan, Technomic Publishing Company~ Westport, Conn., 1973, pages 188-193, Two elastomers, one from a 1000 molecular weigh~
~ polyol and one from a 2000 molecular weight polyol, were ¦ prepared in the following manner. All parts are by weight.
Elasto~er A
. .
Three hundred sixty parts of a 1040 molecular weight poly(oxypropylene3 glycol tipped with ethylene oxide (50~0 primary hydroxyl~ were dried at 100 C. under vacuum (2 mm.
Hg) for 30 minutes. The polyol then was cooled to 50 C.
under a blanket of dry nltrogen and 260 parts of 4,4'-methylenebis(phenyl isocyanate) were added. The mixture I then was heated at 80 C. for two hours under dry nitrogen.
Analysis of the resultant prepolymer showed it to have an amine equivalent of 472.
- 8 _ i . , .
To 150 parts 01 the prepolymer At; 110`' C. were added 13.6 parts of 1,4-butanediol at 60 C. The reactants were well mixed. The product was compression molded into a 8" x 8" x o.o8" plaque and cured ~or one hour at 120 C.
The cured elastomer was then postcured overnight at 110 C.
The ratio of equivalents of polyol/chain extender/diiso-cyanate in the final elastomer was 1/1.9/3.
Elastomer B
.
Using an identical procedure, 316 parts of a 2080 molecular weight polyol of the same structure were allowed to react with 179 parts of 4,4'-meth~lenebis(phenyl isocyanate). The a~ine equivalent of the resultant pre-polymer was 466. Similarl~, 150 parts of the prepolymer were cured with 13.7 parts o~ 1,4-butanediol. The ratio f equivalents of polyol/chain extender/diisocyanate in the final elastomer was 1/3.5/4,7.
Physical Properties The properties o~ the elastomers were obtained.
Elastomer A Elastomer B
Hardness, Shore D 40 40 100% Modulus 860 1000 300% Modulus 1740 1560 Tensile Strength, psi 3590 3480 Elongation, ~ 540 690 Die C Tear, lbs./in.458 533 -20 F. Impact FAIL PASS
The results show that Elastomer B meets the auto-motive low temperature requirement whereas Elastomer A
does not.
~ !
.
In a manner similar to that described in Example 1, the 1040 molecular weight polyol, butanedlol and 4,4'-methylenebis(phen~yl isocyanate) were allowed to re~ct at an equivalents ratio of 1/2.38/3.50 The product was open cast and cured for 20 minutes at 149 C. It was then diced and injection molded into 2" x 6" x o.o8" plaques.
(Elastomer C) Similarly, the 2080 molecular weight polyol was converted to an elastomer using a 1/4.27/5.50 equivalents ratio (Elastomer D).
Physical properties of the elastomers were as follows:
Elastomer CElastomer D
Hardness, Shore D 45 L~5 100% Modulus 1400 1470 300% Modulus 2430 2120 Tensile Strength, psi 3280 2960 Elongation, ~ 400 500 Die C Tear, lbs./in. 550 720 -20 F. Impact F~IL PASS
Heat Sag, inches ~`2" 1 1/2"
The results show the superiority of Elastomer D
over Elastomer C in both low temperature impact strength as well as in heat sag resistance. It was also noted that Elastomer C stuck badly with some distortion when injection molded, while Elastomer D molded without difficulty.
In a manner similar to that described in Example 2, a 2000 molecular weight poly(oxypropylene) glycol tipped .. . . .
with ethylene oxide (50~ primary hydroxyl) was converted to an elastomer using a polyol/1,4-butanediol/4,4'-methylenebis(phenyl isocyanate) equivalents ratio of 1/4.7/6Ø
Physical properties of the in~ection molded elastomer were as follows.
Hardness, Shore D 50 100% Modulus 1880 300~ Modulus 2940 Tensile Strength, psi 3390 Elongation, % 400 Die C Tear, lbs./in. 810 -20 F. Impact PASS
Heat Sag, inches 1 l/li~"
In a manner similar to that described in Example 2, 2000 molecular weight poly(oxypropylene)glycol was con-verted to an elastomer using a polyol/1,4-butanediol/4,4l-methylenebis(phenyl isocyanate) equi~alents ratio of 1/4.27/5.5.
