Faoro of the Rock Island Arsenal Elastomer Laboratory, who performed much of the compounding and testing of the elastomers. literature Cited
Axelrood, S. L., Lajiness, W. J., Final Report, 1 July 1963 to 31 December 1963 and 15 May 1964 to 15 May 1965, Contract DA 20-018-ORD-24883, Wyandotte Chemicals Corp. Axelrood, S. L., Lajiness, W. J., Rubber J . (Brit.) 147 ( l l ) , 34 (1965). Barringer, C. M., “Thermoplastic Urethane Elastomers,” Data Sheets, E. I. du Pont de Nemours & Co., Sept. 30, 1963. Britain, J. W., Gemeinhardt, P. G., J . Appl. Polymer Sci. 4, 207 (1960). Clark, R.A,, Dennis, J. B.,Znd. Eng. Chem. 43,771 (1951). Dickinson, L.A., J . Polymer Sci. 58, 857 (1962). E. I. du Pont de Nemours & Co., “Adiprene C, A Urethane Rubber,” Development Products Rept. 4 (July 15, 1957). Farthing, A. C., Brit. Patent 723,777 (Feb. 9, 1955). Farthing, A. C., J . Chem. Soc. 1955, p. 3648. Furukawa, J., Saegusa, T., “Polymerization of Aldehydes and Oxides,” p. 257, Interscience, New York, 1963. Griffis, C. B., Henry, M. C., Rubber Plastics Age 46, No. 1, 63 (1 965). Gruber, E. E.,Meyer, D. A,, Swart, G. H., Weinstock, K. V., IND. ENG.CHEM.,PROD.RES.DEVELOP. 3,194 (1964). Keplin er, O.,Gruber, E. E., Rubber Age 84, (6), 959-63 (March 19597.
Liska, J. W., “Low Temperature Properties of Elastomers,” Symposium on Effects of Low Temperatures on the Properties of Materials, p. 37, ASTM, STP No. 78 (March 19, 1946). Maine, F. W., Levesque, R. J., “New Polyurethanes from Tetrahydrofuran and Alkylene Oxide Copolymers,” 86th Meeting, Division of Rubber Chemistry, ACS, Chicago, September 1964. Meenvein, H., Delfs, D., Morschel, H., Angew. Chem. 72, 927 (1960). Murbach, W. J., Adicoff, A., Znd. EnE. Chem. 52,773 (1960). Ossefort, Z.T., Testroet, F. B., Rubber Chem. Technol. 39(4), 1308 (1966). Saunders, J. H., Frisch, K. C., “Polyurethanes, Chemistry and Technology,” Part 1, “Chemistry,” p. 273 ff., Interscience, New York, 1962. Siggia, S., “Quantitative Organic Analysis Via Functional Groups,” p. 7, Wiley, New York, 1949. Staudinger, H., Lehmann, H., Ann. 505, 41 (1933). Steyermark, A., “Quantitative Organic Microanalysis,” p. 495, Academic Press, New York, 1961. Willis, W. D., Amberg, L. O., Robinson, A. E., Vandenburg, E. J., Rubber World 153, 88-97 (October 1965). Worsfold, D. J., Eastham, A. M., J . Am. Chem. SOC. 79, 897 (1957). RECEIVED for review October 12, 1966 ACCEPTEDJanuary 13, 1967 Division of Rubber Chemistry, 152nd Meeting, ACS, New York, N. Y., September 1966. The opinions or assertions contained herein are not to be construed as official or reflecting the views of the Department of the Army.
ELASTOMERS FROM 0-TOLUIDINE DIISOCYANATE K. W . R A U S C H , T. R. M c C L E L L A N , A N D A. A. R . S A Y I G H Carwin Research, The Upjohn Go., North Haven, Conn.
