EP0660845A1

EP0660845A1 - Process for the preparation of olefin polymers

Info

Publication number: EP0660845A1
Application number: EP93920694A
Authority: EP
Inventors: Bruno Rotzinger; Alfred Columberg; Jean-Roch Pauquet
Original assignee: Ciba Geigy AG; Ciba Spezialitaetenchemie Holding AG
Current assignee: BASF Schweiz AG
Priority date: 1992-09-17
Filing date: 1993-09-08
Publication date: 1995-07-05
Also published as: CN1042338C; MX9305698A; WO1994006831A1; SK34095A3; JPH08501580A; CA2143103A1; TW321658B; KR950703581A; MY110671A; CN1084181A; AU679453B2; CZ66995A3; AU4815793A

Abstract

The addition of at least one compound of the series of the hydrotalcites, zeolites or metal oxides that does not release water under the reaction conditions to the polymerisation of olefins with solid supported catalysts effects a strong reduction in the corrosive action of the polymers without adversely affecting the polymerisation itself or the properties of the polymers. Further stabilisers may also be added.

Description

Process for the preparation of olefin polymers

The present invention relates to a process for the preparation of olefin polymers in which hydrotalcites, zeolites or metal oxides and optional stabilisers are added during the polymerisation. The invention also relates to the olefin polymers so obtained.

The low-pressure polymerisation of olefins with organometallic complex catalysts (e.g. Ziegler-Natta catalysts) usually results in a finely powdered polymer which is extruded in an extruder before being shaped by processing. In this granulation, substances such as stabilisers, corrosion inhibitors, colour enhancers, antistatic agents or other processing auxiliaries. However, this granulation is not always desired or possible, inter alia, with polymers of high molecular weight.

Recendy, it has proved possible by using solid supported catalysts to prepare spherical, granular-type polymers that no longer have to be granulated by extrusion, but can be processed direct. Suitable supports for these solid catalysts have been found to be in particular spherical magnesium halides of specific particle size as disclosed, inter alia, in DE-A-2641 960. The anhydrous magnesium halide forms with TiCl and electron donors insoluble complexes which are then activated with aluminium alkylene. The stereospecificity and activity are enhanced by using electron donors such as carboxylic acid esters or compounds containing Si-O-C bonds as disclosed, inter alia, in EP-A-45 977.

As the polymers so obtained no longer have to be granulated, it was then desired to add modifiers which are important for processing and long-term stability during polymerisation. The addition of many conventional modifiers (e.g. stabilisers) interferes with the olefin polymerisation and causes discolouration of the polymers.

The machines used in further processing of the polymers, e.g. calanders, are subject to corrosion. The corrosive action of the polymer on metal surfaces is generally attributed to catalyst residues or degradation products of the catalyst system. Up to now it has been necessary to add a corrosion inhibiting compound in a separate processing step.

It is known (EP-A-192987 or EP-A-0350444) that sterically hindered amine stabilisers of the polyalkylpiperidine type do not interfere with the polymerisation and do not substantially discolour the polymer and effect good thermal oxidative stability.

It has further been proposed (EP-A-254348) to add organic phosphites or phosphonites as antioxidants.

It is also known to add sterically hindered amine stabilisers of the polyalkylpiperidine type in conjunction with organic phosphites or phosphonites during the polymerisation (EP-A-0351 360).

Surprisingly, it has now been found that the addition of compounds of the series of the hydrotalcites, zeolites or metal oxides which do not release water under the reaction conditions, in conjunction with optional stabilisers, does not interfere with the polymerisation of olefins and substantially prevents corrosion otherwise occurring during polymerisation, and that excellent long-term stability is achieved by adding further stabilisers.

Accordingly, the invention relates to a process for the preparation of olefin polymers by polymerisation using transition metal catalysts, which comprises carrying out the polymerisation by adding at least one compound of the series of the hydrotalcites, zeolites or metal oxides that do not release water under the reaction conditions.

The polymerisation is preferably carried out witii a solid supported transition metal catalyst which has been prepared by reacting an aluminium compound carrying at least one alkyl group with a compound of a metal of the IVth subgroup of the Periodic Table.

The olefins polymerisable by this process are ethylene and α-olefins such as propylene, but-1-ene, 4-methylpent-l-ene or 5-methylhex-l-ene, as well as mixtures of olefins, typically ethylene-propylene or propylene in admixture with minor amounts of higher α-olefϊns. The process for the polymerisation and copolymerisation of propylene is of particular interest

1

The polymerisation catalysts are transition metal catalysts. They typically consist of a magnesium dihalide in active form and a titanium compound. Catalysts with the other metals of the IVth subgroup of the Periodic Table (Zr and Hf) are also suitable. By magnesium dihalide in active form is meant one in whose X-ray spectrum the line of strongest reflectivity is broader than the corresponding line in the spectrum of the inactive magnesium halide.

It is preferred to use magnesium dichloride or magnesium dibromide as magnesium dihalide. The titanium compounds preferably contain at least one titanium-halide bond. It is particularly preferred to use titanium tetrachloride.

The titanium compound can be used in conjunction with an electron donor, typically a carboxylic acid ester, as disclosed in EP-A-45 977.

After reaction of the magnesium halide component with the titanium compound and, where appropriate, the electron donor, excess titanium compound and excess electron donor are conveniently washed off witii an inert solvent, typically with hexane or heptane.

The catalyst so prepared is activated by reaction with an aluminium compound which carries at least one alkyl group and is used preferably as a solution in an alkane. Exemplary of suitable aluminium alkyls are A C^H^ or A QH^. It is possible to use an electron donor as co-activator, convenienUy an organic silicon compound that contains at least one Si-O-C bond, as disclosed in EP-A-45 977. Typical examples of such silicon compounds are phenyl triethoxysilane, phenyl trimethoxysilane, diphenyl dimethoxysilane, methyl triethoxysilane, dimethyl diethoxysilane or ethyl trimethoxysilane.

Further transition metal catalysts typically consist of a chromium compound on a solid support, e.g. alumina or silica or mixtures thereof. Examples of such catalysts, also called Phillips catalysts, will be found in US-A-2 825 721.

The polymerisation with these catalysts can be carried out by known methods in liquid phase or in the gas phase. The liquid phase may conveniendy be an aliphatic hydrocarbon or the liquid monomer itself.

The compounds of the series of the hydrotalcites, zeolites or metal oxides mat do not release water under the reaction conditions arc added to the polymerisation medium at the start, during, or towards the end of the polymerisation.

