A major disadvantage of the cheap commodity polymers

10 and, in particular, of the thermoplastic hydrocarbon polymers, such as polyolefins, is their chemical inertness. In engineering applications and in the production of disposable packaging this is a serious limitation upon their usefulness since, due to their hydrophobic nature,

15 polyolefins are unable to form strong interactions with inorganic fillers or with most organic fillers. This limits their usefulness in engineering applications and in biodegradable composite materials due to the lack of an ability to undergo physical adhesion between the filler and

20 the hydrophobic polymer matrix. In such applications the filler can be inorganic, such as glass, calcium carbonate, alumina trihydrate and the like, or organic, such as starch, cellulose, or other biodegradable materials, of which there can be mentioned polyhydroxybutyratevalerate (PHBV) .

25 Consequently there has been very considerable commercial interest in recent years in modifying polyolefins so that, whilst retaining their useful mechanical properties, they can form strong chemical and/or physical bonds with modifying agents and inorganic fillers.

30 A number of polymers modified by incorporation of maleic acid or acrylic acid or a derivative thereof have appeared on the market. Amongst these there can be mentioned the product sold under the trade mark Polybond by Polysar and that sold under the trade mark Fusabond by DuPont 35 (Switzerland) . Both of these last-mentioned products are polypropylene which has been modified with maleic anhydride. Similar products are marketed by Exxon in the United States

of America, Atochem in France, and DSM in the Netherlands.

Two main processes are used in the prior art to produce modified polyolefins: -

1. Copolymerisation during polymer manufacture is one technique. In this case a polyolefin is modified by incorporation of a small amount of a second monomer during manufacture. Polypropylene/maleic anhydride copolymers are made in this way by Hercules in the United States of America. Such copolymers have been used as the basis for attaching u.v. stabilisers to the polypropylene backbone by Pennwalt, also in the United States of America. However, since this specialised polymer is produced in relatively small amounts and with a constant low extent of modification, it is relatively expensive and inflexible in its applications. 2. Grafted commodity copolymers have also been proposed. In principle chemical modification of commercial polyolefins by reactive processing is an economically attractive way of producing functional polymers. In such a technique the preformed polyolefin is reacted at elevated temperature in the presence of a free radical generator and under application of shear to the melt in a suitable piece of equipment such as a screw extruder. However, maleic anhydride reacts to a relatively small extent with polyethylene or with polypropylene in the presence of a free radical generator in a screw extruder. Not only is maleic anhydride of low reactivity---in such a polymerisation reaction but also it is believed to have low mutual solubility with a molten polymer such as polypropylene. Hence in practice most of the maleic anhydride remains unreacted following attempts at reactive processing. This is undesirable since the large proportion of unreacted maleic anhydride constitutes a potential toxicity hazard both during manufacture and also in the final product. This results in the need for purification of the graft copolymer product from the unused starting material, such as maleic anhydride. In the case of vinyl compounds the predominant reaction in a graft polymerisation

reaction is homopolymerisation of the vinyl compound, which results in formation of a separate phase that is non-soluble in the host polymer, such as polyethylene or polypropylene. For these reasons the prior art methods for producing modified polyolefins suffer from considerable disadvantages. A method of modifying polyolefins is described in US-A-4743657 in which an ethylenically unsaturated stabiliser precursor molecule that does not undergo homopolymerisation is reacted with a preformed polymer, such as a polyolefin, in the presence of a free radical and thereby bound to it. Such a stabiliser can contain on one or both of the carbon atoms of the ethylenically unsaturated double bond a carboxylic acid, ester, amide or imide group.

