A process for the preparation of polyethers is disclosed in which
an oxetane monomer, or a mixture of an oxetane monomer and an oxolane
monomer, and a carboxylic acid anhydride are contacted with a bleaching
earth catalyst. The process yields ester-terminated polyethers which
may be saponified to obtain hydroxy-terminated polyether polyols.
1. A process for producing a polyether comprised of contacting
an oxetane monomer, a carboxylic acid anhydride, and optionally
an oxolane monomer with an amount of a bleaching earth effective
to accomplish polymerization of the monomers, wherein the resulting
polyether is comprised of from about 5 to 100 weight percent based
on total polyether of recurring units of the oxetane monomer and
from about 0 to 95 weight percent based on total polyether of recurring
units of the oxolane monomer, and wherein the number average molecular
weight of said polyether is within the range of about 250 to 10000.
2. The process of claim 1 wherein the oxetane monomer is selected
from the group consisting of oxetane, 3-methyloxetane, 33-dimethyloxetane,
33-dethyloxetane, 2-methyloxetane, and mixtures thereof.
3. The process of claim 1 wherein the oxolane monomer is tetrahydrofuran.
4. The process of claim 1 wherein the oxetane monomer is 3-methyloxetane
and the oxolane monomer is tetrahydrofuran.
5. The process of claim 1 wherein the carboxylic acid anhydride
is acetic anhydride.
6. The process of claim 1 wherein the bleaching earth is acid-treated.
7. The process of claim 1 wherein the bleaching earth is substantially
8. The process of claim 1 wherein the bleaching earth is acid-treated
and substantially anhydrous.
9. The process of claim 1 wherein the bleaching earth is an aluminum
10. The process of claim 1 wherein the bleaching earth is a montmorillonite
11. The process of claim 1 wherein the polyether consists essentially
of recurring units of the oxetane monomer.
12. The process of claim 1 wherein the polyether consists essentially
of recurring units of 3-methyloxetane.
13. The process of claim 1 wherein the polymerization of the monomers
is carried out in the presence of a solvent.
14. A process of claim 1 comprising the additional step after polymerization
of separating the bleaching earth from the polyether.
15. A process for producing an ester-terminated polyether comprised
of contacting a monomer mixture consisting essentially of one or
more oxetane monomers with a carboxylic acid anhydride and an amount
of a bleaching earth effective to accomplish polymerization of the
monomer mixture wherein the number average molecular weight of said
ester-terminated polyether is within the range of about 250 to 10000.
16. The process of claim 15 wherein the oxetane monomer is selected
from the group consisting of oxetane, 3-methyloxetane, 3-3-bis(chloromethyl)oxetane,
33-dimethyloxetane, 33-diethyloxetane, 2-methyloxetane, and mixtures
17. The process of claim 15 wherein the carboxylic acid anhydride
is acetic anhydride.
18. The process of claim 15 wherein the bleaching earth is acid-treated.
19. The process of claim 15 wherein the bleaching earth is substantially
20. The process of claim 15 wherein the bleaching earth is acid-treated
and substantially anhydrous.
21. The process of claim 15 wherein the bleaching earth is an aluminum
22. The process of claim 15 wherein the bleaching earth is a montmorillonite
23. The process of claim 15 wherein the polymerization of the oxetane
monomer is carried out in the presence of a solvent.
24. The process of claim 15 comprising the additional step after
polymerization of separating the bleaching earth from the ester-terminated
25. A process for producing a hydroxy-terminated polyether comprised
of saponifying the ester-terminated polyether produced in accordance
with the process of claim 15.
26. A process for producing a hydroxy-terminated polyether comprised
of hydrogenating the ester-terminated polyether produced in accordance
with the process of claim 15.
Bleaching earth descriptionThis invention relates to a process
for preparing a polyether which is comprised of recurring units
of an oxetane monomer or recurring units of oxetane and oxolane
monomers. It is more particularly directed to a process where an
oxetane and, optionally, an oxolane are polymerized using a carboxylic
acid anhydride and a bleaching earth catalyst to yield an ester-terminated
polyether. The ester-terminated polyether may be saponified to yield
hydroxy-terminated polyether polyols useful as intermediates in
the preparation of segmented elastomers.
