STABLILIZING MIXTURES FOR ORGANIC POLYMERS

Abstract: Stablizing mixtures for organic polymers comprising: (a) at least one compound belonging to the group of 3-pyrazolidinones; (b) at least one compound belonging to the group of organic phosphites or phosphonites; (c) at least one compound belonging to the group of sterically hindered phenols; and, optionally, (d) at least one compound belonging to the group of sterically hindered amines. The above mixtures can be used as stabilizers of organic polymers to degradation caused by oxygen, heat and/or light.

Description: STABILIZING MIXTURES FOR ORGANIC POLYMERS The present invention relates to stabilizing mixtures for organic polymers. More specifically, the present invention relates to stabilizing mixtures for organic polymers comprising at least one compound belonging to the group of 3- pyrazolidinones, at least one compound belonging to the group of organic phosphites or phosphonites, at least one compound belonging to the group of sterically hindered phenols and, optionally, at least one compound belonging to the group of sterically hindered amines and their use in the stabilization of organic polymers to degradation caused by oxygen, heat and/or light. The present invention also relates to the polymeric compositions stabilized with the above stabilizing mixtures and the end-products obtained by their processing. Japanese patent application JP 56/086165 describes the use of derivatives of 3-pyrazolidinone as colour sta- bilizers and antioxidants in the photographic field. Organic phosphites, organic phosphonites and phos- phoramides are known in the art as co-stabilizers, secondary antioxidants and process stabilizers for organic polymers among which polyolefins . Examples of these com- pounds can be found, for example, in R. Gachter/H. Mϋller (Ed.), "Plastic Additives Handbook" (1990), 3 rd Ed., page 47, Hanser, Munich. U.S. patent 4,360,617 describes stabilizing mixtures comprising symmetrical triarylphosphites and phenolic an- tioxidants, particularly useful in the stabilization to degradation caused by oxygen, heat and/or light, of various organic polymers such as, for example, polyurethanes, polyacrylonitrile, polyamide 12 or polystyrene. Sterically hindered amines, in particular those carrying 2, 2, 6, 6-tetramethylpiperidine groups in the molecule, are known as HALS. The known stabilizers, however, are not capable of completely satisfying all the problems to be solved by a stabilizer such as, for example, storage life, water ab- sorption, sensitivity to hydrolysis, stabilization during the polymer processing, colour properties of the stabilized polymer, volatility, migration within the stabilized polymer, compatibility with the polymer to be stabilized and improvement in light protection. There is consequently a continuous need for stabilizers for or- ganic polymers capable of providing a better stabilization thereof. The Applicant has now found that stabilizing mixtures comprising at least one compound belonging to the group of 3-pyrazolidinones, at least one compound belonging to the group of organic phosphites or phosphonites, and, optionally, at least one compound belonging to the group of sterically hindered phenols and, optionally, at least one compound belonging to the group of sterically hindered amines, are capable of providing a better stabilization to degradation caused by oxygen, heat and/or light, of the organic polymers to which they are added. An object of the present invention therefore relates to stabilizing mixtures for organic polymers comprising: (a) at least one compound belonging to the group of 3-pyrazolidinones ; (b) at least one compound belonging to the group of organic phosphites or phosphonites; and, optionally, (c) at least one compound belonging to the group of sterically hindered phenols; and, optionally, (d) at least one compound belonging to the group of sterically hindered amines. Compounds belonging to the group of 3- pyrazolidinones (a) useful for the purposes of the pres- ent invention are selected from those having general for- ula (I) or (II) wherein: Ai represents a linear or branched QL-C I S alkyl group; a . C5-C 12 cycloalkyl group, said cycloalkyl group optionally mono-, di- or tri-substituted with a linear or branched C1-C 4 alkyl group; a phenyl group, -said phenyl group optionally mono-, di- or tri-substituted with a linear or branched C1-C4 alkyl or alkoxyl group, and/or mono-substituted with a hydroxyl group; a C-Cg phenylalkyl group, said phenylalkyl group optionally' mono-, di- or tri- substituted on the phenyl with a linear or branched C 1 -C 4 alkyl group, and/or mono-substituted with a hydroxyl group; an -Aio-COOAn wherein Aio represents a linear or branched Ci-Cβ alkylene group and An represents a linear or branched Ci-Ciβ alkyl group, a C5-C 1 2 cycloalkyl group, said cycloalkyl group optionally mono-, di- or tri-substituted with a linear or branched C1-C4 alkyl group, a linear or branched C3-C18 alkenyl group, a C-C 9 phenylalkyl group, said phenylalkyl group optionally mono-, di- or tri- substituted on the phenyl with a " linear or branched C1-C4 alkyl group; A 3 , A, A5 and Aε, the same or different, represent a hydrogen atom; a linear or branched C 1 -C 4 alkyl group; a phenyl group; s is 1 or 2; when s is 1, A 2 represents a hydrogen atom; a linear or branched Ci-Ciβ alkyl group; a linear or branched C 3 -C 6 alkenyl group; a C-C 9 phenylalkyl group, said phenylalkyl group optionally mono-, di- or tri- substituted on the phenyl with a linear or branched C1-C4 alkyl group; an -Aio-COOAn wherein Aι 0 and An have the same meanings defined above; and, when A 2 represents a hydrogen atom, A L may also represent a group having general formula (III) : H -A x 0 wherein A 3 , A 4 , A 5 , Aβ and Aio have the same meanings defined above and A i2 represents a linear or branched C2-C12 alkylene group; a C4-C12 alkylene group interrupted by 1, 2 or 3 oxygen atoms; a cy- clohexylene group; a cyclohexylenedimethylene group; an isopropylidenedicyclohexylidene group; when s is 2, A 2 represents a linear or branched C 2 - C12 alkylene group, or a xylylene group; A 7 represents a phenyl group optionally mono-, di- or tri-substituted with a linear or branched C1-C 4 alkyl or alkoxyl group, and/or mono-substituted with a hydroxyl group; A 8 represents a hydrogen atom; a linear or branched C1-C18 alkyl group; a linear or branched C3- 6 alkenyl group; a C 7 -Cg phenylalkyl group, said phenylalkyl group optionally mono-, di-, or tri- substituted on the phenyl with a linear or branched C1-C 4 alkyl group; an -Aι 0 -COOAn group wherein Aio and n have the same meanings defined above; t is 1, 2, 3 or 4; when t is 1, A 9 represents an acyl-aliphatic, cyclo- aliphatic, aromatic, arylaliphatic or heterocyclic group containing not more than 22 carbon atoms; or one of the following groups having general formula (IVa) - (IVc) : -COOA13 (IVa) —CO— A, 5 ( IVb ) Aχ 4 wherein A13 has the same meanings as n described above; Au and A 1 5, the same or different, have the same meanings as n described above, or they represent a hydrogen atom, or a phenyl group, or A i4 and 15 considered jointly with the nitrogen atom to which they are bound, represent a heterocyclic group with 5-7 atoms; Xi and X2, the same or different, represent an -O-A16 group, or a group having the formula: — wherein Ai6, n and Aie, the same or different, have the same meanings as A i4 and A i5 described above, or An and Aie considered jointly with the nitrogen atom to which they are bound, represent a heterocyclic group with 5-7 atoms; when t is 2, A 9 represents a diacyl-aliphatic, cy- cloaliphatic, aromatic, arylaliphatic or heterocy- clic group containing not more than 22 carbon atoms; or one of the following groups having general formula (Va) - (Vc) : -COO-A 19 -OOC- (Va) -CONH- . 20 -NHCO- (Vb) wherein A i9 represents a linear or branched C2-C12 alkylene group, a C4-C 12 alkylene group interrupted by 1, 2 or 3 oxygen atoms, a cyclohexylene group, a cyclohexylenedimethylene group, an isopropylidenedi- cyclohexylidene group, a phenylene group, a xylylene group, an isopropylidenediphenylene group; A 2 o represents a linear or branched C2-C12 alkylene group, a cyclohexylene group, a cyclohexylenedimethylene group, a methylidene-cyclohexylene group, a phenylene group, a methylphenylene group, a xylylene group, a methylenediphenylene group, an oxydiphenyl- ene group, a group having the formula: X 3 ' has the same meanings as Xi and X2 defined above; when t is 3, A 9 represents a triacyl-aliphatic, aromatic or heterocyclic group containing not more than 18 carbon atoms, or a 2, 4, 6-triyl-l, 3, 5-triazine grou ; when n is 4, Ag represents a tetra-acyl-aliphatic or aromatic group containing not more than 18 carbon atoms . Examples of linear or branched alkyl groups, having not more than 18 carbon atoms are: methyl, ethyl, propyl, isopropyl, butyl, 2-butyl, isobutyl, t-butyl, pentyl, 2- pentyl, hexyl, heptyl, octyl, 2-ethylhexyl, t-octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, etc. Examples of linear or branched alkoxyl groups, having not more than 18 carbon atoms are: methoxy, ethoxy, propoxy, isopropoxy, butoxy, isobutoxy, pentoxy, isopen- toxy, hexoxy, heptoxy, octoxy, nonoxy, decyloxy, dodecy- loxy, tetradecyloxy, hexadecyloxy, octadecyloxy, etc. Examples of C5-C 12 cycloalkyl groups, optionally mono-, di- or tri-substituted with a linear or branched C1-C 4 alkyl group, are: cyclopentyl, methylcyclopentyl, dimethylcyclopentyl, cyclohexyl, methylcyclohexyl, di ¬ methylcyclohexyl, trimethylcyclohexyl, t-butylcyclohexyl, cyclo-octyl, cyclodecyl, cyclododecyl, etc. Examples of alkenyl groups having not more than 18 carbon atoms are: allyl, 2-methyallyl, butenyl, hexenyl, undecenyl, octadecenyl. Examples of C-C 8 phenylalkyl groups, optionally mono-, di-, or tri-substituted on the phenyl, are: benzyl, methylbenzyl, di ethylbenzyl, trimethylbenzyl, t- butylbenzyl, 2-phenylethyl, 3, 5-dl-t-butyl-4-hydroxy- benzyl, etc. Examples of substituted phenyl groups are: ethyl- phenyl, dimethyIphenyl, trimethylphenyl, 3, 5-di-t-butyl- 4-methyIphenyl, methoxyphenyl, ethoxyphenyl, dimethoxy- phenyl, trimethoxyphenyl, hydroxyphenyl, 3, 5-di-t-butyl- 4-hydroxyphenyl, etc. Examples of heterocyclic groups with 5-7 atoms are: 1-pyrrolidyl, 1-piperidyl, 4-morpholinyl, 4-methyl-l- piperazinyl, 1-hexahydroazepinyl, etc. Examples of acyl-aliphatic, cycloaliphatic, aromatic, arylaliphatic or heterocyclic groups having not more than 22 carbon atoms are those deriving from the following acids: formic, acetic, propionic, butyric, iso- butyric, valeric, pivalic, hexanoic, heptanoic, octanoic, 2-ethylhexanoic, nonanoic, decanoic, undecanoic, dode- canoic, tetradecanoic, hexadecanoic, octadecanoic, eico- sanoic, docosanoic, acrylic, methacrylic, crotonic, unde- cenoic, octadecenoic, cyclohexanecarboxylic, cyclohexane- acetic, benzoic, methylbenzoic, t-butylbenzoic, ethoxy- benzoic, hydroxybenzoic, 3, 5-di-t-butyl-4-hydroxy- benzoic, phenylacetic, phenoxyacetic, 3-phenylpropionic, 3- (3, 5-di-t-butyl-4-hydroxyphenyl) -propionic, furoic, tetrahydrofurancarboxylic, nicotinic, isonicotinic, pyro- glutamic, 3- (2, 2, 6, 6-tetramethyl-4-piperidylamino) cro- tonic, etc. Examples of alkylene groups having not more than 12 carbon atoms are: methylene, ethylene, propylene, tri- methylene, tetramethylene, pentamethylene, 2,2- trimethyltrimethylene, hexamethylene, heptamethylene, oc- tamethylene, trimethylhexamethylene, decamethylene, dode- camethylene, etc. Examples of C4-C12 alkylene groups interrupted by 1, 2 or 3 oxygen atoms are: 3-oxapentane-l,5-diyl, 4- oxaheptane-1, 7-diyl, 3, 6-dioxa-octane-l, 8-diyl, 4,7- dioxadecane-1, 10-diyl, 4, 9-dioxadodecane-l, 12-diyl, 3, 6, 9-trioxaundecane-l, 11-diyl, 4, 7, 10-trioxadecane-l, 13- diyl, etc. Examples of diacyl-aliphatic, cycloaliphatic, aromatic, arylaliphatic or heterocyclic groups having not more than 22 carbon atoms are those deriving from the following acids: oxalic, malonic, succinic, methylmalo- nic, allyl alonic, glutaric, ethylmalonic, adipic, pi- melic, diethylmalonic, suberic, azelaic, sebacic, 1,12- dodecanoic, oxydiacetic, iminodiacetic, methyli inodiace- tic, maleic, fumaric, itaconic, citraconic, cyclohexane- dicarboxylic, cyclohexenedicarboxylic, bicycloheptenedi- carboxylic, phthalic, isophthalic, terephthalic, phenyl- malonic, benzylidenemalonic, benzylmalonic, butyl-3, 5-di- t-butyl-4-hydroxybenzylmalonic, furandicarboxylic, pyri- dinedicarboxylic, 1, 4-dioxaspiro [4.5] decane-2, 3-dicarb- oxylic, 1, 5-dioxaspiro[5.5]undecane-3, 3-dicarboxylic, 7,7,9, 9-tetramethyl-l, 4-dioxa-8-azaspiro [4.5] decane-2, 3- dicarboxylic, 8, 8, 10, 10-tetramethyl-l, 5-dioxa-9-azaspiro- [5.5]undecane-3, 3-dicarboxylic, N- (2,2, , 6-tetramethyl-4- piperidyl) iminodiacetic, etc. Examples of triacyl-aliphatic, aromatic or heterocyclic groups having not more than 18 carbon atoms are those deriving from the following acids: methanetricar- boxylic, 1, 1,2-ethanetricarboxylic, 1,2,3-propane- tricarboxylic, 1,2, 3-butanetricarboxylic, citric, ni- trilotriacetic, benzenetricarboxylic, or from the acid having the formula: O HOOC- (CH 2 etc. Examples of tetra-acyl-aliphatic or aromatic groups having not more than 18 carbon atoms are those deriving from the following acids: 1, 1,2, 2-ethanetetracarboxylic, 1, 1, 3, 3-propanetetracarboxylic, 1, 2,2, 3-propanetetracar- boxylic, 1, 2, 3, 4-butanetetracarboxylic, ethylenediami- notetra-acetic, pyromellitic, etc. Compounds belonging to the group of 3- pyrazolidinones (a) having general formula (I) or (II) , of interest for the purposes of the present invention, are those wherein Ai is a phenyl group, or a COOA x group, wherein n is a linear or branched Cι 2 -Ci8 alkyl group; A 3 , A 4 , A5 and A 6 are hydrogen; s is 1 or 2; when s is 1, A 2 is hydrogen, a linear or branched C 1 -C 12 alkyl group, or a benzyl group; when s is 2, A 2 is a xylylene group; A is a phenyl group; β is a hydrogen or a methyl; t is 1 or 2; when t is 1, A g is a Cι 0 -C 2 2 acyl- aliphatic group, a benzoyl group, or a group having general formula (IVa) or (IVb) wherein A 1 3 is a linear or branched C 12 -C 1 8 alkyl group, A14 is hydrogen, A15 is a linear or branched C 1 -C 4 alkyl group or a cyclohexyl group; when t is 2, Ag is a -CO (CH 2 ) 2-sCO- group, or a group having general formula (Va) or (Vb) wherein A i9 is a linear or branched C-Cβ alkylene group and Ao has the same meanings defined above. Compounds belonging to the group of 3- pyrazolidinones (a) having general formula (I) or (II) of particular interest for the purposes of the present invention but in no way limiting its scope, are: The compounds belonging to the group of 3- pyrazolidinones (a) having general formula (I) or (II) are known in the art: some are commercially available products, others can be prepared as described, for example, in "Tetrahedron Letters" (1985), Vol. 26, page 5663; or in the following patents: DE 53,834, GB 650,911, JP 11/060559 and U.S. 4,835,285. Compounds belonging to the group of organic phosphites or phosphonites (b) useful for the purposes of the present invention are selected from those having the following general formulae (VI) -(XII): O- R -P' (VI) ; O- -R 1 wherein: n' is 2, 3 or 4; p' is 1 or 2; q' is 2 or 3; r' is an integer ranging from 4 to 12, extremes included; y" is 1, 2 or 3; z' is an integer ranging from 1 to 6, extremes included; when n' is 2, A' represents a C 2 -Cιa alkylene group; a C 2 -Ci 2 alkylene group containing an oxygen atom, a sulfur atom, or an -NR ? 