Low viscosity polymer polyols with improved dispersion stability

The present invention provides polymer polyols and a method for preparing polymer polyols which have (1) exceptional dispersion stability, especially at high styrene contents, and (2) substantially smaller particle sizes than polymer polyols having equivalent viscosity. In a preferred embodiment of the present invention, a first reaction product is obtained by feeding the following materials to a first continuous reactor in the presence of a free radical initiator or catalyst: (a) less than about 50 wt % of a total monomer proportion or monomer mixture, preferably comprising styrene/acrylonitrile at a ratio preferably greater than about 50/50 wt %; (b) at least about 50 wt % of a total base polyol proportion; (c) a majority of a precursor stabilizer; and, (d) a polymer control agent (PCA). The product from this first reaction then is again fed through a continuous reactor, which may be the same as the first reactor, along with additional initiator, at least about 50% of the total monomer proportion, and, optionally, any balance of the total base polyol proportion, precursor stabilizer, and PCA. The product from this second reactor is a high stability, low viscosity polymer polyol.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to polymer polyols, to methods of making 
polymer polyols, and to polyurethanes made from such polymer polyols. 
2. Background 
Polymer polyols commonly are used to produce polyurethane foams. Basically, 
polymer polyols are produced by polymerizing one or more ethylenically 
unsaturated monomers dissolved or dispersed in a polyol in the presence of 
a free radical catalyst to form a stable dispersion of polymer particles 
in the polyol. Polymer polyols are valuable because they can produce 
polyurethane foam which has high load-bearing properties. 
The first commercially accepted polymer polyols primarily were produced 
using acrylonitrile monomer, and had a somewhat higher viscosity than 
desired for some applications. More recently, polymer polyols of lower 
viscosity have been produced using acrylonitrile-styrene monomer mixtures. 
Polyurethane foams made from polymer polyols have a wide variety of uses. 
The two major types of polyurethane foam generally are slabstock and 
molded foam. Slabstock foam made using polymer polyols typically is used 
in the carpet, furniture, and bedding industries. The primary type of 
molded foam, generally termed high resiliency (HR) molded foam, is used 
widely in the automotive industry for applications ranging from molded 
seats to energy-absorbing padding and the like. 
The wide demand for polyurethane foams has spawned a need for polymer 
polyols that can produce foams having a wide variety of characteristics. 
For example, a demand exists for slabstock foam that is virtually 
scorch-free. It also is desirable for these scorch-free foams to have low 
density (viz.--1.5 pounds per cubic foot or less) while maintaining 
satisfactory load-bearing and other foam properties. One way to produce 
such a foam is to use a monomer mixture having a high styrene content 
(e.g., about 65 to 70 percent styrene). 
The preparation of polymer polyols using a monomer mixture with a high 
styrene content creates difficulties. For example, the commercial 
processability of a particular polymer polyol depends upon its stability 
against phase separation, or its stability against the polymer particles 
settling out of the polyol medium. Many applications require rigorous 
stability, which becomes more difficult to achieve when high styrene 
content monomer mixtures are employed. It has been found that a higher 
stability polymer polyol may be obtained if the components used to make 
the polymer polyol are not fed to the reactor all at once. For example, 
U.S. Pat. No. 4,148,840 to Shah attempts to improve the stability of a 
polymer polyol by adding only a minor portion of a preformed polymer 
polyol to the base polyol along with the monomers and initiators. Another 
approach is seen in U.S. Pat. No. 4,242,249 to Van Cleve, et al., which is 
directed to the polymerization of an unsaturated macromonomer with other 
monomers to form a non-aqueous dispersion stabilizer which may be used in 
small amounts, 5% or less, to stabilize a polymer dispersion. 
Other polyurethane foams that are in demand are foams that have high 
load-bearing capacities. A high load bearing capacity is particularly 
desirable in the slabstock area. The load-bearing capacity of a foam may 
be increased by increasing the polymer or solids content of the polymer 
polyol; however, as the solids content of the polymer polyol increases, 
the stability of the polymer polyol tends to decrease. 
The trend toward the use of polymer polyols having a high styrene monomer 
mixture and a high solids content has resulted in polymer polyols that 
sometimes have a higher viscosity than desired. The viscosity of a polymer 
polyol must be low enough for ease in handling during manufacture and 
transport. At the same time, the stability of the polymer polyol must be 
high enough for use in the sophisticated, high-speed, large-volume 
equipment, machines, and systems now used to handle, mix, and react 
polyurethane-forming ingredients. Most importantly, the particles in the 
polymer polyol must be small enough to avoid plugging the filters, pumps, 
etc., used in such equipment. 
Two basic types of processes have been used to produce polymer 
polyols-continuous processes and semi-batch processes. In a continuous 
process, the monomers, polyols, and initiator(s) typically are fed 
continously to a back mixed, stirred reactor in a manner that minimizes 
the monomer to polyol ratio. A continuous process tends to minimize 
settling of the vinyl polymer, and can produce a wide range of polymer 
polyols with acceptable dispersion stability. 
In a semi-batch process, the vinyl monomers are fed slowly to a partially 
charged, agitated reactor to avoid excess free monomer concentration at 
any time during the polymerization. A semi-batch process is more difficult 
to control than a continuous process, which can achieve a steady state 
after line-out. 
