BACKGROUND OF THE INVENTION Ihisinveution relates4eraerallFtwlymer pol3oljormation and, more particularly, to a process for preparing a transesterification stable preformed stabilizer for use in the formation of polymer polyols.

Polymer polyols, also know as graft polyols, are well know in polyurethane chemistry.

They find special use in the formation of certain foams with special properties. Typi- cally, graft polyols are formed as the reaction product of ethylenically unsaturated monomers with a macromer in the presence of a carrier polyol, a reaction moderator, optionally a preformed stabilizer, and a free radical polymerization initiator wherein the monomers copolymerize with the macromer. One of the difficulties associated with current processes for preparing graft polyols is that the reactors tend to accumulate fouling, which is a particularly significant problem for continuous reactors. This fouling causes the reactors to quickly become plugged with sediment of unstable compounds in the reaction. The reactor must be shut down and cleaned, leading to a loss in pro- ductivity of the reactor. Thus, it would be highly advantageous to create a process for the formation of graft polyols having a reduced tendency for fouling.

The typical macromers are polyether polyols having induced unsaturation prepared by reacting any conventional polyol with an organic compound having both ethylenic un- saturation and a carboxyl, anhydride, isocyanate, epoxy, or other group reactive with an active hydrogen-containing group. Suitable unsaturated isocyanates include com- pounds such as isocyanatoethylmethacrylate (IEM) and 1, 1-dimethyl meta-isopropenyl benzyl isocyanate (TMI). Macromers are usually prepared in the presence of a Lewis acid catalyst.

The preformed stabilizers of the present invention, which are also graft polyols, are prepared by reaction of ethylenically unsaturated monomers with the macromer in the presence of a carrier polyol, a reaction moderator, and a free radical polymerization initiator. One problem associated with this reaction is the tendency to have formation of transesterification products between the macromer and the carrier polyol wherein the

unsaturated group on the macromer gets transferred to the carrier polyol. This tran- sesterification product can then cause problems in the subsequent graft polyol formati- on reaction using the preformed stabilizer. Thus, it would be advantageous to develop a method for reducing the transesterification reaction during formation of the preformed stabilizer or final graft polyol product.

SUMMARY OF THE INVENTION In one embodiment, this invention provides a preformed stabilizer comprising the reac- tion product of : a Lewis acid catalyzed macromer; and at least one ethylenically un- saturated monomer; wherein the macromer and the monomer are polymerized in the presence of at least one free radical initiator, a carrier polyol, and at least one phospho- rous compound.

In another embodiment, the present invention is a method for formation of a preformed stabilizer comprising the steps of : providing a Lewis acid catalyzed macromer; provi- ding at least one ethylenically unsaturated monomer; and polymerizing the macromer and the monomer in the presence of at least one free radical initiator, a carrier polyol, and at least one phosphorous compound.

In another embodiment, the present invention is a final graft polyol comprising the reac- tion product of: a Lewis acid catalyzed macromer; and at least one ethylenically un- saturated monomer; wherein the macromer and the monomer are polymerized in the presence of at least one free radical initiator, a carrier polyol, and at least one phospho- rous compound.

In another embodiment, the present invention is a method for formation of a final graft polyol comprising the steps of: providing a Lewis acid catalyzed macromer; providing at least one ethylenically unsaturated monomer; and polymerizing the macromer and the monomer in the presence of at least one free radical initiator, a carrier polyol, and at least one phosphorous compound.