Production of a bound antioxidant polymer concentrate is described in EP-A-0285293. In this process an antioxidant comprising an acrylic or alkyl-acrylic ester or amide containing a hindered a ine group is grafted on to a polyolefin by reaction at 100°C to 350°C in the presence of a free radical generator, the molar ratio of the free radical generator to the antioxidant being from 0.001:1 to 1:1. The reaction is carried out until the melt viscosity of the polymer, which increases initially during the reaction, has reduced to a level which allows the resulting graft copolymer to be homogeneously blended into unstabilised polymer. O-A-90/01506 discloses a process for the production of a modified polyolefin which'',-can be used as an a polymer masterbatch for blending with unmodified polyolefin, in which an additive containing at least one functional polymer-modifying group is incorporated into a polyolefin by reacting a preformed polyolefin under shear conditions in the melt phase in the presence of a free radical generator with a mixture of (a) at least one polymerisable monomer containing an ethylenically unsaturated polymerisable group capable of being attached to the preformed polyolefin and at least one polymer-modifying group and (b) at least one comonomer containing no functional polymer-modifying group but at least

two ethylenically unsaturated polymerisable groups capable of being attached to the preformed polyolefin. The reaction is continued until the torque used in applying shear to the melt passes through a peak and then falls again, thereby producing a copolymer that is thermoplastic with a gel content of less than 0.5% by weight and that can be blended with the unmodified polyolefin.

Tri ethylol propane triacrylate (TMPTA) and divinylbenzene (DVB) contain three and two ethylenically unsaturated polymerisable groups respectively. Such compounds are normally regarded as cross-linking agents in polymerisation and graft polymerisation reactions, since they contain more than one ethylenically unsaturated polymerisable group and so can react with more than one polymer chain, thereby to form cross linkages.

EP-A-0247861 describes the use of a cross linking agent such as triallyl cyanurate and a free radical generator to link a tribromophenoxy or pentabromophenoxy ester of acrylic acid to a polyolefin. The resulting product is described as having a very high degree of crosslinking as shown by the very high gel content.

In EP-A-0044233 there is described a process in which styrene is polymerised in the presence of a rubbery terpolymer of ethylene, propylene and a third component, such as ethylidene norbornene, in the presence of a peroxide characterised in that the rubbery solution of monomers is polymerised in the presence of a monomer selected from divinylbenzene, triallyl cyanurate and glycol acrylate. The resultant product is cross-linked since it has a significant gel content.

JP-A-58/67446 teaches production of cross-linked polypropylene. According to this proposal polypropylene, propylene/ethylene block or random copolymer, propylene/oi- olefin copolymer or a mixture thereof is blended with an unsaturated carboxylic acid such as maleic anhydride, a crosslinking aid, such as divinylbenzene, divinyltoluene,

diallyl glycerate or liquid rubber comprising a diene monomer, and an organic peroxide, and the resulting blend is hot pressed against a metal product at more than the melting point of the polymer and then heated to a temperature higher than the decomposition point of the organic peroxide to crosslink the polymer.

Graft copolymers for use as ion exchange fibres are described in JP-A-53/8693 and JP-A-53/869 ; in the former specification polyamides and in the latter specification polyesters undergo graft polymerisation with hydroxystyrenes and/or acryloxystyrenes, preferably in the presence of polyene compounds, such as divinylbenzene, using ionising radiation.

It would be desirable to provide a modified polyolefin containing a higher proportion of bound maleic anhydride residues than prior art processes have achieved.

It would further be desirable to provide graft copolymers between a thermoplastic hydrocarbon polymer and a monomer enabling the resultant graft copolymer to react with hydrophilic organic fillers containing groups capable of reacting with acidic moieties.

Additionally it would be desirable to provide graft copolymers between a base polymer such as a polyolefin and maleic anhydride or the like which can be used with advantage in systems utilising glass fibre reinforcement.

It would further be advantageous to provide polymer alloys capable of undergoing at least a degree of biodegradation which retain many of the desirable properties of a polyolefin together with the propensity for at least partial biodegradation of the alloy.

The invention accordingly seeks to provide an improved graft copolymer between a thermoplastic hydrocarbon polymer and a monomer containing a moiety capable of undergoing reaction with hydroxyl, sulphydryl, amine and other acid-reactive groups.

