CA1136331A - Process for making and/or modifying polyurethanes - Google Patents
Process for making and/or modifying polyurethanesInfo
- Publication number
- CA1136331A CA1136331A CA000328005A CA328005A CA1136331A CA 1136331 A CA1136331 A CA 1136331A CA 000328005 A CA000328005 A CA 000328005A CA 328005 A CA328005 A CA 328005A CA 1136331 A CA1136331 A CA 1136331A
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- CA
- Canada
- Prior art keywords
- polyurethane
- amine
- aminolysis
- molecular weight
- solid state
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Abstract
ABSTRACT OF THE DISCLOSURE
Polyurethane resins of higher than desired molecular weight with or without gel fractions which comprise insoluble material due to crosslinking or excessive degree of polymer-ization are treated in the solid state with a liquid or gaseous pri-mary or secondary amina under thermal conditions which cause aminolysis of both linear linkages and crosslinkages. By this procedure, the average molecular weights of the products can be reduced to acceptable levels. Also, if the product contains gel fractions, these too can be reduced to negligible levels.
The procedure is applicable to both polyether and polyester urethanes and is effective to provide improved polymer character-istics for thermoplastic processing and solution applications.
Polyurethane resins of higher than desired molecular weight with or without gel fractions which comprise insoluble material due to crosslinking or excessive degree of polymer-ization are treated in the solid state with a liquid or gaseous pri-mary or secondary amina under thermal conditions which cause aminolysis of both linear linkages and crosslinkages. By this procedure, the average molecular weights of the products can be reduced to acceptable levels. Also, if the product contains gel fractions, these too can be reduced to negligible levels.
The procedure is applicable to both polyether and polyester urethanes and is effective to provide improved polymer character-istics for thermoplastic processing and solution applications.
Description
KE~ j c.i~
~363~
BACiCGROU~D OF TIJE l:NVE,N'rl:ON
_ _ _ _ _ . _ FIEI.D OF :[NVEI:IT:LON
__ The lnvention rela-Zes to a process for ir~atincJ poly-urethanes, especially -thermoplastically processable polyuretllar.les, to rèduce the molecular wei~ht thereoE. ~lore particularly, the invention is directed to processes for treating such polyure~anes as contain gel fractions, which comprise insoluble matter due to crosslinking, or excessive degree of poly~erizatlon, al~pical poly-mermization,or like mechanisms, in order to el~inate or subs~antiall~ r~uce these gel fractions and/or to lower the molecular weight of thc polymer.
Thermoplastically processable polyurethanes have been produced commercially fox more than 20 yeaxs. The majority o~
products which are of industrial importance at the presert are prepared by reaction of 4,~'-diphenylmethane diisocyanate with (1) an aliphatic polyesterdiol such as hydro~yl~terminated poly(1,4-butylene adipate) or an aliphatic polyetherdiol such as hydroxyl-terminated poly(oxytetramethylene) and (2) a diol . chain.extender such as 1,4-butanediol or 1,4~bis(2-hydroxl-ethoxy)benzene. Some of the commercially available poly,mers are predominantly hydroxyl-terminated, while others are pre-pared with a slight stoichiometric excess of isocyanate ~nd a-e predominantly isocyanate-terminated. I~e latter polymers undergo ~ur~G~r reaction upon elevated temperature post curiny or aglng in ~he . presence of atmospheric moisture, and ~ay become crosslinked.
All of these polymers commonly are processed into shaped articles by means of thermoplastic processing technlZ~ues such as injection molding, extrusion, calendering,and blo~J mo].ding~
Many of the polymers, particularly those predominantly hydroxyl-X~trLI~l~lC,-~-2 ~3~33~
terminated, are soluble in d:ipolar aprot:ic solvents 5uch as tetrclhydrofuraI1, dimethy:lformamide, cyc]ohexanone arld dioxane, and as solutions in these and other solve~nts,find a variety of applications as coatings and adhesives.
For applications in solution, it is hlghly desirable if not essential that under given conditions of temperature, concentration of polymer and choice o~ solvent, the vi~cosi~y be within certain limits. Moreover, ~hen -thin filrns or coatings are to be prepared from the solutions, it is important that the polymer be entirely soluble, i.e., free of particles of cross1inked polymer commonly called "gel"O It is difficult tG produce consistently thermoplastic polyurethanes which are free of gel. Furthermore, it is equally difficult to achieve precise molecular weight control, and therefore solution viscosity control, in commercial manufacture of the thermoplastics. In addition, even nominally OH-terminated thermoplastic polyurethanes generally contain a residu11m of NCO ~roups sufficient to cause marked increases in molecular weight within normal periods of storage required in co~excial applications prior to final usage of the thermoplastic. Of those products which have viscosity specificatiors, in many cases the dilute solution viscosity may vary as much as by a factor of two, and even with this generous allowance for vari-ation of the molecular weight, a considerable amount of material is produced which is out-of-specificatiorl.
In many coatings artd adhesives applications, it would be desirable to reproduce solution viscosity of a given type of polyurethane thermoplastic to within T 20 percent, or even less, of a p,edetermined level without changing ~he temperature, polymer concentration, or composition of the K~ l;RtCP-2 ~L13~;33~
solvent. Up to the present -time, this has no~ been genera]ly possible. Fur-therMore, many lots of material offeriny the desired viscosity characteristics are rejected due to gel content. Even for thermoplastic processing application~; it is important to control molecula~ weight so as to provide sul-~le and uniform processing characteristics. ~lso, whe~e -thin artlcles are produced, as in blow molding, it is high:ly desirable to utilize polyrners of low gel content. Nevertheless, it is typical to find a noticeable and objectionable amount of gel particles, for example, in blow-molded polyurethane film -manufactured from in-specification lots of polymer.
Also, the storage stability of many polyurethane thermo-plastics, both as solids and in solution, has been a problem.
If free isocyanate is present in the polymer, it is inherently unstable and tends to increase in molecular weight. This is particularly troublesome when the polymer is exposed to moisture. ~hen the polymer is to undergo thermoplastic processing, such aging leads to less favorable processing characteristics and physical properties in the articles produced. In the case of solution applications, the viscosity usually increases, the content of gel may increase, and/or the polymer may become less soluble.
OBJECTS OF T~E INVENTION
It is an object of the invention to pro~ide an improved process ~or modifying polyurethane polymers. It is a further o~ject of the invention to provide a process for reducing the molecular weight of polyurethane polymers. It is a fuxther object of the invention to pro~ide a process for eliminatir.g ;
or reducing the amount of gel fxactions in polyurethane polymers. It is a further object of the invention to provide , - KEMER~C~-~
~L363;3~1L
a process for the recovery of ofE-grade polyurethane polyrners.
It is a further object of the invention to provide a process for upgrading polyurethane polymers. A s-till further object of the invention is to provide a process which obviates diffi-culties heretoEore encountered in the prior art and which has advantages as will be more particularly pointed out as the description proceeds.
BRIEF DESCRIPTION OF THE INV~NTION
.. .. . .. . ... .. _ _ The invention relates -to a process for -treating,in the solid state,polyurethane polymers/ especially thermoplastically processable polyurethane polymers,of higher-than-desired molecular weight with a primary or secondary amine under conditions which cause aminolysis of both linear linkages and crosslinkages characteristic o the polyurethane being treated. Still more particularly, the invention relates to such a process which simultaneously effects reduction of gel fractions in the poly-` urethane polymer, which gel fractions comprise insoluble material due to crosslinking, excessive degree of polymeri7ation, atypical polymeriæation, or like mechanisms.
While the invention is particularly applicable to thermo-plastically processable polyurethanes, which term is to be understood to include those polyurethanes intended for solvent appli-cations as well as for thermoforming, it is to be understood that it is broadly applicable to polyurethanes, including thermosetting types, where it is desired to effect a reduction of the molecular weight either of the basic polymer per se,or of high m~lecular weigh-t and/or insoluble in-clusions due to crosslinking, excess degree of poly~eriza-tion, atypical polymerization, and like mechanisms which may occur during m~nufacture and/or storage of the polyurethanes. The invention, for e~le, can be applied to rigid or micro-cellular foamed polyurethanes, especially where ., Kr~M~RICA-~
~L~3633~
it is desired to alter the surEace characterist;cs o~ such foams. With open cell -type foams, the process can also be utilized to modify the general charac-ter of the foamed s-tructure.
In carrying out the processes o~ the invention, -the poly-urethane polymer, in the solid state, is exposed to the prir~
or secondary a~ine under conditions ef~ectiveto cause diffusion of the amine throughout -t h e polymer, and then, simultane-ously therewith, or, subsequently thereto, the amine-treated polymer is heated in the solid state for a time and at a ternpera-ture effective to cause the desired degree of aminolysis.
In both the diffusion and aminolysis portions of the pro-cess of the invention, substantial advantac~es are realized through treatment of the polymer in its solid state as opposed to treatment concomitant with dissolution of the polymer. In the presence of solvent, the amine is dis-tributed among the solid and liquid phases and, as a result of the dilution Eactor, longer times and/or larger quantities of amine and/or higher temperatures during the aminolysis process may be required.