These and other features and advantages of this invention will become more apparent to those skilled in the art from the detailed description of a preferred embodiment. The drawings that accompany the detailed description are described below.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a comparison overlay of Gel Permeation Chromatography chromatograms of a mixture of a macromer and a carrier polyol heated to 130°C in the presence or absence of phosphoric acid; Figure 2 is a comparison overlay of Gel Permeation Chromatography chromatograms of a preformed stabilizer prepared using a macromer either having or not having phosphoric acid; Figure 3 is a comparison overlay of Gel Permeation Chromatography chromatograms of a preformed stabilizer prepared in the presence or absence of a phosphoric acid reactor charge; Figure 4 is a Gel Permeation Chromatography chromatogram of a macromer showing the presence of a carrier polyol transesterification product; Figure 5 is a Gel Permeation Chromatography chromatogram of a macromer showing the presence of a carrier polyol transesterification product; Figure 6 is a Gel Permeation Chromatography chromatogram of a macromer showing the presence of a carrier polyol transesterification product; and Figure 7 is a Gel Permeation Chromatography chromatogram of a macromer showing the presence of a carrier polyol transesterification product.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT Methods of forming conventional polyether polyols are well known, for example, by the base catalyzed addition of alkylen oxides to an initiator molecule or nucleus contain- ing reactive hydrogens such as a polyhydric alcohol. Examples of such polyhydric al- cohol initiators include: glycerol, 1,1, 1-trimethylolpropane, 1,1, 1-trimethylolethane, 1,2, 6-hexanetriol, pentaerythritol, sucrose, and sorbitol. Other suitable initiators include both aliphatics and aromatics, such as, ethylene glycol, propylene glycol, dipropylene glycol, trimethylene glycol, 1, 2-butanediol, 1, 3-butanediol, 1, 4-butanediol, 1,2- pentanediol, 1, 4-pentanediol, 1, 5-pentanediol, 1, 6-hexanediol, 1, 7-heptanediol. Also included within the term"polyhydric alcohol"are compounds derived from phenol such as 2,2-bis (4-hydroxyphenyl) propane, commonly known as Bisphenol A. Other suitable initiators for the polyether polyols of the present invention comprise hydrogenated starch hydrolysates, such as those available from Roquette under the tradename Lyca- sind !), which are derivatives of maltitol. The polyether polyols may be prepared by any

known process such as, for example, the process disclosed by Wurtz in 1859, Encvc- lonedia of Chemical Technoloav, Vol. 7, pp. 257-262, published by Interscience Publi- shers, Inc. (1951) or in U. S. Patent No. 1,922, 459.

Examples of useful alkylen oxides include ethylene oxide, propylene oxide, butylen oxide, amylene oxide, tetrahydrofurans, epihalohydrins, arylalkylene styrene, and mix- tures thereof. The alkylen oxides are added onto the initiator molecule and chain pro- pagation is carried out in the presence of catalysts by either anionic polymerization or by cationic polymerization.

The preferred alkoxylation catalysts are potassium hydroxide, sodium hydroxide, alco- holates of potassium hydroxide, alcoholates of sodium hydroxide, cesium hydroxide, amines, Lewis acid catalysts, or double metal complex catalysts, all of which are known in the art.

Graft polyols are generally defined as vinyl polymer dispersions in polyether polyols as disclosed generally in U. S. Reissue Number Re. 33,291. Methods for the formation of typical graft polyols are known in the art. In the prior art graft polyols are typically pre- pared by the in situ polymerization of a polyether polyol having induced unsaturation, commonly known as a macromer, and an ethylenically unsaturated monomer or a mix- ture of ethylenically unsaturated monomers in the presence of a carrier polyol, a reacti- on moderator, optionally a preformed stabilizer, and a free radical polymerization initia- tor.

Generally, the macromers have induced unsaturation levels of between about 0.1 and 1 mole per mole of polyol. As used herein, the term macromer means a polyether po- lyol having induced unsaturation. The macromers employed in preparing the prefor- med stabilizer and the final graft polyol according to the present invention may be pre- pared by the reaction of any conventional polyol, described above, with an organic compound having both ethylenic unsaturation and a carboxyl, anhydride, isocyanate, epoxy, or other group reactive with an active hydrogen-containing group in the presen- ce of a Lewis acid catalyst. Suitable unsaturated isocyanates include compounds such as isocyanatoethylmethacrylate (IEM) and 1, 1-dimethyl meta-isopropenyl benzyl isocy- anate (TMI).

Representatives of such organic compounds having ethylenic unsaturation and a reac- tive group include : maleic acid and anhydride, fumaric acid, crotonic acid and anhydri- de, propenyl succinic anhydride, acrylic acid, acryloyl chloride, hydroxyethyl acrylate or methacrylate, hydroxypropyl acrylate or methacrylate, halogenated maleic acids and anhydrides, unsaturated polyhydric alcohols such as 2-butene-1, 4-diol, glycerol allyl ether, trimethylolpropane allyl ether, pentaerythritol allyl ether, pentaerythritol vinyl e- ther, pentaerythritol diallyl ether, and 1-butene-3, 4-diol, unsaturated epoxides such as

