CA1070046A

CA1070046A - Graft copolymer in polyamide polyolefin blends

Info

Publication number: CA1070046A
Application number: CA239,623A
Authority: CA
Inventors: Howard W. Starkweather (Jr.)
Original assignee: EI Du Pont de Nemours and Co
Current assignee: EIDP Inc
Priority date: 1974-11-13
Filing date: 1975-11-12
Publication date: 1980-01-15
Also published as: DE2551023A1; DE2551023C2; FR2291252A1; IT1048705B; NL7513309A; GB1515936A; JPS5847421B2; NL176273C; CH606262A5; US3963799A; JPS5170254A; FR2291252B1; NL176273B

Abstract

AND CLAIMS

TITLE

Graft Copolymer in Polyamide Polyolefin Blends ABSTRACT OF THE DISCLOSURE
Polymeric blend of 60 to 90 parts by weight of a polyamide, e.g., polyhexamethylene adipamide or poly-caprolactam, and 40 to 10 parts by weight of polyethylene, characterized in that there is present in the blend 1.8 to 8.0 parts by weight of a thermoplastic graft co-polymer consisting essentially of a trunk copolymer derived from ethylene and a comonomer providing amine-reactive sites and polycaprolactam side chains linked to said reactive sites through amide or imide linkages. The modified blends are useful as injection molding resins, for wire jacketing, etc.

Description

~ 6 This invention relates to polymeric blencls and par~lcularly to blends of polyamldes and polyolefins - ~ontaining ~ minor portion of graft copol~er.
- Blends of polyamides and polyolefins such a5-pol~ethy'lene ~re kno~m. IJq S. Patent 39093,255 describes ~ process for preparing a blend wherein e~ch component is present in the amount of at 'least 5 percent by weight.
Th~ blends ~re disclosed as being useful as containers, e~g~g bottle or ~apping film9 and fibers. Blends of ~uodified polyethylene ~nd a polyamide are kno~m to make 'not melt coatings and transparent packaging materials ~s ~aught in U. S. Patent 39~4,403. The blends are said to be incompatible ir. the melt state but compatible ' ' as the melt cools and passes into the solid state. U~ S~
Patent 3,626,026 describes another blend of an ethylene i copolymer and a polyamide used as hot melt adhesive com~o~
sitions. The ethylene'copolymer contains vinyl acetate or ethyl acrylate~ The ethylene copolym~r is present in ~ to 9~ parts by weight and the polyamide in 5 to 50 part~ by Z~ ' weight. In one embodiment, improved properties are ac~ved by th~ addition of conditionin~ agents, e.g., low molecular weight polyethylenes, turpentine resins9 etc. None of th~
.
refer2~ces des~ribes the use of a minor amount of graft copo~ymer in the blend which materially aids in pe~it~ing the fine grain dispersi~n of a polyethylène component in a ' p~l~amideO '' . .. ... . . . . ................................. . . . .
" According to this invention, there is provided .
a pol~meric ~lend comprising 60 to gO parts by weight of a polyamide of polyhexamethylene adipamide, polycapro-lactam or copolymers thereof and 40 to lO parts by weight :

~ -2-.

. .