4 - group; a group having general formula (XIII) : a group having general formula (XIV) a phenylene group; when n' is 3, A" represents a group having general formula -C r >H 2r ._ι- wherein r' has the same values described above; when n' is 4, A' represents a group having the for- mula: A' ' has the same meanings defined above for A' when n' is 2; B' represents a direct bond; one of the following groups: -CH 2 -, -CHR T 4 -, -CR'iR^-; a sulfur atom; a C5-C cycloalkylidene group; a cyclohexylidene group substituted with 1-4 C1-C4 alkyl groups in position 3, 4 and/or 5; when p' is 1, D' represents a methyl group; and, when p' is 2, D' represents a -CH 2 OCH 2 - group; when y' is 1, E 1 represents a Ci-Ciβ alkyl group; an -OR'i group; a halogen atom; when y' is 2, E' represents an -O-A' '-0- group; when y' is 3, E 1 represents one of the following groups: R' 4 C (CH 2 0-) 3, N (CH 2 CH 2 0-) 3 ; Q' represents a radical of an alcohol or a phenol with valence z ' , said radical being attached to the phosphorous atom by means of an oxygen atom; R'ι, R' 2 and R*3, each independently, represent a hy- drogen atom; a halogen atom; one of the following groups: -COOR' 4 -, -CN-, -CONR^R'-i; a C 2 -Cι 8 alkyl group containing an oxygen atom," a sulfur atom, an -NR' 4 - group; a C 7 -C 9 phenylalkyl group; a Cs-Cι 2 cycloalkyl group; a phenyl group or a naphthyl group, said phenyl or naphthyl groups optionally substituted with halogen atoms, or with 1-3 Ci-Cis alkyl or alkoxyl groups or with C-C 9 phenylalkyl groups; or they represent a group having general formula (XV) : wherein m' represents an integer ranging from 3 to 6, extremes included; - R' 4 represents a hydrogen atom; a Ci-Cis alkyl group; a C 5 -C 12 cycloalkyl group; a C-C 9 phenylalkyl group; R'5 and R 1 β, each independently, represent a hydrogen atom; a Ci-Cs alkyl group; a Cs-C 6 cycloalkyl group; - when q' is 2, R' 7 and R'a each independently, represent a C 1 -C alkyl group; or, considered jointly, they represent a 2, 3-dihydropentamethylene group; when q' is 3, R' 7 and R'a represent a methyl group; R'i 4 represents a hydrogen atom; a Q_-Cg alkyl group; a cyclohexyl group; R'i5 represents a hydrogen atom; a methyl group; or, when two or more R'ι 4 and R'15 groups are present, said groups are the same as or -different from each other; X τ and Y 1 represent a direct bond; an oxygen atom; - Z' represents a direct bond; a methylene group; a -C(R'ι 6 )2- group; a sulfur atom; R'i6 represents a Ci-Cs alkyl group. Compounds belonging to the group of organic phosphites or phosphonites (b) of particular interest for the purposes of the present invention are those having general formula (VI), (VII), (X) and (XI) wherein: n' is 2 and y' is 1, 2 or 3; A' represents a C 2 -C 1 8 alkylene group; a p-phenylene or p-bisphenylene group; - when y τ is 1, E' represents a Ci-Cia alkyl group; an -OR'- group, a fluorine atom; when y' is 2, E' represents a p-bisphenylene group; when y* is 3, E τ represents an N(CH 2 CH 2 0-)3 group; R'ι, R'2 and R' , each independently represent a Ci-Ciβ alkyl group; a C 7 -C 9 phenylalkyl group; a cy- clohexyl group; a phenyl group; said phenyl group optionally substituted with 1-3 Ci-Ciβ alkyl groups; R' 14 represents a hydrogen atom; a C 1 -C9 alkyl group; R'i 5 represents a hydrogen atom; a methyl group; - X' represents a direct bond; Y' represents an oxygen atom; Z' represents a direct bond; a -CH(R'ι 6 )- group; R'i6 represents a C1-C4 alkyl group. Similarly, compounds belonging to the group of or- ganic phosphites or phosphonites (b) of particular interest for the purposes of the present invention are those having general formula (VI), (VII), (X) and (XI) wherein: n' is 2 and y" is 1 or 3; A' represents a p-bisphenylene group; - when y' is 1, E' represents a Cι-Cι 8 alkoxyl group; a fluorine atom; when y 1 is 3, E' represents an N(CH 2 CH 2 0-)3 group; R'ι, R' 2 and R' 3 , each independently, represent a Ci-Ciβ alkyl group; a phenyl group substituted with 2-3 C 2 -C 12 alkyl groups; R'i 4 represents a methyl group; a t-butyl group; R' 15 represents a hydrogen atom; X τ represents a direct bond; Y' represents an oxygen atom; - Z' represents a direct bond; a methylene group; a -CH(CH 3 )- group. Preferred compounds belonging to the group of organic phosphites or phosphonites (b) for the purposes of the present invention are those having general formula (VI) , (VII) and (XI) ; particularly preferred are those having general formula (XVI) : wherein: R''ι and R''2 each independently, represent a hydrogen atom; a Ci-Cs alkyl group; a cyclohexyl group; a phenyl group; R''3 and R'' 4 , each independently, represent a hydrogen atom; a L -C alkyl group. Specific examples of compounds belonging to the group of phosphites or phosphonites (b) useful for the purposes of the present invention are: triphenyl phosphite; diphenyl alkyl phosphites; phenyl dialkyl phosphites; tris (nonylphenyl)phosphite (known under the trade-name of Alkanox™ TNPP of Great Lakes Chemical Corporation) ; trilauryl phosphite; trioctadecyl phosphite; distearyl pentaerythritol diphosphite; tris (2, 4-di-t- butylphenyl) phosphite (known under the trade-name of Al- kanox™ 240 of Great Lakes Chemical Corporation) ; diiso- decyl pentaerythritol diphosphite; bis (2, 4-di-t-butyl- phenyl)pentaerythritol diphosphite (known under the trade-name of Alkanox™ P24 of Great Lakes Chemical Corporation) ; bis (2, 6-di-t-butyl-4-methyIphenyl) pentaerythritol diphosphite; bis-isodecyloxypentaerythritol diphosphite, bis (2, 4-di-t-butyl-6-methylphenyl) pentaerythritol diphosphite; bis (2, 4, 6-tris-t-butylphenyDpen- taerythritol diphosphite; tristearylsorbitol triphosphi- te; tetra-kis (2, 4-di-t-butylphenyl) -4, 4 ' -diphenylenedi- phosphonite (known under the trade-name of Alkanox™ 24- 44 of Great Lakes Chemical Corporation) ; 6-iso-octyloxy- 2,4,8, 10-tetra-t-butyl-12H-dibenzo- [d, g] -1, 3, 2-dioxapho- sphocine; 6-fluoro-2, 4, 8, 10-tetra-t-butyl-12-methyldiben- zo [d, g] -1, 3, 2-dioxaphosphocine; bis (2, 4-di-t-butyl-6-me- thyIphenyl) methyl phosphite; bis- (2, 4-di-t-butyl-6-me- thyIphenyl) ethyl phosphite (known under the trade-name of Irgafos ® 38 of Ciba Specialty Chemicals); bis (2,4- dicumyIphenyl) pentaerythritol diphosphite. Specific examples of particularly preferred compounds belonging to the group of organic phosphites or phosphonites (b) for the purposes of the present invention are: tris (2, 4-di-t-butylphenyl)phosphite (known un- der the trade-name of Alkanox™ 240 of Great Lakes Che i- cal Corporation); tris (nonyIphenyl) phosphite (known under the trade-name of Alkanox™ TNPP of Great Lakes Chemical Corporation) ; 6-fluoro-2, 4, 8, 10-tetra-t-butyl-12-methyl- dibenzo [d,g]-l,3,2-dioxaphosphocine; 6-iso-octyloxy-2, 4,- 8, 10-tetra-t-butyl-12H-dibenzo- [d, g]-l, 3, 2-dioxaphospho- cine; bis (2, 4-di-t-butylphenyl) entaerythritol diphosphite (known under the trade-name of Alkanox™ P24 of Great Lakes Chemical Corporation); bis (2, 6-di-t-butyl-4- methylphenyl) pentaerythritol diphosphite; bis- (2, 4-di-t- butyl-6-methyIphenyl) ethyl phosphite (known under the trade-name of Irgafos ® 38 of Ciba Specialty Chemicals) ; bis- (2, 4-dicumyIphenyl) pentaerythritol diphosphite; tetrakis (2, 4-di-t-butylphenyl) -4, 4"-diphenylenediphos- phonite (known under the trade-name of Alkanox™ 24-44 of Great Lakes Chemical Corporation) ; triphosphite having formula (XVII) : diphosphite having general formula (XVIII) "374 7 (xvill) Specific examples of compounds belonging to the group of organic phosphites or phosphonites (b) even more preferred for the purposes of the present invention are: tris (2, 4-di-t-butylphenyl) hosphite (known under the trade-name of Alkanox™ 240 of Great " Lakes Chemical Corporation) ; bis- (2, 4-di-t-butyl-6-methyIphenyl) ethyl pho¬ sphite (known under the trade-name of Irgafos ® 38 of Ciba Specialty Chemicals); tetrakis (2, 4-di-t-butylphenyl) - 4, ' -diphenylenediphosphonite (known under the trade-name of Alkanox™ 24-44 of Great Lakes Chemical Corporation) ; bis (2, 4-dicumyIphenyl) pentaerythritol diphosphite. The compounds belonging to the group of organic phosphites or phosphonites (b) described above are known compounds; many of them are commercially available products . Compounds belonging to the group of sterically hindered phenols (c) useful for the purposes of the present invention are selected from those having general formula wherein: Rι f represents a Q_-C 4 alkyl group; n is 1, 2, 3 or 4; X represents a methylene group; "" or a group having general formula (XX) or (XXI) : 0 CH 2 -CH 2 -C-Y (xx) ; O CH 2 _C—0—CH 2 -CH 2 — (xxi) . Y represents an oxygen atom; an -NH- group; - when n is 1, X represents a group having general formula (XX) wherein Y is attached to R 2 ' and R 2 ' represents a Cι-C 2 s alkyl group; when n is 2, X represents a group having general formula (XX) wherein Y is attached to R 2 ' and R 2 T represents a C 2 -Cι 2 alkylene group; a C 4 -Cι 2 alkylene group containing one or more oxygen or sulfur atoms; or, when Y represents an -NH- group, R 2 ' represents a direct bond; when n is 3, X represents a methylene group; a group having general formula (XXI) wherein the ethylene group is bound to R 2 ' and R2' represents a group having formula (XXII) : when n is 4, X represents a group having general formula (XX) wherein Y is bound to R 2 ' and R 2 ' rep- resents a C 4 -Cιo alkane-tetrayl group. Examples of linear or branched alkyl groups having up to 25 carbon atoms are: methyl, ethyl, propyl, isopro- pyl, n-butyl, s-butyl, isobutyl, t-butyl, 2-ethylbutyl, n-pentyl, isopentyl, 1-methylpentyl, 1,3-dimethylbutyl, n-hexyl, 1-methylhexyl, n-heptyl, isoheptyl, 1,1,3,3- tetramethylbutyl, 1-methylheptyl, 3-methylheptyl, n- octyl, 2-ethylhexyl, 1, 1, 3-trimethylhexyl, 1,1,3,3- tetramethylpentyl, nonyl, decyl, undecyl, 1-methyl- undecyl, dodecyl, 1, 1, 3, 3, 5, 5-hexamethylhexyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, eicosyl or doicosyl, etc. Ri' preferably represents methyl or t-butyl. R 2 ' preferably represents a C1-C20 alkyl group, particularly a Ci-Cia alkyl group, for example, a C4-C18 alkyl group. Even more preferably, R 2 ' represents a Cs-Cis alkyl group, particularly a -Ciβ alkyl group, for example octadecyl . Examples of linear or branched C 2 -C 1 2 alkylene groups, are: ethylene, propylene, tetramethylene, pen- tamethylene, hexamethylene, heptamethylene, octamethyl- ene, decamethylene, dodecamethylene, etc. R 2 ' preferably represents a C 2 -Cιo alkylene group, particularly a C 2 -Ca alkylene group. Even more preferably, R 2 ' represents a C 4 -Ca alkylene group, particularly a C 4 -C 6 alkylene group, for example hexamethylene. Examples of C 4 -Cι 2 alkylene groups containing one or more oxygen or sulfur atoms, are: -CH2-0-CH 2 CH 2 -0-CH 2 -, -CH 2 - (0-CH 2 CH 2 ) 2 -0-CH 2 -, -CH 2 - (0-CH 2 CH 2 ) 3-O-CH 2 -, -CH2- (0-CH 2 CH 2 ) 4 -0-CH 2 -, -CH 2 -CH2-0-CH 2 CH 2 -0-CH 2 CH2-, -CH2-CH2-S-CH2CH2-, etc. R 2 ' preferably represents a C 4 -Cιo alkylene group containing one or more oxygen or sulfur atoms, particularly a C 4 -Cs alkylene group containing one or more oxygen or sulfur atoms, for example a C 4 -C 6 alkylene group containing one or more oxygen or sulfur atoms. Even more preferably, R 2 ' represents one of the following groups: -CH 2 -CH 2 -0-CH2CH 2 -0-CH 2 CH 2 -, -CH 2 -CH 2 -S-CH 2 CH 2 - . Examples of C4-C10 alkane-tetrayl groups are: CH 2 I -CH, _C— CH 2 — (pentaerythritol); CH, - -CH, -CH, -CH—CH—CH, -CH. CH, -0* 2 -CE -CH j —CH—CH j —CH^ -CH 2 -CH 2 -CH —CH 2 -CH 2 -CH CH 2 —CH 2 etc. Pentaerythritol is preferred. Specific examples of compounds belonging to the group of sterically hindered phenols (c) useful for the purposes of the present invention are those wherein, in general formula (XIX), when n is 1, R 2 ' represents a Ci- C 2 o alkyl group. Specific examples of preferred compounds belonging to the group of sterically hindered phenols (c) for the purposes of the present invention are those wherein, in general formula (XIX), when n is 2, R 2 ' represents a C 2 -Ca alkylene group, or a C4-C8 alkylene group containing one or more oxygen or sulfur atoms; or, when Y represents an -NH- group, R 2 ' represents a direct bond; and, when n is 4, R 2 ' represents a C-C 8 alkane-tetrayl group. Similarly, examples of preferred compounds belonging to the group of