1-vinylcyclohexene-3, 4, epoxide, butadiene monoxide, vinylglycidyl ether (1-vinyloxy- 2,3-epoxy propane), glycidyl methacrylate and 3-ailyloxypropylene oxide (allyl glycidyl ether), isocyanates such as isocyanatoethylmethacrylate (IEM) and 1, 1-dimethyl meta- isopropenyl benzyl isocyanate (TMI). If a polycarboxylic acid or anhydride is employed to incorporate unsaturation into the polyols, it is preferable to react the unsaturated polyol with an alkylen oxide, preferably ethylene or propylene oxide, to remove the unreacted acid groups prior to employment as a macromer in the present invention.

The amount of alkylen oxide employed is such as to reduce the acid number of the unsaturated polyol to about 5 or less.

In the typical reaction for formation of the macromer a reactor is charged with the de- sired conventional polyol and Lewis acid catalyst at a temperature of from 20 to 40 °C.

The amount of Lewis acid catalyst ranges from 0.2 to 50 parts per million (ppm), prefe- rably from 0.5 to 25 ppm, most preferably from 1 to 15 ppm. The mixture is then hea- ted to a temperature of from 70 to 130 °C and the organic compound having ethylenic unsaturation and a reactive group is added over 0.5 to 1 hours to the reactor. The con- tents are held there for 1 to 3 hours. The formed macromer is then used in the reaction for formation of the preformed stabilizer or final graft polyol as described below.

The suitable Lewis acid catalysts generally comprise tin-based, boron-based, alumi- num-based, gallium-based, rare earth-based, zinc-based, or titanium-based com- pounds. Representative tin-based compounds include: Dibutyltin diacetate, Dibutyltin dibromide, Dibutyltin dichloride, Dibutyltin dilaurate, Dibutyltin dimethoxide, Dibutyltin oxide, Dimethyltin diacetate, Dimethyltin dibromide, Diphenyltin dichloride, Diphenyltin oxide, Methyltin trichloride, Phenyltin trichloride, Tin (IV) acetate, Tin (IV) bromide, Tin (IV) chloride, Tin (IV) iodide, Tin (II) oxide, Tin (II) acetate, Tin (II) bromide, Tin (ii) chlo- ride, Tin (li) iodide, and Tin (II) 2-ethylhexanoate (stannous octoate). Representative boron-based compounds include: Boron tribromide, Boron trichloride, Boron trifluoride, and tris (pentafluorophenyl) borane. Representative aluminum-based compounds inclu- de: Aluminum chloride and Aluminum bromide. Representative gallium-based com- pounds include: Gallium chloride, Gallium bromide, and Gallium (ill) actylacetonate.

Representative rare earth catalysts are generally salts of Scandium, Yttrium, Lantha- num, Praseodymium, Neodymium, Erbium, Thulium, Ytterbium, Neodymium or Luteti- um. Examples include : Ytterbium triflate, Ytterbium (lil) actylacetonate, Erbium (ill) trifluorosulfonate (erbium triflate), Erbium (ill) actylacetonate, Holmium triflate, Terbium triflate, Europium triflate, Europium (Iil) trifluroacetate, Samarium triflate, Neodymium triflate, Neodymium (lil) actylacetonate, Praseodymium triflate, Lanthanum triflate, and Dysprosium triflate. Representative zinc-based compounds include Zinc chloride and Zinc bromide. Representative titanium compounds include Titanium (lV) bromide and Titanium (IV) chloride.

As discussed above the preformed stabilizer of the present invention is formed by re- acting ethylenically unsaturated monomers with a macromer in the presence of a car- rier polyol, a free radical initiator, and optionally a reaction moderator.