A detailed study of the TODI-polyester-glycol system was made to determine the scope of useful TODIbased elastomers prepared b y either the prepolymer or catalyzed one-step process. An isocyanatehydroxyl ratio of 0.99 to 1.01 afforded polymers with best over-all and melt-processing properties. commercially available diisocyanates are suitable for of polyurethane elastomers : 1,5-naphthalene diisocyanate (NDI), toluene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), and 3,3’dimethyldiphenyl-4,4‘-diisocyanate(TODI). Although NDI was important in the early studies of polyurethane elastomers (7) and has found wide use in Europe, it suffers from instability, product discoloration, and difficulty in handling. T h e uses of T D I are limited to nonthermoplastics which are prepared by the curing of its prepolymers with either aromatic diamines or polyols having a functionality greater than 2. M D I has gained prominence in thermoplastic and thermosetting elastomers, but lacks long-term storage stability a t ambient temperatures. TODI, a relative newcomer to the field, is perhaps one of the most promising diisocyanates for the preparation of high quality elastomers. A study of the effect of diisocyanate structure upon the properties of a diamine-cured, polyether prepolymer (2) showed that, of the eight diisocyanates investigated, T O D I polymers exhibited the best over-all balance of properties, including excellent tear resistance, high modulus, and good tensile strength, elongation, and solvent and heat resistance. Similar results were reported from a study of the effect of diisocyanate structure on the physical properties of glycol-cured, polyester prepolymers ( 3 ) ,and from a comparison of several diisocyanates in one-step, diamine-pol yether systems OUR
F the study and fabrication
(4)* 12
I&EC
PRODUCT RESEARCH AND DEVELOPMENT
This paper represents the first detailed study of the TODIpolyester-glycol system which attempts to determine the scope of useful TODI-based elastomers prepared by either the prepolymer or catalyzed, one-step process. Experimental
Polyesters were dried for 2 hours at 110’ to 120’ C. (1.2 mm.) before use, specifications of the supplier being followed in all cases. The diols, except for 1,6-hexanediol, were distilled under reduced pressure and both the 10 to 15yo precuts and the 3 to 5% residues were discarded. T O D I was used without pretreatment. Procedure A. One-Step. T h e polyester-diol mixture (150 grams) was placed in a 250-ml. resin flask and heated to 85’ C. in vacuo; flaked T O D I was then added and dissolved. T h e solution was cooled to 50’ C., the catalyst added, and the mixture again stirred in vacuo. When the temperature of the polymer had increased by the reaction exotherm to approximately 85’ C., the mixture was poured into Teflon-lined molds and oven-cured for 30 minutes a t 105” C. The castings (green stock) were stripped and a sample was pressed a t 300O to 350° C.,so as to ensure the physical testing of all formulations, regardless of molding characteristics after full cure. Prior to testing, the green stock was postcured for 16 hours a t 80’ C., aged for 2 days a t room temperature, and pressed into sheets (noting melt conditions) and the sheets were cured for 16 hours a t 80’ C. A catalyst was needed for acceleration of the isocyanate reaction and for achievement of a balance between the glycolisocyanate and the polyester-isocyanate reactions. I n the absence of catalyst, the urethane derived from the monomeric
glycol precipitated. The resulting two-phase mixture could not be cured to a usable polymer. Procedure €51. Prepolymers for the glycol chain length study were prepared from a two-step, TODI-addition process : A portion of the TODI. was added to the polyester a t 70' to 80' C. and allowed to react for 1 hour a t 100' to 110' C. before addition of the remaining TODI a t 90' C. T h e final mixture was allowed to react 1 hour a t 100' to 110' C. and the prepolymer to stand overnight a t 70' C. T h e glycol curative \vas added to the prepolymer at 45' to 55' C. and the resulting mixture stirred for 15 minutes a t 65' to 70' C. before being cast in Teflon-lined molds, cured for 2 hours a t 100" to 110' C., and p'ostcured for 16 hours a t 70' to 80' C. Sheets were pressed ancl then cured for 16 hours a t 70' to 80'
12 r
C. Procedure B2. The prepolymer for the NCO/PEA-OH study was prepared from a one-step process in which the T O D I was added to the polyester in one portion. Procedure B1 was then followed with one modification: Direct casting of the sheets was necessitated by the high melt point of the polymers.
