Acid-treated double metal cyanide complex catalysts

The amount of high molecular weight impurity present in a polyether polyol produced by alkoxylation of an active hydrogen-containing initiator and a substantially noncrystalline highly active double metal cyanide complex catalyst may be advantageously lowered by treating the catalyst prior to use in polymerization with a protic acid. Suitable protic acids include phosphoric acid and acetic acid. The higher purity polyether polyols thereby produced are particularly useful in the preparation of slab and molded polyurethane foams, which tend to collapse or become excessively tight when elevated levels of high molecular tail are present in the polyether polyol.

FIELD OF THE INVENTION 
This invention pertains to a method of enhancing the performance of a 
highly active substantially noncrystalline double metal cyanide complex 
catalyst characterized by the presence of zinc hydroxyl groups. More 
particularly, the invention relates to contacting such a catalyst with a 
protic acid whereby the acid-treated catalyst thus obtained is capable of 
producing polyether polyols having reduced levels of high molecular tail. 
Such polyether polyols have enhanced processing latitude in the 
preparation of molded and slab polyurethane foam. 
BACKGROUND OF THE INVENTION 
Polyurethane polymers are prepared by reacting a di- or polyisocyanate with 
a polyfunctional, isocyanate-reactive compound, in particular, 
hydroxyl-functional polyether polyols. Numerous art-recognized classes of 
polyurethane polymers exist, for example cast elastomers, polyurethane 
RIM, microcellular elastomers, and molded and slab polyurethane foam. Each 
of these varieties of polyurethanes present unique problems in formulation 
and processing. 
Two of the highest volume categories of polyurethane polymers are 
polyurethane molded and slab foam. In slab foam, the reactive ingredients 
are supplied onto a moving conveyor and allowed to rise freely. The 
resulting foam slab, often 6 to 8 feet (2 to 2.6 m) wide and high, may be 
sliced into thinner sections for use as seat cushions, carpet underlay, 
and other applications. Molded foam may be used for contoured foam parts, 
for example, cushions for automotive seating. 
In the past, the polyoxypropylene polyether polyols useful for slab and 
molded foam applications have been prepared by the base-catalyzed 
propoxylation of suitable hydric initiators such as propylene glycol, 
glycerine, sorbitol, etc., producing the respective polyoxypropylene 
diols, triols, and hexols. As is now well documented, a rearrangement of 
propylene oxide to allyl alcohol occurs during base-catalyzed 
propoxylation. The monofunctional, unsaturated allyl alcohol bears a 
hydroxyl group capable of reaction with propylene oxide, and its continued 
generation and propoxylation produces increasingly large amount of 
unsaturated polyoxypropylene monols having a broad molecular weight 
distribution. As a result, the actual functionality of the polyether 
polyols produced is lowered significantly from the "normal" or 
"theoretical" functionality. Moreover, the monol generation places a 
relatively low practical limit on the molecular weight obtainable. For 
example, a base catalyzed 4000 Da (Dalton) molecular weight (2000 Da 
equivalent weight) diol may have a measured unsaturation of 0.05 meq/g, 
and will thus contain 30 mol percent unsaturated polyoxypropylene monol 
species. The resulting actual functionality will be only 1.7 rather than 
the "nominal" functionality of 2 expected for a polyoxypropylene diol. As 
this problem becomes even more severe as molecular weight increases, 
preparation of polyoxypropylene polyols having equivalent weights higher 
than about 2200-2300 Da is impractical using conventional base catalysis. 
Double metal cyanide ("DMC") complex catalysts such as zinc 
hexacyanocobaltate complexes were found to be catalysts for propoxylation 
about 30 years ago. However, their high cost, coupled with modest activity 
and the difficulty of removing significant quantities of catalyst residues 
from the polyether product, hindered commercialization. The unsaturation 
level of polyoxyproylene polyols produced by these catalysts was found to 
be low, however. 
The relatively modest polymerization activity of these conventional double 
metal cyanide-complex catalysts has been recognized as a problem by 
workers in the field. One method of improving polyether polyol yields 
obtained from such catalysts is proposed in U.S. Pat. No. 4,472,560. This 
publication proposes a process for epoxide polymerization using as a 
catalyst a double metal cyanide-type compound, wherein said process is 
carried out in the presence of one or more non-metal containing acids of 
which a 0.1N solution in water at 25.degree. C. has a pH not exceeding 3. 
The acid is introduced as a solution in an appropriate solvent with 
stirring into a suspension of a double metal cyanide-metal hydroxide 
complex. After evaporation of volatile compounds, the solid thus obtained 
is used or stored for use as a polymerization catalyst without any 
filtration or centrifugation. Example 1 of the patent illustrates the 
preparation of a solid catalyst containing approximately 1 HCl per mole of 
Zn.sub.3 [Co(CN).sub.6 ].sub.2. Example 16 shows that the yield of 
polyether polyol is improved about 90% when 2 HCl per mole of Zn.sub.3 
[Co(CN).sub.6 ].sub.2 ZnCl.sub.2 is present. No mention is made of the 
effect of the acid on other characteristics of the polyether polyol, such 
as the amount of high molecular weight tail. 