An example of a semi-batch process is found in European Patent No. 0 365 
986, in which a semi-batch process is used to form graft copolymer 
dispersions. In order to form the graft copolymer dispersion, a graft 
polyol having 30% or less solids content is formed in a continuous 
process. The graft polyol product then is used as seed in the semi-batch 
process to produce graft polyols having 30% or more solids content and 
having a broad particle size distribution. 
Even with the advanced state of the art in polymer polyol technology, there 
is a need for further improvement of polymer polyols to enhance their 
dispersion stability, to minimize their viscosity at higher solids levels, 
and to minimize the particle size of the polymers in the polyol. 
SUMMARY OF THE INVENTION 
The present invention provides polymer polyols and a method for preparing 
polymer polyols which have (1) exceptional dispersion stability, 
especially at high styrene contents, and (2) substantially smaller 
particle sizes than polymer polyols having equivalent viscosity. In a 
preferred embodiment of the present invention, a first reaction product is 
obtained by feeding the following materials to a first reactor-preferably 
a continuous, stirred, back-mixed reactor-in the presence of a free 
radical initiator or catalyst: (a) less than about 50 wt % of a total 
monomer proportion or monomer mixture, preferably comprising 
styrene/acrylonitrile at a ratio preferably greater than about 50/50 wt %; 
(b) at least about 50 wt % of a total base polyol proportion; (c) a 
majority of a precursor stabilizer; and, (d) a polymer control agent 
(PCA). The product from this first reaction then is fed through at least 
one more reactor (also preferably a continuous, stirred, back mixed 
reactor, which may be the same or a different reactor than was used in the 
first reaction), along with additional initiator, the remainder of the 
total monomer proportion, and, optionally, any balance of the base polyol 
proportion, precursor stabilizer, and PCA. 
DETAILED DESCRIPTION OF THE INVENTION 
In a preferred embodiment of the present invention, a minority of the total 
monomer proportion, preferably less than 50 wt %, and more preferably 
about 33 wt % or less, is fed to a "first" continuous reactor along with 
the requisite amount of free radical initiator or catalyst. At least about 
5 wt % of the total monomer proportion should be added to the first 
reactor. Along with the monomer is fed a majority of the polyol, the 
precursor stabilizer, and the polymer control agent. 
One or more reactors may be used in the present invention, the first two of 
which, either separately or in series, preferably should be a continuous, 
stirred, back-mixed reactor. The foregoing components are pumped into the 
first reactor continuously through an in-line mixer to assure complete 
mixing of the components before they enter the reactor. The internal 
temperature of the reactor preferably is controlled within a range of 
about 100.degree. C.-140.degree. C., more preferably about 
110.degree.-130.degree. C. The contents of the reactor are well mixed with 
a residence time of at least 5 minutes, preferably greater than 10 
minutes. The product of the first reactor is collected as it flows 
continuously out the top of the reactor through a back pressure regulator, 
which preferably has been adjusted to give some positive back-pressure in 
the reactor. 
The product of this "first" reactor then is fed to a "second" reactor. The 
balance of the monomer, the free radical initiator or catalyst, the 
precursor stabilizer, the polymer control agent, and the polyol are fed to 
the second reactor along with the product from the first reactor. This 
"second" reactor may be a separate reactor, or it may simulate a second 
reactor, i.e., by feeding the product from the first reactor back to the 
first reactor. Either way, this second feed is treated using substantially 
the same conditions already described with respect to the first reactor. 
In the following examples, a portion of the product from this "second" 
reactor was stripped of residual monomer by vacuum stripping at about 2 
millimeters absolute pressure and 120 to 130 degrees Centigrade for 
testing. 
The percent by weight of polymer in the resulting polymer polyol may be 
determined from an analysis of the amount of unreacted monomers in the 
crude product before stripping. The product of the "second" reactor either 
may be used as is, or it may be fed to a "third" reactor to increase 
residence time, thereby increasing conversion of the reactants to polymer. 