Even when amine is first applied to the solid polymer and the diffusion process allowed to proceed to a satisfac-tory state of completion, upon addition of solvent to the amine-containing solid polyurethane, prior to aminolysis, some of the absorbed amine will diffuse back out of the polymer and into the liquid phase so as to reduce the amount of amine actually in contact with the polymer. Although a satisfactory result may be obtained through proper control of time/temperature variables during aminolysis together with use of relatively greater quantites of amine in many cases, there will generally be some disadvantage, such as greater overall process time requirements, if aminolysis is carried out concomitant with dissolution as opposed to being -6- followed by page 6-A
KE~ERICA-2 ~g~3;33~
carried out in the absence of solvent.
Moreover, iE the intended app:Lication o~ -the treated polyurethane is thermo~orming oE ~he solid polymer as opposed to a solution application, it is a great disadvantage, if not entirely impractical, to have to recover the solid polymer from solution. In contrast, the process o-E the invention for solid state modification of polyurethanes generally involves only addition of the amine to the particulate solid polymer in a suitable closed container; al:Lowing su-.E~icient time for diffusion of the amine into and throughou-t the solid, which process may be hastened by moderate agitation or tumbling of the mixture together with heating to a temperature below that at which aminolysis proceeds at a substantial rate; and, ater diffùsion of the amine has occurred, heating for a requisite time and temperature sufficient to bring about aminolysis.
If the amount of amine and the time and temperature conditions have been properly adjusted, the treated polymer will have a reduced average molecular weight of predetermined value, and will be essentially free of any gel inclusions which may have been present. If desired, the amine-treated polymer at the conclusion of the aminolysis heating cycle can be stripped under vacuum to remove any residual amine.
If the amine-treated polymer is to be used in a thermoforming operation, it is highly desirable to employ a brief vacuum str.ipping period following aminolysis so as to remove residual amine. Any residual amine could cause further aminolysis during thermoforming under the relatively high temperatures used in such operations. In addition, if the original polymer, prior to treatment with amine, contained objectionable amounts of gel inclusions with respect to its intended thermoforming KEMERLC~-2 ~L13~33~
application, it ma~ be desirable, prior to thermofo~mincJ, to homogenize the amine-treated, vacuum s~rlp~ed polymer by extrusion and pelletization orregrindincJ. This final processiny step serves to dissolve in the continuous polymer phase any aminolyzed gel inclusions which, without such homo~eni~a-tion, might appear as inhomogenieties in the therm~formed en~products.
Homogenization is, of course, unnecessary if the amine-treated polyurethane is to be employed in dissolved form. In that case, the dissolution process provides complete homogenization.
In the process of ~e invention, the prim~ry or seconda~y c~mine attacks such linkages as ester linkages, ure~e linkages, allophanate linkages, and the like, which may be present in the polyurethane. It is effective in causing scission of these linkages whethe. they are linear linkages or cross-linkages. Through control of the amount of amine and of the time and temperature of the thermal treatment, the process can be tailor-made to achieve either controlled re~uction of molecular weight or controlled reduction of molecular weight coupled with lowering or removing gel fractions contained in the polymer. Generally speakiny, additional time for diffusion of the amine is required for the efficien-t breakdown of the gel fractions because it takes longer for the amine to diffuse into the suspended gel particles. Therefore, a longer time at a lower temperature, i.e., low enough so that substan-tial aminolysis does not take place prior to diffusion of amine throughout the gel, may be required -than for simple reduction of molecular weight of gel-free material. In any case, the tempera-ture should be low enough to prevent degradation of the resin by mechanisms other than scission of the aforementioned groups by -t h e a m i n e, a s s u c h other mechanisms may produce an off-color product or one not having the desired character-K~MERICA-2 ~3~33~
istics of thermoplast:icity, elasticity, and the like.
In carrying out -the process of the invention, the polyure-thane polymer to be treated ls exposed in the solid state to the primary or secondary amine under conditions of time and temperature effective to cause diffusion of the amine into the polymer and the amine-treated polyurethane pol~mer in the solid state there-after is heated to a temperature effective to cause aminolysis for a time sufficient to accomplish the desired reduction in molecular weight. Advantayeously, the solid polyurethane polymer is t r e a t e d w i t h the a m i n e at a temperature below tha-t at which substantial aminolysis takes place for a time suffi-cient to obtain effective diffusion of the amine into the polymer, including any gel fractions contained therein. The polymer may be heated to speed up this difEusion, advantage-ously, up to a temperature not greater than about 60~C to promote diffusion of the amine into the polymer.
The amine-treated solid polymer then is heated in the solid state to a temperature sufficient to effect aminolysis and the temperature is maintained for a time sufficient to obtain the desired reduction in molecular weight and/or gel fractions. Ordinarily, this temperature can range from above about 60C to not more than about 120C. Higher temperatures can be used, however, up to the temperature at which thermal degradation occurs at an objectionable rate. It is possible in some instances for diffusion and aminolysis to take place concomitantly, but generally it is desirable that diffusion be substantially complete before appreciable aminolysis is allowed to occur. The solid polyurethane polymer is exposed to the amine, prefera~ly i n a closed container,and heated therein i n t h e pr e s e n ce of the amine for a time and KEM~i~ICA~~
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and at a temperature sufficient to effec-t the desired diffusion and aminolysis and the temperature maintained at aminolysis temperature for a time sufficient to obtain the desired reduc-tion of molecular weight and/or ~el fractions.
The amount of amine required to effec-t its purpose in the process of the invention is relatively small, and depends upon the particular amine used as well as upon other processing variables such as time and temperature variables. In general, there will be a residuum of unreacted amine in the treated polyurethane unless relative extremes of time and/or ternperature are employed during the aminolysis phase of the process, or unless there is employed a subsequent processing step designed to remove or destroy such residuum of unreacted amine. Effec-tive reduction in molecular weight, together with brea~down of any gel fractions present, ordinarily is obtained with less than 1 weight percent of amine, based on dibutylamine and the weight of the polymer. Higher amoun-ts, up to 5 percent or even more can be used when there is substantial unreacted iso-cyanate present in the polymer and/or extensive crosslinking and/or when the conditions of aminolysis employed do not provide for substantially complete reaction of the amine. Also, it might be necessary to employ such higher amounts of amine if there were incomplete diffusion of amine prior to aminolysis.
In such an instance, however, there would be extensive degrada-tion (through aminolysis) of that portion of the polymer into which the amine had diffused prior to aminolysis, and the physical properties of the overall product, after treatment, generally would be seriously harmed. In any case, the equiva-lent of 5 percent of dibutylamine, if uniformly diffused prior to aminolysis and then completely reacted with the polymer, is _g_ ~
KEiMF.RIC~-2 ~L13~33~l sufflcient to cause molecular weight reduction of rnost ~olymers beyond that consistent with preservation o~ norrnal polym~r physical properties.
In general,it is not often necessary or desirable to exceed the equivalent of about 2 percent dibutylamine. rrhe optimum amount for a given transformation under given processing conditions can be determined directly by experimentation.
For each batch of off-grade polyurethane thermoplastic there is an experimentally determinable relationship between the amount of amine employed and the molecular weight (as conven-iently observed in terms of solution viscosity) of the result-ing treated polymer, other processing variables being held constant. The equivalent of 0.1 to 0.5 percent dibutylamine has been employed with complete success in the recovery of a wide variety of off-grade polyurethane thermoplastics, and even with such small amounts of amine there may be a residuum of unreacted amine in the polymer following successful recovery, unless such residuum is removed or otherwise eliminated. It is generally not necessary or desirable to employ less than the equivalent of about 0.01 percent dibutylamine. Where other amines are used, the proportions can be increased or decreased as necessary to account for higher or lower molecular weight and/or higher or lower aminolysis reactivi-ty under given condi-tions relative to the molecularweight and reactivity of dibutylamune.
In carrying ou-t the process of the invention, any basic primary or secondary amine, advantageously one having a PKb less than about 6, can be employed. ~he term amine as used herein is to be understood as referring to amines of this type. Suitable such secondary amines include dimethylamine, methylethylamine, diethylamine, ethylpropylamine, methylpropylamine, ethyliso-KEMr,RIC'~ 2 3~13~
propylamine, me-thylisopropylamine, dip:ropy].amlne, cliisopropyl-amine, dibutylamine, diisobutylamine, methylbutylamlne, ethyl-butylamine, diamylamine, dihexylamine, dihepty].amine, dioctyl-amine, di-2-ethylhexylamine, piperidine, tetxahydropyrrol, morpholine, N-methylethanolamine, die-thanolamine, 2,6~dime-thyl-morpholine, methylcyclohexylamine, dicyclohexylamine, methyl~
benzylamine, and dibenzylamine. Suitable such primary arnines include methylamine, ethylamine, propylamine, isopropylamine, butylamine, isobutylamine, secbutylamine, amylamine, isoamyl-amine, hexylamine, heptylamine, octylamine, 2-ethylhexylamine, cyclohexylamine, benzylamine, 2-methoxyethylamine, 2-ethoxy-ethylamine, decylamine, dodecylamine, tridecylamine, ethanol-amine, isopropanolamine, and 3-aminopropanol-1.
When the amines are liquid at ambient temperature, they can be absorbed on granules of the polymer and allowed to diffuse into the granules~ Solid amines are encountered only infrequently in the practice of the invention, and generally offer no advantages over the variety of llquid and gaseous amines which are suitable and readily available. If a solid amine is to be used, ît should be heated to above its melting point and absorbed on the polymer granules preheated to the same or higher temperature, provided that neither temperature is sufficiently high as to cause substantial aminolysis of the polymer prior to adequate diffusion of the amine throughout the polymer. Gaseous amines, such as methylamine, e-thylamine and dimethylamine, can be employed in a closed system.
