The instant invention is directed to novel low temperature, storage stable liquid diphenylmethane diisocyanates and to the method of their preparation. The diisocyanates of the instant invention are provided by reacting diphenylmethane diisocyanates having a specified 2,4'-isomer content with polyoxyethylene glycols having molecular weights of from 150 to 1500. It has been surprisingly found that the products of the instant invention are both stable and liquid at -5.degree. C for at least 48 hours. In fact, in many instances, the products of the instant invention show no tendency to crystallize even when stored at -22.degree. C for 100 hours.

BACKGROUND OF THE INVENTION 
It is well known that diisocyanates which are liquid at room temperature 
(i.e., about 25.degree. C) have numerous advantages over solid 
diisocyanates because they are easier to mix and work with. However, 
diisocyanates which are liquid at room temperature and which are used on a 
large technical scale, such as toluene diisocyanate or hexamethylene 
diisocyanate, are as a rule physiologically harmful due to their high 
vapor pressure and therefore can only be used if certain safety 
precautions are taken. For this reason, various attempts have been made, 
either to start with diisocyanates that are normally liquid at room 
temperature and to reduce their physiological effects by certain 
procedures or to start with diisocyanates that are solid at room 
temperature and to convert these into liquid form. In both cases, however, 
one usually obtains either isocyanates of higher valency, i.e., tri- or 
polyisocyanates or higher molecular weight diisocyanates or a combination 
of these effects. 
The most important diisocyanates which are solid at room temperature and 
which are readily available on a large commercial scale are 
4,4'-diphenylmethane diisocyanate and the 2,4'-isomer thereof which melt 
at 39.degree. C and 34.5.degree. C respectively. Attempts have already 
been made to liquify both the 4,4'-diphenylmethane diisocyanate and a 
mixture of the 4,4'-diphenylmethane diisocyanate and a small amount of the 
2,4'-isomer. Thus, for example, in U.S. Pat. No. 3,644,457, 1 mol of a 
diphenylmethane diisocyanate is reacted with from about 0.1 to about 0.3 
mols of poly-1,2-propylene ether glycol. While the products made according 
to this patent have met with commercial success, they still suffer from a 
serious drawback. Specifically, it has been found that these adducts 
generally will crystallize anywhere from 5.degree. C to as high as 
25.degree. C. In fact, when supplied in commercial quantities, these 
adducts are generally transported in heated trucks. Additionally, in order 
to thaw the materials it is generally necessary to heat them to somewhere 
in excess of 50.degree. to 60.degree. C. While in warmer climates, there 
may not be any problem, in colder areas where the product may be stored in 
tanks over a period of time, this tendency to crystallize can become a 
very serious problem. Similar attempts to form liquid diphenylmethane 
diisocyanates have been described for example, in U.S. Pat. Nos. 3,384,653 
and 3,394,164. The attempts to liquify in both of these instances were 
based on the addition of, in one case, a trihydrocarbyl phosphate, and, in 
the other case, small amounts of phosphoric acid. In any event, the 
storage stability of both of these types of products in again quite good 
around room temperature, but as the temperature decreases, both types of 
materials tend to crystallize. 
In U.S. application Ser. No. 766,997, filed on Feb. 9, 1977, diisocyanates 
are described which are both stable and liquid at -5.degree. C for at 
least 48 hours. The diisocyanates disclosed therein are produced by 
reacting a diphenylmethane containing at least 15 percent by weight of the 
2,4'-isomer with a propylene glycol or poly-1,2-propylene ether glycol. 
Although such products represent an important advance in the art, the 
search has continued for other liquid organic diisocyanates. 
It is therefore an object of this invention to provide improved liquid 
organic diisocyanates which are liquid and stable at temperatures lower 
than room temperature. A further object of this invention is to provide 
organic diisocyanates which remain liquid even on prolonged storage at low 
temperatures.

DESCRIPTION OF THE INVENTION 
The instant invention is therefore directed to novel diisocyanate compounds 
which are both stable and liquid at -5.degree. C for at least 48 hours 
which diisocyanate compounds comprises the reaction product of a 
diphenylmethane diisocyanate containing at least 20% by weight of the 
2,4'-isomer with polyoxyethylene glycol having a molecular weight of from 
150 to 1500. The materials are reacted in an NCO/OH ratio of from about 3 
: 1 to about 15 : 1, preferably from about 3 : 1 to about 10 : 1 and most 
preferably from about 3 : 1 to about 6 : 1. It has also been found that 
many of the novel diisocyanate compounds herein are both stable and liquid 
at -22.degree. C for 100 hours. 