Compounds of the series of the hydrotalcites, zeolites or metal oxides are the naturally occurring minerals as well as synthetically prepared compounds.

Compounds of the series of the hydrotalcites may be illustrated by the general formula

M²⁺ _!._x ^«M³⁺ _X '(OH)₂ -(A*-)_x ^• mH₂O ^

'n

wherein

M²⁺ = Mg, Ca, Sr, Ba, Zn, Cd, Pb, Sn and or Ni,

M³* = Al, B or Bi,

Aⁿ is an anion of valency n, n is a number from 1 to 4, x is a number from 0 to 0.5, m is a number from 0 to 2, and

A = OH% C1-, Br, I\ CKV, HCO₃-, CH₃COO-, C₆H₅COO-, CO₃ ²-, SO₄ % coo- CH₃CHOHCOO-, SiO₃ ²-, SiO₄ ^4", Fe(CN)₆ ³', Fe(CN)₆ ⁴- orHPO₄ ²\

Other hydrotalcites which may conveniently be used in the process described above are compounds of the general formula la

M^Al^OH^^A"-^ .mH₂O (la)

wherein M²⁺ is at least one metal of the series of Mg and Zn, Mg being preferred, Aⁿ" is an

anion of the series of CO₃ ^2', COO/ , OH^' and S^2', and n is the valency of the anions, m is a positive number, preferably from 0.5 to 5, and x and z are positive numbers, and x is preferably 2 to 6 and z is smaller than 2.

Preferred compounds of the series of the hydrotalcites are those of the general formula I

M²⁺j._x -M³⁺ _x ^«(OH)₂ -(A^»-)_x ^• mH₂O _(I)

'n wherein M²⁺ is Mg or denotes a solid solution of Mg and Zn, A^n" is CO₃ ²% x is a number from 0 to 0.5 and m is a number from 0 to 2.

Particularly preferred hydrotalcites are those of formulae

Al₂O₃-6MgO CO₂- 12H₂O,

Mg₄,₅Al₂(OH)₁₃.CO₃-3,5H₂O,

4MgO-Al₂O₃ CO₂-9H₂O,

4MgO-Al₂O₃-CO₂-6H₂O,

ZnO-3MgO Al₂O₃-CO₂-8-9H₂O oder

ZnO-3MgO Al₂O₃-CO₂-5-6H₂O .

In the practice of this invention it is also possible to use zeolites of the general formula (X)

M_x/n[(AlO₂)_x(SiO₂)_y].wH₂O (X)

wherein n is the charge of the cation M,

M is an element of the first or second main group of the Periodic Table, y : x is a number from 0.8 to 1.2, and w is a number from 0.5 to 10.

The preferred per se known zeolites which may be used in the above process have an average pore diameter of 3-5 A, including those of the NaA type that have an average effective pore diameter of 4 A, for which reason they are also called 4A zeolites.

Illustrative examples of suitable zeolites are the compounds:

Na₁₂[(AlO₂)₁₂(SiO₂)₁₂]-12H₂O

Ca_4,5Na₃[(AlO₂)₁₂(SiO₂)₁₂]-30H₂O K₉Na₃[(AlO₂)₁₂(SiO₂)₁₂]-27H₂O

Metal oxides can also be used in the process of this invention. Oxides of divalent metals are preferred. Oxides of metals of the second main group or subgroup of the Periodic Table are especially preferred, and zinc or magnesium oxide is most preferred.

The novel compounds are dried to remove the unbound or only loosely bound water at 50-800°C, preferably 80-400°C, provided tiiey are not already sufficiendy dry and have been stored with exclusion of moisture. Drying can be caπied out under vacuum or inert gas. The surfaces of the substances can be treated with surface active reagants such as carboxylic acids or linear alcohols of 8 or more carbon atoms, convenienύy stearic acid.

The compounds of the series of the hydrotalcites, zeolites or metal oxides or similar synthetically prepared compounds that do not release water under the reaction conditions are normally added in an amount of 0.005 to 5.0 % by weight, preferably from 0.01 to 1 % by weight, based on the polymer.

The process is preferably carried out using additional stabilisers.

A particularly preferred embodiment of the invention comprises carrying out the above process by the further addition of a compound that contains at least one 2,2,6,6-tetra- methylpiperidine radical and that has a molecular weight above 500, or by the further addition of a phosphorus(III) compound. The use of such a 2,2,6,6-tetramethylpiperidine compound with a phosphorus(III) compound is particularly preferred.

The sterically hindered amines, preferably piperidines, are known in particular as light stabilisers, but they act here also as antioxidants, i.e. tiiey impart thermal oxidative stability to the polymer. These compounds contain one or more than one group of formula I

They may be oligomeric or polymeric compounds.

Particularly important stabilisers are the following classes of tetramethylpiperidines:

a) compounds of formula II

wherein n is a number from 1 to 4, preferably 1 or 2, R¹ is hydrogen, oxyl, C₃-C₈alkenyl, C₃-C₈alkynyl, C₇-C₁₂aralkyl, -Cgalkanoyl, C₃-C₅alkenoyl, glycidyl or a group -CH₂CH(OH)-Z, wherein Z is hydrogen, methyl or phenyl, the preferred meaning of R¹ being C₁-C₄alkyl, allyl, benzyl, acetyl or acryloyl, and R², if n is 1, is hydrogen, which may be interrupted by one or more than one oxygen atom, cyanoethyl, benzyl, glycidyl, a monovalent radical of an aliphatic, cycloaliphatic, araliphatic, unsaturated or aromatic carboxylic acid, carbamic acid or or phosphorus containing acid, or is a monovalent silyl radical, preferably a radical of an aliphatic carboxylic acid of 2 to 18 carbon atoms, of a cycloaliphatic carboxylic acid of 7 to 15 carbon atoms, of an α,β-unsaturated carboxylic acid of 3 to 5 carbon atoms or of an aromatic carboxylic acid of 7 to 15 carbon atoms, and, if n is 2, is C₁-C₁₂alkylene, C₄-C₁₂alkenylene, xylylene, a divalent radical of an aliphatic, cycloaliphatic, araliphatic or aromatic dicarboxylic acid, dicarbamic acid or phosphorus containing acid, or is a divalent silyl radical, preferably a radical of an aliphatic dicarboxylic acid of 2 to 36 carbon atoms, of a cycloaliphatic or aromatic dicarboxylic acid of 8 to 14 carbon atoms, or of an aliphatic, cycloaliphatic or aromatic dicarbamic acid of 8 to 14 carbon atoms, and, if n is 3, is a trivalent radical of an aliphatic, cycloaliphatic or aromatic tricarboxylic acid, of an aromatic tricarbamic acid or of a phosphorus containing acid, or is a trivalent silyl radical, and, if n is 4, is a tetravalent radical of an aliphatic, cycloaliphatic or aromatic tetracarboxylic acid.