A
6
5
Polymers afforded from the catalyzed, one-step process (Method A) exhibited higher tensile strength, modulus, and split tear? lower elongation and die C tear, and possible greater hardness than those prepared from the prepolymer process (Method B2) (see Table I ) . Physical testing !vas accomplished on a iModel T T C Instron universal testing machine.
4
3
1
Materials
Formrez F21-20, 1000 M.\V., 90:lO ratio of ethylenepropylene adipate Formrez F13-99, 2000 M.\V., 90: 10 ratio of ethylenepropylene adipate Formrez F10-13, 1000 M.TV., ethylene adipate Formrez F 7-37. 2000 M.1.V. ethylene adipate 1,2-Ethylene glycol 1,3-Propanediol 1,4-Butanediol 1,5-Pentanediol 1,6-Hexanediol TODI (Isonate 136T) Stannous octoate Triethylenediarnine
TVitco Chemical \l-itco Chemical
0 1 0.95
\Vitco Chemical
1.10
Fisher Scientific Shell Chemical General Aniline S; Film Union Carbide Chemicals Union Carbide Chemicals Upjohn Polymer Chem. Div. Metal & Thermit Houdry Process
Isocyanate Index. T h e effect of a n increase in isocyanate index from 0.95 to 1.10 on physical properties is shown i n Figure 1. T h e series of one-step polymers was based on the following formulation. Equio. Parts
...
I
1.05
Index
Figure 1. Effect of isocyanate index at constant NCO/PEA-OH ratio of 2.0 to 1.0 upon physical properties in a one-step polymer
\Vitco Chemical
Discussion
T-9
I
I
1.00 Isocyanate
"r
Isocyanate Index
0.22
Table I. Properties of Elastomers Made from TODI-Poly(ethylene Adipate)-Pentanediol at NCO/Polyester OH Ratio of 2.0 to 1.0" 1000 M . Tt'. PE.4 2000 itl. U'. P E A PrePret3ne-jteph polymer One-stepb polymer Tensile, p.s.i. 10,444 9,450 7,784 5,000 765 100yc Modulus, p.s.i. 1 .037 441 405 19 12 22 32 Set at rupture 5c 850 Elongation, c/;. 844 1,096 1,170 405 Die C tear, pli 307 327 330 Split tear, pli 318 200 321 175 82.A Hardncss, Shore 82.A 68.4 74x a .VCO index = 1.0. Catalyzed with 0.025 p.p.h. T-9.
0
zoo Tensile
400
Strain
- percent
I
I
I
600
800
1000
Figure 2. Effect of isocyanate index at constant NCO/PEA-OH ratio of 2.0 to 1.0 upon stress-strain properties in a one-step polymer VOL. 6
NO. 1
MARCH 1967
13
11 0.95
I
1
1.05
1.00
Iiocyanate
A
1.10
Index
Figure 3. Effect of isocyanate index upon 600% modulus at constant NCO/PEA-OH ratio of 2.0 to 1.0 in a one-step polymer Table II. Melt Characteristics of One-Step Polymers Prepared from Poly(ethy1ene Adipate), TODI, and Glycola Melt ?ick, Molding Hot Polymer F. Characteristics Condition Prepared at Varying Isocyanate Index Valuesbrc iYC0 / 0H 1.10/1 .oo 41 0 Poor Very soft 1.05/1 .OO 360 Poor Very soft 1 .02/1.00 345 Fair Soft 1.00/1 .oo 325 Excellent Firm 0.98/1 . O O 290 Excellent Firm 0.95/1 . O O 240 Excellent Soft Prepared from Glycols of Varying Chain Lengthcsd IYO.Carbon Atoms i n Glycol Chain Fair Very soft 2 330 3 350 Good Firm 4 325 Excellent Soft 5 325 Excellent Firm 6 290 Excellent Soft Prepared from Polyesters of Varying M.TV.bp~,d
M.W.
oj
Polyester 345 Fair Firm 1000 325 Excellent Firm 1250 325 Good Firm 1500 335 Excellent Firm 1750 335 Good Firm 2000 Prepared from Mixtures of PEA and 1,5-Pentanediol Having Same Average Equivalent Weightd Polyester Eq./ Diol E q . 1 .o/o.o 285 Good Very soft 1.0/0.5 325 Good Soft 1.0/1. o 325 Excellent Firm 1.0/2.1 325 Excellent Firm a Polymers initially cured 30 min. at 105' C. followed by 76 hr. at 80' 7,5-PentaneC. Completed polymer molded at press temp. of 380' F. diol used as glycol. c Prepared at isocyanate-polyester ratio 2.0/1.0. d Prepared at isocyanate index of 7.00.
