Impact Resistant Blends of Thermoplastic Polyamides and Modified Block Copolymers

Thermoplastic polyamides, such as nylon 6,6, are a class of materials which possess a good balance of properties comprising strength and stiffness which make them useful as structural materials. However, for a particular application, a thermoplastic polyamide may not offer the combination of properties desired, and therefore, means to correct this deficiency are of interest.

One major deficiency of thermoplastic polyamides is their poor resistance to impact, especially when dry. A particularly appealing route to achieving improved impact resistance in a thermoplastic is by blending it with another polymer. It is well known that stiff plastics can often be impact modified by addition of an immiscible low modulus rubber. However, in general, physical blending of polymers has not been a successful route to toughen thermoplastic polyamides. This is due to the poor adhesion immiscible polymers typically exhibit with each other. As a result, interfaces between blend component domains represent areas of severe weaknesses, providing natural flows which result in facile mechanical failure.

It is well known to those skilled in the art that hydrogenated block copolymers of styrene and butadiene possess many of the properties which are required for impact modification of plastics. They have a low glass transition, low modulus rubber phase which is required for toughening. Because they contain little unsaturation, they can be blended with high temperature processing temperature plastics without degrading. In addition, they are unique compared to other rubbers in that they contain blocks which are micorphase separated over application and processing conditions. This microphase separation results in physical crosslinking, causing elasticity in the solid and molten states. Such an internal strength mechanism is often required to achieve toughness in the application of plastic impact modification. In addition, melt elasticity of the block copolymer during processing can, under the right conditions, enable it to be finely dispersed with another polymer in a stable interpenetrating co-continuous phase structure. A stable, fine dispersion is desirable in a rubber modified plastic.

Proof that hydrogenated block copolymers of styrene and butadiene are useful plastic impact modifiers can be seen in their widespread use for modifying polyolefins and polystyrene. For these blends, interfacial adhesion is great enough to achieve toughening.

Although the hydrogenated block copolymers do have many of the characteristics required for plastic impact modification, they are deficient in modifying many materials which are dissimilar in structure to styrene or hydrogenated butadiene. Blends of the hydrogenated block copolymer with dissimilar plastics are often not tough due to a lack of interfacial adhesion.

A route to achieve interfacial adhesion between the hydrogenated block copolymer and a dissimilar material is by chemically attaching to the block copolymer functional moieties which interact with the dissimilar material. Such interactions include chemical reaction, hydrogen bonding, and dipole-dipole interactions.

Epstein in U.S. Pat. No. 4,174,358 discloses a broad range of low modulus polyamide modifiers. However, this patent does not disclose or suggest the use of modified block copolymers of styrene and butadiene.

It has been previously proposed to increase the impact strength of polyamides by addition of a modified block copolymer. Hergenrother et al in U.S. Pat. No. 4,427,828 and Shiraki et al in International Kokai Application No. W083/00492 disclose blends of thermoplastic polyamide with a modified block copolymer. Specifically, the block copolymer is a partially hydrogenated monovinyl aryl/conjugated diene to which is attached anhydride moieites by the so-called "ENE reaction". Such modified block copolymers contain functional moieties only in the diene block, unlike the present invention. In addition, such modified block copolymers are deficient because the ENE reaction depends on unsaturation in the base polymer for reaction sites. A reasonable amount of residual unsatauration must be present in order to obtain an advantageous degree of functional moeities onto the base polymer. Since the ENE reaction cannot be carried out so that all double bonds on the base polymer are scavenged, the result of such a process is a modified block copolymer which contains too high a level of unsatauration for successful impact modification of high processing temperature thermoplastic polyamides.

The `ENE` process as described in the prior art results in a modified polymer product which is substituted at a position on the polymer backbone which is allylic to the double bond. The reaction can be shown for maleic anhydride as follows: ##STR1## wherein (a) represents addition across a double bond in the main chain of the base polymer and (b) represents addition across a double bond occuring in a side chain. After addition and isomerization the substitution is positioned on a carbon allylic to the double bond.

The allylically substituted polymers are prone to thermal degradation due to their thermal instability. It is known in the art that allylic substituents can undergo what has been referred to as a retro-ENE reaction, see B. C. Trivedi, B. M. Culbertson, Maleic Anhydride, (Plenum Press, New York, 1982) pp. 172-173.