Substituents defined as C₁-C₁₂alkyl may typically be methyl, ethyl, n-propyl, n-butyl, sec-butyl, tert-butyl, n-hexyl, n-octyl, 2-ethylhexyl, n-nonyl, n-decyl, n-undecyl or n-dodecyl dar. R² as C_j-C_jgalkyl may be the groups listed above and may additionally be n-tridecyl, n-tetradecyl, n-hexadecyl or n-octadecyl.

R¹ as C₃-C₈alkenyl may typically be 1-propenyl, allyl, mediallyl, 2-butenyl, 2-pentenyl, 2-hexenyl, 2-octenyl, 4-tert-butyl-2-butenyl.

R¹ as C₃-C₈alkynyl is preferably propargyl.

R¹ as C₇-C₁₂aralkyl is preferably phenethyl and, most preferably, benzyl.

R¹ as C₁-C₈alkanoyl is typically formyl, propionyl, butyryl, octanoyl, but is preferably acetyl and, as C₃-C₅alkenoyl, is preferably acryloyl.

R² defined as a monovalent radical of a carboxylic acid is typically the radical of acetic acid, capronic acid, stearic acid, acrylic acid, methacrylic acid, benzoic acid or β-(3,5-di- tert-butyl-4-hydroxyphenyl)propionic acid.

R² defined as a divalent radical of a dicarboxylic acid is typically the radical of malonic acid, succinic acid, glutaric acid, adipic acid, suberic acid, sebacic acid, maleic acid, phd alic acid, dibutylmalonic acid, dibenzylmalonic acid, butyl-(3,5-di-tert-butyl-4-hy- droxybenzyl)malonic acid or bicycloheptendicarboxylic acid.

R² defined as a trivalent radical of a tricarboxylic acid is typically the radical of trimellitic acid or of nitrilotriacetic acid.

R² defined as a tetravalent radical of a tetracarboxylic acid is typically the tetravalent radical of butane- 1,2,3 ,4-tetracarbooxylic acid or of pyromellitic acid.

R² defined as a divalent radical of a dicarbamic acid is typically the radical of hexamethylenedicarbamic acid or of 2,4-toluylenedicarbamic acid.

b) Compounds of formula (III)

wherein n is 1 or 2, R¹ is as defined under a), R³ is hydrogen, C_!-C₁₂alkyl, C^-Cshydroxyalkyl, C₅-C₇cycloalkyl, C₇-Cgaralkyl, C₂-C₁₈alkanoyl, C₃-C₅alkenoyl or benzoyl and, R⁴, if n is 1, is hydrogen, C C₁₈alkyl, C₃-C₈alkenyl, C₅-C₇cycloalkyl, C_rC₄alkyl which is substituted by a hydroxyl, cyano, alkoxycarbonyl or carbamido group, glycidyl, a group of formula -CH₂-CH(OH)-Z or of formula -CONH-Z, wherein Z is hydrogen, methyl or phenyl; or, if n is 2, R⁴ is Q₂-C₁₂alkylene, C₆-C₁₂arylene, xylylene, a -CH₂-CH(OH)-CH₂ group or a -CH₂-CH(OH)-CH₂-O-D-O- group, wherein D is Cjj-Cjoalkylene, C_δ-Cisarylene, C₆-C₁₂cycloalkylene, or, with the proviso that R³ is not alkanoyl, alkenoyl or benzoyl, R⁴ is also a divalent radical of an aliphatic, cycloaliphatic or aromatic dicarboxylic acid or dicarbamic acid or may also be the -CO- group, or R³ and R⁴, when taken together, if n is 1, may be the divalent radical of an aliphatic, cycloalipha¬ tic or aromatic 1,2- or 1,3-dicarboxylic acid.

Substituents defined as have the meanings already given under a).

Substituents defined as C₅-C₇cycloalkyl are preferably cyclohexyl.

R³ as C₇-C₈aralkyl is preferably phenylethyl or, most preferably, benzyl. R³ as C₂-C₅hydroxyalkyl is preferably 2-hydroxyethyl or 2-hydroxypropyl.

R³ as C₂-C₁₈alkanoyl is typically propionyl, butyryl, octanoyl, dodecanoyl, hexadecanoyl, octadecanoyl, but is preferably acetyl and, as C₃-C₅alkenoyl, is preferably acryloyl.

R⁴ as C₂-C₈alkenyl is typically allyl, methallyl, 2-butenyl, 2-pentenyl, 2-hexenyl or 2-octenyl.

R⁴ as Cj- alkyl which is substimted by a hydroxyl, cyano, alkoxycarbonyl or carbamido group typically includes 2-hydroxyethyl, 2-hydroxypropyl, 2-cyanoethyl, methoxycarbonylmethyl, 2-ethoxycarbonylethyl, 2-aminocarbonylpropyl or 2-(dimethylcarbamoyl)ethyl.

Substituents defined as C₂-C₁ alkylene may typically be ethylene, propylene, 2,2-dimethylpropylene, tetramethylene, hexamethylene, octamethylene, decamethylene or dodecamethylene.

Substituents defined as C₆-C₁₅arylene may typically be o-, m- or p-phenylene, 1,4-naphthylene or 4,4'-diphenylene.

D as C₆-C₁₂cycloalkylene is preferably cyclohexylene. _

Illustrative examples of polyalkylpiperidine compounds of this class are the following compounds:

N,N'-bis(2,2,6,6-tetramethylpiperidin-4-yl)-N,N'-dibutyladipamide N,N'-bis(2,2,6,6-tetramethylpiperidin-4-yl)-N,N'-dicyclohexyl-2- hydroxypropylene- 1 ,3-diamine the compound of formula

c) Compounds of formula (IV)

wherein n is 1 or 2, R¹ is as defined under a) and R⁵, if n is 1, is C^-Cgalkylene or -Cghydroxyalkylene or Q-C^acyloxyalkylene, and, if n is 2, is the (-CH₂)₂C(CH₂-)₂ group.

R⁵ as Qz- alkylene or Qz-Cghydroxyalkylene may be ethylene, 1-methylethylene, propylene, 2-ethylpropylene or 2-ethyl-2-hydroxymethylpropylene.