BACKGROUND OF THE INVENTION
A variety of polyether polyols are widely used as soft, flexible
segments in the production of elastomeric block copolymers such
as polyurethanes and polyether esters. In general, such polyether
polyols are low to medium molecular weight polymers having low glass
transition temperatures and at least two hydroxyl groups per polymer
chain. The low glass transition temperature provides high elasticity
and good low temperature performance, while the hydroxyl groups
permit the polyether polyol to react with the other components of
the segmented elastomers. Examples of commercially important polyether
polyols include polyethylene glycol, polypropylene glycol, ethylene
oxide/propylene oxide copolyols, and polytetramethylene ether glycol
It is desirable that a polyether polyol used as a soft segment
have primary hydroxyl groups to provide good reactivity towards
the electrophilic functional groups such as isocyanate or carboxylate
present on the hard segment components. Furthermore, to develop
optimum low temperature properties it is generally preferred that
the polyether polyol be amorphous and not crystallizable. In addition,
the polyether polyol should be hydrophobic since the mechanical
properties of the segmented elastomer product can be adversely affected
by absorption of water. The commonly used polyether polyols generally
are either hydrophilic (polyethylene glycol and ethylene oxide/propylene
oxide copolyols) or crystallizable (polytetramethylene ether glycol),
or have secondary hydroxyl end-groups (polypropylene glycol).
For these reasons oxetane polyols and oxetane/oxolane copolyols
have been investigated as polyether polyols of potential commercial
interest since materials which are simultaneously amorphous, hydrophobic,
and which have primary hydroxyl end-groups can be obtained by the
selection of appropriate monomers. However, until now only a limited
number of synthetic methods for the preparation of these oxetane-containing
polyols have been developed.
Conjeevaram et al. (J. Polym. Sci., Polym. Chem. Ed., 23 (1985)
429) teach the preparation of polyoxytrimethylene glycol by either
of two routes. In the first method, high molecular weight polyoxetane
is synthesized using an aluminum coordination catalyst then ozonized
and reduced with lithium aluminum hydride. In the second route,
the polyoxytrimethylene glycol is obtained directly by the cationic
polymerization of oxetane using boron trifluoride/ethyl ether as
catalyst and a diol as co-initiator.
Toga et al. (U.S. Pat. No. 4599460) teach a process for producing
a polyether polyol in which 3-methyloxetane and tetrahydrofuran
are copolymerized at low temperature using a hydroacid catalyst
such as perchloric or fluorosulfonic acid.
Motoi et al. (U.S. Pat. No. 4672141) teach preparation of a 3-methyloxetane
polyol using a hydroacid catalyst to Polymerize the oxetane monomer
at cryogenic temperatures.
All of these known methods for producing oxetane-containing polyols
involve either a tedious, indirect route or the use of very low
temperatures (<-40.degree. C. Such methods are not practical
or economical to carry out on a commercial scale. In addition, the
known methods for forming the polyether polyol directly all employ
a strong acid catalyst which is either expensive, difficult to handle,
or highly toxic. Most of these strong acid catalysts are soluble
in the polymerization mixture and thus difficult to remove and recycle
in subsequent polymerizations.
SUMMARY OF THE INVENTION
In the process of this invention, which provides a polyether comprised
of from about 5 to 100 weight percent based on total polyether of
recurring units of at least one oxetane monomer and from 0 to 95
weight percent based on total polyether of recurring units of an
oxolane monomer, a mixture of an oxetane monomer, an oxolane monomer,
and a carboxylic acid anhydride is contacted with an amount of a
bleaching earth effective to accomplish polymerization of the monomers.
This invention additionally provides a method for producing an
ester-terminated polyether comprising contacting an oxetane monomer
(or a mixture of an oxetane monomer and an oxolane monomer) and
a carboxylic acid anhydride with an amount of a bleaching earth
effective to accomplish polymerization of the monomer(s). The ester-terminated
polyether may be saponified to yield a hydroxyl-terminated polyether
polyol suitable for use as an intermediate in the preparation of
segmented elastomers such as polyurethanes.
DETAILED DESCRIPTION OF THE INVENTION
The polyethers produced by the process of this invention are comprised
of from about 5 to 100 weight percent based on total polyether of
recurring units of an oxetane monomer and from about 0 to 95 weight
percent based on total polyether of recurring units of an oxolane
monomer. The process of this invention is thus useful for the preparation
of oxetane homopolymers or oxetane/oxolane copolymers. Copolymers
of two or more oxetanes may also be prepared.