o~ polyethylene characterized ln that there ia pre~ent in the blend 1.8 to 8~o part~ by weight o~ a thermoplastLc graft c~polymer consi~ting essentially o~ a trunk co-polymer derived ~rom ethylene and a comonomer providing amlne-reactive sites, and polycaprolactam side chain~
having an average degree of polymerization o~ about 5 to 30 linked to the reactive ~tes through amide or ~mide linkages. ~n embodiment~ the gra~t copolymer ha two DTA
melt~ng point~ one at 80 to 115C. and the other at at least 165C.
rrhe polymer blend compri~e~ three prlmary c~mponents:
(1) a polyamide o~ po~yhe~amethylene adipamide, polycaprolactam or copolymers thereof J
60 to 90 parts ~y weight~ pre~erably 70 to 80 parts ~y weight;
: (2) polyethylene, 40 to 10 parts by weightJ
preferably 30 to 20 par~a by wei~ht; and (3) a thermopla~tic gra~t copolymer, as de~ined a~ove, 1~8 to 8~o parts by weightO
The graft copolymers are bleieved to reduce the interfacial ; ~rce energy of the blend o~ poluamide and polyethylene, thu~ perm~tt~ng a uni~o~m ~ine grain di~persion o~ ~.
polyethy7ene in the poly~mide. While not deslrlng to be limited to any theo~, it i~ be~ieved tha~ the graPt c~polymer~ de~ined here~n not ~nly reduce the inter~acial ~ree energy but anchor khem~elve~ in both pha~es through cory~tallizat~on and thus ~unction as an adhe~ive.
m~s i~ important because in a ~olid, unlike ~ llquid emul~ion, an in~er~ace onc~ broken cannot be r~ormed : -3-without melting.
me poly~nide u~ed :Ln the blend ~s ei ther poly-hexamethylene adip~mide or polycaprol.aetam s~hieh ar~
commercially availa~le. For example~ Zyte~ 101~ a nylon (66) resin sold by E. I. du Pont de Nemours and CQmpany~
Inc~ or Pla~ko ~ 8200, a n~lon (66~ resln ~old by Allled Chemical Corp, are useful as are reproces~ed PolYamide textile ~ibers. Copolymers of the pol~ra~des can be u~ed.
T~e polyethylene u~ed ln the blend can be hi.g,h densit~ polyethylene or low den~ty po~yethylene.
The polyethylene~ are generally commercial~y available;
one use~ul polyethylene is Alathon~ 7050 (density 0.95, melt index 6) a polyethylene res~n sold by E. I. du Pont de ~mour~ ~nd Company, Inc~ Another u~eflll commercial polyethylene includes: Alatho ~ 3B (den~ity 0.915, melt index 0.25) low den~lty polyethylene sold by ~. I. du Po~ de ~mours and Co~panyl Inc.
Surprislngly, it ha~ been ~ound that a blend havlng ~mproved properties is achieved when a minor amount, 1.8 to 8.o part~ by weight, pre~erably 2 to 5 parts by wel~ht, o~ a paxticular type thermopla~tic gra~t copolymer as de~ined herein is present in the blend. The gra~t copolymer con~ist~ e~sentially o~ a trunk copolymer derived ~rom ethylene and a comonomer providing amlne-reacti~e site~ and po~y~aprolactam ~lde chains having ~n average degree o~ polymerizat~on o~ about 5 to 30 l~ked to the reactlYe ~ite~ through amide or imide linkage~. In embodlment~ the gra~t copolymer has two DTA melting points on~ at 80 to 115C, a~d the other at at lea~t 165C. 7 pre~erably 175 to 200C. The gra~t c~pol~mer~ are more ~ul~ de~crib~d belawO

4i~i The graft copolymers can be prepared in various w~ys. The co~venient ways described herein can be identi~
: ~ie~l as (l) the acid chloride route~ for use with backbone cvpolymers having free carboxylic acid groups9 (2) the anhydride route, for use with ethylene/maleic anhydri~e and other anhydride-containing backbone copolymers, and (3~ the vicinal acid-ester. route~ for use with backbone copol~mers having monoester of vicinal dicarboxylic acld - substituents~
; lO ~ The acid chloride route in~olves initial conver-sion of the carboxyl groups of the backbone copolymer to . .
acid chloride ~roups by reaction with thionyl chloride, . . ~ the reaction being conducted in solution with a sol~ent such as toluene or ketrachloroethylene. The solution of polymeric polyacid chloride is agitated at 75-105 C. ~or ~0 to 60 minutes with a solution of the amine~ended polycaprolactam dissolved in an inert solvent such as hexamethylphosphoramide to create 9 .in a con~entional man~
ner~ amide 0 linkages between the trunk copolymer and the (-CNH-) si.de chain polyamides. An acid acceptor such as triethyl-amine or pyridine is usually used in the amide-fo~ing stagev The ra~io of acid chloride groups to ~mino end groups can be varied9 with the amino groups being in no more than stoichiometric amounts in relation to the acid chloride groups~ ~en less than the stoichiometric amount ' of polycaprolactam is used~it is desirable to add a.low molecular weight amine (e~g., n-hexyl~mine) or alcohol ; (e~g~ methanol) to react with the excess acid chloride groups in order to avoid ha~ing residual reactive or . ~ .

