NO176182B - Grafted block copolymer, as well as process for preparing the grafted block copolymer - Google Patents

Description

The invention relates to a new grafted block copolymer and a method for producing such a new grafted block copolymer.

It is known that a block copolymer can be obtained by an anionic copolymerization of a conjugated diene compound and an aromatic vinyl compound using an organic alkali metal initiator. These types of block copolymer have diverse characteristics varying from rubber-like characteristics to resin-like characteristics depending on the content of the aromatic vinyl compound.

When the content of the aromatic vinyl compound is small, the produced block copolymer is a so-called thermoplastic rubber. It is a very useful polymer that exhibits rubber elasticity in the unvulcanized state and is useful for various applications such as moldings for shoe soles, impact modifiers for polystyrene resins, adhesives and binders.

Block copolymers with a high content of aromatic vinyl compound, such as more than 70% by weight, provide a resin having both excellent impact resistance and transparency, and such a resin is widely used in the packaging field. Many proposals have been made for methods of making these types of block copolymer, for example as described in U.S. Patent No. 3,639,517.

The elastomeric properties of certain aromatic vinyl polymers also appear to be due in part to their degree of branching. Although the aromatic vinyl polymers are based on a linear carbon chain backbone, those having elastomeric properties always have protruding alkyl radicals. EPR (ethylene propylene rubber), for example, has a structure with protruding methyl radicals that appear to provide elasticity and other elastomeric properties. When it e.g. form an unbranched straight-chain polymer, such as certain polyethylenes, the resulting polymer is essentially non-elastomer or, in other words, relatively stiff, and behaves like a typical thermoplastic without having rubber-like elasticity or strong elongation, tensile strength without flow, low solidification or other properties characteristic of desirable elastomers.

Block copolymers have been prepared, see U.S. Patent Re 27,145, which primarily include such as here a general structure

wherein the two terminal polymer blocks A comprise thermoplastic polymer blocks of aromatic vinyl compounds such as polystyrene, while block B is a polymer block of a selectively hydrogenated conjugated diene. The quantity ratio between the thermoplastic terminal blocks and the elastomeric center elastomer block and the relative molecular weights of each of these blocks are equalized so that a rubber is obtained which has an optimal combination of properties so that it behaves like a vulcanized rubber without the need with a real vulcanization step. Moreover, these block copolymers can be noted not only with this important advantage, but also with the fact that they can be processed in thermoplastic molding equipment and that they are soluble in relatively cheap solvents.

Although these block copolymers have a number of outstanding technical advantages, one of their most important limitations lies in their susceptibility to oxidation. This is due to their unsaturated character which can be minimized by hydrogenating the copolymer, especially in the central part comprising the polymeric diene block. Hydrogenation can be carried out selectively, as disclosed in U.S. Patent Re 27,145. These polymers are hydrogenated block copolymers having a configuration, prior to hydrogenation, of A-B-A, in which each of the A's is an alkenyl-substituted aromatic hydrocarbon polymer block and B is a butadiene polymer block in which 35-55 mol% of the condensed butadiene units in the butadiene polymer -block has 1.2 configuration.

These selective hydrogenated ABA block copolymers are deficient in many applications where adhesion is required, due to their hydrocarbon nature. Examples include toughening and compatibilization of polar polymers such as building thermoplastics, adhesion to high-energy substrates of hydrogenated block copolymer elastomer-based adhesives, sealants and coatings, and the use of hydrogenated elastomers in reinforced polymer systems. However, the application to the block copolymer of functional groups that can provide mutual reactions that are not possible with hydrocarbon polymers solves the adhesion problem and expands the field of application of this material.

Functionalized S-EB-S polymers can be described as essentially commercially prepared S-EB-S polymers which are prepared by hydrogenation of S-B-S polymers chemically attached to either the styrene or the ethylene-butylene block in chemically functionalized proportions .

Many attempts have been made with the aim of improving adhesiveness, raw strength and other properties by modifying block copolymers with acid moieties and various methods have been proposed to modify synthetic conjugated diene gums with acid moieties.

U.S. Patent No. 4,292,414 relates to a process for making monovinyl aryl/conjugated diene block copolymer having a low 1,2 content grafted with maleic acid compounds. U.S. Patent No. 4,427,828 relates to a process for making an acid functionalized block copolymer with a high 1,2 content. However, both of these methods involve the "ENE" type of reaction which relies on residual unsaturation in the block copolymer for the addition of functional groups. It is not possible to prepare functionalized block copolymers containing low residual unsaturation together with reasonable functionalization using the 'ENE' process.

Thermoplastic polyamides, such as nylon 66, are a group of materials that have a good balance of properties that include strength and stiffness, making them useful as structural materials. For a particular application, however, a thermoplastic polyamide may not provide the desired combination of properties, and means to correct this deficiency are therefore of interest.

A main shortcoming of thermoplastic polyamides is their poor impact resistance, especially when dry. A particularly appealing way to achieve impact resistance for a thermoplastic is to blend it with another polymer. It is well known that rigid plastics can often be impact-modified by adding an immiscible elastomer with a low modulus. However, physical mixing of polymers has generally not been a successful way to toughen thermoplastic polyamides. This is due to the poor adhesion that immiscible polymers typically exhibit to each other. As a result, interfaces between blend component regions represent sites of severe weakness, which provide natural flow, resulting in rapid mechanical failure.

It is well known to those skilled in the art that hydrogenated block copolymers of styrene and butadiene have many of the properties required for impact modification of plastics. They have a rubber phase with a low glass transition and low modulus required for toughening. Because they contain little unsaturation, they can be mixed at high temperature with plasters that are processed at high temperature without degradation. They are also unique compared to other rubbers in that they contain blocks that are microphase separated over the area of application and the processing conditions. This microphase separation results in physical cross-linking, causing elasticity in the solid and molten stages. Such an internal strength mechanism is often necessary to achieve toughness when using plastic impact modification.