The oxetane monomer may be any of the four membered saturated cyclic
ethers capable of polymerization by cationic means. The oxetane
monomer may be substituted with one or more alkyl, aryl, halo alkyl,
or other substituents. Examples of suitable oxetane monomers include
oxetane, 3-methyloxetane, 2-methyloxetane, 33-dimethyl-oxetane,
33-diethyloxetane, 33-bis(chloromethyl)oxetane, and mixtures thereof.
In general, if the polyether or its derivatives are to be used as
soft segments in the preparation of elastomers, it is preferred
that the homopolymer of the oxetane employed have a low glass transition
temperature and little or no crystallinity. For these reasons, 3-methyloxetane
is the preferred oxetane monomer.
The oxolane monomer which may optionally be present in the process
of this invention is most preferably tetrahydrofuran, but substituted
oxolanes capable of cationic polymerization such as 2-methyltetrahydrofuran
and 3-methyltetrahydrofuran may also be used. In one embodiment
of this invention, a polyether may be prepared which contains primarily
tetrahydrofuran but which is non-crystalline due to the incorporation
of a significant amount of an oxetane such as 3-methyloxetane. The
properties and characteristics of the polyethers may thus be adjusted
as desired by varying the structure of the monomers used and their
relative proportions. Minor amounts of alkylene oxides (for example,
ethylene oxide and propylene oxide) may also be copolymerized with
the oxetane monomers.
In general, the polyether produced by the process of this invention
may have a number average molecular weight of from about 250 to
10000. Molecular weights of between about 500 and 4000 are particularly
preferred if the polyethers or their derivatives are to be used
in segmented elastomers. The polyethers are generally linear, although
branching may be introduced by the use of difunctional monomers.
The carboxylic acid anhydride used in the process of this invention
serves as a promoter in combination with the bleaching earth catalyst.
The fragments derived from the anhydride generally become incorporated
as ester end groups on the polyether. The degree of polymerization
is influenced by the carboxylic acid anhydride concentration of
the polymerization mixture. The lower the anhydride concentration,
the higher the polyether molecular weight obtained, and vice versa.
However, since the degree of polymerization is also affected by
the properties or activity of the bleaching earth, it is normally
necessary to empirically determine the anhydride concentration which
gives the desired molecular weight for any particular bleaching
earth. To prepare ester-terminated polyethers having a number average
molecular weight of from 1000 to 3000 for example, a carboxylic
acid anhydride concentration of from about 0.5 to 10 mole percent
based on total monomer is normally employed.
The carboxylic acid anhydride may be derived from aliphatic or
aromatic polycarboxylic acids or monocarboxylic acids having 2 to
12 carbon atoms. Examples of suitable anhydrides include, but are
not limited to, butyric anhydride, valeric anhydride, caproic anhydride,
phthalic anhydride, succinic anhydride, maleic anhydride, and, most
preferably, propionic anhydride and acetic anhydride. Mixtures of
anhydrides may be used. For reasons of cost and ready availability,
acetic anhydride is preferred.
Suitable bleaching earths are aluminum silicates and aluminum magnesium
silicates, which are generally referred to as montmorillonite clays.
Bleaching earths of this type are commonly also referred to as "fuller's
earth". The ratio of silica to the oxides of divalent and trivalent
metals in these minerals is in most cases 4:1. It is preferred that
the bleaching earth be activated by treating with a mineral acid
such as sulfuric acid, hydrochloric acid, phosphoric acid, or nitric
acid. Methods of treating a bleaching earth with a relatively concentrated
mineral acid solution which will yield catalysts suitable for use
in the process of this invention are described in U.S. Pat. No.
4127513 the teachings of which are incorporated herein by reference.
Alternatively, the bleaching earth may be acid-activated by treating
with dilute (<15 weight mineral acid solution and then drying
the catalyst. The bleaching earth used is preferably substantially
anhydrous and contains less than 3 weight percent water. U.S. Pat.
No. 4243799 the teachings of which are incorporated herein by
reference, teaches the preparation of substantially anhydrous bleaching
earths suitable for use in the process of this invention.
The amount of bleaching earth employed is not critical, although
the rate of polymerization is somewhat dependent on the catalyst
concentration. The properties of the polyether are not substantially
affected by the quantity of bleaching earth employed. Advantageous
results are obtained if the bleaching earth is present in an amount
of from about 1 to 20 weight percent based on the total weight of
the polymerization mixture. The bleaching earth may be used in the
form of a powder suspended in the mixture or as molded pellets in
a fixed catalyst bed. Unlike prior art methods for preparing oxetane
polyols, the process of the invention has the advantage that the
catalyst can be readily removed from the polyether product and can
normally be reused in subsequent polymerizations.
