WO1993005109A1

WO1993005109A1 - Preparation of polyurethane compositions

Info

Publication number: WO1993005109A1
Application number: PCT/US1992/005906
Authority: WO
Inventors: John C. Clark; James E. Sax; John A. Temperante
Original assignee: Minnesota Mining and Manufacturing Co
Current assignee: 3M Co
Priority date: 1991-09-05
Filing date: 1992-07-15
Publication date: 1993-03-18
Anticipated expiration: 1994-03-05

Abstract

A method for the preparation of polyurethane compositions comprising polymerization of a mixture comprising polyisocyanate, polyol, and non-reactive fluoroaliphatic group-containing compound. Shaped articles, such as pellets and films, comprising the polyurethane compositions have improved low energy surface properties, such as non-blocking.

Description

PREPARATION OF POLYURETHANE COMPOSITIONS

This invention relates to methods of making polyurethane compositions and shaped articles thereof with low surface energy surfaces. In another aspect it relates to polyurethane precursor compositions therefor comprising polyisocyanate, polyol, and fluoroaliphatic group-containing compound.

Polyurethanes are extremely important and useful with a wide range of applications. Shaped articles of polyurethane such as pellets and films, however, can have problems with mold release and self-adhesion or "blocking". For example, it can be difficult to separate layers of polyurethane film from one another, and pellets of polyurethane are often not free-flowing and may clump together and thereby make processing of the pellets very difficult. Flow-control and mold-release additives such as silica, silicone, and calcium stearate have been used to impart non-blocking properties to polyurethane films - see, for example, E. N. Doyle, "The Development and Use of Polyurethane Products," pp. 75, 77, 274-275, McGraw-Hill (1971). Various fluoroaliphatic group-containing compounds, or fluorochemicals, have been used in preparing polyurethanes. For example, U.S. Pat. Nos. 4,356,273 (Soch) , 4,289,892 (Soch) , and 3,880,782 (Rambosek) describe the use of certain active hydrogen-containing fluorochemicals as foam stabilizers in the preparation of polyurethane foams.

Japanese Pat. Nos. 59[1984]-157190 (Matsuo et al.) and 59[1984]-213716 (Noritake et al.) describe the use of certain active hydrogen group-containing fluorochemicals as internal mold-release agents for reaction injection molding of polyurethanes. U.S. Pat. No. 5,025,052 (Crater et al.) describes certain fluoroaliphatic-containing oxazolidinones useful as melt additives in thermoplastic polymers, for example polyurethanes, the additives imparting low surface energy to fibers, films, and molded articles made from such polymers.

Briefly, the present invention, in one aspect, provides a method for the preparation of polyurethane compositions from which shaped articles, such as films, can be made with low surface energy, said method comprising polymerizing a mixture comprising polyisocyanate, polyol, and fluoroaliphatic group-containing compound such as a fluoroalkyl oxazolidinone. Said fluoroaliphatic group-containing compound, which is thus present during the polymerization, is free of moieties (for example, active hydrogen atoms) reactive with either of said polyisocyanate or polyol during the polymerization (viz. , under urethane bond forming conditions, e.g. 200°C) that is, it is inert or non-reactive. The compound is partially miscible with the resulting polyurethane product.

As used herein, the term "partially miscible" means that the fluoroaliphatic group-containing compound is miscible with, or soluble in, the resulting polyurethane at polymerizing or shaping temperatures and is less miscible with the resulting polyurethane at use or room temperatures.

The resulting polyurethane composition may conveniently be shaped or formed, for example by reaction injection molding or extrusion, into a variety of shaped articles, for example, fiber, pellets, and film. The shaped articles may be in the form of foamed polyurethane or dense (not foamed) polyurethane. The fluoroaliphatic group-containing compound imparts desirable properties to the surfaces of such articles, for example, low surface energy, which precludes the films and pellets from blocking or sticking together.

