1,3,5-tris(1-isocyanatomethylethyl)benzene in polyurethanes

1,3,5-tris(1-isocyanatomethylethyl)benzene is disclosed as a component in coating formulations and the like.

This invention relates to a novel tertiary aralkyl triisocyanate which is 
particularly useful in formulation of systems for producing light stable 
polyurethane coatings. 
Triisocyanates have been found useful in a number of applications, for 
example, as components in polyurethane coating formulations, and RIM 
applications, as cross-linking agents, etc. The aliphatic isocyanates are 
particularly desirable in that products derived from them are known to be 
light stable. The commonly available aliphatic isocyanates, however, have 
low molecular weights and consequent high vapor pressures. 
Characteristically they are toxic and hazardous to handle. Aliphatic 
triisocyanates have been developed which are more suitable for commercial 
applications by reacting low molecular weight polyisocyanates to form 
higher molecular weight polyisocyanates which as a result have lower vapor 
pressure and are consequently safer to handle. One example is the reaction 
of hexamethylene diisocyanate with water to form the biuret derivative. 
Such compounds have disadvantages, such as the presence of unreacted 
isocyanate monomer and short shelf life, and typically have relatively low 
isocyanate content. 
It is an important object of this invention to provide a polyisocyanate 
having the light stability imparting properties of the aliphatic 
isocyanates, but which is characterized by the low vapor pressure and 
consequent low toxicity of high molecular weight compounds by the 
introduction of an aromatic moiety while at the same time retaining a high 
NCO content. 
It is also an important object of this invention to provide such a 
polyisocyanate which is inexpensive to manufacture, which is storage 
stable and which is readily blended in formulating polyurethane coating 
systems. 
The polyisocyanate of this invention is 
1,3,5-tris(1-isocyanato-1-methyl-ethyl) benzene represented by the 
formula: 
##STR1## 
Surprisingly, despite the known stability of tertiary alkyl isocyanates the 
triisocyanate of this invention is highly reactive and is useful in 
providing polyurethane coating formulations which can be cured, tack-free, 
at room temperature. 
1,3,5-tris(1-isocyanato-1-methyl-ethyl) benzene is readily prepared from 
triisopropyl benzene which is available in quantity as a byproduct in 
cumene manufacture. A variety of processes for manufacture of the 
triisocyanate from triisopropyl benzene are available. These include 
either chlorination of the triisopropyl benzene to form tris 
.alpha.-chloroisopropyl benzene or dehydrogenation to the olefin, 
triisopropenylbenzene, either of which can be converted by reaction with 
isocyanic acid to 1,3,5-tris(1-isocyanato-methyl-ethyl) benzene. 
Alternatively, the olefin can be reacted with a carbamic acid ester to 
form a tertiary aralkyl urethane which then can be cracked to the 
triisocyanate. The chloro compound product can also be reacted with sodium 
isocyanate to form the triisocyanate. It is also possible to form the 
triisocyanate of this invention by converting triisopropyl benzene to the 
corresponding triol which then can be reacted with a carbamic acid ester 
to form the corresponding tertiary aralkyl urethane and obtain the 
triisocyanate by cracking the urethane. 
These reactions are as follows:

EXAMPLE 1 
1,3,5-Tris(1-Isocyanato-1-Methylethyl) Benzene 
A catalyst solution was prepared by stirring a mixture of zinc chloride 
(1.0 moles), pyridine (2.0 mole) and methylene dichloride until the solid 
dissolved. 1.42 moles of 90% sodium cyanate containing 0.5% H.sub.2 O were 
added to 100 ml. of the solution so prepared which contained the 
equivalent of 24m. moles of Zn(pyr).sub.2 Cl.sub.2. The mixture was 
stirred for an hour, and thereafter 0.33 moles of 
1,3,5-tris(1-chloro-1-methylethyl) benzene dissolved in 530 ml. methylene 
chloride was added. 
After stirring overnight at room temperature gas chromatographic analysis 
indicated 81% conversion to triisocyanate had veen achieved. The solent 
was evaporated, and the product was recrytallized from hexane giving a 59% 
yield; M.P. 65.5.degree.-66.5.degree. C. 
The product was recrytallized in hexane solution, and dried, yielding a 
colorless solid having a melting point of 71.degree.-72.degree. C. Purity 
by gas chromatograph was 98.2 area percent 
1,3,5-tris(isocyanatemethylethyl) benzene, 0.5 area percent of the 
diisocyanate and 0.5 area percent of the monoisocyanate. The NCO content 
was determined as 9.02 meg/g. which was 98.4 percent of theory. The 
product further contained 71 PPM zinc and 151 PPM total chloride. 