sterically hindered phenols (c) for the purposes of the present invention are those wherein, in general formula (XIX), Ri' represents methyl or t-butyl; n is 1, 2 or 4; X represents a group having general formula (XX) ; Y represents an oxygen atom or an -NH- group; and, when n is 1, R 2 ' represents a C 1 4-C 1 8 alkyl group; and, when n is 2, R 2 ' represents a C 4 -Cδ alkylene group, or a C-C6 alkylene group containing one or more oxygen or sulfur atoms; and, when n is 4, R 2 ' represents a C4-C6 alkane-tetrayl group. Similarly, of interest for the purposes of the present invention are compounds belonging to the group of sterically hindered phenols (c) having general formula (XIX), selected from: N,N'-hexamethylene bis [3- (3, 5-di-t- butyl-4-hydroxyphenyl)propionamide] (known under the trade-name of Lowinox ® HD-98 of Great Lakes Chemical Corporation) ; octadecyl 3- (3 τ , 5 ' -di-t-butyl-4 ' -hydroxyphen- yl) propionate (known under the trade-name of Anox™ PP18 of Great Lakes Chemical Corporation) ; tetrakismethylene- (3, 5-di-t-butyl-4-hydroxy-hydrocinnamate) methane (known under the trade-name of Anox™ 20 of Great Lakes Chemical Corporation); triethylene glycol bis [3- (3-t-butyl-4- hydroxy-5-methyIphenyl) propionate] (known under the trade-name of Lowinox GP-45 of Great Lakes Chemical Corporation) ; 2,2'-thiodiethylene bis [3 (3, 5-di-t-butyl-4- hydroxyphe-nyl) propionate] (known under the trade-name of Anox™ 70 of Great Lakes Chemical Corporation); 1,3,5- tris (3, 5-di-t-butyl-4-hydroxybenzyl) isocyanurate (known under the trade-name of Anox™ IC-14 of Great Lakes Chemical Corporation) ; the compound having the formula: (known under the trade-name of Irganox 259 of Ciba Specialty Chemicals) ; the compound having the formula: (known under the trade-name of Irganox ® 3125 of Ciba Spe- cialty Chemicals) . Also of interest for the purposes of the present invention are compounds belonging to the group of sterically hindered phenols (c) consisting of reactive anti- oxidant: compounds containing a sterically hindered phenol group having general formula (I 1 ) or (I'a): more specifically, reactive antioxidant compounds containing sterically hindered phenol groups having general formula (I 1 ) or (I'a) useful for the purposes of the present invention, are selected from those having general formula (II') or (Il'a): said reactive antioxidant compounds containing sterically hindered phenol groups having general formula (I'), (I'a), (II') and (II 'a), are described in European patents EP 162,523 and EP 182,415 which should be considered as forming an integrant part of the present patent application. The above reactive antioxidant compounds may produce complex resinous structures by means of hydrolysis and condensation of the hydrolyzable silicic function. A specific example of the above reactive antioxidant compounds is the following compound having general formula (II''): consisting of a mixture of linear oligomers wherein Ri = OH and R 2 = H, and cyclic oligomers wherein Ri and R 2 represent a direct bond, having a number average molecular weight equal to 3,900. As said above, the compounds belonging to the sterically hindered phenols (c) group are known compounds and, in some cases, are commercially available. Or, said compounds, can be prepared according to processes described, for example, in patents U.S. 3,330,859, U.S. 3,960,928, or in European patents EP 162,523 and EP 182,415. Compounds belonging to the group of sterically hin- dered amines (d) useful for the purposes of the present invention are selected from those comprising at least one group having general formula (XXIII) or (XXIV) : (XXIII) wherein: G represents a hydrogen atom; or a methyl group; Gi and G 2 , the same or different, represent a hydro- gen atom; a methyl group; or, they jointly represent an oxygen atom. Of particular interest for the purposes of the present invention are compounds belonging to the group of sterically hindered amines (d) selected from compounds (a')-(h') which comprise at least one group having general formula (XXIII) or (XXIV) . (a') Compounds having general formula (XXV): wherein n is a number ranging from 1 to 4, extremes in- eluded; G and Gi, independently represent a hydrogen atom or a methyl; Gu represents a hydrogen atom, 0, a hydroxyl group, an NO group, a -CH 2 CN group, a Ci-Ciβ alkyl group, a C3-C8 alkenyl group, a C3-C8 alkinyl group, a C- C 12 arylalkyl group, a Cι-C 18 alkoxyl group, a C 5 -C 8 cyclo- alkoxyl group, a C-Cg phenylalkoxyl group, a Ci-Cβ alka- noyl group, a C3-C5 alkenoyl group, a Ci-Cia alkanoyloxyl group, a benzyloxyl group, a glycidyl group, an OGn' group, wherein Gu 1 represents a linear or branched C1-C10 alkyl group; a -CH 2 CH(OH)-Z group wherein Z represents a hydrogen atom, a methyl, or a phenyl, G u preferably being hydrogen, a C1-C 4 alkyl group, an allyl, a benzyl, an acetyl or an acryloyl; Gι 2 , when n is 1, represents a hydrogen atom, a Ci-Cis alkyl group, said alkyl group optionally containing one or more oxygen atoms, a cyano- ethyl group, a benzyl, a glycidyl group, a monovalent radical of a carboxylic acid, of a carbamic acid or of an acid containing phosphorous, aliphatic, cycloaliphatic or arylaliphatic, unsaturated or aromatic, or a monovalent silyl radical, preferably a radical of an aliphatic car- boxylic acid having from 2 to 18 carbon atoms, of a cycloaliphatic carboxylic acid having from 7 to 15 carbon atoms, of an α,β-unsaturated carboxylic acid having from 3 to 5 carbon atoms, of an aromatic carboxylic acid having from 7 to 15 carbon atoms, said carboxylic acids op- tionally substituted in the aliphatic, cycloaliphatic or aromatic part, with 1-3 -COOZ12 groups wherein Z i represents a hydrogen atom, a C1-C 2 0 alkyl group, a C3~Cι 2 alkenyl group, a Cs-C 7 cycloalkyl group, a phenyl or a benzyl; Gι 2 , when n is 2, represents a C 2 -Cι 2 alkylene group, a C 4 -Cι 2 alkenylene group, a xylylene group, a di- i valent radical of a dicarboxylic acid, of a dicarbamic acid or of an acid containing phosphorous, aliphatic, cycloaliphatic, arylaliphatic or aromatic, or a divalent silyl radical, preferably a radical of an aliphatic di- carboxylic acid having from 2 to 36 carbon atoms, of a cycloaliphatic or aromatic dicarboxylic acid having from 8 to 14 carbon atoms, of an aliphatic, cycloaliphatic or aromatic dicarbamic acid, having from 8 to 14 carbon atoms, said dicarboxylic acids optionally substituted in the aliphatic, cycloaliphatic or aromatic part, with 1 or 2 -COOZι 2 groups wherein Z x2 has the same meanings defined above; G 1 2, when n is 3, represents a trivalent radical of an aliphatic, cycloaliphatic or aromatic tricarboxylic acid, optionally substituted in the aliphatic, cyclo- aliphatic or aromatic part, with a -COOZ12 group wherein Z 12 has the same meanings defined above, or of an aromatic tricarbamic acid or of an acid containing phosphorous, or it represents a trivalent silyl radical; G12, when n is 4, is a tetravalent radical of an aliphatic, cycloaliphatic or aromatic tetracarboxylic acid. Radicals of tetracarboxylic acids comprise, in all cases, radicals having the formula (-CO) n R wherein n has the same meaning described above and R can be easily deduced from the above definition. Examples of C 1 -C 12 alkyl groups are: methyl, ethyl, n-propyl, n-butyl, s-butyl, t-butyl, n-hexyl, n-octyl, 2- ethylhexyl, n-nonyl, n-decyl, n-undecyl, n-dodecyl, etc. Examples of Gu and G 1 2 substituents, when they represent a Ci-Cia alkyl group, are: in addition to the groups described above: n-tridecyl, n-tetradecyl, n- hexadecyl, n-octadecyl, etc. Examples of the Gn substituent, when it represents a C3-C8 alkenyl group, are: 1-propenyl, allyl, methallyl, 2-butenyl, 2-pentenyl, 2-hexenyl, 2-octenyl, 4-t-butyl-2- butenyl, etc. When the Gn substituent represents a C3-C8 alkinyl group, it is preferably propargyl. When the Gn substituent represents a C-Cι 2 arylal- kyl group, it is, in particular, phenethyl, preferably benzyl. Examples of the Gn substituent, when it represents a Ci-Cs alkanoyl group, are: formyl, propionyl, butyryl, octanoyl, preferably acetyl and, when it represents a C3- C5 alkenoyl group, preferably acryloyl. Examples of the G 12 substituent, when it represents a monovalent radical of a carboxylic acid, are radicals of the following acids: acetic, caproic, stearic, acrylic, methacrylic, benzoic, β- (3,5-di-t-butyl-4- hydroxyphenyl) propionic, etc. An example of the Gι 2 substituent, when it represents a monovalent silyl radical, is: a radical having general formula - (C j H 2 j) -Si (Z' ) 2 Z' ' wherein j is an integer ranging from 2 to 5, extremes included, and Z r and Z'', each independently, represent a C1-C4 alkyl group or a Cι-C alkoxyl group. Examples of the G i2 substituent, when it represents a divalent radical of a dicarboxylic acid, are radicals of the following acids: malonic, succinic, glutaric, adipic, suberic, sebacic, aleic, itaconic, phthalic, di- butylmalonic, dibenzyl alonic, butyl (3,5-di-t-butyl-4- hyd oxybenzyl) alonic, bicycloheptenedicarboxylic, etc. Examples of the G12 substituent, when it represents a trivalent radical of a tricarboxylic acid, are radicals of the acids: trimellitic, citric, ' nitrilotriacetic, etc. Examples of the G 12 substituent, when it represents a tetravalent radical of a tetracarboxylic acid, are radicals of the following acids: butane-1,2,3, 4- tetracarboxylic, pyromellitic, etc. Examples of the Gι 2 substituent, when it represents a divalent radical of a dicarbamic acid, are radicals of the following acids: hexamethylenedicarbamic, 2,4- toluylenedicarba ic, etc. Compounds having general formula (XXV) wherein G represents a hydrogen atom, Gn represents a hydrogen atom or a methyl, n is 2 and G 12 represents a diacyl radical of an aliphatic dicarboxylic acid having from 4 to 12 carbon atoms, are preferred. Specific examples of polyalkylpiperidines having general formula (XXV) are: 1) 4-hydroxy-2, 2, 6, 6-tetramethylpiperidine; 2) l-allyl-4-hydroxy-2,2, 6, 6-tetramethylpiperidine; 3) l-benzyl-4-hydroxy-2, 2, 6, 6-tetramethylpiperidine; 4) 1- (4-t-butyl-2-butenyl) -4-hydroxy-2, 2, 6, 6-tetramethylpiperidine; 5) 4-stearyloxy-2, 2, 6, 6-tetramethylpiperidine; 6) l-ethyl-4-salicyloyloxy-2, 2, 6, 6-tetramethylpiperidine; 7) 4-methacryloyloxy-l,2,2, 6, 6-pentamethylpiperidine; 8) 1,2,2,6, 6-pentamethylpiperidin-4-yl-β- (3, 5-di-t- butyl-4-hydroxyphenyl) propionate; 9) di (l-benzyl-2, 2, 6, 6-tetramethylpiperidin-4-yl) male- ate ; 10) di (2, 2, 6, 6-tetramethylpiperidin-4-yl) succinate; 11) di (2,2, 6, 6-tetramethylpiperidin-4-yl) glutarate; 12) di (2,2, 6, 6-tetramethylpiperidin-4-yl) adipate; 13) di (2, 2, 6, 6-tetramethylpiperidin-4-yl) sebacate; 14) di (1,2,2, 6, 6-pentamethylpiperidin-4-yl) sebacate; 15) di (1, 2, 3, 6-tetramethyl-2, -diethylpiperidin-4-yl) - sebacate; 16) di (l-allyl-2,2, 6, 6-tetramethylpiperidin-4-yl)phthal- ate; 17) l-hydroxy-4-β-cyanoethyloxy-2, 2, 6, 6-tetramethylpiperidine; 18) (l-acetyl-2, 2, 6, 6-tetramethylpiperidin-4-yl) acetate; 19) tris (2, 2, 6, 6-tetramethylpiperidin-4-yl) trimellitate; 20) l-acryloyl-4-benzyloxy-2, 2, 6, 6-tetramethylpiperidine; 21) di (2, 2, 6, 6-tetramethylpiperidin-4-yl) diethylmalon- ate; 22) di (1, 2,2, 6, 6-pentamethylpiperidin-4-yl) dibutylmalon- ate; 23) di (1, 2,2, 6, 6-pentamethylpiperidin-4-yl) butyl- (3, 5- di-tert-butyl-4-hydroxybenzyl)malonate; 24) di (l-octyloxy-2,2, 6, 6-tetramethylpiperidin-4-yl) seb- acate; 25) di (l-cyclohexyloxy-2, 2, 6, 6-tetramethylpiperidin-4- yl) sebacate; 26) hexane-1' , 6'-bis (4-carbamoyloxy-l-n-butyl-2,2, 6, 6- tetramethylpiperidine) ; ■ 27) toluene-2' , '-bis (4-carbamoyloxy-l-n-propyl-2, 2, 6, 6- tetramethylpiperidine) ; 28) dimethyl-bis (2,2, 6, 6-tetramethylpiperidin-4-oxy) silane; 29) phenyl-tris (2,2, 6, 6-tetramethylpiperidin-4-oxy) silane; 30) tris (l-propyl-2, 2, 6, 6-tetramethylpiperidin-4-yl) - phosphite; - _ 31) tris (l-propyl-2, 2, 6, 6-tetramethylpiperidin-4-yl) - phosphate; 32 ) bis (1,2,2,6, 6-pentamethylpiperidin-4-yl) phenylphos- phonate; 33) 4-hydroxy-1, 2,2, 6, 6-pentamethylpiperidine; 34) 4-hydroxy-N-hydroxyethyl-2, 2, 6, 6-tetramethylpiperidine; 35) 4-hydroxy-N- (2-hydroxypropyl) -2,2,6, 6-tetramethylpiperidine; 36) l-glycidyl-4-hydroxy-2, 2,6, 6-tetramethylpiperidine . (b') Compounds having general formula (XXVI): wherein n is 1 or 2 ; G, Gi and Gn have the same meanings described above under point ( a 1 ) ; Gι 3 represents a hydrogen atom, a Cι~Cι 2 alkyl group, a C 2 -Cs hydroxyalkyl group, a C 5 -C7 cycloalkyl group, a C7-C8 arylalkyl group, a C 2 -Ci8 alkanoyl group, a C 3 -C5 alkenoyl group, a benzoyl group, or a group having the following general formula : wherein G, Gi and Gn have the same meanings defined above under point (a'); G 1 4, when n is 1, represents a hydrogen atom, a Ci-Cia alkyl group, a C3-C8 alkenyl group, a C5-C7 cycloalkyl group, a Cι~C 4 alkyl group substituted with a hydroxyl group, with a cyano group, with an alkoxycarbonyl group or with a carbamide group, a glycidyl group, a group having the formula -CH 2 -CH(OH) -Z or a group having the formula -CONH-Z wherein Z represents a hydrogen atom, a methyl or a phenyl; G 14 , when n is 2, represents a C2-C12 alkylene group, a C 6 -Cι 2 arylene group, a xylylene group, a group having the formula -CH 2 -CH(OH) -CH 2 - or a group having the formula -CH 2 -CH(OH) -CH 2 -0-D-0 wherein D represents a C 2 -Cι 0 alkylene group, a Cβ-Cι 5 arylene group, a C 6 -Cι 2 cycloalkylene group; or, on the condition that G 1 3 does not represent an alkanoyl group, an alkenoyl group or a benzoyl group, G14 can also represent a 1-oxo- (C2-C1 2 ) -alkylene group, a divalent radical of a dicarboxylic acid or of a dicarbamic acid, aliphatic, cycloaliphatic or aromatic, or also a -CO- group; or, when n is 1, G 1 3 and G 14 considered jointly, can also represent a divalent radical of a 1,2- or 1, 3-dicarboxylic acid, ali- phatic, cycloaliphatic or aromatic. The C1-C12 alkyl or Ci-Cia