CA1087800A - Biodegradable hydrophilic polyurethane foams and method - Google Patents

Abstract

Abstract of the Disclosure The invention disclosed is directed to biodegradable hydrophilic polyurethane structures prepared by using an isocyanate capped hydroxyester polyol reactant with large amounts of aqueous reactant. The resultant foam has economy in handling, and upon contact with liquids or body fluids, the foam is highly absorptive while being readily biodegradable after use.

Description

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Thls invention relates to a me-thod for preparing new biodegradeable Eoams. More particularly, the present invention provides ne~ dental and b~iomed~cal foams usiny a hydrophilic polyurethane foam having a biodegradable moiety.
Numerous devices have been proposed in the prior art for use as dental and biomedical foams for absorbing or removing body fluids. Typically, the prior art appro- -aches have relied upon natural materials such as cotton, which is now becoming relatively expensive while providing a resultant structure which is generally fragile in use.
Also, the amount of adsorption by natural materials is relatively low.
Various polyurethanes have been used as dentàl and biomeaical foams but suffer a disadvantage in that such foams are not readily biodegradable. It has now been found, however, that by practice of the present invention, there is provided a method for preparing new simple and highly ;
efficient dental and biomedical foams which are readily biodegradable after use, and which are characterized by high adsorptive ability of body fluids in use.
Various attempts have also been made in the prior art to prepare foams of organic substances for use in cavities of the human body. However, such organic sub-stances typically require, for example, catalysts or the like during the foaming reaction. These additives remain in the foam after foaming and are readily leached into the human body when in contact with body fluids. Thus, although artificial foams, especially those o polyurethane, of the prior art possess the capacity of high absorptivity of body -

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fluids, usage within the human body typicall~ invites disadvantayes beyond advantages ~ealiæed b~ low cost and high absorptivity. Thus, artificial foams such as polyurethanes of the prior art have received limited practical acceptance by the medical, dental and government regulatory agencies when proposed ~or internal usage in the human body. There is especia~ly a disadvantage of such foams.
By the present method, new biodegradable foams may be prepared having utility dental and biomedical foam structures, using hydrophilic crosslinked polyurethane ;
foams by reacting a particular isocyanate capped poly-hydroxyester polyol with large amounts of an aqueous reactant. The thus generated forms may be configurated to handy size as desired. Such structures may be readily used in the oral cavity and while in the oral cavity, the structure absorbs oral fluids, and thereafter may be discarded since it is biodeyradable.
Thus, in accordance with the present teachings, a method is provided for forming a biodegradable polyurethane foam which has a three-dimensional network and comprises reacting a first component comprising an isocyanate-capped, ester containing polyol mixture which has an isocyanate functionality of at least two, the ester-containing polyol mixture prior to capping comprises a member o~ the group consisting of: ;
(a) an essentially linear, hydroxy terminated poly-ether which has a molecular weight not exceeding about 4,000 and a reaction product which is formed by reacting an aliphatic alcohol having from 3 to 8 hydroxyl groups per mole and a molecular weight of less than about 1,000 with a monobasic hydroxy carboxylic acid to esterify the hydroxyl groups of E~ - -~ . , .. . . . . . ~ .......... . .