I 4
I
3
No.
Carbon
14
I&EC PRODUCT RESEARCH A N D DEVELOPMENT
6
A t o m s in G l y c o l
Figure 4. Effect of glycol chain length upon physical properties of TODI polymers prepared from 2000-molecular weight polyester
The stress-strain relationship at various isocyanate-hydroxyl ratios within the same series of one-step polymers is shown in Figure 2. The large change in modulus a t higher elongations suggests the use of high modulus as a tool for production quality control. T h e enlarged 600% modulus curve (Figure 3) shows that the NCO/OH-stoichiometric ratio is the inflection point of the curve. Polymers prepared from the range of NCO-index values represented by the dotted box in Figure 3 had both adequate physical properties and good moldability. The molding characteristics of this series of one-step polymers is summarized in Table 11. Crosslinkage apparently raised the melt stick of samples equally cured. A correlation of physical and molding properties showed the optimum NCO/OH ratio to be from 0.99 to 1.01. Effect of Glycol Chain Length. T o test the effect of glycol chain length, the following formulation was used. The results are summarized in Figures 4, 5 , and 6 and Table 11.
~
Tensile strength and tensile set exhibited the greatest changes, the former increasing from 2600 to 10,800 p.s.i. and the latter decreasing from 120 to 7%. T h e sharp decrease in set may be attributable to crosslinking via allophanate and/or biuret formation. The die C tear strength rose slightly, while split tear remained nearly constant. Elongation a t break decreased with increased crosslinkage. Variation in hardness was exceedingly small.
I
5
Formrez F7-37 or Formrez F21-20 and Formrez F13-99 nr
Fo;mrez F10-13 TODI Diol", HO(CH2),0H, n = 2-6 a Ethylene glycol, 1,6-hexanediol.
7,3-propanediol,
Equiv.
Parts
1 .oo
100.0
0.75
375.0
0.25
250.0
1 .oo
500,O 264.0
2.00 1 .oo
I,&butanediol,
...
7,5-pentanediol,
'' r
1:
11
/ * l o o %Modulus psi x lo-=
I1
9
I
x 10-3
8
'ult.
tensile 10-1
7
A
b
5
4
3
1
.................. Tensile %
....
x
set 10-1 2
......I...
O 2
,
1
4
No. C a r b o n A t o m s
5
in
I
1
6
Glycol
Figure 5. Effeci of glycol chain length upon physical properties of TODl polymers prepared from 1250-molecular weight polyester
A graphic representation of the physical properties of polymers prepared from either procedure depicts the sawtooth curve so frequently observed in comparisons of polymeric properties \\ith the number of glycolic carbon atoms. T h e pattern is most distinct for 100% modulus, die C tear, and hardness, all of hich are related to chain fit and crystallinity. Better chain fit gives ricje to a more highly ordered and, therefore, harder polymer (Figures 4, 5, and 6). As tensile strength, tensile set, elongation and split tear are not particularly affected by this characteristic, one expects the observed, lesspronounced pattern (Figures 4, 5, and 6). The sawtooth pattern is also evident in the melt characteristics. Melt stick values of polymers prepared from even-numbered glycols were 20' to 25' F. lower ihan those from odd-numbered, their melting points were much sharper, and their viscosities were lower (see Table 11). For tensile strength a different pattern was observed. As the glycol chain length increased, the tensile strength of the 1000 equivalent iveight prepolymer elastomer increased, that of the 500 equivalent weight remained relatively constant a t higher values of n, and that (of the 625 equivalent weight one-step \+as similar to the 500, except for n = 4. T h e anomalous behavior of butanediol ( a = 4) is evidenced in the stressstrain curves (Figure 7:1 and reflected in the exceptionally low tensile strength of the TODI-PEA, one-shot elastomer. The general correlation of high strength with low set also holds for the n = 4 case. Both molecular weight and crosslinking from hydrogen bonding and/or crystallization are instrumental in the control of tensile pattern. Assuming that molecular ireight does not vary appreciably, the controlling characteristics must be in the degree of crystallization, which reflects
0
N o . Carbon
Atoms i n G l y c o l
Figure 6. Effect of glycol chain length upon physical properties of TODl polymers prepared from 1000molecular weight polyester
'r
Tensile S t r o i n
-
percent
Figure 7. Effect of glycol chain length in a one-step system at NCO/PEA-OH ratio of 2.0 to 1.O upon stress-strain properties VOL. 6
NO. 1
MARCH 1967
15
\
.\.\. '.