The product was found to be very soluble in toluene, chloroform and 
methylene chloride, slightly soluble in hexane, and reactive with water 
and methanol. 
The elemental analysis, calculated as C.sub.18 H.sub.21 N.sub.3 O.sub.3, 
was: 
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Carbon Hydrogen Nitrogen 
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Calculated 
66.03 6.47 12.83 
Found 65.67 6.70 12.58 
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Structure was confirmed by NMR spectrum and infrared absorption spectral 
analysis as follows: 
NMR .delta.-Value (CDCl.sub.3) (60-MH.sub.z): 
7.28 (S, 3H, arom) and 1.73 S (18H aliph.) 
IR Spectrum, cm.sup.-1 : 2980, 2250, 1600, 1230, 1160, 920, 885, 785, and 
710. 
EXAMPLES II-IV 
Comparable formulations of a proprietary polyester resin (MULTRON-221-75) 
with 1,3,5-tris(1-isocyanato-1-methylethyl)benzene (TPTI), Desmodur-N, a 
proprietary triisocyanate which is the biuret derivative of hexamethylene 
diisocyanate, and T-1890, a proprietary triisocyanate which is the trimer 
of isophorone isocyanate, were prepared using an isocyanate to hydroxyl 
ratio of 1.1/1.0 on an equivalent weight basis. 1% of UL-28, a proprietary 
catalyst which is dimethyl tin dilaurate, was used with the TPTI 
formulation; 0.03% of UL-28 was used with the T-1890 formulation; and 
0.015% UL-28 plus 0.015% lead napthenate was used with the Desmodur-N 
formulation. 
Draw downs were made on 1200 S aluminum using a No. 40 wirecator. The 
coatings were then cured at various temperatures, as indicated, and tested 
for hardness and solvent resistance, as indicated below. 
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Example II III IV 
Isocyanate TPTI Desmodur N T-1890 
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Cured at 125.degree. C. - 20 minutes 
Thickness 0.95 0.95 0.95 
Knoop hardness 16.8 18.6 7.8 
MEK, MAR, rubs -- -- -- 
MEK, remove, rubs 
200+ 200+ 200+ 
Cured at 100.degree. C. - 20 minutes 
Thickness 0.95 -- -- 
Knoop hardness 15.6 -- -- 
MEK, MAR, rubs 70 -- -- 
MEK, remove, rubs 
115 -- -- 
Cured at 80.degree. C. - 20 minutes 
Thickness 0.95 0.95 0.9 
Knoop hardness 11.5 17.4 1.8 
MEK, MAR, rubs 20 5 -- 
MEK, remove, rubs 
40 20 200+ 
Cured at 125.degree. C. - 20 minutes 
Thickness 0.95 0.95 0.95 
Knoop hardness 16.8 18.6 7.8 
MEK, MAR, rubs -- -- -- 
MEK, remove, rubs 
200+ 200+ 200+ 
Cured at 100.degree. C. - 20 minutes 
Thickness 0.95 -- -- 
Knoop hardness 15.6 -- -- 
MEK, MAR, rubs 70 -- -- 
MEK, remove, rubs 
115 -- -- 
Cured at 80.degree. C. - 20 minutes 
Thickness 0.95 0.95 0.9 
Knoop hardness 11.5 17.4 1.8 
MEK, MAR, rubs 20 5 -- 
MEK, remove, rubs 
40 20 200+ 
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EXAMPLE V 
A suitable coating formulation using a proprietary, 60% solids acrylic 
resin, G-cure 867, was made with an NCO/OH ratio of 1.1/1.0 using TPTI at 
50% solids in toluene and 1% of UL 28. Draw downs were made on 1200S 
aluminum sheets using a NO. 46 wirecator and were cured 20 minutes at 
80.degree., 100.degree. and 125.degree. C. with the following results: 
______________________________________ 
Cure, T.degree. C. 
80.degree. 
100.degree. 
125.degree. 
