The present invention relates to a graf t copolymer of a pol ylactone and a polymer backbone , which is preferably a polyol ef in of rubbery character ( ie . of low E-modulus) , and a process for its preparation . It also relates to a blend of a resi n and the graf t copolymer , which blend has an improved impact strength. Engineering resins such as polycarbonate possess outstanding mechanical properties and heat distortion temperature but generally have a poor impact strength at low temperature i.e. the resin fractures too easily when struck. Thus it is desirable to modify such engineering resins to improve their deficient properties without sacrificing desirable properties. Polymers which show greater impact strength eg. polyolefin rubbers, cannot be successfully blended with engineering resins. Each polymer tends to form its own domains for ther odynamic reasons. Lack of interfacial adhesion between the domain types gives poor overall mechanical properties to the resulting blend; thus the two types of polymer are incompatible. Impact strength modifiers are therefore sought which are compatible with engineering resins and which impart to the blend a greater impact strength than the resin has on its own. It has been found that a graft copolymer of a "rubbery" polymer, such as certain polyolefins, and a polylactone is an effective impact modifier and can easily be produced.

_j EP-A-0181587 relates to anti-static or

2 electr ically-se iconductive thermoplastic polymer blends in

3 which a first polymer containing an electrically conductive

4 substance forms a continuous phase, and a second polymer, of

5 higher Belt viscosity than the first, is blended in this

6 first polymer. The first polymer may be polycaprolactone and η the second polymer may be a maleic-acid-anhydride-

8 modified polyethylene or maleic-acid-anhydride-modified-

9 ethylene-propylene-diene ter polymer. Copolymers may form at

10 the interface between the two polymer phases.

H US 3897513 and its divisional, US 4029718, both

12 relate to a random, graft copolymer obtained by polymerising

13 an alpha-substituted beta-propiolactone onto a base polyner.

14 Typically the lactone used is pivalolactone. The highly

15 crystalline nature of the polymer obtained from pivalolacton-e

16 provides a graft copolymer which can be moulded into a shape-3

17 article eg. by compression or injection moulding.

18 The present invention relates to a novel graft

19 copolymer comprising a polylactone and a polymer backbone

20 which copolymer is useful as an impact strength modifier in

21 an engineering resin.

22 The present invention provides a polymer comprising

23 continuous phase amorphous or semi-crystalline polymer

24 backbone which incorporates or on which are grafted

25 unsaturated dicarboxylic acid anhydride groups, and

26 discontinuous phase polylactone in which the repeat unit

27 chain length contains 5 to 7 carbon atoms, which polylactone

28 is attached to the backbone via the anhydride groups.

- 3 -

The expression "repeat unit chain length" is used to mean the length, exclusive of any optional branching, of the repeat unit in the polylactone chain and corresponds to the atoms in the monomer lactone ring.

The polymer backbone in the copolymers of the invention may be grafted with unsaturated dicarboxylic acid anhydride groups, in which case the copolymers of the present invention may be schematically represented as follows:

Backbone

where PL is the polylactone, and the anhydride is represented by maleic anhydride. Alternatively the polymer backbone may incorporate the anhydride groups as part of the polymer chain (rather than being grafted thereto). Such incorporation may be accomplished by including the anhydride as a comonomer during the polymer backbone production process. Such copolymers of the invention may be schematically represented as follows:

Backbone

(ID

where PL is the polylactone and the anhydride is represented by maleic anhydride. In both structures (I) and (II) unreacted maleic anhydride groups nay be present, but for simplicity these have been omitted. In the copolymers of the invention the important feature is that the elasto eric polymer and the polylactone are grafted together, rather than the manner in which such graft is achieved. The terms "backbone" and "backbone polymer" as used hereafter in this description refer to the backbone on which the anhydride groups have been grafted or in which the anhydride groups have been incorporated. The term "amorphous or semi-crystalline polymer backbone" or "backbone elasto-neric polymer" refers to the backbone without any anhydride functional ising groups since this should be elastomeric. Thus this term refers to the polymers before any anhydride-functionalising groups are grafted thereto, or to the polymer without incorporated anhydride groups which otherwise is produced from the same other (co)aonomers and under the same conditions as the backbone polymer which does have such anhydride-functionalising comonomer incorporated in the molecular chain. in order for the graft copolymer to confer on the engineering resin an improvement in impact strength, it is necessary for the backbone elastomeric polymer to be amorphous (eg. ethylene propylene rubber) or semicrystalline (eg. low density polyethylene) . The backbone elastomeric polymer preferably has "soft rubbery" characteristics, it has been found that graft copolymers of the invention which