Evidence that hydrogenated block copolymers of styrene and butadiene are useful plastic impact modifiers can be seen in their extensive use for the modification of polyolefins and polystyrene. For these mixtures, the interfacial adhesion is strong enough to cause toughening.

Although the hydrogenated block copolymers have many of the characteristics required for plastic impact modification, they are deficient in modifying many materials that are structurally different from styrene or hydrogenated butadiene. Blends of the hydrogenated block copolymers with different plastics are often not tough enough due to a lack of interfacial adhesion.

One way to achieve interface adhesion between different materials is by chemically attaching, to one or more of the materials, functional parts that increase their mutual reaction. Such interactions include chemical reaction, hydrogen bonding and dipole-dipole interactions.

U.S. Patent No. 4,174,358 relates to a wide 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 previously been proposed to increase the impact resistance of polyamides by adding a modified block copolymer. U.S. Patent No. 4,427,828 and International Kokai Application No. WO83/00492 relate to blends of thermoplastic polyamide with a modified block copolymer. However, these blends are deficient because the blended components, especially the block copolymer, are relatively expensive. Polyamides also have a tendency to absorb water and the properties are consequently degraded. Mixing polyolefins with polyamides will reduce the water absorption of the mixture since part of the polyamide that absorbs water will be replaced with polyolefin that absorbs relatively little water. In recent times, attempts to extend impact-modified polyamides with polyolefins have been unsuccessful due to the polyamides being incompatible with the polyolefins.

It is an object of the present invention to produce functionalized block copolymers which contain low residual unsaturation and high functionality.

The present invention relates to grafted block copolymers comprising a selectively hydrogenated block copolymer according to the formula

which has been grafted with (a) an acidic compound or a derivative of such an acidic compound and (b) a polyolefin. Such a grafted block copolymer has been found to be very well suited for use in a mixture which further comprises a polyamide and a polyolefin, such mixtures being the subject of Norwegian patent no. 173 283. The mixture has been found to have desirable combinations of properties, such as impact strength, flexural modulus and elongation at break.

The polyolefins used in the present invention are crystalline or crystallisable poly-(α-olefins) and their copolymer. The α-olefin or 1-olefin monomers used in the present invention have 2 to 5 carbon atoms per molecule. Examples of particularly useful polyolefins, both plastic and elastomeric, include low or high density polyethylenes, polypropylene, poly-(1-butene), poly-3-methyl-l-butene, poly-(4-methyl-l-pentene) , copolymers of monoolefins with other olefins (mono- or diolefins) or vinyl monomers such as ethylene-propylene copolymers or with one or more additional monomers, i.e. EPDM, ethylene/butylene copolymer, ethylene/vinyl acetate copolymer, ethylene/ethyl acrylate copolymer, propylene/4-methyl-1-pentene copolymer, ethylene/methacrylic acid, ethylene/acrylic acid and their ionomers and the like. The number-average molecular weight of the polyolefins is preferably above approx. 10,000, and more preferably over approx. 50,000. It is also preferred that the apparent crystalline melting point is above approx. 100°C, preferably between approx. 100 and approx. 250°C, and more preferably between approx. 140 and approx. 250°C. The preparation of these various polyolefins is well known. See generally "Olefin Polymers", Volume 14, Kirk-Othmer Encyclopedia of Chemical Technology, Pages 217-335 (1967).

The high-density polyethylene used has an approximate crystallinity of over approx. 75% and a density in grams per cubic centimeter (g/cm<3>) of between approx. 0.94 and 1.0, while the low-density polyethylene used has an approximate crystallinity of over approx. 35% and a density of between approx. 0.90 and 0.94 g/cm<3>. Most commercial polyethylenes have a number-average molecular weight of approx. 50,000 to approx. 500,000.

The polypropylene used is the so-called isotactic polypropylene as opposed to atactic polypropylene. This polypropylene is described in the above-mentioned Kirk-Othmer reference and in U.S. Patent No. 3,112,300. The number average molecular weight of the polypropylene used is typically above approx. 100,000. Polypropylene which is suitable for this invention can be produced using previous methods in the field. Depending on the specific catalyst and the polymerization conditions used, the polymer formed may contain atactic and also isotactic, syndiotactic or so-called stereo-block molecules. These can, if desired, be separated by selective solvent extraction to give products with a low atactic content, which crystallize more completely. The preferred commercial polypropylenes are usually prepared using a solid, crystalline, hydrocarbon insoluble catalyst formed from a titanium trichloride material and an aluminum alkyl compound, e.g. triethyl aluminum or diethyl aluminum chloride. If desired, the polypropylene used can be a copolymer containing smaller amounts (1 to 20% by weight) of ethylene or other α-olefin comonomers.

The poly(1-butene) preferably has an isotactic structure. The catalysts used in the production of poly(1-butene) are typically organometallic compounds which are usually referred to as Ziegler-Natta catalysts. A typical catalyst is the mutual reaction product obtained by mixing equimolar amounts of titanium tetrachloride and triethylaluminum. The manufacturing process is usually carried out in an inert diluent such as hexane. The production is carried out in all phases of the polymer formation in such a way that the strict exclusion of water, even in trace amounts, is guaranteed.

