Urethane Rubber from a Polyether 6lycol PROPERTIES OF RAW POLYMER AND VULCANIZATES F. B. HILL, C. A. YOUNG, J. A. NELSON, AND R. 6.ARNOLD E. 1. do Ponf de Nemours & Co., Wilmingfon, Del.
I
N RECENT years, the synthesis of polymers by reacting organic diisocyanates with compounds containing two or more active hydrogens has been studied extensively. Much of the pioneering work on the chemistry of organic polyisocyanates and their reaction products was carried out by Du Pont chemists ( 2 , S , 7, 9). The products were fibers, elastomers, and plastomeric solids. In Great Britain, research of the Imperial Chemical Industries, Ltd., was directed toward the reaction of polyesteramides with organic diisocyanates to produce vulcanizable polymeric plasticizers, designated Vulcaprenes (4). In Germany, Bayer and coworkers developed the elastomer known as Vulcollan (1, 6) through their study of the reaction of polyester glycols with organic diisocyanates. Recently, interest in isocyanate-based addition polymers has been stimulated by the commercial availability of a number of polyisocyanates. An elastomer, Chemigum SL polyester-urethane, was announced by the Goodyear Tire & Rubber Co. in 1953 (8). Both Vulcollan and Chemigum SL are addition polymers of polyester glycols and organic diisocyanates, and both exhibit outstanding toughness and abrasion resistance relative to GR-S or natural rubber. Adiprene B urethane rubber is a new addition polymer. It differs from other diisocyanate elastomers in that its polymeric segments are aliphatic polyethers rather than polyesters. Adiprene B is a distinctive elastomer which combines in a single product high strength, abrasion resistance, solvent and ozone resistance, and excellent low temperature properties. Adiprene B urethane rubber resembles commercial diene hydrocarbon polymers
Raw Adiprene B is a transparent amber-colored polymer with a density at room temperature of 1.07 gram per cc. It is stable to chemical change during storage and shows no tendency to freeze even after prolonged exposure a t -40” C. Although the viscosity of the polymer as measured in a Mooney viscometer is considerably higher than that of GR-S 1500 or natural rubber, Adiprene B mills smoothly and can be worked easily on large or small rubber mills:
Rotor Size Small Large
Moonev Viscositv kt 250” . F .____ ‘ At 212’ F. Bdiprene GR-S 1500 Adiprene GR-S 1500 5 5 f 5 23f3 60f5 3 0 f 4 90 3t 8 42 =t5 100 i:8 52 f 6
I n contrast to the familiar hydrocarbon elastomers, Adiprene B is a polar material. Although polar in character, it is not notably more hygroscopic than conventional elastomers:
Elastomer Adiprene B Xatural rubber (smoked sheet) GR-S 1500 Keoprene Type GN
May 1956
Equilibrium Water Contents a t 25” C., 70 R.H.50% R.H.100% 0 9 2.5 0 4 3.1 0 07 6 0 0 06 2.5
Because of its polar nature, i t is soluble only in certain polar solvents and is resistant to the action of hydrocarbon solvents and oils. Solubility data for Adiprene B are: Solvent Tetrahydrofuran Plus 1.0% water“ Plus 5.07, watera Plus 2074 dimethylformamide” Dimethylforrnamide a
Solubility, Grams/100 hll. of Solvent
5 15 >25 >25
By volume.
The intrinsic viscosity of Adiprene B measured in a mixture of tetrahydrofuran and dimethylformamide (87/13 by volume) is about 0.80 corresponding to a molecular weight of about 30,000. Vulcanization accomplished by heating with diisocyanate curing agent
The transformation of raw Adiprene B t o the elast,ic state is accomplished by heating with a diisocyanate curing agent. The structure and chemical activity of the curing agent are important since they are primary determinants governing processing safety and vulcanizate physical properties. In addition such factors as toxicity, volatility, storage stability, and ultimate cost must be considered. Adiprene B has been cured with a variety of organic diisocyanates representing different structural types as follows: Tol~ene-2~4-diisocyanate 4-Methoxy-m-phenylenediisocy anate 4,4‘-Biphenyldiisocyanate 3,3 ’-Dimethoxy-4,4’-biphenyldiisocyanate 4,4’-Methylenediphenylisocyanate 4,4’-Methylenedi-o-tolylisocyanate Tol~ene-2~4-diisocyanate dimer 3,3’-Diisocganato-4,4‘-dimethylcarbanilide Two of these compounds, specifically 4,4’-methylenedi-otolylisocyanate and 3,3’-diisocyanato-4,4’-dimethy1carbanilideJ have been studied extensively since they represent the best compromise in properties and cost. This urethane rubber is compounded or mixed with curing agents, fillers, and plasticizers on conventional rubber mills. Compounded stocks are shaped by calendering or extrusion and vulcanized in standard molds. Since isocyanates react with mater, it is important that stocks be kept dry until they are cured. Vulcanization is effected at temperatures of 100’ to 1.50’ C. Curing times of 15 to 60 minutes a t 134” C. are the preferred conditions for molding. The reaction of the isocyanate curing agent with Adiprene B does not go to completion during the molding cycle. Vulcanization is completed by storing the product at room temperature for 7 to 14 days. The rate of the “aftercure” reaction is influenced by humidity. Figure 1 shows the effect of room teinperature storage a t 50% relative humidity on the modulus of a vulcanizate. Other properties such as tensile strength, compres-
INDUSTRIAL AND ENGINEERING CHEMISTRY
927
ENGINEERING, DESIGN, AND PROCESS DEVELOPMENT
2
/
7 0 0 ~
sn
'AOIPRENE~ B 3,3' - DIISOCYANATO4,4'-DIMETHYLCARBANILIDE
600
100 4
/
CURED 15 MIN., 134°C.