Polymerization generally may be carried out from about -80.degree.
C. to 100.degree. C. However, since he rate of polymerization may
be fairly slow at low temperatures and since side reactions or a
broadening of the molecular weight distribution may occur at high
temperatures, the temperature range of from about 10.degree. to
50.degree. C. is preferred. The polymerization time required to
achieve the desired molecular weight and monomer conversion will
vary depending on the monomers, temperature, catalyst concentration,
and anhydride concentration used, among other factors. For the most
part, polymerization times of from 0.5 to 10 hours will be sufficient.
Oxetane monomers generally polymerize more rapidly than oxolane
In order to keep the polymerization mixture liquid and to permit
efficient heat removal, it may be desirable to use an inert solvent
in the process of this invention. Non-protic solvents such as chloroform
and toluene are generally suitable. When the polymerization is carried
out in solvent, the polyether obtained appears to contain approximately
equimolar amounts of hydroxyl and ester end-groups.
Because of the generally higher reactivity of oxetane monomers
compared to oxolane monomers, it is preferred when preparing a random
copolyether to have only a portion of the oxetane monomer charged
to the reaction vessel initially with the oxolane monomer and to
continuously add the remaining oxetane monomer to the mixture. The
formation of oxolane homopolymer may be avoided in this way.
After polymerization has taken place, the reaction is stopped by
removing the bleaching earth catalyst. This may be done by any of
the methods known for separating solids from a liquid medium, including
filtration and centrifugation. If unreacted monomer, carboxylic
acid anhydride, and/or solvent are present, these constituents may
be removed by any appropriate distillation or stripping method.
The ester-terminated polyethers obtained by the process of this
invention may be converted to hydroxy-terminated polyether polyols
by any of the methods known to effect hydrolysis of a carboxylic
ester functionality. The saponification may be accomplished, for
example, by heating the ester-terminated polyether with an alkali
metal or alkaline earth hydroxide or alkoxide in the presence of
water or an alcohol. Alternatively, the ester groups may be converted
to hydroxyl groups by either treatment with a hydride reducing agent
or by hydrogenation using a strong base and a transition metal catalyst
as described in U.S. Pat. No. 4608422. The teachings of this patent
are incorporated herein by reference.
The polyether polyols thus produced may be used in the same manner
as any other conventionally-obtained polyol, not only as the soft
segment components of polyesters, polyamides, polyurethanes, and
the like but also as lubricants, functional fluids, adhesives, and
The following examples are meant to illustrate, but not limit,
the process of this invention.
The 3-methyoxetane was prepared from 3-chloro-2-methyl propyl acetate
using known procedures (U.S. Pat. No. 4599460) and dried by distillation
from calcium hydride prior to use. The catalyst was prepared by
placing 200 g fuller's earth (Aldrich) in a column and washing with
400 ml 5% (v/v) sulfuring acid at 5.degree.-10.degree. C. The flow
rate through the column was adjusted so that the acid wash required
ca. 20 minutes. The catalyst was then washed with 800 mL water and
400 mL acetone, blown dry with a nitrogen stream, and dried at 130.degree.
C. for 16 hours (100 mm).
The 3-methyloxetane, catalyst, acetic anhydride, and (optionally)
chloroform were combined at room temperature in the amounts shown
in Table I. A round bottom glass flask equipped with nitrogen bubbler
and stirrer was used. Polymerization was initiated in the neat mixtures
(Example 1-3) by warming slightly. The examples using chloroform
as solvent (Examples 4-6) were refluxed. After 1-2 hours the reaction
product was filtered through a pad of diatomaceous earth filter
aid and stripped of volatiles under vacuum on a rotary evaporator.
Yields were calculated from the weight of polyether obtained compared
to the weight of 3-methyloxetane charged. Molecular weight and molecular
weight distribution (Mw/Mn were determined by gel permeation chromatography
using poly(tetrahydrofuran) calibration standards. Analysis by .sup.13
C NMR and infra-red spectroscopy determined that the polyethers
obtained in Examples 1-3 were ester-terminated, while the products
of Examples 4-6 contained approximately equimolar amounts of hydroxyl
and ester end-groups.