': ' ' ' '' '":
'. ~

~ ~ 7 0 ~ ~ ~

corrosive acid chloride groups in the graft copolymer.
With relatively large de~iciencies in the polycaprolactam reactant~ it is desirable to add any additional monomeric amine along with the oligomer during the grafting reaction.
~ith small deficiencies of polycaprolactam any additional amine may be employed after the grafting reaction with the polycaprolactam has been substantially completed.
- The anhydride route which is preferred involves simply heating together the trunk copolymer with car-10 boxylic anhydride groups, pr~ferably maleic anhydride, and the polycaprolactam in the molten state9 at a temperature in the range 175 to 250~C.9 preferably at abouk 225C~9 or in a solution at a temperature of about 100C~ to 105~C. In the melt the heating temperature is above the me]ting point of the trunk copolymer and the polycaprolactam. The time of reaction, which is dependent upon the temperature~ can vary from less than about 15 seconds to 60 minutes in ~he mel~ preferably 1 to 10 minutes, and from 15 seconds to five hours in solution, preferabIy 1 to 10 minutes. Reac-20 tion in the melt9 an especially preferred procedure~ can conveniently b~ carried out on a roll mill, in a melt extruder, or in internal mixers having convoluted rollers, sigma bladee7 etc., using a temperature that will give I ~short reaction time and as many passes as necessary to insure complete reaction~ The reaction-time may be limited by the speed of mixingO Completeness of reaction can be judged by the appearance o~ the product~ good clarity in the melt indicating essentially complete reaction. With a roll mill as the reactor, the trunk copolymer and poly-30 caprolactam can be premlxed or mixed during reaction on the ........ ..

mill~ and because of the exposure it may be desirable to include stabilizing agents such as inhibitors or antioxi dants, or to carry out the operation in a protective atmos-phere such as nitrogen. With an extruder as the reactor~
premixing is desirable. On the basis of IR analysis of the products, an interpretation of the course of the thermal reaction is that it may proceed through initial ~ormation Or amic acids to ultimate formation of amide or imide link-ages between the backbone copolymer and the polyamide side lo chains, eOg.~:

t , + ~2n- ~ ¦ ~ G~ ~ N ~ H20 ~
The amount of amino polycaprolactam used can vary from a stoichiometrical deficiency to an equi~alent amount, ; - depending upon the extent of side chain substitution d~sired on the graft copolymer.
The vicinal acid-ester route has in general the operating characteristics of *he anhydride route, i.e., it `can be carried out in solution or in the melt for reaction times similar to those for the anhydride route described above~ Graft copolymer is believed to be obtained by attachment of the polycaprolactam side chain to the trunk copolymer through imide linkages ~with elimination of a:lco~ol and water) which may be derived through interme-diate fo~mation of amic acids, e.g., , ';

:.