R⁵ as C₄-C₂ acyloxyalkylene may be 2-ethyl-2-acetoxymethylpropylene.

d) Compounds of formulae VA, VB and VC

wherein n is 1 or 2, R¹ is as defined under a), R⁶ is hydrogen, C -C₁₂alkyl, allyl, benzyl, glycidyl or C₂-C₆alkoxyalkyl, and R⁷, if n is 1, is hydrogen, C C₁₂alkyl, C₃-C₅alkenyl, C₇-C₉aralkyl, Cs-G_/cycloalkyl, -Qhydroxyalkyl, C₂-C₆alkoxyalkyl, C₆-C₁₀aτyl, glycidyl or a group of formula -(CH₂)p-COO-Q or of formula -(CH^p-O-CO-Q, wherein p is 1 or 2 and Q is C₁-C₄alkyl or phenyl, or if n is 2, is C₂-C₁₂alkylene, C -C₁₂alkenylene, C₆-C₁₂arylene, a -CH₂-CH(OH)-CH₂-O-D-O-CH₂-CH(OH)-CH₂- group, wherein D is C^-C_joalkylene, C₆-C₁₅arylene, C₆-C₁₂cycloalkylene, or is a -CH₂CH(OZ')CH₂- (OCH₂-CH(OZ')CH₂)₂- group, wherein Z' is hydrogen, C_rC₁₈alkyl, allyl, benzyl, C₂-C₁₂alkanoyl or benzoyl, T_t and T are each independendy of the other hydrogen or C₆-C₁₀aryl or C₇-C₉aralkyl which may be substimted by halogen or C₁-C₄alkyl, or T_x and T₂, together with the linking carbon atom, form a C₅-C₁₂cycloalkane ring.

Substiments defined as C₁-C₁₂alkyl may typically be methyl, ethyl, n-propyl, n-butyl, sec-butyl, tert-butyl, n-hexyl, n-octyl, 2-ethylhexyl, n-nonyl, n-decyl, n-undecyl or n-dodecyl.

Substiments defined as Cj-Cigalkyl may be the groups cited above and may additionally be n-tridecyl, n-tetradecyl, n-hexadecyl or n-octadecyl.

Substiments defined as C^-Cgalkoxyalkyl may typically be methoxymethyl, ethoxymethyl, propoxymethyl, tert-butoxymethyl, ethoxyethyl, ethoxypropyl, n-butoxyethyl, tert-butoxyethyl, isopropoxyethyl or propoxypropyl.

R⁷ as C₃-C₅alkenyl may be 1-propenyl, allyl, methallyl, 2-butenyl or 2-pentenyl.

R⁷, T_l and T₂ as C₇-C₉aralkyl are preferably phenethyl or, most preferably, benzyl. A cycloalkane ring formed by Tj and T₂ togedier with the linking carbon atom may be a cyclopentane, cyclohexane, cyclooctane or cyclododecane ring.

R⁷ as -Qhydroxyalkyl may be 2-hydroxyethyl, 2-hydroxypropyl, 2-hydroxybutyl or 4-hydroxybutyl.

R⁷, T_x and T₂ as C₆-C₁₀aryl are preferably phenyl, α- or β-naphthyl, which may be substituted by halogen or C₁-C₄alkyl.

R⁷ as C^-C^alkylene may typically be ethylene, propylene, 2,2-dimethylpropylene, tetramethylene, hexamethylene, octamethylene, decamethylene or dodecamethylene.

R⁷ as C -C₁₂alkenylene is preferably 2-butenylene, 2-pentenylene or 3-hexenylene.

R⁷ as C₆-C₁₂arylene is typically o-, m- or p-phenylene, 1,4-naphthylene or 4,4'-diphenylene.

Z' as C₂-C₁₂alkanoyl may be propionyl, butyryl, octanoyl, dodecanoyl, but is preferably acetyl.

D as -Cjoalkylen, -C^arylene or Ce-C₁₂cycloalkylene is as defined under b).

Illustrative examples of polyalkylpiperidines of this class are the following compounds:

2,2,4,4-tetramethyl-7-oxa-3,20-diaza-21-oxo-dispiro[5.1.11.2]-heneicosane 8-acetyl-3-dodecyl-l,3,8-triaza-7,7,9,9-tetramethylspiro[4,5]decane-2,4-dione

or the compounds of die following formulae:

e) Compounds of formula VI

wherein n is 1 or 2 and R⁸ is a group of formula

wherein R¹ is as defined under a), E is -O- or -NR¹¹-, A is and x is 0 or 1, R⁹ has die meaning of R⁸ or is a group -NRⁿR¹², -OR¹³, -NHCH₂OR¹³ or -N(CH₂OR¹³)₂, R¹⁰, if n = 1, has the meaning of R⁸ or R⁹, and, if n = 2, is a group -E-B-E-, wherein B is -Cgalkylene which may be interrupted by -N(Rⁿ)-, R¹¹ is Cj-C₁₂alkyl, cyclohexyl, benzyl or Cj-Qhydroxyalkyl or a group of formula

R¹² is Cι-C₁₂alkyl, cyclohexyl, benzyl, C₁-C hydroxyalkyl, and R¹³ is hydrogen, C₁-C₁ alkyl or phenyl, or R¹¹ and R¹², when taken together, are -Csalkylene or C₄-C₅θxaalkylene, typically

-CH₂CH₂ -CH₂CH₂

^v

P , or are a group of formula N — R

-CH CH₂ -CH₂CH or R¹¹ and R¹² are also each a group of formula

Substiments defined as Cι-C₁₂alkyl may typically be methyl, ethyl, n-propyl, n-butyl, sec-butyl, tert-butyl, n-hexyl, n-octyl, 2-ethylhexyl, n-nonyl, n-decyl, n-undecyl or n-dodecyl dar.

Substiments defined as - hydroxyalkyl may typically be 2-hydroxyethyl, 2-hydroxypropyl, 3-hydroxypropyl, 2-hydroxybutyl or 4-hydroxybutyl.

A as C^-Cgalkylene may be ethylene, propylene, 2,2-dimethylpropylene, tetramethylene or hexamethylene.

R¹¹ and R¹² together as -Csalkylene or oxaalkylene may be tetramethylene, pentamethylene or 3-oxapentamethylene.