A preferred monomer for use in the present invention is a mixture of 
acrylonitrile/styrene (hereinafter sometimes called A/S) at a ratio 
preferably less than about 50/50 wt %. Other commonly used ethylenically 
unsaturated monomers may be used, alone or together with styrene and/or 
acrylonitrile. For example, suitable monomers include, but are not limited 
to, butadiene; isoprene; 1,4-pentadiene; 1,6-hexadiene, 1,7-octadiene; 
acrylonitrile; methacrylonitrile; .alpha.-methyl styrene; methylstyrene; 
2,4-dimethylstyrene; ethyl styrene; isopropylstyrene; butylstyrene; 
substituted styrenes such as cyanostyrene; phenylstyrene; 
cyclohexylstyrene; benzylstyrene; nitrostyrene; N,N-dimethylaminostyrene; 
acetoxystyrene; methyl 4-vinylbenzoate; phenoxystyrene; .rho.-vinyl 
diphenyl sulfide; .rho.-vinylphenyl phenyl oxide; acrylic and substituted 
acrylic monomers such as acrylic acid; methacrylic acid; methyl acrylate; 
2-hydroxyethyl acrylate; 2-hydroxyethyl methacrylate; methyl methacrylate; 
cyclohexyl methacrylate; benzyl methacrylate; isopropyl methacrylate; 
octyl methacrylate; ethyl .alpha.-ethoxyacrylate; methyl 
.alpha.-acetoaminoacrylate; butyl acrylate; 2-ethylhexyl acrylate; phenyl 
acrylate; phenyl methacrylate; N,N-dimethylacrylate; 
N,N-dibenzylacrylamide; N-butylacrylamide; methacrylyl formamide; vinyl 
esters; vinyl ethers; vinyl ketones; vinyl acetate; vinyl alcohol; vinyl 
butyrate; isopropenylacetate; vinyl formate; vinyl acrylate; vinyl 
methacrylate; vinyl methoxy acetate; vinyl benzoate; vinyl toluene; vinyl 
naphthalene; vinyl methyl ether; vinyl ethyl ether; vinyl propyl ether; 
vinyl butyl ether; vinyl 2-ethylhexyl ether; vinyl phenyl ether; vinyl 
2-methoxyethyl ether; methoxybutadiene; vinyl 2-butoxyethyl ether; 
3,4-dihydro-1,2-pyran; 2-butoxy-2'-vinyl diethyl ether; vinyl 
2-ethylmercaptoethyl ether; vinyl methyl ketone; vinyl ether ketone; vinyl 
phenyl ketone; vinyl ethyl sulfide; vinyl ethyl sulfone; N-methyl-N-vinyl 
acetamide; N-vinylpyrrolidone; vinyl imidazole; divinyl sulfide; divinyl 
sulfoxide; divinyl sulfone; sodium vinyl sulfonate; methyl vinyl 
sulfonate; N-vinyl pyrrole; dimethyl fumarate; dimethyl maleate; maleic 
acid; crotonic acid; fumaric acid; itaconic acid; monomethyl itaconate; 
t-butylaminoethyl methacrylate; glycidyl acrylate; allyl alcohol; glycol 
monoesters of itaconic acid; vinyl pyridine; maleic anhydride; maleimide; 
N-substituted maleimides; such as N-phenylmaleimide and the like. 
A preferred initiator for use in the invention is 
2,2'azobis(iso-butyronitrile) ("AIBN"). However, any catalyst commonly 
employed for addition polymerization may be used, e.g., the free radical 
type of vinyl polymerization catalysts, such as the peroxides, 
persulfates, percarbonates, azo compounds, and the like. Other specific 
examples besides AIBN include, but are not limited to, dibenzoyl peroxide; 
lauroyl peroxide; di-t-butyl peroxide; diisopropyl peroxy carbonate; 
t-butyl peroxy-.omega.-ethylhexanoate; t-butylperpivalate; 
2,5-dimethyl-hexane-2,5-di-per-2-ethyl hexoate; t-butylperneodecanoate; 
t-butylperbenzoate; t-butyl percrotonate; t-butyl perisobutyrate; 
di-t-butyl perphthalate; 2,2'-azo-bis(2-methylbutanenitrile) for example. 
Other suitable catalysts may be employed, of course. The wt % of the free 
radical initiator or catalyst in the feed to both the first and second 
reactors may range between about 0.1 to 5.0 wt %, preferably between about 
0.3-0.8 wt %. A chain transfer agent such as dodecylmercaptan also may be 
added. 
The polyol used in the present invention may be a polyoxyalkylene polyether 
polyol having a molecular weight of from about 500 to 15,000, preferably 
from about 2000 to 10,000. Such polyols typically are made by the reaction 
of an initiator or starting material having a plurality of reactive 
hydrogens thereon with one or more alkylene oxides. Ethylene oxide, 
propylene oxide, butylene oxide and mixtures of these may be used. Often, 
a mixture of ethylene oxide and propylene oxide is preferred. The 
resulting polyols can range from having predominantly primary to 
predominantly secondary hydroxyl groups. In one embodiment, at least 50 wt 
% of the total base polyol proportion is added to the first reactor, the 
balance being added to the second reactor. Preferably at least 75 wt % of 
the polyol is added to the first reactor, and most preferably, all of it 
(100 wt %) is added to the first reactor. 
Suitable starting materials or initiators for the polyol include, but are 
not limited to, di, tri- or tetra-hydric initiators, such as glycerin, 
alkanolamines, alkylamines, aryl or aromatic amines, sucrose, sorbitol, 
trimethylol propane (TMP) .alpha.-methylglucoside, .beta.-methylglucoside 
or other methylglucoside, resins of phenol, aniline and mixed phenol 
aniline, such as methylenedianiline or bisphenol A, Mannich condensates 
and mixtures thereof, for example. The polyol may be made by alkoxylating 
the initiator with a desired number of moles of an alkylene oxide. 
Preferably, the alkylene oxide has two to four carbon atoms, and is thus 
ethylene oxide, propylene oxide, butylene oxide or mixtures of these 
oxides. The oxides may be mixed upon addition, or may be added to the 
polyol initiator chain separately to form blocks or caps. The alkoxylation 
generally is catalyzed; KOH is a commonly used catalyst, although others 
may be employed. For example, double metal cyanide catalysts may be 
employed, in particular zinc hexacyanocobaltate, and the polyols may be 
prepared in accordance with the methods described in U.S. Pat. Nos. 