Representative ethylenically unsaturated monomers which may be employed in prepar- ing the preformed stabilizer or graft polyols of the present invention include: butadiene, isoprene, 1,4-pentadiene, 1,6-hexadiene, 1,7-octadiene, styrene, alpha-methylstyrene, 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, 2, 4-dimethylstyrene, ethylstyrene, isopropylstyrene, butylstyrene, phenylstyrene, cyclohexylstyrene, benzylstyrene, and the like ; substituted styrenes such as cyanostyrene, nitrostyrene, N, N- dimethylaminostyrene, acetoxystyrene, methyl 4-vinylbenzoate, phenoxystyrene, p- vinylphenyl oxide, and the like ; the acrylic and substituted acrylic monomers such as acrylonitrile, acrylic acid, methacrylic acid, methylacryl acrylate, 2-hydroxyethyl acry- late, methyl methacrylate, cyclohexyl methacrylate, benzyl methacrylate, isopropyl me- thacrylate, octyl methacrylate, methacrylonitrile, ethyl alpha-ethoxyacrylate, methyl alpha-acetaminoacrylate, butyl acrylate, 2-ethylhexyl acrylate, phenyl acrylate, phenyl methacrylate, N, N-dimethylacrylamide, N, N-dibenzylacrylamide, N-butylacrylamide, methacryloyl formamide, and the like ; the vinyl esters, vinyl ethers, vinyl ketones, etc., such as vinyl acetate, vinyl butyrate, isopropenyl acetate, vinyl formate, vinyl acrylate, vinyl methacrylate, vinylmethoxyacetate, vinyl benzoate, vinyl toluene, vinyinaphtha- lene, vinyl methyl ether, vinyl propyl ethers, vinyl butyl ethers, vinyl 2-ethylhexyl ether, vinylphenyl ether, vinyl 2-methoxyethyl ether, methoxybutadiene, vinyl 2-butoxyethyl ether, 3, 4-dihydro-1, 2-pyran, 2-butoxy-2'-vinyloxy diethyl ether, vinyl methyl ketone, vinylethyl ketone, vinyl phosphonates such as vinyl phenyl ketone, vinyl ethyl sulfone, N-methyl-N-vinyl acetamide, N-vinylpyrrolidone, vinyl imidazole, divinyl sulfoxide, divi- nyl sulfone, sodium vinylsulfonate, methyl vinylsulfonate, N-vinyl pyrrole and the like ; dimethyl fumarate, dimethyl maleat, maleic acid, crotonic acid, fumaric acid, itaconic acid, monomethyl itaconate, t-butylaminoethyl methacrylate, dimethylaminoethyl me- thacrylate, glycidyl acrylate, allyl alcohol, glycol monoesters of itaconic acid, vinyl pyri- dine, and the like.

Any of the known polymerizable ethylenically unsaturated monomers can be used and the compounds listed above are illustrative and not restrictive of the monomers suitable for use in this invention. In a preferred embodiment of the present invention, the mo- nomer comprises acrylonitrile, styrene, or a mixture thereof. Preferably the mixture comprises from 20 to 80% acrylonitrile with the remainder comprising styrene.

The amount of ethylenically unsaturated monomers employed in the graft polymeriza- tion reaction for the preformed stabilizer is generally from 3 to 15% by weight, based on the total weight of the product; preferably from 5 to 10 percent by weight monomers.

The amount of ethylenically unsaturated monomers employed in the graft polymeriza-

tion reactions for a final graft polyol is generally from 25 to 70% by weight, based on the total weight of the product; preferably from 40 to 55 percent by weight monomers.

Free radical polymerization initiators that may be used include the well-known free radical polymerization initiators such as the peroxides, persulfates, perborates, percar- bonates, azo compounds, etc. These include hydrogen peroxide, dibenzoyl peroxide, acetyl peroxide, benzoyl hydroperoxide, t-butyl hydroperoxide, di-t-butyl peroxide, lauroyl peroxide, butyryl peroxide, diisopropylbenzene hydroperoxide, cumene hydrop- eroxide, paramenthane hydroperoxide, diacetyl peroxide, di-alpha-cumyl peroxide, dipropyl peroxide, diisopropyl peroxide, isopropyl-t-butyl peroxide, butyl-t-butyl perox- ide, difuroyl peroxide, bis (triphenylmethyl) peroxide, bis (p-methoxybenzoyl) peroxide, p-monomethoxybenzoyl peroxide, rubene peroxide, ascaridol, t-butyl peroxybenzoate, diethyl peroxyterephthalate, propyl hydroperoxide, isopropyl hydroperoxide, n-butyl hydroperoxide, t-butyl hydroperoxide, cyclohexyl hydroperoxide, trans-decalin hydrop- eroxide, alpha-methylbenzyl hydroperoxide, alpha-methyl-alpha-ethyl benzyl hydroper- oxide, tetralin hydroperoxide, triphenylmethyl hydroperoxide, diphenylmethyl hydroper- oxide, alpha, alpha'-azobis- (2-methylheptonitrile), 1,1'-azobis (cyclohexane carbonitrile), 4, 4' azobis- (4-cyanopentanoic acid), 2,2'-azobis (isobutyronitrile), 1-t-butylazo-1- cyanocyclohexane, persuccinic acid, diisopropyl peroxydicarbonate, 4,4'-azobis (2,4- dimethylvaleronitrile), 2-t-butylazo-2-cyano-4-methoxy-4-methylpentane, 2,2'-azobis-2- methylbutanenitrile, 2-t-butylazo-2-cyanobutane, 1-t-amylazo-1-cyanocyclohexane, 2,2'-azobis (2, 4-dimethyl-4-methoxyvaleronitrile), 2, 2'-azobis-2-methylbutyronitrile, 2-t- butylazo-2-cyano-4-methylpentane, 2-t-buylazo-2-isobutyronitrile, 2-butylperoxy- isopropyl carbonate, 1, 1-tertiary-amylperoxy cyclohexane, tertiary-amylperoxy-2- ethylhexanoate, and the like ; a mixture of initiators may also be used. In a preferred embodiment of the present invention a mixture of 1, 1-tertiary-amylperoxy cyclohexane and tertiary-amylperoxy-2-ethylhexanoate is used as the initiator.