Further, because the ENE reaction requires a reasonable amount of unsaturation in the precursor base polymer, as discussed previously, the resulting functionalized copolymer product will have a significant amount of residual unsaturation and will be inherently unstable to oxidation.

According to the present invention, there is provided an impact resistant blend of a thermoplastic polyamide and a thermally stable modified selectively hydrogenated high 1,2 content monovinyl aromatic/conjugated diene block copolymer wherein at least one functional group is grafted to the block copolymer primarily in the vinyl aromatic block. Examples of such modified block copolymers are described in U.S. patent application Ser. No. 766,217, filed Aug. 16, 1985, which is incorporated herein by reference. Said patent application describes the preparation of modified block copolymers by metallation, a process which does not require a base polymer with an undesirably high level of residual unsaturation.

More particularly there is provided an impact resistant polymeric composition comprising

(a) from 50 to 97 percent by weight of a polamide having a number average molecular weight of a least 5000; and

(b) from 3 to 50 percent by weight of a functionalized selectively hydrogenated block copolymer of the formula B.sub.n (AB).sub.o A.sub.p where n=0,1, o=1,2 . . . ; p=0,1 to which has been grafted at least one electrophilic graftable molecule or electrophile wherein substantially all of said graftable molecules are grafted to the block copolymer in the vinylarene block.

The polyamide matrix resin of the toughened compositions of this invention is well known in the art and embraces those semi-crystalline and amorphous resins having a molecular weight of at least 5000 and commonly referred to as nylons. Suitable polyamides include those described in U.S. Pat. Nos. 2,071,250; 2,071,251; 2,130,523; 2,130,948; 2,241,322; 2,312,966; 2,512,606; and 3,393,210. The polyamide resin can be produced by condensation of equimolar amounts of a saturated dicarboxylic acid containing from 4 to 12 carbon atoms with a diamine, in which the diamine contains from 4 to 14 carbon atoms. Excess diamine can be employed to provide an excess of amine end groups over carboxyl end groups in the polyamide. Examples of polyamides include polyhexamethylene adipamide (nylon 66), polyhexamethylene azelaamide (nylon 69), polyhexamethylene sebacamide (nylon 610), and polyhexamethylene dodecanoamide (nylon 612), the polyamide produced by ring opening of lactams, i.e., polycaprolactam, polylauric lactam, poly-11-aminoundecanoic acid, bis(paraaminocyclohexyl) methane dodecanoamide. It is also possible to use in this invention polyamides prepared by the copolymerization of two of the above polymers or terpolymerization of the above polymers or their components, e.g., for example, an adipic isophthalic acid hexamethylene diamine copolymer. Preferably the polyamides are linear with a melting point in excess of 200.degree. C. As great as 99 percent by weight of the composition can be composed of polyamide; however, preferred compositions contain from 60 to 99 percent, and more narrowly 80 to 95 percent, by weight of polyamide.

The modified block copolymers according to the present invention are grafted or substituted in the vinylarene block as shown in the exemplary reactions given below: ##STR2##

The structure of the substituted block copolymer specifically determined by the location of the functionality on the polymer backbone in the vinylarene block gives the block copolymer a substantially greater degree of thermal stability.

Block copolymers of conjugated dienes and vinyl aromatic hydrocarbons which may be utilized include any of those which exhibit elastomeric properties and those which have 1,2-microstructure contents prior to hydrogenation of from about 7% to about 100%. Such block copolymers may be multiblock copolymers of varying structures containing various ratios of conjugated dienes to vinyl aromatic hydrocarbons including those containing up to about 60 percent by weight of vinyl aromatic hydrocarbon. Thus, multiblock copolymers may be utilized which are linear or radial symmetric or asymmetric and which have structures represented by the formulae A-B, A-B-A, A-B-A-B, B-A, B-A-B, B-A-B-A, (AB).sub. 0,1,2 . . . BA and the like wherein A is a polymer block of a vinyl aromatic hydrocarbon or a conjugated diene/vinyl aromatic hydrocarbon tapered copolymer block and B is a polymer block of a conjugated diene.