The glycol and the isocyanate can be reacted at temperatures ranging 
anywhere from room temperature (i.e., about 25.degree.) up to 125.degree. 
C. Preferably, the reaction temperature is from room temperature to about 
90.degree. C and most preferably, from about 40.degree. C to about 
80.degree. C. 
In general, the diphenylmethane diisocyanates usable according to the 
instant invention must contain at least 20 percent by weight of the 
2,4'-isomer. While theoretically, there is no upper limit to the amount of 
2,4'-isomer which could be present in the isocyanate, as a practical 
matter, due to availability in the present day isocyanate market, it is 
generally not possible to have the 2,4'-isomer content in excess of 70 
percent. Thus, as a practical rule, the diphenylmethane diisocyanates used 
according to the instant invention will contain from about 20 to about 70 
percent by weight of the 2,4'-isomer with the balance being the 
4,4'-isomer and 2,2'-isomer and/or various MDI dimers (the 2,2'-isomer and 
any dimer are generally present only in trace amounts, i.e., less than 1 
percent by weight). The lower limit of 20 percent by weight of the 
2,4'-isomer is in fact somewhat marginal. In fact, it has been found that 
at the 20 percent level, some of the reaction products formed are low 
temperature storage stable while others are not. Preferably, the 
2,4'-isomer content is from about 25 to about 65 percent by weight and 
most preferably from about 40 to about 65 percent by weight. 
The liquid diisocyanates which can be prepared according to the instant 
invention have a relatively low viscosity and can therefore be worked up 
very easily, e.g., they can be cast or metered through pumps. In addition, 
they have a very low vapor pressure and are therefore substantially 
physiologically harmless. Since the reaction can generally be carried out 
at relatively low temperatures, the diisocyanate structure of the product 
of the process is completely preserved. Allophanate formation by the 
reaction of the resulting urethane groups with the isocyanate group to 
produce a polyisocyanate apparently does not take place to any large 
degree. This is true even when forming the reaction product at a 
temperature of 125.degree. C. 
The polyoxyethylene glycols usable in the instant invention include 
essentially any ranging from a molecular weight of 150 (i.e. triethylene 
glycol) up to molecular weights of about 1500. Specific examples include 
triethylene glycol, tetraethylene glycols, and various polyoxyethylene 
glycols. 
The process of the instant invention may be carried out by introducing the 
glycols into the diisocyanate at temperatures of from room temperature up 
to about 125.degree. C with stirring. Alternatively, the diisocyanate can 
be introduced into the glycols. The isocyanate content of the products of 
the process generally amounts to from as low as about 10 percent to as 
high as about 30 percent. 
The products of the process can be used for all types of different 
polyaddition reactions in the lacquer and plastics industries, e.g. for 
the production of polyurethane foams or polyurethane elastomers which are 
in turn useful for the preparation of cushions or gear wheels 
respectively. Because of their low freezing point, the materials can be 
transported and stored at reasonably cold temperatures. In fact, it will 
be clear from the examples which follow, many of the products of the 
instant invention do not freeze when stored at -22.degree. C for 100 
hours. Yet a further advantage of the reaction products of the instant 
invention resides in the fact that even if the products should freeze, 
they will readily thaw at room temperature. This is completely different 
from the materials disclosed in U.S. Pat. No. 3,644,457, which upon 
freezing, must be heated to in excess of 50.degree. C. 
The invention is further illustrated by the following examples in which all 
parts are by weight unless otherwise specified. 
EXAMPLES 
EXAMPLES 1 THROUGH 8 
In these eight examples, a diphenylmethane diisocyanate (containing 35 
percent by weight of the 4,4'-isomer and 65 percent by weight of the 
2,4'-isomer) and the various glycols specified in TABLE I were combined 
under vigorous stirring at 25.degree. C. After a few minutes, the reaction 
mixtures turned clear and slight exotherm of up to about 50.degree. to 
60.degree. C was observed. After the exotherm had leveled off, stirring 
was continued for an additional 5 hours. Samples were then analyzed for 
viscosity and NCO content and then stored in a freezer for 48 hours at 
-5.degree. C. After the 48 hours storage, the samples were removed from 
the freezer. Results are set forth in TABLE I. The amounts of glycols and 
isocyanates added were such that the NCO/OH ratio was as specified in the 
table. Examples 1 and 2 represent comparative examples. 