have particularly useful properties as impact modifiers for engineering resins are those wherein the backbone elastomeric polymer is elastomeric and soft-rubbery in nature, as characterised by having eg. an E-Modulus (ASTM D638) of from 1 to 400 MPa preferably from 10 to 150 MPa. Preferred polymers for use as the backbone elastomeric polymer are homopolymers of monoethylenically unsaturated monomers, such as those of C ₂ -C, ₂ alpha-mono olefins, and copolymers of any two or more thereof. Such backbone homo- or copolymers may be for example (provided they have the required amorphous or semi-crystalline character) , those formed from the monomers ethylene, propylene, 1-hexene, 1-octene and their derivatives, and in the case of copolymers, optionally with non-conjugated diene or vinyl ester. Especially preferred polymers are those homo- or co-polymers comprising ethylene units. Particular preferred backbone elastomeric polymers include: Ho opolyethylene: eg. low density polyethylene, linear-low density polyethylene. Ethylene/C _j -C,- alpha-mono olefin copolymers: eg. ethylene/propylene copolymer, ethylene/1-butene copolymer, ethyl ene/1-pentene copolymer, ethylene/4-methyl pentene copolymer, ethylene/1-octene copolymer, ethyl ene/1-decene copolymer, ethylene/1-dodecene copolymer. Ethylene/C _j -C _j ^ alpha-mono olefin/non conjugated diene terpoly er:

For example a terpolymer of ethylene/propylene, 1-butene and/or 1-pentene/ and a diene such as: 5-ethylene-2-norbornene (ENB) ; 1,4-hexadiene; 5-methylene-2-norbornene (HNB); 1,6-octadiene; 5-methyl-l, 4-hexadiene; 3,7-dimethyl-l,6-octadiene; I _f 3-cyclopentadiene; 1,4-cyclohexadiene; tetrahydroindene; methyltetrahydroindene; dicyclopentadiene; 5-isoρropylidene-2-norbornene; or 5-vinyl-norbornene. (D) Ethylene/vinylester copolymers and terpolymers: in which the vinylester is a member of the group consisting of acrylate- or methacrylate-esters having from 4 to 22 carbon atoms and nitriles having from 2 to 6 carbon atoms eg: vinyl acetate, methyl acrylate, ethyl acrylate, propyl acrylate, iso-butyl acrylate, tert. -butyl acrylate, pentyl acrylate, acrylonitr ile , methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, pentyl methacrylate, stearyl methacrylate, iso-butyl methacrylate, tert. -butyl methacrylate, 2-ethylhexyl methacrylate, lauryl methacrylate, or methacrylonitrile. (E) Traditional natural and synthetic rubbers like polybutadiene, polyisoprene, chloroprene, polyisobutylene, isobutylene- conjugated multi olefin copolymers, halogenated isobutylene- conjugated multiolefin copolymers, or polybute.ne.

- 1 -

. (F) Mixtures of any two or more of the polymers exemplified in (A) through (E) above.

. In the graft copolymers of the invention the backbone

, polymer, preferably soft-rubbery, is grafted with the

₅ polylactone. Such grafting is via anhydride groups which

₆ effectively modify the basic backbone elastomeric polymer. . Such modification may be achieved by incorporating the

_ anhydride function during polymerisation of the backbone

₉ elastomeric polymer, or by grafting the anhydride

10 functionality onto the already formed backbone elastomeric

11 polymer.