A very suitable polyolefin is poly(4-methyl-1-pentene). Poly(4-methyl-1-pentene) typically has an apparent crystalline melting point of between 240 and 250°C and a relative density of between approx. 0.80 and 0.85. Monomeric 4-methyl-1-pentene is commercially produced by alkali metal-catalyzed dimerization of propylene. The homopolymerization of 4-methyl-1-pentene with Ziegler-Natta catalysts is described in the Kirk-Othmer Encyclopedia of Chemical Technology, Supplemental Volume, pages 789-792 (Second Edition, 1971). However, the isotactic homopolymer of 4-methyl-1-pentene has certain technical shortcomings, such as brittleness and insufficient transparency. Therefore, in reality, commercially available poly(4-methyl-1-pentene) is a copolymer with small proportions of other α-olefins, together with added suitable oxidation and melt stabilization systems. These copolymers are described in Kirk-Othmer Encyclopedia of Chemical Technology, Supplement Volume, pages 792-907 (Second Edition, 1971), and are available from Mitsui Chemical Company under the trade name "TPX resin". Typical α-olefins are linear α-olefins that have from 4 to 18 carbon atoms per molecule. Suitable resins are copolymers of 4-methyl-1-pentene with from approx. 0.5 to approx. 30% by weight of a linear α-olefin.

If desired, the polyolefin can be a mixture of different polyolefins. However, the most preferred polyolefin is isotactic polypropylene.

The modified polyolefins which are suitable for use in the present invention are produced by reacting a polyolefin with, for example, an unsaturated mono- or polycarboxylic acid or derivatives thereof.

The modified polyolefins are readily prepared according to the process described in U.S. Patent No. 3,480,580 or No. 3,481,910. The polyolefins that can be modified are produced from monoolefins containing at least 2 carbon atoms per molecule. Such polyolefins include homopolymers and copolymers of e.g. propylene, 1-butene, 4-methyl-1-pentene, 3-methyl-1-butene, 4,4-dimethyl-1-pentene, 3-methyl-1-pentene, 4-methyl-1-hexene, 5- ethyl-1-hexene, 6-methyl-1-heptene, 1-hexene, 1-heptene, 1-octene, 1-nonene, 1-decene and 1-dodecene.

Examples of suitable polyolefins, both plastic and elastomeric, include low or high density polyethylenes, polypropylene, poly-l-butene, poly-3-methyl-l-butene, poly-4-methyl-l-pentene, ethylene-propylene- copolymers or copolymers with one or more additional monomers, e.g. EPDM, ethylene-butylene copolymers, ethylene-vinyl acetate copolymers, ethylene/ethyl acrylate copolymers and propylene/4-methyl-1-pentene copolymers.

The reaction of the polyolefin, which for ease of reaction is usually low viscosity polyolefin, with an unsaturated mono- or polycarboxylic acid, and derivatives thereof, can be carried out in the presence of a free-radical source. These homopolymers or copolymers of low viscosity poly-α-olefins are produced by thermal decomposition of conventional high molecular weight α-olefin polymers produced by conventional polymerization processes. A suitable such conventional polymer is, for example, highly crystalline polypropylene prepared according to U.S. Patent No. 2,969,345. Thermal degradation of conventional homopolymers or copolymers is accomplished by heating them at elevated temperatures that cause the polymer chain to apparently break at the points of chain branching on the polymer material. The degree of degradation is regulated by reaction time and temperature to give a thermally degraded low molecular weight crystalline polymer material which has a melt viscosity range of approx. 100 - 5000 cp. at 190°C (ASTM D12 38-57T using apertures of 0.01016 ± 0.0000508 mm) and an inherent viscosity of approx. 0.1 to 0.5 [Schulken and Sparks, Journal Polymer Science, 26 227, (1957)]. By careful regulation of time, temperature and agitation, a thermally degraded poly-α-olefin with a relatively narrower molecular weight range than the high molecular starting polymer is obtained. The decomposition is carried out at a temperature from 290 to approx. 425°C.

The poly-a-olefins with low viscosity are characterized in that they have a melt viscosity of less than approx. 100 to 5000 cp. measured at 190°C (ASTM-D12 38-57T using openings of 0.01016 ± 0.0000508 mm). These low viscosity poly-α-olefins are reacted with unsaturated mono- or poly-carboxylic acids, and derivatives thereof, at temperatures which are usually lower than 300°C, preferably from about 150 to 250°C in the presence of free-radical sources. Suitable free radical sources are, for example, peroxides such as ditertiary butyl peroxide, tertiary butyl hydroperoxide, cumene hydroperoxide, p-menthane peroxide, p-menthane hydroxide compounds or azo compounds, such as azobis(isobutyronitrile), or radiation sources. Suitable radiation sources include e.g. such as from cobalt, uranium and thorium, and ultraviolet light. It can preferably be used approx. 1 to 10% organically unsaturated polycarboxylic acid, anhydride or esters thereof, based on the weight of the low viscosity polyolefin. The amount of peroxide or free radical agent used is usually quite low, being of the order of approx. 0.01 to approx. 0.5%, based on the weight of the low viscosity poly-α-olefin. The turnover can be carried out either in batches or continuously with contact times of the order of approx. 10 minutes to approx. 2 hours. Suitable unsaturated mono- or poly-carboxylic acids and derivatives thereof are described later in the section entitled Functionalized block copolymers, and they include maleic acid, maleic anhydride, fumaric acid, citaconic anhydride, aconitric anhydride, itaconic anhydride, half and full esters derived from methyl- , ethyl and dimethyl maleate, dimethyl fumarate, methyl ethyl maleate, dibutyl maleate, dipropyl maleate and the like, or such compounds which form these compounds at elevated reaction temperatures, such as, for example, citric acid. These modified low molecular weight poly-α-olefin materials have a melt viscosity of 100 - 5000 cp. at 190°C and a saponification number of from at least 6 to approx. 60, preferably approx. 7 - 30. It has been observed that the melt viscosity of the product increases slightly. This increase in melt viscosity may be due to a small degree of crosslinking or copolymerization of the wax material with maleic anhydride.