TABLE I 
__________________________________________________________________________ 
% NCO Storage 
Example NCO/OH 
by weight 
Viscosity 
Stability 
No. Glycol used ratio calc. found 
cps, 25.degree. C 
48 hours at -5.degree. C 
__________________________________________________________________________ 
1 Ethylene glycol (62.1) 
4.95 25.5 
-- phase separation, 
completely 
rock-hard solids 
solid 
2 Diethylene glycol (106.1) 
4.95 24.7 
24.3 
very high visco- 
gel 
sity, gel-type 
material 
3 Triethylene glycol (150.2) 
4.95 23.8 
23.7 
685 liquid 
4 Tetraethylene glycol 
4.95 22.9 
22.9 
795 liquid 
(194.2) 
5 Polyethylene glycol, 
4.95 21.7 
21.5 
910 liquid 
average MW 297 
6 Polyethylene glycol, 
4.95 20.3 
20.0 
1100 liquid 
average MW 397 
7 Polyethylene glycol, 
8.0 22.6 
22.2 
265 liquid 
average MW 600 
8 Polyethylene glycol, 
8.0 19.6 
19.3 
455 liquid 
average MW 1000 
__________________________________________________________________________ 
After bringing the products of Examples 3 through 8 back to room 
temperature, viscosities and % NCO were rechecked and found to be 
unchanged. 
EXAMPLES 9 THROUGH 13 
The process of Examples 1 through 8 were followed except that the isomer 
distribution was varied as set forth in TABLE II. A constant NCO/OH ratio 
of 4.95 was used in each instance. The glycol used in each example was 
tetraethylene glycol. Results are set forth in TABLE II. After bringing 
the products of Examples 11 through 13 back to room temperature, 
viscosities and % NCO were rechecked and found to be unchanged. 
TABLE II 
__________________________________________________________________________ 
MDI % NCO by 
Viscosity 
Storage 
Example 
4,4'/2,4' 
NCO/OH 
weight Stability 48 
No. Ratio 
ratio found cps, 25.degree. C 
hours at -5.degree. C 
__________________________________________________________________________ 
9 100 : 0 
4.95 -- rock-hard solids, 
completely 
mp &gt; 80.degree. C 
solid 
10 80 : 20 
4.95 22.7 685 completely 
solid 
11 60 : 40 
4.95 22.8 800 liquid 
12 57 : 43 
4.95 22.7 685 liquid 
13 35 : 65 
4.95 22.9 795 liquid 
__________________________________________________________________________ 
EXAMPLES 14 THROUGH 17 
The process of Examples 1 through 8 was followed using diphenylmethane 
diisocyanate containing 65 percent by weight of the 2,4'-isomer and a 
polyethylene glycol having an average molecular weight of 600. The 
reaction temperature was 25.degree. C and exotherms were found to be 
between 35.degree. C and 50.degree. C. After the exotherm had leveled off, 
stirring was continued for 5 hours. Various NCO/OH ratios were used as 
specified in TABLE III. Results are set forth in TABLE III. After bringing 
the products back to room temperature, viscosities and % NCO were 
rechecked and found to be unchanged. 
TABLE III 
______________________________________ 
% NCO Storage 
Ex. NCO/OH by weight Viscosity 
Stability 
No. Ratio calc. found 
cps, 25.degree. C 
48 hrs. at -5.degree. C 
______________________________________ 
14 10 24.4 24.0 115 liquid 
15 8 22.6 22.2 266 liquid 
16 4.9 17.9 17.2 1660 liquid 
17 3.0 12.4 11.7 7130 liquid 
______________________________________ 
EXAMPLES 18 THROUGH 21 
The process of Examples 1 through 8 was followed using an NCO/OH ratio of 
3.72, a diphenylmethane diisocyanate containing 65% by weight of the 
2,4'-isomer, and triethylene glycol, but using various reaction 
temperatures, and heated for the times specified in TABLE IV. The 
temperature, times of reaction and results were as set forth in TABLE IV. 