The fluoroaliphatic group-containing compound does not react with the polyisocyanate or polyol during the polyurethane polymerization process and appears to be free to migrate to some extent to the surface of the polyurethane article. In addition, it is believed that the migration is enhanced by the partial miscibility of the compound. In contrast, it is known that compounds which are immiscible with a polymer will form a second phase dispersed within the polymer and do not migrate as well to the surface as would an evenly distributed, dissolved or partially miscible compound. Also, compounds which remain equally miscible in a polymer at all relevant temperatures have less driving force to migrate to the surface and do not migrate as well as an initially dissolved compound which becomes less miscible at use temperatures than at polymerizing or processing temperatures. The addition of the fluoroaliphatic group-containing compound to the polyol-polyisocyanate reaction mixture before the completion of the polymerization thereof imparts surface properties to the polyurethane articles made therefrom which are comparable to that resulting when fluoroaliphatic group-containing compounds are mixed with a melt of a polyurethane, that is, added after the polymerization is complete. Addition of fluoroaliphatic group-containing compound into the polyurethane precursor mixture, rather than after the polymerization, results in elimination of some processing steps.

The fluoroaliphatic group-containing compounds useful in this invention can be normally liquid or solid (including meltable solids) and they are stable at the polymerizing and shaping temperatures. The fluoroaliphatic group-containing compound is partially miscible in an amount sufficient to impart desired properties to the surfaces of resulting shaped polyurethane articles, said amount generally being 0.05 to 10% by weight, preferably from 0.2 to 10% by weight. In the method of this invention, polyurethane compositions may be conveniently prepared by reactive extrusion polymerization, a method of polymer preparation that has grown in importance recently. See, for example, C. Tzoganakis, "Reactive Extrusion of polymers: A Review", Advances in Polymer Technology Methods. Vol. 9, No. 4, pp 321-330 (1989) . Methods and equipment for extruder polymerization of polyurethanes are described, for example, in U.S. Pat. No. 4,948,859 (Echols et al.), which descriptions of Tzoganakis and Echols et al. are incorporated herein by reference. The fluoroaliphatic group-containing compound can be first mixed with either the polyol or the polyisocyanate, or alternatively, be fed as a powder from a solids weigh-feeder, or as a liquid, into the throat of the twin-screw extruder at the same, or at a different, location as where the polyol and polyisocyanate streams are entering.

In the method of this invention, the polyurethane compositions may also conveniently be prepared by reaction injection molding and the resulting shaped and cured article can be readily released from the mold, the fluoroaliphatic group-containing compound acting as an internal mold-release agent.

Shaped articles made by the methods of this invention possess surfaces with excellent anti-blocking properties, for example, pellets can be prepared which are free-flowing, or films can be prepared which have interlayer adhesion as low as 100 grams/2.54 cm.

The resulting polyurethane composition, or product, can be extruded in the form of a fiber which can be pelletized into particles that are free-flowing and can be used in a standard extrusion operation to form various articles of various shapes, such as gaskets. A polyurethane film of this invention can be made by the conventional blown-film process. Such a process and equipment therefor are described, for example, in S. Middleman, "Fundamentals of Polymer Processing", pp 249-260, McGraw-Hill (1977), which descriptions are incorporated herein by reference. In the blown-film process, often an initial bubble is collapsed and then re-opened for post-processing steps or slitting. The excellent non-blocking or anti-blocking properties of the compositions of this invention are beneficial for such a blown-film process because a polyurethane film with high interlayer adhesion cannot be reopened after the collapsing step. The polyurethane films of this invention have lower surface energy and consequently reduced solvent wettability.

Because of their lower surface energy and adhesion properties, the fibers of this invention will have enhanced soil and stain resistance.

The presence of the fluoroaliphatic group- containing compound allows otherwise normally tacky polyurethanes to be processed on conventional equipment. The method of this invention provides a convenient method for the production of polyurethanes with low glass transition temperatures (T_g) for example less than -50°C, which would otherwise be difficult to produce.