~7~

1~ N~ C~

+ROH ~2~

or by prior conversion of the vicinal acid-ester by loss of alcohol to an anhydride and reaction of the latter with the polycaprolactam as described above. The description above of the anhydride route as carried out on a roll mill or in an extruder applies as well to the vicinal acid-ester route conducted in the same way.
The reaction of the amine group with the anhy-dride is fast, so that the effective reaction rate of IO ~polymers containing these groups may be limited by other factors such as the rate of mixingO When two polymers are dissolved in solution, separately, and the two solutions poured together, rapid intimate mixing is obtainedO
The graft copolymers have a trunk copolymer of ethylene a~d a comonomer providing amine~reactive sites . ~;
for attaching the side chain polymers theretoO The amine-reactive sites are provided by a comonomer seIected from the group consisting of an anhydride group, a vicinal pair of carb~xylic groups and a carboxylic group adjacen~ to alkoxycarbonyl group, wherein the alkoxy group contains up to 20 carbon atoms, pregerably 1 to 4 carbon atoms~ Pref-erably the amine~reactive sites are provided by a comonomer selected from the group consisting of maleic anhydride, half ester of maleic acid, and the half ester of itaconic acid9 The comonomer is reacted with the e~hylenec Suita~
trunk copolymers include the reaction product of ethy:Lene ' -B-:

~7~

with one or more of the follo~ing monome~so maleic an}ly~
dride~ (lower mono~alkyl C1 to C4) maleate~ (lower mono all~yl C1 to C~) itaconate9 (lower mono-allcyl Cl to C!~
fumarate. Th~ preferred ~runk copolymer is ~he reac~ion product of ethylene and maleic anhydride or ethyl hydro~en m~leateO
m e trunk copolymers can be prepared by known vinyl poly~rization techniques~ The ethylene and comonomers ar~ randomly interconnected through C~C linkages and c~ntai.n 1~ 70~99J pre~erably ~5 to 99~ percent by weight of ethylene~
The trunk copolymers have a melt index in the range o~ 5 ~o 200~ preferably 100 to 200. The crystallin~ rnelti~g point of the trunk copolymer is ~bov~ normal ambient ~emperatur~
e ~g~, about 100C.
The side chain polymers are linked to the re~
~cti~e sites on the trunk copolrmer through amide or imide linkages and are polymers of caprolactam. ~le side chains are limited in len~th having an average degree of polymerization of 5 to 30, preferably 6 to 10, and more pre~erably 6 to 8. The polycaprolactam side chains are terminated with one pr.imary amine end group and the other ~ ends ox groups are substantially unreactive with the re-; active sites of. the trunk copolymer. These non-reactive end groups include N-alkyl amide wherein alkyl is in the range of 1 to 20, preferably 4-6, carbon atoms, carboxylic - aci~, etc. Based on the weight of the graft copolymer 15 to 50~preferably 15 to 35, percent by weight o~ the gra~t copolymer is fxom the caprolactam side chains.
The graft copol~mers as described herein are plasti~ in nature rather than elastomeric. To dist:inguish _g_ :

. ' : ' : ' - ' -, . , - . . . ~ :.

the plastic graft copolymers from elastomeric graft co-polymers several properties have been selected, e.g., differential thermal analysis (~TA), flexural modulus, cold draw, etc. The plastic graft copolymers are pre-pared from a crystalline trunk copolymer and poly~apro-lactam and have two DTA melting points, one at 80 to 115C~
and the other at a~ least 165C., preferably 175 to 200C.
The elastomeric graft copolymers exhibit only one DTA
melting point, the higher temperature stated above~
Flexural modulus is another property, whereby the graft copolymers can be differentiated. The flexural modulus is affected not only by the difference in components and the amount of each component present, but the length of the side chain polymers. Below a flexural modulus of 28,000 p.s.i. (1.93 x 109 dynes/cm.2~ at room temperature khe graft copolymers are elastomeric. The flexural modulus dividing point is not sharply drawn particularly when the polyamide content approaches fifty percent by weight. At lower concentxations of polyamide, however, e.g., ~5 percent or less, the flexural modulus of the elastomeric graft copolymers is well below ~8,000 p.s.i.
(1.93 x 109 dynes/cm.~). The trunk copolymers of the plastic graft copolymers described herein when cold drawn at temperatures below their crystalline melting ~points and held for one minuke before release become oriented and do not appreciably recover from the deforma-tion within a one minute period. The elastomeric trunk copolymers when crosslinked retract within one minute ko less than 1.5 kimes their original lenyths af~er being stretched at 18-29~C. to twice kheir lengths and held for - . :