% NCO and viscosities remained unchanged after the products were brought 
back to room temperature. 
TABLE IV 
______________________________________ 
Storage 
Reaction Stability 
Ex. Reaction Time % NCO Viscosity .sup.+ 
48 hours 
No. Temperature 
in hours Found cps, 25.degree. C 
at -5.degree. C 
______________________________________ 
18 ambient 8 hrs. 21.2 4000 liquid 
19 40.degree. C 
8 hrs. 21.1 4300 liquid 
20 65.degree. C 
3 hrs. 21.1 4200 liquid 
21 105.degree. C 
1 hr. 20.7 4425 liquid 
______________________________________ 
.sup.+ All viscosities are measured the day materials were prepared. It 
was observed that these materials have a thixotropic character. 
The products of Examples 2 through 21 were all stored in a deep-freezer for 
100 hours at -22.degree. C and checked for stability against freezing 
and/or crystallization. The results were as set forth in TABLE V. 
TABLE V 
______________________________________ 
Example 100 hrs./-22.degree. C 
No. Storage Stability 
Comments 
______________________________________ 
2 gel very high viscosity, gel-like 
material 
3 liquid none 
4 liquid " 
5 liquid " 
6 liquid " 
7 complete material melted to a perfect liquid 
at ambient temperature without 
solid heating, shaking or stirring. 
8 " 
9 complete materials do not melt at ambient 
temperature; they remain a white 
solid crystalline solid. 
10 " 
11 liquid none 
12 " " 
13 " " 
14 " " 
15 " " 
16 " " 
17 " " 
18 " " 
19 " " 
20 " " 
21 " " 
______________________________________ 
EXAMPLE 22 
To 300 grams of diphenylmethane diisocyanate with a 2,4'-isomer content of 
20 percent were added 240 grams of polyethylene glycol (molecular weight 
of 600) at 50.degree. C under stirring. The temperature of the reaction 
mixture increased to about 85.degree. C and then dropped within 1 hour to 
about 55.degree. C. Stirring was continued for 3 hours at 55.degree. C. 
The NCO/OH ratio used was 3. The percent NCO in the product was found to 
be 11.8 percent while the viscosity at 25.degree. C was found to be 15,400 
cps. The product remained in the liquid state when stored at -5.degree. C 
for 48 hours and when stored at -22.degree. C for 100 hours. After storage 
stability was established, no change in either NCO content or viscosity 
could be determined. 
This example serves to illustrate that, as noted earlier, at the 20 percent 
2,4'-isomer content level it is certainly possible to produce liquid 
products within the defined invention (compare Example 10). 
EXAMPLES 23 THROUGH 26 
The process of Examples 1 through 8 was followed using an NCO/OH ratio of 
4.95, a diphenylmethane diisocyanate containing 65 percent by weight of 
the 2,4'-isomer and triethylene glycol, but using various reaction 
temperatures and heated for the times specified in TABLE VI. The 
temperatures, times of reaction and results were as set forth in TABLE VI. 
Percent NCO and viscosities remained unchanged after the products were 
brought back to room temperature. 
TABLE VI 
______________________________________ 
Storage 
Reaction Stability 
Ex. Reaction Time % NCO Viscosity 
48 hours 
No. Temperature 
in hours Found cps, 25.degree. C 
at -5.degree. C 
______________________________________ 
23 25.degree. C 
19 hrs. 23.9 570 liquid 
24 40.degree. C 
5 hrs. 23.9 570 liquid 
25 65.degree. C 
4 hrs. 24.2 550 liquid 
26 105.degree. C 
1 hr. 23.8 605 liquid 
______________________________________ 
When stored for 100 hours at -22.degree. C, the products of Examples 23 
through 26 remained liquid. 
It is to be understood that the foregoing examples are given for the 
purpose of illustration and that various other materials within the 
definition of the claims could be used. Although the invention has been 
described in detail for the purpose of illustration, it is to be 
understood that such detail is solely for that purpose and that variations 
can be made therein by those skilled in the art without departing from the 
spirit and scope of the invention except as it may be limited by the 
claims.