The reaction of the polyolefin can also be carried out in an extruder or Banbury mixer. This method can be used for conversion of polyolefins which have a greater melt viscosity than 5000 cp. at 190°C, up to a viscosity of 500,000 cp. at 190°C. The modified polyolefins produced in this way, such as polypropylene, can have a melt viscosity of 150,000 cp. or higher at 190°C and a saponification number of up to 60.

A procedure for determining the saponification number for maleated polypropylene is as follows: Weigh approximately 4 g of the sample into a 500 ml alkali-resistant Erlenmeyer flask and add 1000 ml of distilled xylene. It is heated under a reflux condenser for 1 hour. The solution is cooled to 75°C or lower, and 30 ml of standardized 0.10 N KOH in ethyl alcohol is added from a burette. It is heated under reflux for 45 min. It is cooled, and standardized 0.10 N CH3COOH in xylene is added from a burette until the mixture is acidic to phenolphthalein. At least 1 ml in excess of CH3C00H is added. The solution is reheated under reflux for 15 min. The heating is removed, it is added

5 ml of water, and it is titrated to a faint pink end point

with 0.10 N KOH in ethyl alcohol. A blank test is carried out in this way using the same amounts of reagents and the same heating times. Calculation:

The unreacted unsaturated polycarboxylic acid can be separated from the reaction mixture by flushing the reaction mixture with an inert gas while the melting temperature is between 200 and 300°C. After the unreacted unsaturated polycarboxylic acid has been removed, the modified poly-α-olefin can be further purified by vacuum stripping, solvent extraction or by dissolution in a hydrocarbon medium and isolation by precipitation with a non-solvent such as acetone.

It may be desirable to use an effective polyolefin stabilizer to prevent gelatinization or degradation of blend properties. Some suitable stabilizers include dilaurylthiodipropionate, butylated hydroxytoluene, dioctadecyl-p-cresol, pentaerythritol-tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], dodecyl-stearyl-thiodipropionate, 2,2 '-methylene-bis(6-tert-butyl-p-cresol) and the like or combinations of such stabilizers. Desirable stabilizer concentrations include approx. 0.5 to approx. 1.0% by weight stabilizer in the mixture.

If desired, the functionalized polyolefin can be mixed with non-functionalized polyolefins, e.g. a highly functionalized polyolefin can be diluted with unfunctionalized polyolefin to improve properties or reduce costs.

Elastomers useful in the compositions of the present invention may include elastomeric olefin copolymers, selectively hydrogenated block copolymers, and elastomeric acrylic compounds containing polymers formed by the emulsion process. These elastomers can be functionalized or non-functionalized.

Elastomeric acrylic compounds containing polymers are well known in the art and are described in U.S. Patent Nos. 3,668,274 and 4,584,344.

Elastomeric copolymers of ethylene, at least one C3 to C6 α-olefin and at least one non-conjugated diene are well known in the art. These copolymers have a substantially saturated hydrocarbon backbone causing the copolymer to be relatively inert to ozone attack and oxidative degradation and to have side chain unsaturation available for sulfur curing.

These copolymers are conveniently prepared by copolymerizing the monomers in the presence of a coordination catalyst system such as diisobutylaluminum chloride and vanadium oxytrichloride. The copolymerization can be carried out in an inert solvent or in a slurry or in a particle form reactor. Details regarding their manufacture are e.g. set forth in U.S. Patent Nos. 2,933,480, 2,962,451, 3,000,866, 3,093,620, 3,093,621, 3,063,973, 3,147,230, 3,154,528, 3,260,708, and M. Sittig, "Stereo Rubber and Other Elastomer Processes", Noyes Development Corporation, Park Ride, N.J. 1967.

Propylene is usually chosen as the α-monoolefin in the preparation of such copolymers because of its availability and for economic reasons. Other lower α-monoolefins, such as 1-butene, 1-pentene and 1-hexene, may be chosen instead of or in addition to propylene in the preparation of elastomeric copolymers useful in the practice of the invention. The term EPDM, when used herein, means the preferred copolymers of ethylene, propylene and at least one non-conjugated diene.

A particularly preferred group of EPDM is one in which the non-conjugated diene is monoreactive. Monoreactive non-conjugated dienes have one double bond that readily enters into the copolymerization reaction with ethylene and propylene, and another double bond that does not, to any appreciable extent, enter into the copolymerization reaction. Copolymers of this group have maximum lateral unsaturation for a given diene content, and this unsaturation is available for adduct formation. Gel content in these copolymers is also minimal since there is minimal crosslinking during the copolymerization.

Monoreactive non-conjugated dienes which may be selected in the preparation of this preferred group of EPDM copolymers include linear aliphatic dienes of at least six carbon atoms having a terminal double bond and an internal double bond, and the cyclic dienes in which one or both of the carbon-to-carbon -the double bonds are parts of a carbo-cyclic ring. Of linear dienes, copolymers of ethylene, propylene and 1,4-hexadiene with an inherent viscosity of at least 1.5 are particularly preferred.

Groups of cyclic dienes useful in preparing the preferred group of EPDM copolymers for adduct formation include alkylidenebicycloalkenes, alkenylbicycloalkenes, bicycloalkadienes, and alkenylcycloalkenes. Representative of alkylidenebicycloalkenes are 5-alkylidene-2-norbornenes such as 5-ethylidene-2-norbornene and 5-methylene-2-norbornene. Representative of alkenylbicycloalkenes are 5-alkenyl-2-norbornenes such as 5-(1'-propenyl)2-norbornene, 5-(2'-butenyl)-2-norbornene and 5-hexenyl-2-norbornene. Dicyclopentadiene and 5-ethyl-2,5-norbornadiene are illustrative of bicycloalkadienes, and vinylcyclohexane is representative of alkenylcycloalkenes which may be chosen as the diene monomer. EPDM copolymers prepared from cyclic dienes preferably have an inherent viscosity in the range of approx. 1.5 to 3.0, measured on 0.1 gram of copolymer dissolved in 100 ml of perchlorethylene at 30°C, for optimum processing properties. Of the cyclic dienes, 5-ethylidene-2-norbornene is preferred.