alkyl groups have already been described above under point (a') . The C5-C 7 cycloalkyl groups are preferably cyclo- hexyl . When G 1 3 represents a C-Ce arylalkyl group, it is phenylethyl, preferably benzyl. When G 1 3 represents a C2-C5 hydroxyalkyl group, it is 2-hydroxyethyl, 2-hydroxypropyl, etc. Examples of G 1 3 / when it represents a C 2 -Cι 8 alkanoyl group, are: propionyl, butyryl, octanoyl, dodecanoyl, hexadecanoyl, octadecanoyl, etc. preferably acetyl and, when it represents a C3-C5 alkenoyl group, it is preferably acryloyl. Examples of Gι 4 , when it represents a C 2 -C 8 alkenyl group, are: allyl, methallyl, 2-butenyl, 2-pentenyl, 2- hexenyl, 2-octenyl, etc. Examples of G i4 , when it represents a C 1 -C4 alkyl group substituted by a hydroxyl, cyano, alkoxycarbonyl or carbamide group, are: 2-hydroxyethyl, 2-hydroxypropyl, 2- cyanoethyl, methoxycarbonylmethyl, 2-ethoxycarbonylethyl, 2-aminocarbonylpropyl, 2- (dimethylaminocarbonyl) ethyl, etc. Examples of C2-C 1 2 alkylene groups, are: ethylene, propylene, 2,2-dimethylpropylene, tetramethylene, hex- amethylene, octamethylene, decamethylene, dodecamethyl- ene, etc. Examples of Cβ-Cis arylene groups, are: o-, m- or p- phenylene, 1, 4-naphthylene, 4, 4 '-diphenylene, etc. An example of a C6-C 12 cycloalkylene group is pref- erably cyclohexylene. Preferred compounds having general formula (XXVI) are those wherein n is 1 or 2, G represents a hydrogen atom, Gn represents a hydrogen atom or a methyl, G13 represents a hydrogen atom, a C 1 -C 12 alkyl group or a group having the formula: and G 14 , when n is 1, represents a hydrogen atom or a Ci- C12 alkyl group and, when n is 2, it represents a C 2 -Cs alkylene group or a 1-oxo- (C 2 -C 8 ) -alkylene group. Specific examples of polyalkylpiperidines having general formula (XXVI) are: 1) N, N'-bis (2,2,6, 6-tetramethylpiperidin-4-yl)hexameth- ylene-1, 6-diamine; 2) N, N'-bis (2, 2, 6, 6-tetramethylpiperidin-4-yl) hexameth- ylene-1, 6-diacetamide; 3) bis (2,2,6, 6-tetramethylpiperidin-4-yl) amine; 4) 4-benzoylamino-2,2, 6, 6-tetramethylpiperidine; 5) N,N'-bis (2,2,6, 6-tetramethylpiperidin-4-yl)-N,N'-di- butyladipamide; 6) N,N'-bis (2,2,6, 6-tetramethylpiperidin-4-yl)-N,N'-di- cyclohexyl-2-hydroxypropylene-l, 3-diamine; 7) N,N'-bis (2,2, 6, 6-tetramethylpiperidin-4-yl) -p- xylylenediamine; 8) N, N'-bis (2, 2, 6, 6-tetramethylpiperidin-4-yl) succin- amide; 9) bis (2,2, 6, 6-tetramethylpiperidin-4-yl) -N- (2,2, 6, 6- tetramethylpiperidin-4-yl) -β-aminodipropionate; 10) compound having the formula: 11) 4- [bis (2-hydroxyethyl) amino] -1, 2 , 2, 6, 6-pentamethyl- piperidine; 12) 4- (3-methyl-4-hydroxy-5-tert-butylbenzamide) -2 , 2 , - 6, 6-tetramethylpiperidine; 13) 4-methacrylamide-l, 2, 2, 6, 6-pentamethylpiperidine; (c ' ) Compounds having general formula (XXVII) : (XXVII) wherein n is 1 or 2; G, Gi and Gu have the same meanings described above under point (a'); Gi5r when n is 1, rep ¬ resents a C 2 -Ce alkylene or hydroxyalkylene group, or a C 4 -C 22 acyloxyalkylene group, and, when n is 2, it is a (-CH 2 ) 2 C(CH 2 -) 2 group. Examples of G 15 , when it represents a C 2 -Ca alkylene or hydroxyalkylene group, are: ethylene, 1- ethylethylene, propylene, 2-ethylpropylene, 2-ethyl-2- hydroxymethyl-propylene, etc. An example of G 1 5, when it represents a C 4 -C2 2 acy- loxyalkylene group is 2-ethyl-2-acetoxy-methylpropylene. Specific examples of polyalkyipiperidines having general formula (XXVII) are: 1) 9-aza-8, 8, 10, 10-tetramethyl-l, 5-dioxaspiro [5.5] un- decane; 2) 9-aza-8, 8, 10, 10-tetramethyl-3-ethyl-l, 5-dioxaspiro- [5.5]undecane; 3) 8-aza-2 ,7,7,8,9, 9-hexamethyl-l, 4-dioxaspiro [4.5]- decane; 4) 9-aza-3-hydroxymethyl-3-ethyl-8, 8, 9, 10, 10-penta- methyl-1, 5-dioxaspiro- [5.5]undecane; 5) 9-aza-3-ethyl-3-acetoxymethyl-9-acetyl-8, 8, 10, 10- tetramethyl-l, 5-dioxaspiro [5.5] undecane; 6) 2,2, 6, 6-tetramethylpiperidine-4-spiro-2 ' - (1' ,3'- dioxane) -5'-spiro-5' '- (1' ' ,3 T '-dioxane) -2* '-spiro- 4"'-(2".,2"' / 6"',6" '-tetramethylpiperidine) . (d') Compounds having general formula (XXVIIIA) , (XXVIIIB) and (XXVIIIC) , compounds having general formula (XXVIIIC) being preferred: (XXVIIIA) VIIIB) (XXVIIIC) wherein n is 1 or 2, G, Gi and Gn have the same meanings defined above under point (a'); G X β represents a hydrogen atom, a Cι-Cι 2 alkyl group, an allyl group, a benzyl, a glycidyl group or a C 2 -C6 alkoxyalkyl group; Gι 7 , when n is 1, represents a hydrogen atom, a Cι-C 12 alkyl group, a C3-C5 alkenyl group, a C 7 -Cg arylalkyl group, a C5-C-7 cycloalkyl group, a C 2 -C 4 hydroxyalkyl group, a C 2 -Cβ alkoxyl group, a Cβ-Cio aryl group, a glycidyl group, or a group having the formula - (CH 2 ) p -COO-Q or - (CH 2 ) p -0-CO-Q wherein p is 1 or 2 and Q represents a Cι-C 4 alkyl group or a phenyl; Gι, when n is 2, represents a C 2 -Cι 2 al- kylene group, a C-Cι 2 alkenylene group, a C 6 - L2 arylene group, a group having the formula: -CH2-CH(OH)-CH 2 -0-D-0-CH 2 -CH(OH)-CH2- wherein D represents a C2-C10 alkylene group, a C δ -Ci5 arylene group, a C6-C12 cycloalkylene group, or a group having the formula: -CH 2 CH(OZ')CH 2 -(OCH 2 -CH(OZ' )CH 2 ) 2 wherein Z' represents a hydrogen atom, a Ci-Ciβ alkyl group, an allyl, a benzyl, or a C 2 -C 12 alkanoyl group or a benzoyl; 1χ and T 2 each independently represent a hydrogen atom, a Ci-Cis alkyl group, a C6-C10 aryl group, a C 7 -Cg arylalkyl group, said groups optionally substituted with a halogen atom or with a C1-C4 alkyl group; or T x and T 2 , considered jointly with the carbon atom to which they are bound, form a C5-C α4 cy- loalkane ring. Examples of C 1 -C 1 2 alkyl groups are: methyl, ethyl, n-propyl, n-butyl, s-butyl, t-butyl, n-hexyl, n-octyl, 2- ethylhexyl, n-nonyl, n-decyl, n-undecyl, n-dodecyl, etc. Examples of Ci-Cia alkyl groups are, in addition to those listed above: n-tridecyl, n-tetradecyl, n- hexadecyl, n-octadecyl, etc. Examples of C 2 -C6 alkoxyalkyl groups are: meth- oxymethyl, ethoxymethyl, propoxymethyl, t-butoxymethyl, ethoxyethyl, ethoxypropyl, n-butoxyethyl, t-butoxyethyl, isopropoxyethyl, propoxypropyl, etc. Examples of G i7 , when it represents a C3-C5 alkenyl group are: 1-propenyl, allyl, methallyl, 2-butenyl, 2- pentenyl, etc. Examples of Gι, T x and T 2 , when they represent a C- Cg arylalkyl group are: phenethyl, preferably benzyl. Examples of cycloalkane rings, formed by Tα and T 2 when said substituents are considered jointly with the carbon atom to which they are bound, are: cyclopentane, cyclohexane, cyclo-octane, cyclododecane, etc. Examples of Gι 7 , when it represents a C 2 -C 4 hy- droxyalkyl group, are: 2-hydroxyethyl, 2-hydroxypropyl, 2-hydroxybutyl, 4-hydroxybutyl, etc. Examples of Gι , Ti and T 2 , when they represent a Cβ~ Cio aryl group are: phenyl, - or β-naphthyl, optionally substituted with a halogen atom or a Cι~C 4 alkyl group, etc. Examples of G i7 , when it represents a C 2 -Cι 2 alkylene group, are: ethylene, propylene, 2, 2-dimethylpropylene, tetramethylene, hexamethylene, octamethylene, decamethyl- ene, dodeca ethylene, etc. Examples of Gι, when it represents a C 4 -Cι 2 alkenylene group, are: 2-butenylene, 2-pentenylene, 3- hexenylene, etc. Examples of Gι, when it represents a C 6 -Cι 2 arylene group, are: o-, m- or p-phenylene, 1, 4-naphthylene, 4,4'- diphenylene, etc. Examples of Z', when it represents a C 2 ~Cι 2 alkanoyl group, are: propionyl, butyryl, octanoyl, dodecanoyl, preferably acetyl. Examples of D, when it represents a C 2 -Cιo alkylene group, a Cβ-Cis arylene group or Cβ-Ci2 cycloalkylene group, are described above relating to point (b'). Specific examples of polyalkyipiperidines having general formula (XXVIIIA) , (XXVIIIB) and (XXVIIIC) are: 1) 3-benzyl-l, 3, 8-triaza-7, 7, 9, 9-tetramethylspiro [4.5]- decane-2 , 4-dione; 2) 3-n-octyl-l, 3, 8-triaza-7, 7, 9, 9-tetramethylspiro- [4.5] -decane-2 , 4-dione; 3) 3-allyl-l, 3, 8-triaza-l, 7,7,9, 9-pentamethylspiro- [4.5] -decane-2 , 4-dione; 4) 3-glycidyl-l, 3, 8-triaza-7, 7, 8, 9, 9-pentamethylspiro- [4.5] -decane-2, 4-dione; 5) 1,3,7,7,8,9, 9-heptamethyl-l, 3, 8-triazaspiro [4.5] - decane-2, 4-dione; 6) 2-isopropyl-7,7, 9, 9-tetramethyl-l-oxa-3, 8-diaza-4- oxospiro [4.5]decane; 7) 2, 2-dibutyl-7, 7, 9, 9-tetramethyl-l-oxa-3, 8-diaza-4- oxospiro [4.5] decane; 8) 2,2, 4,4-tetramethyl-7-oxa-3,20-diaza-21-oxodispiro- [5.1.11.2]heneicosane; 9) 2-butyl-7,7,9,9-tetramethyl-l-oxa-4,8-diaza-3-oxo- spiro [4.5] decane; and, preferably, 10) 8-acetyl-3-dodecyl-l, 3, 8-triaza-7, 7, 9, 9-tetramethylspiro [4.5] -decane-2, 4-dione; or a compound having one of the following formulae: (XXVIII (XXVIII) -12; (XXVIII) -13; (e') Compounds having general formula (XXIX) wherein n is 1 or 2, and Gι 8 represents a group having one of the following formulae: wherein G and Gn have the same meanings defined above under point (a'); Gi and G 2 represent a hydrogen atom, a methyl, or, considered jointly, they form a substituent =0, E represents -0- or -NG 1 3-; A represents a C 2 -C 5 alkylene group or a -(CH 2 ) 3 -0- group; x is 0 or 1; G13 represents a hydrogen atom, a C 1 -C12 alkyl group, a C 2 -C 5 hy- droxyalkyl group, a C5-C7 cycloalkyl group; Gig has the same meanings as Gι 8 or it represents one of the following groups: -NG21G22, -OG23, -NHCH 2 0G 2 3 or -N (CH 2 0G 2 3) 2; G 2 o, when n is 1, has the same meanings as Gie, or Gig, if n is 2, it represents an -E-B-E- group wherein B represents a C2-C8 alkylene group optionally interrupted by 1 or 2 -N(G 2 ι)- groups; G 21 represents a C1-C12 alkyl group, a cy- clohexyl group, a benzyl, a Cι~C 4 hydroxyalkyl group, or a group having the following general formula: G 22 represents a Cι~Cι 2 alkyl group, a cyclohexyl group, a benzyl, a Cι~C hydroxyalkyl group; G 2 3 represents a hydrogen atom, a C 1 -C12 alkyl group, a phenyl, or, G 2 ι and G 22 , considered jointly, represent a C-C 5 alkylene or oxyalkylene group, for example: - H 2 H 2 v O -CH 2 CH 2 or a group having the formula : G2 1 is a group having the general formula: G X Examples of C1-C12 alkyl groups are: methyl, ethyl, n-propyl, n-butyl, s-butyl, t-butyl, n-hexyl, n-octyl, 2- ethylhexyl, n-nonyl, n-decyl, n-undecyl, n-dodecyl, etc. Examples of C 1 -C 4 hydroxyalkyl groups are: 2- hydroxyethyl, 2-hydroxypropyl, 3-hydroxypropyl, 2-hydro- xybutyl, 4-hydroxybutyl, etc. Examples of A, when it represents a C2-C6 alkylene group, are: ethylene, propylene, 2, 2-dimethylpropylene, tetramethylene, hexamethylene, etc. Examples of G 2i and G 22 /* when, considered jointly, they represent a C 4 -C5 alkylene or oxyalkylene group, are: tetramethylene, pentamethylene, 3-oxapentamethylene, etc. Specific examples of polyalkyipiperidines having general formula (XXIX) are: (XXIX) -1; CHa R-NH-(CH 2 ) 3 - fN-(CH 2 ) 2 -N f-(CH 2 )3-NH-R wherein R is H -N I-(CH 2)2 -N f-(CH 2 ) 3 -NH-R wherein R s R-NH- (CH 2 ) 3 CH 3 CH 3 R R CH 3 R-N-(CH 2 ) 3 -N-(CH 2 ) 2 -N-(CH 2 ) 3 -N-R wherein R is (XXIX) -9; (XXIX) -10; (XXIX)-11. (f) Oligomeric or polymeric compounds whose recurrent structural unit contains a 2,2, 6, 6-tetramethylpiperidine radical, in particular polyesters, polyethers, polyam- ides, polyamines, polyurethanes, polyureas, polyaminotri- azines, poly (meth) acrylates, poly(meth) acrylamides, and their copolymers containing said radical. Specific examples of the above 2,2,6,6- polyalkylpiperidines are represented by the following formulae wherein m is a number ranging from 2 to 200: (XXX) -1; (XXX) -2; (XXX) -3; (XXX) -4; (XXX) -5; (XXX) -6; (XXX) -9; (XXX) -11; (XXX) -12; (XXX) -13; (XXX) -14; wherein R wherein ' and m' ' are an integer ranging from 0 to 200, extremes included, on the condition that m' + m' ' is . Further examples of polymeric compounds (f) useful for the purposes of the present invention are: the reaction products between compounds having formula (XXXI) : and epichlorohydrin; polyesters obtained from the reaction of butane- 1,2, 3, 4-tetracarboxylic acid with a bifunctional alcohol having formula (XXXII) : (XXXII) whose carboxylic termination deriving from tetracar- boxylic acid has been esterified with a 2,2,6,6- tetramethyl-4-hydroxypiperidine group; compounds having general formula (XXXIII) : (XXXIII) wherein about a third of the R radicals represent a -C 2 H5 group and the remainder a group having the formula: and m is a number ranging from 2 to 200, extremes included; copolymers whose recurrent unit consists of two units having the formula: and, in each case, of a unit having the formula: C- L 3 H 2 η and a unit having the formula: (g') Compounds having general formula (XXXIV) (XXXIV) wherein n is 1 or 2, G and Gn have the same meanings defined above under point (a') and G i has the same meanings described above under point (b'), on the condition that Gi 4 can never represent the group -CONH-Z or the group -CH 2 -CH (OH) -CH 2 -0-D-0. Examples of compounds having general formula (XXXIV) are the following: (XXXIV) -1; (XXXIV) -2; (h 1 ) Compounds having general formula (XXXV) : wherein Ri represents a Ci-Cio alkyl group, a C5-C12 cycloalkyl group optionally substituted with a C1-C4 alkyl group, a phenyl optionally substituted with a Ci-Cjo alkyl group; R2 represents a C3-C10 alkylene group; R3 represents a hydrogen atom, a Cι-C 8 alkyl group, 0", a - CH 2 CN group, a C 3 -C 6 alkenyl group, a C-C 9 phenylalkyl group optionally substituted in the phenyl radical with a C1-C4 alkyl group, a Ci-Cg acyl group, an -OR' 3 group wherein R'3 represents a C1-C10 alkyl group; and n is a number ranging from 1 to 50, extremes included. Of particular interest for the purposes of the present invention are compounds belonging to the group of sterically hindered amines (d) , selected from: Tinuvin 123 of Ciba Specialty Chemicals; Tinuvin ® 144 of Ciba Specialty Chemicals; Lowilite ® 76 of Great Lakes Chemical Corporation; Lowilite ® 62 of Great Lakes Chemical Corporation; Lowilite ® 94 of Great Lakes Chemical Corporation; Chimassorb ® 119 of Ciba Specialty Chemicals; the compound having formula (XXXV) -1: poly-methylpropyl-3-oxy-[4- (2,2, 6, 6-tetramethyl)piperid- inyl] siloxane, known under the trade-name of UVASIL ® 299 of Great Lakes Chemical Corporation; polymethylpropyl-3- oxy- [4- (1,2, 2, 6, 6-pentamethyl)piperidinyl] siloxane. Compounds belonging to the group of sterically hindered amines (d) useful for the purposes of the present invention are those having an average molecular weight M n ranging from 500 to 10,000, in particular from 1,000 to 10,000. The stabilizing mixtures, object of the present invention, are capable of stabilizing organic polymers against degradation caused by oxygen, heat and/or light. Examples of organic polymers to which they can be added are: 1. Polymers of mono-olefins and di-olefins such as, for example, polypropylene, polyisobutylene, polybut-1-ene, poly-4-methylpent-l-ene, polyisoprene or polybutadiene; as well as polymers of cyclo-olefins such as, for example, cyclopentene or norbornene; polyethylene (which can be op- tionally cross-linked) such as, for example, high density polyethylene (HDPE) , high density and high molecular weight polyethylene (HDPE-BMW) , high density and ultrahigh molecular weight polyethylene (HDPE-UHMW) , medium density polyethylene (MDPE) , low density polyethylene (LDPE) , lin- ear low density polyethylene (LLDPE) , branched low density polyethylene (BLDPE) , (VLDPE) , (ULDPE) . Polyolefins such as, for example the mono-olefins mentioned in the above paragraph, preferably polyethylene and polypropylene, can be prepared with many methods known in literature, preferably using the following methods: (a) radicalic polymerization (generally carried out at a high pressure and high temperature) ; (b) catalytic polymerization using a catalyst which normally contains one or more metals of groups IVb, Vb, VIb or VIII of the Periodic Table. These metals generally have one or more ligands such as, for example, oxides, halides, alcoholates, esters, ethers, amines, alkyls, alkenyls and/or aryls which can be π- or σ- coordinated. These metal complexes can be in free form or supported on substrates such as, for example, activated magnesium chloride, titanium (III) chloride, alumina or silicon oxide. Said catalysts can be soluble or insoluble in the polymerization medium. The catalysts can be used alone or in the presence of other activators such as, for example, metal alkyls, metal hydrides, halides of metal alkyls, oxides of metal alkyls or metal alkyloxanes, these metals being elements belonging to groups la, Ila and/or Ilia of the Periodic Table. The activators can be conve- niently modified with other ester, ether, amine or silyl-ether groups. These catalytic systems are usually called Phillips, Standard Oil Indiana, Zieg- ler(-Natta), TNZ (Du-Pont) , metallocene or "single site catalyst" (SSC) . 2. Mixtures of the polymers described under point (1) such as, for example, mixtures of polypropylene with poly- isobutylene; mixtures of polypropylene with polyethylene (for example, PP/HDPE, PP/LDPE) ; mixtures of different types of polyethylene (for example, LDPE/HDPE) . 3. Copolymers of mono-olefins and di-olefins with each other or with other vinyl monomers such as, for example, ethylene/propylene copolymers, linear low density polyethylene (LLDPE) and its mixtures with low density polyethylene (LDPE) , propylene/but-1-ene copolymers, propylene/ isobutylene copolymers, ethylene/but-1-ene copolymers, ethylene/hexene copolymers, ethylene/methylpentene copolymers, ethylene/heptene copolymers, ethylene/octene copolymers, propylene/butadiene copolymers, isobutylene/isoprene copolymers, ethylene/alkyl acrylate copolymers, ethyl- ene/alkyl methacrylate copolymers, ethylene/vinyl acetate copolymers and their copolymers with carbon monoxide or ethylene/acrylic acid copolymers and- their salts (iono- mers) as well as terpolymers of ethylene with propylene and a diene such as, for example, hexadiene, dicyclopenta- diene or ethylidene-norbornene; and also mixtures of said copolymers with each other or with the polymers cited in under point (1) such as, for example, polypropylene/ethylene/propylene copolymers, LDPE/ethylene/vinyl- acetate (EVA) copolymers, LDPE/ethylene/acrylic acid (EAA) copolymers, LLDPE/EVA, LLDPE/EAA, and alternating or random polyalkylene/carbon monoxide copolymers and their mixtures with other polymers such as, for example, polyam- ides. 4. Hydrocarbon resins (for example, Cs-Cg) comprising their hydrogenated modifications (for example, adhesive resins) and mixtures with polyalkylene and starch. 5. Polystyrene, poly (p-methylstyrene) , poly(α- methylstyrene) . 6. Copolymers of styrene or -methylstyrene with dienes or acrylic derivatives such as, for example, styre- ne/butadiene, styrene/acrylonitrile, styrene/alkyl ethac- rylate, styrene/butadiene/alkyl acrylate, styrene/ butadi- ene/alkyl methacrylate, styrene/maleic anhydride, sty- rene/acrylonitrile/methyl acrylate; mixtures, having a high impact strength, between copolymers of styrene and another polymer such as, for example, a polyacrylate, a polymer of a diene or an ethylene/propylene/diene terpoly- mer, block copolymers of styrene such as, for example, styrene/butadiene/styrene, styrene/isoprene/styrene, sty- rene/ethylene/butylene/styrene or styrene/ethylene/pro- pylene/styrene . 7. Grafted copolymers of styrene or of α-methylstyrene such as, for example, styrene in polybutadiene, styrene in polybutadiene/styrene or polybutadiene/acrylonitrile co- polymers; styrene and acrylonitrile (or methacrylonitrile) in polybutadiene; styrene, acrylonitrile and methyl- methacrylate in polybutadiene; styrene and maleic anhydride in polybutadiene; styrene, acrylonitrile and maleic anhydride or maleimide in polybutadiene; styrene and male- imide in polybutadiene; styrene and alkylacrylates or alkyImethacrylates in polybutadiene; styrene and acrylonitrile in ethylene/propylene/diene terpolymers, styrene and acrylonitrile in polyalkyl acrylates or polyalkyl methacrylates, styrene and acrylonitrile in ac- rylate/butadiene copolymers, as well as mixtures of the copolymers listed above with the copolymers cited under point (6) such as, for example, mixtures of known copolymers such as ABS, MBS, ASA or AES. 8. Polymers containing halogens such as, for example, polychloroprene, chlorinated rubbers, chlorinated or bro- minated isobutylene-isoprene copolymers ("halobutyl rubber"), chlorinated or chlorosulfonated polyethylene, ethylene and chlorinated ethylene copolymers, homopolymers and copolymers of epichlorohydrin, in particular polymers of vinyl compounds containing halogens such as, for example, polyvinyl chloride, polyvinylidene chloride, polyvi- nyl fluoride or polyvinylidene fluoride; and also their copolymers such as, for example, vinyl chloride/vinylidene chloride, vinyl chloride/vinyl acetate or vinylidene chlo- ride/vinyl acetate. 9. Polymers deriving from α, β-unsaturated acids and their derivatives such as, for example, polyacrylates and polymethacrylates, polymethyl methacrylates, polyacryla- mides and polyacrylonitriles, impact modified with butyl acrylate. 10. Copolymers of monomers according to point (9) with each other or with other unsaturated monomers such as, for example, acrylonitrile/butadiene copolymers, acryloni- trile/alkyl acrylate copolymers, acrylonitrile/alkoxyalkyl acrylate copolymers or acrylonitrile/vinyl halide copoly- mers or acrylonitrile/alkyl methacrylate/butadiene ter- polymers . 11. Polymers deriving from unsaturated alcohols and amines, or their acyl or acetal derivatives such as, for example, polyvinyl alcohol, polyvinyl acetate, polyvinyl stearate, polyvinyl benzoate, polyvinyl maleate, polyvinyl butyral, polyallyl phthalate or polyallyl melamine; and also their copolymers with the olefins listed under point (1) • 12. Homopolymers and copolymers of open-chain ethers or cyclic ethers such as, for example, polyalkylene glycols, polyethylene oxide, polypropylene oxide, or copolymers of the compounds described above with bis-glycidyl ethers. 13. Polyacetals such as, for example, polyoxymethylene and those polyoxymethylenes containing comonomers, for example, ethylene oxide; polyacetals modified with thermoplastic polyurethanes, acrylates or MBS. 14. Polyphenylene oxides and sulfides and their mixtures with styrene polymers or polyamides. 15. Polyurethanes deriving from hydroxyl-terminated poly- ethers, polyesters or polybutadienes on the one hand and aliphatic or aromatic polyisocyanates on the other, as well as their precursors. 16. Polyamides and copolyamides deriving from diamines and dicarboxylic acids and/or aminocarboxylic acids or from the corresponding lactams such as, for example, polyamide 4, polyamide 6, polyamide 6/6, 6/10, 6/9, 6/12, 4/6, 12/12, polyamide 11, polyamide 12, aromatic polyamides obtained starting from m-xylene diamine and adipic acid; polyamides prepared from hexamethylenediamine and isoph- thalic and/or terephthalic acid and with or without an elastomer as modifier, for example., poly-2, 4,4-trime- thylhexamethylene terephthalamide or poly-m-phenylene isophthalamide; and also block copolymers of the above polyamides with polyolefins, olefinic copolymers, ionomers or elastomers chemically bound or grafted; or with polye- thers such as, for example, polyethylene glycol, polypropylene glycol or polytetramethylene glycol; as well as polyamides or copolyamides modified with EPDM or ABS; and polyamides condensed during processing ("RIM polyamide system") . 17. Polyureas, polyimides, polyamide-imides, polyetherim- ides, polyesterimides, polyhydantoins, and polybenzoimid- azoles. 18. Polyesters deriving from dicarboxylic acids and diols and/or from hydroxycarboxylic acids or from the corresponding lactones such as, for example, polyethylene ter- ephthalate, polybutylene terephthalate, poly-l,4-dime- thylolcyclohexane terephthalate and polyhydroxybenzoates, as well as block copolyether esters deriving from polyeth- ers with hydroxyl-ter inated groups; and also polyesters modified with polycarbonates or MBS. 19. Polycarbonates and polyester carbonates. 20. Polysulfones, polyethersulfones and polyetherketones . 21. Cross-linked polymers deriving from aldehydes on the one hand and from phenols, urea and melamines on the other, such as, for example, phenol/formaldehyde resins, urea/formaldehyde resins and melamine/formaldehyde resins. 22. Dried or non-dried alkyd resins. 23. Resins based on unsaturated polyesters deriving from copolyesters of dicarboxylic acids saturated and unsaturated with polyhydric alcohols and vinyl compounds as cross-linking agents, and also the above resins containing halogens and having a good flame-resistance. 24. Cross-linkable acrylic resins deriving from substituted acrylates such as, for example, epoxy acrylates, urethane acrylates or polyester acrylates. 25. Alkyd resins, resins based on polyesters or acrylated resins cross-linked with mela ine resins, resins based on urea, resins based on isocyanates, resins based on iso- cyanurates, resins based on polyisocyanates or epoxy resins. 26. Cross-linked epoxy resins deriving from aliphatic, cycloaliphatic, heterocyclic or aromatic glycidyl com- pounds such as, for example, products of diglycidyl ethers of bisphenol A and bisphenol F, which are cross-linked with the usual cross-linking agents such as, for example, anhydrides or amines, in the presence of or without accel- erating agents . 27. Natural polymers such as, for example, cellulose, natural rubber, gelatin, and their derivatives chemically modified to give homologous polymers such as, for example, cellulose acetates, propionates and butyrates, or cellu- lose ethers such as methyl-cellulose; as well as hydrocarbon resins ("rosins") and their derivatives. 28. Mixtures of the above polymers ("polyblends") such as, for example, PP/EPDM, polyamides/EPDM or ABS, PVC/EVA, PVC/ABS, PVC/MBS, PC/ABS, PBTP/ABS, PC/ASA, PC/PBT, PVC/CPE, PVC/acrylates, POM/thermoplastic PUR, PC/thermoplastic PUR, POM/acrylates, POM/MBS, PPO/HIPS, PPO/PA 6.6 and copolymers, PA/HDPE, PA/PP, PA/PPO, PBT/PC/ABS, PBT/PET/PC. 29. Natural or synthetic organic materials which are pure monomeric compounds or mixtures of said compounds, such as, for example, mineral oils, animal or vegetable oils, fats or waxes, oils, fats or waxes based on synthetic esters (for example, phthalates, adipates, phosphates, trimellitates) , as well as mixtures of synthetic esters with mineral oils in any weight ratio, in particu- lar those used in spinning compositions, as well as aqueous emulsions of said organic materials. 30. Aqueous emulsions of natural or synthetic rubbers such as, for example, natural latex or latexes based on carboxylated styrene-butadiene copolymers . The organic polymers which can be stabilized with the mixtures, object of the present invention, are, preferably, natural, semi-synthetic or synthetic polymers selected from those described above. More preferably, the mixtures, object of the present invention, are useful in the stabilization of thermoplastic polymers, especially polyolefins, in particular polyethylene and polypropylene or their copolymers with mono- and di-olefins. A further object of the present invention therefore relates to polymeric compositions containing an organic polymer and an effective quantity of one of the stabilizing mixtures, object of the present invention. Yet another object of the present invention relates to the end- products obtained from the processing of the above poly- eric compositions. The stabilizing mixtures, object of the present invention, are particularly useful against degradation caused by oxygen and heat and are consequently exceptionally useful as process stabilizers. Compounds (a) , (b) and (c) and, optionally, (d) of the above stabilizing mixtures can be added to the organic polymers to be stabilized either individually or mixed with each other. Compound (a) is added to the organic polymers to be stabilized in a quantity ranging from 0.001% to 2.5% with respect to the weight of the organic polymer to be stabilized, preferably from 0.005% to 2%, for example, from 0.01% to 1%. Compounds (b) , (c) and, optionally, (d) , are added to the organic polymers to be stabilized in a quantity ranging from 0.01% to 10% with respect to the weight of the organic polymer to be stabilized, for example from 0.01% to 5%, preferably from 0.025% to 3%, even more preferably from 0.025% to 1%. The stabilizing mixtures object of the present invention can optionally contain other stabilizers (co- stabilizers) . Stabilizers for organic polymers useful for the purpose are selected from the following groups: 1. Antioxidants 1.1 Alkylated monophenols such as, for example: 2,6-di- t-butyl-4-methylphenol; 2-t-butyl-4, 6-dimethylphenol; 2, 6-di-t-butyl-4-ethylphenol; 2, 6-di-t-butyl-4-n-butyl- phenol; 2, 6-di-t-butyl-4-isobutylphenol; 2,6-dicyclo- pentyl-4-methylphenol; 2- (α-methylcyclohexyl) -4, 6-dime- thylphenol; 2, 6-dioctadecyl-4-methylphenol; 2,4,6-tri- cyclohexylphenol; 2, 6-di-t-butyl-4-methoxymethylphenol; nonylphenols with a linear or branched alkyl chain such as, for example, 2, 6-dinonyl-4-methylphenol; 2,4-dime- thyl-6- (1 '-methylundec-l'-y1) phenol; 2, 4-dimethyl-6- (1 '- methylheptadec-l'-yl) phenol; 2, 4-dimethyl-6- (l'-methyl- tridec-l'-yl) phenol; and their mixtures. 