Physical properties of the inje~ti~n molded elastomer were as follows:
Hardness, Shore D 43 100~ ~odulus 1820 : 25 300% Modulus 2810 Tensile Strength, psi 3200 Elongation, % 400 : Die C Tear, lbs./in. 730 -20 F. Impact PASS
Heat Sag, inches 1 10/16"
-- 11 -- ~.
.
- . . . . . .
.. . ' ~ ' '- ., ' ' ' " ~ ' - '~ ' ' ' ' -1~43~
This example demonstrates that a 2000 molecular weight untipped poly(ox~propylene) glycol produces an elastomer with acceptable properties~
In a manner slmilar to that described in Example 1~ a 1500 molecular wei~ht po:Ly(oxypropylene) glycol tipped with ethylene oxide (5~,~ primary hydroxyl) was converted to an elastomer using a polyol/1,4-butanediol/4,4'-methylenebis(phenyl isocyanate) equivalents ratio of 1/3.3/4.5. Two compression molded samples had the following properties:
Sam~le A Sa~ple B
Hardness, Shore D 40 40 100~ Modulus 1480 1480 3% Modulus 3090 3070 Tensile Strength, psi4560 4300 Elongation, ~ 420 370 Die C Tear, lbs./in.690 632 -20 F. Impact PASS FAIL
Although the properties were generally acceptable, the failure o~ one sample in the low temperature impact test indicates that 1500 molecular weight for the polyol segment is not completely acceptable with regard to low temperature properties.
In a manner similar to that described in Example 1, a 3000 molecular weight poly(oxypropylene) glycol was converted to an elastomer using a polyol/1,4-butanediol/4, methylenebis(phenyl isocyanate) equivalents ratio of .. - -.. :
~f~ 3~3 1/7.6/9Ø Because of the relatively high molecular weight of the polyol and the high level o~ equivalents of chain extender and isocyanate, this system turned white early in the cure and tended to ~ive poor "cheezy"
cures. This is believed to ble due to separation of soft and hard phases early enough in the polymerization to immobilize reactive end groups and thereby inhibit chain extension One sample prepared, using about 0.1 part of triethylene diamine catalyst per 100 parts of prepolymer, gave the following compression molded properties:
Hardness, Shore D 35 100% Modulus 1370 300% Modulus Tensile Strength, psi2550 Elongation, % 280 Die C Tear, lbs./in. 558 The results show that a 3000 molecular weight for the polyol segment is not completely acceptable with respect to attaining desirable strength properties and elongation.
The automobile flexlble body parts, which are a desired end-product of this invention, are fabricated by injection molding using the already prepared poly-urethane elastomer as the molding material. In this method, the elastomer is made into small dice or pellets suitable for feeding to in~ection molding machines. Using the same preformed material, a part may also be prepared by extrusion techniques including profile extrusion and sheet extrusion followed by vacuum forming.
~ - 13 -. ~ . . .
.. - . - .
.
~ 3~
Alternatively, the part may be formed by the method termed "liquid reaction molding", in which the reactants are rapidly injected into a mold wherein they cure to form the shaped elastomeric article directly.
In this method, the polyol, chain extender and diisocyanate may be reacted in one step (on.e shot method) or the polyol and diisocyanate may be prereacted and then injected along with the chain extender to form the molded article (pre-. polymer method).
- 13a ---
~lexible exterior body parts ~`or automobiles, including parts associate~ with energy-absorbin~ bumper systems such as sight shields, fender extensions and full fascia ~ront and rear ends, require a material with a particular set of properties. The material must bc capable of ~lexing under impact and then returning to its original shape. Therefore, it must be elastomeric in nature. It must have strength as typified by high tensile strength and high tear strength.
In addition, there are two more stringent require-ments. It must be capable of withstanding dynamic impact at -20~ F. and it must be resistant to distortion at 250 F~
The latter requirement is imposed by t~rpical conditions under which painted pieces are dried.