Often in the case of gaseous or solid amines, and sometimes with liquid amines, it is desirable to dissolve the amine in an inert diluent so as to facilitate measurement and handling of the amine and/or to improve uniform absorption and/or dif-K~ LI~IC~-2 ~L~3~33~
fusion of khe amine throughout the soLid polyurethane. Suitable inert diluen-ts include solvents which dlssoLve the part:icular amine in question and which may also tend -to diffuse :in-to the solid polymer, but not cause the polymer partlcles to agylo~rate.
Whether or not a given solvent/diluen-t for the amine is suitable depends in generally upon which polyuxethane is being treated.
Lower aromatic hydrocarbons such as benzene, toluene and the xylenes are generally sui-table, as are lower alcohols such as isopropyl alcohol. Alcohols, of course, tend to diEfuse into the polymer, and may compete with the amine, dependlng upon the relative amount of alcohol employed, for reac-tion with any residual isocyanate groups presen-t in the polyurethane.
The amount of any diluent used may vary from much less than the amount of amine, such as ten percent of the weight of amine, to any larger amount. In general, it is not desirable to use more diluent than can be absorbed by the polymer, as any liquid phase remaining after absorption will contain some of the amine and therefore will reduce the amount of amine absorbed by the polymer and immediately available for aminolysis at the beginning of the aminolysis step~ Furthermore, if the amine-treated polyurethane is to be used in thermoforming, it often will be necessary to remove the diluentanyway by means of vacuum stripping.
Even when the polyurethane is to be dissolved following the amine treatment, an excessive amoun-t of diluent may interfere with the dissolution process and/or have other deleterious effects in the course of the end use of the polyurethane solution.
Where it is an object to reduce the content of gel fractions, adequate diffusion of the amine into the polymer, including the gel fractions thereof, should be effected before applying heat sufficient to cause substantial aminolysis.
KEMI~R:~C~~2 ~3~3~
Otherwise, non-uniEorm and overall ine~ficient ac-tion of the amine will result, and -there will he some v:iscosi-ty reduction accompanied by incomplete breakdown of the gel fractions.
In accordance with one form of the invention, the amine is added to the polymer in thegranulclr form, pre~erably with at least some mechanical blending, and allowed to dif~use into the granules. For this purpose, amines which are non solvents for the polyurethane polymer being treated are of particular advantage. When a non-solvent amine is used, the particles of the polymer do not agglomerate during the solid state treatment. The term "non-solvent amine" as used herein is to be understood to mean an amine which is a suEficiently poor solvent for the polyurethane polymer undergoing treatment that it is absorbed by the particles or granules without causing them to stick together. For -the most part, such non-solvent amines are unsubstituted, higher m~lecular weight primary or secondary aliphatic and cycloaliphatic amines, for example, those having at least 7 carbon atoms, such as methylcyclohexylamine, di-butylamine, diamylamine, diisobutylamine, dihexylamine, di-cyclohexylamine, dioctylamine, di-2-ethylhexylamine, heptyl-amine, octylamine, 2-e-thylhexylamine, benzylamine, decylamine, dodecylamine, and tridecylamine, and advantageously containing not more than twelve carbon atoms.
A wide range of temperature variations may be used in carrying out the process of the invention because it is a time:temperature relation which is essentially important. Thus, during the diffusion of the amine into and throughout the solid polymer, any temperature below the aminolysis temperature, that is to say, the temperature at which substantial aminolysis takes place can be used and the higher the temperature the KEMli.RIC~-2 31 13633~
shorter will be the time necessary to effec-t the diffusion.
The aminolysis -temperature varies accordiny to the reac-tivi-ty of the particular amine. In general, however, aminolysis begins to proceed at a substan-tial ra-te at about 60~C, particu-larly with secondary amines, though with some of the more re-active primary amines, the aminolysis temperature may be some-what lower. The upper tempera-ture limit for the diffusion process generally is lower for pr.imary am.ines than for second-ary amines, as the primary amino g r~up generally is the more reactive in aminolysis. In the aminolysis stage, or molecular weight reduction stage, any temperature above that at which substantial aminolysis takes place, but below that which would cause substantial thermal degradation of the polymer can be used, it being understood that the lower the tet~era-ture, the longer the time that will be required,and vice versa. In genera~ also, the shorter the time, the higher the temperature that can be used without excessi~e thermal degradation. mus, in such case, the amine-treated granules in which the amine has been allowed or caused to difuse throughout the polymer structure can be heated rapidly, preferably with conccmi-tant tut~bling of the granules,to a temperature up to 90C, or higher, without deleter-iously effecting color, strength, and elasticity of many polymers. In general, however, it is not desirable to employ t e m peratures above 120C. Also, if adequate diffusion of the amine through the polymer granules was first obtained, then the product also is essential.ly free of gel fractions and clear,colorless, strong and elastic film can be drawn from the resulting product which, at the same time, has an acceptable mDlecular weight, from a starting polymer having a large amount of gel fractions and/or undesirably high molecular weight.
Alternatively, the amine-treated polymer is slo~ly and gradually heated over a considerable period before it is brought to the temperature K~ML, RI Cl~- 2 ~3~33~
at which arninolysis p.roc~ls at a significan-t rate (md t~n slowly and gradually heated up to a temperature substant:i.ally belol~7 that at which decornposition takes place, so that the mechanisms of dlffuslon and arnln~
olysis are qiven adequate time to be accomplished.
I t will be understood that, as the polyurethane polymer starting materials contemplated by the invention dlffer widely in constitution and gel fraction content, no hard and East rules can be set down as to precise temperatures, times, selection of g amines, and amounts of amines . I t may be said, however, tha t a ... _ . ... _ . .
~15-` KE~E~CA-2 3~3~
gradual increase in temperature or heating ove~r longer periods at low temperatures promo-tes diffusion. Consequently, the mixture of polymer and secondary amine should be heated slowly over a considerable period of time and, at the same time, the maximum temperature should be kep-t relatively low, prefera~ly below about 120C.
The invention is applicable to both the polyester-type polyurethanes and polyether-type polyurethanes,as well as o-ther types of po:Lyurethanes,and conditions yenerally effec-tive for one type are efEective for the other types.
DETAILED DESCRIPTIO~ OF T~IE INVENTION
The invention may be more fully understood by reference tothe following examples which are given by way of illustration only.
Parts and percentages are by weight unless otherwise specified.
EXAMP~E 1 An off-grade lot of intermediate hardness (87 Shore A) polyesterurethane granules (Estane~5701 F1) was obtained from B. F. Goodrich Chemical Company. This material was high in molecular weight and contained a substantial amount of gel.
PART lA
To a 100 g poxtion of Estane 5701 Fl of this example in a one pint can was added 0O5 ml dibutylamine. The can was closed, shaken and set aside at room temperature for 10 days.
Then it was placed in an oven at 73~C for 20 hours. There was no sticking together of the granules upon opening the hot can.
The granules were transferred to a larger can and 300 g cyclo-hexanone was added and the mixture was stirred at high speed with an air-powered mixer. After 90 minutes, dissolution appeared complete, but the viscosity was high. A portion of the solution was diluted with cyclohexan~ne to 19.5 percent NVS.
After standing overnight, the viscosity of the 25 percent C
~ER[(~~2 ~L~3~;~}3~
solution at 25C was 29,760 cps, and that oE -the 19.6 percent solution at 25C was 1,220 cps. A film prepared from -this solution was free of gel particles.
PART lB
A 300 g portion of the Estane 5701 Fl of this example was weighed into a one quart can and 1.5 ml dlbuty]amine was added. The can was closed and rolled for 20 minutes and set aside at room temperature for three clays. Then it was rolled again for 15 minukes and placed in an oven at 180F for 19 hours. It was again rolled for 10 minutes, and 60 g of the granules was transferred to a one quart can. Tetrahydrofuran (340 g) was added -to make 15 percent NVS. The can was closed and put on an electric roller for 90 minutes. The solids had dissolved, and the viscosity of the solution at room tempera-ture was 370 cps.
A 50 pound lot of off-grade polyetherurethane thermo-- ~ ~r~lneSS
plastic of 80 Shore A hardono~ was obtained from B. F. Goodrich Chemical Company. This material, Estané~5714 Fl, was not within normal product specifica-tions due to its high solution viscosity and gel content. The viscosity specification for this product is 600-1,200 cps at 15 percent NVS in tetrahydro-furan at 25C.
A 300 g portion of this lot of Estane 5714 Fl was weighed into a one quart can and 1.5 ml dibutylamine was added. The can was closed and rolled on an electric roller for 30 minutes.
There was no sticking together of the granules before or after rolling and the can was closed and heated in an oven at 85C
for 18 hours. The oven temperature then was increased to 100C
for three hours, and the can was removed and rolled immediately ~ ~ ~ Q ~
:
KEME~IC~~2 ~L~3~i33~
for 15 minutes. There was little i~ any tendency fo~ the granules to stick together whi:Le hot. Forty-five g of the granules then was transferred to a one pint can and 255 g tetrahydrofuran was added (for 15 percent NVS). Thi~ solution was stirred at room temperature to dissolve the granules, and additional tetrahydrofuran was added to compensate ~or evapora~
tion losses. The granules dissolved completely, and -the vis-cosity of the solution a-t 25C was found to be 285 cps.
A 50 pound lot of hard (50 Shore D) thermoplas-tic poly-esterurethane granules (Estane~5707) was obtained from B. F.