1.2 Alkylthiomethylphenols such as, for example: 2,4-di- octylthiomethyl-6-t-butylphenol; 2, 4-dioctylthiomethyl-6- methylphenol; 2, 4-dioctylthiomethyl-6-ethylphenol; 2,6- didodecylthiomethyl-4-nonylphenol. 1.3 Hydroquinones and alkylated hydroquinones such as, for example: 2, 6-di-t-butyl-4-methoxyphenol; 2,5-di-t- butylhydroquinone; 2, 5-di-t-amylhydroquinone; 2,6-di- phenyl-4-octadecyloxyphenol; 2, 6-di-t-butylhydroquinone; 2, 5-di-t-butyl-4-hydroxyanisol; 3, 5-di-t-butyl-4-hydroxy- anisol; 3, 5-di-t-butyl-4-hydroxyphenyl stearate; bis (3, 5- di-t-butyl-4-hydroxyphenyl) adipate. 1.4 Tocopherols such as, for example: α-tocopherol, β- tocopherol, γ-tocopherol, δ-tocopherol and their mixtures (Vitamin E) . 1.5 Hydroxylated thiodiphenyl ethers such as, for example 2,2'-thiobis-(6-t-butyl-4-methylphenol) ; 2,2'-thiobis- (4- octylphenol) ; 4,4' -thiobis- (6-t-butyl-3-methylphenol) ; 4,4'-thiobis-(6-t-butyl-2-methylphenol) ; 4, 4'-thiobis- (3,6- di-s-amylphenol) ; 4, 4'-bis- (2, 6-dimethyl-4-hydro- xyphenyl) disulfide. 1.6 Alkylidene-bisphenols such as, for example: 2,2'- methylenebis- (6-t-butyl-4-methylphenol) ; 2,2'-methylene- bis- (6-t-butyl-4-ethylphenol) ; 2, 2 '-methylenebis [4-methyl -6- (α-methylcyclohexyl) phenol] ; 2, 2 '-methylene-bis (4- methyl-6-cyclohexylphenol) ; 2, 2 '-methylenebis (6-nonyl-4- methylphenol) ; 2, 2* -methylenebis (4, 6-di-t-butylphenol) ; 2,2'-ethylidenebis (4, 6-di-t-butylphenol) ; 2, 2 '-ethylide- nebis ( 6-t-butyl-4-isobutylphenol) ; 2,2' -methylenebis [ 6- (α-methylbenzyl) -4-nonylphenol] ; 2, 2 '-methylenebis [6- (α,α-dimethylbenzyl) -4-nonylphenol] ; 4, 4 '-methylenebis (2, 6-di-t-butylphenol) ; 4, 4 '-methylenebis (6-t-butyl-2- ethylphenol) ; 1, 1-bis (5-t-butyl-4-hydroxy-2-methylphe- nyl)butane; 2, 6-bis (3-t-butyl-5-methyl-2-hydroxybenzyl) - 4-methylphenol; 1,1, 3-tris- (5-t-butyl-4-hydroxy-2-methyl- phenyl) butane; 1, 1-bis (5-t-butyl-4-hydroxy~2-methylphe- nyl) -3-n-dodecylmercaptobutane; ethyleneglycol bis [3,3- bis- (3'-t-butyl-4'-hydroxyphenyl)butyrate] ; bis-(3-t- butyl-4-hydroxy-5-methyIphenyl) dicyclopentadiene; bis [2- (3 ' -t-butyl-2 '-hydroxy-5 ' -methylbenzyl) -6-t-butyl-4-me- thylphenyl] terephthalate; 1, 1-bis (3, 5-dimethyl-2-hydroxy- phenyl) butane; 2,2-bis (3, 5-di-t-butyl-4-hydroxy-phenyl) propane; 2, 2-bis (5-t-butyl-4-hydroxy-2-methyIphenyl) -4-n- dodecylmercaptobutane; 1, 1,5, 5-tetra (5-t-butyl-4-hydroxy- 2-methyIphenyl) pentane . 1.7 Benzyl compounds containing 0, N or S such as, for example : 3, 5, 3 ' , 5 ' -tetra-t-butyl-4, 4 ' -dihydroxydibenzyl- ether; octadecyl-4-hydroxy-3, 5-dimethylbenzylmercapto- acetate; tridecyl-4-hydroxy-3, 5-di-t-butyl-benzylmercap- toacetate; tris (3, 5-di-t-butyl-4-hydroxybenzyl) amine; bis (4-t-butyl-3-hydroxy-2, 6-dimethylbenzyl) dithioterephtha- late; bis (3, 5-di-t-butyl-4-hydroxybenzyl) sulfide; iso- octyl-3, 5-di-t-butyl-4-hydroxybenzylmercaptoacetate . 1.8 Hydroxybenzylated malonates such as, for example: dioctadecyl-2, 2-bis (3, 5-di-t-butyl-2-hydroxybenzyl)malon- ate; dioctadecyl-2- (3-t-butyl-4-hydroxy-5-methylbenzyl) - malonate; didodecylmercaptoethyl-2, 2-bis (3, 5-di-t-butyl- 4-hydroxybenzyl)malonate; bis [4- (1, 1, 3,3-tetramethyl- butyl) phenyl] -2, 2-bis (3, 5-di-t-butyl-4-hydroxybenzyl) - malonate. 1.9 Aromatic hydroxybenzyl compounds such as, for example: 1, 3, 5-tris (3, 5-di-t-butyl-4-hydroxybenzyl) -2, 4, 6- trimethylbenzene; 1, -bis- (3, 5-di-t-butylhydroxybenzyl) - 2, 3, 5, 6-tetramethylbenzene; 2, 4, 6-tris (3, 5-di-t-butyl-4- hydroxybenzyl) phenol . 1.10 Triazine compounds such as, for example: 2,4- bis (octylmercapto) -6- (3, 5-di-t-butyl-4-hydroxyaniline) - 1, 3, 5-triazine; 2-octylmercapto-4, 6-bis (3, 5-di-t-butyl-4- hydroxyaniline) -1,3, 5-triazine; 2-octylmercapto-4, 6-bis- (3, 5-di-t-butyl-4-hydroxyphenoxy) -1,3, 5-triazine; 2,4,6- tris- (3, 5-di-t-butyl-4-hydroxyphenoxy) -1,2,3-triazine; 1, 3, 5-tris (3, 5-di-t-butyl-4-hydroxybenzyl) isocyanurate; 1,3, 5-tris (4-t-butyl-3-hydroxy-2, 6-dimethylbenzyl) iso- cyanurate; 2,4, 6-tris- (3, 5-di-t-butyl-4-hydroxyphenyleth- yl) -1, 3, 5-triazine; 1, 3, 5-tris (3, 5-di-t-butyl-4-hydroxy- phenylpropionyl) hexahydro-1, 3, 5-triazine; 1,3, 5-tris (3,5- dicyclohexyl-4-hydroxybenzyl) isocyanurate. 1.11 Benzylphosphonates such as, for example: dimethyl- 2,5-di-t-butyl-4-hydroxybenzylphosphonate; diethyl-3, 5-di -t-butyl-4-hydroxybenzylphosphonate; dioctadecyl-3, 5-di- t-butyl-4-hydroxybenzylphosphonate; dioctadecyl-5-t-bu- tyi-4-hydroxy-3-methylbenzylphosphonate; calcium salts of monoethyl ester of 3, 5-di-t-butyl-4-hydroxybenzylpho- sphonic acid. 1.12 Acylaminophenols such as, for example: 4-hydroxy- lauranilide; 4-hydroxystearanilide; octyl-N- (3, 5-di-t- butyl-4-hydroxyphenyl) carbamate. 1.13 Esters of β- (3, 5-di-t-butyl-4-hydroxyphenyl) prop- ionic acid with monohydric or polyhydric alcohols such as, for example: methanol, ethanol, n-octanol, i-octanol, octadecanol, 1, 6-hexanediol, 1, 9-nonanediol, ethylene glycol, 1, 2-propanediol, neopentyl glycol, thiodiethylene glycol, diethylene glycol, triethylene glycol, pentae- rythritol, tris (hydroxyethyl) isocyanurate, N,N'-bis (hy- droxyethyl) oxalamide, 3-thioundecanol, 3-thiopentadeca- nol, trimethylhexanediol, trimethylolpropane, 4-hydro- xymethyl-l-phospho-2, 6,7-trioxabicyclo- [2.2.2] -octane. 1.14 Esters of β- (5-t-butyl-4-hydroxy-3-methyIphenyl)pro- pionic acid with monohydric or polyhydric alcohols such as, for example: methanol, ethanol, n-octanol, i-octanol, octadecanol, 1, 6-hexanediol, 1, 9-nόhanediol, ethylene glycol, 1,2-propanediol, neopentyl glycol, thiodiethylene glycol, diethylene glycol, triethylene glycol, pentae- rythritol, tris (hydroxyethyl) isocyanurate, N,N'-bis- (hydroxyethyl) oxamide, 3-thioundecanol, 3-thiopenta- decanol, trimethylhexanediol, trimethylolpropane, 4- hydroxymethyl-l-phospho-2, 6, 7-trioxabicyclo [2.2.2] octane. 1.15 Esters of β- (3, 5-dicyclohexyl-4-hydroxyphenyl) propionic acid with monohydric or polyhydric alcohols such as, for example: methanol, ethanol, n-octanol, i-octanol, octadecanol, 1, 6-hexanediol, 1, 9-nonanediol, ethylene glycol, 1,2-propanediol, neopentyl glycol, thiodiethylene glycol, diethylene glycol, triethylene glycol, pentaerythritol, tris (hydroxyethyl) isocyanurate, N,N'-bis- (hydroxyethyl) oxamide, 3-thioundecanol, 3-thiopentadeca- nol, trimethylhexanediol, trimethylolpropane, 4-hydroxy- methyl-l-phospho-2, 6, 7-trioxabicyclo [2.2.2] -octane. 1.16 Esters of (3, 5-di-t-butyl-4-hydroxyphenyl) acetic acid with monohydric or polyhydric alcohols such as, for example: methanol, ethanol, n-octanol, i-octanol, octadecanol, 1, 6-hexanediol, 1, 9-nonanediol, ethylene glycol, 1,2-propanediol, neopentyl glycol, thiodiethylene glycol, diethylene glycol, triethylene glycol, pentaerythritol, tris (hydroxyethyl) isocyanurate, N, N'-bis (hydroxyethyl) - oxamide, 3-thioundecanol, 3-thiopentadecanol, trimethylhexanediol, trimethylolpropane, 4-hydroxymethyl-l-phos- pho-2, 6, 7-trioxabicyclo [2.2.2] octane. 1.17 Amides of β- (3, 5-di-t-butyl-4-hydroxyphenyl) propionic acid such as, for example: N,N'-bis (3, 5-di-t-butyl-4- hydroxyphenylpropionyl) hexamethylenediamide; N,N' -bis- (3, 5-di-t-butyl-4-hydroxyphenylpropionyl) trimethylenedi- amide; N,N'-bis (3, 5-di-t-butyl-4-hydroxyphenylpropionyl) hydrazide; N,N'-bis [2- (3- [3, 5-di-t-butyl-4-hydroxyphenyl] propionyloxy) ethyl] oxamide (Naugard ® XL-1 of Uniroyal) . 1.18 Ascorbic acid (vitamin C) . 1.19 Aminic antioxidants such as, for example, N, N'-di- isopropyl-p-phenylenediamine; N,N' -di-s-butyl-p-phenyl- enediamine; N,N'-bis (1,4-dimethylpentyl) -p-phenylenedi- amine; N,N'-bis (l-ethyl-3-methylpentyl) -p-phenylenediami- ne; N, '-bis (1-methylheptyl) -p-phenylenediamine; N,N'- dicyclohexyl-p-phenylenediamine; N,N' -diphenyl-p-phenyle- nediamine; N,N' -bis (2-naphthyl) -p-phenylenediamine; N- isopropyl-N' -phenyl-p-phenylenediamine; N- (1, 3-dimethyl- butyl) -N' -phenyl-p-phenylenediamine; N- (1-methylheptyl) - N' -phenyl-p-phenylenediamine; N-cyclohexyl-N' -phenyl-p- phenylenediamine; 4- (p-toluenesulfonamide) diphenylene- amine; N, N' -dimethyl-N,N' -di-s-butyl-p-phenylenediamine; diphenylamine; N-allyldiphenylamine; 4-isopropoxy- diphenylamine; N-phenyl-1-naphthylamine; N- (4-t-octyl- phenyl) 1-naphthylamine; N-phenyl-2-naphthylamine; di- phenylamine octylate such as, for example, p,p'-di-t- octyldiphenylamine; 4-n-butylaminophenol; 4-butiryl- aminophenol; 4-nonanoylaminophenol; 4-dodecanoyl- aminophenol; 4-octadecanoylaminophenol; bis (4- methoxyphenyl) amine; 2, 6-di-t-butyl-4-dimethylamino- methylphenol; 2,4' -diaminodiphenylmethane; 4,4' -diamino- diphenylmethane; N,N,N' ,N' -tetramethyl-4, 4' -diaminodi- phenyImethane; 1, 2-bis [ (2-methylphenyl) amino] ethane; 1, 2-bis (phenylamino) propane; (o-tolyl) biguanide; bis [4- (1' , 3' -dimethylbutyl) phenyl] amine; N-phenyl-1-naphthylamine t-octylate; mixture of mono- and dialkylated t- butyl/t-octyldiphenylamines; mixture of mono- and dial- kylated nonyldiphenylamines; mixture of mono- and dialkylated dodecyldiphenylamines; mixture of mono- and dialkylated isopropyl/isohexyldiphenylamines; mixture of mono- and dialkylated t-butyldiphenylamines; 2,3-dihydro- 3, 3-dimethyl-4H-l, 4-benzothiazine; phenothiazine; mixture of mono- and dialkylated t-butyl/t-octylphenothiazines; mixture of mono- and dialkylated t-octyl-phenothiazines; N-allyl-phenothiazine; N,N,N' ,N' -tetraphenyl-1, -diamino- but-2-ene; N,N-bis (2,2,6, 6-tetramethylpiperid-4-yl) hexa- methylenedia ine; bis- (2, ( 2, 6, 6-tetramethylpiperidin-4-yl) sebacate; 2, 2, 6, 6-tetramethylpiperidin-4-one; 2,2,6,6- tetramethylpiperidin-4-ol . 2. UV ray and light stabilizers. 2.1 Derivatives of 2- (2'-hydroxyphenyl)benzotriazoles such as, for example: 2- (2 '-hydroxy-5 'methylphenyl) - benzotriazole; 2- (3 ' , 5'-di-t-butyl-2 ' -hydroxyphenyl)ben- zotriazole; 2- (5 ' -t-butyl-2 ' -hydroxyphenyl) benzotriazole; 2- [2'-hydroxy-5 T - (1,1,3, 3-tetramethylbutyl) phenyl]benzotriazole; 2- (3 ' , 5 ' -di-t-butyl-2 ' -hydroxyphenyl) -5-chlo- robenzotriazole; 2- (3 '-t-butyl-2 '-hydroxy-5 '-methyIphe- nyl) -5-chlorobenzotriazole; 2- (3' -s-butyl-5' -t-butyl-2 ' - hydroxyphenyl) benzotriazole; 2- (2'-hydroxy-4'-octyloxy- phenyl) benzotriazole; 2- (3' , 5 '-di-t-amyl-2' -hydroxyphenyl) benzotriazole; 2- [3' , 5 '-bis (α,α-dimethylbenzyl) -2'- hydroxyphenyl] benzotriazole; 2- [3 ' -t-butyl-2 ' -hydroxy-5 ' - (2-octyloxycarbonylethyl) phenyl] -5-chlorobenzotriazole, 2- [3 ' -t-butyl-5 ' - (2- (2-ethylhexyloxy) carbonylethyl) -2 ' - hydroxyphenyl] -5-chlorobenzotriazole, 2- [3 '-t-butyl-2 ' - hydroxy-5 ' - (2-methoxycarbonylethyl) phenyl] -5-chlorobenzotriazole, 2- [3 '-t-butyl-2 '-hydroxy-5'- (2-methoxycarbo- nylethyl) phenyl] benzotriazole, 2- [3 '-t-butyl-2 '-hydroxy- 5 ' - (2-octyloxycarbonylethyl) phenyl]benzotriazole, 2- [3 ' - t-butyl-5'- (2- (2-ethylhexyloxy) carbonylethyl) -2 '-hydroxyphenyl]benzotriazole, 2- (3 τ -dodecyl-2' -hydroxy-5 '-methylphenyl) benzotriazole; 2- [3 '-t-butyl-2 '-hydroxy-5'- (2-iso- octyloxycarbonylethyl) phenyl] benzotriazole, 2, 2'-methyle- ne-bis [4- (1,1,3, 3-tetramethylbutyl) -6-benzotriazol-2-yl- phenol] ; transesterification product of 2- [3 '-t-butyl-5' - (2-methoxycarbonylethyl) -2 '-hydroxyphenyl] -2H-benzotria- zole with polyethylene glycol 300; [R-CH 2 CH 2 -COO-CH 2 CH 2 -] 2 -wherein R = 3'-t-butyl-4' -hydroxy- 5 '-2H-benzotriazol-2-yl-phenyl; 2- [2'-hydroxy-3 T - (α,α- dimethylbenzyl) -5 ' - (1, 1, 3, 3-tetramethylbutyl) phenyl]benzotriazole; 2- [2'-hydroxy-3'- (1,1,3, 3-tetramethylbutyl) - 5 '- ( ,α-dimethyIbenzyl) phenyl]benzotriazole . 2.2 Benzotriazoles deriving from hydantoin such as those described, for example in patent applications EP 867,435, WO 99/23093. and WO 99/37638. ■2.3 Derivatives of 2-hydroxybenzophenones such as, for example: 4-hydroxy-; 4-methoxy-; 4-octyloxy-; 4-decyloxy- ; 4-dodecyloxy-; 4-benzyloxy-; 4,2' , 4'-trihydroxy-; 2'- hydroxy-4, 4 ' -dimethoxy. 2.4 Esters of benzoic acids, optionally substituted, such as, for example: phenyl salicylate, 4-t-butylphenyl salicylate, octylphenyl salicylate, benzoyl resorcinol, bis (4-t-butylbenzoyl) resorcinol, dibenzoyl resorcinol, 2, 4-di-t-butylphenyl-3, 5-di-t-butyl-4-hydroxybenzoate, hexadecyl-3, 5-di-t-butyl-4-hydroxybenzoate, octadecyl- 3, 5-di-t-butyl-4-hydroxybenzoate, 2-methyl-4, 6-di-t-bu- tylphenyl-3, 5-di-t-butyl-4-hydroxybenzoate . 2.5 Acrylates such as, for example, ethyl or iso-octyl α-cyano-β,β-diphenylacrylate; methyl α-carbomethoxy- cinnamate, methyl or butyl -cyano-β-methyl-p-methoxy- cinnamate, methyl α-carbomethoxy-p-methoxycinnamate, N- (β-carbomethoxy-β-cyanovinyl) -2-methylindoline. 