One class of materials which has been used ~or this purpose is polyurethane elastomers. Polyuretha~e elastomers are "block" type polymers resulting from the reaction of a polymeric diol of molecular weight of from about 500 to 5000 with a diisocyanate and a low molecular weight difunctional compound commonly referred to as the "chain extender". The chain extender has a molecular weight below 500 and generally below 300.
The polymeric diol is recognized as the "soft"
segment of the elastomer, conferring elasticity and soft-ness to the polymer. Typically, this component has a molecular weight of about 1000 to 2000 and may be a poly-(alkylene ether) glycol such as poly(tetramethylene ether) glycol or poly(oxypropylene) glycol, a polyester diol, a polycaprolactone diol or polybutadiene diol.
The combination of the diisocyanate and the chain .. ~. . . .
.
1~)4~
extender comprises the h~rd' ~e~ment OI the elastomer, contributing rigidity and strength Typical diisocyfln~tes include 2,4-tolylene diisocyRnate and methylenebis(4-phenylisocyanate). The chain extenders are typically diamines or diols. T~pical diols which may be used are listed, for example, in U.S. Patents 3,233,025 (col 4, lines 20-26), 3,620,905 (col. 2, lines 53_5a) and 3,718,622 (col. 2, lines 10-18).
While polyurethane elastomers as a class have excellent tear strength and tensile strength and can be designed to the required modulus and elongation, not all polyurethane elastomers can meet the two requirements of low temperature impact resistance and resistance to heat distortion. In fact, a polyurethane elastomer b~sed on poly(oxypropylene) glycol as the polymeric diol and 1,4-butanediol as the chain extender has not yet been used ~or flexible automobile body parts because of the previous def~ciencies of such an elastomer in these two areas. It is generally recognized (N. E. Rustad and R. G. Krawiec, Rubber Age, Nov. 1973, pp. 45-49) that elastomers based on poly(oxypropylene) glycols have poorer low temperature properties than those based on poly(tetramethyleneether) glycol, another polyol used in polyurethane elastomers but higher in cost. One known way to improve the low temperature properties is to increase the molecul~r weight of the polyol while keeping the mol ratios of ingredients constant.
Unfortunately, while the low temperature properties are indeed improved, the hardness and rigidity are normally lowered markedly. See Table II, page 47 of the Rustad et al. article.
J
I have now discovered that~ by the use o~ a unique set o~ formulation variables, it is possible to design a poly(oxypropylene) ~]ycol based elastomer suitable for ~utomobile flexible e~terior body parts.
Such a material can be prepared ~rom a polyol of approxi-mately 1750 to 2500 molecular weight, methylenebis(4-phenylisocyanate) and 1,4-butanediol, the molar ratio of butanediol to polyol being about 3.0:1 to about 9.0:1.
It was most unexpected to be able to make hard elastomers with the necessary high and low temperature properties - from poly(oxypropylene) glycol.
While the specific formulation ~or a poly(oxy-propylene) glycol based elastomer necessary to achieve the proper combination of properties has not been described previously, there has appeared a paper describing a similar concept applied to flexible automobile body parts using elastomers based on polycaprolactone diol as the polyol This paper, by F. E. Critchfield, J. V. Koleske and C. G.
Seefried, Jr., was presented at the Automobile Engineering Meeting o~ the Society of Automotive Engineers in Detroit, Michigan during the week of May 14-18, 1973. Summarizing their data on the polycaprolactone diol based elastomers, the authors stated "~or automotive elastomer applications, the thermoplastic polyurethanes based on an approximately 2000 Mn diol are more desirable since they show less modulus-temperature dependence in the use region." They also concluded: "Apparently at similar hard segment con-centrations, the molecular weight Or the urethane polymer soft segment has a greater effect on the temperature dependence of physical properties than the molecular length _ 3 _ 10~
of the hard se~ent seqllences." The~ ~ttributed th~
unique properties of these matelials to l~e the l~e~ult o~`
incompatibility on a microscopic scale between the hard and soft segments. In turn, "Incompatibillty quite probably is due to the molecular weight of the soft segment being high enough to be immiscible in a thermodynamic sense with the hard segment."