A class of the fluoroaliphatic group-containing compounds useful in this invention can be represented by Formula I:

In Formula I, R_f is a fluoroaliphatic group or radical and y is l or 2, the compound thus containing 1 or 2 of such groups. R_f is saturated, mono-valent and has at least 4 fully-fluorinated carbon atoms. It can be straight, branched, or, if sufficiently large, cyclic, or combinations thereof, such as alkylcycloaliphatic radicals. The skeletal chain in the fluoroaliphatic group can include catenary hetero atoms bonded only to carbon atoms or the skeletal chain, such hetero atoms providing stable linkages between fluorocarbon portions of the R_f radical. A fully fluorinated group is preferred, but hydrogen or chlorine atoms may be present as substituents provided that not more than one atom of either is present for every two carbon atoms. While R_f can contain a large number of carbon atoms, compounds where R_f is not more than 20 carbon atoms will be adequate and preferred since larger radicals usually represent a less efficient utilization of the fluorine than is possible with shorter chains. Fluoroaliphatic groups containing from about 6 to about 12 carbon atoms are most preferred. Generally R_f will contain 40 to 78 weight percent fluorine. The terminal portion of the R_f group preferably has at least four fully fluorinated carbon atoms, e.g., CF₃CF₂CF₂CF₂-, and the preferred compounds are those in which the R_f group is fully or substantially completely fluorinated, as in the case where R_f is perfluoroalkyl, e.g. CF₃(CF₂)_n-. Suitable R_f groups include for example, C₈F₁₇-, C₆F₁₃CH₂CH₂-, F₅SC₃F₆-, and C₁₀F₂₁CH₂CH₂-.

In Formula I, R is an organic group which can contain from 2 to 35 carbon atoms. R preferably contains from 12 to 25 carbon atoms. R is such that the fluoroaliphatic group-containing compound is partially miscible with the polyurethane resulting from polymerization of the polyisocyanate-polyol mixture containing such compound. Such miscibility can be confirmed by testing the mixture or blend of the polyurethane and fluoroaliphatic group-containing compound, for example, testing the melting point, modulus, phase separation or cloud-point, or by differential scanning calorimetry (DSC) , of the mixture or blend - see, for example, the techniques described in D. Paul, and S. Newman, "Polymer Blends", Vol. 1, pp 15-20, Academic Press (1978) , and in references cited therein, which descriptions are incorporated herein by reference. Because perfluoroaliphatic compounds are generally immiscible in polyurethane, in general the larger the R_f group in the fluoroaliphatic group- containing compound used in this invention, the larger will the R group have to be in order for the compound to be partially miscible in the polyurethane. Suitable R groups include, for example, ~C₁₈H₃₇

-[CH(CH₃)CH₂]_nH -[CH(CH₃)CH₂]_n- -[CH₂CH(CH₃)]_nH

-[CH₂CH(CH₃)]_n- -[CH(C₂H₅)CH₂]_nH -[CH(C₂H₅)CH₂]_n-

^"C18^H36~ "^C16^H32"

~^C14^H28~ -C₆H₄- -C₆H CH₂- -C₆H₄CH₂CH₂- -C₆H₂(CH₃)₂-

A preferred class of the fluoroaliphatic group- containing compounds useful in this invention are those where R comprises one or more oxazolidinone moieties. See, for example, the fluoroaliphatic group-containing compounds described in U.S. Pat. No. 5,025,052 (Crater et al.) , which description is incorporated herein by reference. Suitable R groups include, for example:

In Formula I, Q is a linking group and Z is 0 or 1. Note that when z is 0, Q is absent and R_f and R are joined by a covalent bond. Q and R together preferably contain from 5 to 35 carbon atoms. The linking group, Q, can comprise a hetero atom-containing group, e.g., a group containing -S-, -0-, and or -NCH₃-, or a combination of such groups, for example -CO-, -C0NR-, -S0₂-, S0₂N(CH₃)-, -C₃H₅C1-, or -OC₂H₄-. Q is free of groups reactive with polyisocyanate or polyol.