It is a further object of the invention to provide a

graft copolymer between a polyolefin and a monomer comprising a C ₄ dicarboxylic acid or an amide, imide or anhydride thereof which contains a higher proportion of the bound monomer than is present in prior art graft copolymers of this type. Yet a further object of the invention is to provide a graft copolymer between a base polymer, such as a polyolefin, and a C ₄ dicarboxylic acid, amide, imide or anhydride thereof which is useful in environments utilising glass fibre reinforcement. The invention also seeks to provide a polymeric material which can be added to otherwise incompatible mixtures of a polyolefin and a biodegradable hydrophilic organic filler, such as starch, thereby to result in production of polymer alloys. According to the present invention there is provided a process for forming a graft copolymer between a thermoplastic hydrocarbon polymer and an ethylenically unsaturated monomer selected from a C ₄ unsaturated dicarboxylic acid, an amide of a C ₄ unsaturated dicarboxylic acid, an imide of a C ₄ unsaturated dicarboxylic acid, and an anhydride of a C ₄ unsaturated dicarboxylic acid, which comprises reacting together in the presence of free radicals and under shear conditions (i) a molten thermoplastic hydrocarbon polymer, (ii) at least one ethylenically unsaturated monomer selected from a C ₄ unsaturated dicarboxylic acid, an amide of a C ₄ unsaturated dicarboxylic acrd, an imide of a C ₄ unsaturated dicarboxylic acid, and an anhydride of a C ₄ unsaturated dicarboxylic acid, and (iii) at least one comonomer containing at least two ethylenically unsaturated polymerisable groups capable of being attached to the thermoplastic hydrocarbon polymer, the reaction being continued for a sufficient length of time to yield a graft copolymer containing bound residues of said at least one ethylenically unsaturated monomer. In this process the ethylenically unsaturated monomer is preferably maleic anhydride. The preferred thermoplastic

hydrocarbon polymer is a polyolefin such as polypropylene. The invention thus provides a process for preparing polypropylene/maleic anhydride adducts which are particularly valuable in polymer technology due to their ability not only to modify polypropylene physically but also to react with a variety of amines, alcohols, and other compounds which contain groups which react with acidic groups, such as sulphydryl groups, in very high yield. As will be appreciated by those skilled in the art the success of the process of the invention is based upon the use of the polyfunctional comonomer (iii) . The resulting graft copolymers are compatible with hydrophilic organic fillers such as starch, cellulose or polyhydroxybutyratevalerate and with inorganic fillers such as glass fibres. In the course of experiments leading to the making of the present invention it was found by the inventors that the maximum yield of maleic anhydride-grafted polypropylene that can be obtained by a conventional grafting procedure (in the absence of the comonomer) by reacting 1 g of maleic anhydride with 100 g of polypropylene in the presence of a dialkyl peroxide is 0.2 g (i.e. an adduct yield of only 20%) . Not only is the adduct yield so low because maleic anhydride is unreactive under polymerisation conditions but also, according to the opinion of the inventors, because it has low solubility in a polymer melt. The evidence currently available to the inventors is 'consistent with the theory that the comonomer used in the process of the present invention reacts with the maleic anhydride or other ethylenically unsaturated monomer to form an intermediate low molecular weight co-polymer which not only has higher solubility in the molten polymer than the ethylenically unsaturated monomer but also is more readily grafted to the thermoplastic hydrocarbon polymer. Using the process of the invention it is possible to achieve adduct yields of 80% or higher. Under favourable reaction conditions the adduct yield can be such that essentially no unreacted ethylenically unsaturated monomer