EXPOSITION OF THE INVENTION
Completely independently of the paper last mentioned above, I have found that polyurethane elastomers suitable for the preparation of flexible automobile exterior body parts may be obtained from the reaction o~ a mixture comprising:
a) a polymeric diol selected Prom the group consisting ~ poly(oxypropylene) glycol and ethylene oxicle "tipped"
poly(oxypropylene) glycol Or molecular weight ~rom about 1750 to about 2500 (preferably about 2000);
b) methylenebis(4~phenylisocyanate);
c) 1,4-butanediol.
Suitable elastomers are those which have a hardness of about 40 to 55 Shore D, preferably 45 to 50 Shore D.
They should have an elongation greater than 300~, an ultimate tenslle strength o~ about 3000 psi or greater and a Die C
tear strength of 500 pli or greater.
Painted parts made from these elastomers must remain intact under a 5 MPH impact at -20 F. To simulate the dynamic conditions involved in a 5 MPH impact at -20 F., a drop impact test system was developed. The unit consists basically of a vertical guide tube, a drop weight of appropriate design and associated instrumentation.
10~3~3~
Polymers to be evaluated were molded into 2" x 6" x o.o8" specimens, which were conditioned in an environmental chamber to -20 F. and then fitted into ~wo slots 3 inches apart so that the s~mple formed an inverted "U" with a total flexed height of 2 inches. The sample was impacted at its center line with a force of 50 ft. lbs., the weight traveling at 5 MPH at impact.
Drop height above the top of the sample was 38 inches.
The drop weight is an 18 inch long cylinder weighing 16 lbs, It is 2.5 inches in diameter for 16.5 inches of its length and then tapers to a blunt end, which is the striking surface.
Polymers with inadequate low temperature impact resistance invariably fractured in this test. This test correlates well with the automobile manufacturer's testlng where full size parts are made and mounted on a car or a portion o~ a car. After cooling to -2~ F., the full size part is hit with a pendul~um weight which is traveling at 5 MPH.
Parts made from these elastomers must also with-stand paint oven temperatures of 250 ~. without objection-able shrinkage or distortion. To evaluate materials for heat distortion characteristics, a sag resistance test (Heat Test O'S) was developed The apparatus consists of a jig to hold a 2" x 6" x o.o8" injection molded sample in a horizontal plane. The sample is mounted with 4 inches suspended beyond the edge of the cla~p. The jig with the sample is then placed in an oven pre-heated at 250 F.
for 1/2 hour. The amount of sag is the difference in height ~rom the end of the sa~nple to a horizontal plane before and , ,. - . ,, ., - - - . - . .
- lQ4~'3 after exposure to heat. Experience with a material that was acceptable to automobile manufacturers has shown that polyurethane elastomers with a sag less than 2.0 inches by this test will perform satisfactorily ~n paint bake ovens used to cure painted large autQmotive parts.
To demonstrate the ef~ect of the polyol molecular weight on the required properties, two elastomers were prepared at a hardness of about 40 Shore D. One elastomer was prepared with a 1000 molecular weight polyol, the second from a 2000 molecular weight polyol. Both polyols were poly(oxypropylene) glycols "tipped" with ethylene oxide. The ethylene oxide content was about 10% by weight, with about 50% of the polyol hydroxyl groups being primary.
These materials are described in Example 1. It is shown that the elastomer based on the 1000 molecular weight polyol failed the low temperature impact test while the material based on the 2000 molecular weight polymer passed the test.
In a similar manner, two elastomers were prepared at a hardness o~ 45 Shore D and injection molded as described in Example 2. The polymer based on the 1000 molecular weight polyol failed the low temperature impact and heat distortion tests, while the polymer based on the 2000 molecular weight polyol passed both tests.
A 50 Shore D elastomer meetlng the required properties is described in Example 3.
- An elastomer based on an untipped poly(oxypropylene) glycol of 2000 molecular weight is described in Example 4.
While the preferred molecular weight of the polyol is about 2000, it is recognized that the molecular weight ~.
-~o~
may be somewhat below or above this fi~ure ancl still ~ive acceptable elastomers. The lower limit of acceptable molecular weight is 1750, with an elastomer prepared ~rom 1500 molecular weight polyol being not completely acceptable with respect to low temperature lmpact (Example 5).
