Process for the dispersion of chain extender in polyol

The present invention provides a process for preparing stable, uniform dispersions of chain extenders in polyurethane-forming polyol. The preferred chain extender is hydroquinone di(.beta.-hydroxyethyl)ether. The process comprises an adiabatic quenching step in combination with an annealing step. The inventive process avoids the need for slow, carefully controlled cooling schemes.

DESCRIPTION 
Background 
The present invention relates to a process for preparing dispersions of 
chain extender in polyurethane-forming polyol. More particularly, the 
process is directed to preparing dispersions of hydroquinone 
di(.beta.-hydroxyethyl)ether in polyurethane-forming polyol. Such 
dispersions are useful in the preparation of polyurethanes and are 
especially useful in the context of reaction injection molding techniques. 
The process is also advantageously used in conjunction with recently 
developed modified reaction injection molding (MIM) processes. These newly 
developed, quasi-one component processes require dispersions which are 
tailored for longer pot life. 
Chain extenders, such as hydroquinone di(.beta.-hydroxyethyl)ether (HQEE), 
have found increasing utility in polyurethane-forming systems. These chain 
extenders are incorporated into the polyurethane-forming system in order 
to join together relatively low molecular weight polyurethane chains so as 
to form higher molecular weight polymer chains. In order to produce a 
useful end polymer having desirable properties, these chain extenders must 
be distributed uniformly throughout the polyurethane-forming system. This 
end can be accomplished by dispersing the chain extender in the polyol 
component of a two-component polyurethane-forming system (the other 
component being the isocyanate component). 
Chain extender/polyol dispersions have been prepared in the past by 
agitating the chain extender/polyol mixture at temperatures higher than 
the melting point of the chain extender. The mixture was then cooled to 
room temperature to give the final dispersion. This method suffered from 
the high dependence of final product viscosity on the cooling rate of the 
mixture. Rapid cooling and/or cooling without proper agitation resulted in 
product solidification. Thus, the material tended to solidify during the 
cooling step on heat transfer surfaces such as the vessel walls. Little or 
no control was available over the final product viscosity. 
Other methods for preparing chain extender/polyol dispersions have involved 
dispersing ground chain extender in a polyol at room temperature. This 
method was not suitable because of the cost of grinding the chain 
extender. There also were indications that the final polyurethane product 
was inferior to that obtained when prior melt phase processes were used in 
preparing chain extender/polyol dispersions. 
It has further been disclosed in a 1980 Research Disclosure (No. 19,540) 
that dispersions of chain extender in polyol can be obtained by heating a 
mixture of chain extender and polyol to a temperature above the melting 
point of the chain extender and then cooling the mixture at a controlled 
rate to room temperature. The cooling rate is selected so that the 
solution does not freeze into a nonequilibrated, glassy state. Following 
cooling, the viscosity of the product can be adjusted as desired by the 
addition of additional polyol. 
The processes described above all suffer the disadvantage of requiring an 
extremely slow cooling step (i.e., on the order of 8-24 hours). Attempts 
to speed the cooling step result in excessive crystal growth on heat 
transfer surfaces and/or a solid, non-equilibrated, glassy product. The 
present invention overcomes these disadvantages by providing a process 
wherein dispersions are rapidly prepared without the need for a prolonged 
cooling step and the final dispersions properties are easily controlled. 
SUMMARY OF THE INVENTION 
The present invention provides a process for preparing dispersions of 
hydroquinone di(.beta.-hydroxyethyl)ether in polyurethane-forming polyol. 
The process comprises steps of: 
(a) heating and blending an initial mixture of about 5 to 30 parts by 
weight of HQEE and about 10 to 50 parts by weight of the polyol until a 
condensed phase is formed by the melting of HQEE at a temperature of at 
least about 90.degree. C.; 
(b) combining with the initial mixture an additional quantity of polyol 
sufficient to bring the total amount of polyol in the resulting dispersion 
to about 100 parts by weight, the additional polyol being at a temperature 
substantially below that of the initial mixture so that the addition 
thereof to the initial mixture results in adiabatic quenching of the 
resulting dispersion to a temperature in the range of about 70.degree. to 
85.degree. C.; 
(c) annealing the dispersion by heating the dispersion to a temperature 
which is at least about 5.degree. C. greater than the quenching 
temperature and which is in the range of about 84.degree. to 90.degree. 
C.; and 
(d) cooling the dispersion to a desired handling temperature which is less 
than about 60.degree. C. 
DETAILED DESCRIPTION OF THE INVENTION 
The present invention relates to a process for preparing dispersions of 
polyurethane chain extenders in polyurethane-forming polyol. While it is 
contemplated that a number of currently available chain extenders may be 
used in the process of the present invention, the process is directed 
particularly toward the use of hydroquinone di(.beta.-hydroxyethyl)ether 
(HQEE). 
