Polyether Polyols in Urethane Coatings
MOST
of the published information on urethane coatings relates to polyester or castor oil-diisocyanate technology, with relatively few references to polyether urethanes (7-8). A more complete investigation of polyether poly01 diisocyanate polymers in urethane coatings was undertaken. The polyether polyols were used as: components of isocyanate-terminated intermediates, components of hydroxylterminated urethane intermediates, chain extenders for the above intermediates, and curing or cross-linking agents for isocyanate-terminated intermediates. Isocyanate-terminated and hydroxylterminated intermediates were developed from polyols and tolylene diisocyanate. An ordered procedure for their preparation was used. Instead of simple diand triols as previously reported (3, d ) , polyether polyols of low molecular weight were used. Preliminary work indicated the propylene oxide adduct of trimethylolpropane of 400 molecular weight (Pluracol TP-440 Wyandotte Chemicals) to b: of special interest in the preparation of urethane intermediates and coatings. Three isocyanate-terminated intermediates (NCO-1, NCO-2, and NCO-3) were prepared. Intermediate NCO-1 was made by reaction of 3 moles of T D I with 1 mole of TP-440, and consisted of a simple adduct. Intermediates KCO-2 and iVC0-3 comprised Intermediate XCO-1 extended with dipropylene glycol and polypropylene glycol of 400 molecular weight, respectively (Pluracol P-410). Ideal structures for the NCO-terminated intermediates may be represented as follows:
1
amine nitrogen was made by reaction of 2 moles of T D I with 1 mole of P-410 to form a n isocyanate-terminated intermediate, which was combined afterward with 2 moles of tetrakis-(2-hydroxypropyl)-ethylenediamin (Quadrol tetraol). Ideal structures of the hydroxylterminated intermediates may be represented as follows: OH - -~ OH
i OH-3 YO,
Ho\
One-component urethane coatings were prepared from the isocyanateterminated intermediates. I n these systems, curing occurred by reaction of the terminal NCO groups with moisture from the atmosphere. Two-component coatings were pre-
CURED
URETHANE COATIhGS
*oT""
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300
400
AVERAGE
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Properties of moisturecured urethane coatings
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500
600
FPUIVALENT WEIGHT NCO G R O U P
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PROPESTIES 3F CURED K O - 2 G04TIluG5 NCOIOH
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TP 4 4 0
properties of the final coating. S o external catalysts were used and the curing rate was regulated only by variations in polymer design and cross-link density. The structure, chemical composition, and equivalent weight of the raw mate-
PROPERTIES OF
MOISTURE
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I
1
NCO-I
pared by curing isocyanate-terminated intermediates with either polyols or hydroxyl-terminated intermediates. The polyols consisted of simple polyols, polyether polyols, or a combination of the two. The use of hydroxyl-terminated intermediates as curing agents for isocyanate-terminated intermediates allowed additional latitude in varying the
C EXTENDING
:
12/10 I
O
TP 4 4 0
DIOL
Intermediate OH-1 was made by coupling 2 moles of TP-440 with 1 mole of TDI. Intermediate 013-2 was made by reaction of 1 mole of polypropylene glycol of 400 molecular weight (Pluracol P-410) with 2 moles of TDI to form a n isocyanate-terminated intermediate. This then reacted with 2 moles of TP-440 to form a n intermediate with four terminal hydroxyl groups, on the average. Intermediate OH-3 containing tertiary
1 386
INDUSTRIAL AND ENGINEERING CHEMISTRY
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2010 QUIOROL EPUIVILENT
TP.440 WEIGHT
OF
TP-740 CURING
POLYOLS
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Properties of polyolcured NCO-2 coatings
NCO/OH = 1.2/1.0
POLY UR ET H A N E CO A T l N 0 S NCO/OH
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IC
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EQUIVALENT OF
WEIGHT
ISOCYANATE
PER
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INTERMEDIATE
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400
300
