The present invention provides substantially difunctional hydroxyl-terminated polyether-esters and a process for preparing the same. The process comprises reacting ethylene carbonate with a substituted or unsubstituted epsilon-caprolactone in the presence of a catalytic amount of a specified catalyst at a temperature of at least about 200.degree. C. The catalyst comprises an alkali metal salt, a quaternary ammonium salt, or a mixture thereof. The products of the invention are pourable liquid urethane-forming polyols at room temperature.

DESCRIPTION 
Background of the Invention 
The present invention relates to hydroxyl-terminated polyether-esters. The 
polyether-esters are prepared from the reaction of substituted or 
unsubstituted epsilon-caprolactone and ethylene carbonate in the presence 
of a specified catalyst system comprising an alkali metal salt, a 
quaternary ammonium salt, or a mixture thereof. The copolymers are useful 
as urethane-forming polyols. 
The use of caprolactone-based polymers as polyols in urethane manufacture 
is known in the art. However, prior art homopolymers and copolymers of 
epsilon-caprolactone are characterized and identified as polyester polyols 
and tend to crystallize upon standing. This characteristic of prior art 
polymers necessitates the heating of storage tanks in order to keep the 
product in a flowable form. These prior art products are therefore 
disadvantageous from a practical commercial standpoint. Such prior art 
polymers are disclosed, for example, in the Kirk-Othmer Encyclopedia of 
Chemical Technology, Third Edition, Vol. 23, page 585, where it is 
disclosed that polyester polyols can be made by the reaction of 
caprolactone with suitable glycols. The resulting product is essentially a 
homopolymer of caprolactone (i.e., polycaprolactone) having terminal 
hydroxyl groups provided by the glycol component. 
The prior art also discloses hydroxyl-terminated polyester-carbonates 
prepared from lactones and cyclic carbonate compounds. In particular, U.S. 
Pat. No. 3,301,824 discloses the copolymerization of cyclic carbonates 
containing at least six atoms in the ring nucleus with at least one cyclic 
ester (i.e., a lactone; see Column 16, lines 7-12). The patent discloses 
the use of organometallic catalysts comprising Group II, Group III-B, or 
Group I-A metals covalently bonded to furyl radicals, pyridyl radicals, 
and/or hydrocarbon radicals. The resulting products contain a plurality of 
carbonate groups in the essentially linear polymeric chain thereof. 
Similar disclosures are found in U.S. Pat. Nos. 3,324,070 and3,379,693, 
which describe the use of an initiator having reactive hydrogen in 
combination with an ester exchange catalyst; the resulting product again 
is a polycarbonate (U.S. Pat. No. 3,379,693, Col. 10, lines 32-45). 
In contrast to these teachings of the prior art, the present invention 
provides hydroxyl-terminated polymers containing ester linkages and ether 
linkages. The products of the present invention provide pourable liquid 
polyols which can be used to advantage in polyurethane reaction systems. 
SUMMARY OF THE INVENTION 
In one aspect of the present invention, there is provided a process for 
preparing substantially difunctional hydroxyl-terminated polyether-esters. 
The process comprises reacting ethylene carbonate with a specified lactone 
in the presence of a catalytic amount of a catalyst comprising an alkali 
metal salt, a quaternary ammonium salt, or a mixture thereof at a 
temperature of at least about 200.degree. C. The lactone component has the 
following formula 
##STR1## 
wherein R, R.sup.1, R.sup.2, and R.sup.3 each independently represents H, 
alkyl, cycloalkyl, alkoxy, or single-ring aromatic radicals. 
In another aspect of the present invention, there is provided a liquid, 
pourable, substantially difunctional, hydroxyl-terminated polyether-ester. 
The novel polymer consists essentially of the recurring units 
EQU --CH.sub.2 --CH.sub.2 --O-- 
and 
##STR2## 
wherein each of R, R.sup.1, R.sup.2, and R.sup.3 independently represents 
H, alkyl, cycloalkyl, alkoxy, or single-ring aromatic radicals. The 
polyether-ester has a number average molecular weight of about 1,000 to 
2,000. 
DETAILED DESCRIPTION OF THE INVENTION 
The present invention relates to hydroxyl-terminated polyether-esters and 
to a process for preparing the same. In the process of the present 
invention, ethylene carbonate (1,3-dioxolan-2-one) is reacted with a 
specified lactone in the presence of a catalytic amount of a specified 
catalyst. 