Illustrative examples of polyalkylpiperidines of this class are the compounds of die following formulae:

R

75) R-NH-(CH₂)₃-N - (CH₂)2 N-(CH₂)₃-NH-R

76) R-NH-(CH₂)₃-N - (CH₂)₂ N-(CH₂)₃-NH-R

CH, CH,

77)

R-N — (CH₂)₃ — N — (CH₂)₂— N I — (CH₂)₃— N I R

f) Oligomeric or polymeric compounds whose structural repeating unit contains one or more than one 2,2,6,6-tetraalkylpiperidine radical of formula (I), preferably polyesters, polyethers, polyamides, polyamines, polyurethanes, polyureas, polyaminotriazines, poly(meth)acιylates, polysiloxanes, poly(mem)acrylamides and tiieir copolymers which contain such radicals.

Illustrative examples of 2,2,6,6-polyalkylpiperidine light stabilisers of this class are the compounds of d e following formulae, wherein m is a number from 2 to about 200.

82)

83)

87)

H₉C₄(R)N ^N^_N(R)C₄H₉

Among these classes of light stabilisers, classes e) and f) are especially suitable, in particular those tetraalkylpiperidines which contain s-triazine groups. Other particularly suitable compounds are compounds 74, 76, 84, 87, 92 und 95.

The amount of tetramethylpiperidine added will depend on die desired degree of stabilisation. Normally 0.01 to 5 % by weight, preferably 0.05 to 1 % by weight, based on die polymer, will be added. It is preferred that the molar ratio of tetramethylpiperidine and aluminium alkyl should not be substantially greater then 1.

The phosphorus(m) compounds added as optional additional stabilisers to the polymerisation may be phosphites, phosphonites or phosphimtes. They may contain one or more than one phosphoric ester group. It is preferred to use a phosphorus(III) compound of formula A, B, C or D

R n₅₂ H₂

I I

P -OR₃ R₃0— P — R₄— P — OR₃

R₅

B

C D

wherein R_x and R₂ are each independendy of die otiier C₁-C₁₂alkyl, C₅-C₈cycloalkyl, phenyl, phenyl which is substimted by one to tiiree -C^alkyl groups, or are a radical

-OR₃,

R₃ is Cg-C^alkyl, Cs-Cgcycloalkyl, phenyl or phenyl which is substimted by one to three groups, and

R is unsubstituted phenylene or naphthylene or phenylene or naphthylene which are substimted by C C₁₂alkyl, or is a radical-O-Rs-O-, wherein

R- is unsubstimted phenylene or naphthylene or phenylene or naphthylene which are substimted by or is a radical -Phen-Rg-Phen-, wherein Phen is phenylene,

R₆ is -O-, -S-, -SO₂-, -CH₂-, or -C(CH₃)₂-,

R₇ and R₈ are each independendy of the other phenyl or phenyl which is substimted by one to tiiree groups, and the two substiments R and R₈ may also be linked by a C_j-C^alkylene group, and R₉ is F, Cl, Br or I, preferably F.

Among die compounds of formula A it is preferred to use those compounds wherein Rj and R₂ are a radical -OR₃ and R₃ is - oalkyl, phenyl or phenyl which is substimted by one to tiiree C C₁₂alkyl groups.

Among the compounds of formula B it is preferred to use those compounds wherein R₂ is a radical -OR₃, R₃ is phenyl or phenyl which is substimted by one to three C₁-C₁ alkyl groups, and R is a diphenylene radical.

Among the compounds of formula C it is preferred to use tiiose compounds wherein Rj is a radical -OR₃, R₃ is phenyl or phenyl which is substimted by one to tiiree Ci-C^alk l groups.

It is preferred to use a phosphorus (HI) compound which contains at least one P-O-Ar group, and Ar is a mono-, di- or trialkylphenyl radical.

Illustrative examples of eligible phosphorus (HI) compounds are:

triphenyl phosphite, decyl diphenyl phosphite, phenyl didecyl phosphite, tris(nonylphenyl) phosphite, trilauryl phosphite, trioctadecyl phosphite, distearyl pentaerythritol diphosphite, tris(2,4-di-tert-butylphenyl) phosphite, diisodecyl pentaerythritol diphosphite, bis(2,4-di- tert-butylphenyl) pentaerythritol diphosphite, tristearyl sorbitol triphosphite, tetrakis(2,4-di-te_rt-butylphenyl)-4,4'-biphenylene diphosphonite, bis(2,6-di-tert-butyl-4- methylphenyl) pentaerythritol diphosphite.

The amount of phosphorus (HI) compound will depend on d e amount of piperidine compound added. Normally 0.01 to 1 % by weight, preferably 0.05 to 0.5 % by weight, is added, based on the polymer.

Besides d e phosphorus(IH) compound, it is possible to add further co-stabilisers and modifiers mat do not interfere with the polymerisation. It is preferred at add antioxidants of die sterically hindered phenol type to the polymerisation. These phenols are standard antioxidants for organic materials and are frequentiy used for stabilising polymers. Illustrative examples of such phenolic antioxidants are: 1. Alkylated monophenols, for example 2,6-di-tert-butyl-4-methylphenol, 2-tert-butyl- 4,6-dimedιylphenol, 2,6-di-tert-butyl-4-edιylphenol, 2,6-di-tert-butyl-4-n-butylphenol, 2,6-di-tert-butyl-4-isobutylphenol, 2,6-dicyclopentyl-4-methylphenol, 2-(α-methylcyclo- hexyl)-4,6-dimemylphenol, 2,6-dioctadecyl-4-methylphenol, 2,4,6-tricyclohexylphenol, 2,6-di-tert-butyl-4-methoxymethylphenol, 2,6-dinonyl-4-methylphenol, 2,4-dimethyl-6- ( 1 '-methylundec- 1 '-yl)phenol, 2,4-dimemyl-6-( 1 '-methylheptadec- 1 '-yl)phenol, 2,4-di- medιyl-6-( -methyltridec- -yl)phenol and mixtures thereof.

2. Alkylthiomethylphenols. for example 2,4-dioctylthiomethyl-6-tert-butylphenol, 2,4-di- octylthiomethyl-6-methylphenol, 2,4-dioctylthiomethyl-6-ethylphenol and 2,6-didodecyl- thiomethyl-4-nonylphenol.

3. Hvdro uinones and alkylated hvdro uinones. for example 2,6-di-tert-butyl-4-methoxy- phenol, 2,5-di-tert-butylhydroquinone, 2,5-di-tert-amylhydroquinone, 2,6-diphenyl-4-octa- decyloxyphenol, 2,6-di-tert-butylhydroquinone, 2,5-di-tert-butyl-4-hydroxyanisole, 3,5- di-tert-butyl-4-hydroxyanisole, 3,5-di-tert-butyl-4-hydroxyphenyl stearate and bis-(3,5- di-tert-butyl-4-hydroxyphenyl) adipate.