In formula I, the subscript x is 1 to about 4. In preparing polyurethanes according to the method of this invention, polyisocyanate and polyol can be reacted, in the presence of or in admixture with the fluoroaliphatic group-containing compound, in a conventional polyurethane polymerization manner in the presence of catalyst.

Polyols useful in the present invention include diols of a polyester, polyether such as poly(oxyalkylene) , silicone diols, or a combination thereof, such as those described for example in U.S. Pat. No. 4,948,859 (Echols et al.).

Polyisocyanates useful in the present invention include conventional aliphatic or aromatic polyisocyanates used in making polyurethanes, for example, toluene diisocyanate. Other useful polyisocyanates which can be used are hexamethylene-1,6,-diisocyanate, diphenylmethane-4,4'-diisocyanate, meta- or para-phenylene diisocyanate, and 1,5-naphthalene diisocyanate. Polymeric polyisocyanates can also be used, such as methylene bis(4-phenyl)isoσyanate and polyaryl polyisocyanate. A list of useful polyisocyanates is found in "Encyclopedia of Chemical Technology," by Kirk-Othmer, 2nd Ed., Vol. 12, pp 46-47, Interscience Pub., (1967), and in Appendix A of Polyurethanes: Chemistry & Technology, Part I, by Saunders and Frisch, Interscience Publishers, (1962) . See also the description of useful polyisocyanates described in the Echols et al. patent supra.

Objects and advantages of this invention are illustrated in the Examples below.

EXAMPLES

Fluoroaliphatic group-containing compounds were incorporated into a reactive polyurethane precursor mixture of polyol and polyisocyanate during reactive extrusion polymerization of the mixture. The resulting polyurethanes were shaped into pellets and films which were tested for non-blocking and other properties.

Example 1

Four-hundred-fifty grams of N-methyl-perfluorooctanesulfonamide was placed in a two liter three-necked round-bottom flask and heated to 80°C. , and then 101 grams of epichlorohydrin was added, followed by 91 grams of methanol. The temperature was reduced to 65°C after which a 25 weight percent solution of sodium methoxide in methanol was slowly added, keeping the temperature below 70°C. After the addition was complete, the reaction was stirred at 65°C overnight. Water aspirator vacuum was applied and the excess methanol and epichlorohydrin were removed. 450 grams of water was then added to the flask with stirring at 65°C to wash the product. The water was decanted after allowing the product to settle. This washing step was repeated a second time. Vacuum was applied at 20 mm Hg and the temperature of the flask was raised to 90°C to remove volatile materials, leaving behind the product, N-methyl-N-glycidyl-perfluorooctanesulfonamide. The fluorochemical oxazolidinone of the formula

was prepared from the N-methyl-N-glycidyl-perfluoro¬ octanesulfonamide and octadecylisocyanate using the method described in U.S. Pat. No. 5,025,052 (Crater et al.) .

One-half percent by weight of the powdered fluorochemical oxazolidinone was dispersed in liquid polyol, Tetrathene Resin # 1000 (commercially available from K.J. Quinn and Company) , using a high velocity stirring bar. The resulting mixture was fed into the feedport of a counter-rotating twin screw extruder (a 34 mm Liestritz extruder Model # ISM 34GI) running at 75 rpm. The stirring was kept constant during the extrusion. Simultaneously, liquid toluene diisocyanate was fed to the feedport of the twin screw extruder. Both liquid feedstreams were fed at a flow rate of 5.5 kg/hr. The twin screw extruder was kept at a uniform temperature of 200°C. The effluent of the twin screw extruder was fed to a 5.3 cc/rev. gear pump, available from Zenith

Corporation, and subsequently formed into a fiber, which was passed through a 6 foot (1.8 m) water bath and pelletized using a pelletizer available as Tonea Model #304 from Berlyn Corporation. Some of the pellets were extruded into film using a standard extrusion process. The pellets were fed into a 1-1/4" (3.175 cm) single screw extruder available as Model # KPS-125 from Killion Corp. The four zones in the extruder were set to 149, 204, 232 and 232°C, respectively. A 25.4 cm wide single manifold die was used, with a temperature of 232°C. The die is available from Extrusion Dies Incorporated. The extruded film was cast onto a chill roll at 16°C and subsequently wound onto a 3" (7.62 cm) core. The film was extruded at 5 mils (127 microns) thickness and 50 yards (45.7 meters) were collected.