can be found in the graft copolymer product. Hence the process of the invention allows the possibility of using a C ₄ dicarboxylic acid, or an amide, imide or anhydride thereof for forming graft copolymers not only with greater technological efficiency than the prior art but also to yield graft copolymers which can be used in applications for which the prior art graft copolymers could not have been used previously. Examples of such applications include uses in the biomedical field or for food contact applications where migration of low molar mass additives from a polymer would constitute a toxicity hazard. It further allows the possibility of producing engineering polymers based on polyolefins for use in applications in which the inert nature of a conventional polyolefin limits its usefulness in composite materials. The use of the graft copolymers produced by the process of the invention for the production of starch-polyolefin composites, which are increasingly favoured by the packaging industry because of their increased biodegradability in compost disposal, can also be envisaged. Conventional starch-polyolefin composites are made by mixing low density polyethylene that has been modified by incorporation of maleic anhydride (MA-modified LDPE) with 50% or more of starch to give films with very acceptable properties. However, the present cost of conventional food grade MA-modified polyethylene rules out this route as a commercially viable route ti such biodegradable starch-filled polyolefins. In view of the high adduct yields achievable using the process of the present invention the resulting MA-modified graft copolymers have promise as the basis for biodegradable polyolefin-starch composites. Hence the invention envisages use of graft copolymers produced in accordance with the invention as polymer masterbatches for admixture with unmodified polyolefins (e.g. unmodified low density polyethylene or polypropylene) and starch, typically in a single step process, for production of new biodegradable polymer alloys.

In the process of the invention the thermoplastic hydrocarbon polymer may be selected from polyolefins and rubber modified plastics materials. Thus it may be selected from, for example, high density polyethylene, low density polyethylene, polypropylene, ethylene/propylene block copolymers, and ethylene/propylene random copolymers. Ethylene-propylene terpolymers with another -olefin such as butene-1 or ethylidene norbornene can alternatively be used. Preferably the ethylenically unsaturated monomer is selected from maleic acid, fumaric acid, maleimide, and maleic anhydride.

Conveniently the reaction is effected in a screw extruder with a residence time therein of from about 1 to about 15 minutes. In one preferred procedure the reaction is conducted in the presence of a free radical generator which decomposes when heated to form free radicals and at a temperature of from about 100°C to about 350°C, the temperature being higher than the melting point of the thermoplastic hydrocarbon polymer and higher than the decomposition point of the free radical generator. As examples of free radical generators there can be mentioned dicumyl peroxide (DCP) ,

2, 5-dimethyl-t.-butyl-peroxy-hexane (BPH) , di-£.-butyl peroxide (DTBP) , and di-£.-butyl peroxy carbonate (DTBPC) . The comonomer contains at least two ethylenically unsaturated polymerisable groups capable of being attached to the thermoplastic hydrocarbon polymer. Preferably the comonomer contains two or more vinyl, maleate, or fumarate groups in the molecule. Examples include trimethylol propane triacrylate (TMPTA) , tris-acryloyl trimethylol butane

(TMBTA) , divinylbenzene (DVB) , and triallyl cyanurate (TAC) . Other examples of comonomer include benzene-1, 3-Jbis-maleimide.

In the process according to the invention it is preferred that the molar ratio of the comonomer to the ethylenically unsaturated monomer is from about 0.001:1 to

about 1:1, for example from about 0.005:1 to about 0.1:1, even up to about 0.5:1.

In the process of the invention the amount of ethylenically unsaturated monomer used may vary within wide limits, for example from about 0.1% up to about 25% by weight or more, preferably from about 0.5% up to about 15% by weight, and even more preferably from about 1% up to about 10% by weight, based upon the weight of thermoplastic hydrocarbon polymer. It is also preferred that the molar ratio of the free radical generator to the ethylenically unsaturated monomer is from about 0.00005:1 to about 0.1:1, and even more preferably from about 0.0001:1 to about 0.02:1.

The process may include the further step of extracting from the resulting crude graft copolymer substantially all of any remaining unreacted ethylenically unsaturated monomer; one method of achieving this result is to effect extraction with an organic solvent for the ethylenically unsaturated monomer in which the graft copolymer is substantially insoluble, for example dichloromethane, acetone, or a mixture thereof .