Goodrich Chemical Company. This par-ticular lot was rated"off-grade" by the manuacturer due to its high solutlon viscosity in dimethylformamide (3,048 cps at 15 percent non-volatile solids by weight [NVS] at 25~C) and to the signi~icant amount of loosely crosslinked gel which it contained. The standard viscosity specification for this product is 670-1,290 cps at 15 percent NVS in dimethyl~ormamide at 25C.
Two hundred g of the Esta ne 5707 of this example was weighed intoa one pint can and 2.0 ml dibutylamine was added.
The can was closed and shaken intermittently for 20 minutes and then was placed in an oven at 110C for 18 hours. Forty-five g of the granules was then weighed into a one pint can and 225 g dimethylformamide (for 15 percent NVS) was added.
The mixture was stirred at low speed for 30 minutes, during which time the granules dissolved completely and the solution did not rise above room temperature. The viscosity was deter-mined to be 52 cps. This shows that, when desired, a viscosity whlch is far below the manufacturer's specification of 670~1,290 cps can be obtained.
~ l ~QI~
KEM~l~ï CA- 2 ~3~333L
By usiny a smaller amount of dibutylamine arld/or lower oven tempera-ture and/or shorter heatinf~ time, this pol~es-ter-ure-thane, originally of high gel content and 3,04~3 cps -viscosity under the above measurement conditions, can be brou~ht to a viscosity within the manufacturer's specification.
EXAM~?LE 4 A 50-pound lot of r elatively soft (7~ Shore ~) thermo- s plastic polyesterurethane granules (Est ane~5710) was obtained from B. F. Goodrich Chemical Company. This sample was from a 10 lot rated "off-grade" b,v the manufacturer due to its high solution viscosity in tetrahydrofuran (1,900 cps at 15 percent NVS and 25C). The standard viscosity specification for this product is 400-800 cps at 25C and 15 percent NVS in tetrahydro-furan. This sample was rated by the manufacturer as having "no gel present". However, the method of ge:l rating used evidently reflects the degree of gel control which it has been possible to achieve in commercial production up to the present time . The much more sensitive f ilm examina tion procedure described herein reveals that this sample of Est a ne 5710 in 20 fact contains a large amount of small gel particles, which produce dozens of imper Eections per square inch in films pre-pared from solutions of the untreated thermoplastic.
Following the procedure of Example 3, the Estane~571Q of this example was treated wi th dibutylamine in the solid state at elevated temperature. At 15 percent NVS in tetrahydrofuran, in which the product dissolved completely, the viscosity at 25C was 32 cps.
As in Example 3, by using a smaller rela tive amount of dibutylamine, lower oven temperature and/or shorter heating 30 period, this polyesterurethane can be brought to a viscosity K~M~RIC~-2 ~13~3~
with the standard v:iscosity specification of ~0()-800 cps under the above measurement condi-t:ions.
~X~PLE 5 Two hundred g of the granula-ted polyesterurethane -thexmo plastic of Example 1 was charged to a one-pi.nt paint can and 0.5 ml of a 71.6% aqueous solution of ethylamine was added from a syringe. The amine solution caused no immediate stick-ing of the granules, and the can.was closed promptly to avoid evaporation losses and shaken :for about 30 seconds to distrib-ute the amine. Ater standing overnight at room temperature,the can was placed in an oven at 93C and maintained a-t 93-95 C fox 22 hours. The can then was removed from the oven and shaken while hot. There was no sticking together of the hot granules. Upon opening the hot can, there was a very weak odor of the amine present. The open can was immediately placed in a vacuum chamber and evacuated to 1 mm Hg for 15 minutes.
Upon removal from the vacuum chamber, there was no residual ~ odor of amine emanating from the still-warm granules. After standing at room temperature for two daysr 30 g of the granules was dissolved in 170 g tetrahydrofuran with stirring at room temperature. It was noted that the amine-treated granules dissolved without swelling, while in a parallel experiment with untreated granules there was extensive swelling during dissolution. The control solution (15% NVS) of untreated granules had a viscosity at 18C of 1,860 cps, which clearly is far above the manufacturer's specification of 300-700 cps at 2SC. The 15% NVS solution of treated granules had a vis-cosity at 18C of 155 cps, which, although below the specifi-cation, illustrates the effectiveness of ethylamine in reduc-ing the polymer molecular weight.
KF,MER~CA~2 ~IL3~ 3 3L
To 200 g of the granulated thermoplastic polyurethane of Example 5 in a one-pint pai.nt can was ad~ed 0.8 g of mono-isopropanolamine dissolved in a g isopropyl alcohol. The can was closed and shaken to distribute the liquid. A~-ter standlng -for two days at room temperature, the can was shaken again;
there was no sticking together of the granules. The can then was placed in an oven at 102C for 21 hours, then removed and set aside at room temperature. A-fter standing overnight, the can was opened, and the granules were found to have become fused together in one lump. A 45 g portion of the fused lump then was cut into small pieces and dissolved in 255 g tetra-hydrofuran at room temperaturer The viscosity of this 15% NVS
solution at 16.5C was 55.~ cps. A 35~ NVS solution of the treated granules in dimethylformamide also was prepared and was found to have a viscosity of 6,180 cps at 16C. These results illustrate -the effectiveness of monoisopropanolamine in isopropyl alcohol for reducing the molecular weight of the polyurethane, although the amount of reagent used was more than that needed to reduce the molecular weight to within the manufacturer's specifications.
In the manner of Example 3, 200 g oE the granulated poly-urethane thermoplastic of Example 4 was treated with 0.8 ml of n-octylamine. The temperature of the oven, however, was 92-95C. The viscosity of a 15~ NVS solution of the treated granules in tetrahydrofuran at 21C was 640 cps, which i5 clearly within the manuEacturer's specification of 400-800 29 cps at 25C.
K~MERICA~2 ~13t~33~
EXAMP _ _ To 200 g of the granulated polyurethane thermoplastic of Example 2 in a one-plnt can was added 1.0 ml of a solution prepared by dissolving 10 g gaseous methyla~ine in benzene so as to make 100 ml of the stock solution. The can was closed immediately, shaken for 30 seconds, and then placed in an oven at 85C for 18 hours. The can then was removed from the oven and allowed to cool to room temperature. It was opened, and the odor of benzene together with a faint odor of methylamine was noted. The open can was placed in a vacuum chamber at 1 mm Hg for 15 minutes, and then examined. The vacuur.l stripping had removed both the odor of benzene and of methylamine. A portion of the granulate then was dissolved in tetrahydrofuran at room temperature so as to make a 15% NVS
solution. The viscosity of this solution at 24C was found to - be 720 cps, within the manufacturer's specification of 600~
1,200 cps at 25C.
It is to be understood that the inven-tion is not to be limited to the exact details of operation or structures shown ~20 and described~ as obvious modifications and equivalents will be apparent to one skilled in the art.
.
~ -22-
~363~
BACiCGROU~D OF TIJE l:NVE,N'rl:ON
_ _ _ _ _ . _ FIEI.D OF :[NVEI:IT:LON
__ The lnvention rela-Zes to a process for ir~atincJ poly-urethanes, especially -thermoplastically processable polyuretllar.les, to rèduce the molecular wei~ht thereoE. ~lore particularly, the invention is directed to processes for treating such polyure~anes as contain gel fractions, which comprise insoluble matter due to crosslinking, or excessive degree of poly~erizatlon, al~pical poly-mermization,or like mechanisms, in order to el~inate or subs~antiall~ r~uce these gel fractions and/or to lower the molecular weight of thc polymer.
Thermoplastically processable polyurethanes have been produced commercially fox more than 20 yeaxs. The majority o~
products which are of industrial importance at the presert are prepared by reaction of 4,~'-diphenylmethane diisocyanate with (1) an aliphatic polyesterdiol such as hydro~yl~terminated poly(1,4-butylene adipate) or an aliphatic polyetherdiol such as hydroxyl-terminated poly(oxytetramethylene) and (2) a diol . chain.extender such as 1,4-butanediol or 1,4~bis(2-hydroxl-ethoxy)benzene. Some of the commercially available poly,mers are predominantly hydroxyl-terminated, while others are pre-pared with a slight stoichiometric excess of isocyanate ~nd a-e predominantly isocyanate-terminated. I~e latter polymers undergo ~ur~G~r reaction upon elevated temperature post curiny or aglng in ~he . presence of atmospheric moisture, and ~ay become crosslinked.
All of these polymers commonly are processed into shaped articles by means of thermoplastic processing technlZ~ues such as injection molding, extrusion, calendering,and blo~J mo].ding~
Many of the polymers, particularly those predominantly hydroxyl-X~trLI~l~lC,-~-2 ~3~33~
terminated, are soluble in d:ipolar aprot:ic solvents 5uch as tetrclhydrofuraI1, dimethy:lformamide, cyc]ohexanone arld dioxane, and as solutions in these and other solve~nts,find a variety of applications as coatings and adhesives.