Example 2

Pellets and film were prepared as in Example 1 except 1.0 wt% of the fluorochemical oxazolidinone of Example 1 was used instead of 0.5 wt.%.

Comparative Example Cl

Pellets and film were prepared as in Example 1 except no fluorochemical was used.

Inspection of the pelletized polyurethane materials generated in Examples 1 and 2 showed that the fluorochemical greatly improved the bulk flow properties of the polyurethane pellets. The pellets of Examples 1 and 2 could easily be separated and they freely and readily flowed into a pile when poured on a flat surface. In contrast, the pellets generated in Comparative Example Cl adhered aggressively to each other, clumped and formed an agglomerated mass.

Example 3

Pellets and film were prepared as in Example 1, except that there was used as the fluoroaliphatic group- containing compound 0.5 wt.% of the fluorochemical acrylate of structure C₈F₁₇S0₂N(CH₂CH₃)CH₂CH₂0₂CCH=CH₂, (prepared as in Example 3 of U.S. Pat. No. 2,803,615 using acrylic acid instead of methyl methacrylate) which was introduced in the feed-port of the twin-screw extruder with a powder weigh-feeder available from Accurate Company. Example 4

Pellets and film were prepared as in Example 3 except using 0.5 wt.% of the fluorochemical oxazolidinone of same structure as in Example 1 except that the fluorochemical oxazolidinone was prepared from

C₈F₁₇S0₂N(CH₃)CH₂CH(OH)CH₂Cl and octadecylisocyanate, as described in U.S. Pat. No. 5,025,052 (Crater et al.).

Example 5 Pellets and film were prepared as in Example 3 except using 0.5 wt.% of the fluorochemical oxazolidinone of structure

which was prepared as

at. No. 5,025,052 (Example 1).

Example 6

Pellets and film were prepared as in Example 3 except using 0.5% of the fluorochemical compound of structure C₈F₁₇S0₂N(CH₃)CH₂CH₂0₂CCH=CH₂, prepared as described in U.S. Pat No. 2,803,615 (Ahlbrecht et al.).

Comparative Example C2

Pellets and film were prepared as in Example 3 except that the fluorochemical used was 0.5 wt.% of the reactive fluoroaliphatic acrylate of structure C_nF_2n+1CH₂CH₂0₂CCH=CH₂, where n is 6 to 12, and which is commercially available from DuPont as Zonyl™ TA-N.

Comparative Example C3

Pellets and film were prepared as in Example 3 except that the fluorochemical used was 0.5 wt.% of the immiscible perfluoroaliphatic compound polytetrafluoroethylene resin #203, commercially available from Scientific Polymer Products, Inc. , Ontario, N.Y.

Comparative Example C4

Pellets and film were prepared as in Example 3 except that the fluorochemical used was 0.5 wt.% of an immiscible, perfluoroaliphatic, high molecular weight fluorocarbon elastomer composition of 3 wt.% calcium carbonate and 97 wt.% elastomer (commercially available from 3M Company as FLUOREL™ 2211) .

Pellets of Examples 3-6 exhibited the same excellent free-flowing flow properties as the pellets of Examples 1 and 2. In contrast, pellets of Comparative Examples C2-C4 tended to adhere to one another and formed an agglomerated mass.

The amounts of fluorine at the surfaces of the above-described films were measured using electron spectroscopy for chemical analysis (ESCA) . The bulk fluorine contents of the films were also measured. The surface energy of the film samples were measured using the contact-angle method set forth in "Estimation of the Surface Free Energy of Polymers", Journal of Applied Polymer Science. Vol. 13, pp 174-177 (1969) using Lubinol™ mineral oil (commercially available from Purepac Pharmaceutical Co., a division of Kalipharma, Inc.) and glycerin. The results are listed in Table 1.