4. Hvdroxylated thiodiphenyl ethers, for example 2,2'-thiobis(6-tert-butyl-4-methylphe- nol), 2,2'-thiobis(4-octylphenol), 4,4'-thiobis(6-tert-butyl-3-methylphenol), 4,4'-thiobis- (6-tert-butyl-2-methylphenol), 4,4'-thiobis(3,6-di-sec-amylphenol) and 4,4'-bis-(2,6-di- medιyl-4-hydroxyphenyl) disulfide.

5. Alkylidene bisphenols, for example 2,2'-methylenebis(6-tert-butyl-4-methylphenol), 2,2'-methylenebis(6-tert-butyl-4-ethylphenol), 2,2'-methylenebis[4-methyl-6-(α-methyl- cyclohexyl)phenol], 2,2'-methylenebis(4-πιethyl-6-cyclohexylphenol), 2,2'-methylenebis- (6-nonyl-4-methylphenol), 2,2'-methylenebis(4,6-di-tert-butylphenol), 2,2'-ethylidenebis- (4,6-di-tert-butylphenol), 2,2'-ethylidenebis(6-tert- butyl-4-isobutylphenol), 2,2'-methy- lenebis[6-(α-methylbenzyl)-4-nonylphenol], 2,2'-methylenebis[6-(α,α-dimethylbenzyl)- 4-nonylphenol], 4,4'-methylenebis(2,6-di-tert-butylphenol), 4,4'-methylenebis(6-tert-bu- tyl-2-methylphenol), l,l-bis(5-tert-butyl-4-hydroxy-2-methylphenyl)butane, 2,6-bis(3- tert-butyl-5-methyl-2-hydroxybenzyl)- 4-methylphenol, 1 , 1 ,3-tris(5-tert-butyl-4-hydroxy- 2-methylphenyl)butane, l,l-bis(5-tert-butyl-4-hydroxy-2-methylphenyl)-3-n-dodecylmer- captobutane, ethylene glycol bis[3,3-bis-(3'-tert-butyl-4'-hydroxyphenyl)butyrate], bis(3- tert-butyl-4-hydroxy-5-methylphenyl)dicyclopentadiene, bis[2-(3 ' -tert-butyl-2' hydroxy- 5 '-methylbenzyl)-6-tert-butyl-4-memylphenyl] terephthalate, 1 , l-bis(3,5-dimethyl-2-hy- droxyphenyl)butane, 2,2-bis(3,5-di-tert-butyl-4hydroxyphenyl)propane, 2,2-bis(5-tert- butyl-4-hydroxy-2-methylphenyl)-4-n-dodecylmercaptobutane and l,l,5,5-tetra(5-tert- butyl-4-hydroxy-2-methylphenyl)pentane.

6. Q-, N- and S-Benzyl compounds, for example 3,5,3',5^l-tetra-tert-butyl-4,4'-dihydroxydi- benzyl ether, octadecyl 4-hydroxy-3,5-dimethylbenzyl-mercaptoacetate, tris(3,5-di-tert- butyl-4-hydroxybenzyl)amine, bis(4-tert-butyl-3-hydroxy-2,6-dimethylbenzyl)-didιio- terephthalate, bis(3,5-di-tert-butyl-4-hydroxybenzyl) sulfide and isooctyl 3,5-di-tert- butyl-4-hydroxybenzylmercaptoacetate.

7. Hydroxybenzylated malonates, for example dioctadecyl 2,2-bis(3,5-di-tert-butyl-2- hydroxybenzyl)malonate, dioctadecyl 2(3-tert-butyl-4-hydroxy-5-methylbenzyl)malonate, didodecylmercaptoethyl 2,2-bis(3,5-di-tert-butyl-4-hydroxybenzyl)malonate and bis[4- (1,1 ,3,3-tetramethylbutyl)phenyl] 2,2-bis(3,5-di-tert-butyl-4-hydroxybenzyl)malonate.

8. Aromatic hydroxybenzyl compounds, for example l,3,5-tris(3,5-di-tert-butyl-4- hydroxybenzyl)-2,4,6-trimethylbenzene, l,4-bis(3,5-di-tert-butyl-4-hydroxybenzyl)- 2,3,5,6-tetramethylbenzene and 2,4,6- tris(3,5-di-tert-butyl-4-hydroxybenzyl)phenol.

9. Triazine compounds, for example 2,4-bis(octylmercapto)-6-(3,5-di-tert-butyl-4-hy- droxyanilino)- 1 ,3,5-triazine, 2-octylmercapto-4,6-bis(3,5-di-tert-butyl-4-hydroxyanilino)- 1,3,5-triazine, 2-octylmercapto-4,6-bis(3,5-di-tert-butyl-4-hydroxyphenoxy)-l,3,5-triazine, 2,4,6-tris(3,5-di-tert-butyl-4-hydroxyphenoxy)- 1 ,2,3-triazine, 1 ,3,5-tris(3,5-di-tert-butyl- 4-hydroxybenzyl) isocyanurate, l,3,5-tris(4-tert-butyl-3-hydroxy-2,6-dimethylbenzyl) iso¬ cyanurate, 2,4,6-tris(3,5-di-tert-butyl-4-hydroxyphenyledιyl)-l,3,5-triazine, l,3,5-tris(3,5- di-tert-butyl-4-hydroxyphenylpropionyl)hexahydro-l,3,5-triazine and l,3,5-tris(3,5-di- cyclohexyl-4-hydroxybenzyl) isocyanurate.

10. Benzylphosphonates, for example dimethyl 2,5-di-tert-butyl-4-hydroxybenzylphospho- nate, died yl 3,5-di-tert-butyl-4-hydroxybenzylphosphonate, dioctadecyl 3,5-di-tert-butyl- 4-hydroxybenzylphosphonate, dioctadecyl 5-tert-butyl-4-hydroxy-3-methylbenzylphos- phonate and the calcium salt of monoethyl 3,5-di-tert-butyl-4-hydroxybenzylphosphonate.

11. Acylaminophenols, for example 4-hydroxylauranilide, 4-hydroxystearanilide and octyl N-(3,5-di-tert-butyl-4-hydroxyphenyl)carbamate. 12. Esters of β-(3,5-di-tert-butyl-4-hvdroxyphenyl)propionic acid with mono- or polyhy- dric alcohols, for example with methanol, ethanol, octadecanol, 1,6-hexanediol, 1,9-no- nanediol, ethylene glycol, 1,2-propanediol, neopentyl glycol, thiodiediylene glycol, di- ediylene glycol, triethylene glycol, pentaerytiiritol, tris(hydroxyethyl) isocyanurate, N,N'- bis(hydroxyethyl)oxamide, 3-thiaundecanol, 3-thiapentadecanol, trimethylhexanediol, tri- methylolpropane and 4-hydroxymethyl-l-phospha-2,6,7-trioxabicyclo[2.2.2]octane.