Another group of preferred copolymers includes branched tetrapolymers formed from ethylene, at least one C3 to C6 α-monoolefin with propylene being preferred, at least one monoreactive non-conjugated diene and at least one direct-reactive non-conjugated diene such as 2,5-norbornadiene or 1 ,7-octadiene. By "direactive" is meant that both double bonds are capable of polymerizing during the preparation of the copolymer. Tetrapolymers of this group preferably have an inherent viscosity of approx. 1.2 to 3.0, measured on 0.1 gram of copolymer dissolved in 100 ml of perchlorethylene at 30°C, for optimum processing properties. A preferred copolymer of this group is a tetrapolymer of ethylene, propylene, 1,4-hexadiene and 2,5-norbornadiene. Such copolymers are described in Canadian Patent Nos. 855,774 and 897,895.

Copolymers of the groups defined above have low gel content, a substantially saturated hydrocarbon backbone that is resistant to ozone and oxidative degradation, and hydrocarbon side chain unsaturation that provides sites for thermal addition of maleic anhydride, fumaric acid, and other species capable of thermal addition to the above side chain unsaturated sites. Low gel content is a sign that the polymer has advantageous processing properties.

Although the present invention will be discussed in relation to the thermal addition of maleic anhydride to form a graft, it should be understood that in the present invention maleic acid or fumaric acid can directly replace maleic anhydride to form the same adduct. The adduct containing amber groups attached to the elastomeric copolymer is given a content of these groups by using a starting material of maleic anhydride, maleic acid or fumaric acid Maleic anhydride, maleic acid and fumaric acid are equivalent to each other with regard to forming the same type of graft that contains same amber groups. Therefore, the comments made here when using maleic anhydride also apply to maleic acid and fumaric acid. Application of other thermal reactions with this hydrocarbon side chain unsaturation can also be carried out by the present invention.

When using a copolymer of ethylene, propylene and 1,4-hexadiene, the thermal addition of maleic anhydride to the copolymer takes place theoretically according to the following equation:

One molecule of maleic anhydride is added to the polymer at the site of side chain unsaturation to give a succinic anhydride radical attached to the side chain. Side chain unsaturation is exchanged at one carbon atom. It will be understood that side chain unsaturation can also be exchanged away from the backbone chain when the unsaturation is several carbon atoms from the terminal side chain carbon atom, as in copolymers of ethylene, propylene and 1,4-octadiene.

However, it has also been found that in addition to the adduct containing succinic anhydride attached to the elastomeric copolymer, succinic groups may also be attached to the copolymer. Typically, the adduct will contain succinic groups attached to the copolymer as a mixture of succinic anhydride and succinic acid.

Here, the disclosure "succinic groups" will include succinic anhydride, succinic acid or a combination of succinic anhydride and succinic acid.

The adducts according to this invention can be prepared by any method which intimately mixes maleic anhydride with the copolymer without appreciable development of free radicals, and which simultaneously or afterwards heats the mixture to a temperature at which thermal addition takes place. Selected temperatures will usually be at least 225°C for adduct formation to be achieved at acceptable rates and lower than approx. 350°C to avoid any significant polymer degradation. Preferred temperature ranges will vary with the particular polymer and can be readily determined by those skilled in the art.

Blending of maleic anhydride and copolymer can be accomplished by mixing molten anhydride with copolymer in an internal mixer or extruder, or by mixing finely divided dry maleic anhydride with copolymer in a well-aerated rubber mill with simultaneous or subsequent heating, such as in a hot press or shape. Temperatures necessary to achieve thermal grafting are sufficiently high to dehydrate maleic acid, forming maleic anhydride in situ. Maleic acid can thus be mixed with the copolymer instead of maleic anhydride when this is desired. The maleic anhydride can be replaced with groups, such as bromine or chlorine, which do not adversely affect the grafting reaction.

Preferred copolymers of ethylene, propylene and 1,4-hexadiene are highly resistant to free radical formation under high shear conditions, and are easily mixed on conventional pulp processing equipment without gelation. However, care must be taken when choosing mixing ratios for copolymers derived from deformed ring dienes such as ethylidene norbornene. Such copolymers will readily develop free radicals when sheared at low temperatures and are preferably mixed with maleic anhydride at high temperatures such as above 90°C to avoid appreciable gelation.

It is usually desirable to form adducts containing 0.02 to 20% by weight, and preferably 0.1 to 10% by weight

maleic anhydride. Adducts containing such amounts of maleic anhydride have sufficient carboxylated sites for ionic curing or grafting of the copolymer. In order to achieve a desired degree of adduct formation within a reasonable time, it is helpful to have high concentrations of reactants. One will

usually choose a polymer that has approx. twice as much side-chain unsaturation as that stoichiometrically required for the desired amount of maleic anhydride incorporation. In the same way, approx. twice as much maleic anhydride as the amount desired in the polymer adduct. A conversion of approx. 40 - 50% of the maleic anhydride in a copolymer adduct with the desired composition. If you e.g. wish to obtain an ethylene/propylene/1,4-hexadiene copolymer having a maleic anhydride content of 2.2% by weight, one can conveniently mix a copolymer having 0.49 moles of side chain unsaturation per kg of polymer with 0.49 mol of maleic anhydride and heat the mixture to convert 45% of the anhydride, thereby obtaining the desired product.