For applications in solution, it is hlghly desirable if not essential that under given conditions of temperature, concentration of polymer and choice o~ solvent, the vi~cosi~y be within certain limits. Moreover, ~hen -thin filrns or coatings are to be prepared from the solutions, it is important that the polymer be entirely soluble, i.e., free of particles of cross1inked polymer commonly called "gel"O It is difficult tG produce consistently thermoplastic polyurethanes which are free of gel. Furthermore, it is equally difficult to achieve precise molecular weight control, and therefore solution viscosity control, in commercial manufacture of the thermoplastics. In addition, even nominally OH-terminated thermoplastic polyurethanes generally contain a residu11m of NCO ~roups sufficient to cause marked increases in molecular weight within normal periods of storage required in co~excial applications prior to final usage of the thermoplastic. Of those products which have viscosity specificatiors, in many cases the dilute solution viscosity may vary as much as by a factor of two, and even with this generous allowance for vari-ation of the molecular weight, a considerable amount of material is produced which is out-of-specificatiorl.
In many coatings artd adhesives applications, it would be desirable to reproduce solution viscosity of a given type of polyurethane thermoplastic to within T 20 percent, or even less, of a p,edetermined level without changing ~he temperature, polymer concentration, or composition of the K~ l;RtCP-2 ~L13~;33~
solvent. Up to the present -time, this has no~ been genera]ly possible. Fur-therMore, many lots of material offeriny the desired viscosity characteristics are rejected due to gel content. Even for thermoplastic processing application~; it is important to control molecula~ weight so as to provide sul-~le and uniform processing characteristics. ~lso, whe~e -thin artlcles are produced, as in blow molding, it is high:ly desirable to utilize polyrners of low gel content. Nevertheless, it is typical to find a noticeable and objectionable amount of gel particles, for example, in blow-molded polyurethane film -manufactured from in-specification lots of polymer.
Also, the storage stability of many polyurethane thermo-plastics, both as solids and in solution, has been a problem.
If free isocyanate is present in the polymer, it is inherently unstable and tends to increase in molecular weight. This is particularly troublesome when the polymer is exposed to moisture. ~hen the polymer is to undergo thermoplastic processing, such aging leads to less favorable processing characteristics and physical properties in the articles produced. In the case of solution applications, the viscosity usually increases, the content of gel may increase, and/or the polymer may become less soluble.
OBJECTS OF T~E INVENTION
It is an object of the invention to pro~ide an improved process ~or modifying polyurethane polymers. It is a further o~ject of the invention to provide a process for reducing the molecular weight of polyurethane polymers. It is a fuxther object of the invention to pro~ide a process for eliminatir.g ;
or reducing the amount of gel fxactions in polyurethane polymers. It is a further object of the invention to provide , - KEMER~C~-~
~L363;3~1L
a process for the recovery of ofE-grade polyurethane polyrners.
It is a further object of the invention to provide a process for upgrading polyurethane polymers. A s-till further object of the invention is to provide a process which obviates diffi-culties heretoEore encountered in the prior art and which has advantages as will be more particularly pointed out as the description proceeds.
BRIEF DESCRIPTION OF THE INV~NTION
.. .. . .. . ... .. _ _ The invention relates -to a process for -treating,in the solid state,polyurethane polymers/ especially thermoplastically processable polyurethane polymers,of higher-than-desired molecular weight with a primary or secondary amine under conditions which cause aminolysis of both linear linkages and crosslinkages characteristic o the polyurethane being treated. Still more particularly, the invention relates to such a process which simultaneously effects reduction of gel fractions in the poly-` urethane polymer, which gel fractions comprise insoluble material due to crosslinking, excessive degree of polymeri7ation, atypical polymeriæation, or like mechanisms.
While the invention is particularly applicable to thermo-plastically processable polyurethanes, which term is to be understood to include those polyurethanes intended for solvent appli-cations as well as for thermoforming, it is to be understood that it is broadly applicable to polyurethanes, including thermosetting types, where it is desired to effect a reduction of the molecular weight either of the basic polymer per se,or of high m~lecular weigh-t and/or insoluble in-clusions due to crosslinking, excess degree of poly~eriza-tion, atypical polymerization, and like mechanisms which may occur during m~nufacture and/or storage of the polyurethanes. The invention, for e~le, can be applied to rigid or micro-cellular foamed polyurethanes, especially where ., Kr~M~RICA-~
~L~3633~
it is desired to alter the surEace characterist;cs o~ such foams. With open cell -type foams, the process can also be utilized to modify the general charac-ter of the foamed s-tructure.
In carrying out the processes o~ the invention, -the poly-urethane polymer, in the solid state, is exposed to the prir~
or secondary a~ine under conditions ef~ectiveto cause diffusion of the amine throughout -t h e polymer, and then, simultane-ously therewith, or, subsequently thereto, the amine-treated polymer is heated in the solid state for a time and at a ternpera-ture effective to cause the desired degree of aminolysis.
In both the diffusion and aminolysis portions of the pro-cess of the invention, substantial advantac~es are realized through treatment of the polymer in its solid state as opposed to treatment concomitant with dissolution of the polymer. In the presence of solvent, the amine is dis-tributed among the solid and liquid phases and, as a result of the dilution Eactor, longer times and/or larger quantities of amine and/or higher temperatures during the aminolysis process may be required.
Even when amine is first applied to the solid polymer and the diffusion process allowed to proceed to a satisfac-tory state of completion, upon addition of solvent to the amine-containing solid polyurethane, prior to aminolysis, some of the absorbed amine will diffuse back out of the polymer and into the liquid phase so as to reduce the amount of amine actually in contact with the polymer. Although a satisfactory result may be obtained through proper control of time/temperature variables during aminolysis together with use of relatively greater quantites of amine in many cases, there will generally be some disadvantage, such as greater overall process time requirements, if aminolysis is carried out concomitant with dissolution as opposed to being -6- followed by page 6-A
KE~ERICA-2 ~g~3;33~
carried out in the absence of solvent.
Moreover, iE the intended app:Lication o~ -the treated polyurethane is thermo~orming oE ~he solid polymer as opposed to a solution application, it is a great disadvantage, if not entirely impractical, to have to recover the solid polymer from solution. In contrast, the process o-E the invention for solid state modification of polyurethanes generally involves only addition of the amine to the particulate solid polymer in a suitable closed container; al:Lowing su-.E~icient time for diffusion of the amine into and throughou-t the solid, which process may be hastened by moderate agitation or tumbling of the mixture together with heating to a temperature below that at which aminolysis proceeds at a substantial rate; and, ater diffùsion of the amine has occurred, heating for a requisite time and temperature sufficient to bring about aminolysis.
If the amount of amine and the time and temperature conditions have been properly adjusted, the treated polymer will have a reduced average molecular weight of predetermined value, and will be essentially free of any gel inclusions which may have been present. If desired, the amine-treated polymer at the conclusion of the aminolysis heating cycle can be stripped under vacuum to remove any residual amine.
If the amine-treated polymer is to be used in a thermoforming operation, it is highly desirable to employ a brief vacuum str.ipping period following aminolysis so as to remove residual amine. Any residual amine could cause further aminolysis during thermoforming under the relatively high temperatures used in such operations. In addition, if the original polymer, prior to treatment with amine, contained objectionable amounts of gel inclusions with respect to its intended thermoforming KEMERLC~-2 ~L13~33~
application, it ma~ be desirable, prior to thermofo~mincJ, to homogenize the amine-treated, vacuum s~rlp~ed polymer by extrusion and pelletization orregrindincJ. This final processiny step serves to dissolve in the continuous polymer phase any aminolyzed gel inclusions which, without such homo~eni~a-tion, might appear as inhomogenieties in the therm~formed en~products.
Homogenization is, of course, unnecessary if the amine-treated polyurethane is to be employed in dissolved form. In that case, the dissolution process provides complete homogenization.
In the process of ~e invention, the prim~ry or seconda~y c~mine attacks such linkages as ester linkages, ure~e linkages, allophanate linkages, and the like, which may be present in the polyurethane. It is effective in causing scission of these linkages whethe. they are linear linkages or cross-linkages. Through control of the amount of amine and of the time and temperature of the thermal treatment, the process can be tailor-made to achieve either controlled re~uction of molecular weight or controlled reduction of molecular weight coupled with lowering or removing gel fractions contained in the polymer. Generally speakiny, additional time for diffusion of the amine is required for the efficien-t breakdown of the gel fractions because it takes longer for the amine to diffuse into the suspended gel particles. Therefore, a longer time at a lower temperature, i.e., low enough so that substan-tial aminolysis does not take place prior to diffusion of amine throughout the gel, may be required -than for simple reduction of molecular weight of gel-free material. In any case, the tempera-ture should be low enough to prevent degradation of the resin by mechanisms other than scission of the aforementioned groups by -t h e a m i n e, a s s u c h other mechanisms may produce an off-color product or one not having the desired character-K~MERICA-2 ~3~33~
istics of thermoplast:icity, elasticity, and the like.
In carrying out -the process of the invention, the polyure-thane polymer to be treated ls exposed in the solid state to the primary or secondary amine under conditions of time and temperature effective to cause diffusion of the amine into the polymer and the amine-treated polyurethane pol~mer in the solid state there-after is heated to a temperature effective to cause aminolysis for a time sufficient to accomplish the desired reduction in molecular weight. Advantayeously, the solid polyurethane polymer is t r e a t e d w i t h the a m i n e at a temperature below tha-t at which substantial aminolysis takes place for a time suffi-cient to obtain effective diffusion of the amine into the polymer, including any gel fractions contained therein. The polymer may be heated to speed up this difEusion, advantage-ously, up to a temperature not greater than about 60~C to promote diffusion of the amine into the polymer.