/
/
/ l o o % Modulus psi x IO-'
0
''-
tensile psi x
10-1
''-
x
x 10-1
lo-'
i
/'
10'1
A :
t
A
pli x 10-1
............ " /' ...............................................Tensile
01
1000
1250
Molecular
1500
of
Weight
1
I
1750
2000
Polyester
Figure 8. Effect of polyester molecular weight at constant NCO/PEA-OH ratio of 2.0 in a one-step polymer
I
I
0.5
Equiv.
1.1
1.0
Glycol
set
%, x lo-'
per
Equiv.
2.0
Polyester
Figure 10. Effect of glycol-polyester ratio at constant over-all hydroxyl equivalent weight of 363 upon physical properties of a one-step polymer
Effect of Molecular Weight of Polyester. T h e molecular weight of the polyester was varied by blending two polyesters in different proportions with constant glycol and NCO/OH ratio, as exemplified in the following catalyzed, one-shot formulation.
Formrez F21-20 Formrez F13-99 1,5-Pentanediol TODI T-9
Equiv. 1 . 0 to 0.0 0 . 0 to 1 . o 1 .o
2.0
Parts
500 to 0 0 to 1000 52 264 0.025 p.p.h.
The properties of polyester used, their theoretical molecular weights, and the theoretical hydroxyl equivalent weights of the total diol systems are: Tensile
Strain
-
percent
Figure 9. Effect of polyester molecular weight upon stress-strain properties of an elastomer equiv. TODl per equiv. 1000-M.W. polyester .2.5 equiv. TODl per equiv. 2000-M.W. polyester -4.2 equiv. TODl per equiv. 2000-M.W. polyester
.......
l & E C P R O D U C T RESEARCH A N D D E V E L O P M E N T
Theor. Eq. Wt.O Diol Syst.
1.oo/o. 00
1000 1250 1500 1750 2000
284 348 412 476 540
0.00/1 a
16
Theor. M . W . PEA
0.75/0.25 0,50/0.50 0.25/0.75
- - -2.0
molecular fit, and the amount of hydrogen bonding, which reflects urethane concentration. An increase in glycol chain length would cause a reduction in hydrogen bonding and, therefore, weaker tensile properties. Tear strength and elongation generally increased with increasing chain length.
Eq. F21-20/ Eq. F13-79
.oo
Including glycol.
Tensile strength, modulus, and hardness decreased with increasing molecular weight, while elongation a t break increased and both tensile set and melt stick remained unchanged. The maximum and minimum reflected in the split-tear curves, respectively, probably reflect a more even distribution in the
11-
i
; 10
Tensile
ret
x
10-1
2
_,”
P -
a-
.
‘‘.
i 6 7 -
u
;6 a 0
0 c
5 -
: 0
f , 4 -
e v)
-u
-
-
\’
C I-u
1 -
100 X Modulus psi x 1 0 - 2
Tensile
Strain
-
percent
Figure 11. Effect of glycol-polyester ratio at constant over-all hydroxyl equivalent weight of 363 upon stressstrain properties of a one-step polymer
3
Equiv.