3,029,505; 3,900,518; 3,941,049; and 4,355,100, incorporated herein by 
reference. 
A preferred polyol for use in the invention is a product made by reacting 
propylene oxide, then ethylene oxide, or ethylene oxide and propylene 
oxide, then additional propylene oxide, successively, with glycerine in 
the presence of potassium hydroxide catalyst, and refining the product of 
said reaction to remove the catalyst. The resulting polyol (Polyol I) 
contains 10% ethylene oxide and has a hydroxyl number of about 52. Another 
preferred polyol is obtained by reacting propylene oxide and ethylene 
oxide, successively, with a polyhydric initiator such as glycerine in the 
presence of potassium hydroxide or another suitable catalyst and refining 
the product to remove the catalyst. The resulting polyol (Polyol II) 
contains 16.5 weight percent ethylene oxide and has a hydroxyl number of 
35.5. 
Precursor stabilizers may be used, if desired, in the preparation of the 
polymer polyols of this invention to assist in imparting desired stability 
to the resulting polymer polyols. Suitable precursor stabilizers are, in 
general, prepared by the reaction of the selected reactive unsaturated 
compound with the selected polyol. 
The terminology "reactive unsaturated compound," refers to any compound 
capable of forming an adduct with a polyol, either directly or indirectly, 
and having carbon-to-carbon double bonds which are adequately reactive 
with the particular monomer system being utilized. More specifically, 
compounds containing alpha, beta unsaturation are preferred. Suitable 
compounds satisfying this criteria include the maleates, fumarates, 
acrylates, and methacrylates. While not alpha, beta unsaturated compounds, 
polyol adducts formed from substituted vinyl benzenes such as 
chloromethylstyrene likewise may be utilized. Illustrative examples of 
suitable alpha, beta unsaturated compounds which may be employed to form 
the precursor stabilizer include maleic anhydride, fumaric acid, dialkyl 
fumarates, dialkyl maleates, glycol maleates, glycol fumarates, 
isocyanatoethyl methacrylate, 1,1-dimethyl-m-isopropenylbenzyl-isocyanate, 
methyl methacrylate, hydroxyethyl methacrylate, acrylic and methacrylic 
acid and their anhydride, methacroyl chloride and glycidyl methacrylate. 
With respect to the polyol reactant, any of the polyol types used for the 
base polyol may be employed. It is preferred to utilize polyoxyalkylene 
polyols. The molecular weight of the polyol should be relatively high, 
preferably above about 4000 (number average) and, more preferably, at 
least about 4500. However, polyols having molecular weights of no less 
than about 3000 may be utilized if desired. 
The level of ethylenic unsaturation in the precursor stabilizer may vary 
widely. The minimum and maximum levels of unsaturation both are 
constricted by the dispersion stability that the precursor stabilizer is 
capable of imparting to the polymer polyol composition. On the one hand, 
the minimum level of unsaturation is the level sufficient to permit the 
precursor stabilizer to assist in the dispersion stability of the polymer 
polyol. Typically, the lower limit of unsaturation is about 0.03 or so 
millequivalents per gram of precursor. 
On the other hand, the maximum level is constricted by crosslinking of the 
precursor stabilizer which may occur. More particularly, when higher 
levels of unsaturation are attempted to be added in preparing the 
precursor stabilizer, there is a greater probability that species will be 
formed having more than one double bond per molecule. An undue population 
of such specie may cause crosslinking and thus may adversely affect the 
ability of the stabilizer to provide the requisite dispersion stability 
enhancement, and also may substantially increase the viscosity. 
Accordingly, the maximum level of unsaturation added should be below that 
at which significant crosslinking occurs, that is, on the average no more 
than about one carbon-to-carbon double bond per molecule of precursor 
stabilizer should occur. 
The specific level of unsaturation utilized further will depend on the 
molecular weight of the polyol used to prepare the precursor stabilizer 
and on the viscosity of the precursor stabilizer itself. Thus, from less 
than about 0.02 milliequivalents per gram of precursor up to about 0.15, 
or perhaps up to about 0.20 or more may be used. More particularly, 
unsaturation levels of at least about 0.04 or 0.05, up to about 0.10 or so 
are particularly suitable. 
It is preferred to prepare the precursor stabilizer in such a fashion that 
the unsaturation is retained to the extent possible. The use of such 
precursor stabilizers particularly are useful in improving polymer polyol 
stability. 
Loss of unsaturation may occur in precursor stabilizer preparation with any 
of the alpha, beta unsaturated compounds. For example, it has been 
recognized that when maleic anhydride is employed, anywhere from about 25 
percent to essentially all of the unsaturation may be lost. Loss of 
unsaturation generally appears to be accompanied by an increase in 
viscosity of the precursor stabilizer. Accordingly, it is desirable to 
utilize an efficient process in the preparation of the precursor such that 
at least half of the added unsaturation is retained. 
Preferably, the unsaturation is of the fumarate type. Thus, it is preferred 
to utilize a compound having fumarate-type unsaturation or an unsaturated 
compound which, under the reaction conditions used in forming the adduct, 
the polyol will form a high proportion of fumarate-type unsaturation. 