Recently, as indicated by U.S. Pat. Nos. 5,470,813, 5,482,908, 5,545,601, 
and 5,712,216, researchers at ARCO Chemical Company have produced 
substantially noncrystalline or amorphous DMC complex catalysts with 
exceptional activity, which have also been found to be capable of 
producing polyether polyols having unsaturation levels in the range of 
0.002 to 0.007 meq/g (levels previously obtainable only through the use of 
certain solvents such as tetrahydrofuran). The polyoxypropylene polyols 
thus prepared were found to react in a quantitatively different manner 
from prior "low" unsaturation polyols in certain applications, notably 
cast elastomers and microcellular foams. However, substitution of such 
polyols for their base-catalyzed analogs in molded and slab foam 
formulations is not straightforward. In molded foams, for example, foam 
tightness increases to such an extent that the necessary crushing of the 
foams following molding is difficult if not impossible. In both molded 
foams and slab foams, foam collapse often occurs, rendering such foams 
incapable of production. These effects occur even when the high actual 
functionality of such polyols is purposefully lowered by addition of lower 
functionality polyols to achieve an actual functionality similar to that 
of base-catalyzed polyols. 
DMC-catalyzed polyoxypropylene polyols have exceptionally narrow molecular 
weight distribution, as can be seen from viewing gel permeation 
chromatograms of polyol samples. The molecular weight distribution is 
often far more narrow than analogous base-catalyzed polyols, particularly 
in the higher equivalent weight range, for example. Polydispersities less 
than 1.5 are generally obtained, and polydispersities in the range of 1.05 
to 1.15 are common. In view of the low levels of unsaturation and low 
polydispersity, it was surprising that DMC-catalyzed polyols did not prove 
to be "drop-in" replacements for base-catalyzed polyols in polyurethane 
foam applications. Because propoxylation with modern DMC catalysts is 
highly efficient, it would be very desirable to be able to produce 
DMC-catalyzed polyoxypropylene polyols which can be used in slab and 
molded polyurethane foam applications without causing excessive foam 
tightness or foam collapse. 
Surprisingly, when one or more molar equivalents of an acid such as 
hydrochloric acid are combined with a highly active, substantially 
noncrystalline double metal cyanide complex catalyst of the type described 
in U.S. Pat. Nos. 5,470,813, 5,482,908, 5,545,601 and 5,712,216, complete 
deactivation of the catalyst is observed. This result was unexpected in 
view of the teaching of U.S. Pat. No. 4,472,560 that such acids will 
function as promoters for conventional double metal cyanide complex 
catalysts. 
SUMMARY OF THE INVENTION 
It has now been discovered that polyether polyols which contain polymerized 
propylene oxide and which mimic the behavior of base-catalyzed analogs in 
slab and molded polyurethane foams may be obtained using a highly active 
substantially noncrystalline double metal cyanide complex catalyst if the 
catalyst is first treated with a protic acid. Excess acid is separated 
from the acid-treated catalyst prior to its use in epoxide polymerization. 
DETAILED DESCRIPTION OF THE INVENTION 
Intensive research into the chemical and physical characteristics of 
polyoxypropylene polyols has led to the discovery that despite the narrow 
molecular weight distribution and low polydispersities of polyols 
catalyzed by substantially noncrystalline highly active double metal 
cyanide complex catalysts, small high molecular weight fractions are 
responsible in large part for excessive foam tightness (stabilization) and 
foam collapse. 
A comparison of gel permeation chromatograms of base-catalyzed and 
DMC-catalyzed polyols exhibit significant differences. For example, a 
base-catalyzed polyol exhibits a significant "lead" portion of low 
molecular weight oligomers and polyoxypropylene monols prior to the main 
molecular weight peak. Past the peak, the weight percentage of higher 
molecular weight species falls off rapidly. A similar chromatogram of a 
DMC-catalyzed polyol reveals a tightly centered peak with very little low 
molecular weight "lead" portion, but with a higher molecular weight 
portion (high molecular weight "tail") which shows the presence of 
measurable species at very high molecular weights. Due to the low 
concentration of these species, generally less than 2-3 weight percent of 
the total, the polydispersity is low. However, intensive research has 
revealed that the higher molecular weight species, despite their low 
concentrations, are largely responsible for the abnormal behavior of 
DMC-catalyzed polyols in molded and slab polyurethane foam applications. 
It is surmised that these high molecular weight species exert a 
surfactant-like effect which alters the solubility and hence the phase-out 
of the growing polyurethane polymers during the isocyanate-polyol 
reaction. 
By fractionation and other techniques, it has been determined that the high 
molecular weight tail may be divided into two molecular weight fractions 
based on the different effects these fractions influence. The first 
fraction, termed herein "intermediate molecular weight tail," consists of 
polymeric molecules having molecular weights ranging from about 20,000 Da 
to 400,000 Da, and greatly alters the foam tightness in molded foam and 
high resilience (HR) slab foam. A yet higher molecular weight fraction 
(hereinafter, "ultra-high molecular weight tail") dramatically influences 
foam collapse both in molded foam and in slab foam of both conventional 
and high resilience (HR) varieties. 
Thus far, no completely effective method of avoiding production of high 
molecular weight tail during propoxylation employing DMC complex catalysts 
has been known in the art. Use of processes such as continuous addition of 
starter in both batch and continuous polyol preparation, as disclosed in 
WO 97/29146 and U.S. Pat. No. 5,689,012, have proven partially effective 
in lowering the amount of high molecular weight tail in some cases. 