2.6 Nickel compounds such as, for example, Ni-complexes of 2, 2 '-thio-bis- [4- (1, 1, 3, 3-tetramethylbutyl) phenol] , for example 1:1 or 1:2 complexes, with or without additional ligands such as n-butylamine, triethanolamine or N-cyclohexyldiethanolamine, nickel dibutyldithiocarbama- te, nickel salts of monoalkyl esters of 4-hydroxy-3, 5-di- t-butyl-benzylphosphonic acid, such as methyl or ethyl esters, nickel complexes with ketoximes such as 2- hydroxy-4-methyIphenyl undecyl ketoxime, nickel complexes of l-phenyl-4-lauroyl-5-hydroxypyrazol with or without additional ligands. 2.7 Sterically hindered amines and their N-alkoxy derivatives such as, for example: poly-methylpropyl-3-oxy- [4- (2,2, 6, 6-tetramethyl)piperidinyl] siloxane, polymethyl- propyl-3-oxy- [4- (1,2,2, 6, 6-pentamethyl) piperidinyl] silo- xane, bis- (2, 2, 6, 6-tetramethyl-4-piperidinyl) sebacate; bis (2,2, 6, 6-tetramethyl-4-piperidinyl) succinate; bis (1,2,2,6, 6-pentamethyl-4-piperidinyl) sebacate;bis (1-oc- tyloxy-2, 2, 6, 6-tetramethyl-4-piperidinyl) sebacate;bis- (1,2,2,6, 6-pentamethyl-4-piperidyl) -n-butyl-3, 5-di-t-but- yl-4-hydroxybenzylmalonate;condensation product between l-(2- hydroxyethyl) -2, 2, 6, 6-tetramethyl-4-hydroxy-piperidine and succinic acid;condensation product, linear or cyclic,between N,N'-bis (2,2, 6, 6-tetramethyl-4-piperid-yl)hexamethylen- diamine and 4-t-octylamino-2, 6-dichloro-l, 3, 5-s- triazine;tris (2, 2, 6, 6-tetramethyl-4-piperidyl) nitrilo- triacetate; tetrakis (2,2, 6, 6-tetramethyl-4-piperidyl) - 1,2,3, 4-butanetetracarboxylate; 1, 1 ' - (1, 2-ethanodiyl) bis (3, 3, 5, 5-tetramethylpiperazinone; 4-benzoyl-2, 2, 6, 6-tetramethylpiperidine;4-stearyloxy-2, 2,6, 6-tetramethylpi- peridine;bis (1,2,2,6, 6-penta-methylpiperidyl) -2-n-butyl- 2- (2-hydroxy-3, 5-di-t-butylbenzyl) malonate; 3-n-octyl- 7,7,9, 9-tetramethyl-l, 3, 8-triazaspiro [4.5] decane-2, 4-di- one;bis (l-octyloxy-2, 2, 6, 6-tetramethylpiperidyl) seba- cate;bis (l-octyloxy-2, 2, 6, 6-tetramethylpiperidyl) succi- nate;condensation product, linear or cyclic,between N, N'- bis (2,2,6, 6-tetramethyl-4-piperidyl) hexamethylenediamine and 4-morpholine-2, 6-di-chloro-l, 3, 5-triazine; condensation product between 2-chloro-4, 6-di- (4-n-butylamino- 2,2, 6, 6-tetramethyl-piperidyl) -1, 3, 5-triazine and 1,2- bis (3-aminopropylamino) ethanecondensation product be- tween 2-chloro-4, 6-di- (4-n-butylamino-l, 2, 2, 6, 6-pentame- thylpiperidyl) -1, 3, 5-triazine and 1, 2-bis (3-aminopropylamino) ethane; 8-acetyl-3-dodecyl-7, 7, 9, -tetramethyl- 1,3, 8-triazaspiro- [4.5] decane-2, 4-dione; 3-dodecyl-l- (2,2, 6, 6-tetramethyl-4-piperidyl)pyrrolidin-2, 5-dione;3- dodecyl-1- (1,2,2,6, 6-pentamethyl-4-piperidyl)pyrrolidin- 2,5-dione; mixture of 4-hexadecyloxy- and 4-stearyloxy- 2, 2, 6, 6-tetramethylpiperidine; condensation product between N-N' -bis (2,2,6, 6-tetramethyl-4-piperidyl) hexame- thylenediamine and 4-cyclohexylamino-2, 6-dichloro-l, 3, 5- triazine; condensation product between 1, 2-bis (3-aminopropylamino) ethane and 2, 4, 6-trichloro-l, 3, 5-triazine, as well as 4-butylamino-2, 2, 6, 6-tetramethylpiperidine (CAS Reg. Nr. [136504-96-6]; N- (2, 2, 6, 6-tetramethyl-4-piperi- dyl) -n-dodecylsuccinimide; N- (1, 2,2, 6, 6-pentamethyl-4-pi- peridyl) -n-dodecylsuccinimide;2-undecyl-7, 7, 9, 9-tetrame- thyl-l-oxa-3, 8-diaza-4-oxospiro [4, 5] decane; reaction product between 7, 7, , 9-tetramethyl-2-cycloundecyl-l-oxa- 3, 8-diaza-4-oxospiro-[4, 5] decane and epichlorohydrin; 1, 1-bis (1,2,2,6, 6-pentamethyl-4-piperidyloxycarbonyl) -2- (4-methoxyphenyl) ethene; N,N'-bis-formyl-N,N'-bis (2, 2, 6, 6-tetramethyl-4-piperidyl)hexamethylenediamine; diester of 4-methoxy-methylenemalonic acid with 1,2,2, 6, 6-pen- tamethyl-4-hydroxypiperidine; reaction product of maleic anhydride/α-olefin copolymer with 2, 2, 6, 6-tetramethyl-4- aminopiperidine or with 1, 1, 2, 2, 6-pentamethyl-4-ami- nopiperidine . 2.8 Oxamides such as, for example: 4,4'-dioctyloxyox- anilide; 2,2 '-diethoxyoxanilide; 2,2 '-dioctyloxy-5, 5'- di-t-butoxanilide; 2, 2 '-didodecyloxy-5, 5'-di-t-butyloxa- nilide; 2-ethoxy-2 '-ethyloxanilide; N,N'-bis (3-dime- thylaminopropyl) oxamide; 2-ethoxy-5—t-butyl-2 ' -ethyloxanilide and its mixtures with 2-ethoxy-2'-ethyl-5, 4 '-di-t- butoxanilide; and mixtures of di-substituted ortho- and para-methoxy oxanilides and mixtures of di-substituted ortho and para-ethoxy oxanilides . 2.9 2- (2-hydroxyphenyl) -1, 3, 5-triazines such as, for example: 2, 4, 6-tris (2-hydroxy-4-octyloxyphenyl) -1, 3, 5-triazine; 2- (2-hydroxy-4-octyloxyphenyl) -4, 6-bis (2, 4-dime- thyIphenyl) -1, 3, 5-triazine; 2- (2, 4-dihydroxyphenyl) -4, 6- bis (2, 4-dimethylphenyl) -1,3, 5-triazine; 2, 4-bis- (2-hydro- xy-4-propyloxyphenyl) -6- (2, -dimethylphenyl) -1,3, 5-triazine; 2- (2-hydroxy-4-octyloxyphenyl) -4, 6-bis (4-me- thylphenyl) -1, 3, 5-triazine; 2- (2-hydroxy-4-dodecyloxy- phenyl) -4, 6-bis (2, 4-dimethylphenyl) -1, 3, 5-triazine; 2- [2-hydroxy-4- (2-hydroxy-3-butyloxypropyloxy) phenyl] -4, 6- bis (2, 4-dimethylphenyl) -1, 3, 5-triazine; 2- [2-hydroxy-4- (2-hydroxy-3-octyloxypropyloxy) phenyl] -4, 6-bis- (2, 4-dimethylphenyl) -1, 3, 5-triazine; 2- (2-hydroxy-4-tridecyl- oxyphenyl) -4, 6-bis (2, 4-dimethylphenyl) -1, 3, 5-triazine; 2- [4- (dodecyloxy/tridecyloxy-2-hydroxypropoxy) -2-hydroxy- phenyl]-4, 6-bis (2, 4-dimethylphenyl) -1,3, 5-triazine; 2- [2- hydroxy-4- (2-hydroxy-3-dodecyloxypropoxy) phenyl] -4, 6-bis- (2, 4-dimethylphenyl) -1, 3, 5-triazine; 2- (2-hydroxy-4-hex- yloxyphenyl) -4, 6-diphenyl-l, 3, 5-triazine; 2- (2-hydroxy-4- methoxyphenyl) , 6-diphenyl-l, 3, 5-triazine; 2,4, 6-tris [2- hydroxy-4- (3-butoxy-2-hydroxypropoxy) henyl] -1,3, 5-triazine; 2- (2-hydroxyphenyl) -4- (4-methoxyphenyl) -6-phenyl- 1, 3, 5-triazine; 2-hydroxy-4- [3- (2-ethylhexyl-l-oxy) -2- hydroxypropyloxy]phenylr"-4, 6-bis (2, 4-dimethylphenyl) - 1, 3, 5-triazine. 3. "Metal-deactivators" such as, for example: N,N'-di- phenyloxamide, N-salicylal-N'-salicyloyl-hydrazine, N,N'- bis (salicyloyl) hydrazine, N,N' -bis (3, 5-di-t-butyl-4-hy- droxyphenylpropionyl) hydrazine, 3-salicyloylamino-l, 2, 4- triazole, bis (benzylidene) oxallyl dihydrazide, oxani- lide, isophthaloyl dihydrazide, sebacoyl bisphenylhy- drazide, N,N'-diacetyladipoyl dihydrazide, N,N'-bis (salicyloyl) oxallyl dihydrazide, N, -N'-bis (salicyloyl) thiopropionyl dihydrazide. 4. Phosphites and phosphonites such as, for example: tri- phenyl phosphite, diphenyl alkyl phosphites, phenyl dial- kyl phosphites, tris (nonyIphenyl) phosphite, trilauryl phosphite, trioctadecyl phosphite, distearyl pentaeryth- ritol diphosphite, tris (2, 4-di-t-butylphenyl) phosphite, diisodecyl pentaerythritol diphosphite, bis (2, 4-di-t- butylphenyl) pentaerythritol diphosphite, bis (2, 6-di-t- butyl-4-methylphenyl) pentaerythritol diphosphite, diiso- decyloxypentaerythritol diphosphite, bis (2, 4-di-t-butyl- 6-methylphenyl)pentaerythritol diphosphite, bis [2,4,6- tris (t-butylphenyl) ]pentaerythritol diphosphite, tristearyl sorbitol triphosphite, tetrakis- (2, 4-di-t- butylphenyl) -4,4' -diphenylenediphosphonite, 6- isooctyloxy-2, 4,8, 10-tetra-t-butyl-12H-dibenzo- [d, g] - 1, 3,2-dioxaphosphocine, 6-fluoro-2, 4, 8, 10-tetra-t-butyl- 12-methyldibenzo [d, g] -1, 3, 2-dioxaphosphocine, bis- (2, 4- di-t-butyl-6-methylphenyl)methylphosphite, bis (2, 4-di-t- butyl-6-methylphenyl) ethylphosphite; 2, 2 ',2' '-nitrilo [triethyl-tris (3, 3' ,5, 5' -tetra-t-butyl-1, l'-biphenyl- 2, 2 τ -diyl) -phosphite] ; 2-ethylhexyl- (3, 3' , 5, 5 '-tetra-t- butyl-1, 1 ' -biphenyl-2, 2 ' -diyl) phosphite. 5. Hydroxylamines such as, for example: N,N-dibenzyl- hydroxylamine; N,N-diethylhydroxylamine; N,N-dioctyl- hydroxylamine; N,N-dilaurylhydroxylamine; N,N-ditetra- decylhydroxylamine; N,N-dihexadecylhydroxylamine; N,N- dioctadecylhydroxylamine; N-hexadecyl-N-octadecylhydro- xylamine; N-heptadecyl-N-octadecylhydroxylamine; N,N-di- alkylhydroxylamines deriving from hydrogenated tallow amines . 6. Nitrons such as, for example: N-benzyl-α-phenyl- nitron; N-ethyl-α-methyl-nitron; N-octyl-α-heptyl-nitron; N-lauryl-α-undecyl-nitron; N-tetradecyl-α-tridecyl-ni- tron; N-hexadecyl- -pentadecyl-nitron; N-octadecyl-α- heptadecyl-nitron; N-hexadecyl- -heptadecyl-nitron; N- octadecyl-α-pentadecyl-nitron; N-heptadecyl-α-heptadecyl- nitron; N-octadecyl-α-hexadecyl-nitron; nitrons deriving from hydrogenated tallow amines . 7. Thiosynergizing agents such as, for example: dilauryl thiodipropionate; distearyl thiodipropionate. 8. Agents which are capable of destroying peroxides such as, for example, esters of β-thiodipropionic acid such as lauryl, stearyl, myristyl or tridecyl esters, mercapto- benzimidazole or zinc salt of 2-mercaptobenzimidazole, zinc dibutyldithiocarbamate, dioctadecyldisulfide, pen- taerythritol tetrakis (β-dodecylmercapto) propionate. 9. Polyamide stabilizers such as, for example, copper salts combined with compounds of iodine and/or phosphorous, divalent manganese salts. 10. Basic co-stabilizers such as, for example: melamine, polyvinylpyrrolidone, dicyanodiamide, triallyl cyanurate, derivatives of urea, derivatives of hydrazine, amines, polyamides, polyurethanes, salts of alkaline metals and salts of earth-alkaline metals of fatty acids with a high molecular weight such as, for example, Ca-stearate, Zn- stearate, Mg-stearate, Mg-behenate, Na-ricinoleate, K- palmitate, antimonium-pyrocatecholate, tin-pyrocatech- olate, zinc-pyrocatecholate. 11. Nucleating agents such as, for example: inorganic substances such as talc, metal oxides (for example, tita- nium dioxide or magnesium oxide) , phosphates, carbonates or sulfates (preferably of earth-alkaline metals) ; organic compounds such as mono- or polyearboxylic acids and their salts (for example, 4-t-butylbenzoic acid, adipic acid, diphenylacetic acid, sodium succinate, sodium ben- zoate) ; polymeric compounds such as ionic copolymers ("ionomers") . 12. Fillers and reinforcing agents such as, for example: calcium carbonate, silicates, glass fibres, glass beads, asbestos, talc, kaolin, mica, barium sulfate, metal ox- ides and hydroxides, carbon black, graphite, wood flour and flours or fibres of other natural products, synthetic fibres. ., ■ 13. Other additives such as, for example: plasticizers, pigments, lubricants, emulsifying agents, rheological ad- ditives, catalysts, slip agents, optical brighteners, flame-retardants (for example bromurates, chlorurates, phosphorates and phosphorous/halogen mixtures) , antistatic agents, blowing agents. 14. Benzofuranones and indolinones such as, for example: 3- [4- (2-acetoxyethoxy)phenyl] -5, 7-di-t-butyl-benzofuran- 2-one; 5,7-di-t-butyl-3- [4- (2-stearoyloxyethoxy)phenyl] - benzofuran-2-one; 3, 3 '-bis [5, 7-di-t-butyl-3- [4- (2-hyd- roxyethoxy) phenyl]benzofuran-2-one; 5, 7-di-t-butyl-3- (4- ethoxyphenyl) benzofuran-2-one; 3- (4-acetoxy-3, 5-dimethyl- phenyl) -5, 7-di-t-butyl-benzofuran-2-one; 3- (3, 5-dimethyl- 4-pivaloyloxyphenyl) -5, 7-di-t-butyl-benzofuran-2-one; or those described in U.S. patents Nr. 4,325,863, 4,338,244, 5,175,312, 5,216,052 and 5,252,643; in German patents DE 4,316,611, 4,316,622 and 4,316,876; or in European patent applications Nr. 589,839 and 591,102. The above stabilizers (co-stabilizers) can be optionally added to the organic polymers to be stabilized in a quantity ranging from 0.01% to 10% with respect to the total weight of the organic polymer to be stabilized. The incorporation of compounds (a), (b) , (c) and, optionally, (d) , as single compounds or mixed with each other and possibly other stabilizers (co-stabilizers), in the organic polymers to be stabilized, can be carried out according to the methods known in the art, for example, before or during the processing, or the mixture dissolved or dispersed in a solvent, before or after its evaporation, can be applied to the organic polymer to be stabilized. The stabilizing mixture, object of the present invention, can also be used in masterbatch form containing from 2.5% to 25% by weight of said mixture. The above mixture, optionally in the presence of other stabilizers (co-stabilizers), can also be added to the organic polymers to be stabilized, either after or during polymerization or before cross-linking. The above mixture, optionally in the presence of other stabilizers (co-stabilizers) , can be added to the organic polymers to be stabilized, in pure form or encapsulated in waxes, oils or polymers. The above mixture, optionally in the presence of other stabilizers (co-stabilizers) which can be diluted or used in the molten state, can be sprayed into the organic polymers to be stabilized. This spraying can be advantageously effected during the deactivation of the polymerization catalyst, as the spraying can be effected using, for example, the vapor used for the deactivation. In the case of spherically polymerized polyolefins, it may be advantageous to add the above mixture, optionally in the presence of other stabilizers (co- stabilizers), by means of spraying. The organic polymers stabilized as described above can be used in a wide variety of forms such as, for example, films, fibers, tapes, moulding compositions, profiles, ligands for coating materials such as powder coatings, adhesives or plaster, in particular. The present invention also relates to a method for stabilizing organic polymers against degradation caused by oxygen, heat and/or light, which comprises the addition or application to said organic polymers of the stabilizing mixture, object of the present invention. The 3-pyrazolidinones having general formula (I) or (II) can be used as such, as process stabilizers for organic polymers. A further object of the present invention is consequently the use of said compounds as process stabilizers for organic polymers, the polymeric compositions thus stabilized and the end-products obtained from their processing. Some illustrative but non-limiting examples are provided hereunder for a better understanding of the present invention and for its embodiment. EXAMPLE 1 Stabilization of