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the aliphatic alcohols;
(b) an aliphatic alcohol which has ~rom 3 to 8 hydroxyl groups per mole and a molecular weight o~ less than about 1,000 and an essentially linear hydroxy terminated polyether which has a molecular weight not exceeding about 4,000 and wherein the hydroxyl groups of the polyether are esterified by reaction with a monobasic hydroxy carboxylic acîd; and (c) the esterification products of an aliphatic hydroxy carboxylic acid with the hydroxyl groups of 1) a hydroxy terminated essentially linear polyether and 2) a monomeric low molecular weight aliphatic alcohol containing from 3 to 8 hydroxyl groups per mole, with a second component comprising an a~ueous reactant wherein the H2O index value is about 1,300 to 78,000.
In accordance with a further embodiment of the present teachings there is provided a biodegradable polyurethane foam-forming composition upon the addition of an aqueous reactant wherein the H2O index value is about 1,300 to 78,000 and :
comprises an isocyanate-capped, ester-containing polyol mixture which has an isocyanate functionality of at least two, the ester-containing polyol mixture prior to capping comprises a member of the group consisting of ta) an essentially linear, hydroxy terminated polyether which has a molecular weight nok exceeding about 4,000 and a reaction product which is ormed by reacting an aliphatic :
alcohol which has from 3 to 8 hydroxyl groups per mole and a .
molecular weight of less than about 1,000 with a monobasic hydroxy carboxylic acid to esteriy the hydroxyl groups o~
the aliphatic alcohol;
(b) an aliphatic alcohol which has from 3 to 8 hydroxyl groups per mole and a molecular weight of less than 1,000 and an essentially linear hydroxy terminated polyether which has a ', ~(~8~
molecular weigh-t not exceeding about 4,000, and wherein the hydroxyl groups o the polyether are esterified by reaction with a monobasic hydroxy carboxylic actd; and (c) the esterification product of an aliphatic hydroxy carboxylic acid with the hydroxyl groups o 1) a hydroxy terminated essentially linear polyether and 2) a monomeric low molecular weight aliphatic alcohol containing f`rom 3 to 8 hydroxyl groups per mole. ;
The present foams have utility as handy expandable sponges for personal use. The sponges are easily carried and may be readily prepared with detergents, lotions, perfumes, biostats and the like and upon contact with water, the sponges are found to be very soft, very .
hydrophilic and biodegradable. The sponges may be used for washing, wiping, cleaning, etc. for external body cleaning; or alternatively for internal body usage `~
such as is necessary in dental and medical applications.
The present sponges also have utility as intimate absorptive products, such as diapers, sanitary napkins, incontinent pads and the like.

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~87~0 Polyurethane foam structures prepared herein with hydroxye~ter polyisocyanates, ~ater and certain surfact-ants, have an exceptionally Eine, uniform, soft, hydro-philic cell structure.
The following condi-tions seem to be important to obtaining foams of the above mentioned desirable proper-ties.
One mole of a polyoxyethylene diol of molecular weight less than 4,000 containing about 0.1 to about 4.0 ~ `
mole, preferably about 0.2 to about 2.5 moles of polyols with 3 or greater hydroxyl groups per molecule, preferably tri- or polyhydroxy ester crosslinking agent such as trimethylolpropane trilactate or the like.
The prepolymer is next capped with diisocyanates.
The useful range of polyisocyanates is about 0.60 to about 1.3 moles of diisocyanate per equivalent group in the polyol mixture. The preferred range of diisocyanate is about 0.95 to about 1.15 moles of diisocyanate per equivalent of the polyol mixture.

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The resultant polyester polyisocyanate prepoly-mers are foamed by reacting with about 10 to about 200 parts of water, preferred range of about 50 to about 160 part.s of water, to 100 parts of prepolymer in the presence of about Q.05 to about 30 parts surfackant, preferred range of about 0.1 to about 15 parts surfactant, per 100 parts of prepolymer.
The suractants can be added either to the prepolymer or the water. Surfactants which are soluble in water and/or ` `~
in their own right are hydrophilic, are preferred.
The polyurethane foams made in the manner described above are exceptionally soft, hydrophilic and biodegradable r ~ 4 ~

1tl87~(~0 as compared to conventional polyurethane Eoams. The foams described above can be dried to form so~t dense materials which, upon exposure to water, almost instantly absorb the water.
A l~w density foam is thus prepared for ease and economy in handling and shipping, but is readily biodegrad- ~ `
able after usage. When warm and/or wet the foam is useful ~
for its flexibility, softness and hydrophilicity. ~-The original foam is biodegradable within about 7 days by contacting the foam with certain enzymes. The foam is soft and flexible when wet and~or warm and rigid or soft when cold and/or dry.
The present foams may be characterized as low density polyurethane foam (1 to 6 lbs/ft3) which is easily biodegradable.
Preparation of the present foam structures will be-come more apparent from the following detailed description. ~-During capping, it is desirable that the polyiso-cyanate be reacted such that the reaction product, i.e., the capped product, is substantially void of reactive hydroxy groups while containing more than two reactive isocyanate sites per average molecule. Another route for achieving this de~ired result is to react a polyisocyanate having two reactive active isocyante sites per average molecule, in a rea~tion system during foaming having a polyfunctional reactive component such as one having from three up to about eight or m~re reac~ive amine, hydroxy, thiol, or carboxylate sites per average molecule. These latter sites are highly reactive with the two reactive isocya-nate sites and thereby form a three dimensional product.