12 The anhydride functionality derives from an

13 unsaturated dicarboxylic acid anhydride entity such as maleic

14 anhydride, citraconic anhydride, itaconic anhydride, himic

15 anhydride (ie. 5-norbornene endo 2,3 dicarboxy anhydride) ,

16 tetrahydrophthallic anhydride, nadic anhydride, nadic methyl

17 anhydride, dodecenylsuccinic anhydride and their derivatives;

18 of these, maleic anhydride is the preferred source of

19 anhydride functionality.

20 The amount of anhydride present in the backbone

21 polymer is preferably from 0.01 to 10 wt % based on the

22 backbone elastomeric polymer. If the proportion of anhydride

23 function is below 0.01 wt % then the amount of polylactone

24 which can be incorporated into the copolymer by grafting is

25 low. If the proportion is above 10 wt % then the amount of

26 polylactone which can be grafted, or the proportion of free

27 anhydride groups remaining, is high.

28 In use of the graft copolymers of the invention as

29 impact modifiers for engineering resins, it is believed that

30 the polylactone component of the graft copolymer provides a

- 8 - means of improving the miscibility or mechanical compatibility between the backbone elastomeric polymer and the engineering resin. The discontinuous phase polylactone component provides anchoring of the graft copolymer into the matrix of the engineering resin, and thus if the anhydride level in or on the backbone polymer is too low, the maximum possible polylactone level in the copolymer is low and hence the desired improvement in mechanical and impact properties of the graft copoly er/engineering resin blend cannot be achieved: the interfacial adhesion between the phases will be insu ficient. If the amount of polylactone grafted onto the backbone is too great, then even though the anchoring may be improved, the impact improvement of the engineering resin is not proportionately observed. Within the 0.01 to 10 wt% range for the anhydride content of the backbone polymer, the amount of anhydride is more preferably from 0.1 to 3 wt %, most preferably from 0.2 to 0.7 wt %. Production of the backbone polymer which is one component of the gra ft copolymers of the invention may be by methods wel l under stood in the art. For example the anhydr ide may be grafted onto the already formed base backbone elastomer ic polymer in solution or in the melt phase , with or without a radical initiator such as a peroxide . Such grafting techniques are disclosed for example in GB 1512137 (Mitsui) and US 3953655 (Steinka p) .

To incorporate the anhyd r ide functional ity into the backbone elastomer ic pol ymer dur ing i ts production , the anhyd r ide enti tity may simply be incorporated into the polymer isat ion system as a monomer under free rad ical polymer isa tion cond itions . The polylactone to be grafted onto the backbone (via the anhydride groups) is a polymer of a lactone in which the lactone ring contains 5 to 7 carbon atoms. Although eg. polyvalerolactone may be used, it is preferred to use polycaprolactone since this has been found to give optimised results. The graft copolymers according to the invention may contain crosslinks between the backbone polymer chains. Such crosslinks occur when the backbone contains or carries free anhydride groups after all available polylactone polymer units have been grafted to the backbone. In this case crosslinking might occur directly between the anhydride groups of adjacent backbone polymer chains. Alternatively crosslinking can occur via a polylactone entity, when such polylactone contains more than one hydroxy group. When cross-linking between the polymer chains is minimised or, more preferably, avoided altogether the graft copolymer is particularly effective at increasing the impact strength of resins. It is therefore preferred that the polylactone to be grafted onto the backbone possesses only one hydroxy group capable of reacting with the anhydride grafted on or incorporated in the backbone. In some circumstances, however, it may be desired for the graft