Similarly, the upper limit of acceptable molecular weight is 2500, l'olymer based on 3000 molecular weight polyol has lowered physical properties (Example 6). This is believed to be due to separation of soft and hard phases early enough in the polymerization to immobilize reactive end groups and thereby inhibit chain extension.
The molar ratio of chain extender to polyol which may be used depends on the molecular weight o~ the polyol.
It ranges from 3.0:1 ~or a 1750 molecular weight polyol to 9.0:1 for a 2500 molecular weight ~olyol. The pre~erred molar ratio of chaln extender to polyol for a 2000 molecular weight polyol ranges ~rom 3.5:1 to 5.0:1, ~ith 4.0:1 - 4,5:1 being preferred. The NCO/OH ratio used to prepared the elastomer may range from 0.95 to 1.2, with 1.00 to 1.05 being preferred.
- Although the elastomer may be prepared by a "one shot" technique in which the polyol, chain extender and isocyanate are reacted together in one step, this me-thod is not preferred because of separation of the reacting mass into incompatible phases resulting from the difference in reactivity between the polyol and the chain extender.
Although this may be overcome to a large extent by the careful choice of a catalyst, it is preferred to prepare the elastomer by the prepolymer process in which the polyol is first reacted with the diisocyanate and subsequently reacted with -the chain extender in a separate step. A
., .
- .. ~.: . ;:
lQ~
catalyst ~ay Ol~ may not ~e used as desired. Some exc~mples Ol uselul ca~al~sts are N-methyl-~orpholine, N-ethyl-morpholine, tliethyl amine, trie-thylene ~iamine I (Dabco), N,N'-bis(2-l~d~o~ylprop~1)-2-methyl pipera~ine, ¦ dimetl~l ethanol amine, tertiary amino alcohols, tertiar~
I ester amines, stannous octoate~ dibut~l tin dilaurnte and ¦ the like.
"Tipping" of poly(oxypropylene) glycol with ethylene oxide provides the glycol with primary hydroxyl end groups. These "tipped" diols provide greater reactivity with diisocyanates when such is desired. This technique is described in "Advances in Urethane Science and Techno-logy", by K.C. Frisch and S.L. Reegan, Technomic Publishing Company~ Westport, Conn., 1973, pages 188-193, Two elastomers, one from a 1000 molecular weigh~
~ polyol and one from a 2000 molecular weight polyol, were ¦ prepared in the following manner. All parts are by weight.
Elasto~er A
. .
Three hundred sixty parts of a 1040 molecular weight poly(oxypropylene3 glycol tipped with ethylene oxide (50~0 primary hydroxyl~ were dried at 100 C. under vacuum (2 mm.
Hg) for 30 minutes. The polyol then was cooled to 50 C.
under a blanket of dry nltrogen and 260 parts of 4,4'-methylenebis(phenyl isocyanate) were added. The mixture I then was heated at 80 C. for two hours under dry nitrogen.
Analysis of the resultant prepolymer showed it to have an amine equivalent of 472.
- 8 _ i . , .
To 150 parts 01 the prepolymer At; 110`' C. were added 13.6 parts of 1,4-butanediol at 60 C. The reactants were well mixed. The product was compression molded into a 8" x 8" x o.o8" plaque and cured ~or one hour at 120 C.
The cured elastomer was then postcured overnight at 110 C.
The ratio of equivalents of polyol/chain extender/diiso-cyanate in the final elastomer was 1/1.9/3.
Elastomer B
.
Using an identical procedure, 316 parts of a 2080 molecular weight polyol of the same structure were allowed to react with 179 parts of 4,4'-meth~lenebis(phenyl isocyanate). The a~ine equivalent of the resultant pre-polymer was 466. Similarl~, 150 parts of the prepolymer were cured with 13.7 parts o~ 1,4-butanediol. The ratio f equivalents of polyol/chain extender/diisocyanate in the final elastomer was 1/3.5/4,7.
Physical Properties The properties o~ the elastomers were obtained.