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1(11*7 !3(~0 Polyoxyethylene polyol used as a reactant in pre-paring the capped product to be foamed may have a weight average molecular weight of about 200 to about 4,0Q0, and pre~erably between about 600 to 3500, with a hydroxyl ~unc-tionality o~ 2 or greater, preferably from about 3 -to about 8.
The polyoxyethylene polyol is combined with a cross-linking agent for the prepolymer.
Trimethylolpropane trilactate or the like can be used in combination with other polyols or trimethlolpropane trilactate can be oxyethylated or oxypropylated to yield the appropriate polyol. Other hydroxy acids may be used for the crosslinking agent esterification. These include but are not limited to hydroxyacetic acid and other y, ~, etc., hydroxy acids.
The polyoxyethylene polyol ester mixture is term-inated or capped by reaction with a polyisocyanate. The reaction may be carried out according to conventional prac-tice. The polyisocyanates used for capping the polyoxyethylene polyol include polyisocyanates which are PAPI (polyaryl poly-isocyanate as de~ined in the United States Patent No.
2,683,730), tolylene diisocyanate, triphenylmethane-4, 4', 4", triisocyanate~ benzene-1,3,5-triisocyanate, toluene-2,4,6-toluene-2,4,6-triisocyanate, diphenyl-2,4,4'-triiso-cyanate, hexamethylene diisocyanate, xylene diisocyanate, chlorophenylene diisocyanate, diphenylmethane-4,4'-diisocyanate, naphthalene-l, 5-diisocyanate, xylene-alpha, alpha'-diisothiocyanate, 3,3'-dimethyl-4,4l-biphenyl~
lene diisocyanate, 4,4'-methylenebis (phenylisocyanate), 4,4'-sulfonylbis (phenylisocyanate), 4,4'-methylene bis(orthotolylisocyanate), ethylene diisocyanate, ethylene ,,~ ,`. :' ,, . , . ., . ,. " .. ,,. ., . . , . , ~ .

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diisothiocyanate, trimethylenediisocyanate and the like.
Mixtures of any one or more of the above mentioned organic isothiocyanates or isocyanates may be used as desired.
The aromatic diisocyanates and polyisocyanates or mixtures thereof which are especially suitable are those which are readily commercially available, have a high degree of reactivity and a relatively low cost.
Capping of the polyoxyethylene polyol may be ef-fected using stoichiometric amounts of reactants. Desir-ably, however, an excess of isocyanate is used to insure complete capping of ~he polyol. Thus, the ratio of iso-cyanate groups to the hydroxyl groups used for capping is between about 1 to about 4 isocyanate to hydroxyl, and pre-ferably about 2 to about 3 isocyanate to hydroxyl molar ratio.
In order to achieve an infinite crosslinked network for-mation on foaming, the reactive components may be formu-lated in one of the following by way of example. First, when water is the sole reactant with the isocyanate groups leading to chain growth during the foaming-process, the isocyanate capped reaction product must have an average isocyanate functionality greater than 2 and up to about 6 or more depending upon the composition of the polyol and capping agent components. Secondly, when the isocyanate capped reaction product has an isocyanate functionality of only about two, then the aqueous reactant, may contain a dissolved or dispersed isocyanate-reactive crosslinking agent having an effective functionality greater than two. In this case, the reactive crosslinking agent is reacted with the capped resin when admixed during and after the foaming process has been initiated. Thirdly, when the isocyanate " `' , . ; . . ... .. . .

-7~3~0 capped resin has an isocyanate functionality of only about two, then a polyisocyanate crosslinking agent when an isocyanate functionality greater than two may be incor-porated therein, either preformed or formed in situ, and the resultant mixture may -then be reacted with the aqueous reactant, optionally containing dissolved or dispersed reactive isocyanate-reactive crosslinking agent, leading to a crosslinked, infinite network hydrophilic polyurethane foam.
Water soluble or water dispersible crosslinking agents operable in this invention desirably should be poly-- functional and reactive with isocyanate groups and include t but are not limited to materials such as diethylenetriamine, '::
`~ triethylenetetramine, tetraethylenepentamine, polyethylenei-mine, glycerol, trimethylolpropane, pentaerythritol, tolylene 2,~ r 6-triamine, ethylenediamine, aminoethanol, trimethylenediamine, tetramethylenediamine, pentamethylene-diamine, hexamethylenediamine, ethanolamine, diethanola-amine, hydrazine, triethanolamine, benzene-1,2,~-tricarboxy-. .
~ 20 lic acid, nitrolotriacetic acid, citric acid, 4,4'-methy r, lenebis (o-chloroaniline), and the like. The water soluble or water dispersible crosslinking agents chosen are those which cause a crosslinked network to form during or after ~; the foaming process begins to take place.
It has also been found that the capped resin having an isocyanate functionality greater than two used to prepare ~ a three dimensional network polymer must be present in an ; amount sufficient to insure formation of the dimensional ,.j :. ~
network. Thus, amounts of the capped polyoxyethylene polyol having an isocyanate ~unctionality greater than 2 ~;