Generally the graft polymerization reaction for formation of the preformed stabilizer will employ from about 0.1 weight percent to about 10 weight percent of a free radical po- lymerization initiator based on the total weight of the monomers utilized. The graft po- lymerization reaction for formation of the final graft polyol will generally employ from about 0.1 to about 3 weight percent and more preferably from about 0.3 to 1 weight percent of a free radical polymerization initiator based on the total weight of the mono- mers utilized.

The presence of a reaction moderator during formation of the preformed stabilizer and the graft polyol is optional, but useful. The reaction moderator is preferably an alcohol, mercaptan, a haloalkane, or mixtures thereof. Among the reaction moderators which may be employed are the following : acetic acid, bromoacetic acid, chloroacetic acid, ethyl dibromoacetate, iodoacetic acid, tribromoacetic acid, ethyl tribromoacetate, tri- chloroacetic acid, ethyl trichloroacetate, acetone, p-bromophenylacetonitrile, p-

nitrophenylacetylene, allyl alcohol, 2,4, 6-trinitroaniline, p-ethynylanisole, 2,4, 6- trinitroanisole, azobenzene, benzaldehyde, p-cyanobenzaldehyde, 2-butylbenzene, bromobenzene, 1,3, 5-trinitrobenzene, benzochrysene, ethyl trinitrobenzoate, benzoin, benzonitrile, benzopyrene, tributylborane, 1, 4-butanediol, 3, 4-epoxy-2-methyl-1-butene, t-butyl ether, t-butyl isocyanate, 1-phenylbutyne, p-cresol, p-bromocumene, dibenzo- naphthacene, p-dioxane, pentaphenyl ethane, ethanol, 1, 1-diphenylethylene, ethylene glycol, ethyl ether, fluorene, N, N-dimethylformamide, 2-heptene, 2-hexene, isobutylral- dehyde, diethyl bromomalonate, bromotrichloromethane, dibromoethane, diiodometha- ne, naphthalene, 1-naphthol, 2-napthol, methyl oleate, 2,4, 4-triphenyl-1-pentene, 4- methyl-2-pentene, 2, 6-diisopropyl phenol, phenyl ether, phenylphosphine, diethyl- phosphine, dibutylphosphine, phosphorus trichloride, 1,1, 1-tribromopropane, dialkyl phthalate, 1, 2-propanediol, 3-phosphinopropionitrile, 1-propanol, pyrocatechol, pyrogal- lol, 1,4-benzoquinone, methyl stearate, tetraethylsilane, triethylsilane, dibromostilbene, alpha-bromostyrene, alpha-methylstyrene, tetraphenyl succinonitrile, 2,4, 6- trinitrotoluene, p-toluidine, N, N-dimethyl-p-toluidine, alpha-cyano-p-tolunitrile, al- pha, alpha'-dibromo-p-xylene, 2, 6-xylenol, diethyl zinc, dithiodiacetic acid, ethyl dithio- diacetic acid, 4, 4'-dithio-bisanthranilic acid, benzenethiol, o-ethoxybenzenethiol, 2,2'- dithiodiacetic acid, 4, 4'-dithio-bisanthranilic acid, benzenethiol, o-ethoxybenzenethiol, 2, 2'-dithiobisbenzothiazole, benzyl sulfide, 1-dodecanethiol, ethanethiol, 1-hexanethiol, 1-napthalenethiol, 2-naphthalenethiol, 1-octanethiol, 1-heptanethiol, 2-octanethiol, 1- tetradecanethiol, benzyl thiol, isopropanol, 2-butanol, carbon tetrabromide, bromotrich- loromethane, tertiary-dodecylmercaptan, and any combination of the above com- pounds. Preferred reaction moderators are 2-propanol, 2-butanol, and mixtures there- of. The amount of reaction moderator that is employed preferably ranges from 0.5 to 25 weight percent, based on the total weight of the monomers.