However, the portion which remains is still higher than is optimal if the 
polyether polyol is to be used for preparation of polyurethane foam. 
Commercially acceptable methods for removing or destroying high molecular 
weight tail have also not been developed. Destruction of high molecular 
weight species by cleavage induced by peroxides is somewhat effective, but 
also cleaves the desired molecular weight species as well. Fractionation 
with supercritical CO.sub.2 is effective with some polyols but not others, 
and is too expensive to be commercially acceptable. 
It has been observed that the highly active substantially noncrystalline 
double metal cyanide complex catalysts that contain higher levels of free 
(unbonded) zinc hydroxyl groups ("Zn--OH") tend to be the catalysts which 
produce polyether polyols having higher amounts of high molecular tail 
impurity. Without wishing to be bound by theory, it is thought that the 
zinc hydroxyl groups are in some way involved in the formation of such 
impurities. 
It has unexpectedly been found that the problem of reducing the high 
molecular tail in a polyether polyol obtained using a substantially 
amorphous highly active double metal cyanide complex catalyst 
characterized by the presence of zinc hydroxyl groups may be readily 
solved by contacting the catalyst with a protic acid for a time and at a 
temperature effective to react the catalyst with at least a portion of the 
protic acid. In this context, the term "react" includes chemical 
interactions which lead to the formation of covalent or ionic bonds 
between the protic acid and the catalyst such that the reacted protic acid 
becomes in some fashion bound to or otherwise associated with the catalyst 
and is not readily removed by solvent washing, evaporation or other such 
means. At least a portion, and preferably essentially all, of any excess 
(unreacted) protic acid is separated from the acid-treated catalyst prior 
to use in an epoxide polymerization reaction. By proper adjustment of the 
protic acid to catalyst ratio and careful selection of the acid treatment 
conditions, the time required to activate the catalyst and the rate at 
which the catalyst polymerizes an epoxide may also be significantly 
improved as compared to catalyst which has not been contacted with acid. 
The choice of protic acid is not believed to be critical, although as 
mentioned previously the use of hydrogen halides such as hydrochloric acid 
at high concentrations should be avoided. Protic acids include the class 
of chemical substances, both organic and inorganic, which when placed in 
water are capable of donating hydrogen ions (H.sup.+) to water molecules 
to form hydronium ions (H.sub.3 O.sup.+). Both strong and weak protic 
acids may be utilized in the present invention. Illustrative examples of 
suitable protic acids include, but are not limited to, phosphorus oxyacids 
(e.g., phosphorous acid, hypophosphorous acid, phosphoric acid), sulfur 
oxyacids (e.g., sulfuric acid, sulfonic acids), carboxylic acids (e.g., 
acetic acid, halogenated acetic acids), nitrogen oxyacids (e.g., nitric 
acid) and the like. Phosphorus acid, sulfuric acid, and acetic acid are 
particularly preferred protic acids. 
The optimum amount of protic acid used relative to the amount of catalyst 
to be treated will vary depending upon, among other factors, the acidity 
(i.e., acid strength or pKa) of the protic acid and the treatment 
conditions (acid concentration, temperature, contact time, etc.). At a 
minimum, the ratio of protic acid to catalyst must be sufficiently high so 
as to reduce the amount of high molecular weight tail the catalyst 
produces when used to catalyze the formation of a polyether polyol. 
However, care must be taken to avoid using such a large amount of protic 
acid that the activity of the catalyst is adversely affected. It will 
normally be advantageous to select acid treatment conditions such that the 
polymerization activity of the untreated catalyst (as measured by the 
quantity of propylene oxide reacted per minute per 250 ppm catalyst at 
105.degree. C.) is not reduced by more than 20% (more preferably, not more 
than 10%). Routine experimentation wherein the acid:catalyst ratio is 
systematically varied at a given set of reaction conditions will permit 
rapid determination of the preferred range of ratios. Generally speaking, 
when the protic acid is a relatively strong acid such as hydrochloric acid 
the amount of acid used should be low relative to the quantity of catalyst 
to be treated. Conversely, relatively high concentrations of weak protic 
acid such as acetic acid are typically favored. 
Without wishing to be bound by theory, it is believed that the improvements 
in catalyst performance realized by application of the present invention 
are at least in part due to the reaction of the protic acid with the zinc 
hydroxyl groups initially present in the catalyst. That is, it has been 
observed that when the catalyst is treated with a protic acid such as 
acetic acid, the infrared absorption bands assigned to free (unassociated) 
Zn--OH are largely eliminated and replaced with absorption bands 
attributed to zinc acetate groups. 
The double metal cyanide catalysts treated with the protic acid are 
substantially amorphous (i.e., non-crystalline) and are comprised of a 
double metal cyanide, an organic complexing agent and a metal salt. The 
catalyst has very high polymerization activity; i.e., it is capable of 
polymerizing propylene oxide at a rate in excess of 3 g (more preferably, 
5 g) propylene oxide per minute per 250 ppm catalyst (based on the 
combined weight of initiator and propylene oxide) at 105.degree. C. Double 
metal cyanide complex catalysts meeting these requirements and methods for 
their preparation are described in detail in U.S. Pat. Nos. 5,470,813, 
5,482,908, 5,545,601, and 5,712,216, each of which is incorporated herein 
by reference in its entirety. 