Likewise, under appropriate conditions, maleate-type unsaturation can be 
isomerized to fumarate, as is known. 
The formation of the precursor stabilizer using maleic anhydride may be 
carried out at elevated temperatures using appropriate catalysts. It has 
been found satisfactory to maintain the ratio of the maleic anhydride to 
polyol in the range of from about 0.5 to perhaps about 1.5 moles of maleic 
anhydride per mole of polyol, more preferably 0.75 to about 1.00 mole per 
mole of polyol. 
The precursor stabilizer preferably is prepared in the presence of a 
catalytic amount of a strong base. Suitable bases include inorganic bases 
such as alkali and alkaline earth metal hydroxides and the weak acid salts 
of alkali and alkaline earth metals, and organic bases such as quaternary 
ammonium hydroxides, 4-dimethylaminopyridine, 4-pyrrolidinopyridine, and 
imidazole. Potassium hydroxide has been found to be useful. The amount of 
catalyst is not critical; and may, for example, be as low as about 6 
p.p.m. or even less when potassium hydroxide is used. 
Suitable reaction temperatures may vary from about 100.degree. to 
125.degree. C. or so up to about 180.degree. C., or even higher. 
Desirably, the reaction should be carried out in a reactor capable of 
agitation and subsequent pressurization. It is necessary to introduce an 
alkylene oxide, preferably ethylene or propylene oxide, either with the 
other reactants or subsequently, which is reacted with the adduct until 
the acid number is below at least about 3.0, preferably below about 1.0. 
The product then may be cooled and stripped to remove excess alkylene 
oxide and then is ready for use in preparing polymer polyols. 
When maleic anhydride is employed, precursor stabilizers having adequate 
viscosities can be prepared by utilizing catalytic amounts (e.g., 20 parts 
per million or so) of a strong base such as potassium hydroxide. This will 
likewise allow retention of about 50 percent of the unsaturation, with up 
to about 70 percent or so of the unsaturation being of the fumarate type 
under appropriate reaction times and conditions. Viscosities of about 3000 
cks. (25.degree. C.) or so typically are provided. 
The maximum viscosity of useful precursor stabilizers typically will be 
dictated by practical considerations. More specifically, the viscosity of 
the precursor stabilizer should not be so high that it cannot be 
conveniently handled. Viscosities up to perhaps 10,000 to 15,000 cks or so 
should be capable of being satisfactorily handled. Moreover, by blending 
with base polyol in the reactor used to form the precursor stabilizer, 
even substantially higher viscosities (e.g., up to 25,000 to 30,000 cks. 
or higher) should be suitable. 
Precursor stabilizers employing polyoxypropylene oxide addition products 
with starters having functionalities equal to or in excess of 3 are 
preferred, although starters having lower functionalities are acceptable. 
A variety of tetrols and higher functionality starters are well known and 
may be used. Mixtures likewise may be employed. It is particularly 
preferred to use sorbitol as a starter. Such precursor stabilizers further 
are characterized by an hydroxyl number of about 28, unsaturation of the 
fumarate type and a level of unsaturation of about 0.06 or even 0.05 or 
so, to 0.1 milliequivalents unsaturation or so per gram of polyol. The 
precursor stabilizer accordingly may be made by reacting the 
sorbitol-initiated polyol with maleic anhydride in the presence of 
potassium hydroxide catalyst. This may be accomplished by using a 
temperature of about 125.degree. C. to preserve a high proportion of the 
charged (i.e.--added) unsaturation. The maleate unsaturation then may be 
isomerized to fumarate using morpholine as is well known. Alternatively, 
higher temperatures (e.g. --175.degree. to 180.degree. C. or so) may be 
utilized to achieve relatively high levels of fumarate-type unsaturation 
directly. The techniques involved are well known and may be used as 
desired. 
The use of the preferred precursor stabilizers offers several advantages. 
The use of high functionality starters, such as, for example, sorbitol, 
provide highly effective, yet relatively low viscosity, precursor 
stabilizers, which, in turn, allows the polymer polyol viscosity to be 
minimized. Similarly, stability of precursor stabilizers can be 
problematical, sometimes resulting in marked viscosity increases upon 
usage. This well may be due to reaction of precursor stabilizer molecules 
with each other. The utilization of propylene oxide-capped precursor 
stabilizers substantially minimizes this problem. 
A stabilizer, as previously described, may be added to the base polyol in 
an amount sufficient to provide the desired stability assistance for the 
resulting polymer polyol. Generally, it will be suitable to incorporate a 
stabilizer in amounts up to perhaps about 20 percent or so, based upon the 
weight of the polyol. Levels from about 3 to 5 percent to about 17 percent 
by weight or so generally should be satisfactory for slabstock 
applications, while levels of about 12 percent by weight or less should be 
suitable for polymer polyols used in high resiliency molded foam 
applications. If desired, a mixture of stabilizers can, of course, be 
used. 