The polyol in which the chain extender is to be dispersed can be any of the 
well known, commercially available polyurethane-forming polyol 
formulations. Such polyols have been described at length in the 
literature. See, for example, Polyurethanes: Chemistry and Technology, 
Part 1. Chemistry, by J. H. Saunders and K. C. Frisch, Interscience 
Publishers (New York: 1962), pages 32-46, and Polyurethane Technology, ed. 
Paul F. Bruins, Interscience Publishers (New York: 1969), pages 12-19. The 
best known and most widely used type of polyurethane-forming polyol are 
the polyether polyols. Examples of such polyols are the 
poly(oxypropylene)glycols; the 
poly(oxypropylene)-poly(oxyethylene)glycols; and the poly(oxypropylene) 
adducts of glycerine, trimethylol propane, 1,2,6-hexanetriol, 
pentaeythritol, and sorbitol. Such polyols are available commercially 
under the trademarks Niax.RTM. (Union Carbide), Pluracol.RTM. and 
Tetronic.RTM. (Wyandotte Chemicals), Voranol.RTM. (Dow chemical), 
Poly-G.RTM. (Olin Chemicals), Triol G.RTM. (Jefferson Chemical), and 
Actol.RTM. (Allied Chemical). Specific commercial polyols which are 
preferred for use in the process of the present invention include 
Pluranol.RTM. P-581 and Niax.RTM. D-440. However, it is to be understood 
that the process of the present invention is not limited to the use of 
these preferred polyols. 
The process of the present invention provides dispersions comprising 5 to 
30 parts by weight of hydroquinone di(.beta.-hydroxyethyl)ether and about 
100 parts by weight of polyol. Especially preferred dispersions comprise 
about 20 parts by weight of HQEE and about 100 parts by weight of polyol. 
In accordance with the process of the present invention, an initial mixture 
of about 5 to 30 parts by weight of HQEE (preferably about 20 parts by 
weight) and about 10 to 50 parts by weight of polyol is heated and blended 
until a condensed phase is formed by the melting of HQEE. The term 
"blended" as used herein is intended to connote mixing in conjunction with 
agitation. Any of a number of well-known agitation systems can be used in 
this regard. Thus, means for accomplishing agitation can include static 
mixers, dynamic mixers, pumps, heat exchange equipment, shear devices, 
screens, homogenizers, and other apparatus which accomplishes the desired 
objectives of mixing in conjunction with agitating. 
In preferred embodiments, the initial mixture comprises about half of the 
total amount of polyol to be included in the final dispersion (i.e., about 
40-50 parts by weight). 
Typically, the initial mixture is heated to a temperature of at least about 
90.degree. C. in order to form a condensed phase by the melting of the 
HQEE. Preferably, the mixture is heated to a temperature within the range 
of about 90.degree.-105.degree. C. 
After the initial mixture has been heated to a desired temperature at which 
a condensed phase is observed, an additional quantity of polyol is 
combined with the initial mixture. The additional quantity of polyol 
required is that which is sufficient to bring the total amount of polyol 
in the resulting dispersion to about 100 parts by weight. The temperature 
of the additional polyol is substantially below that of the heated initial 
mixture so that the addition of the additional polyol results in adiabatic 
quenching of the resulting dispersion. In especially preferred 
embodiments, the additional polyol is at room temperature before being 
added to the initial mixture. However, it is contemplated that it may be 
necessary and/or desirable for the additional polyol to be at a 
temperature below room temperature in order to accomplish adiabatic 
quenching of the resulting dispersion. It is also conceivable that the 
additional polyol could be at a temperature above room temperature upon 
its addition to the initial mixture. However, the extra heating required 
to obtain a temperature above room temperature would in most instances be 
wasteful; the same results could be achieved by varying the amount of 
polyol utilized in the initial mixture relative to the amount of room 
temperature polyol utilized in the subsequent quenching. 
The additional polyol is combined with the initial mixture so as to achieve 
adiabatic quenching of the resulting dispersion to a temperature in the 
range of about 70.degree. to 85.degree. C. By the term "adiabatic 
quenching", it is meant that there is no transfer of heat energy to or 
from the dispersion system other than between the initial mixture and the 
additional polyol. The amount of additional polyol and the temperature at 
which it is combined with the initial mixture are adjusted so that the 
temperature of the resulting dispersion is within the range of 70.degree. 
to 85.degree. C. 