~'7~

one minute before rQlease.
The graft copolymers are identified as such, rather than as mere mixtures or blends of polyamides with predominantly hydrocarbon ethylenic polymers, by their clarity in the melt, by their solubility properties, and by their retention of physical properties, e.g., tensile strength, modulus, etc., at elevated temperatures. Blended mixtures of the carboxylic backbone copolymers and the poly-caprolactam are characteristical~y cloudy in the melt prior to completion of the grafting reaction. The mixtures, in contrast to the graft copolymers, can be separated by ex-traction with suitable solvents.
Knowing the degree of polymerization (DP) of each starting polymer side chain, it is possible to plot DP versus the peak melting point of each resulting graft copolymer, as determined with a differential scanning calorimeter tDsc)o It has been observed that the peak melting point increases as the DP of the side chains increases. Such a plot can serve as a calibration curve which can be used for the determination of the DP
of the grafts in the copolymers of the present invention.
The graft copolymers must be conditioned for testing by first heating to 250C., then cooling at the xate of 10C. per minute to 50C. During the test, the sample is heated at the rate of 10C. per minute.
DSC techniques are discussed in Thermoanalyti-cal Methods of Investigation, by P. D. Garn~ Academic . , Press, New York, 196S.

A ~onvenient and somewhat relates technique for correlating the DP of the grafted polymer side .

:,' '' . , " ' ' ' ' ~

~L~7(~6 chain with its melting point is differential thermal analysis (DTA). The sample also must be preconditioned and is heated during the test at the rate of 20Co per minute. The details of the DTA technique are described in Differential Thermal Analysis, R. CO MacKenzie, Editor, Academic Press, New York, 1970; especially in Chapter 23, by C. B. Murphy, dealing with polymers, Vol. I, pp. 643-671.
A preferred polymeric blend comprises 75 parts ~ 10 by weight of polyamide, 25 parts by weight polyethylene, ; and 2 parts by weight of graft copolymer having polycapro-lactam branches with a degree of polymerization of about 7.
It has been found that by the presence of a small amount of the graft copolymer in a blend of polyamide and polyethylene the uniformity o~ blend as well as its toughness and elongation in the dry state are improved.
The compatibility of the components of the blend is excellent.
The polyolefin segments between the side chains in the graft copolymer are believed to enter the polyethylene phase and return to the interface therefore they should be longer than the side chains. -The blends are useful as jacketing over insu-lated wir~ and ~or making various parts and components.
The following example-s wherein the parts are by ~ weight unless indicated illustrate the invention. The ; degree of polymerization (DP) of the amine-terminated oligomer side chain is determined by end gro~p analysis.
The amine end groups are determined by titration with a ~tron~ acid, either in the presence of an indicator or by 34 a potentiQme~ric or a conductometric method. Acid end ' groups are determined by titration with a strong base.
These techniques are discussed in Nylon P:Lastics, M. I~
Xohan, Editor, pp. 38 and 105, John Wiley and Sons, New York (1973), and in Enc~clopedia of Polymer Science And Technology, Vol. 10, pp. 542 and 543, John Wiley and Sons, -New York (1969). Flexural modulus is measured by standard ASTM D-790-71. 5amples are injection molded u~ing a cylinder temperature of 280C. and a mold temperature of 50C. to form bars 5" x 0.5" x 0.125" (12.7 x 1.27 x 0.32 cm.). The bars are conditioned at room temperature 16-24 hours beore testing. The test is conducted using a 2" (5.08 cm.~ span at a crosshead speed of 0.05"
~0.13 cm.)/min. The tangent modulus of elasticity (flexural modulus) is calculated using the equation given in the ASTM procedure. The value obtained is expressed in flex ~`` modulus in dynes/cm.2. Percent elongation at break (Elongation), tensile strength at yield in dynes~cm.2 (Yield Point) and ultimate tensile strength in dynes~cm.
(Ultimate Strength) are measured by the standard ASTM
~o D-638-72 test. The Izod Impact Strength test (I~od) was determined by standard ASTM~D-256-73 on injection molcled bars with machined notches. Samples are allowed to condition at room temperature for 16-24 hours, after cutting and notching, before testing. Five bars of each sample are tested and the average value reported as the Izod Impact Strength in kg.cm./cm. of notch. The diameter of polyethylene particles was determined by scanning electron microscopy EXAMPLES 1 to 15 Pellets of polyamide ~nylon`, an ~thylene polymer ~L~7~