The block copolymers may be produced by any well known block polymerization or copolymerization procedures including the well known sequential addition of monomer techniques, incremental addition of monomer technique or coupling technique as illustrated in, for example, U.S. Pat. Nos. 3,251,905; 3,390,207; 2.598,887 and 4,219,627. As is well known in the block copolymer art, tapered copolymer blocks can be incorporated in the multiblock copolymer by copolymerizing a mixture of conjugated diene and vinyl aromatic hydrocarbon monomers utilizing the difference in their copolymerization reactivity rates. Various patents describe the preparation of multiblock copolymers containing tapered copolymer blocks including U.S. Pat. Nos. 3,251,905; 3,265,765; 3,639,521 and 4,208,356 the disclosures of which are incorporated herein by reference.

Conjugated dienes which may be utilized to prepare the polymers and copolymers are those having from 4 to 8 carbon atoms and include 1,3-butadiene, 2-methyl-1,3-butadiene (isoprene), 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, 1,3-hexadiene, and the like. Mixtures of such conjugated dienes may also be used. The preferred conjugated diene is 1,3-butadiene.

Vinyl aromatic hydrocarbons which may be utilized to prepare copolymers include styrene, o-methylstyrene, p-methylstyrene, p-tert-butylstyrene, 1,3-dimethylstyrene, alpha-methylstyrene, vinylnaphthalene, vinylanthracene and the like. The preferred vinyl aromatic hydrocarbon is styrene.

It should be observed that the above-described polymers and copolymers may, if desired, be readily prepared by the methods set forth above. However, since many of these polymers and copolymers are commercially available, it is usually preferred to employ the commercially available polymer as this serves to reduce the number of processing steps involved in the overall process. The hydrogenation of these polymers and copolymers may be carried out by a variety of well established processes including hydrogenation in the presence of such catalysts as Raney Nickel, noble metals such as platinum, palladium and the like and soluble transition metal catalysts. Suitable hydrogenation processes which can be used are ones wherein the diene-containing polymer or copolymer is dissolved in an inert hydrocarbon diluent such as cyclohexane and hydrogenated by reaction with hydrogen in the presence of a soluble hydrogenation catalyst. Such processes are disclosed in U.S. Pat. Nos. 3,113,986 and 4,226,952, the disclosures of which are incorporated herein by reference. The polymers and copolymers are hydrogenated in such a manner as to produce hydrogenated polymers and copolymers having a residual unsaturation content in the polydiene block of from about 0.5 to about 20 percent of their original unsaturation content prior to hydrogenation.

In general, any materials having the ability to react with the base polymer, are operable for the purposes of this invention.

In order to incorporate functional groups into the base polymer, monomers capable of reacting with the base polymer are necessary. Monomers may be polymerizable or nonpolymerizable, however, preferred monomers are nonpolymerizable or slowly polymerizing.

The class of preferred electrophiles which will form graft polymers within the scope of the present invention include reactants from the following groups carbon dioxide, ethylene oxide, aldehydes, ketones, carboxylic acid salts, their esters and halides, epoxides, sulfur, boron alkoxides, isocyanates and various silicon compounds.

These electrophiles may contain appended functional groups as in the case of N,N-dimethyl-p-amino benzaldehyde where the amine is an appended functional group and the aldehyde is the reactive electrophile. Alternatively, the electrophile may react to become the functional site itself; as an example, carbon dioxide (electrophile) reacts with the metalated polymer to form a carboxylate functional group. By these routes, polymers could be prepared containing grafted sites selected from one or more of the following groups of functionality type carboxylic acids, their salts and esters, ketones, alcohols and alkoxides, amines, amides, thiols, borates, and functional groups containing a silicon atom.

These functionalities can be subsequently reacted with other modifying materials to produce new functional groups. For example, the grafted carboxylic acid described above could be suitably modified by esterifying the resulting acid groups in the graft by appropriate reaction with hydroxy-containing compounds of varying carbon atom lengths. In some cases, the reaction could take place simultaneously with the grafting process but in most examples it would be practiced in subsequent post modification reaction.

The grafted polymer will usually contain from 0.02 to 20, preferably 0.1 to 10, and most preferably 0.2 to 5 weight percent of grafted portion.

The block copolymers, as modified, can still be used for any purpose for which an unmodified material (base polymer) was formerly used. That is, they can be used for adhesives and sealants, or compounded and extruded and molded in any convenient manner.

The polymers may be prepared by any convenient manner one of which is described in copending U.S. application Ser. No. 766,622, filed Aug. 19, 1985, now abandoned, which is herein incorporated by reference.

An example of a method to incorporate functional groups into the base polymer primarily in the vinylarene block is metalation.