The carrier polyol used to form either the preformed stabilizer or the final graft polyol according to the present invention may comprise any conventional polyol described above. The carrier polyol used in the formation of the preformed stabilizer and the final graft polyol need not be the same; however, they can be the same. The carrier polyol may comprise initiator plus propylene oxide with an ethylene oxide cap of from 0 to 30 percent by weight. Alternatively, the carrier polyol can comprise an initiator plus a he- teric mixture of alkylen oxides with or without an ethylene oxide or propylene oxide cap. The characteristics of the desired carrier polyol are in part determined by the de- sired properties of the foam to be prepared using the graft polyol. The amount of car- rier polyol in the formula ranges from 50 to 90 percent by weight, with about 60 to 75 percent by weight more preferred and approximately 68 weight percent most preferred.

The amount of carrier polyol used in the reaction for formation of the preformed stabili- zer based on the total amount of carrier polyol used in the whole process generally ranges from 1 to 10% by weight.

In general, the preformed stabilizer is made in a reactor under an inert atmosphere by a semi-batch process. A free radical polymerization of ethylenically unsaturated monomers in the presence of the macromer, a free radical initiator, a carrier polyol, and optionally a reaction modifier is carried out. The reaction is run at a temperature of from 90 to 140 °C, with a preferred temperature of 110 to 130 °C. To form the preformed stabilizer some of the carrier polyol, some or none of the reaction modifier, and all of the macromer are charged to the reactor, agitated and heated to 110 to 130 °C. The amount of macromer used based on the total weight of macromer and carrier polyol in this reactor ranges from 24 to 28% by weight. The unsaturated monomers and any remaining reaction modifier are charged to a monomer feed tank while the remainder of the carrier polyol and the free radical initiator are charged to a polyol feed tank. Streams from the monomer feed tank and the polyol feed tank are pumped together through an in-line static mixer and charged into the hot mixture in the reactor. Once the reaction is complete, the preformed stabilizer can be stored in the unstripped state for use in the formation of a final graft polyol. Prefe- rably, the preformed stabilizer is stripped prior to use in formation of a final graft polyol.

Preferably, the final-calculated solids content in the preformed stabilizer is from about 5 to 20% by weight; more preferred between 10 and 15 % by weight, most preferred is about 14% by weight.

Generally, formation of the final graft polyol is the same as described for the preformed stabilizer above. However, the amount of monomers used is higher to achieve the desi- red solids content for a final graft polyol. The final calculated solids content in final graft polyols is generally from about 25 to 70% by weight; more preferred between 30 and 60 % by weight, most preferred is from about 40 to 55% by weight. Optionally, the preformed stabilizer described above may be used in formation of the final graft polyol, in which case the preformed stabilizer generally replaces the macromer used as a reactant in the pro- cess described above. The benefits of using a preformed stabilizer is well known in the art, for example, as described in U. S. Patent 5,223, 570, the disclosure of which is incor- porated herein by reference.

As discussed above, one observation that has been made is that during the formation of the preformed stabilizer a certain amount of transesterification product is formed.

This product is an adduct of the unsaturated organic compound used to form the mac- romer and the carrier polyol. This adduct can interfere with the filterability of the final graft polyol, alter its viscosity, increase fouling of the reactor, and alter the chemical properties of the final graft polyol. Thus preventing the transesterification is very bene- ficial. The present inventors have unexpectedly found a straight-forward method for preventing this transesterification reaction.