and a graft copolymer having an ethylene copolymer backbone and caprolactam slde chains were mi~ced and fed to a twin screw extruder for melt blending. The resulting composi-tions were injection molded at 285C. and subjected to the ~ests indicated in Tables I and II below. Specimens were cooled in liquid nitrogen, fractured, and the fractured surfaces were examined by means of a scanning electron microscope~ It was found that the presence of the graft copolymer caused the reg;ons of the ethylene polymer to be smaller and more uniform and to have better adhesion to the nylon matrix.
In the Examples and Controls listed in Table I
the polyethylene was Alathon~ 7050, a high density resin and the nylon was either Zytel~ 101 (66) or Plaskon~ 8200 (6~. The graft copolymers were derived from copolymers of ethylene and maleic anhydride.
The ~xamples and Controls listed in Table II
were all based on Zytel~ 101 nylon resin. Alathon~ 3B, and Alathon~ 7050 are polymers of ethylene. In Examples 13 to 15 the graft copolymer was based on a copolymer of ethylene with ethyl hydrogen maleate rather than maleic anhydride. In the graft copolymer of Example 14, the poly-amide branches terminate in carboxyl groups. In the other examples, they terminate in n-hexyl groups.

The following composition was dry blended and processed in a 2.79 cm. twin screw extruder at 280C.:
parts rep~cessed nylon (66~ fibers ~5 parts Alathon~ 7050

2 parts graft copolymer made from a copolymer ,~

~14-. . : . . .

of ethylene and 13.3~ ethyl hydrogen maleate melt index 102 reacted with 25% of a nylon 6 oligomer of DP 6~55 having n-hexyl end groups 0.112 part potassium iodide 0.037 part cuprous iodide 0.037 part aluminum distearate A 0.13 mm jacket of this material was extruded over wire insulated with polyvinyl chloride. The jacket had a tensile strength of 7930 p.s.i. ~S.5 x 108 dynes/
cm.2) and an elongation at break of 240%. After vacu~
; drying 16 hours at 80C~, the tensile strength was 8590 p.s.i. (5.9 x 10 dynes/cm.2), and the elongation was 145~.
The jacket wire passed a mandrel bend test (UL83) after aging for 24 hours at 95~C. in coil form and after aging for 7 days at 150C. It also passed cold bend tests (Uh83) at -25 and -40C. as well as the UL83 and FRI vertical flame tests.
~ EXAMPLE 17 The following composition was dry blended and processed in a 2.79 cm twin screw extruder at about 285C:
367.5 g Zytel~ 101 12~.5 g Alathon~ 7050 (average diameter 0.2-0.5u) 9.8 g ~raft copol~mer derived from ethylene~
methacrylic acid copolymer containing 8.6% meth-acrylic acid by an acid chloride method melt index 46 and a nylon (6) oligomer of DP 7.0 having n-hexyl end groups, the graft copolymer containing 36~ polyamide. DSC melting points occurrecl at 104 and 183C.

,:, , .
- ~.

~7~6 The blend was tested for the following properties with the following results:
Yield Point 8060 p.s.i~ ~5.56 x 10 dynes/cm. ) Ultimate Strength 7410 p.s.i. (5.11 x 108 dynes/cm.~) Elongation 230%
Izod 1.28 ft.lb./in. (7.0 kg.-cm./'cm.