The amine-treated solid polymer then is heated in the solid state to a temperature sufficient to effect aminolysis and the temperature is maintained for a time sufficient to obtain the desired reduction in molecular weight and/or gel fractions. Ordinarily, this temperature can range from above about 60C to not more than about 120C. Higher temperatures can be used, however, up to the temperature at which thermal degradation occurs at an objectionable rate. It is possible in some instances for diffusion and aminolysis to take place concomitantly, but generally it is desirable that diffusion be substantially complete before appreciable aminolysis is allowed to occur. The solid polyurethane polymer is exposed to the amine, prefera~ly i n a closed container,and heated therein i n t h e pr e s e n ce of the amine for a time and KEM~i~ICA~~
~L~L3633~
and at a temperature sufficient to effec-t the desired diffusion and aminolysis and the temperature maintained at aminolysis temperature for a time sufficient to obtain the desired reduc-tion of molecular weight and/or ~el fractions.
The amount of amine required to effec-t its purpose in the process of the invention is relatively small, and depends upon the particular amine used as well as upon other processing variables such as time and temperature variables. In general, there will be a residuum of unreacted amine in the treated polyurethane unless relative extremes of time and/or ternperature are employed during the aminolysis phase of the process, or unless there is employed a subsequent processing step designed to remove or destroy such residuum of unreacted amine. Effec-tive reduction in molecular weight, together with brea~down of any gel fractions present, ordinarily is obtained with less than 1 weight percent of amine, based on dibutylamine and the weight of the polymer. Higher amoun-ts, up to 5 percent or even more can be used when there is substantial unreacted iso-cyanate present in the polymer and/or extensive crosslinking and/or when the conditions of aminolysis employed do not provide for substantially complete reaction of the amine. Also, it might be necessary to employ such higher amounts of amine if there were incomplete diffusion of amine prior to aminolysis.
In such an instance, however, there would be extensive degrada-tion (through aminolysis) of that portion of the polymer into which the amine had diffused prior to aminolysis, and the physical properties of the overall product, after treatment, generally would be seriously harmed. In any case, the equiva-lent of 5 percent of dibutylamine, if uniformly diffused prior to aminolysis and then completely reacted with the polymer, is _g_ ~
KEiMF.RIC~-2 ~L13~33~l sufflcient to cause molecular weight reduction of rnost ~olymers beyond that consistent with preservation o~ norrnal polym~r physical properties.
In general,it is not often necessary or desirable to exceed the equivalent of about 2 percent dibutylamine. rrhe optimum amount for a given transformation under given processing conditions can be determined directly by experimentation.
For each batch of off-grade polyurethane thermoplastic there is an experimentally determinable relationship between the amount of amine employed and the molecular weight (as conven-iently observed in terms of solution viscosity) of the result-ing treated polymer, other processing variables being held constant. The equivalent of 0.1 to 0.5 percent dibutylamine has been employed with complete success in the recovery of a wide variety of off-grade polyurethane thermoplastics, and even with such small amounts of amine there may be a residuum of unreacted amine in the polymer following successful recovery, unless such residuum is removed or otherwise eliminated. It is generally not necessary or desirable to employ less than the equivalent of about 0.01 percent dibutylamine. Where other amines are used, the proportions can be increased or decreased as necessary to account for higher or lower molecular weight and/or higher or lower aminolysis reactivi-ty under given condi-tions relative to the molecularweight and reactivity of dibutylamune.
In carrying ou-t the process of the invention, any basic primary or secondary amine, advantageously one having a PKb less than about 6, can be employed. ~he term amine as used herein is to be understood as referring to amines of this type. Suitable such secondary amines include dimethylamine, methylethylamine, diethylamine, ethylpropylamine, methylpropylamine, ethyliso-KEMr,RIC'~ 2 3~13~
propylamine, me-thylisopropylamine, dip:ropy].amlne, cliisopropyl-amine, dibutylamine, diisobutylamine, methylbutylamlne, ethyl-butylamine, diamylamine, dihexylamine, dihepty].amine, dioctyl-amine, di-2-ethylhexylamine, piperidine, tetxahydropyrrol, morpholine, N-methylethanolamine, die-thanolamine, 2,6~dime-thyl-morpholine, methylcyclohexylamine, dicyclohexylamine, methyl~
benzylamine, and dibenzylamine. Suitable such primary arnines include methylamine, ethylamine, propylamine, isopropylamine, butylamine, isobutylamine, secbutylamine, amylamine, isoamyl-amine, hexylamine, heptylamine, octylamine, 2-ethylhexylamine, cyclohexylamine, benzylamine, 2-methoxyethylamine, 2-ethoxy-ethylamine, decylamine, dodecylamine, tridecylamine, ethanol-amine, isopropanolamine, and 3-aminopropanol-1.
When the amines are liquid at ambient temperature, they can be absorbed on granules of the polymer and allowed to diffuse into the granules~ Solid amines are encountered only infrequently in the practice of the invention, and generally offer no advantages over the variety of llquid and gaseous amines which are suitable and readily available. If a solid amine is to be used, ît should be heated to above its melting point and absorbed on the polymer granules preheated to the same or higher temperature, provided that neither temperature is sufficiently high as to cause substantial aminolysis of the polymer prior to adequate diffusion of the amine throughout the polymer. Gaseous amines, such as methylamine, e-thylamine and dimethylamine, can be employed in a closed system.
Often in the case of gaseous or solid amines, and sometimes with liquid amines, it is desirable to dissolve the amine in an inert diluent so as to facilitate measurement and handling of the amine and/or to improve uniform absorption and/or dif-K~ LI~IC~-2 ~L~3~33~
fusion of khe amine throughout the soLid polyurethane. Suitable inert diluen-ts include solvents which dlssoLve the part:icular amine in question and which may also tend -to diffuse :in-to the solid polymer, but not cause the polymer partlcles to agylo~rate.
Whether or not a given solvent/diluen-t for the amine is suitable depends in generally upon which polyuxethane is being treated.
Lower aromatic hydrocarbons such as benzene, toluene and the xylenes are generally sui-table, as are lower alcohols such as isopropyl alcohol. Alcohols, of course, tend to diEfuse into the polymer, and may compete with the amine, dependlng upon the relative amount of alcohol employed, for reac-tion with any residual isocyanate groups presen-t in the polyurethane.
The amount of any diluent used may vary from much less than the amount of amine, such as ten percent of the weight of amine, to any larger amount. In general, it is not desirable to use more diluent than can be absorbed by the polymer, as any liquid phase remaining after absorption will contain some of the amine and therefore will reduce the amount of amine absorbed by the polymer and immediately available for aminolysis at the beginning of the aminolysis step~ Furthermore, if the amine-treated polyurethane is to be used in thermoforming, it often will be necessary to remove the diluentanyway by means of vacuum stripping.
Even when the polyurethane is to be dissolved following the amine treatment, an excessive amoun-t of diluent may interfere with the dissolution process and/or have other deleterious effects in the course of the end use of the polyurethane solution.
Where it is an object to reduce the content of gel fractions, adequate diffusion of the amine into the polymer, including the gel fractions thereof, should be effected before applying heat sufficient to cause substantial aminolysis.
KEMI~R:~C~~2 ~3~3~
Otherwise, non-uniEorm and overall ine~ficient ac-tion of the amine will result, and -there will he some v:iscosi-ty reduction accompanied by incomplete breakdown of the gel fractions.
In accordance with one form of the invention, the amine is added to the polymer in thegranulclr form, pre~erably with at least some mechanical blending, and allowed to dif~use into the granules. For this purpose, amines which are non solvents for the polyurethane polymer being treated are of particular advantage. When a non-solvent amine is used, the particles of the polymer do not agglomerate during the solid state treatment. The term "non-solvent amine" as used herein is to be understood to mean an amine which is a suEficiently poor solvent for the polyurethane polymer undergoing treatment that it is absorbed by the particles or granules without causing them to stick together. For -the most part, such non-solvent amines are unsubstituted, higher m~lecular weight primary or secondary aliphatic and cycloaliphatic amines, for example, those having at least 7 carbon atoms, such as methylcyclohexylamine, di-butylamine, diamylamine, diisobutylamine, dihexylamine, di-cyclohexylamine, dioctylamine, di-2-ethylhexylamine, heptyl-amine, octylamine, 2-e-thylhexylamine, benzylamine, decylamine, dodecylamine, and tridecylamine, and advantageously containing not more than twelve carbon atoms.
A wide range of temperature variations may be used in carrying out the process of the invention because it is a time:temperature relation which is essentially important. Thus, during the diffusion of the amine into and throughout the solid polymer, any temperature below the aminolysis temperature, that is to say, the temperature at which substantial aminolysis takes place can be used and the higher the temperature the KEMli.RIC~-2 31 13633~
shorter will be the time necessary to effec-t the diffusion.