The double metal cyanide most preferably is zinc hexacyanocobaltate, while 
the metal salt (used in excess in the reaction to form the double metal 
cyanide) is preferably selected from the group consisting of zinc halides 
(zinc chloride being especially preferred), zinc sulphate and zinc 
nitrate. The organic complexing agent is desirably selected from the group 
consisting of alcohols, ethers and mixtures hereof, with water soluble 
aliphatic alcohols such as tert-butyl alcohol being particularly 
preferred. The double metal cyanide complex catalyst is desirably modified 
with a polyether, as described in U.S. Pat. Nos. 5,482,908 and 5,545,601. 
The catalyst is contacted with the protic acid for a time and at a 
temperature effective to react the catalyst with at least a portion of the 
protic acid. The extent of reaction may be readily monitored by standard 
analytical techniques. For example, where the protic acid is phosphoric 
acid or sulfuric acid, the elemental composition of the treated catalyst 
may be measured to determine the amount of residual phosphorus or sulfur 
in the catalyst after removal of any unreacted protic acid. When a 
carboxylic acid such as acetic acid is utilized, the relative 
concentration of zinc carboxylate groups as compared to free zinc hydroxyl 
groups may be ascertained by infrared spectroscopy. 
Generally speaking, the catalyst treatment method of this invention may be 
most conveniently practiced by suspending the catalyst (which is normally 
in a powder or particulate form) in a suitable liquid medium having the 
protic acid dissolved therein. The suspension is heated at a suitable 
temperature for the desired period of time, preferably while being 
agitated or otherwise mixed. In an alternative embodiment, the catalyst is 
deployed in a fixed bed with the liquid medium containing the protic acid 
being passed through the catalyst bed under conditions effective to 
achieve the desired level of catalyst reaction with the protic acid. Since 
many of the protic acids usable in the present invention are 
water-soluble, it will normally be advantageous for the liquid medium to 
be aqueous in character. While water alone could be used, one or more 
water miscible organic solvents such as a lower aliphatic alcohol or 
tetrahydrofuran may also be present. 
The acid treatment procedure of this invention thus may be conveniently 
incorporated into the catalyst preparation procedures described in U.S. 
Pat. Nos. 5,470,813, 5,482,908, 5,545,601 and 5,712,216. The highly active 
substantially amorphous double metal cyanide complex catalysts taught by 
these patents are commonly synthesized by combining an aqueous solution of 
a metal cyanide salt such as potassium hexacyanocobaltate with an aqueous 
solution of an excess of a metal salt such as zinc chloride. The double 
metal cyanide thereafter precipitates from solution to form an aqueous 
suspension. An organic complexing agent such as a water soluble aliphatic 
alcohol (e.g., tert-butyl alcohol) may be present in one or both of the 
initial aqueous solutions or added to the aqueous suspension. The 
resulting aqueous suspension may be conveniently treated with protic acid 
in accordance with the present invention prior to isolating the catalyst 
in dry form as described in the aforementioned patents. Alternatively, of 
course, a dry soluble metal cyanide complex catalyst prepared by the prior 
art procedures or a wet filter cake of such a catalyst may be resuspended 
in a liquid medium and treated with acid if so desired. 
As mentioned previously, the type of acid selected for use will affect the 
reaction conditions needed to modify the catalytic performance to the 
desired extent. Generally speaking, the use of a weak acid such as acetic 
acid will require higher acid concentrations in the liquid medium, higher 
reaction temperatures, and/or longer reaction times than will be the case 
for a strong protic acid such as sulfuric acid or hydrochloric acid. 
Suitable acid concentrations thus may typically be in the range of from 
0.01 to 10 N, suitable reaction temperatures may be in the range of from 
0.degree. C. to 200.degree. C., and suitable reaction times may be in the 
range of from 1 minute to 1 day. 
After contacting with the protic acid, the treated catalyst is separated 
from unreacted (excess) protic acid by any suitable means such as 
filtration, centrifugation or decantation. Preferably, all or essentially 
all of the unreacted protic acid is removed. To achieve this, it will 
often be desirable to wash unreacted protic acid from the catalyst using 
water, a water-miscible organic solvent such as an alcohol, a mixture of 
water and a water-soluble organic solvent, or an organic solvent in which 
the protic acid is soluble. The washing solvent may, for example, be 
passed through a filter cake of the catalyst or the catalyst may be 
resuspended in the washing solvent and then separated again by filtration 
or other such means. After washing, the acid-treated catalyst may be dried 
if so desired to reduce the amount of residual washing solvent or other 
volatiles. Typically, the drying step is performed at relatively moderate 
conditions (e.g., room temperature to 100.degree. C.). A vacuum may be 
applied to accelerate the rate of drying. 
In an alternative embodiment of the invention, the double metal cyanide 
complex catalyst is exposed to the protic acid in the vapor phase. For 
example, a gaseous stream containing the protic acid may be passed through 
a filter cake of the catalyst at a suitable temperature until the desired 
extent of catalyst reaction is accomplished. This approach may be 
conveniently utilized where the protic acid selected for use in treating 
the catalyst is relatively volatile (e.g., acetic acid or other light 
carboxylic acid). Residual unreacted protic acid is separated from the 
acid-treated catalyst prior to use of the catalyst in epoxide 
polymerization. 