copolymer to contain crosslinks between the backbone polymers. In this case, crosslinking may be achieved by having anhydride groups present in excess and/or by having the polylactone component of the copolymer contain more than one hydroxyl group. For efficient grafting of the polylactone on to the backbone it is preferred that the ratio of moles of dicarboxylic acid anhydride to moles of polylactone is greater than 1. However, to minimise cross-linking reactions between remaining anhydride/acid groups it is preferred that this ratio be close to 1 eg. 1:1 to 1.5:1. The present invention also provides a process for producing the novel graft copolymer, which process comprises melt mixing an amorphous or semi-crystalline polymer backbone which incorporates or on which are grafted dicarboxylic acid anhydride groups, and a polylactone in which the repeat unit chain length contains 5 to 7 carbon atoms the proportions of backbone polymer and polylactone being such that in the resulting graft copolymer, the backbone polymer portion constitutes a continuous phase and the polylactone constitutes a discontinuous phase. Preferably the dicarboxylic acid anhydride containing, eg. maleated, backbone polymer is melted in a mixer eg. internal or extruder mixer and the polylactone is added to this melt and mixed for a time from 1 to 30 minutes. The resulting graft copolymer may be mixed with an engineering resin, such as polycarbonate or styreneacrylonitrile (SAN), polybutene terephthalate (PBT) , polyethyleneterephthalate (PET), polyamide,

styrene aleicanhydr ide copolymer, acrylonitrile/butadiene/

2 styrene copolymer (ABS) , polyacetal, polyvinylchloride

3 (insofar as this may be considered an engineering resin), or

4 mixtures of two or more thereof.

5 Improvements may be seen in the low temperature

6 impact strength of the resin when it is blended with the

7 graft copolymer. Typical weight ratios of resin to graft

8 copolymer are from 98:2 to 60:40 depending on the particular

9 resin and copolymer used, and on the degree of improvement 10 _.. which is required.

11 The effectiveness of the graft copolymers of the

12 invention as modifiers for engineering plastics is believed

13 to derive from the fact that they enable a backbone

₁₄ elastomeric polymer with preferably soft-rubbery

15 characteristics to be compatibly admixed with the normally

16 incompatible resin. The copolymer is of a form where the

17 backbone polymer constitutes a continuous phase, whilst the

18 polylactone component constitutes a discontinuous phase. It

19 is believed that the polylactone chains grafted to the

20 backbone almost coalesce with other polylactone chains to

21 form distinct discrete phases or globules; and that it is the

22 anchoring of these polylactone phases into the matrix of the

23 engineering resin which leads to the fixing of the rubbery

24 backbone polymer in the mixture, ie. the improved inter facial

25 adhesion between otherwise incompatible polymer species.

It will be appreciated, therefore, that the manner in which the graft copolymer interacts with the matrix resin will depend on the relative amounts of backbone polymer and polylactone component, and to some extent on the molecular weights of these two copolymer components. The degree of grafting of the polylactone onto the backbone will depend of course on the concentration of anhydride units in or on the backbone polymer and on the amount of polylactone employed in the grafting, as explained hereinbefore. In the graft copolymer it is preferred that, on the basis of the total weight of the copolymer, the polylactone component comprises from 2 to 50 wt %, more preferably from 5 to 35 wt \ , especially from 7 to 30 wt % and particularly from 10 to 25 wt %. These ranges have been found to give optimised phase relationships in the copolymer. Correspondingly, the preferred proportion of the modified backbone polymer comprises from 50 to 98 wt %, more preferably from 65 to 95 wt I, especially from 70 to 93 wt % 9 and particularly from 75 to 90 wt %. 0 The molecular weight of the backbone polymer can be i selected for optimum results depending on the polymer type. 2 It is preferred that the backbone polymer types based on 3 ethylene/propylene copolymer have a number average molecular 4 weight in the range of 20000 to 1000000, more preferably 5 30000 to 100000. 6 In general too low a molecular weight leads to poor 7 impact-improving properties for the graft copolymer; too high 8 a molecular weight leads to mixing problems in preparation of 9 the graft copolymers.