The aminolysis -temperature varies accordiny to the reac-tivi-ty of the particular amine. In general, however, aminolysis begins to proceed at a substan-tial ra-te at about 60~C, particu-larly with secondary amines, though with some of the more re-active primary amines, the aminolysis temperature may be some-what lower. The upper tempera-ture limit for the diffusion process generally is lower for pr.imary am.ines than for second-ary amines, as the primary amino g r~up generally is the more reactive in aminolysis. In the aminolysis stage, or molecular weight reduction stage, any temperature above that at which substantial aminolysis takes place, but below that which would cause substantial thermal degradation of the polymer can be used, it being understood that the lower the tet~era-ture, the longer the time that will be required,and vice versa. In genera~ also, the shorter the time, the higher the temperature that can be used without excessi~e thermal degradation. mus, in such case, the amine-treated granules in which the amine has been allowed or caused to difuse throughout the polymer structure can be heated rapidly, preferably with conccmi-tant tut~bling of the granules,to a temperature up to 90C, or higher, without deleter-iously effecting color, strength, and elasticity of many polymers. In general, however, it is not desirable to employ t e m peratures above 120C. Also, if adequate diffusion of the amine through the polymer granules was first obtained, then the product also is essential.ly free of gel fractions and clear,colorless, strong and elastic film can be drawn from the resulting product which, at the same time, has an acceptable mDlecular weight, from a starting polymer having a large amount of gel fractions and/or undesirably high molecular weight.
Alternatively, the amine-treated polymer is slo~ly and gradually heated over a considerable period before it is brought to the temperature K~ML, RI Cl~- 2 ~3~33~
at which arninolysis p.roc~ls at a significan-t rate (md t~n slowly and gradually heated up to a temperature substant:i.ally belol~7 that at which decornposition takes place, so that the mechanisms of dlffuslon and arnln~
olysis are qiven adequate time to be accomplished.
I t will be understood that, as the polyurethane polymer starting materials contemplated by the invention dlffer widely in constitution and gel fraction content, no hard and East rules can be set down as to precise temperatures, times, selection of g amines, and amounts of amines . I t may be said, however, tha t a ... _ . ... _ . .
~15-` KE~E~CA-2 3~3~
gradual increase in temperature or heating ove~r longer periods at low temperatures promo-tes diffusion. Consequently, the mixture of polymer and secondary amine should be heated slowly over a considerable period of time and, at the same time, the maximum temperature should be kep-t relatively low, prefera~ly below about 120C.
The invention is applicable to both the polyester-type polyurethanes and polyether-type polyurethanes,as well as o-ther types of po:Lyurethanes,and conditions yenerally effec-tive for one type are efEective for the other types.
DETAILED DESCRIPTIO~ OF T~IE INVENTION
The invention may be more fully understood by reference tothe following examples which are given by way of illustration only.
Parts and percentages are by weight unless otherwise specified.
EXAMP~E 1 An off-grade lot of intermediate hardness (87 Shore A) polyesterurethane granules (Estane~5701 F1) was obtained from B. F. Goodrich Chemical Company. This material was high in molecular weight and contained a substantial amount of gel.
PART lA
To a 100 g poxtion of Estane 5701 Fl of this example in a one pint can was added 0O5 ml dibutylamine. The can was closed, shaken and set aside at room temperature for 10 days.
Then it was placed in an oven at 73~C for 20 hours. There was no sticking together of the granules upon opening the hot can.
The granules were transferred to a larger can and 300 g cyclo-hexanone was added and the mixture was stirred at high speed with an air-powered mixer. After 90 minutes, dissolution appeared complete, but the viscosity was high. A portion of the solution was diluted with cyclohexan~ne to 19.5 percent NVS.
After standing overnight, the viscosity of the 25 percent C
~ER[(~~2 ~L~3~;~}3~
solution at 25C was 29,760 cps, and that oE -the 19.6 percent solution at 25C was 1,220 cps. A film prepared from -this solution was free of gel particles.
PART lB
A 300 g portion of the Estane 5701 Fl of this example was weighed into a one quart can and 1.5 ml dlbuty]amine was added. The can was closed and rolled for 20 minutes and set aside at room temperature for three clays. Then it was rolled again for 15 minukes and placed in an oven at 180F for 19 hours. It was again rolled for 10 minutes, and 60 g of the granules was transferred to a one quart can. Tetrahydrofuran (340 g) was added -to make 15 percent NVS. The can was closed and put on an electric roller for 90 minutes. The solids had dissolved, and the viscosity of the solution at room tempera-ture was 370 cps.
A 50 pound lot of off-grade polyetherurethane thermo-- ~ ~r~lneSS
plastic of 80 Shore A hardono~ was obtained from B. F. Goodrich Chemical Company. This material, Estané~5714 Fl, was not within normal product specifica-tions due to its high solution viscosity and gel content. The viscosity specification for this product is 600-1,200 cps at 15 percent NVS in tetrahydro-furan at 25C.
A 300 g portion of this lot of Estane 5714 Fl was weighed into a one quart can and 1.5 ml dibutylamine was added. The can was closed and rolled on an electric roller for 30 minutes.
There was no sticking together of the granules before or after rolling and the can was closed and heated in an oven at 85C
for 18 hours. The oven temperature then was increased to 100C
for three hours, and the can was removed and rolled immediately ~ ~ ~ Q ~
:
KEME~IC~~2 ~L~3~i33~
for 15 minutes. There was little i~ any tendency fo~ the granules to stick together whi:Le hot. Forty-five g of the granules then was transferred to a one pint can and 255 g tetrahydrofuran was added (for 15 percent NVS). Thi~ solution was stirred at room temperature to dissolve the granules, and additional tetrahydrofuran was added to compensate ~or evapora~
tion losses. The granules dissolved completely, and -the vis-cosity of the solution a-t 25C was found to be 285 cps.
A 50 pound lot of hard (50 Shore D) thermoplas-tic poly-esterurethane granules (Estane~5707) was obtained from B. F.
Goodrich Chemical Company. This par-ticular lot was rated"off-grade" by the manuacturer due to its high solutlon viscosity in dimethylformamide (3,048 cps at 15 percent non-volatile solids by weight [NVS] at 25~C) and to the signi~icant amount of loosely crosslinked gel which it contained. The standard viscosity specification for this product is 670-1,290 cps at 15 percent NVS in dimethyl~ormamide at 25C.
Two hundred g of the Esta ne 5707 of this example was weighed intoa one pint can and 2.0 ml dibutylamine was added.
The can was closed and shaken intermittently for 20 minutes and then was placed in an oven at 110C for 18 hours. Forty-five g of the granules was then weighed into a one pint can and 225 g dimethylformamide (for 15 percent NVS) was added.
The mixture was stirred at low speed for 30 minutes, during which time the granules dissolved completely and the solution did not rise above room temperature. The viscosity was deter-mined to be 52 cps. This shows that, when desired, a viscosity whlch is far below the manufacturer's specification of 670~1,290 cps can be obtained.
~ l ~QI~
KEM~l~ï CA- 2 ~3~333L
By usiny a smaller amount of dibutylamine arld/or lower oven tempera-ture and/or shorter heatinf~ time, this pol~es-ter-ure-thane, originally of high gel content and 3,04~3 cps -viscosity under the above measurement conditions, can be brou~ht to a viscosity within the manufacturer's specification.
EXAM~?LE 4 A 50-pound lot of r elatively soft (7~ Shore ~) thermo- s plastic polyesterurethane granules (Est ane~5710) was obtained from B. F. Goodrich Chemical Company. This sample was from a 10 lot rated "off-grade" b,v the manufacturer due to its high solution viscosity in tetrahydrofuran (1,900 cps at 15 percent NVS and 25C). The standard viscosity specification for this product is 400-800 cps at 25C and 15 percent NVS in tetrahydro-furan. This sample was rated by the manufacturer as having "no gel present". However, the method of ge:l rating used evidently reflects the degree of gel control which it has been possible to achieve in commercial production up to the present time . The much more sensitive f ilm examina tion procedure described herein reveals that this sample of Est a ne 5710 in 20 fact contains a large amount of small gel particles, which produce dozens of imper Eections per square inch in films pre-pared from solutions of the untreated thermoplastic.
Following the procedure of Example 3, the Estane~571Q of this example was treated wi th dibutylamine in the solid state at elevated temperature. At 15 percent NVS in tetrahydrofuran, in which the product dissolved completely, the viscosity at 25C was 32 cps.
As in Example 3, by using a smaller rela tive amount of dibutylamine, lower oven temperature and/or shorter heating 30 period, this polyesterurethane can be brought to a viscosity K~M~RIC~-2 ~13~3~
with the standard v:iscosity specification of ~0()-800 cps under the above measurement condi-t:ions.
~X~PLE 5 Two hundred g of the granula-ted polyesterurethane -thexmo plastic of Example 1 was charged to a one-pi.nt paint can and 0.5 ml of a 71.6% aqueous solution of ethylamine was added from a syringe. The amine solution caused no immediate stick-ing of the granules, and the can.was closed promptly to avoid evaporation losses and shaken :for about 30 seconds to distrib-ute the amine. Ater standing overnight at room temperature,the can was placed in an oven at 93C and maintained a-t 93-95 C fox 22 hours. The can then was removed from the oven and shaken while hot. There was no sticking together of the hot granules. Upon opening the hot can, there was a very weak odor of the amine present. The open can was immediately placed in a vacuum chamber and evacuated to 1 mm Hg for 15 minutes.
Upon removal from the vacuum chamber, there was no residual ~ odor of amine emanating from the still-warm granules. After standing at room temperature for two daysr 30 g of the granules was dissolved in 170 g tetrahydrofuran with stirring at room temperature. It was noted that the amine-treated granules dissolved without swelling, while in a parallel experiment with untreated granules there was extensive swelling during dissolution. The control solution (15% NVS) of untreated granules had a viscosity at 18C of 1,860 cps, which clearly is far above the manufacturer's specification of 300-700 cps at 2SC. The 15% NVS solution of treated granules had a vis-cosity at 18C of 155 cps, which, although below the specifi-cation, illustrates the effectiveness of ethylamine in reduc-ing the polymer molecular weight.