In a preferred process the ethylenically unsaturated monomer is maleic anhydride and the process includes the further step of reacting the graft copolymer with a diamine, for example an alkylene diamine containing from 2 to 10 carbon atoms, such as hexam thylene diamine. In this further reaction step the diamine:maleic anhydride molar ratio may lie, for example, in the range of from about 0.1:1 to about 3:1, preferably from about 0.5:1 to about 2:1, e.g. about 1:1 to about 1.5:1. The step of reacting the graft copolymer with a diamine is preferably conducted at elevated temperature, for example a temperature of from about 100°C up to about 240°C, preferably from about 150°C to about 220°C, e.g. at about 200°C. This reaction step is preferably conducted while mixing the reaction mixture. The resultant product can be used to compatibilise otherwise immiscible

polymer blends. For example, a graft copolymer obtained by reacting a mixture of polypropylene and ethylene-propylene- diene terpolymer with maleic anhydride and with trimethylol propane trisacrylate in the presence of a free radical generator, followed by reaction with hexamethylene diamine, can be used to compatibilise a blend of otherwise substantially immiscible polymer, such as polypropylene and ethylene-propylene-diene terpolymer, at levels of from about 0.5% to about 5% by weight of graft copolymer based upon the weight of the resultant blend of the graft copolymer and the polymer mixture. In such blends the weight ratio of the otherwise immiscible polymers may vary within wide limits, e.g. from about 0.1:1 to about 10:1 by weight.

The invention further provides a process for the production of a polymer masterbatch which comprises:

(a) forming a graft copolymer between a thermoplastic hydrocarbon polymer and an ethylenically unsaturated monomer selected from a C ₄ unsaturated dicarboxylic acid, an amide of a C ₄ unsaturated dicarboxylic acid, an imide of a C ₄ unsaturated dicarboxylic acid, and an anhydride of a C ₄ unsaturated dicarboxylic acid, by reacting together in the presence of free radicals and under shear conditions (i) a molten thermoplastic hydrocarbon polymer, (ii) at least one ethylenically unsaturated monomer selected from a C ₄ unsaturated dicarboxylic acid, an amide of a C ₄ unsaturated dicarboxylic acid, an imide Jof. a C ₄ unsaturated dicarboxylic acid, and an anhydride of a C ₄ unsaturated dicarboxylic acid, and (iii) at least one comonomer containing at least two ethylenically unsaturated polymerisable groups capable of being attached to the thermoplastic hydrocarbon polymer; and

(b) reacting the resulting graft copolymer with a hydrophilic organic filler.

In such a process reacting step (b) can be conducted in the presence of added unmodified thermoplastic hydrocarbon polymer or another compatible polymer.

The invention further relates to a process for forming

a graft copolymer between a thermoplastic hydrocarbon polymer and an organic hydrophilic filler which comprises reacting together in the presence of free radicals and under shear conditions (i) a molten thermoplastic hydrocarbon polymer, (ii) an organic hydrophilic filler, (iii) at least one ethylenically unsaturated monomer selected from a C ₄ unsaturated dicarboxylic acid, an amide of a C ₄ unsaturated dicarboxylic acid, an imide of a C ₄ unsaturated dicarboxylic acid, and an anhydride of a C ₄ unsaturated dicarboxylic acid, and (iv) at least one comonomer containing at least two ethylenically unsaturated polymerisable groups capable of being attached to the thermoplastic hydrocarbon polymer.