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J878C~0 in the component to be foamed range from about 3~ by weight of this component up to 100~ by weiyht. Thus, it is possible , to include a capped polyoxyethylene polyol having a terminal member with an isocyanate functionality of two ite., a diisocyanate in an amount from 0% by weight up to about 97~ by weight of the component to be foamed. The maximum amounts of diisocyanate used are limited to that necessary to permit crosslinking to take place during foaming, as ;~
contrasted to formation of a linear polymeric structure, -and the properties desired in the finally prepared foam.
``~1 To effect foaming and preparation of the crosslink-~ ed network polymer, the component including the isocyanate - capped polyoxyethylene polyol having a functionality about 2 or greater is simply combined with the aqueous component.
For simplicity, this isocyanate capped reaction component will herein be referred to as resin reactant.
The aqueous component, i.e., water slurry or sus-,.~ .
`, pension, may include various additives such as detergents, :~1 biostats, perfumes or the~like as desired for use in a given 20~ produc~. Obviously, additives are avoided ar carefully selected for specific purposes for foam structures intended for internal body usage. `~
, ! The dramatic way in which additions of water in-~j fluences practice of the present invention is by considera-tion of the following water index value, .
1 equivalents of H2O `~
;~ Water Index Value = X 100 I equivalents of NCO
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Thus, because one-half mole of water is equal to one equivalent of isocyanate, where O.S m H2O is used with 1 eq. NCO, the water index value is 100.
An Index of 100 indicates that both equi~alents are equal or "balanced". An Index of 95 indicates that there is a ~ shortage of water while an Index of 105 indicates a 5% surplus of water. A slight theoretical excess of isocyanate, usually 3 S~, is common pr~ctice, in tha prior art particularly with flexible foams.
Vsing the present resin xeactant and water in amounts from about H2O Index Value of 100 up to about H2O Index Value of 200, poor foaming results unless materials such :`
as surfactants or the like are includ~. Amounts up to about H2O Index Value of 200 require a catalyst. When using about H2O Index Value 78,000, surprisingly good foams result which improve in characteristics with added amounts of molar water. Thus, the available water content in the aqueous reactant is ffom about an H2O Index Value of about 1300 to about 78,000 and desirably from about i 20 4,000 to about 40,000.
`,i "Available water" in the aqueous reactant is that water accessible for reaction with the resin reactant, and which is exclusive of water which may layer during reaction, or supplemental water which may be necessary because of addi~ives present in and forming the a~ueous reactant.
~ecause large amounts of water are in the aqueous reactant during reaction, i.e., the present system is not dependent upon a lar NCO-water type reaction, it is possi-ble to combine a great variety of materials in the aqueous :`
reactant which are otherwisa not p~ssi~ie ~ith`l-imited water reacting system6.