Preferred precursor stabilizers for use in the invention are an adduct of 
an unsaturated compound with a polyol, the product of which contains 
unsaturation that readily copolymerizes with either styrene and/or 
acrylonitrile. A preferred precursor stabilizer for use in the present 
invention ("Stabilizer A") is made by reacting a 34 hydroxyl number, 15 
weight percent ethylene oxide capped polyoxypropylene triol with maleic 
anhydride and subsequently with ethylene oxide. The resulting precursor 
stabilizer has a hydroxyl number of 32, an unsaturation of 0.1 meq/gm, 
with the unsaturation being 30/70 maleate/fumarate, the retained 
unsaturation being 50 percent of the unsaturation added with the maleic 
anhydride. 
For a given polymer polyol system, adjustment of the process variables to 
provide the desired polymer crosslinking coefficient and intrinsic 
viscosity can result in polymer polyol compositions having higher than the 
indigenous viscosity for the particular system, viz.--the minimum product 
viscosity for a given polymer polyol composition made under the particular 
reaction conditions. This may occur, for example, where the level of the 
polymer control agent having at least moderate chain transfer activity 
(e.g.--isopropanol) is minimized in order to achieve the desired polymer 
intrinsic viscosity. The desired product viscosity of such polymer polyol 
compositions thus can be significantly higher than the indigenous 
viscosity for the system. 
It has been discovered that product viscosities of essentially the 
indigenous system viscosity can be provided by either of two general 
methods. For example, suitable treatment can result in reduction in a 
product viscosity from about 5,000 centipoise to about 4,000 centipoise or 
so, the latter considered to be the indigenous system viscosity. This 
reduction in product viscosity is accompanied by an observed change in the 
somewhat rough surfaces of the polymer particles to a predominance 
(i.e.,--at least a majority) of particles appearing to have relatively 
smooth exteriors. 
Thus, according to another aspect of the present invention, the 
polymerization of the monomers in the polyol is carried out in the 
presence of a polymer control agent having at most minimal chain transfer 
activity. Exemplary polymer control agents of this type include water, 
methanol, cyclohexane and benzene. 
This preparative technique allows the polymer polyol to be prepared with 
what is considered to be its indigenous system viscosity. Yet, the polymer 
portion by use of this technique possesses a desirably low crosslinking 
coefficient and an acceptably high intrinsic viscosity. This is in sharp 
contrast to what occurs when the polymer control agent employed has 
moderate or high chain transfer activity. Under these latter 
circumstances, it generally is quite difficult to satisfy all three 
objectives. The reason for this surprising behavior when minimal chain 
transfer activity materials are used as the polymer control agent simply 
is not understood. Regardless, this technique is considered to be highly 
useful, providing a facile method for readily providing optimum 
characteristics for the polymer and for the polymer polyol product 
viscosity. 
In accordance with a further aspect of this invention, the polymer polyol 
composition prepared with higher than its indigenous system viscosity may 
be subjected to a post treatment to increase the polymer particle fluidity 
sufficiently to concomitantly cause the desired reduction in product 
viscosity to essentially its indigenous system viscosity. This post 
treatment can be carried out by using a heat treatment, by using a 
solvating agent for the polymer particles, or by using a combination of 
the two. 
The reduction in product viscosity resulting from the heat treatment is 
believed to be the result of lowering the melt viscosity of the polymer in 
the dispersed polymer particles to such an extent that the surface force 
(surface tension) associated with a particle is sufficient to cause the 
molten polymer in the particle to flow into the shape of lowest energy--a 
smooth sphere. Likewise, the use of a solvating agent, alone or in 
conjunction with a higher temperature, is believed to reduce the melt 
viscosity of the polymer in the particles by a plasticization mechanism, 
thereby enabling the polymer in the particle to flow towards a smooth 
spherical shape. 
The general concept is to increase the fluidity of the polymer within the 
particles to obtain at least a predominance of smooth particles with a 
concurrent reduction in product viscosity. Any technique capable of 
increasing the fluidity of the polymer particles may be used in addition 
to the techniques discussed herein. 
Obviously, it will be more desirable to carry out these viscosity reduction 
techniques in such a fashion that essentially the indigenous system 
viscosity is provided, due to the relative ease with which such techniques 
can be effected and the advantages derived from lower product viscosity 
polymer polyols. Likewise, it is within the scope of the present invention 
to carry out such techniques so that the product viscosity is reduced only 
to a point between the starting product viscosity and the indigenous 
system viscosity. 
Use of a polymer control agent having significant chain transfer activity 
often tends to decrease the stability of the polymer polyol composition, 
apparently because of the competition during polymerization between the 
chain transfer agent and the grafting reaction between the growing polymer 
chain and the base polyol. Accordingly, it may be desirable to include in 
the polymerization reaction, a precursor stabilizer. The utilization of a 
precursor stabilizer seems to minimize the adverse effects caused by the 
use of this type of polymer control agent. The amount of the precursor 
stabilizer employed may be varied within wide limits. Functionally, the 
level used should be sufficient to adequately minimize adverse effects 
caused by using relatively high chain transfer activity polymer control 
agents. Typically, this may be achieved by using up to about 10 weight 
percent or so of the precursor stabilizer, based on the weight of the base 
polyol. 