The lactones which are useful in the process of the present invention 
comprise unsubstituted and substituted epsilon-caprolactone (2-oxepanone) 
as represented by the following formula: 
##STR3## 
In the above formula, each of R, R.sup.1, R.sup.2, and R.sup.3 
independently represents H, alkyl, cycloalkyl, alkoxy or single-ring 
aromatic radicals. The alkyl, cycloalkyl, alkoxy, and single-ring aromatic 
radicals contain from 1 to about 12 carbon atoms. Suitable alkyl groups 
include methyl, ethyl, propyl, isopropyl, hexyl, octyl, and dodecyl 
radicals; suitable cycloalkyl radicals include cyclopentyl, cyclohexyl, 
etc.; suitable alkoxy radicals include methoxy, ethoxy, etc.; and suitable 
aromatic radicals include phenyl, benzyl, etc. This listing is not 
intended to be exhaustive but is indicative of the various types of 
radicals which can be found in a suitable substituted 
epsilon-caprolactone. Thus, among the substituted epsilon-caprolactones 
considered most suitable for purposes of this invention are monoalkyl 
epsilon-caprolactones such as monomethyl-, monoethyl-, monopropyl-, and 
monoisopropyl-epsilon-caprolactones; dialkyl epsilon-caprolactones in 
which the two alkyl groups are substituted on the same or different carbon 
atoms; trialkyl epsilon-caprolactones; alkoxy epsilon-caprolactones, such 
as methoxy- and ethoxy-epsilon-caprolactones; and cycloalkyl, aryl, and 
aralkyl epsilon-caprolactones, such as cyclohexyl-, phenyl-, and 
benzyl-epsilon-caprolactones. Preferably, however, the lactone component 
comprises unsubstituted epsilon-caprolactone. 
The ethylene carbonate and caprolactone components are preferably provided 
to the reaction system in approximately stoichiometric quantities. 
However, small excesses of one or the other of the reactants does not 
significantly affect the results of the reaction. 
The reaction of ethylene carbonate with the lactone component is conducted 
in the presence of a catalytic amount of a catalyst comprising an alkali 
metal salt, a quaternary ammonium salt, or a mixture thereof. Of the 
alkali metal salts, especially useful salts include the carboxylates 
having about 2 to 12 carbon atoms, the halides, and the hydroxides of one 
or more of the alkali metals. Thus, the alkali metal salts may comprise 
the acetates, propionates, butyrates, etc., chlorides, bromides, iodides, 
and hydroxides of lithium, sodium, potassium, rubidium, and cesium. Of the 
alkali metals, sodium and potassium are especially preferred. Thus, 
preferred alkali metal salts include sodium hydroxide, potassium 
hydroxide, sodium acetate, potassium acetate, sodium chloride, sodium 
bromide, sodium iodide, potassium chloride, potassium bromide, potassium 
iodide, and mixtures thereof. 
The quaternary ammonium salts which are useful as catalysts in the process 
of the present invention have the general formula (R.sup.4).sub.4 N.sup.+ 
X.sup.-. In the above formula, each R.sup.4 group independently represents 
a linear or branched alkyl of 1 to about 18 carbon atoms, and X.sup.- 
represents halide, hydroxide, or a carboxylate anion having 2 to about 12 
carbon atoms. The term "branched alkyl" includes aralkyl radicals, such as 
benzyl radicals. Thus, suitable R.sup.4 radicals include methyl, ethyl, 
n-propyl, isopropyl, n-butyl, isobutyl, tertiary butyl, the isomeric hexyl 
radicals, the isomeric octyl radicals, dodecyl radicals, etc. Preferred 
quaternary ammonium salts include ethyltrimethylammonium hydroxide, 
tetraethylammonium hydroxide, benzyltriethylammonium hydroxide, 
propyltrimethylammonium hydroxide, butyltrimethylammonium hydroxide, 
tetraethylammonium bromide, tetrabutylammonium bromide, tetrabutylammonium 
hydroxide, tetraethylammonium acetate, and mixtures thereof. 
The catalyst is employed in the process of the present invention in an 
amount of about 0.05 to 1.2 mole percent, based upon the number of moles 
of ethylene carbonate present in the reaction system. Surprisingly, the 
molecular weight of the final polymer appears to be relatively independent 
of the catalyst concentration. Therefore, relatively low concentrations of 
catalyst are preferred. However, the time required for the polymerization 
reaction may become unnecessarily lengthy at extremely low catalyst 
concentrations. 
The process of the present invention is conducted at a temperature of at 
least about 200.degree. C. It is preferable to avoid conducting the 
reaction above the boiling point of ethylene carbonate; therefore, at 
atmospheric pressure, the reaction temperature is preferably held to less 
than about 250.degree. C. (e.g., about 220.degree. to 240.degree. C.). The 
reaction typically is conducted at atmospheric pressure. However, higher 
pressures may be satisfactory or even desirable under certain 
circumstances. During the course of the reaction, evolution of carbon 
dioxide occurs, and entrainment of the reactants in the evolved carbon 
dioxide can commonly be avoided at elevated pressures. Thus, pressures as 
high as about 10 atmospheres can be employed where desired. 
The reaction is conducted for a period of time which is sufficient to allow 
the virtual cessation of evolution of carbon dioxide. Typically, reaction 
times of about 2 to 6 hours are sufficient. However, as noted above, the 
time of reaction is dependent upon the catalyst concentration. 
In the process of the present invention, the reaction mixture may further 
comprise about 0.01 to 0.5 mole of a polyfunctional alcohol per mole of 
ethylene carbonate. The addition of a polyfunctional alcohol, such as a 
glycol, to the reaction mixture operates to produce a polymer of lower 
molecular weight than otherwise would be obtained. Suitable polyfunctional 
alcohols include ethylene glycol, propylene glycol, neopentyl glycol, 
pentaerythritol, etc. Preferably, the polyfunctional alcohol comprises 
ethylene glycol. 
