Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From heterocyclic reactant containing as ring atoms oxygen,...
Reexamination Certificate
2000-07-07
2003-04-22
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,...
C523S332000, C528S410000, C528S414000, C528S493000, C528S494000, C528S495000
Reexamination Certificate
active
06552163
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to methods for purifying poly(ethylene oxide) polymers.
Polyethers are prepared in large commercial quantities through the polymerization of alkylene oxides such as propylene oxide and ethylene oxide. This polymerization reaction is usually conducted in the presence of an initiator compound and a catalyst. The initiator compound determines the functionality (number of hydroxyl groups per molecule) of the polymer and in some instances imparts some desired functional group to the polymer. The catalyst is used to provide an economical rate of polymerization.
It is desirable to produce polyethers having low polydispersities. While this is true as a general matter for many types of polyethers, it is particularly true for many poly(ethylene oxide) polymers. Polyethylene oxides tend to be solids at room temperature when the molecular weight exceeds about 700. Thus, molecular weight control is especially important when a liquid poly(ethylene oxide) is desired. Moreover, the presence of even a small amount of a high (above about 1000) molecular weight fraction in a poly(ethylene oxide) polymer can cause the entire polymer to become hazy or solidify. Even if the entire polymer is not solidified, the solid high molecular weight fraction can occlude a significant amount of low molecular weight species. As a result, yields of the desired liquid polymer are significantly reduced. To recover the desired low molecular weight portion of the reaction product, it is necessary to remove the high molecular weight fraction.
Thus, a process by which poly(ethylene oxide) polymers can be fractionated efficiently to remove a high molecular weight fraction would be desirable.
SUMMARY OF THE INVENTION
This invention is a method for purifying a poly(ethylene oxide) polymer containing a lower molecular weight fraction and at least one higher molecular weight fraction, comprising
(a) mixing said poly(ethylene oxide) polymer with a compound or mixture of compounds, said compound or mixture of compounds being a solvent for said low molecular weight fraction but not for said high molecular weight fraction, in relative amounts and under conditions such that a solution of said low molecular weight fraction in said compound or mixture of compounds forms and
(b) separating said solution from said high molecular weight fraction.
In a second aspect, this invention is a method for removing a metal cyanide catalyst from a poly(ethylene oxide) polymer containing a metal cyanide catalyst, a lower molecular weight fraction and at least one higher molecular weight fraction, comprising
(a) mixing a poly(ethylene oxide) polymer with a compound or mixture of compounds, said compound or mixture of compounds being a solvent for said low molecular weight fraction but not for said high molecular weight fraction, in relative amounts and under conditions such that a solution of said low molecular weight fraction in said compound or mixture of compounds forms and
(b) separating said solution from said high molecular weight fraction, and
(c) recovering said low molecular weight fraction from said solution.
The method of the invention provides a simple and effective method for recovering a low molecular weight fraction from a poly(ethylene oxide) polymer.
An additional benefit is seen when the poly(ethylene oxide) is prepared with a metal cyanide catalyst. Surprisingly, the metal cyanide catalyst is effectively removed with the high molecular weight fraction. Thus, this invention provides a simple and effective means for removing the metal cyanide catalyst from the desired low molecular weight fraction of the product. Removal of the catalyst to levels of less than one part per million of the low molecular weight fraction is often achieved.
Even more surprisingly, the metal cyanide catalyst that is removed with the high molecular weight fraction remains active. Thus, the high molecular weight fraction that contains the catalyst can be recycled into subsequent polymerization reactions.
DETAILED DESCRIPTION OF THE INVENTION
The poly(ethylene oxide) polymer to be fractionated is one having a low molecular weight fraction and at least one distinct higher molecular weight fraction. The molecular weights of the fractions are sufficiently distinct that the fractions have different solubility characteristics. It is this difference in solubility characteristics that provides the basis upon which the method of the invention operates. Thus, polymers having continuous polydispersities over a wide range of molecular weights are less preferred, as it is difficult to obtain a good separation of the lower molecular weight species from the higher molecular weight species. On the other hand, polymers having molecular weight distributions that are often characterized as “bimodal” or “multimodal” are preferred, as the differences in molecular weights between the various fractions relates to solubility differences between the fractions.
Thus, the preferred poly(ethylene oxide) polymers have two or more fractions having distinct molecular weights, and are further characterized by containing a low amount of material in the intermediate range(s) of molecular weights. It is also preferred that the lowest molecular weight fraction has a relatively narrow polydispersity, such as less than 2.0 and more preferably less than about 1.7.
In order for the various molecular weight fractions to have sufficiently different solubility characteristics, it is preferred that the number average molecular weight of the higher molecular weight fraction be at least 1.2, more preferably at least 1.5 times, even more preferably at least about 2 times, and most preferably at least 3 times that of the low molecular weight fraction.
The low molecular weight fraction can be of any molecular weight, provided that it can be dissolved in a suitable solvent that is a poor solvent for the high molecular weight fraction. Thus, the low molecular weight fraction may have a weight average molecular weight of up to about 5000 or more. However, the relatively low molecular weight fraction more typically has an M
w
in the range of from about 150, preferably from about 200, more preferably from about 250, up to about 3000, preferably up to about 2000, more preferably up to about 1000. In the case where the low molecular weight fraction has a M
w
of 700 or less, the low molecular weight fraction is usually a liquid when separated from the high molecular weight fraction. The relatively low molecular weight fraction generally constitutes about 40-99%, preferably about 70-99%, more preferably about 90-99%, of the weight of the poly(ethylene oxide) before fractionation.
Poly(ethylene oxide) polymers having molecular weight distributions as described above can be prepared by reacting an initiator compound and ethylene oxide in the presence of a metal cyanide catalyst complex, as described below. Poly(ethylene oxide) polymers made using such catalysts tend to contain a small high molecular weight fraction.
The poly(ethylene oxide) polymer typically has one or more terminal hydroxyl groups, with the number of these in most cases being determined by the choice of initiator compound that is used to make the polymer. The poly(ethylene oxide) may have as few as one or as many as 8 or more terminal hydroxyl groups per molecule. Poly(ethylene oxide) polymers having up to about 4 hydroxyl groups per molecule are preferred, with those having up to about 3 hydroxyl groups per molecule being more preferred and those having one or two hydroxyl groups per molecule being of most interest. Poly(ethylene oxide) polymers based on functionalized initiators are of particular interest, especially those based on initiators containing alkenyl or alkynyl groups. Initiators including alkenyl or alkynyl groups include, for example, 2,5-dimethyl-3-hexyn-2,5-diol and 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 3-butyn-1-ol, 3-butene-1-ol, propargyl alcohol, 2-methyl-3-butyn-2-ol, 2-methyl-3-butene-2-ol, allyl alcohol and the like. Halogenated initiators include, for example, 2-chlo
Clement Katherine S.
Walker Louis L.
Lovering Richard D.
The Dow Chemical Company
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