Not wishing to be bound by theory, it is believed that the Lewis acid catalyst used to form the macromer, which is added when the macromer is used in the reaction for for- mation of the preformed stabilizer, catalyzes the transesterification. It has been surpri-

singly found that use of phosphorous compounds based on the amount of Lewis acid can prevent the transesterification reaction. Suitable phosphorous compounds include compounds containing phosphorus-oxygen bonds, by way of non-limiting example : phosphoric acid, phosphorous acid, compounds containing the phosphate and/or phosphite anion, and mixtures of all of these compounds. In the present specification and claims all of these compounds are intended to be encompassed by the term phosphorous compounds. It is preferable that the amount of phosphorous compound be used in a weight to weight ratio of from 1: 1 to 10: 1 relative to the weight of the Lewis acid catalyst used in the reaction for formation of the macromer. Thus, the preferred amounts range from 0.2 to 500 ppm, more preferably from 0.5 to 250 ppm, and most preferably from 1 to 150 ppm of phosphorous compound. The phosphorous compound can be added either to the macromer before it is used in the reaction for the formation of the preformed stabilizer or as an initial charge to the reactor for formation of the pre- formed stabilizer.

EXAMPLES A macromer is formed as follows. The conventional polyol used is a sucrose and water co-initiated polyol having a theoretical number average molecular weight of approxima- tely 6,800 Daltons. The conventional polyol has an intrinsic unsaturation of approxima- tely 0.09-0. 15 meq/g. The conventional polyol contains approximately 93 wt. % propy- lene oxide and initiators based on the total weight of the polyol and approximately a 7 wt. % ethylene oxide cap based on the total weight. The hydroxyl number of the conventional polyol is approximately 25. The conventional polyol has a theoretical average functionality of approximately 4.51 to 4.97 based on Gel Permeation Chromatography analysis. The macromer is formed by first charging to a reactor the conventional polyol and 50 ppm dibutyltin dilaurate (T-12) catalyst at room temperature. The mixture is heated to 80 °C and the TMI is added dropwise to the mixture over 0.5 hours. The mixture was allowed to react another hour after completion of the addition. The macromer is subsequently bottled for storage.

Approximately 0.36 to 0.4 moles of TMI are added to each mole of polyol in the final macromer. Essentially all of the unsaturation is retained in the resulting macromer.

A carrier polyol for use in the preformed stabilizer reaction is a glycerin-initiated con- ventional polyol comprising a heteric portion formed from propylene oxide and ethylene oxide at a molar ratio of 4.2 : 1. The carrier polyol also has a propylene oxide cap of 10 wt. % based on the total weight of the polyol and a hydroxyl number of 51.

In one experiment two mixtures were prepared. A first mixture included : macromer, carrier polyol and phosphoric acid present in a weight to weight ration of 1: 1 based on the weight of the T-12. A second mixture included the macromer and the carrier polyol only. Both mixtures were heated to 130 °C and held there for a period of time. This

temperature is the stripping temperature usually used to strip the unreacted compo- nents from the preformed stabilizer reaction. Then Gel Permeation Chromatography (GPC) was performed on each sample and the overlayed results are shown in Figure 1. In Figure 1, chromatogram 40 represents the second mixture while chromatogram 42 represents the first mixture, which contained the phosphoric acid. Shoulder 44 in Figure 1 represents the position of the transesterification product of the TMI and the carrier polyol. The results demonstrate that in the absence of phosphoric acid, chromatogram 40, there is significant formation of this product. In the presence of the phosphoric acid there is none.

In another experiment a preformed stabilizer was prepared as follows. A portion of the carrier polyol, no reaction modifier, and all of the macromer are charged to a reactor, agitated and heated to 110 °C. The amount of macromer used based on the total weight of macromer and carrier polyol in this reaction ranges from 24 to 28% by weight.

The ethylenically unsaturated monomers, acrylonitrile and stryrene at a weight to weight ratio of 1: 20, are charged to a monomer feed tank while the remainder of the carrier polyol and the free radical initiator, t-amyl peroxy-2-ethyl hexanoate (TRIGO- NOX 121), are charged to a polyol feed tank. The streams from the monomer feed tank and the polyol feed tank are pumped together through an in-line static mixer and charged into the hot mixture in the reactor. The reaction temperature is 126 °C and the total feed time is 70 minutes. Once the reaction is complete, the preformed stabilizer is stripped at 130 °C. Preferably, the final calculated solids content in the preformed sta- bilizer is from about 5 to 20%. In a first reaction the macromer, described above, did not contain any phosphoric acid. In a second reaction the macromer did contain phosphoric acid at a weight to weight ratio of 1: 1 based on the weight of the T-12.