The reaction mixture can be anhydrous, but water can also be present in the 
reaction system. For example, water may be introduced in the form of 
hydrated catalysts, such as lithium acetate dihydrate. It may also be 
desirable to add water to the reaction system with the catalyst. However, 
the amount of water in the reaction system should not exceed about 5 moles 
of water for each mole of catalyst present in the reaction system. 
The process of the present invention produces a liquid, pourable, 
substantially difunctional, hydroxyl-terminated polyether-ester. The 
polyether-esters consist essentially of the following recurring units: 
EQU --CH.sub.2 --CH.sub.2 --O-- 
and 
##STR4## 
In the above formulas, each of R, R.sup.1, R.sup.2, and R.sup.3 
independently represents H, alkyl, cycloalkyl, alkoxy, or single-ring 
aromatic radicals, as described above. The polyether-esters typically 
exhibit a number average molecular weight of about 1,000 to 2,000. The 
molecular weight of the products can be established by determining the 
boiling point elevation of the product in methylene chloride. 
The polyether-ester product can be further characterized on the basis of 
its acid number and hydroxyl number. These determinations are made by 
standard ASTM measurements (ASTM D-2849-69). The acid number of the 
polyether-ester product preferably is less than about 1.00 mg KOH/g and, 
more preferably, is less than about 0.5 mg KOH/g. Acid number values 
greater than these indicate a tendency of the polymer to yield a urethane 
product having an undesirably short pot life. 
The hydroxyl number of the polyether-ester of the present invention is 
significant as a factor in the determination of the functionality of the 
polyether-ester product. The functionality of the product can be 
determined from the OH number by the following calculations: 
##EQU1## 
The polyether-ester products of the present invention have been found to 
be substantially difunctional. Preferably, the polyether-ester products 
exhibit a functionality of about 1.8 to 2.5. 
It has been observed that the polyether-ester products of the present 
invention are formed by an approximately equimolar reaction between the 
ethylene carbonate and unsubstituted or substituted epsilon-caprolactone. 
The polyether-ester product of the reaction appears to be predominantly an 
alternating type of copolymer. Spectroscopic evidence, such as obtained by 
infrared and NMR spectroscopy, indicates the presence of ether and ester 
linkages in the polymer chain and the absence of carbonate linkages from 
the polymer chain. These results comport with the observation of carbon 
dioxide evolution during the course of the reaction process. Thus, while 
not intending to be bound by theoretical considerations, it appears that 
during the course of the reaction, the lactone ring is opened so as to 
provide an ester linkage in the polymer product, and the ethylene 
carbonate ring is opened and carbon dioxide is evolved so as to provide an 
ether linkage (represented by the --CH.sub.2 --CH.sub.2 --O-- group) in 
the polymer product. This product differs substantially from prior art 
products which incorporated only ester linkages in the polymer chain or 
which incorporated carbonate linkages within the polymer chain. Unlike 
polycaprolactone, the products of the present invention do not tend to 
crystallize upon standing. This characteristic of the products of the 
present invention is quite significant for obvious practical reasons. 
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 reaction of ethylene carbonate and 
epsilon-caprolactone to produce a pourable liquid polyol. 
Into a 300 ml, three-neck flask were placed 57.0 g (0.5 mole) of 
epsilon-caprolactone, 44.0 g (0.50 mole) of ethylene carbonate, and 0.049 
g (0.5 millimole; 0.1 mole % based on ethylene carbonate) of potassium 
acetate. 
The mixture was heated with stirring in a 240.degree. C. metal bath for 150 
minutes, after which time carbon dioxide evolution appeared to have 
ceased. The product was a liquid at room temperature. The hydroxyl number 
of the product was 77 mg KOH per g product, and the acid number was 0.74 
mg KOH per g product. The number average molecular weight by boiling point 
elevation was determined to be 1554, and the functionality of the 
polyether-ester product was 2.1. 
EXAMPLE 2 
Example 1 was repeated except that 0.051 grams of lithium acetate dihydrate 
was employed as catalyst. The time of reaction was 235 minutes. The 
product was a liquid at room temperature and exhibited an acid number of 
0.49 mg KOH per g product and a hydroxyl number of 75.0 mg KOH per g 
product. The number average molecular weight by boiling point elevation 
was determined to be 1344, and the functionality of the polyether-ester 
product was 1.8. 
EXAMPLE 3 
This Example illustrates the addition of a glycol to the reaction system. 
Example 1 was repeated except that 39.6 g (0.45 mole) of ethylene carbonate 
was used and 3.1 g (0.05 mole) of ethylene glycol was added to the 
reaction mixture. Heating for 345 minutes in a 240.degree. C. metal bath 
gave a product having a hydroxyl number of 104.8 mg KOH per g product and 
an acid number of 0.10 mg KOH per g product. 
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.