The films were also characterized in terms of their non-blocking property by measurement of the force necessary to unwind a roll of film ("unwind force") , and the force needed to peel a pressure sensitive adhesive tape, 3M Co. tape #STA-115, from the surface of the film ("peel force") .

For the unwind force test, 5.08 cm wide film samples were wound onto 3 inch (7.6 cm) diameter cores. The unwind test then consisted of mounting a 50 yard (45.7 meters) long roll of the film onto the stationary arm of a peel tester platen (model SP-102C-3M90, commercially available from Instrumentors Inc. , Strongsville Ohio) and connecting the free edge of the film to the force transducer on the peel tester base. The platen was then moved away from the base at a set speed. The roll of film was allowed to freely rotate on a low friction set of bearings. The force required to unwind the film from the roll was then measured and recorded according to the procedure described by the peel tester manual published by Instrumentors, Inc., Copyright 1987. The unwind force data obtained are shown in Table 2.

For the peel force test, a 1-inch (2.54 cm) wide strip of adhesive tape is adhered to the outside portion of the film sample under the weight of a 4.5 Lb (2Kg) hard rubber roller, 2 passes in each direction. The tape is then peeled from the film at 180° from the surface at a rate of 30.5 cm/min. The peel force data obtained are shown in Table 2.

TABLE 1

*unable to measure due to poor film quality.

The data in Table 1 show that the films of this invention, namely those of Examples 1-6, had lower surface energy than the films of Comparative Examples C1-C4.

The data in Table 2 show that the films of Examples 1-6 had significantly improved anti-blocking properties as seen by the low unwind force of the film; these films also had low peel force required to release a pressure sensitive adhesive tape from the polyurethane film. The films of Comparative Examples Cl, C3, and C4 had poor anti-blocking properties as seen by the high unwind force. The film of Comparative Example C2 could not be tested due to the presence of gels in the extruded film which resulted in holes in the film. The presence of the gels shows that an additional reaction has occurred.

The fluoroaliphatic group-containing compounds useful in this invention are those which are partially miscible with the resulting polyurethane at temperatures under which the polyurethane preparation or processing actually occurs. Partial miscibility was demonstrated in a conventional manner by measuring cloud point temperatures and by observing the phase volumes of fluorochemical-polyurethane mixtures as a function of temperature and composition.

The cloud points and phase volume changes of mixtures of polyurethanes and fluorochemicals were measured with an Olympus BH2 microscope fitted with a Mettler FP82HT hot stage attachment with a Mettler FP80HT Central Processor controller allowing for fine control of the temperature from room temperature to 375°C. All observations were made at 50X or 100X magnification. Mixtures were prepared containing the fluorochemical compounds used in Examples 1 and 5, and used in Comparative Examples C3 and C4. Mixtures were prepared by cryogrinding the fluorochemical free polyurethane resin of Comparative Example Cl in a Spex Freezer/Mill at liquid nitrogen temperature to form a powder and mixing the resulting powder with the various fluorochemicals in a flat glass capillary obtained from Vitrodynamics Inc. Charged capillaries were dried under vacuum, sealed with a flame and the charge allowed to mix at high temperatures (200-250°C) for approximately 1 hour before observation in the microscope hot stage. The microslide samples were short enough to be completely contained within the hot stage to prevent temperature gradient effects within the sample. Cloud points were determined by lowering the temperature (for miscible samples) at 10°C per minute and observing the temperature at which phase separation occurs. For partially miscible and immiscible samples, phase volume changes were observed while cycling the temperatures up and down over the range of interest. Results are shown in Table 3.