The concentration of the acid-treated catalyst when used in an epoxide 
polymerization process is generally selected such that sufficient catalyst 
is present to polymerize the epoxide at a desired rate or within a desired 
period of time. It is desirable to minimize the amount of catalyst 
employed, both for economic reasons and to avoid having to remove the 
catalyst from the polyether polyol produced. The activities of the 
catalysts obtained by practice of this invention are extremely high; 
catalyst concentrations in the range of from 5 to 50 parts per million 
based on the combined weight of active hydrogen-containing initiator and 
epoxide thus are typically sufficient. 
The catalysts obtained by practice of this invention are particularly 
useful for polymerizing propylene oxide alone since propylene oxide 
homopolymerization is particularly apt to form undesirably high levels of 
high molecular weight tail. However, the process may also be employed to 
polymerize other epoxides such as ethylene oxide, 1-butene oxide and the 
like either alone or in combination with other epoxides. For example, 
copolymers of ethylene oxide and propylene oxide may be produced. 
The active hydrogen-containing initiator may be any of the substances known 
in the art to be capable of alkoxylation by epoxide using a double metal 
cyanide complex catalyst and is selected based on the desired 
functionality and molecular weight of the polyether polyol product. 
Typically, the initiator (which may also be referred to as "starter") will 
be oligomeric in character and have a number average molecular weight in 
the range of from 100 to 1000 and a functionality (number of active 
hydrogens per molecule) of from 2 to 8. Alcohols (i.e., organic compounds 
containing one or more hydroxy groups) are particularly preferred for use 
as initiators. 
The polymerization may be conducted using any of the alkoxylation 
procedures known in the double metal cyanide complex catalyst art. For 
instance, a conventional batch process may be employed wherein the 
catalyst and initiator are introduced into a batch reactor. The reactor is 
then heated to the desired temperature (e.g., 70 to 150.degree. C.) and an 
initial portion of epoxide introduced. Once the catalyst has been 
activated, as indicated by a drop in pressure and consumption of the 
initial epoxide charge, the remainder of the epoxide is added 
incrementally with good mixing of the reactor contents and reacted until 
the desired molecular weight of the polyether polyol product is achieved. 
The initiators, monomers and polymerization conditions described in U.S. 
Pat. No. 3,829,505 (incorporated herein by reference in its entirety) may 
be readily adapted for use in the present process. 
Alternatively, a conventional continuous process may be employed whereby a 
previously activated initiator/catalyst mixture is continuously fed into a 
continuous reactor such as a continuously stirred tank reactor (CSTR) or 
tubular reactor. A feed of epoxide is introduced into the reactor and the 
product continuously removed. The process of this invention may also be 
readily adapted for use in continuous addition of starter (initiator) 
processes, either batch or continuous operation, such as those described 
in detail in U.S. application Ser. No. 08/597,781, filed Feb. 7, 1996, now 
U.S. Pat. No. 5,777,177, and U.S. Pat. No. 5,689,012, both of which are 
incorporated herein by reference in their entirety. 
The polyether polyols produced by operation of the process of the invention 
preferably have functionalities, molecular weights and hydroxyl numbers 
suitable for use in molded and slab foams. Nominal functionalities range 
generally from 2 to 8. In general, the average functionality of polyether 
polyol blends ranges from about 2.5 to 4.0. The polyether polyol 
equivalent weights generally range from somewhat lower than 1000 Da to 
about 5000 Da. Unsaturation is preferably 0.015 meq/g or lower, and more 
preferably in the range of 0.002 to about 0.008 meq/g. Hydroxyl numbers 
preferably range from 10 to about 80. Blends may, of course, contain 
polyols of both lower and higher functionality, equivalent weight, and 
hydroxyl number. 
The performance of polyether polyols may be assessed by testing these 
polyether polyols in the "Tightness Foam Test" (TFT) and "Super Critical 
Foam Test" (SCFT). Polyether polyols which pass these tests have been 
found to perform well in commercial slab and molded foam applications, 
without excessive tightness, and without foam collapse. The SCFT consists 
of preparing a polyurethane foam using a formulation which is expressly 
designed to magnify differences in polyether polyol behavior. 
In the SCFT, a foam prepared from a given polyether polyol is reported as 
"settled" if the foam surface appears convex after blow-off and is 
reported as collapsed if the foam surface is concave after blow-off. The 
amount of collapse can be reported in a relatively quantitative manner by 
calculating the percentage change in a cross-sectional area taken across 
the foam. The foam formulation is as follows: polyether polyol, 100 parts; 
water, 6.5 parts; methylene chloride, 15 parts; Niax.RTM. A-1 amine-type 
catalyst, 0.10 parts; T-9 tin catalyst, 0.34 parts; L-550 silicone 
surfactant, 0.5 parts. The foam is reacted with a mixture of 80/20 2,4- 
and 2,6-toluene diisocyanate at an index of 110. The foam may be 
conveniently poured into a standard 1 cubic foot cake box, or a standard 1 
gallon ice cream container. In this formulation, conventionally prepared, 
i.e. base catalyzed polyether polyols having high secondary hydroxyl cause 
the foam to settle approximately 10-20%, generally 15%.+-.3%, whereas 
polyether polyols prepared from DMC catalysts containing unacceptably high 
levels of high molecular weight tail cause the foam to collapse by 
approximately 35-70%. 