Preferred polymer control agents (PCA's) preferably are low molecular 
weight compounds that result in polymer polyols with crosslinking 
coefficients of less than 55. A preferred PCA used in the following 
examples is isopropanol ("ISOP"). Other suitable PCA's include, but are 
not limited to, water, methanol, cyclohexane, benzene, toluene, etc. 
Polymer polyols produced according the present invention have inherently 
enhanced stability. Therefore, less precursor stabilizer is required, and 
the final viscosity of the polymer polyol is reduced. 
The following procedures were used to analyze the polymer polyols made in 
the following examples: 
CENTRIFUGABLE SOLIDS 
After stripping unreacted monomer, the polymer polyol composition was 
centrifuged for about 24 hours at about 3000 revolutions per minute and 
1470 radial centrifugal "g" force. The centrifuge tube then was inverted 
and allowed to drain for four hours. The nonflowing cake remaining at the 
bottom of the tube was reported as weight percentage of the initial weight 
of the composition tested. 
CROSSLINKING COEFFICIENT (XLC) 
This test determines the light transmission through a dispersion (or 
solution) of polymer polyol in dimethylformamide (DMF) in which one 
percent of the polymer is present. The dispersion (or solution) was 
transferred to one of two matched 1 cm transmission cells while the second 
matched cell was filled with DMF. A Bausch & Lomb Spectronic 710 
spectrophotometer was used to measure the light transmission of the sample 
at 500 millimicrons after setting a reference cell containing only DMF to 
100% transmission. This measurement was referred to as LT for light 
transmission. 
The crosslinking coefficient (XLC) was calculated using the following 
formula: 
EQU XLC=100-LT 
MEAN TICLE SIZE 
The mean particle size was determined by a light scattering technique using 
a Leeds & Northrup MICROTRAC 7991-3 sub-MICRON Particle Size Analyzer with 
isopropanol as the diluent. The values were obtained at a material index 
of 016. This setting was used to compensate for the difference between the 
refractive index of the particles and the diluent using this Analyzer. 
PREATION OF POLYURETHANE FOAMS 
Polyurethanes may be made by reacting the polymer polyols described above 
with an organic polyisocyanate in the presence of a polyurethane formation 
catalyst. If a foam is desired, a blowing agent such as a halocarbon 
(trichlorofluoromethane, for example), water, or carbon dioxide, etc., 
also may be present. The polyurethane formation catalysts typically are 
tin catalysts or tertiary amine compounds. Other conventional additives 
such as silicone surfactants, fire retardant additives (melamine, for 
example), etc. also may be present. For more information related to 
parameters for use in preparing polyurethanes, particularly flexible 
polyurethanes, see U.S. Pat. No. 4,338,408; 4,342,687 and 4,381,353, 
incorporated herein by reference. Another preferred catalyst is a solution 
consisting of 70 wt % bis(2-dimethylaminoethyl) ether and 30 weight 
percent dipropylene glycol ("Catalyst A-1"). 
A typical free-rise slab polyurethane foam is prepared by first charging 
polymer polyol, water, catalyst and silicone surfactant into a vessel 
while stirring vigorously. Next, the polyisocyanate is added to the vessel 
with stirring, and the resulting mixture is immediately poured into a 
cardboard cakebox. Then, the polyurethane foam is allowed to rise and cure 
at room temperature. In the following examples, free rise foams were 
prepared from the Control polymer polyol and several of the polymer 
polyols identified in the Examples using the proportion of components 
shown in Table A. 
TABLE A 
______________________________________ 
FREE RISE FOAM FORMULATION 
Components Parts 
______________________________________ 
Polymer polyol 100 
Water 2.3 
Catalyst A-1 0.05 
Stannous Octoate (tin catalyst) 
0.09-0.12 
Silicone Surfactant A* 
0.9 
80/20 2,4/2,6 Tolylene 
Diisocyanate 
(110 index) 
______________________________________ 
* "Silicone Surfactant A" may be obtained from Union Carbide as a product 
called "L5750."- 
The polymer polyol, water, amine catalyst, and silicone surfactant were 
charged to a one/half gallon paper container equipped with a baffle 
assembly and mixed at 2400 rpm for 60 seconds with a 2.4-inch diameter, 
4-blade turbine stirrer placed one inch above the bottom of the container. 
The mixture was allowed to set for 15 seconds to degas. Tin catalyst was 
added after degassing and mixing was re-initiated for ten seconds at 2400 
rpm. Tolylene Diisocyanate (TDI) was added, and mixing was continued for 
five seconds. The mixture then was poured into a 14 in.times.14 
in..times.6 in. cardboard cake box. The foam mixture was allowed to rise 
freely until the reaction was complete. The foam then was placed in a 
convection oven preheated to 250 degrees F. for five minutes.

EXAMPLES 
The following examples more clearly illustrate the advantages of the 
present invention. The results of these examples are shown in Table 1. 
CONTROL 
The Control polymer polyol used for comparison in the following examples 
was prepared in a single continuous, stirred, back-mixed reactor using the 
components shown in Table 1 and the same procedures as described above for 
the "first" reactor. The control polymer polyol was collected from the 
first reactor, stripped, as described above, and the percent by weight 
polymer in the polymer polyol was determined by analyzing the amount of 
unreacted monomers in the crude product before stripping. 