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1~1!8'78~) The aqueous reactant may be used at temperatures from about 2C. to about 100C. as desired.
Al-though foaming of the present resin reactant, i.e., -;
prepolymer, is effected simply, it is also possible to add, although not necessary, supplemental foaming materials such as those well known to the artifical sponge foaming art.
After foaming has been effected, the foam may be dried, if desired, under vacuum from 1 to 760 Torr at a tem-perature of about 0 to about 150C. When used internally, the foams may be heat or chemically sterilized prior to use.
The following examples will aid in explaining, but should not be deemed as limiting, practice of the present invention. In all cases, unless otherwise noted, all parts ~: .
i~, and percentages are by weight.
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Example 1 Polyethyleneglycol PEG 1000 (actual M.W. 1064) and trimethylolpropane trilactate (361g and 60g respectively) ~^ were dried for 2.5 hours at 103C. and 4 Torr. This mixture :
was added to 225g of toluenediisocyanate and 0.2g of Metal and Thermit ~ T-9 catalyst, a catalyst containing stannous octoate, over a period o~ 80 minutes at a temperature of 60C.
After completion of addition, the reaction mixture was maintained at 60C. for an additional hour. To the reaction mixture there was then added an additional 12g of tolylene-` diisocyanate and heating continued for another hour at 60C.
The final viscosity was 24,500 cp at 25C. and the NCO was 2.38 1 meq/g (theory 2.33 meq/g).
From the above reaction mixture, a foam was prepared ~i using lOOg of prepolymer, lOg of Union Carbide Silicone surfactant L-520 ~ and lOOg of water. Aqueous solutions of enzymes, 1%, J! were prepared and tested on this foam. Maxa-tase, ~ H.T.
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proteolytic concen-trate, and protease amylase, gave essentially comple-te degrada-tion after seven days at 25C. Several others, such as mucinase, trypsin and some experimental enzyme broths, showed some evidence oE degradation. A standard polyurethane foam prepared from 100 pts of prepolymer, iso-cyanate capped polyoxyethylene polyol, 1 pt 1-520 and 100 pts of water gave no change over the same period of time with . .
these enzymes. ~
The oam was buried in a compost heap for three months. ~:
. 10 On removal from the compost heap, the foam had started to :~ fragment and could not be washed without falling apart.
The foam was then compared with a foam made in a . .
5 jmilar manner with trimethylolpropane instead of the tri-methylolpropane trilactate. The trimethylolpropane lactate based foam in ten minutes at 250F. turned tacky and begun to degrade. The trimethylolpropane based oam showed no change i.n 20 minutes at 250F. Conventional polyoxypropylene based polyurethanes show no change in three hours. ~:
. A similar comparison at 100C. in boiling water gave .: .
.. : 20 breakdown into viscous lumps in 240 minutes after becoming .
: tacky in 30 minutes for the trimethylolpropane trilactate :; biodegradable polymeric foam. The trimethylolpropane based - foam showed no change in 240 minutes at 100C.

Example 2 ` The procedure of Example 1 was repeated for foam ;;

generation. Next a synthetic sewage sludge was allowed to . react with the foam for one week. The trimethylolpropane ~

.`.......... trilactate based foam had completely disintegrated. The ;~ :

~ . standard polyurethane foam was intact.

: 30 Example 3 ` The trimethylolpropane trilactate that had been pre-' ,.
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~8~7~ao pared was used with a different polyol. ~ mixture of one mole each of trimethylolpropane trilactate and Pluronic ~ lO-R-5 (a Wyandotte polyol with a molecular weight of 1970, an equivalent weight of 985 and end-capped with oxypropylene on an oxyethylene backbone with approximately 50% by weight of oxypropylene and 50% by weigh~ of oxyethylene) was dried at 110Co and 3 torr for three hours. The mixture was then added to 4.75 moles of the standard 80-20 mixture of 2,4 and 2,6-tolylenediisocyanate over a period of one hour maintaining the temperature at 60C. The reaction was completed by heating ~ for an addi~ional three hours at 60C. with the addition of - Metal and Thermits' T-9 stannous octoate catalyst (5 drops).
To the final prepolymer was added 0.75 moles of tolylenediiso-cyanate to give a prepolymer with a viscosity of 17,250 cp.
The prepolymer was converted to a foam by the addition of l part of silicon surfactant L-520 to the prepolymer (lO0 parts) and then adding lO0 parts water to the prepolymer phase. The polymeric foam when placed in a synthekic sewer sludge dis-~` integrated within one week.
Example 4 The trimethylolpropane trilactate was prepared as above in Example 3. A mixture was prepared from one mole of trimethylolpropane lactate and 0.5 mole Pluronic P-65 supplied ~; by Wyandotte (this polyol has a molecular weight of 3500 and has a polyoxypropylene base, end-capped with oxyethylene units, being 50% oxyethylene and 50% oxypxopylene by weight) and was dried by heating for a period of three hours at 115C and 5 torr. This mixture was added to 3.8 moles of commercial TDI ~;
`~i over a period of one hour with the temperature maintained at 60C. After completion of the addition, 10 drops of Metal and Thermit catalyst T-9 was added and the reaction mixture was .~