Elastomer A Elastomer B
Hardness, Shore D 40 40 100% Modulus 860 1000 300% Modulus 1740 1560 Tensile Strength, psi 3590 3480 Elongation, ~ 540 690 Die C Tear, lbs./in.458 533 -20 F. Impact FAIL PASS
The results show that Elastomer B meets the auto-motive low temperature requirement whereas Elastomer A
does not.
~ !
.
In a manner similar to that described in Example 1, the 1040 molecular weight polyol, butanedlol and 4,4'-methylenebis(phen~yl isocyanate) were allowed to re~ct at an equivalents ratio of 1/2.38/3.50 The product was open cast and cured for 20 minutes at 149 C. It was then diced and injection molded into 2" x 6" x o.o8" plaques.
(Elastomer C) Similarly, the 2080 molecular weight polyol was converted to an elastomer using a 1/4.27/5.50 equivalents ratio (Elastomer D).
Physical properties of the elastomers were as follows:
Elastomer CElastomer D
Hardness, Shore D 45 L~5 100% Modulus 1400 1470 300% Modulus 2430 2120 Tensile Strength, psi 3280 2960 Elongation, ~ 400 500 Die C Tear, lbs./in. 550 720 -20 F. Impact F~IL PASS
Heat Sag, inches ~`2" 1 1/2"
The results show the superiority of Elastomer D
over Elastomer C in both low temperature impact strength as well as in heat sag resistance. It was also noted that Elastomer C stuck badly with some distortion when injection molded, while Elastomer D molded without difficulty.
In a manner similar to that described in Example 2, a 2000 molecular weight poly(oxypropylene) glycol tipped .. . . .
with ethylene oxide (50~ primary hydroxyl) was converted to an elastomer using a polyol/1,4-butanediol/4,4'-methylenebis(phenyl isocyanate) equivalents ratio of 1/4.7/6Ø
Physical properties of the in~ection molded elastomer were as follows.
Hardness, Shore D 50 100% Modulus 1880 300~ Modulus 2940 Tensile Strength, psi 3390 Elongation, % 400 Die C Tear, lbs./in. 810 -20 F. Impact PASS
Heat Sag, inches 1 l/li~"
In a manner similar to that described in Example 2, 2000 molecular weight poly(oxypropylene)glycol was con-verted to an elastomer using a polyol/1,4-butanediol/4,4l-methylenebis(phenyl isocyanate) equi~alents ratio of 1/4.27/5.5.
Physical properties of the inje~ti~n molded elastomer were as follows:
Hardness, Shore D 43 100~ ~odulus 1820 : 25 300% Modulus 2810 Tensile Strength, psi 3200 Elongation, % 400 : Die C Tear, lbs./in. 730 -20 F. Impact PASS
Heat Sag, inches 1 10/16"
-- 11 -- ~.
.
- . . . . . .
.. . ' ~ ' '- ., ' ' ' " ~ ' - '~ ' ' ' ' -1~43~
This example demonstrates that a 2000 molecular weight untipped poly(ox~propylene) glycol produces an elastomer with acceptable properties~
In a manner slmilar to that described in Example 1~ a 1500 molecular wei~ht po:Ly(oxypropylene) glycol tipped with ethylene oxide (5~,~ primary hydroxyl) was converted to an elastomer using a polyol/1,4-butanediol/4,4'-methylenebis(phenyl isocyanate) equivalents ratio of 1/3.3/4.5. Two compression molded samples had the following properties:
Sam~le A Sa~ple B
Hardness, Shore D 40 40 100~ Modulus 1480 1480 3% Modulus 3090 3070 Tensile Strength, psi4560 4300 Elongation, ~ 420 370 Die C Tear, lbs./in.690 632 -20 F. Impact PASS FAIL
Although the properties were generally acceptable, the failure o~ one sample in the low temperature impact test indicates that 1500 molecular weight for the polyol segment is not completely acceptable with regard to low temperature properties.
