Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From heterocyclic reactant containing as ring atoms oxygen,...
Reexamination Certificate
2000-05-19
2002-05-07
Lovering, Richard D. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From heterocyclic reactant containing as ring atoms oxygen,...
C502S153000, C502S156000, C524S414000, C524S415000, C568S606000
Reexamination Certificate
active
06384183
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to metal catalysts for alkylene oxide polymerization.
Alkylene oxides such as ethylene oxide, propylene oxide and 1,2-butylene oxide are polymerized to form a wide variety of polyether products. For example, polyether polyols are prepared in large quantities for polyurethane applications. Other polyethers are used as lubricants, brake fluids, compressor fluids, and many other applications.
These polyethers are commonly prepared by polymerizing one or more alkylene oxides in the presence of an initiator compound and an alkali metal catalyst. The initiator compound is typically a material having one or more hydroxyl, primary or secondary amine, carboxyl or thiol groups. The function of the initiator is to set the nominal functionality (number of hydroxyl groups/molecule) of the product polyether, and in some instances to incorporate some desired functional group into the product.
Until recently, the catalyst of choice was an alkali metal hydroxide such as potassium hydroxide. Potassium hydroxide has the advantages of being inexpensive, adaptable to the polymerization of various alkylene oxides, and easily recoverable from the product polyether.
However, to a varying degree, alkali metal hydroxides catalyze an isomerization of propylene oxide to form allyl alcohol. Allyl alcohol acts as a monofunctional initiator during the polymerization of propylene oxide. Thus, when potassium hydroxide is used to catalyze propylene oxide polymerizations, the product contains allyl alcohol-initiated, monofunctional impurities. As the molecular weight of the product polyether increases, the isomerization reaction becomes more prevalent. Consequently, poly(propylene oxide) products having equivalent weights of about 800 or more prepared using KOH as the catalyst tend to have very significant quantities of the monofunctional impurities. This tends to reduce the average functionality and broaden the molecular weight distribution of the product.
More recently, the so-called double metal cyanide (DMC) catalysts have been used commercially as polymerization catalysts for alkylene oxides. Because some of these catalysts do not significantly promote the isomerization of propylene oxide, polyethers having low unsaturation values and higher molecular weights can be prepared, compared to potassium hydroxide-catalyzed polymerizations.
These DMC catalysts are described, for example, in U.S. Pat. Nos. 3,278,457, 3,278,458, 3,278,459, 3,404,109, 3,427,256, 3,427,334, 3,427,335 and 5,470,813, among many others. The composition of these catalysts can vary widely, but can generally be represented by the formula
M
b
[M
1
(CN)
r
(X)
t
]
c
·zL·aH
2
O·nM
x
A
y
wherein M is a metal ion that forms an insoluble precipitate with the metal cyanide grouping M′(CN)
r
(X)
t
and which have at least one water soluble salt;
M
1
is a transition metal ion;
X represents a group other than cyanide that coordinates with the M
1
ion;
L represents an organic complexing agent;
A represents an anion that forms a water-soluble salt with M ion;
b and c are numbers that reflect an electrostatically neutral complex;
r is from 4 to 6; t is from 0 to 2; and
z, n and a are positive numbers (which may be fractions) indicating the relative quantities of the complexing agent, water molecules and M
x
A
y
, respectively.
However, experience has shown that most of the possible combinations of M, M
1
, X, L, r and t do not provide a catalyst having sufficient activity to be of commercial interest. Most combinations show virtually no activity at all. In addition, not all of those possible combinations of M, M
1
, X, L, r and t provide very low unsaturation poly(propylene oxide) polymers. Recently, developmental and commercial efforts have focussed almost exclusively on zinc hexacyanocobaltate, together with a specific complexing agent, t-butanol.
Zinc hexacyanocobaltate (together with the proper complexing agent and an amount of a poly(propylene oxide)) has the advantages of being active and of not significantly catalyzing the propylene oxide isomerization reaction. Because of the activity of this catalyst, it can be used in such small amounts that it is less expensive to replace it than to recover it from the product polyether. As a result, finishing operations such as are commonly used to remove alkali metal hydroxides from polyethers can be avoided, thereby reducing the overall production cost. However, as the catalyst is often left in the product, it must be replaced. Thus, it would be desirable to reduce the cost of the catalyst as much as possible consistent with obtaining efficient polymerizations and desirable products.
As described in U.S. Pat. No. 5,470,813, one disadvantage of DMC catalysts is that they tend to require an induction period of close to an hour to many hours in some cases before becoming active. Little polymerization occurs during this induction period. For some operations, it would be desirable to reduce this induction period.
It would be desirable, therefore, to provide an active catalyst for polymerizing alkylene oxides, which is less expensive to prepare than zinc hexacyanocobaltate complexes. It would be even more desirable to provide a catalyst that exhibits a short induction period before rapidly polymerizing alkylene oxides.
SUMMARY OF THE INVENTION
In one aspect, this invention is a metal hexacyanocobaltate nitroferricyanide catalyst complexed with one or more organic complexing agents, wherein the metal is any that forms a water-insoluble precipitate with hexacyanocobaltate and nitroferricyanide groups, and the molar ratio of hexacyanocobaltate to nitroferricyanide groups is from about 20:80 to about 98:2.
In another aspect, this invention is a method of making an active polymerization catalyst, comprising (a) forming a first solution of water soluble hexacyanocobaltate and nitroferricyanide compounds, said hexacyano-cobaltate and nitroferricyanide compounds being present in proportions such that said solution contains a molar ratio of hexacyanocobaltate to nitroferricyanide ions of about 20:80 to about 98:2,
(b) mixing said first solution with a second solution of a water soluble salt of a metal that forms a water-insoluble precipitate with hexacyanocobaltate and nitroferricyanide groups, in an amount sufficient to provide a stoichiometric excess of the metal salt relative to the combined amounts of hexacyanocobaltate and nitroferricyanide ions contained in said first solution, so as to precipitate a metal hexacyanocobaltate nitroferricyanide, and
(c) either simultaneously or after step (b), contacting said metal hexacyanocobaltate nitroferricyanide with an organic complexing agent.
In a third aspect, this invention is an improvement in a process for polymerizing an epoxide compound in the presence of a catalyst, in which the catalyst is a metal hexacyanocobaltate nitroferricyanide complexed with one or more organic complexing agents, said metal being any that forms a water-insoluble precipitate with hexacyanocobaltate and nitroferricyanide groups.
It has been found that the metal hexacyanocobaltate nitroferricyanide complex of the invention has excellent activity as an epoxide polymerization catalyst, and in particular exhibits unusually low induction periods. Because some of the expensive hexacyanocobaltate starting materials of conventional DMC catalysts are replaced with nitroferricyanide compounds, the overall cost of the catalyst is reduced significantly.
In addition, it has been found that poly(propylene oxide) polymers produced using the catalysts of this invention having extremely low unsaturation content, even when complexing agents such as glyme are used. Using materials such as glyme instead of t-butanol as a complexing agent for the catalyst provides significant advantages in preparing and handling the catalyst complex. t-Butanol tends to cause gelling and to make it difficult to isolate double metal cyanide catalysts. Thus, this invention provides a method by which low unsaturation polyethers can be prepared with a less expensive, mor
Flagler Kendra L.
Gulotty, Jr. Robert J.
Laycock David E.
Lovering Richard D.
The Dow Chemical Company
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