It is often desirable to carry out further reactions with the derivatized elastomeric olefin copolymer. A copolymer containing amber groups can e.g. esterified with hydroxy-containing compounds.

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Block copolymers of conjugated dienes and vinyl aromatic hydrocarbons which may be used include any of those exhibiting elastomeric properties and those having 1,2 microstructure content prior to hydrogenation of from about 7 to approx. 100%, preferably from 35 to 55%, more preferably from 35 to 50% and especially from 40 to 50%. Such block copolymers may be multiblock copolymers of varying structure containing different ratios of conjugated dienes to vinyl aromatic hydrocarbons, including those containing up to approx. 60% by weight of vinyl aromatic hydrocarbon. It is thus possible to use multi-block copolymers which are linear or radical, symmetrical or asymmetrical and which have structures represented by the formulas A-B, A-B-A, A-B-A-B, B-A-B, (AB)01j2 BA and the like where A is a polymer block of a vinyl aromatic hydrocarbon or a decreasing copolymer block of conjugated diene/vinyl aromatic hydrocarbon, and B is a polymer block of a conjugated diene.

The block copolymers can be prepared by any well-known block polymerization or block copolymerization process, and include the well-known techniques of sequential addition of monomers, incremental addition of monomers or coupling, such as e.g. is disclosed in U.S. Patent Nos. 3,251,905, 3,390,207, 3,598,887 and 4,219,627. As is well known in the block copolymer art, decreasing copolymer blocks can be incorporated into the multiblock copolymer by copolymerizing a mixture of conjugated diene and vinyl aromatic hydrocarbon monomers by exploiting the difference in their relative copolymerization rates. Various patents that describe the preparation of multiblock copolymers containing decreasing copolymer blocks include U.S. Patent Nos. 3,251,905, 3,265,765, 3,639,521 and 4.2 08.3 56, the disclosures of which are incorporated herein by reference.

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

Vinylaromatic hydrocarbons which can be used to prepare copolymers include e.g. styrene, o-methylstyrene, p-methylstyrene. p-tert-butylstyrene, 1,3-dimethylstyrene, α-methylstyrene, vinylnaphthalene and vinylanthracene. The preferred vinyl aromatic hydrocarbon is styrene.

It should be noted that the polymers and copolymers described above can, if desired, be easily prepared by the methods indicated above. However, since many of these polymers and copolymers are commercially available, it is generally preferred to use the commercially available polymers as this serves to reduce the number of processing steps involved in the overall process. The hydrogenation of these polymers and copolymers can be carried out by a number of well-established methods, including hydrogenation in the presence of such catalysts as Raney nickel, noble metals, for example platinum and palladium, and soluble transition metal catalysts. Suitable hydrogenation processes which can be used include one where 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 methods are disclosed in U.S. Patent Nos. 3,113,986 and 4,226,952, and these disclosures are incorporated herein by reference. The polymers and copolymers are hydrogenated in such a way that hydrogenated polymers and copolymers are formed which have a content of residual unsaturation in the polydiene block B of from 0.5 to 20%, and preferably less than 10 and especially less than 5% of their original unsaturation content before hydrogenation. It is preferred that on average less than 10% of the monoalkenyl aromatic hydrocarbon units in block A are hydrogenated. However, it is not excluded that on average from 25 to 50% of the monoalkenyl aromatic hydrocarbon units are hydrogenated. The average unsaturation of the hydrogenated block copolymer is preferably reduced to less than 20% of its original value.

Block A preferably has an average molecular weight in the range from 4,000 to 60,000 and block B preferably has an average molecular weight in the range from 35,000 to 150,000.

Generally, any material capable of reacting with the block copolymer in question by free-radical initiated reactions, as described in U.S. Patent No. 4,578,429, which is incorporated herein by reference, or by thermal addition reactions , applicable for the purposes of the invention.

The monomers may be polymerizable or non-polymerizable, however, preferred monomers are non-polymerizable or they polymerize slowly. U.S. Patent No. 4,427,828 relates to block copolymers formed by thermal addition reactions. Free radical formed block copolymers and free radical processes are disclosed in U.S. Pat. patent applications no. 646,391, 646,389 and 657,294, which are incorporated herein by reference.

In the case of free radical reactions, the monomers must be ethylenically unsaturated in order to be grafted. It has been found that by grafting unsaturated monomers having a slow polymerization rate, the resulting graft copolymers will contain little or no homopolymer of the unsaturated monomer, and only contain short grafted monomer chains that do not phase separate into separate regions.

The group of preferred monomers which will form grafted polymers within the scope of the present invention have one or more functional groups or derivatives thereof, such as carboxylic acid groups and their salts, anhydrides, esters, imide groups, amide groups, acid chlorides and the like, in addition to at least one point of unsaturation.

These functionalities can then be reacted with other modifying materials to form new functional groups. A grafting of an acidic monomer can e.g. suitably modified by esterification of the resulting acid groups in the grafting by appropriate reaction with hydroxy-containing compounds of varying carbon lengths. The turnover can take place at the same time as the inoculation or by a 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% by weight of the grafted portion.

The preferred modifying monomer is unsaturated mono- and poly-carboxylic acids (C3-C10) with preferably at least one olefinic unsaturation, and anhydrides, salts, esters, ethers, amides, nitriles, thiols, thioacids, glycidyl, cyano, hydroxy, glycol and other substituted derivatives of said acids.