Also provided in accordance with the invention is a process for forming a polymer alloy of a thermoplastic hydrocarbon polymer and an hydrophilic organic filler which comprises admixing a graft copolymer product prepared according to the invention with at least one material selected from a thermoplastic hydrocarbon polymer and a hydrophilic organic filler. According to another aspect of the present invention there is provided a graft copolymer comprising a thermoplastic hydrocarbon polymer having bound thereto, by means of residues of at least one comonomer containing at least two ethylenically unsaturated polymerisable groups capable of being attached to the thermoplastic hydrocarbon polymer, residues of at leadt one ethylenically unsaturated monomer selected from a C, unsaturated dicarboxylic acid, an amide of a C ₄ unsaturated dicarboxylic acid, an imide of a C ₄ unsaturated dicarboxylic acid, and an anhydride of a C ₄ unsaturated dicarboxylic acid.

It further provides a graft copolymer between a thermoplastic hydrocarbon polymer and a hydrophilic organic filler comprising a thermoplastic hydrocarbon polymer having bound thereto, by means of residues of at least one comonomer containing at least two ethylenically unsaturated polymerisable groups capable of being attached to the

thermoplastic hydrocarbon polymer, residues of at least one ethylenically unsaturated monomer selected from a C ₄ unsaturated dicarboxylic acid, an amide of a C ₄ unsaturated dicarboxylic acid, an imide of a C ₄ unsaturated dicarboxylic acid, and an anhydride of a C ₄ unsaturated dicarboxylic acid, said residues of said at least one ethylenically unsaturated monomer having been reacted with said organic filler.

The invention also extends to homogeneous blends between a thermoplastic hydrocarbon polymer and a hydrophilic organic filler, such as starch, cellulose, or polyhydroxybutyratevalerate, or with an inorganic filler such as glass fibres, wherein the otherwise incompatible components of the blend are rendered compatible with one another by virtue of the presence of an effective amount of a graft copolymer according to the invention between a polyolefin and the ethylenically unsaturated monomer, and the comonomer.

Such a hydrophilic organic filler can be, for example, in the form of natural fibres. Examples of such natural fibres include plant fibres such as cotton, sisal, jute, hemp, flax, oil palm empty fruit bunch fibres, coconut fibres, and the like. When using starch the filler may be in the form of a powder. Typical starches include potato starch, corn starch, and the like. Regenerated cellulose can also be used in powder, pellet or fibre form.

The amount of filler used can vary within wide limits, for example from about 0.5% by weight up to about 50% by weight or more, preferably from about 1% to about 30%, and even more preferably from about 2% by weight up to about 20% by weight, based upon the weight of the resulting composite. Since the graft copolymers produced in accordance with the invention contain reactive groups, e.g. anhydride, amide, imide or carboxylic acid groups, which can be reacted with other reactive groups such as -OH, >NH, and -SH, a graft copolymer produced according to the invention can be blended with a compatible polymer containing such other reactive

groups (e.g. -OH, >NH and/or -SH groups) and reacted therewith by bringing them into intimate mixture by means of a high-shear extension process. When such co-reacted blended polymers contain more or less equivalent molar ratios of the disparate components, the resultant block or graft copolymers can be used as solid phase dispersants (or compatibilisers) for the same or different polymer blends.

Surprisingly, despite the use during the product of the graft copolymer of a comonomer containing at least two ethylenically unsaturated polymerisable groups (i.e. a compound which is normally a cross-linking agent) , the resulting graft polymers are thermoplastic and can be blended with other polymers .

The invention is further illustrated in the following Examples in which all parts and percentages are by weight. Examples 4, 13 and 17 are Comparative Examples. Example 1

A mixture of 90 parts of polypropylene (PP) and 10 parts of a mixture of maleic anhydride (MA) and trimethylol propane triacrylate (TMPTA) was processed in an internal mixer at 180°C with the addition of

2, 5-dimethyl-£.-butyl-peroxy-hexane (BPH) . The molar ratio of TMPTA to MA was 0.04:1 and the molar ratio of BPH to the mixture of TMPTA and MA was 0.002:1. The reaction time was 10 minutes.