While the SCFT is used to assess differences in foam stability, the 
Tightness Foam Test (TFT) magnifies reactivity differences, as reflected 
by foam porosity. In the tightness foam test, the resin component consists 
of 100 parts polyether polyol, 3.2 parts water (reactive blowing agent), 
0.165 parts C-183 amine catalyst, 0.275 parts T-9 tin catalyst, and 0.7 
parts L-620 silicone surfactant. The resin component is reacted with 80/20 
toluene diisocyanate at an index of 105. Foam tightness is assessed by 
measuring air flow in the conventional manner. Tight foams have reduced 
air flow. 
The analytical procedure useful for measuring the quantity of high 
molecular weight tail in a given DMC-catalyzed polyether polyol is a 
conventional HPLC technique, which can easily be developed by one skilled 
in the art. The molecular weight of the high molecular weight fraction may 
be estimated by comparing its elution time in the GPC column with that of 
a polystyrene standard of appropriate molecular weight. As is well known, 
high molecular weight fractions elute from a GPC column more rapidly than 
lower molecular weight fractions, and to aid in maintaining a stable 
baseline, it is appropriate, following the elution of the high molecular 
weight fraction, to divert the remainder of the HPLC eluate to waste, 
rather than allowing it to pass through the detector, overloading the 
latter. Although many suitable detectors may be utilized, a convenient 
detector is an evaporative light scattering detector (ELSD) such as those 
commercially available. 
In the preferred analysis method, a Jordi Gel DVB 10.sup.3 Angstrom 
column,10.times.250 mm, 5 micron particle size, is employed with a mobile 
phase which consists of tetrahydrofuran. The detector used is a Varex 
Model IIA evaporative light scattering detector. Polystyrene stock 
solutions are made from polystyrenes of different molecular weights by 
appropriate dilution withtetrahydrofuran, to form standards containing 2, 
5, and 10 mg/L of polystyrene. Samples are prepared by weighing 0.1 gram 
of polyether polyol into a 1 ounce bottle, and adding tetrahydrofuran to 
the sample to bring the total weight of sample and tetrahydrofuran to 10.0 
grams. Samples of the 2, 5, and 10 mg/L polystyrene calibration solutions 
are sequentially injected into the GPC column. Duplicates of each 
polyether polyol sample solution are then injected, following by a 
reinjection of the various polystyrene standards. The peak areas for the 
polystyrene standards are electronically integrated, and the 
electronically integrated peaks for the two sets of each candidate polyol 
are electronically integrated and averaged. Calculation of the high 
molecular weight tail in ppm is then performed by standard data 
manipulation techniques.

Having generally described this invention, a further understanding can be 
obtained by reference to certain specific examples which are provided 
herein for purposes of illustration only and are not intended to be 
limiting unless otherwise specified. 
EXAMPLES 
Example 1 
This example demonstrates the treatment of a double metal cyanide complex 
catalyst with acetic acid in accordance with the invention. 
A 62.5% solution of zinc chloride in water (120 g) was diluted using a 
mixture of 230 mL deionized water and 50 mL tert-butyl alcohol. 
Separately, 7.5 g potassium hexacyanocobaltate was dissolved in a mixture 
of 100 mL deionized water and 20 mL tert-butyl alcohol. The potassium 
hexacyanocobaltate solution was added to the zinc chloride solution over 
35 minutes while homogenizing at 20% of the maximum intensity. After 
addition was completed, homogenization was continued at 40% of the maximum 
intensity for 10 minutes. The homogenizer was then stopped and a solution 
of 8 g of a 1000 molecular weight polypropylene glycol diol in a mixture 
of 50 mL deionized water and 2 mL tetrahydrofuran added to the mixture. 
After stirring slowly for 3 minutes, the mixture was pressure filtered at 
40 psig through a 20 micron nylon membrane. The catalyst cake was 
reslurried in a mixture of 130 mL tert-butyl alcohol, 55 mL deionized 
water and 3 g acetic acid at 40% of the maximum homogenization intensity 
for 10 minutes. The homogenizer was then stopped and 2 g of the 
polypropylene glycol diol dissolved in 2 g tetrahydrofuran was added. 
After stirring slowly for 3 minutes, the slurry was refiltered as 
previously described. The catalyst cake was reslurried in 185 mL 
tert-butyl alcohol at 40% of the maximum homogenization intensity for 10 
minutes. The homogenizer was then stopped and 1 g of the polypropylene 
glycol diol in 2 g tetrahydrofuran was added. After stirring slowly for 3 
minutes, the slurry was refiltered as described previously. The catalyst 
cake thus obtained was dried at 60.degree. C. under vacuum (30 in Hg) 
until a constant weight was obtained. 
Example 2 
This example illustrates an alternative procedure for treating a double 
metal cyanide complex catalyst with acetic acid in accordance with the 
present invention. 
A 62.5% aqueous solution (302.6 g) of zinc chloride was diluted with 580 mL 
deionized water and 126 mL tert-butyl alcohol. Separately, a solution of 
18.9 g potassium hexacyanocobaltate in 252 g deionized water and 50 mL 
tert-butyl alcohol was prepared. The potassium hexacyanocobaltate solution 
was added to the zinc chloride solution over 2 hours at 50.degree. C. 
under 900 rpm agitation. After addition was completed, agitation was 
continued for another hour at 900 rpm. Agitation was decreased to 400 rpm 
and a solution of 15 g of a 1000 molecular weight polypropylene glycol 
diol in 120 mL deionized water and 10 mL tetrohydrofuran was added. After 
stirring for 3 minutes, the mixture was pressure filtered at 40 psig 
through a 20 micron nylon membrane. The catalyst cake was reslurried in a 
mixture of 328 mL tert-butyl alcohol in 134 mL deionized water at 
50.degree. C. for 1 hour (900 rpm agitation). The agitation rate was 
decreased to 400 rpm and 5.1 g of the polypropylene glycol diol dissolved 
in 5.1 g tetrahydrofuran added. After stirring for 3 minutes, the mixture 
was pressure filtered as previously described. The catalyst cake was 
reslurried in 185 mL tert-butyl alcohol and stirred 1 hour at 50.degree. 