Each preformed stabilizer was then subjected to GPC and the overlayed results are shown in Figure 2.

In Figure 2, chromatogram 50 represents a preformed stabilizer formed without phosphoric acid and chromatogram 52 represents a preformed stabilizer prepared with phosphoric acid. Peak 54 represents the transesterification product of the TMI and the carrier polyol. The results demonstrate that the presence of the phosphoric acid signi- ficantly reduces the formation of the transesterification product.

In another experiment a preformed stabilizer was prepared with phosphoric acid at a 1: 1 weight ratio based on the T-12 or a preformed stabilizer was prepared without phosphoric acid as described above. In Figure 3 the results of the experiment are shown. Chromatogram 70 represents a preformed stabilizer formed using no phospho- ric acid. Chromatogram 72 represents a preformed stabilizer in the presence of a 1: 1 weight ratio of phosphoric acid to T-12 from the macromer. Peak 74 represents the transesterification product of TMI and the carrier polyol. The results show that the pre- formed stabilizer made in the presence of the phosphoric acid has a dramatically redu-

ced level of transesterification products. In addition, a graft polyol made with the pre- formed stabilizer having phosphoric acid had a low viscosity and could readily be filte- red through a 25 micron filter, however, a graft polyol prepared with the preformed sta- bilizer not having phosphoric acid had a higher viscosity and could not be filtered through a 25 micron filter.

In another experiment a series of preformed stabilizers were made as described above using other lower molecular weight carrier polyols in the absence of phosphoric acid to demonstrate that the transesterification products can also form with these carrier poly- ols in the preformed stabilizer. The results are shown in Figures 4 to 7. In Figure 4 the carrier polyol used is a glycerine-initiated polyol containing only propylene oxide. The polyol had a hydroxyl number of 112 and a number average molecular weight of 1434 Daltons. Peak 82 is the transesterification product of TMI and the carrier polyol. In Figure 5 the carrier polyol used is a propylene glycol and water co-initiated polyol con- taining only propylene oxide. The polyol had a hydroxyl number of 56 and a number average molecular weight of 1942 Daltons. Peak 92 is the transesterification product of TMI and the carrier polyol. In Figure 6 the carrier polyol used is a glycerine-initiated polyol containing only propylene oxide. The polyol had a hydroxyl number of 64 and a number average molecular weight of 2495 Daltons. Peak 100 is the transesterification product of TMI and the carrier polyol. In Figure 7 the carrier polyol used is a glycerine- initiated polyol formed as a propylene oxide ethylene oxide heteric containing approxi- mately 13% ethylene oxide. The polyol also has a propylene oxide cap of 10%. The polyol had a hydroxyl number of 64 and a number average molecular weight of 2937 Daltons. Peak 102 is the transesterification product of TMI and the carrier polyol.

The inventors have also found that use of the preformed stabilizer prepared according to the present invention in formation of graft polyols dramatically reduces the reactor fouling that usually accompanies graft polyol reactions, in fact it has been found that the reactor can be run at least 17% longer than before resulting in enhanced productivi- ty.

The present invention finds utilization at a number of different points in the usual proc- ess for formation of graft polyols. The present invention specifically prevents transeste- rification reactions that can occur when a macromer is combined with the carrier polyol in the presence of heating. The phosphoric acid can be added to the macromer after formation of the macromer and during storage of the macromer. The phosphoric acid can be added to a reactor during the formation reaction for forming of a preformed sta- bilizer as described above. In addition, the phosphoric acid can be added to a graft polyol formation reaction either in the presence or the absence of a preformed stabil- zer.

The foregoing invention has been described in accordance with the relevant legal stan- dards, thus the description is exemplary rather than limiting in nature. Variations and modifications to the disclosed embodiment may become apparent to those skilled in the art and do come within the scope of the invention. Accordingly, the scope of legal protection afforded this invention can only be determined by studying the following claims.