The mixture containing the fluorochemical of Example 1 showed partial miscibility as observed by large changes in phase volumes as a function of temperature. At high temperature, complete miscibility was achieved as the phase volume of the fluorochemical-rich phase became zero. Samples prepared with lower weight % of fluorochemical exhibited complete miscibility at lower temperatures. At lower fluorochemical levels, for example, 0.5 to 1.5%, phase separation will occur at lower temperatures, giving rise to a state of partial miscibility. This partial miscibility is an important requirement of the fluorochemical-polyurethane system.

The mixture containing the fluorochemical used in Example 5 had the extent of miscibility significantly reduced compared to the mixture containing the fluorochemical of Example 1, at a given temperature and concentration, as seen by cloud points which are much higher in temperature. Indeed, complete miscibility was not achieved with above 12.5% by weight fluorochemical at any temperature less than 325°C (a practical limit on the temperature due to degradation of the mixture as seen by darkening of the mixture) . However, partial miscibility was observed as manifested by the change in phase volumes. As the temperature was increased, the fluorochemical-rich phase decreased in volume, and as the temperature was lowered, the fluorochemical rich phase increased in volume. Below 12.5% by weight of fluorochemical, complete miscibility was achieved at experimentally accessible temperatures.

The mixture containing the fluorochemical used in Comparative Example C3 (polytetrafluoroethylene) and the mixture containing the fluorochemical used in Comparative Example C4 (FLUOREL™ 2211) , showed no miscibility or partial miscibility. No changes in phase volume were observed, even at temperatures as high as 325°C. This lack of phase volume changes shows that these fluorochemicals are not measurably miscible with the polyurethane, even at elevated temperatures. Table 3

Mixture

Containing Amount of Phase-Volume

Fluorochemical Fluorochemical Cloud Point Changes

Used in Exam le ( eiσht %) CO Observed

1

5

C3

C4

Various modifications and alterations of this invention will be apparent to those skilled in the art without departing from the scope and spirit of this invention and this invention should not be restricted to that set forth herein for illustrative purposes.

Claims

CLAIMS :

1. A method for the preparation of a polyurethane composition comprising polymerizing a mixture comprising polyisocyanate, polyol, and luoroaliphatic group-containing compound which is free of moieties reactive with either of said polyisocyanate or polyol and which is partially miscible with the resulting polyurethane.

2. A method for the preparation of shaped articles comprising the method of claim 1 and further comprising shaping the resulting polyurethane composition.

3. The method of claim 2 wherein said polymerizing and shaping are carried out by reaction injection molding, or by reactive extrusion.

4. The method of claim 1 or claim 2 wherein said fluoroaliphatic group-containing compound and polyol are mixed together prior to said polymerizing.

5. The method of claim 1 or claim 2 wherein said fluoroaliphatic group-containing compound is fed as a powder or liquid into a twin screw extruder independent of the feeding thereto of the polyisocyanate or the polyol.

6. A polyurethane precursor mixture comprising polyisocyanate, polyol, and fluoroaliphatic group-containing compound which is free of moieties reactive with either of said polyisocyanate or polyol and which is partially miscible with the polyurethane product resulting upon polymerization of said precursor composition.

7. The method of claims 1 or 2 or the composition of claim 6 wherein said fluoroaliphatic group-containing compound is represented by the formula

wherein R_f is a fluoroaliphatic group of at least 4 fully- fluorinated carbon atoms, y is 1 or 2, Q is a linking group, z is 0 or 1, x is from 1 to 4, R is an organic group having 2 to 35 carbon atoms, and the sum of carbon atoms in R and Q is 5 to 35.

8. The methods of claim 7, or the composition of claim 7 wherein said R comprises one or more 2- oxazolidinone moieties.

9. The method of claims 1 or 2, or the composition of claim 14 wherein said fluoroaliphatic group-containing compound is present in an amount sufficient to impart desired low surface energy to surfaces of shaped articles made from said polyurethane product.

10. The method of claim 1 or 2, or the composition of claim 6 wherein said fluoroaliphatic group-containing compound is present in from 0.05 to 10% by weight of said mixture.