Metalation is carried out by means of a complex formed by the combination of a lithium component which can be represented by R'(Li).sub.x with a polar metalation promoter. The polar compound and the lithium component can be added separately or can be premixed or pre-reacted to form an adduct prior to addition to the solution of the hydrogenated copolymer. In the compounds represented by R'(Li).sub.x`, the R' is usually a saturated hydrocarbon radical of any length whatsoever, but ordinarily containing up to 20 carbon atoms, and can be an aromatic radical such as phenyl, napthyl, tolyl, 2-methylnaphthyl, etc., or a saturated cyclic hydrocarbon radical of e.g. 5 to 7 carbon atoms, a mono-unsaturated cyclic hydrocarbon radical of 5 to 7 carbon atoms, an unconjugated, unsaturated aliphatic hydrocarbon radical of 1 to 20 carbon atoms, or an alkyllithium having one or more aromatic groups on the alkyl group, the alkyl group containing 1 to 20 carbon atoms. In the formula, R'(Li).sub.x x is an integer of 1 to 3. Representative species include, for example: Methyllithium, isoporpyllithium, sec-butyllithium, n-butyllithium, t-butyllithium, n-dodecyllithium, 1,4-dilithiobutane, 1,3,5-trilithiopentane, and the like. The lithium alkyls must be more basic than the product metalated alkyl. Of course, other alkali metal or alkaline earth metal alkyls could be used but the lithium alkyls are preferred due to their ready commercial availability. In a similar way, metal hydrides could be employed as the metalation reagent but the hydrides have only limited solubility in the appropriate solvents. Therefore, the metal alkyls are preferred and their greater solubility which makes them easier to process.

Lithium componds alone usually metalate copolymers containing aromatic and olefinic functional groups with considerable difficulty and under high temperatures which may tend to degrade the copolymer. However, in the presence of tertiary diamines and bridgehead monoamines, metalation proceeds rapidly and smoothly. Some lithium compounds can be used alone effectively, notably the menthyllithium types.

It has been shown that the metalation occurs at a carbon to which an aromatic group is attached, or in an aromatic group, or in more than one of these positions. In any event, it has been shown that a very large number of lithium atoms are positioned variously along the polymer chain, attached to internal carbon atoms away from the polymer terminal carbon atoms, either along the backbone of the polymer or on groups pendant therefrom, or both, in a manner depending upon the distribution of reactive or lithiatable positions. This distinguishes the lithiated copolymer from simple terminally reactive polymers prepared by using a lithium or even a polylithium initiator in polymerization thus limiting the number and the location of the positions available for subsequent attachment. With the metalation procedure described herein, the extent of the lithiation will depend upon the amount of metalating agent used and/or the groups available for metalation. The use of a more basic lithium alkyl such as tert-butyllithium alkyl may not require the use of a polar metallation promoter.

The polar compound promoters include a variety of tertiary amines, bridgehead amines, ethers, and metal alkoxides.

The tertiary amines useful in the metalation step have three saturated aliphatic hydrocarbon groups attached to each nitrogen and include, for example:

(a) Chelating tertiary diamines, preferably those of the formula (R.sup.2).sub.2 N--C.sub.y H.sub.2y ----N(R.sup.2).sub.2 in which each R.sup.2 can be the same or different straight- or branched-chain alkyl group of any chain length containing up to 20 carbon atoms or more all of which are included herein and y can be any whole number from 2 to 10, and particularly the ethylene diamines in which all alkyl substituents are the same. These include, for example: tetramethylethylenediamine, tetraethylethylenediamine, tetradecylenediamine, tetraoctylhexyienediamine, tetra-(mixed alkyl) ethylene diamines, and the like.

(b) Cyclic diamines can be used, such as, for example, the N,N,N',N'-tetraalkyl 1,2-diamino cyclohexanes, the N,N,N',N'-tetraalkyl 1,4-diamino cyclohexanes, N,N'-dimethylpiperazine, and the like.

(c) The useful bridgehead diamines include, for example, sparteine, triethylenediamine, and the like.

Tertiary monamines such as triethylenediamine are generally not as effective in the lithiation reaction. However, bridgehead monoamines such as 1-azabicyclo[2.2.2] octane and its substituted homologs are effective.

Ethers and the alkali metal alkozides are presently less preferred than the chelating amines as activators for the metalation reaction due to somewhat lower levels of incorporation of functional group containing compounds onto the copolymer backbone in the subsequent grafting reaction.