I 5
4
I
b
7
D i i s o c y a n a t e per Lquiv. Polyester
Figure 12. Effect of NCO/PEA-OH ratio upon properties of polymers based upon 2000-molecular weight polyester and butanediol
Table Ill. Properties of Elastomers Prepared via Prepolymer from TODI, Poly(ethy1ene Adipate), and Butanediol at NCO Index of 1.0 B2, B 7, A, 2000-M. 1ooo-M. w. 2000-‘44. PEA at 2.0 PEA at 4.25 PEA at 2.5 NCOlPEANCOIPEA- NCO/PEAOH. O’Ha O’H Tensile 8850 6550 6000 870 1160 1180 10070 Modulus 890 707 795 Elongation 41 12 62 Set at rupture 812 470 Die C tear 474 612 310 Split tear 187 36 D 36 D 52 D Hardness
w.
a
w.
[NHCOO] = 2.44 eq./7000 g. polymer.
molecular weight of polyester. T h e polymers molded well a t a constant press temperature (Figure 8 and Table 11). A comparison of the data given in Figure 8 with those in Figures 4, 5, and 6 indicates that the changes in physical properties resulting from increased molecular weight of polyester are in the same direction as those for increased glycolchain length. I n view of the fact that these increases are accompanied by a decrease in the density of urethane linkages and in the aromatic nature of the backbone and, therefore, a decrease in rigidity and hydrogen bonding, a n elastomer of less strength is obtained. Effect of Glycol-Polyester Ratio. Polymers prepared from polyesters of different molecular weight, but formulated to have an identical urethane concentration, are compared in Table 111. Any variations in the properties of these polymers should
Tensile S t r a i n
-
percent
Figure 13. Effect of NCO/PEA-OH ratio upon stress-strain behavior of polymers based upon 2000-molecular weight polyester and butanediol VOL. 6
NO. 1 M A R C H 1 9 6 7
17
5-
4-
3-
A
2
4
3
Equiv.
5
,Diisoeyanate per
6
7
Equiv. Polyester
Figure 14. Effect of NCO/PEA-OH ratio upon properties of polymers based upon 2000molecular weight polyester and butanediol -Elastic limit (p.s.i.-A , , .Elastic modulus (P
.
X 1 03) X 1 04)
10‘
Y
a
d $0’
u a 7 C
a 0
a
c 0
*
v) c
0 C
2 10‘ r
\
10’
I
I
Temperature
I
I
-
1
‘C
Figure 15. Effect of NCO/PEA-OH ratio upon torsion stittness modulus of polymers based upon 2000molecular weight polyester and butanediol
be independent of aromatic and urethane Concentration, and therefcre reflect the distribution of elements within the polymer chain. From a prepolymer system of a polyester of 1000 M.W. and a polyester of 2000 M.W. cured with butanediol a t a n over-all hydroxyl equivalent of 277, it was found that the A polymer evenly distributed the urethane and the B1 polymer did not. The presence of concentrated areas in the B1 poly18
l & E C P R O D U C T RESEARCH A N D D E V E L O P M E N T
mer enhanced crystallinity and afforded a material of greater plasticity, higher tensile set, and lower ultimate tensile strength, in comparison to the A polymer (Figure 9). Although the B1 polymer exhibited greater resistance to initial deformation, once its elastic limit was reached, deformation was more facile. A comparison of similar polymers on the basis of equal hardness showed the B2 polymer to have lower tensile strength and modulus, and higher tensile set, elongation, and split tear than the A polymer (Table 111). Hence, polymers having the same Shore hardness may exhibit very different properties. A series of one-step polymers in which urethane concentration was constant at an over-all hydroxyl equivalent weight of 363 to 365 was examined for sensitivity toward the glycolpolyester ratio. Using a n O H component entirely of polyester a t one extreme and a polyester of 2000 E.W. blended with 1,5pentanediol in a ratio of 2.1 to 1.0 glycol to PEA a t the other, it was found that the tensile strength, split, die C tear, and hardness increased significantly with an increased glycolpolyester ratio (Figure 10). The parabolic shape of the tensileset curve indicates that while low ratios (