KF,MER~CA~2 ~IL3~ 3 3L
To 200 g of the granulated thermoplastic polyurethane of Example 5 in a one-pint pai.nt can was ad~ed 0.8 g of mono-isopropanolamine dissolved in a g isopropyl alcohol. The can was closed and shaken to distribute the liquid. A~-ter standlng -for two days at room temperature, the can was shaken again;
there was no sticking together of the granules. The can then was placed in an oven at 102C for 21 hours, then removed and set aside at room temperature. A-fter standing overnight, the can was opened, and the granules were found to have become fused together in one lump. A 45 g portion of the fused lump then was cut into small pieces and dissolved in 255 g tetra-hydrofuran at room temperaturer The viscosity of this 15% NVS
solution at 16.5C was 55.~ cps. A 35~ NVS solution of the treated granules in dimethylformamide also was prepared and was found to have a viscosity of 6,180 cps at 16C. These results illustrate -the effectiveness of monoisopropanolamine in isopropyl alcohol for reducing the molecular weight of the polyurethane, although the amount of reagent used was more than that needed to reduce the molecular weight to within the manufacturer's specifications.
In the manner of Example 3, 200 g oE the granulated poly-urethane thermoplastic of Example 4 was treated with 0.8 ml of n-octylamine. The temperature of the oven, however, was 92-95C. The viscosity of a 15~ NVS solution of the treated granules in tetrahydrofuran at 21C was 640 cps, which i5 clearly within the manuEacturer's specification of 400-800 29 cps at 25C.
K~MERICA~2 ~13t~33~
EXAMP _ _ To 200 g of the granulated polyurethane thermoplastic of Example 2 in a one-plnt can was added 1.0 ml of a solution prepared by dissolving 10 g gaseous methyla~ine in benzene so as to make 100 ml of the stock solution. The can was closed immediately, shaken for 30 seconds, and then placed in an oven at 85C for 18 hours. The can then was removed from the oven and allowed to cool to room temperature. It was opened, and the odor of benzene together with a faint odor of methylamine was noted. The open can was placed in a vacuum chamber at 1 mm Hg for 15 minutes, and then examined. The vacuur.l stripping had removed both the odor of benzene and of methylamine. A portion of the granulate then was dissolved in tetrahydrofuran at room temperature so as to make a 15% NVS
solution. The viscosity of this solution at 24C was found to - be 720 cps, within the manufacturer's specification of 600~
1,200 cps at 25C.
It is to be understood that the inven-tion is not to be limited to the exact details of operation or structures shown ~20 and described~ as obvious modifications and equivalents will be apparent to one skilled in the art.
.
~ -22-
Claims (26)
1. A process for treating polyurethanes of higher than desired molecular weight to reduce the molecular weight thereof which comprises treating the polyurethane exclusively in the solid state with a basic primary or secondary amine under conditions which cause scission of polymer linkages ex-clusively by solid state aminolysis to produce a polyurethane having a lower average molecular weight than the starting polyurethane.
2. The process of Claim 1, in which the amine is admixed with the polyurethane in a solid particulate state.
3. A process for treating polyurethanes of higher than desired molecular weight to reduce the molecular weight thereof, which comprises treating the polyurethane exclusively in the solid state with a basic primary or secondary amine under conditions which cause scission of polymer linkages ex-clusively by solid state aminolysis to produce a polyurethane having a lower average molecular weight than the starting polyurethane, in which the admixture is first heated below the temperature at which substantial aminolysis takes place in order to promote diffusion of the amine into the polyurethane and, thereafter, above the temperature at which aminolysis takes place in order to promote scission of polyurethane linkages by aminolysis.
4. The process of Claim 3, in which the admixture is first heated to a temperature not greater than about 60°C and,there-after, at a temperature sufficiently greater than in the first step so as to promote aminolysis but not substantially greater than about 120°C.
5. The process of Claim 4, in which the amine is an ali-phatic or cycloaliphatic hydrocarbon amine having at least 7 carbon atoms and not more than 12 carbon atoms.
-23- (Claims page 1) KEMERICA-2: 784,258
-23- (Claims page 1) KEMERICA-2: 784,258
6. The process of Claim 5, in which the amine is dibutylamine.
7. A process for treating polyurethanes of higher than desired molecular weight to reduce the molecular weight thereof, which comprises treating the polyurethane exclusively in the solid state with a basic primary or secondary amine under conditions which cause scission of polymer linkages ex-clusively by solid state aminolysis to produce a polyurethane having a lower average molecular weight than the starting polyurethane, and in which the polyurethane in the solid state is heated in the presence of the amine in two stages; first, at a temperature below that at which appreciable aminolysis takes place until substantial diffusion of the amine into and throughout the solid polyurethane is obtained and, second, at a temperature sufficient to promote aminolysis, but insuffi-cient to cause thermal degradation.
8. The process of Claim 7, in which the temperature in the first stage is not greater than about 60°C and i n t h e second stage is greater than that in the first stage, but not substantially greater than about 120°C.
9. The process of Claim 8, in which the amine is an ali-phatic or cycloaliphatic hydrocarbon amine having at least 7 carbon atoms and not more than 12 carbon atoms.
10. The process of Claim 9, in which the amine is dibutylamine.
11. A process for treating polyurethanes of higher than desired molecular weight to reduce the molecular weight thereof, which comprises treating the polyurethane exclusively in the solid state with a basic primary or secondary amine under conditions which cause scission of polymer linkages ex--24- (Claims page 2) KEMERICA-2: 784,258 clusively by solid state aminolysis to produce a polyurethane having a lower average molecular weight than the starting polyurethane, and in which the amount of amine is between about 0.01 and 10 percent based on the weight of the polyurethane.
12. The process of Claim 5, in which the amount of amine is between about 0.01 and 10 percent based on the weight of the polyurethane.
13. The process of Claim 6, in which the amount of amine is between about 0.01 and 10 percent based on the weight of the polyurethane.
14. The process of Claim 9, in which the amount of amine is between about 0.01 and 10 percent based on the weight of the polyurethane.
15. The process of Claim 10, in which the amount of amine is between about 0.01 and 10 percent based on the weight of the polyurethane.
16. A process for treating thermoplastic polyurethanes of higher than desired molecular weight which contain dispersed therein gel particles for the purpose of reducing the molecular weight and the content of such gel particles which comprises treating the polyurethane exclusively in the solid state and exclusively by aminolysis with a basic primary or secondary amine under conditions which cause scission of both linear linkages and crosslinkages characteristic of the polyurethane being treated.
-25- (Claims page 3) KEMERICA-2: 784,258
-25- (Claims page 3) KEMERICA-2: 784,258
17. The process of Claim 16, in which the solid state poly-urethane is treated in the presence of the amine in two stages;
first, at a temperature below that at which appreciable amin-olysis takes place until substantial diffusion of the amine into and through-out the solid polyurethane is obtained and, second, at a tempera-ture sufficient to promote aminolysis, but insufficient to cause substantial thermal degradation.
first, at a temperature below that at which appreciable amin-olysis takes place until substantial diffusion of the amine into and through-out the solid polyurethane is obtained and, second, at a tempera-ture sufficient to promote aminolysis, but insufficient to cause substantial thermal degradation.
18. The process of Claim 17, in which the temperature in the first stage is not greater than about 60°C, and that in the second stage is greater than that in the first stage, but not substantially greater than about 120°C.
19. The process of Claim 18, in which the amine is an aliphatic or cycloaliphatic hydrocarbon amine having at least 7 carbon atoms and not more than 12 carbon atoms.
20. The process of Claim 19, in which the amine is dibutylamine.
21. The process of Claim 16, in which the amount of amine is between about 0.01 and 10 percent based on the weight of the polyurethane.
22. The proces of Claim 20, in which the amount of amine is between about 0.01 and 10 percent based on the weight of the polyurethane.
23. A s o l i d polyurethane composition comprising poly-urethane molecules obtained by scission of a urethane or ester linkage exclusively by solid state aminolysis with a basic primary or secondary amine.
-26- (Claims page 4)
-26- (Claims page 4)
24. A polyurethane composition comprising polyurethane molecules obtained by scission of a urethane or ester linkage exclusively by solid-state aminolysis with an aliphatic or cycloaliphatic hydrocarbon amine having at least 7 carbon atoms and not more than 12 carbon atoms.
25. A polyurethane composition comprising polyurethane molecules obtained by scission of a urethane or ester linkage exclusively by aminolysis with dibutylamine.
26. A process for treating polyurethanes of higher than desired molecular weight to reduce the molecular weight thereof which comprises treating the polyurethane in the solid state with a basic primary or secondary amine under conditions which cause scission of polymer linkages by solid state aminolysis to produce a polyurethane having a lower average molecular weight than the starting polyurethane.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000328005A CA1136331A (en) | 1979-05-22 | 1979-05-22 | Process for making and/or modifying polyurethanes |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000328005A CA1136331A (en) | 1979-05-22 | 1979-05-22 | Process for making and/or modifying polyurethanes |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1136331A true CA1136331A (en) | 1982-11-23 |
Family
ID=4114254
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000328005A Expired CA1136331A (en) | 1979-05-22 | 1979-05-22 | Process for making and/or modifying polyurethanes |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1136331A (en) |
-
1979
- 1979-05-22 CA CA000328005A patent/CA1136331A/en not_active Expired
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