13. Esters of β-(5-tert-butyl-4-hydroxy-3-methylphenyl)propionic acid with mono- or polyhydric alcohols, for example with methanol, etiianol, octadecanol, 1,6-hexanediol, 1,9-nonanediol, ethylene glycol, 1,2-propanediol, neopentyl glycol, thiodiethylene glycol, diediylene glycol, triethylene glycol, pentaerythritol, tris(hydroxyethyl) isocyanurate, N,N'-bis-(hydroxyethyl)oxamide, 3-thiaundecanol, 3-thiapentadecanol, trimethylhexane¬ diol, trimethylolpropane and4-hydroxymethyl-l-phospha-2,6,7-trioxabicyclo- [2.2.2]octane.

14. Esters of β-(3.5-dicvclohexyl-4-hvdroxyphenyl)propionic acid with mono- or polyhy¬ dric alcohols, for example with methanol, ethanol, octadecanol, 1,6-hexanediol, 1,9-no- nanediol, ethylene glycol, 1,2-propanediol, neopentyl glycol, thiodiediylene glycol, di¬ ethylene glycol, triethylene glycol, pentaerythritol, rris(hydroxyethyl) isocyanurate, N,N'- bis-(hydroxyethyl)oxamide, 3-tiιiaundecanol, 3-thiapentadecanol, trimethylhexanediol, tri¬ methylolpropane and 4-hydroxymethyl- l-phospha-2,6,7-trioxabicyclo-[2.2.2]-octane.

15. Esters of 3,5-di-tert-butyl-4-hvdroxyphenylacetic acid with mono- or polyhydric alcohols, for example with methanol, ethanol, octadecanol, 1,6-hexanediol, 1,9-nonane- diol, ethylene glycol, 1,2-propanediol, neopentyl glycol, thiodiediylene glycol, diethylene glycol, triethylene glycol, pentaerythritol, tris(hydroxyethyl) isocyanurate, N,N'-bis- (hydroxyethyl)oxamide, 3-thiaundecanol, 3-thiapentadecanol, trimethylhexanediol, trimethylolpropane and 4-hydroxymethyl- l-phospha-2,6,7-trioxabicyclo[2.2.2]octane.

16. Amides of β-(3,5-di-tert-butyl-4-hvdroxyphenyl)propionic acid, for example N,N'-bis- (3,5-di-tert-butyl-4-hydroxyphenylpropionyl)hexamethylenediamine, N,N'-bis(3,5-di- tert-butyl-4-hydroxyphenylpropionyl)trimethylenediamine and N,N'-bis(3,5-di-tert-butyl- 4-hydroxyphenylpropionyl)hydrazine.

Preferred antioxidants are those listed in 6, 8, 9, 12, 13, 14 and 16, especially 6, 8, 9 and 12. Particularly suitable antioxidants are octadecyl β-(3,5-di-tert-butyl-4-hydroxyphenyl)- propionate and 1 ,3,5-tris(3,5-di-tert-butyl-4-hydroxybenzyl)-2,4,6-trimethylbenzene.

The amount of antioxidant added will depend on die amount of phosphorus(m) compound. Normally 0.005 to 0.5 % by weight, preferably 0.01 to 0.2 % by weight, based on d e polymer, is added.

The invention is illustrated in more detail by die following non-limitative Examples in which, and also in the description and claims, parts and percentages are by weight, unless otherwise stated.

Example 1: Preparation of die catalyst

25 g of anhydrous magnesium chloride and 5 g of titanium tetrachloride-etiiyl benzoate complex are milled in in a ball mill with stainless steel balls for 24 hours at room temperature (c. 22°C) under argon. The solid catalyst component so obtained contains 2 % titanium.

Polymerisation of propylene

The polymerisation is carried out in a 3 litre stirred and tiiermostatically controlled stainless steel autoclave which is evacuated before the start of the polymerisation for 30 minutes at 110°C (13 Pa) and is afterwards flushed for 30 minutes with propylene gas at 110°C. The autoclave is cooled to 20°C and 300 mg of S-l, 300 mg of H-l and 300 mg of P-l are added to die autoclave as solid or as 5-10 % solution in hexane. Then 25 mg of the solid catalyst component are activated for 10 minutes with half of a solution of 4 mmol of triethyl aluminium and 1.6 mmol of triethoxyphenylsilane in 25 ml of hexane and suspended in d e autoclave under argon. The autoclave is flushed with the second half of the hexane solution. The autoclave is closed and charged with hydrogen (6 kPa) and 600 g of liquid propylene. Widi stirring, the contents of the autoclave are heated to 70°C and kept at tiiis temperature for 4 hours. Excess propylene is then discharged and the resultant polymer is treated with 10 ml of isopropanol at 70°C to deactivate d e catalyst and tiien dried under vaccum for 1 hour at 70°C.

The following tests are carried out on die polymer:

For the corrosion test, the polymer is compression moulded on a hot press for 30 minutes at 280°C between carefully cleaned iron plates. The iron plates are then stored for 24 hours at 100 % humidity at room temperature (c.22°C). Corrosion is assessed visually.

The colour of die polymer is characterised by the Yellowness Index (YI) according to ASTM D 1925-70.

The polymer corrodes the iron plates only insignificandy. It has a YI of 2.3.

Comparative Example 2:

The procedure of Example 1 is repeated, but without using 300 mg of S-l, to give a polymer which, with the same catalyst yield, severely corrodes the iron plates and has a YI of 2.5.

Examples 3 and 4:

The procedure of Example 1 is repeated, replacing S-l witii 300 mg of S-2/300 mg of S-5, to give a polymer that corrodes the iron plates insignificandy/slighdy and has a YI of 2.3/

2.2.

Example 5:

Polypropylene powder, prepared as in Example 3, is processed in a Brabender plastograph for 10 minutes at 230°C. The melt is taken from die kneader and compressed to a c.5 mm board. In the corrosion test, the iron plates exhibit no corrosion after the melt processing.

Comparative Example 6:

The polymer prepared according to comparative Example 2 is processed as described in

Example 5. The iron plates are severely corroded after the melt processing.