In general, it is most desirable to carry out the lithiation reaction in an inert solvent such as saturated hydrocarbons. Aromatic solvents such as benzene are lithiatable and may interfere with the desired lithiation of the hydrogenated copolymer. The solvent/copolymer weight ratio which is convenient generally is in the range of about 5:1 to 20:1. Solvents such as chlorinated hydrocarbons, ketones, and alcohols, should not be used because they destroy the lithiating compound.

Polar metalation promotors may be present in an amount sufficient to enable metalation to occur, e.g. amounts between 0.01 and 100 or more preferably between 0.1 to about 10 equivalents per equivalent of lithium alkyl.

The equivalents of lithium employed for the desired amount of lithiation generally range from such as about 0.001-3 per vinyl arene unit in the copolymer, presently preferably about 0.01-1.0 equivalents per vinyl arene unit in the copolymer to be modified. The molar ratio of active lithium to the polar promoter can vary from such as 0.01 to 10.0. A preferred ratio is 0.5.

The amount of alkyl lithium employed can be expressed in terms of the Li/vinylarene molar ratio. This ratio may range from a value of 1 (one lithium alkyl per vinylarene unit) to as low as 1.times.10.sup.-3 (1 lithium alkyl per 1000 vinylarene units).

The process of lithiation can be carried out at temperatures in the range of such as about -70.degree. C. to +150.degree. C., presently preferably in the range of about 25.degree. C. to 60.degree. C., the upper temperatures being limited by the thermal stability of the lithium compounds. The lower temperatures are limited by considerations of production cost, the rate of reaction becoming unreasonably slow at low temperatures. The length of time necessary to complete the lithiation and subsequent reactions is largely dependent upon mixing conditions and temperature. Generally the time can range from a few seconds to about 72 hours, presently preferably from about 1 minute to 1 hour.

The next step in the process of preparing the modified block copolymer is the treatment of the lithiated hydrogenated copolymer, in solution, without quenching in any manner which would destroy the lithium sites, with a species capable of reacting with a lithium anion. These species must contain functional groups capable of undergoing nucleophilic attack by a lithium anion. Such species contain functional groups including but not limited to

The process also includes further chemistry on the modified block copolymer. For example, converting of a carboxylic acid salt containing modified block copolymer to the carboxylic acid form can be easily accomplished.

The toughened compositions of this invention can be prepared by melt blending, in a closed system, a polyamide and at least one modified block copolymer into a uniform mixture in a multi-screw extruder such as a Werner Pfleiderer extruder having generally 2-5 kneading blocks and at least one reverse pitch to generate high shear, or other conventional plasticating devices such as a Brabender, Banbury mill, or the like. Alternatively, the blends may be made by coprecipitation from solution, blending or by dry mixing together of the components followed by melt fabrication of the dry mixture by extrusion.

The modified polyamide resin may be prepared by melt-blending from about 50 percent to about 97 percent by weight preferably from about 70 percent to about 95 percent or more preferably 75 percent to about 90 percent of the polyamide, and from about 3 percent to about 50 percent by weight preferably from about 5 percent to about 30 percent or more preferably 10 percent to about 25 percent functionalized block copolymer.

The compostions of the invention may be modified by one or more conventional additives such as stablizers and inhibitors of oxidative, thermal, and ultraviolet light degradation; lubricants and mold release agents, colorants including dyes and pigments, fibrous and particulate fillers and reinforcements, nucleating agents, plasticizers, etc.

The stablizers can be incorporated into the composition at any stage in the preparation of the thermoplastic composition. Preferably the stabilizers are included early to preclude the initiation of degradation before the composition can be protected. Such stabilizers must be compatible with the composition.

The oxidative and thermal stabilizers useful in the materials of the present invention include those used in addition polymers generally. They include, for example, up to 1 percent by weight, based on the weight of polyamide of Group I metal halides, e.g., sodium, potassium, lithium with cuprous halides, e.g., chloride, bromide, iodide, hindered phenols, hydroquinones, and varieties of substituted members of those groups and combinations thereof.

The ultraviolet light stabilizers, e.g., up to 2.0 percent, based on the weight of polyamide, can also be those used in addition polymers generally. Examples of ultraviolet light stabilizers include various substituted resorcinols, salicylates, benzotriazoles, benzophenones, and the like.