Using infrared spectrdscopy the amount of maleic anhydride remaining in the processed polymer was estimated to be 4.5 g/100 g. This figure was obtained by measuring the total carbonyl area in the infrared spectrum and calculation using calibration curves. It is believed that the losses of maleic anhydride during processing were due to volatilisation at the high processing temperature used.

The product was compression moulded to film and the amount of maleic anhydride remaining after extraction with dichloromethane was estimated by spectroscopy to be 3.8 parts. This corresponded to 84% of the amount present before

extraction.

The amount of maleic anhydride grafted was determined by Soxhlet extraction with xylene followed by precipitation in acetone, drying and spectrophotometric analysis. This was found to be 3.6 g/lOO g, i.e. 40% of the initial amount of maleic anhydride added. Example 2

Example 1 was repeated but using a weight ratio of polypropylene to a mixture of maleic anhydride and TMPTA of 93:7 and a molar ratio of TMPTA:MA of 0.07:1. The molar ratio of BPH to the mixture of MA and TMPTA was 0.002:1. The amount of MA remaining after extraction with dichloromethane was 87% of the amount before extraction and the amount of MA grafted, based on the initial amount of MA, was found to be 82%.

Example 3

A mixture of 96 parts of polypropylene (PP) and 4 parts of a mixture of maleic anhydride (MA) and divinyl benzene (DVB) was processed in an internal mixer at 180°C with the addition of 2, 5-dimethyl-i-butyl-peroxy-hexane (BPH) . The molar ratio of DVB:MA was 0.32:1, while the molar ratio of BPH to the mixture of MA and DVB was 0.013:1. The amount of MA remaining after extraction with dichloromethane was 71% of the amount present before extraction. Example 4

94 parts of polypropylene and 6 parts of maleic anhydride were processed following the general procedure of Example 1 with the addition of BPH in a ratio of BPH: A of 0.01:1, but with no addition of TMPTA. The amount of MA remaining after extraction with dichloromethane was found to be 9% of the amount before extraction and the amount of MA grafted, based on the initial amount of MA, was found to be 5.6% only. Example 5 The procedure of each of Examples 1 to 4 is repeated except that benzene-1, 3-bis-dimaleimide is used in place of

TMPTA or DVB. Similar results are obtained. Example 6

90 parts of polypropylene and 10 parts of a mixture of TMPTA and maleic anhydride (TMPTA:MA molar ratio 0.14:1) were processed under the same general conditions as used in

Example 1. The molar ratio of BPH to the mixture of TMPTA and MA was 0.002:1. The amount of maleic anhydride (MA) grafted amounted to 93%, as determined by Soxhlet extraction with xylene followed by precipitation with acetone. Example 7

The procedure of Example 6 was repeated except that the following molar ratios were used:

TMPTA:MA 0.08:1

BPH: (TMPTA + MA) 0.005:1 The amount of MA grafted corresponded to 91%. Example 8

In this experiment 90 parts of ethylene-propylene terpolymer (an ethylene-propylene-ethylidene norbornene terpolymer) were reacted under the general reaction conditions of Example 1 with 10 parts of a mixture of MA and TMPTA. The TMPTA:MA molar ratio was 0.33:1 and the BPH: (TMPTA + MA) molar ratio was 0.001:1. The amount of MA remaining after extraction with dichloromethane, as estimated by spectroscopy, represented 88% of that present before extraction.

Example 9 ,

90 parts of a 3:1 by weight mixture of polypropylene (PP) and ethylene-propylene-diene terpolymer (EPDM) and 10 parts of a 6:4 by weight mixture of maleic anhydride (MA) and trimethylolpropane trisacrylate (TMPTA) were processed in an internal mixer at 180°C with the addition of 2,5-dimethyl-t _. - butyl-peroxy-hexane (BPH) . The molar ratio of BPH to the mixture of MA and TMPTA was 0.002:1. After 10 minutes reaction time, 10 parts of hexamethylenediamine (HEMDA) was added to the reaction mixture. The reaction was then continued for a further 10 minutes.