In a manner similar to that described in Example 1, a 3000 molecular weight poly(oxypropylene) glycol was converted to an elastomer using a polyol/1,4-butanediol/4, methylenebis(phenyl isocyanate) equivalents ratio of .. - -.. :
~f~ 3~3 1/7.6/9Ø Because of the relatively high molecular weight of the polyol and the high level o~ equivalents of chain extender and isocyanate, this system turned white early in the cure and tended to ~ive poor "cheezy"
cures. This is believed to ble due to separation of soft and hard phases early enough in the polymerization to immobilize reactive end groups and thereby inhibit chain extension One sample prepared, using about 0.1 part of triethylene diamine catalyst per 100 parts of prepolymer, gave the following compression molded properties:
Hardness, Shore D 35 100% Modulus 1370 300% Modulus Tensile Strength, psi2550 Elongation, % 280 Die C Tear, lbs./in. 558 The results show that a 3000 molecular weight for the polyol segment is not completely acceptable with respect to attaining desirable strength properties and elongation.
The automobile flexlble body parts, which are a desired end-product of this invention, are fabricated by injection molding using the already prepared poly-urethane elastomer as the molding material. In this method, the elastomer is made into small dice or pellets suitable for feeding to in~ection molding machines. Using the same preformed material, a part may also be prepared by extrusion techniques including profile extrusion and sheet extrusion followed by vacuum forming.
~ - 13 -. ~ . . .
.. - . - .
.
~ 3~
Alternatively, the part may be formed by the method termed "liquid reaction molding", in which the reactants are rapidly injected into a mold wherein they cure to form the shaped elastomeric article directly.
In this method, the polyol, chain extender and diisocyanate may be reacted in one step (on.e shot method) or the polyol and diisocyanate may be prereacted and then injected along with the chain extender to form the molded article (pre-. polymer method).
- 13a ---
Claims (3)
1. A polyurethane elastomer which is a reaction product of: (1) a prepolymer formed by the interaction of a polymeric diol selected from the group consisting of poly(oxgpropylene) glycol and poly(oxypropylene) glycol tipped with about 10% by weight of ethylene oxide and having a molecular weight of from about 1750 to about 2500 and methylenebis(4-phenyl isocyanate); and (2) 1,4-butanediol, the NCO/OH equivalents ratio being from about 0.95 to about 1.20 and the molar ratio of said butanediol to said polymeric diol being from about 3.0:1 to about 9.0:1; said elastomer having a hardness of about 40 to 55 Shore D, an elongation of greater than 300%, an ultimate tensile strength of at least 3000 psl and a Die C tear strength of at least 500 pli.
2. A polyurethane elastomer as in claim 1 in which the molecular weight of said polymeric diol is about 2000.
3. A shaped article prepared from the polyurethane elastomer of claim 1 and characterized, when having a thickness of 0. o8 inch, by remaining intact under a 5 mile per hour impact at -20°F. and by having a sag of less than 2 inches as determined by the Heat Test O'S.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US469143A US3915937A (en) | 1974-05-10 | 1974-05-10 | Poly(oxypropylene) glycol based polyurethane elastomers suitable for automotive body parts |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1043939A true CA1043939A (en) | 1978-12-05 |
Family
ID=23862589
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA211,254A Expired CA1043939A (en) | 1974-05-10 | 1974-10-11 | Flexible automobile exterior body parts produced from poly(oxypropylene) glycol based polyurethane elastomer |
Country Status (7)
| Country | Link |
|---|---|
| US (1) | US3915937A (en) |
| JP (1) | JPS541600B2 (en) |
| CA (1) | CA1043939A (en) |
| DE (1) | DE2518050A1 (en) |
| FR (1) | FR2270279B1 (en) |
| GB (1) | GB1513462A (en) |