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o heated for an additional -three hours at 65C. to force the pre-polymer formation. Then 0.6 mole of TDI was added to the reaction mixture and the reaction heated for an additional two hours to give a prepolymer with a viscosity of 16,000 cp ; at 25C. A foam was prepared from this prepolymer using 100 parts of prepolymer, 1.0 part of Plurafac ~ B-26, 1.7 parts of tertiary amine of Thancat ~ DD catalyst by Jefferson Chemicals, and 50 parts of water (the latter three all being in the aqueous phase). The foam that was formed decomposed in a compost heap in two months. The conventional polyoxypropyl-ene polyurethane foam showed no change.
Example 5 Trimethylolpropane hydroxyacetate (glycolate) is - prepared by simple esterification using one mole trimethylol-propane and 3.12 moles glycolic acid (hydroxylacetic acid).
The mixture was heated for four hours at reflux and then strip-i ?
; ped at 125C. and 12 Torr.
~l The prepolymer was prepared by adding a dried mixture of 2.0 moles o~ PEG-1000 (molecular weight 1064) and 1.0 mole of trimethylolpropane triglycolate to 6.7 moles of tolylene-diisocyanate over a period of one hour at a reaction flask temperature of 60C. The reaction was continued at 60C. for ~ `
an additional three hours and the measured NCO content in meq/g. was 1.82 meq/g(theory 1.78 meq/g.). To the reaction mixture was then added an additional 1.0 mole of TDI with '~
heating and stirring continued for an additional two hours at 60C. The NCO was 2.18 meq/g(theory 2~23 meq/q.), viscosity ' at 25C. 19,000 cp.
,, A foam was prepared from this prepolymer by using 100 g. of prepolymer and 100 parts of 5~ so-ution of Pluratac B-26 ~By Wyandotte) in water. The generated foam was found to de~
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grade with Mexatase enzyme in six days at 25C. while the foam ,~
prepared from trimethylolpropane was intact. In boiling water, decomposition occurred in 200 minutes with -the trimethylol-propane glycolate based material. With the trimethylolpropane based prepolymer, no change was noted in the same time period.
Example 6 Instead of preparing the hydroxyacid ester of the crosslinking agent as in the previous example, the hydroxy~
acid ester of polyoxyalkylene glycol was prepared. To 1 mole of polyethylene glycol having a molecular weight of 1064 (PEG-1000) there was added 2.22 moles of 88~ lactic acid. The mixture was refluxed for four hours after which the resi~ual lactic acid was stripped at 130C. and 4 Torr.
The product weighing 1215 g., mainly polyethylene glycol dilactate, was combined with 67 g. o trimethylolpropane and stripped of residual water at 105C. and 3 Torr for four hours. This mixture was then added at 60C. flask temperature to 574 g. of tolylenediisocyanate over a period of two hours.
The reaction mixture was then heated for an additional four ,.~", :
20 hours at 60C. To the reaction mixture was then added an ` additional 87 g. of tolylenediisocyanate in thirty minutes at 60C. and the reaction mixture heated for an addltional two hours at 60C. The NCO content was 2.06 meq/g.(theory 2.11 : . .
meq/g.); the viscosity was 18,000 cp at 25C.
., , ` A foam was prepared from the prepolymer of this ex- ~
.:, ~' ample using 100 parts of prepolymer and 100 parts of 5% solution . .
;~ of Pluronic P-75 in water. The final foam was dried and on ;
treatment with a synthetic sewer sludge, disintegrated within . , .~ .
ten days. A similar sample was prepared from a prepolymer 30 containing polyethylene glycol 1000 and trimethylolpropane showed no signs of decomposition in the same period of time.
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It is understood that the foregoing detailed descrip-tion is given merely by way of illustration and that many variations may be made therein without departing from ~he spirit of this invention.

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Claims (11)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method for forming a biodegradable polyurethane foam having a 3-dimensional network comprising reacting a first component comprising an isocyanate-capped, ester containing polyol mixture having an isocyanate functionally of at least 2, said ester-containing polyol mixture prior to capping comprising a member of the group consisting of:
(a) an essentially linear, hydroxy terminated poly-ether having a molecular weight not exceeding about 4,000 and a reaction product formed by reacting an aliphatic alcohol having from 3 to 8 hydroxyl groups per mole and a molecular weight of less than about 1,000 with a monobasic hydroxy carboxylic acid to esterify the hydroxyl groups of said aliphatic alcohol;
(b) an aliphatic alcohol having from 3 to 8 hydroxyl groups per mole and a molecular weight of less than about 1,000 and an essentially linear hydroxy terminated polyether having a molecular weight not exceeding about 4,000, wherein the hydroxyl groups of the poly-ether are esterified by reaction with a monobasic hydroxy carboxylic acid; and (c) the esterification products of an aliphatic hydroxy carboxylic acid with the hydroxyl groups of (1) a hydroxy terminated essentially linear polyether and (2) a monomeric low molecular weight aliphatic alcohol containing from 3 to 8 hydroxyl groups per mole , with a second component comprising an aqueous reactant wherein the H2O Index Value is about 1,300 to 78,000.