Example 10

1 part of the product of Example 9 was used as a compatibiliser for an immiscible polymer blend by mixing it with 99 parts of a 3:1 by weight mixture of polypropylene (PP) and ethylene-propylene-diene terpolymer (EPDM) . The resultant polymer blend mixture was processed in an internal mixer at 200°C for 10 minutes. The toughness factor (FT) of the product obtained was 112 MPa, the elongation to break was 566% and the tensile strength was 21 MPa. Example 11

90 parts of a 3:2 by weight mixture of polypropylene (PP) and ethylene-propylene-diene terpolymer (EPDM) and 10 parts of a 6:4 by weight mixture of MA and TMPTA were processed in an internal mixer at 180°C with addition of BPH. The molar ratio of BPH to the mixture of MA and TMPTA was 0.005:1. After 10 minutes reaction time 3 parts of HEMDA were added to this mixture. The reaction was then continued for a further 10 minutes. Example 12 1 part of the product of Example 11 was then used as a compatibiliser for an immiscible polymer blend by mixing it with 99 parts of a 3:1 by weight mixture of polypropylene (PP) and ethylene-propylene-diene terpolymer (EPDM) . The resultant mixture was processed in an internal mixer at 200°C for 10 minutes. The product blend had a toughness factor

(FT) of 99 MPa, the elongation to break was 475%, the Young's modulus was 661 MPa, and the tensile strength was 22 MPa. Example 13

For comparison purposes, 94 parts of a 3:2 by weight PP:EPDM polymer mixture and 6 parts MA were processed in an internal mixer at 180°C with the addition of BPH. The BPH:MA molar ratio was 0.005:1. After 10 minutes under these conditions 3 parts of HEMDA were added to the resultant mixture. Reaction was continued for a further 10 minutes. 1 part of the resultant product was mixed with 99 parts of a 3:1 by weight mixture of PP and EPDM. After processing

this mixture at 200°C for 10 minutes in an internal mixer, the toughness factor (FT) was 39 MPa, the elongation to break was 267%, the Young's modulus was 555 MPa, and the tensile strength was 19 MPa. Example 14

90 parts of polypropylene and 10 parts of a 7:3 by weight mixture of maleic anhydride (MA) and trimethylol- propane tris-acrylate were processed at 180°C in an internal mixer for 10 minutes with the addition of BPH. The molar ratio of BPH to the mixture of MA and TMPTA was 0.002:1. Analysis of the product by titration indicated that it contained 5 parts of MA. Thus approximately 1 part of MA was lost by vaporisation. Solvent extraction followed by re- analysis by titration indicated that the product contained 2.78 parts of bound MA in total. Example 15

90 parts of polypropylene was mixed with 5 parts of natural fibres from oil palm empty fruit bunches and with 5 parts of the product of Example 14 at 180°C for 10 minutes in an internal mixer. The resulting polymer composite exhibited a tensile strength of 35 MPa, a toughness factor (FT) of 7.5 MPa, an elongation to break of 51%, and a Young's modulus of 83 MPa. Example 16 85 parts of polypropylene, 5 parts of the product of

Example 14 and 10 parts of tlhe same natural fibres as used in Example 15 were processed under the same conditions as in Example 15. The resulting polymer composite had a tensile strength of 36 MPa, its toughness factor (FT) was 7.6 MPa, its elongation to break was 54%, and its Young's modulus was 80 MPa. Example 17

As a comparison with the results of Examples 15 and 16, 95 parts of polypropylene were mixed with 5 parts of natural fibres from oil palm empty fruit bunches at 180°C in an internal mixer for 10 minutes. The resulting polymer

composite had the following properties _: -

Tensile strength 29 MPa Toughness factor ₄ .4 MPa Elongation to break ₃ 3% Young's modulus ₁ 0 ₇ MPa