EXAMPLES 1-3 
In examples 1-3, the components shown in Table 1 were fed to two stirred, 
back-mixed reactors in series (simulated). The resulting product had 
improved dispersion stability (low values of Centrifugable Solids), small 
Particle Size, and low viscosity at high levels of % Polymer. Note that, 
with regard to free rise foam properties, the 25% IFD's of the Example 
foams are high when compared with the Control polymer polyol considering 
the % Polymer. This is most evident when Example 3 is compared to the 
Control. The viscosity of the product in Example 3 is less than 4,000 cks 
at 42.4% Polymer, while the control has a viscosity of 6900 cks. at 43.2% 
Polymer. When the product of Example 3 was foamed at 40.7% Polymer and 
compared to the control, foamed at 43.2% Polymer, the Example 3 product 
had a 25% IFD within the experimental error of the Control. 
TABLE 1 
__________________________________________________________________________ 
Example No. Con- 
1 1 2 2 3 3 4 4 5 5 
Reactor trol 
1st. 
2nd. 
1st. 
2nd. 
1st. 
2nd. 1st. 
2nd. 
1st. 
2nd. 
__________________________________________________________________________ 
Reaction Temp. C. 
125 125 125 125 125 125 125 125 125 125 125 
Wt. % Catalyst in Feed 
0.6 0.4 0.6 0.4 0.6 0.3 0.3 0.6 0.6 0.8 0.6 
Polymer Control Agent 
ISOP 
ISOP 
ISOP 
ISOP 
ISOP 
ISOP 
ISOP ISOP 
-- ISOP 
ISOP 
Wt. % PCA in Feed 
2 1.7 1 1.7 1 3 3 2.0 -- 3 3.9 
Wt. % Monomers in Feed 
44.3 
11.3 
33.3 
11.3 
33 15 33 15.0 
15.0 
12 39 
Monomer Type A/S A/S A/S A/S A/S A/S A/S A/S A/S A/S A/S 
Ratio of Monomers 
30/70 
30/70 
30/70 
30/70 
30/70 
30/70 
30/70 30/70 
30/70 
30/70 
30/70 
Polyol Type I I -- I -- I -- II -- I I 
Wt. % Polyol and Stabilizer 
-- 100 -- 100 -- 100 -- 100 -- 53 47 
Wt. % Stabilizer in Polyol Mix 
10 4.4 7.2 4.4 -- 4.0 -- 10.0 
-- 10.7 
-- 
Total Stabilizer, % 
-- 11.6 4.4 -- 4.0 -- 10.0 
-- 6 
Residence Time, minutes 
12 12 12 12 12 12 12 12 12 12 12 
Wt. % Polymer 43.4 38.4 36.3 42.4 28.8 43.7 
Viscosity, cks 6901 4847 3160 3987 4068 5991 
XLC 2.5 1.6 3 -- 3.8 
Centrifugable Solids, Wt. % 
4.9 3.4 3.2 2.4 2.3 6.9 
Mean Particle Size, 
1.49 1.06 1.05 1.11 62 1.42 
microns 
Foam Evaluation 
140 115 110 132 139 
25% IFD, pol (40.7 wt. % (41 wt. % 
Polymer) Polymer) 
__________________________________________________________________________ 
EXAMPLE 4 
Example 4, the parameters and results of which are also shown in Table 1, 
illustrates the invention using a higher molecular weight polyol. In this 
case, the resulting Particle Size is very low, 0.6 microns, as a result of 
the novel process combined with known effects derived from high molecular 
weight polyols. 
EXAMPLE 5 
In Example 5, shown in Table 1, 50 parts of Polyol I, 6 parts of Stabilizer 
A, 2 parts of isopropanol, and 0.56 parts of AIBN were fed continuously to 
the stirred, back mixed reactor, along with 8 parts of a 30/70 mixture of 
acrylonitrile and styrene. The residence time was 12 minutes and the 
reaction temperature was 125.degree. C. The product from the "first" 
reactor was collected and not stripped of residual monomer. 66.56 parts of 
this product, along with 44 parts of Polyol I, 7.7 parts of isopropanol, 
1.2 parts of AIBN, and 76.3 parts of a 30/70 mixture of acrylonitrile and 
styrene, were fed continuously to the "second" reactor and treated using 
the same residence time and temperature as in the first reactor. The 
product of this second reactor was collected and stripped of residual 
monomer, as described above. The final product contained 43.7% polymer, 
had a viscosity of 5991 cks, centrifugable solids of 6.9%, and a mean 
particle size of 1.42. When foamed at 41% polymer, using the formulation 
of Table A, the 25% IFD of the resultant foam was 139 psi. 
A slightly majority of the polyol, 53%, was fed to the first reactor and 
the balance to the second reactor in this Example. Comparing the product 
data and foam data with the control and Examples 1 through 3, this Example 
illustrates that the advantages of this novel process, particularly low 
viscosity, are achieved even when the amount of polyol fed to the first 
reactor is near its lower limit of 50%. 
One of skill in the art will recognize that many modifications may be made 
to the present invention without departing from the spirit and scope of 
the present invention. The embodiment described herein is means to be 
illustrative only and should not be taken as limiting the invention, which 
is defined in the following claims.