3,3'- DIISOCYANATO4,4'- DIMETHYLCARBANILIDE CURED
5001
I 2
0
Figure 1.
I I I I 4 6 8 IC I2 DAYS A T 25'C. A N 0 50% R.H.
AS SHOWN
15 M I N , 134'C.
I
14 60
Rate of aftercure of Adiprene B urethane rubber vulcanizate
I
I I I 4 6 8 DIISOCYANATE CONCENTRATION,
2
Figure 2.
I IO PARTS
Diisocyanate concentration vs. hardness
16001 0
> 14002- 1200 I
L
Lc
3 1000 0 0
=
w a
100
3
3 , 3 ' - DIISOCYANATO4,4'- DIMETHYLCARBANILIDE
800-
P 2
I I I 4 6 8 DIISOCYANATE CONCENTRATION, PARTS
z 30001/ 1
1 IO
Figure 4. Figure 3.
Diisocyanate concentration
vs. modulus
A S SHOWN
I
I
I
4 D I ISOCYANATE
2
15 MIN, 134'C.
I 8
6
I IO
CONCEUTRATION, PARTS
Diisocyanate concentration vs. strength
25" C.
tensile
canizate properties is shown in Figures 2 to i . 3.3 '-Diisocyanato4,4'-diniethylcarbanilide was used as the curing agent. The composition was cured 15 minutes a t 134" C. Figures 2 and 3 show that thc hardness and modulus rise steadilv as the concentration of the curing agent is increased
sion set, and resilience also show improvement hut to a smaller degree. Therefore, our test procedure includes storage of the vulcanizate a t SOYc relative humidity for 14 days before a final determination of properties is made. The effect of curing agent concentration on a number of vul-
Table 1.
IC0
CURED
CURED 15 MIN,, 134%.
6001
3500
A5 SHOWN
B
3 , 3 ' - O l l SOCYANATC4 , 4 ' - DIMETHYLCARBANILIDE
'ADIPRENE"
B
Properties of Adiprene
Urethane Rubber Vulcanizates
(Test procedures: ASTII Standards, P a r t 6, 1952) Adiprene B 3,3'-Diisocyanato-4,4'-dimeth3-icarbanilide 4.4'-RIethylenedi-o-tolylisoc3.anate E P C black (Wyex) H.4F black (Philblack 0 ) Conductive channel black (Sp!ieron N) Surface esterified amorphous silica Cab-0-Fil flame s,ilica Cure, 1 3 4 O C., min.
Stress-strain a t 25' C. in air Modulus a t 300Y0, Ib./sq. inch Tensile strength lb./sq. inch Elongati,on a t br'eak. % Stress-strain a t 7 0 O C. in water Modulus at 300Y0, Ib./sq. inch Tensile strength Ih./sq. inch Elongation a t b k k , % Shore hardness Yerzley resilience, 7~ Compression seta, % Bureau of Standards abrasionb H a n d tear % Volume increase, 100' C . I n water, 3 days I n ASTM S o . 3 oil, 7 days D u P o n t solenoid brittle temp., a C. Shore hardness, 14 days, -20' C. a b
928
100.
100
100
100
4
.. 3 .. .. ..
..
3
15
15
30
790 5000 070
650 4.500 070
1400 5200
600 2300 870
525
2360
.. .. ..
.. .. .. ..
I
..
..
..15
09
4 3'7