2. The method of Claim 1 wherein the isocyanate-capped hydroxyester polyol is present in the first component in an amount from about 3% by weight up to 100% by weight, wherein an isocyanate-capped polyoxyethylene polyol having a terminal member with an isocyanate functionality of two is present in an amount from 0% up to about 97% by weight.

3. The method of Claim 1 wherein the polyol moiety of the isocyanate-capped member has a weight average molecular weight of about 200 to 4,000, and a hydroxyl functionality of about 2 to about 8.

4. The method of Claim 3 wherein the weight average molecular weight is about 600 to 3,500.

5. The method of Claim 3 wherein the H2O Index Value is from about 4,000 to about 40,000.

6. A biodegradable polyurethane foam having a 3-dimensional network comprising the reaction product of an isocyanate-capped, ester-containing polyol mixture having an isocyanate functionality of at least 2, said ester-containing polyol mixture prior to capping comprising a member of the group consisting of:
(a) an essentially linear, hydroxy terminated polyether having a molecular weight not exceeding about 4,000 and a reaction product formed by reacting an aliphatic alcohol having from 3 to 8 hydroxyl groups per mole and a molecular weight of less than about 1,000 with a monobasic hydroxy carboxylic acid to esterify the hydroxyl groups of said aliphatic alcohol;
(b) an aliphatic alcohol having from 3 to 8 hydroxyl groups per mole and a molecular weight of less than about 1,000 and an essentially linear hydroxy terminated polyether having a molecular weight not exceeding about 4,000, wherein the hydroxyl groups of the poly-ether are esterified by reaction with a monobasic hydroxy carboxylic acid; and (c) the esterification products of an aliphatic hydroxy carboxylic acid with the hydroxyl groups of (1) a hydroxy terminated essentially linear polyether and (2) a monomeric low molecular weight aliphatic alcohol containing from 3 to 8 hydroxyl groups per mole, and an aqueous reactant wherein the H2O Index Value is about 1,300 to 78,000. .

7. A biodegradable polyurethane foam-forming composition upon the addition of an aqueous reactant wherein the H2O Index Value is about 1,300 to 78,000 comprising an isocyanate-capped ester-containing polyol mixture having an isocyanate function-ality of at least 2, said ester-containing polyol mixture prior to capping comprising a member of the group consisting of (a) an essentially linear, hydroxy terminated polyether having a molecular weight not exceeding about 4,000 and a reaction product formed by reacting an aliphatic alcohol having from 3 to 8 hydroxyl groups per mole and a molecular weight of less than about 1,000 with a mono-basic hydroxy carboxylic acid to esterify the hydroxyl groups of said aliphatic alcohol;
(b) an aliphatic alcohol having from 3 to 8 hydroxyl groups per mole and a molecular weight of less than about 1,000 and an essentially linear hydroxy terminated polyether having a molecular weight not exceeding about 4,000, wherein the hydroxyl groups of the polyether are esterified by reaction with a monobasic hydroxy car-boxylic acid; and (c) the esterification products of an aliphatic hydroxy carboxylic acid with the hydroxyl groups of (1) a -hydroxy terminated essentially linear polyether and (2) a monomeric low molecular weight aliphatic alcohol containing from 3 to 8 hydroxyl groups per mole.

8. A foam as in Claim 6 or 7 wherein the polyether is a polyoxyalkylene copolymer containing at least % by weight of oxyethylene units.

9. A foam as in Claim 6 or 7 wherein the hydroxy acid is lactic acid.

10. A foam as in Claim 6 or 7 wherein component (b) is the trilactate ester formed by reacting trimethylolpropane and lactic acid.

11. A foam as in Claim 6 or 7 wherein the polyether has a molecular weight of less than about 4,000.