The polylactone component of the graft copolymer preferably has a number average molecular weight in the range of 5000 to 100000, more preferably 15000 to 60000. Too low a molecular weight leads to poor anchoring effect (phase adhesion); and too high a molecular weight leads to too low a concentration of polylactone chains, ie. reactive groups for the preparation of the graft copolymer. The following Examples illustrate the invention. Example 1 - Preparation of Graft Copolymer 30.0 g of ethylene/propylene copolymer (EP) maleated with 0.7 wt% maleic anhydride was placed in a Brabender mixer preheated to 225 C. The EP copolymer was VISTALO 457 containing 48 wt% ethylene and having M »54000 and ML (1+4) at 125°C « 28. VISTALON is a registered Trade Mark of Exxon Corporation. To the EP, was added 10.0 g of monohydroxy terminated polycaprolactone. The polycaprolactone had been produced from caprolactone monomer using an organometallic (diethylzinc) polymerisation catalyst, and had M w «21000. Furthermore it was characterised by a UV extinction coefficient of 448 at 220nm and showed the expected resonances in its NMR spectrum, both indicating the polymer to be pure polycaprolactone. The polymers were mixed for 10 minutes during which time the temperature rose to 235°C. Grafting was indicated by stress-strain behaviour before and after grafting. Unless otherwise stated, the maleated EP and polycaprolactone used in subsequent examples were as described in this Example 1.

Example 2 - Preparation of Graft Copolymer 225.0 g of maleated EP was placed in a Brabender mixer and preheated to 225°C. Then 52.5 g of onohydroxyl terminated polycaprolactone was added incrementally. After all the polymer had been added, the blend was mixed for 10 minutes at 225°C. Example 3 - Preparation of Graft Copolymer 175.0 g of maleated EP was placed in a Brabender mixer previously heated to 225°C. Polycaprolactone (75.0 g) was added incrementally and the blend was mixed for 10 minutes at 225°C. Example 4 - Preparation of Graft Copolymer 75.0 g of monohydroxyl terminated polycaprolactone (PC ) (weight average molecular weight 53,200; number average molecular weight 37,400) was reacted with 175 g of maleated EP in a midget Banbury for 2 minutes at 350°F (177°C) . N ?. analysis of the product showed a composition of 10.4 mole % PCL, 27.9 mole I ethylene, and 61.8 mole % propylene. Example 5 - use of Graft Copolymer as Impact Modifier for Polycarbonate The graft copolymer (EP-g-PCL) (4% by weight) prepared in Example 2 was mixed with polycarbonate (96% by we ight) in a sing le screw Brabender extruder at 20-32 PM and 230°C to form a blend . The polycarbonate was LEXAN 141 ( trade mark) resin of Dupont of melt flow rate 9. 5 g/10 min (ASTM D1238 , condition 0) . The blend was molded into spiral molds and into test pieces using a Boy-15 injection molder at 240°C The spiral molds were used to gauge relative flow; and the test pieces were subjected to an impact strength test at

least 24 hours after molding. The notched impact strengths of the test pieces were measured according to ASTM D256 at four temperatures. The results are shown in Table 1. These results show that the graft copolymer greatly improves the low temperature impact strength of polycarbonate. It also greatly enhances the polycarbonate's 1/4 inch (6.5 mm) impact strength at room temperature, demonstrating the usefulness of the graft copolymer as an impact modifier. Correspondingly, there is no significant adverse effect on molding capability (spiral flow) or on flexural modulus. The spiral flow was assessed by measuring the length of molten material injected into a die comprising circles of successively decreasing radius. Results are comparative, and the higher the reported value, the higher the flow of the material. The flexural modulus was measured by ASTM D790-81, Method J. Unless otherwise stated, the same measurement methods were employed in subsequent Examples.

TABLE 1

- 96% Polycarbonatt +

² Polycarbonate 4% EP-q-PC

3 1/8 inch (3.2 mm) Izod impact strength in units of

4 ft lb/in and [J/m] :

9 1/4 inch (6.5mm) Izod impact strength in units of

10 ft.lb/in and [J/m] :

U RT 1.9 [101] 14.3 [764]

12 Spiral Plow:

13 cm 5.5 6.3

14 Flex Modulus;

15 psi 318000 299000

16 MPa 2193 2061

- 17 -

Example 6 - Use of EP-PCL Graft Copolymer as Impact Modifier for SAN (without peroxide) Styrene/acrylonitrile copolymer, SAN, (Tyril 1000B resin of the Dow Chemical Company of melt flow rate 7.5 g/lOmin according to ASTM 01238) was dried overnight at 75°C in an air oven. 20 Parts by weight of the graft copolymer prepared in Example 3 was extruded with 80 parts by weight of the SAN in a single screw Braebender extruder at 20-32 RPM at 230°C to form a blend. The blend was molded into test pieces using a Boy-15 injection molder at 240 c. Notched izod strength testing of the pieces was carried out according to ASTM D256 at least 24 hours after molding. Table 2 shows the results.