Examples of such acids, anhydrides and derivatives thereof include maleic acid, fumaric acid, itaconic acid, citraconic acid, acrylic acid, glycidyl acrylate, cyanoacrylates, hydroxy CL- C20 alkyl methacrylates, acrylic polyethers, acrylic anhydride, methacrylic acid, crotonic acid, isocrotonic acid, mesaconic acid, angelic acid, maleic anhydride, itaconic anhydride, citraconic anhydride, acrylonitrile, methacrylonitrile, sodium acrylate, calcium acrylate and magnesium acrylate. Other monomers which can be used either alone or in combination with one or more carboxylic acids or derivatives thereof include C2-C50 vinyl monomers such as acrylamide, acrylonitrile and monovinyl aromatic compounds, e.g. styrene, chlorostyrenes, bromostyrenes, α-methylstyrene and vinylpyridines.

Other monomers that can be used are C4 to C50 vinyl esters, vinyl ethers and allyl esters, such as vinyl butyrate, vinyl laurate, vinyl stearate and vinyl adipate, and monomers having two or more vinyl groups, such as divinylbenzene, ethylene dimethacrylate, triallyl phosphite, dialkyl cyanurate and triallyl cyanurate.

The preferred monomers to be grafted to the block copolymers according to the present invention are maleic anhydride, maleic acid, fumaric acid and derivatives thereof. It is well known in the field that these monomers are not easily polymerised.

The block copolymer can also be grafted with a sulphonic acid or a derivative thereof.

Mixtures of monomers can of course also be added so that graft copolymers are obtained in which the grafted chains originate from at least two different monomers therein (in addition to the base polymer monomers).

The modified block copolymer for mixing according to the present invention can be prepared in any manner known in the art, for example by grafting an acid moiety or a derivative thereof with a block copolymer of aromatic vinyl compound/conjugated diene compound which contains at least one polymer block AB mainly composed of a conjugated diene compound and at least one polymer block BA mainly composed of an aromatic vinyl compound, where said graft reaction is carried out by melt or solution mixing of said block copolymer and is a polymerized monoalkenyl aromatic hydrocarbon block which has an average molecular weight of approx. 2,000 to 115,000, where B is a polymerized conjugated diene hydrocarbon block having an average molecular weight of approx. 20,000 to 450,000, blocks A constitute 5-95% by weight of the copolymer, 40-55 mol% of the condensed butadiene units in block B have a 1,2 configuration, the unsaturation in block B is reduced to less than 10% of the original unsaturation, and the unsaturation in the A blocks is over 50% of the original unsaturation.

The invention provides a grafted block copolymer comprising a selectively hydrogenated block copolymer having the general formula Bn(AB)0Ap in which each A is predominantly a polymerized monoalkenyl aromatic hydrocarbon block having an average molecular weight in the range of 2000 to 115,000, each B before hydrogenation is predominantly a polymerized conjugated diene hydrocarbon block having an average molecular weight in the range of 20,000 to 450,000, n = 0 or 1, o is in the range of 1 to 100 and p = 0 or 1, where the blocks A constitute from 5 to 95% by weight of the copolymer, the unsaturation of block B is less than 20% of the original unsaturation and the unsaturation of the blocks A is greater than 50% of the original unsaturation, which block copolymer is grafted with (a) an acid moiety or a derivative thereof, and (b) a polyolefin.

The grafted block copolymer according to the present invention can be produced by any known method in the field. A preferred method of preparing the grafted block copolymer comprises melt mixing the following components: (a) a selectively hydrogenated block copolymer having the general formula I set forth above, (b) an acid compound or a derivative of an acid compound and

(c) a polyolefin,

adding a free radical initiator, grafting under free radical conditions and recovering the graft block copolymer product.

The grafting reaction is initiated by a free radical initiator which is preferably an organic peroxygen compound. Particularly preferred peroxides are 2,5-dimethyl-2,5-di(t-butyl-peroxy)hexane, di-t-butyl peroxide, 2,5-dimethyl-2,5-di-tert-butylperoxy)-3-hexyne (known under the trademark Lupersol 130), a.a'-bis-(tert-butylperoxy)diisopropylbenzene (known under the trademark VulCup R), or any free radical initiator that has a short half-life under the processing conditions of the base polymer. See Modem Plastics, November 1971, pages 66 and 67, regarding several initiators.

The concentration of the initiator used to prepare the polymer can also vary within wide limits and is determined by the desired degree of functionality and permissible degradation. Typical concentration ranges are from approx. 0.001 to approx. 5.0% by weight, and more preferably between 0.01 and 1.0% by weight.

Reaction temperatures and pressures should be sufficient to melt the reactants and also sufficient to thermally cleave the free radical initiator to form the free radical. The reaction temperatures will depend on the base polymer used and the free radical initiator used. Typical reaction conditions can be obtained by using a screw type extruder to mix and melt the reactants and heat the reactant mixture to the desired reaction temperature.

The temperatures that can be used in the reaction in the method according to the present invention can be varied within wide limits such as from +75 to 450°C, preferably from approx. 200 to approx. 300°C.

The method of the invention is very flexible and many modifications, such as those suggested above, are available to achieve any particular desired purpose.

The following examples further illustrate the invention, and parts and percentages are by weight unless otherwise stated.

Examples 1-11 and comparative experiments A-D

Production of modified block copolymer by melting process

The block copolymer used to prepare modified polymer Y was KRATON G.1652 Rubber, a commercial S-EB-S material, which can be melt processed in the pure state. This polymer was melt-reacted with maleic anhydride and Lupersol 101 in a co-rotating twin-screw extruder with a diameter of 30 mm. "Lupersol 101" is a trade name for 2,5-dimethyl-2,5-di(t-butyl-peroxy)hexane.

The reactants were premixed by drumming in a polyethylene bag, and were then fed into the extruder. All extrusion conditions, except reactant concentrations, were held constant. The melting temperature was varied from 150°C in the feed zone to 260°C at the nozzle. A screw speed of 350 rpm was used. my.