| IT (1) | IT1032847B (en) |
Families Citing this family (17)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3983094A (en) * | 1975-09-11 | 1976-09-28 | Uniroyal, Inc. | Thermally stable polyurethane elastomers produced from poly(oxypropylene)-poly(oxyethylene)glycols of high oxyethylene group content |
| US4010146A (en) * | 1975-09-29 | 1977-03-01 | Samuel Moore And Company | Polyol blends and polyurethane prepared therefrom |
| US4049636A (en) | 1976-02-25 | 1977-09-20 | Uniroyal, Inc. | Thermally stable polyurethane elastomer useful in molding flexible automobile exterior body parts |
| US4041105A (en) * | 1976-02-26 | 1977-08-09 | Uniroyal, Inc. | Polyurethane elastomer derived from graft of ethylenically unsaturated monomer on polyalkylene ether glycol |
| US4124572A (en) * | 1977-07-05 | 1978-11-07 | Uniroyal, Inc. | Thermoplastic polyurethane elastomer |
| US4124574A (en) * | 1977-08-29 | 1978-11-07 | Olin Corporation | Poly (oxyalkylene) glycol based polyurethane with improved paint adhesion properties |
| US4225696A (en) * | 1979-02-21 | 1980-09-30 | Polythetics, Inc. | Prosthetic denture prepared from polyurethane elastomer |
| US4297444A (en) * | 1980-02-11 | 1981-10-27 | Texaco Development Corp. | Process for rim elastomers with superior high temperature dimensional stability |
| JPS5967113U (en) * | 1982-10-29 | 1984-05-07 | マツクス・フアクタ−株式会社 | multifaceted compact |
| US4532316A (en) * | 1984-05-29 | 1985-07-30 | W. L. Gore & Assoc., Inc. | Phase separating polyurethane prepolymers and elastomers prepared by reacting a polyol having a molecular weight of 600-3500 and isocyanate and a low molecular weight chain extender in which the ratios of reactants have a limited range |
| GB8908495D0 (en) * | 1989-04-14 | 1989-06-01 | Ici Plc | Polyisocyanate compositions |
| US5976371A (en) * | 1997-12-09 | 1999-11-02 | H.B. Fuller Licensing & Financing, Inc. | White-opalescent adhesives for the preparation of bonded filters |
| ES2233682T3 (en) * | 2000-09-11 | 2005-06-16 | Dow Global Technologies Inc. | METHOD AND DEVICE TO PREPARE A TIRE SUPPORT. |
| BR0114124B1 (en) * | 2000-09-11 | 2010-11-30 | flat tire (rft), flat tire (rft), wheel assembly, method for making a flat tire (rft) and method for making a flat tire (rft) ). | |
| JP5154573B2 (en) * | 2006-12-20 | 2013-02-27 | コンパニー ゼネラール デ エタブリッスマン ミシュラン | Polyurethane |
| EP2495264B1 (en) * | 2011-03-04 | 2013-05-08 | Borealis AG | Exterior automotive article with reduced paintability failure |
| KR101626055B1 (en) * | 2014-06-19 | 2016-06-01 | 주식회사 대성하이테크 | grommet manufacturing mold using Thermoplastic elastomer composition |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB731071A (en) * | 1951-07-19 | 1955-06-01 | Du Pont | Preparation of elastomers from polyalkylene ether glycols and diisocyanates |
| BE608757A (en) * | 1960-10-03 | |||
| US3517062A (en) * | 1966-08-05 | 1970-06-23 | Mobay Chemical Corp | Process for the preparation of substantially pure 4,4'-diaminodiphenylmethane |
| US3620905A (en) * | 1969-10-21 | 1971-11-16 | Du Pont | Optically clear thermoplastic polyurethanes |
-
1974
- 1974-05-10 US US469143A patent/US3915937A/en not_active Expired - Lifetime
- 1974-10-11 CA CA211,254A patent/CA1043939A/en not_active Expired
-
1975
- 1975-04-23 DE DE19752518050 patent/DE2518050A1/en active Pending
- 1975-05-08 JP JP5533875A patent/JPS541600B2/ja not_active Expired
- 1975-05-09 IT IT68192/75A patent/IT1032847B/en active
- 1975-05-09 FR FR7514553A patent/FR2270279B1/fr not_active Expired
- 1975-05-10 GB GB14814/75A patent/GB1513462A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| FR2270279B1 (en) | 1979-10-19 |
| GB1513462A (en) | 1978-06-07 |
| JPS50158696A (en) | 1975-12-22 |
| IT1032847B (en) | 1979-06-20 |
| JPS541600B2 (en) | 1979-01-26 |
| AU8017175A (en) | 1976-10-21 |
| FR2270279A1 (en) | 1975-12-05 |
| DE2518050A1 (en) | 1975-11-13 |
| US3915937A (en) | 1975-10-28 |
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