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Claims

The embodiments of the invention in which an exclu-sive property or privilege is claimed are defined as follows:
l. A polymeric blend comprising 60 to 90 parts by weight of a polyamide selected from the group consisting of polyhexamethylene adipamide, polycaprolactam and copolymers thereof and 40 to 10 parts by weight of polyethylene, characterized in that there is present in the blend 1.8 to 8.0 parts by weight of a plastic graft copolymer consisting essentially of a trunk copolymer derived from 70-90 percent by weight ethylene and a comonomer providing amine-reactive sites and polycaprolactam side chains having an average degree of polymierization of about 5 to 30 linked to said reactive sites through amide or imide linkages, said graft copolymer having a polycaprolactam side chain content of 15 to 50 percent by weight based on the weight of the graft copolymer and having two DTA melting points, one at 80 to 115°C and the other at at least 165°C.
2. A blend according to claim 1 wherein the comonomer providing amine-reactive sites is selected from the group consisting of an anhydride group, a vicinal pair of carboxylic groups, and a carboxylic group adjacent to an alkoxycarbonyl group wherein the alkoxy group contains up to 20 carbon atoms.
3. A blend according to claim 1 wherein the trunk copolymer has a melt index of 5 to 200.
4. A blend according to claim 3 wherein the caprolactam side chains are present in the amount of 15 to 35 percent by weight based on the weight of graft copolymer .
5. A blend according to claim 1 wherein the polycaprolactam side chains of the graft copolymer are terminated with end groups non-reactive with the reactive sites of the trunk copolymer.
6. A blend according to claim 5 wherein the non-reactive end groups are selected from the group con-sisting of N-alkyl amide wherein alkyl is in the range of 1 to 20 carbon atoms and carboxylic acid.
7. A blend according to claim 6 wherein the non-reactive end groups are N-alkyl amide wherein alkyl is in the range of 4 to 6 carbon atoms.
8. A blend according to claim 1 wherein the comonomer of the trunk copolymer providing the amine-reactive sites is selected from the group consisting of maleic anhydride, half ester of maleic acid and half ester of itaconic acid.
9. A blend according to claim 1 wherein the trunk copolymer is derived from ethylene and maleic anhydride.
10. A blend according to claim 1 wherein the trunk copolymer is derived from ethylene and ethyl hydro-gen maleate.
11. A blend according to claim 1 wherein the trunk copolymer and polycaprolactam side chains are linked through imide linkages.
12. A blend according to claim 1 wherein the trunk copolymer and polycaprolactam side chains are linked through amide linkages.
13. A blend according to claim 4 comprising 75 parts by weight of polyamide, 25 parts by weight polyethylene and 2 parts by weight of graft copolymer in which the polycaprolactam branches have a degree of polymerization of about 7.
14. A blend according to claim 1 wherein flexural modulus of the graft copolymer at room tempera-ture is at least 28,000 p.s.i.
15. A blend according to claim 1 wherein the polyamide is polyhexamethylene adipamide.
16. A blend according to claim 1 wherein the polyamide is polyhexamethylene
17. A polymeric blend comprising 60 to 90 parts by weight of a polyamide selected from the group consisting of polyhexamethylene adipamide, polycapro-lactam and copolymers thereof and 40 to 10 parts by weight of polyethylene, characterized in that there is present in the blend 1.8 to 8.0 parts by weight of a plastic graft copolymer consisting essentially of a trunk copolymer derived from 70-90 percent by weight ethylene and a comonomer providing amine-reactive sites and polycaprolactam site chains having an average degree of polymerization of about 6 to 8 linked to said reactive sites through amide or imide linkages, said graft copolymer having a polycaprolactam side chain content of 15 to 50 percent by weight based on the weight of the graft copolymer and having two DTA melting points, one at 80 to 115°C and the other at at least 165°C.