Properties of isocyanate intermediates cured with intermediate OH-1 not containing tertiary amine nitrogen
AVERAGE
600
500
EQUIVALENT WEIGHT PER NCO-GROUP OF ISOCYANATE INTERMEDIATE
Properties of isocyanate intermediates cured with intermediate OH-3 containing tertiary amine nitrogen NCO/OH = 1.2/1.0
rials used were related to resulting coating properties. Moisture-Cured Coatings were harder and less flexible than polyol or hydroxyl-terminated intermediate-cured ones. Their solvent resistance was excellent. Flexibility of moisture-cured coatings increased \\vith the length of the chain-extending diol. Poly01 Cured Coatings. Polyols having equivalent weights between about 50 and 160 gave acceptable drying and curing times of the coatings. Polyols of higher equivalent weight yielded softer and more flexible cured films. Polyols of lower equivalent weight provided harder and more brittle cured films. Triols and tetraols gave a shorter pot life than diols of the same equivalent weight. Coating formulations made from polyols containing tertiary amine nitrogen had a shorter pot life than those where the amine nitrogen was absent. The former polyols also contributed to the hardest coatings with the most rapid curing rate and best solvent resistance of those tested. Coatings Cured with Hydroxyl-TerHydroxylminated Intermediates. terminated intermediates (equivalent weight between 150 to 350 for those without tertiary amine nitrogen, and from 200 to 400 for those with tertiary amine nitrogen) cured isocyanate-terminated intermediates effectively. They imparted antisagging properties to the coatings. The intermediates containing amine nitrogen produced harder, more solventresistant, and faster curing films than intermediates where nitrogen was absent. The length of the diol used for chain ex-
tension of each intermediate defined the degree of film flexibility. Abrasion loss values were very low. After 1000 hours of Weatherometer exposure, no loss of gloss was observed. literature Cited (1) Bailey, M. E., SPE Journal 14, 41 ( 1958). (2) Brushwell, W., Am. Paint J.41, No. 44, 107(1957). (3) Hudson, G. A., Heiss, M. L., Saunders, J. H., Division of Paint, Plastics, and Printing Ink Chemistry, 130th Meeting .4CS, Atlantic City, N. J., September 1956. (4) Mobay Chemical Co., “L’rethane Surface Coatings.”
( 5 ) Owen, G. E., Jr., .4they, R. J., Remington, W.J., Elastomer Chemicals Dept., E. I. du Pont de Nemours 8r Co., Paint Bull. PB-4. ( 6 ) Pansing. H. E., 086. Digest Federaiion Paint & Varnish Production Clubs 30, 37 11958). ( 7 ) Rkmington, UT. J., Athey, R. J., Ibid., 31, 612-23 (1959). (8) Remington, W. J., Lorenz, J. C., Elastomer Chemical Dept., E. I. du Pont de Nemours & Co.. Paint Bull. PB-2 and PB-3. ADOLFAS DAMUSIS, J. M. McCLELLAN, Jr., and K. C. FRISCH Wyandotte Chemicals Corp., Wyandotte, Mich.
Stable Pigmented Coatings Systems
POLYURETHANE
coatings vehicles show substantial promise in many applicatioris where satisfactory coatings are not a t present available. ‘One factor which has impeded their progress has been a difficulty in pigmenting many of the systems. This investigation indicates that the instability of pigmented polyurethane prepolymers is caused primarily by adsorbed moisture and other reactive contaminants present in the pigments. A promising method for overcoming many of these problems consists of prereacting these impurities with iFocyanate by slurry grinding in a ball mill prior to addition of the prepolymer. Such a procedure utilizes conventional manufacturing techniques and equipment and should be practical for volume production.
For the purpose of this discussion, polyurethane vehicles may be divided into four categories.
1. One-package urethanes containing no free isocyanate. 2. Semiprepolymer two-package systems consisting of a polyisocyanate or isocyanate prepolymer containing free NCO, designed to react with substantial quantities of a polyol shortly before use. 3. One-package prepolymers containing free isocyanate but capable of conversion to films in the presence of ambient moisture. 4. Two-package prepolymer systems, containing free NCO, which are converted by small amounts of catalysts added a t time of application. The systems of 1, containing no free NCO, can be pigmented by conventional VOL. 51. NO. 11
NOVEMBER 1959
1387