C. (900 rpm agitation). After decreasing the agitation rate to 400 rpm, a 
solution of 2.5 g of the polypropylene glycol diol in 5 g tetrahydrofuran 
was added. After stirring 3 minutes, 70 g acetic acid was added and the 
mixture stirred for 2 hours before pressure filtering as previously 
described. The catalyst cake was dried at 60.degree. C. under vacuum (30 
in Hg) until a constant weight was obtained. 
Examples 3A-3C 
These examples demonstrate the treatment of zinc hexacyanocobaltate complex 
catalyst with a variety of protic acids. 
A 62.5% aqueous solution (302.6 g) of zinc chloride was diluted with 580 mL 
deionized water and 126 mL tert-butyl alcohol. Separately, a solution of 
18.9 g potassium hexacyanocobaltate in 252 mL deionized water and 50 mL 
tert-butyl alcohol was prepared, then added to the zinc chloride solution 
over 2 hours at 50.degree. C. (900 rpm). After addition was completed, 
agitation was continued at 900 rpm for 1 hour before decreasing the 
agitation rate to 400 rpm and adding a solution of 15 g of a 1000 
molecular weight polypropylene glycol diol in 120 mL deionized water and 
10 mL tetrahydrofuran. After stirring for 3 minutes, the mixture was 
pressure filtered at 40 psig through a 20 micron nylon membrane. The 
catalyst cake was reslurried in a mixture of 328 mL tert-butyl alcohol and 
134 mL deionized water at 50.degree. C. for 1 hour (900 rpm agitation). 
The slurry was then divided into three equal portions (A,B,C). Each 
portion was combined with aqueous acid as follows: 
______________________________________ 
Portion Acid 
______________________________________ 
A 0.33 g acetic acid + 8 g water 
B 0.54 g 37% HCl + 8 g water 
C 0.36 g hypophosphorus acid + 8 g water 
______________________________________ 
Each portion was then homogenized at 40% of the maximum intensity for 10 
minutes, then combined with 1.7 g of the polypropylene glycol diol 
dissolved in 2 g tetrahydrofuran. After stirring slowly for 3 minutes, 
each portion was pressure filtered as described previously, and then 
reslurried in 156 mL tert-butyl alcohol at 50.degree. C. for 10 minutes 
while mixing with a homogenizer. Homogenization was stopped and 0.83 g of 
the polypropylene glycol diol dissolved in 2 g tetrahydrofuran was added 
to each portion. After stirring slowly for 3 minutes, the catalyst was 
again collected by pressure filtration and then dried at 60.degree. C. 
under vacuum (30 in Hg) until a constant weight was obtained. 
Example 4 
This example demonstrates the effect of treating highly active 
substantially amorphous double metal cyanide complex catalysts 
characterized by the presence of zinc hydroxyl groups with varying 
concentrations of acetic acid. The catalysts used were comprised of zinc 
hexacyanocobaltate, zinc chloride, tert-butyl alcohol (organic complexing 
agent), and a polyether polyol and had been prepared in accordance with 
the general procedures outlined in U.S. Pat. No. 5,482,908. Acid treatment 
was performed by stirring the wet filter cake in aqueous tert-butyl 
alcohol solutions of acetic acid (1, 5 and 15% concentrations) following 
the methods described in Example 1 hereinabove. 
The catalytic performances of the acid-treated catalysts were compared with 
that of a control catalyst which had not been acid-treated in the 
preparation of 3200 number average molecular weight polypropylene glycol 
triol containing 12 wt. % ethylene oxide. The polymerizations were carried 
out in a 1L Buchi reactor at 130.degree. C. using a 2-hour feed time after 
initiation of epoxide addition and a catalyst concentration of 30 ppm 
based on the final weight of the polypropylene glycol triol. The results 
obtained are shown in the following table. 
TABLE I 
______________________________________ 
Example 4A.sup.1 
4B 4C 
______________________________________ 
Acid Treatment None 5% Acetic 15% Acetic 
Product 
Hydroxyl No., mg KOH/g 51.9 51.5 52.0 
Molecular Weight 1.027 1.028 1.057 
Distribution (GPC) 
Viscosity, cps 521 531 558 
High Molecular Weight Tail, ppm 
&gt;100 K 171 172 73 
&gt;400 K 15 14 ND 
Supercritical Foam Test Failed Failed Passed 
______________________________________ 
.sup.1 Comparative (control) 
ND = None Detected 
When the acetic acid concentration during acid treatment was only 1 or 5%, 
little reduction in the amount of high molecular tail was observed as 
compared to the control catalyst (compare Example 4B with Example 4A). 