The resulting dispersion is then annealed by heating the dispersion to a 
temperature which is at least about 5.degree. C. greater than the 
quenching temperature and which is in the range of about 84.degree. to 
90.degree. C. During this annealing step, the dispersion is gently heated 
and agitated. As discussed above, the agitation can be accomplished using 
a wide variety of apparatus. After annealing, the dispersion is then 
cooled to a desired handling temperature which is less than about 
60.degree. C. Typically, the desired handling temperature will be less 
than 50.degree. C. and preferably about 40.degree. C. 
While not wishing to be bound by theoretical considerations, it appears 
that the advantages realized by the process of the present invention are 
due to transformations which occur in the crystalline content of the 
material. For example, in prior processes, slow cooling without agitation 
yielded a hard matrix of crystals having varying compositions. In 
contrast, in accordance with the process of the present invention, rapid 
quenching by the addition of polyol yields a large number of smaller 
crystallites having nearly the same composition. Subsequent reheating 
(annealing) accomplishes the transformation of some of these crystallites 
to a softer, poly-rich phase. That is, the crystallites are diminished in 
size and/or number, and the result is a smoother, more stable, and more 
uniform dispersion. 
It has further been observed that the properties of the final dispersion 
are strongly dependent upon the exact temperature-transformation-time 
sequence which is followed and upon the shear inputs. In other words, 
varying the quenching rate, the extent of quenching, and/or the agitation 
rate influences the types and sizes of the suspended phases. For example, 
in order to achieve a final dispersion with a relatively low viscosity, 
the adiabatic quenching should be accomplished relatively quickly. 
Conversely, If a higher viscosity is desired, the additional polyol should 
be added more slowly for a decreased quenching rate. Therefore, by 
adjusting the various parameters within the limits defined by the process 
of the present invention, the skilled artisan can optimize the present 
process for any particular HQEE/polyol dispersion system. 
It has also been observed that dispersions which have been previously 
prepared, either by the present process or by some less advantageous prior 
art process, can be upgraded in quality by subjecting the 
previously-formed dispersion to the annealing procedure of the present 
process. That is, a lower quality dispersion comprising about 5 to 30 
parts by weight of HQEE and about 100 parts by weight of polyol can be 
upgraded by heating the dispersion to a temperature in the range of about 
70.degree. to 85.degree. C., annealing the dispersion by further gently 
heating the dispersion with agitation at least an additional 5.degree. C. 
to a temperature which is in the range of about 84.degree. to 90.degree. 
C., and then cooling the dispersion again to the desired handling 
temperature. In this manner, the properties of the lower quality 
dispersion are improved, presumably by transformation of the crystallites 
which may be present in the dispersion, as described above. 
In contrast to prior processes for forming HQEE/polyol dispersions, the 
process of the present invention avoids the necessity of slow, expensive, 
time-consuming cooling steps. Rapid adiabatic quenching is accomplished by 
the addition of a portion of one of the components of the system (i.e., 
the polyol component), and, after annealing, the resulting dispersion can 
be cooled to a desired processing temperature without regard to any slow, 
critical cooling schedule. Thus, according to the process of the present 
invention, dispersions can be rapidly prepared, and operating costs are 
reduced. In addition, final dispersion properties can be controlled for 
specific applications by adjusting the extent and rate of quenching. In 
addition, poor quality dispersions can easily be upgraded.

This invention will be further illustrated by the following examples, 
although it will be understood that these examples are included merely for 
purposes of illustration and are not intended to limit the scope of the 
invention. 
EXAMPLE 1 
This example illustrates the preparation of a 20:100 HQEE:polyol 
dispersion. The polyol which is used in the present example is Niax.RTM. 
D-440, which is a graft copolymer of polytetramethylene glycol with 
acrylonitrile and styrene and which exhibits an average molecular weight 
of about 4066. 
Twenty parts by weight of HQEE and 50 parts by weight of the polyol are 
heated and agitated in a stirred vessel until the HQEE is fully melted at 
about 100.degree. C. An additional 50 parts of polyol is added at room 
temperature to this initial mixture. The mixture is thereby adiabatically 
quenched to about 78.degree. C. The resulting dispersion is then gently 
heated with continued agitation to a temperature of about 84.degree. C. 
During this annealing step, a decrease in viscosity is observed. The 
dispersion is then passed through a gear pump into a 3/8".times.15' 
jacketed tube coil. Cooling water is passed through the jacket, thereby 
cooling the dispersion flowing through the interior of the coil to a 
desired product temperature of about 40.degree. C. The cooled dispersion 
exits the coil through a relief valve, which functions as a homogenizer. 
The resulting product is observed to be a readily flowable, uniform 
dispersion of HQEE and polyol. 
The invention has been described in detail with particular reference to 
preferred embodiments thereof, but it will be understood that variations 
and modifications can be effected within the spirit and scope of the 
invention.