Samples prepared in the manner indicated above were analyzed for bound maleic anhydride by extraction of the soluble fraction in refluxing tetrahydrofuran, recovery of the soluble fraction by decantation of the extract in isopropyl alcohol, and determination of the maleic acid content of the dried decantation by calorimetric titration with potassium -methoxide and phenolphthalein indicator.

Table 1 shows the investigated reactant concentrations, and also the analytical results for the produced material.

Blend of nylon 66 and modified block copolymers

Before mixing, the modified block copolymer was dried at 100°C under sub-atmospheric pressure with a nitrogen purge for 4 hours. The thermoplastic polyamide used in this example was a commercial casting grade of nylon 66 which has the trade name Zytel 101 and which is available from E.I. DuPont Company. Prior to all processing steps, nylon 66 and its blends were dried at 120°C for 4 hours at sub-atmospheric pressure with nitrogen purging.

Blends of nylon 66 with both unmodified and modified block copolymer were produced in a 30 mm diameter co-rotating double-skinned extruder. The mixture components were premixed by drum treatment in polyethylene bags. A stabilizer pack, 0.5% by weight of the total material, formed with a 3:1 ratio of a phosphite to sterically hindered phenolic antioxidant, was included in the material. The temperature profile during the melting in the extruder varied from 270°C in the feed zone to 285°C at the nozzle. The screw rotated at 300 revolutions per minute (rev. per min.). The extrudate was pelletized and injection molded into test-sample pieces.

In the following examples are

block copolymer 1 - S-EB-" 33% styrene m.v. 181,000

PP 552 0 Injection molding grade of propylene homopolymer from Shell Chemical

PP MA 0.16 and Maleic anhydride-grafted polypropylenes

with

PP MA 1.0 functionalization indicated in wt%

Physical properties of dry cast mixtures that exemplify the present invention are given in Table 2.

Examples 12 and 13

In the following examples, Zytel ST 901, an EPDM-maleic anhydride/toughened nylon compound manufactured by duPont, was used.

Examples 14-16

In the following examples, modified block copolymer Z is an S-EB block copolymer modified with maleic anhydride and polypropylene as described in U.S. Patent Application No. 911,559 (K-4841). The ratio between polypropylene and block copolymer in the starting material was 1:3.

Comparative Tests A-D and Examples 1-11 show that in nylon blends containing polyolefins and block copolymers, when one or both of the polyolefin or block copolymer is functionalized, the balance of ultimate and low stress properties is significantly improved.

Examples 12 and 13 show that similar improved properties are obtained when the elastomer is maleic anhydride-functionalized olefin copolymer.

Examples 14-16 show that improved properties can also be obtained by mixing with a modified mixture of polyolefin and elastomer which has been prepared by simultaneously subjecting both components to a functionalization reaction.

Examples 17-30

The process can also be carried out in melt by adding a polyolefin flow promoter such as polypropylene. Also, melt-processable polymers or blends will benefit from the addition of a polyolefin flow promoter. The following examples show that such a modified block copolymer processed with a polyolefin also toughens thermoplastic polyamides.

In one example, a high molecular weight unprocessable S-EB-S block copolymer in the neat state and homopolypropylene in a ratio of 3:1 were simultaneously subjected to free-radical graft reaction conditions in an extruder, as described in Examples 1-11. The resulting product was subjected to an extraction with tetrahydrofuran and the fractions were analyzed by gel permeation chromatography, maleic anhydride titration and by infrared spectroscopy. The product was found to contain block copolymer grafted with maleic anhydride and homopolypropylene, block copolymer grafted with maleic anhydride, homopropylene grafted with maleic anhydride along with minor amounts of scission products and crosslinking products.

The block copolymer used in the following was Kraton G 1651, a high molecular weight commercial SEBS copolymer. This polymer cannot be melt processed in pure form. Different ratios of this polymer to different polyolefins were simultaneously run through the maleic anhydride melt modification process described in Examples 1-11. In these examples, 0.2% by weight Lupersol 101 initiator was used. Again, all the reactants were simply premixed by drum treatment before feeding into the extruder. Table 5 gives a description of the polyolefins used.

Blends of nylon 66 with the melt-modified Kraton G-I651 block copolymers described above were prepared in the manner described in Examples 1-11. Physical properties in a dry, cast state for these mixtures are given in tables 6 and 7.

The examples show that mixtures of a thermoplastic polyamide with modified block copolymers in which polyolefins have been added retain impact resistance and show an increase in flexural modulus compared to corresponding mixtures without polyolefins.

The data in Table 6 show that the concentration of block copolymer can be reduced to 5% by weight of the total mixture while still maintaining a good balance of stiffness and toughness.

Claims (2)

1. Grafted block copolymer, characterized in that it comprises a selectively hydrogenated block copolymer having the general formula Bn(AB)0Ap in which each A is predominantly a polymerized monoalkenylaromatic hydrocarbon block having an average molecular weight in the range from 2,000 to 115,000, each B before hydrogenation is predominantly a polymerized conjugated diene hydrocarbon block having an average molecular weight in the range from 20,000 to 450,000, n = 0 or 1, o is in the range from 1 to 100 and p = 0 or 1, the blocks A constitute from 5 to 95% by weight of the copolymer, the unsaturation in block B is less than 20% of the original unsaturation and the unsaturation in the blocks A is greater than 50% of the original unsaturation, which block copolymer is grafted with (a) an acid moiety or a derivative thereof and (b) a polyolefin . 2. Method for producing a grafted block copolymer according to claim 1, characterized in that it comprises melt blending (a) a selectively hydrogenated block copolymer having the general formula Bn (AB) QAp, (b) an acid compound or a derivative of an acid compound and (c) a polyolefin, adding a free radical initiator , grafting reaction under free radical conditions and recovering grafted block copolymer product.