This was consistent with IR spectroscopic analysis of the acid-treated 
catalysts, which showed no change in the sharp absorption bands at 3609 
cm.sup.-1 (assigned to free or unbonded Zn--OH stretching vibration) and 
642 cm.sup.-1 (assigned to Zn--OH bending vibration). A weak absorption 
band was visible at 1620 cm.sup.-1 which is assigned to the carboxylate 
(zinc acetate) stretching vibration. In the catalyst which had been 
treated with 15% acetic acid for 2 hours, however, the IR absorption bands 
at 3609 cm.sup.-1 and 642 cm.sup.-1 were no longer present and the band at 
1620 cm.sup.-1 was more intense (indicating that a higher degree of 
conversion of the zinc hydroxyl groups to zinc acetate groups had taken 
place). The polypropylene glycol triol prepared using the catalyst treated 
with 15% acetic acid (Example 4C) contained undetectable levels of 
impurities having molecular weights in excess of 400,000 and passed the 
Supercritical Foam Test. 
Example 5 
Portions of a highly active substantially noncrystalline double metal 
cyanide complex catalyst comprised of zinc hexacyancobaltate, tert-butyl 
alcohol, zinc chloride and polyether polyol and prepared in accordance 
with the procedure described in U.S. Pat. No. 5,482,908 were treated with 
either phosphoric acid or sulfuric acid. The residual phosphorus in the 
phosphoric acid-treated catalyst was only 0.4 wt % by elemental analysis. 
The catalytic performance of each catalyst was compared to that of a 
control (no acid treatment) in the preparation of a 3000 number average 
molecular weight polypropylene glycol triol using 40 ppm catalyst (based 
on final weight of the polypropylene glycol triol) at 1050.degree. C. The 
control catalyst required approximately 100 minutes until rapid 
polymerization of the propylene oxide was initiated. In contrast, the 
initiation (activation) times for the acid-treated catalysts under 
comparable conditions were only about 30 to 40 minutes. Moreover, the 
proportion of the polypropylene glycol triols made from the acid-treated 
catalysts having a molecular weight in excess of 100,000 was reduced by 
about 35% as compared to the triol prepared using the control (untreated) 
catalyst. 
Example 6 
The effects of treating a highly active substantially noncrystalline double 
metal cyanide catalyst of the type utilized in Examples 4 and 5 with 
varying amounts of phosphoric acid were examined. To prepare Catalyst 6-B, 
for example, a solution of 0.83 g of 85% phosphoric acid dissolved in a 
mixture of 80 g tert-butyl alcohol and 20 g distilled water was used at 
room temperature to treat the catalyst. Zinc hexacyanocobaltate complex 
catalyst (6 g) was added slowly and the resulting mixture stirred at room 
temperature for 2 hours. The catalyst was collected by filtration and 
dried for 4 hours at 50.degree. C. Catalysts 6-C and 6-D were prepared in 
a similar manner using higher phosphoric acid concentrations. The 
catalysts were evaluated in the preparation of a 3000 molecular weight 
polypropylene glycol triol at 120.degree. C. (30 ppm catalyst). The 
results obtained are summarized in the following table. 
TABLE II 
______________________________________ 
Ex- H.sub.3 PO.sub.4 /Double 
Activation High Molecular 
Super- 
am- Metal Cyanide Time Tail, ppm critical 
ple molar ratio 
(min.) P/Co.sup.1 
&gt;100 K 
&gt;400 K 
Foam Test 
______________________________________ 
6-A* 0 20-25 0 150- 15-20 failed 
160 (collapse) 
6-B 1.2 5-7 0.070 135 n/a not tested 
6-C 2.2 8 0.394 115 n/a passed.sup.3 
6-D 3.8 49 0.561 n/a.sup.2 .sup. n/a.sup.2 not tested 
______________________________________ 
*Comparative example (control) 
.sup.1 By analysis in catalyst 
.sup.2 Catalyst deactivated during polymerization 
.sup.3 The foam settled approximately 37% and a split in the foam was 
observed. 
Examples 7-9 
Polypropylene glycol triols of approximately 3200 number average molecular 
weight and containing 12 wt % ethylene oxide (the balance being propylene 
oxide) were prepared using a polymerization temperature of 130.degree. C. 
and an epoxide feed time of 2 hours to compare the performance of 
acid-treated Catalysts 3B and 3C (see Example 3) with that of an analogous 
double metal cyanide catalyst which had not been treated with acid. The 
results obtained are shown in the following table. 
TABLE III 
______________________________________ 
Example 7.sup.1 8 9 
______________________________________ 
Catalyst Control 3B 3C 
Acid Used None HCl Hypophos- 
phorous 
Acid/Zn Molar Ratio -- 0.02 0.06 
Product 
Hydroxy No., mg KOH/g 51.9 51.8 52.6 
Molecular Weight Distribution (GPC) 1.027 1.030 1.032 
Viscosity, cps 521 540 547 
High Molecular Weight Tail, ppm 
&gt;100 K 171 153 153 
&gt;400 K 15 7 ND 
______________________________________ 
.sup.1 Comparative 
ND = None detected 
Both of the acid-tested catalysts yielded products containing lower levels 
molecular tail impurities (particularly those impurities having a 
molecular weight greater than 400,000) than did the control catalyst used 
in Example 7. At the same time, no adverse effects of acid treatment on 
other product characteristics such as hydroxy number, polydispersity or 
viscosity were observed.