Suitable lubricants and mold release agents, e.g., up to 1.0 percent, based on the weight of the composition, are stearic acid, stearic alcohol, stearamides, organic dyes such as nigrosine, etc., pigments, e.g., titanium dioxide, cadmium sulfide, cadmium sulfide selenide, phthalocyamines, ultramarine blue, carbon black, etc. up to 50 percent, based on the weight of the composition, of fibrous and particulate fillers and reinforcements, e.g., carbon fibers, glass fibers, amorphous silica, asbestos, calcium silicate, aluminum silicate, magnesium carbonate, kaolin, chalk, powdered quartz, mica, fildspar, etc.; nucleating agent, e.g., talc, calcium fluoride, sodium phenyl phosphinate, alumina, and finely divided polytetrafluoroethylene, etc.; plasticizers, up to about 20 percent, based on the weight of the composition, e.g., dioctyl phthalate, dibenzyl phthalate, butyl benzyl phthalate, hydrocarbon oils, N-normal butyl benzene sulfonamide, ortho and para toluene ethyl sulfonamide, etc. The colorants (dyes and pigments) can be present in an amount of up to about 5.0 percent by weight, based on the weight of the composition.

It is to be understood that in the specification and claims herein, unless otherwise indicated, when in connection with melt-blending, the amount of the polyamide or block copolymer is expressed in terms of percent by weight it is meant percent by weight based on the total amount of these materials which is employed in the melt-blending.

To assist those skilled in the art in the practice of this invention. the following Examples are set forth as illustrations, parts and percentages being by weight unless otherwise specifically noted. The molded bars were tested using the following test procedures in the dry-as-molded state:

Notched Izod toughness: at each end ASTM D-256-56

The base polymer used was a styrene-ethylene/butylene-styrene block copolymer which contained 29 wt % styrene and had a molecular weight of 66,000. 2270 gm of this polymer were dissolved in 15 gallons of cyclohexane. This mixture was placed in a 20 gallon stainless steel pressurized reaction vessel and pressurized to about 25 psi. 0.8 meq/gm polymer of tetramethylethylene diamine was then added to the vessel. A small amount, 0.5 ml of 1-1 diphenylethylene (an indicator), was then added to the reactor. Sec-butyllithium was then added incrementally until a yellow color was obtained, indicating the absence of impurities.

The reactor contents were then heated to 60.degree. C. Next, 0.4 meq/gm polymer of additional sec-butyllithium was added to the reactor. After 2 1/2 hours reaction time, the contents of the vessel were transferred to another vessel which contained a stirring mechanism. This second vessel contained 2-3 lbs of dry ice (solid CO.sub.2), 10 gallons of tetrahydrofuran, and 5 gallons of diethylether. The solution was stirred for 30 minutes. Next, 85 grams of acetic acid in an isopropanol solution was added to the reactor. This solution was stirred for 16 hours. The modified block was then recovered by steam stripping.

Infrared analysis of the polymer showed the presence of both bound carboxylic acid at 1690 cm.sup.-1 and bound lithium carboxylate salt at 1560-1600 cm.sup.-1. By colorimetric titration with 0.01N KOM in methanol using a phenothalein indicator, it was found that the level of bound acid was 0.3 wt % COOH. After repreated washings of the polymer with alcoholic hydrochloric acid, infrared showed that complete conversion of salt to acid took place. Titration of the washed polymer have a bound acid level of 0.4 wt % COOH.

The thermoplastic polyamide used in this example was a commercial nylon 6,6, Zytel 101, a molding grade obtained from Dupont. Prior to all processing steps, the nylon 6,6 and its blends were dried at 120.degree. C. for 4 hours under vacuum with a nitrogen purge.

Blends of nylon 6,6 with both unmodified and modified block copolymer were prepared in a 30 mm diameter corotating twin screw extruder. The blend components were premixed by tumbling in polyethylene bags, and then fed into the extruder. The extruder melt temperature profile varied from 270.degree. C. in the feed zone to 285.degree. C. at the die. A screw speed of 300 rpm was used. The extrudate was pelletized and injection molded into test specimens. The formulations and physical properties are shown in Table 1.

The above example shows that the compositions according to this invention exhibit an unexpected improvement in impact strength over the thermoplastic polyamide or blends of the thermoplastic polyamide with unmodified block copolymer.

The foregoing embodiments are intended to illustrate but not to limit the invention. Various modifications can be made in the invention without departing from the spirit and scope.