______________________________________ 
Thickness 1.0 1.0 1.0 
Knoop hardness 14.0 17.5 17.5 
MEK, MAR, rubs 150 -- -- 
MEK, remove, rubs 
200+ 200+ 200+ 
______________________________________ 
EXAMPLES VIII and IX 
Samples as prepared in Examples VI and VII were also cured at room 
temperature and evaluated after 4 days as follows: 
______________________________________ 
TPTI T-1890 
Example No. VIII IX 
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Thickness 1.1 1.05 
Knoop, hardness 10.8 13.1 
MEK, MAR rubs 60 20 
MEK, remove, rubs 110 120 
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EXAMPLE X 
Synthesis of 1,3,5 tri(1-chloro-1-methylethyl) benzene (TPTC) 
90 grams of 1,3,5 triisopropenyl benzene (90% pure) was added to 300 ml of 
methylene chloride and cooled to 0.degree.-5.degree. C. HCl gas was 
bubbled into the solution through a glass sparger and after the HCl 
addition (3.2 equivalents) was complete, nitrogen gas was bubbled through 
the solution to remove any traces of HCl. Methylene chloride was removed, 
and the solid recrystallized from hexane. The yields of the trichloride 
were 86-99% before recrystallization and 68-76% after recrystallization. 
The trichloride product is a white solid melting at 69.degree.-71.degree. 
C. Both .sup.13 C and proton NMR confirmed the proposed structure. The 
proton NMR showed a singlet at delta-7.6 corresponding to the aromatic 
hydrogens and a singlet at delta-2.0 for the methyl hydrogens. 
EXAMPLE XI 
TPTI From TPTC and Isocyanic Acid 
To 60 ml of toluene containing 12.9 grams of isocyanic acid (300 m moles) 
was added 5 grams of TPTC (24.5 m moles). The solution was cooled to 
0.degree. C. using an ice bath, and 4 ml. of a 1 molar solution of 
ZnCl.sub.2 in diethyl ether slowly added over 25 minutes. At the end of 
that time, volatiles were stripped off under vacuum (80.degree./25 mm Hg) 
and the crude residue analyzed by GLC (0.7% monoisocyanate diolefin; 11.9% 
diisocyanate mono-olefin; and 83% triisocyanate-TPTI). The triisocyanate 
was isolated by dissolving the crude mixture in hot hexane, filtered to 
remove small amounts of insolubles and cooled. Pure TPTI (m.p. 
71.degree.-72.degree. C.) crystallized out on standing. 
EXAMPLE XII 
TPTI From TRIPEB (1,3,5-Tri-isopropenyl Benzene) 
To 200 ml of toluene containing 40 grams of isocyanic acid (930 m moles) 
and 1 gram of dodecylbenzene sulfonic acid catalyst at 50.degree. C. is 
added 20 grams (200 m moles) of TRIPEB over a period of one hour. 
Volatiles are stripped from the reaction mixture (.about.80.degree./25 mm 
Hg) and the residue taken up in hot hexane. On cooling 15 g of pure 
tri-iso-cyanate (TPTI) is isolated in a first crop. 
EXAMPLE XIII 
TPTU From TPTO (1,3,5-tri(1-hydroxy-1-methylethyl) Benzene 
To 50.6 grams (200 m moles) of the triol (TPTO) is added 43 g (1 mole) of 
methyl carbamate, followed by the addition of 0.98 gram (10 m moles) of 
sulfuric acid. The mixture is heated at .about.90.degree. for 2 hours, 
cooled to room temperature and neutralized with aqueous sodium carbonate. 
Organics are extracted with methylene chloride, separated from the water 
layer, and dried over magnesium sulfate. Addition of hot hexane to the 
dried solution on standing yields 40 grams of TPTU, the desired 
tri-urethane. 
EXAMPLE XIV 
TPTU from TRIPEB(1,3,5-Triisopropenyl Benzene) & Methyl Carbamate 
To 2.33 g (10 m moles) of 1,3,5-triisopropenyl benzene (85%) in 100 ml of 
methylene chloride solution was added 9.0 gram (209 m moles) of methyl 
carbamate and 0.19 gram of p-toluene sulfonic acid catalyst dissolve in 20 
ml methylene chloride. After standing three days at room temperature, 
water (.about.20 ml) was added to the mixture and the methylene chloride 
layer separated and dried over magnesium sulfate. Addition of hot hexane 
to the dried solution gave on standing 1.1 g of the corresponding desired 
tri-urethane, m.p. 150.degree.-151.degree. C. 
EXAMPLE XV 
Cracking of TPTU To TPTI (Tri-Isocyanate) 
To 2 g of TPTU is added 0.2 g of CaO and the mixture heated at 
220.degree.-240.degree. (.about.20 mm Hg) for one hour. The solids are 
extracted with methylene chloride, filtered and hot hexane added. After 
standing, 1.2 grams of pure TPTI crystals separate; the tri-isocyanate 
melts at 71.degree.-72.degree. C.