Examples 7 and 8:

The stability to oxidative degradation is measured by the time taken until marked embritdement of the polymer occurs in oven ageing at elevated temperature. This test is carried out with boards which are obtained by compression moulding polypropylene powder obtained as described in Example 1 by adding 300 mg of S-l, 300 mg of H-l and 300 mg of P-l and 300 mg of S-5, 300 mg of H-l and 300 mg of P-l at 230°C. The time taken until embritdement is 11 days for both polymers at an oven temperature of 135°C.

Comparative Example 9:

A polymer prepared and tested in accordance with the particulars of Examples 7 and 8, but without die addition of S-l and S-5, also becomes britde after 11 days. This finding means mat the addition of S-l and S-5 does not affect the stability of the polymer to oxidative degradation.

Comparative Example 10:

A polymer prepared and tested in accordance with die particulars of Examples 7 and 8, but without the addition of S-l and S-5 as well as H-l and P-l, becomes britde after 1 day.

Examples 11-14:

Polymerisation is carried out as described in Example 1, but using 44 mg of solid catalyst component, 6.4 mmol of triethyl aluminium and 2.4 mmol of triethoxyphenylsilane. The following compounds are used instead of compounds S-l and H-l:

The following additives are used in die Examples:

S-l: [Mg₄^Al₂(OH)₁₃CO₃-3^H₂O] (this compound is sold by by Kyowa Chemicals, Japan, under the tradename DHT-4A). The compound is vacuum dried over phosphorus pentoxide at 95°C for 24 hours.

S-2: [Mg₄^Al₂(OH)₁₃CO₃-3,5H₂O] calcined (this compound is sold by by Kyowa Chemicals, Japan, under die tradename DHT-4C).

S-3: zink oxide (dried)

S-4: molecular sieve 4A (dried)

S-5: magnesium oxide (dried) H-l , where

M_n > 2500

R

H-2: R-NH-(CH₂)₃-N - (CH₂)₂ N-(CH₂)₃-NH-R

P-l

Claims

What is claimed is:

1. A process for the preparation of an olefin polymer by polymerisation with a transition metal catalyst, which comprises carrying out the polymerisation by adding at least one compound of d e series of the hydrotalcites, zeolites or metal oxides tiiat does not release water under the reaction conditions.

2. A process according to claim 1, which comprises preparing an olefin polymer by using a solid supported catalyst which has been prepared by reacting an aluminium compound carrying at least one alkyl group with a compound of a metal of the IVth subgroup of the Periodic Table.

3. A process according to claim 1, wherein the catalyst is a chromium compound which is on a support.

4. A process according to claim 1, wherein the compound of die series of the hydrotalcites, zeolites, metal oxides or a similarly synthetically prepared compound tiiat does not release water under the reaction conditions is used after drying at 50-800°C, preferably from 80-400°C.

5. A process according to claim 1, which comprises the use of a syndietically prepared hydrocalcite or zeolite.

6. A process according to claim 1, wherein the hydrotalcite conforms to the general formulae

M ⁺ι._x -M³⁺ _x -(OH)₂ '(Aⁿ-)_χ ^• mH₂O _(I)

'n

wherein

M²⁺ = Mg, Ca, Sr, Ba, Zn, Cd, Pb, Sn and/or Ni,

M³⁺ = Al, B or Bi,

A = OH", C1-, Br, I^", ClO₄ ^", HCO₃-, CH₃Cθσ, C₆H₅COO^", CO₃ ²\ SO₄ ^2", COO- COO", (CHOHCOO)₂ ²-, (CHOH)₄CH₂OHCOO\ C^COO);,²-, (CH₂COO)₂ ²-, CH₃CHOHCOO-, SiO₃ ^2", SiO₄ ^4", Fe(CN)₆ ^3", Fe(CN)₆ ^4" or HPO₄ ²-, or

M²⁺Al₂(OH)_2x^_nz(Aⁿ-)₂.mH₂O (la)

wherein M²⁺ is at least one metal of the series of Mg and Zn, Mg being preferred, A^n" is an

anion of die series of CO₃ ²\ \ COOy , OH^" and S^2', and n is die valency of die anions, is a positive number, preferably from 0.5 to 5, and x and z are positive numbers, and x is preferably 2 to 6 and z is smaller than 2.

7. A process according to claim 1, wherein the zeolite conforms to die general formula

M_x/n[(AlO₂)_x(SiO₂)_y]-wH₂O (X)

wherein n is the charge of the cation M,

8. A process according to claim 1, which comprises the use of an oxide of a divalent metal.

9. A process according to claim 1, which comprises the use of an oxide of a metal of the second main group and subgroup of the Periodic Table.

10. A process according to claim 1, which comprises the use of an oxide of zinc or magnesium.

11. A process according to claim 1, wherein a 2,2,6,6,-tetramethylpiperidine having a molecular weight above 500 or a phosphorus(III) compound is added as additional stabiliser during the polymerisation.

12. A process according to claim 1, wherein a 2,2,6,6,-tetramethylpiperidine having a molecular weight above 500 is used as additional stabiliser.

13. A process according to claim 1, wherein a 2,2,6,6,-tetramethylpiperidine having a molecular weight above 500 that contains in its molecule at least one s-triazine group is used as additional stabiliser.

14. A process according to claim 1, wherein a compound of formula

HNR _ (CH₂)₆-

R-NH-(CH₂)₃-N - (CH₂)₂ N-(CH₂)₃-NH-R

is used as additional stabiliser.

15. A process according to claim 1, wherein a phosphorus (III) compound is used as additional stabiliser.

16. A process according to claim 1, which comprises the use of a phosphorus(III) compound as additional stabiliser that contains at least one P-O-Ar group, where Ar is a mono-, di- or trialkylphenyl radical.

17. A process according to claim 1, which comprises the use of tris(2,4-di-tert-butylphen- yl)phosphite or tetrakis(2,4-di-tert-butylphenyl)-4,4'-biphenylenediphosphonite as an additional stabiliser.

18. A process according to claim 1, wherein an antioxidant of the sterically hindered phenol type is used as additional stabiliser.

19. A process according to claim 1, which comprises the use of octadecyl β-(3,5-di-tert- butyl-4-hydroxyphenyl)propionate and 1 ,3,5-tris(3,5-di-tert-butyl-4-hydroxybenzyl)- 2,4,6-trimethylbenzene as additional stabiliser.

20. A stabilised polyolefin prepared according to the process of claim 1.

21. Stabilised polypropylene prepared according to d e process of claim 1.