SAM

1/8 inch (3.2 mm) Izod impact strength in units of ft lb/in and [J/m] :

1/4 inch (6.5mm) Izod impact strength in units of ft. lb/ in and tf/m] :

RT 0.58 [31.0] 0.85 [45.4]

Spiral Flow: cm 20 20.5 Flex Modulus; psi 501000 350000 MPa 3454 2413

- 19 - Example 7 - Use of Graft Copolymer as Impact Modifier In SAN (with Peroxide) The SAN resin of Example 6 was dried in a circulating oven, weighed into jars and put back into the oven to await mixing. The EP-PCL graft copolymer prepared in Example 4 was weighed into a plastic bag and kept separately. The peroxide initiator (dicu ylperoxide (diCup, Supplied by Hercules Inc.) was weighed into a paper cup and kept separately, as well. The graft rubber (20 parts) and peroxide (0.1 part) were mixed and poured into the hopper of the extruder and then added to the SAN (80 parts) under ₂ in a single screw Brabender extruder at ca. 220°C at 18 RPM. The torque reading was about 800 psi (5.5 MPa) . Each mixture took about 20 minutes to extrude. Later the blends were ground, placed in an 80 C oven and injection molded on a Boy-15 at 220°C, 650 psi (4.5 MPa). Izod impact testing was run according to ASTM D256 at several different temperatures on samples which were 24 hours old. The -40°C impact strength of the blend containing the graft copolymer was 160% higher than that of the control without the graft copolymer. Examples 8-20 Maleated ethylene/propylene copolymer rubbers and polycaprolactone were fed into a counterrotating twin screw extruder operated at the following conditions: screw speed 200 RPM; temperature profile: 180 ^o C-190°C-190 ^o C-190°C.

The rubbers employed were EXXELOR VA 1801 of Exxon Chemical Belgium, being a high ethylene content ethyl ene/propylene copolymer rubber grafted with 0.7 wt % maleic anhydride, having a melt flow rate (230°C/10 kg) of 7.8; and EXXELOR Vλ 1803 of Exxon Chemical Belgium, being a low ethylene content ethylene/propylene copolymer rubber grafted with 0.5 wt % maleic anhydride, having a melt flow rate (230°C/2.16 kg) of 3. The polycaprolactones employed were CAPA 630, 640, 650 of INTEROX SA having number average molecular weights of 30000, 40000 and 500.00 respectively. Also present in Example 17 was an amine catalyst, DABCO, more specifically 1,4 diazobicyclo 2,2,2 octane. The pellets produced by the extruder, being graft copolymer according to the invention, were heated in air at 50 °C for 24 hours and then compression molded into test pieces at 150 °C/10 tonnes for 5 minutes in a Daniels 100T press. The test pieces were then subjected to various physical property measurements as follows: Melt Flow Rate (MFR) at 230°C/10 kg ISO 1133, DIN 53735 Tensile Strength and Elongation at break (ASTM D638). The copolymer compositions and properties are shown in Table 3. From this it may be seen that the melt flow rate and tensile strength of the graft copolymer increase with increasing polycaprolactone content, but the elongation at break decreases. Furthermore, by comparison of Examples 12 and 17 it may be seen that the copolymer prepared in the presence of the added catalyst has a lower melt flow rate than the otherwise identical copolymer prepared without added

catalyst. At the same time, the tensile strength is substantially unchanged and the elongation at break is only marginally changed. This thus represents a means by which the melt flow rate of the copolymer may be controlled, so as to match it with the melt flow rate of the engineering resin into which it is to be incorporated as impact strength modifier. Matching of melt flow rates greatly facilitates the mixing procedures employed to obtain the final blend.

TΛHLK 3