polypropylene subjected -bo multiple high -temperature extrusions 100 g of polypropylene in powder (Moplen FLF 20 of Montell Italia) , having a melt flow index (MFI) of 12 g/min measured in accordance with ASTM D638 at 230°C with 2.16 kg, are mixed with 0.05 g of calcium stearate and with the other stabilizers indicated in Table 1, which also specifies the quantities of the stabilizers used. The above homogenized mixture is fed to a Brabender laboratory extruder with a feeding screw having a length of 475 mm, a diameter of 19 mm, a compression ratio of 1:4, which has the possibility of differentiated heating in four different zones of the feeding screw. The mixture is extruded through a hole having a diameter of 2 mm, with a screw rotation rate of 60 rpm and a temperature profile of 190°C, 230°C, 250°C, 280°C and the MFI values obtained, measured as described above, at the 1st, 3_cd and 5th extrusion, are indicated in Table 1. Table 1 EXAMPLE 2 Stabilization of polypropylene subjected to multiple high temperature extrusions 100 g of polypropylene in powder (Moplen FLF 20 of Montell Italia), having a melt flow index (MFI) of 18 g/min measured in accordance with ASTM D638 on a Ceast Automatic Melt Flow Tester at 230°C and under a 2.16 kg load, are mixed with 0.05 g of calcium stearate and with the other stabilizers indicated in Table 2, which also specifies the quantities of the stabilizers used. The above homogenized mixture is fed to a Brabender PL 200 single screw laboratory extruder with a feeding screw having a length of 475 mm, a diameter of 19 mm, a compression ratio of 1:4, which has the possibility of differentiated heating in four different zones of the feeding screw. The mixture is extruded through a hole having a diameter of 2 mm, with a screw rotation rate of 60 rpm and a temperature profile of 200°C, 225°C, 250°C, 275°C and the MFI values obtained, measured as described above, at the 1 st , 3 rd and 5 th extrusion, are indicated in Table 2 Table 2 *Compound (IA) was crystallized after treatment with active charcoal; ** Compound (IA) was crystallized twice from methylene Chloride/Cyclohexane 1:3 v/v. The Yellow Index (Yl) was measured on the granules after each extrusion for the polypropylene formulations reported in Table 2 using a Macbeth Colour Eye., instrument mounting a light source D65 according to ASTM-E-313 and the data are reported in Table 3 Table 3 ^Compound (IA) was crystallized after treatment with active charcoal; ** Compound (IA) was crystallized twice from methylene Chloride/Cyclohexane 1:3 v/v. EXAMPLE 3 Stabilization of polypropylene subjected to multiple high temperature extrusions 100 g of polypropylene in powder form (Moplen FLF 20 of Montell Italia), having a melt flow index (MFI) equal to 18 g/min measured in accordance with the regulation ASTM D638 on a Ceast Automatic Melt Flow Tester at 230°C and under a 2.16 kg load, are mixed with 0.05 g of calcium stearate and with the other stabilizer-s indicated in Table 4: Table 4 also specifies the quantities of the stabilizers used. The above homogenized mixture is fed to a Bra- bender PL 200 single screw laboratory extruder with a feeding screw having a length of 475 mm, a diameter of 19 mm, a compression ratio of 1:4, which has the possibility of differentiated heating in four different zones of the feeding screw. The mixture is extruded through a hole hav- ing a diameter of 2 mm, with a screw rotation rate of 60 rpm and a temperature profile of 200°C, 225°C, 250°C, 275 °C and the MFI values obtained, measured as described above, at the 1st, 3rd and 5til extrusion, are indicated in Table 4. Table 4

Claims: CLAIMS 1. Stabilizing mixtures for organic polymers comprising: (a) at least one compound belonging to the group of 3-pyrazolidinones ; (b) at least one compound belonging to the group or organic phosphites or phosphonites; and optionally (c) at least one group belonging to the group of sterically hindered phenols; and, optionally, (d) at least one group belonging to the group of sterically hindered amines. 2. The stabilizing mixtures for organic polymers according to claim 1, wherein the compounds belonging to the group of 3-pyrazolidinones (a) are selected from those having general formula (I) or (II) : wherein: Ai represents a linear or branched Ci-Ciβ alkyl group; a C5-C 12 cycloalkyl group, said cycloalkyl group optionally mono-, di- or tri- substituted with a linear or branched C 1 -C 4 alkyl group; a phenyl group, said phenyl group optionally mono-, di- or tri-substituted with a linear or branched C 1 -C4 alkyl or alkoxyl group, and/or mono-substituted with a hydroxyl group; a C-C 8 phenylalkyl group, said phenylalkyl group optionally mono-, di- or tri- substituted on the phenyl with a linear or branched C 1 -C 4 alkyl group, and/or mono- substituted with a hydroxyl group; an -Aio-COOAu wherein Aio represents a linear or branched Ci-Cβ alkylene group and An represents a linear or branched Ci-Cis alkyl group, a Cs~Cι 2 cycloalkyl group, said cycloalkyl group optionally mono-, di- or tri-substituted with a lin- ear or branched C 1 -C4 alkyl group, a linear or branched C3-C18 alkenyl group, a C-C 9 phenylalkyl group, said phenylalkyl group optionally mono-, di- or tri-substituted on the phenyl with a linear or branched C 1 -C4 alkyl group; - A 3 , A 4 , A 5 and A 6 , the same or different, repre- sent a hydrogen atom; a linear or branched Ci- C 4 alkyl group; a phenyl group; s is 1 or 2; when s is 1, A 2 represents a hydrogen atom; a linear or branched Ci-Cis alkyl group; a linear or branched C3~C 6 alkenyl group; a C 7 -C 9 phenylalkyl group, said phenylalkyl group optionally mono-, di- or tri-substituted on the phenyl with a linear or branched C 1 -C 4 alkyl group; an -Aio-COOAu wherein Aio and n have the same meanings defined above; and, when A 2 represents a hydrogen atom, Ai may also represent a group having general formula (III) : H wherein A3, A4, A 5 , A 6 and Ao have the same meanings defined above and A12 represents a linear or branched C 2 -Cι 2 alkylene group; a C 4 - C 12 alkylene group interrupted by 1, 2 or 3 oxygen atoms; a cyclohexylene group; a cyclohexylenedimethylene group; an isopropylidenedi- cyclohexylidene group; when s is 2 , A 2 represents a linear or branched C 2 -C 12 alkylene group, or a xylylene group; A 7 represents a phenyl group optionally mono-, di- or tri-substituted with a linear or branched C 1 -C 4 alkyl or alkoxyl group, and/or mono-substituted with a hydroxyl group; A 8 represents a hydrogen atom; a linear or branched Ci-Cis alkyl group; a linear or branched C3-C6 alkenyl group; a C-C 9 phenylalkyl group, said phenylalkyl group optionally mono-, di-, or tri-substituted on the phenyl with a linear or branched C1-C4 alkyl group; an -A 1 0-COOA 11 group wherein Aio and An have the same meanings defined above; t is 1, 2, 3 or 4; when t is 1, A 9 represents an acyl-aliphatic, cycloaliphatic, aromatic, arylaliphatic or heterocyclic group containing not more than 22 carbon atoms; or one of the following groups having general formula (IVa)-(IVc): -COOA13 (IVa) wherein A i3 has the same meanings as An described above; Au and A i5 , the same or different, have the same meanings as An described above, or they represent a hydrogen atom, or a phenyl group, or A i4 and A 1 5 considered jointly with the nitrogen atom to which they are bound, represent a heterocyclic group with 5-7 atoms; Xi and X 2 , the same or different, represent an -O-A 1 6 group, or a group having the formula: wherein Aι 6 , A i7 and Aia, the same or different, have the same meanings as A i and A 1 5 described above, or A i7 and A i8 considered jointly with the nitrogen atom to which they are bound, represent a heterocyclic group with 5-7 atoms; when t is 2, A 9 represents a diacyl-aliphatic, cycloaliphatic, aromatic, arylaliphatic or het- erocyclic group containing not more than 22 carbon atoms; or one of the following groups having general formula (Va)-(Vc): -CONH-A 20 -NHCO- (Vb) wherein A i9 represents a linear or branched C 2 - C12 alkylene group, a C4~Cι 2 alkylene group interrupted by 1, 2 or 3 oxygen atoms, a cyclohexylene group, a cyclohexylenedimethylene group, an isopropylidenedicyclohexylidene group, a phenylene group, a xylylene group, an isopropylidenediphenylene group; A 20 represents a linear or branched C 2 -Cι 2 alkylene group, a cyclohexylene group, a cyclohexylenedimethylene group, a methylidene-cyclohexylene group, a phenylene group, a methyIphenylene group, a xylylene group, a methylenediphenylene group, an oxydiphenylene group, a group having the formula: X3 has the same meanings as Xi and X 2 defined above; when t is 3, Ag represents a triacyl-aliphatic, aromatic or heterocyclic group containing not more than 18 carbon atoms, or a 2,4,6-triyl- 1, 3, 5-triazine group; when n is 4, A 9 represents a tetra-acyl- aliphatic or aromatic group containing not more than 18 carbon atoms. The stabilizing mixtures for organic polymers according to claim 1, wherein the compounds belonging to the group of organic phosphites or phosphonites (b) are selected from those having the following general formulae (VI) -(XII): 0- -R 1 R' -P' (VI) ; O- -R 1 wherein: - n' is 2, 3 or 4; p' is 1 or 2; q' is 2 or 3; r' is an integer ranging from 4 to 12, extremes included; y' is 1, 2 or 3; z ' is an integer ranging from 1 to 6, extremes included; when n' is 2, A' represents a C 2 -Ci8 alkylene group; a C 2 -Cι 2 alkylene group containing an oxygen atom, a sulfur atom, or an -NR'4- group; a group having general formula (XIII) : a group having general formula (XIV) : a phenylenic group; when n' is 3, A' represents a group having general formula _ C r <H2 r '-ι- wherein r' has the same values described above; when n' is 4, A' represents a group having the formula: CH 2 —- Cxi 2 H 2 . CH, — A' ' has the same meanings defined above for A' when n' is 2; B' represents a direct bond; one of the following groups: -CH 2 -, -CHR' 4 ~, -CR'ιR'4-; a sulfur atom; a C5-C-7 cycloalkylidene group; a cyclo- hexylidene group substituted with 1-4 Cι-C 4 alkyl groups in position 3, 4 and/or 5; when p' is 1, D' represents a methyl group; and, when p' is 2, D' represents a -CH 2 0CH 2 - group; when y' is 1, E' represents a Cι-Cι 9 alkyl group; an -OR'i group; a halogen atom; when y' is 2, E' represents an -0-A''-0- group; when y' is 3, E' represents one of the follow- ing groups : R' 4 C (CH 2 0-) 3, N (CH 2 CH 2 0-) 3; Q' represents a radical of an alcohol or a phenol with a valence z', said radical being attached to the phosphorous atom by means of an oxygen atom; R'ι, R'2 and R'3, each independently, represent a hydrogen atom; a halogen atom; one of the following groups: -COOR' -, -CN-, -CONR' R' 4 ; a C2-C 1 8 alkyl group containing an oxygen atom, a sulfur atom, an -NR' 4 - group; a C 7 -Cg phenylal- kyl group; a C5-C 12 cycloalkyl group; a phenyl group or a naphthyl group, said phenyl or naphthyl groups optionally substituted with halogen atoms, or with 1-3 Ci-Cis alkyl or alkoxyl groups or with C-Cg phenylalkyl groups; or they represent a group having general formula wherein m' represents an integer ranging from 3 to 6, extremes included; R' 4 represents a hydrogen atom; a Ci-Ciβ alkyl group; a C5-C 1 2 cycloalkyl group; a C-C 9 phen- ylalkyl group; R' and R'β each independently, represent a hydrogen atom; a Ci-Cs alkyl group; a Cs-C 6 cycloalkyl group; when q' is 2, R' 7 and R' 8 each independently, represent a C 1 -C4 alkyl group; or, considered jointly, they represent a 2, 3-dihydropentame- thylene group; when q' is 3, R' and R' 8 represent a methyl group; R' 14 represents a hydrogen atom; a C1-C9 alkyl group; a cyclohexyl group; R'i5 represents a hydrogen atom; a methyl group; or, when two or more R'ι and R'ι 5 groups are present, said groups are the same or different to each other; X' and Y' represent a direct bond; an oxygen atom; Z' represents a direct bond; a methylene group; a -C(R'i6)2- group; a sulfur atom; R'i6 represents a Ci-Cs alkyl group. The stabilizing mixtures for organic polymers according to claim 1, wherein the compounds belonging to the group of sterically hindered phenols (c) are selected from those having general formula (XIX) : wherein: Ri ' represents a Cι~C alkyl group; n is 1, 2 , 3 or 4 ; X represents a methylene group; or a group having general formula (XX) or (XXI) : O CH 2 -CH, -C-Y (xx) . O —CH, -C—O-CH 2 -CH 2 — (XXD . - Y represents an oxygen atom; an -NH- group; when n is 1, X represents a group having general formula (XX) wherein Y is attached to R 2 ' and R2' represents a C1-C25 alkyl group; when n is 2, X represents a group having gen- eral formula (XX) wherein Y is attached to R2' and R 2 ' represents a C 2 -Cι 2 alkylene group; a C4-C 1 2 alkylene group containing one or more oxygen or sulfur atoms; or, when Y represents an -NH- group, R2 1 represents a direct bond; - when n is 3, X represents a methylene group; a group having general formula (XXI) wherein the ethylene group is bound to R2' and R 2 ' represents a group having formula (XXII) : when n is 4, X represents a group having general formula (XX) wherein Y is bound to R 2 ' and R 2 ' represents a C4-C10 alkane-tetrayl group. The stabilizing mixtures for organic polymers according to claim 1, wherein the compounds belonging to the group of sterically hindered phenols (c) consist of reactive antioxidant compounds containing a sterically hindered phenol group having general formula (I* ) or (I'a) : and more specifically, of reactive antioxidant compounds containing sterically hindered phenol groups having general formula (I') and (I'a) selected from those having general formula (II') or (Il'a): ) The stabilizing mixtures for organic polymers according to claim 1, wherein the compounds belonging to the group of sterically hindered amines (d) are selected from those comprising at least one group having general formula (XXIII) or (XXIV) : (XXIII) wherein: G represents a hydrogen atom; or a methyl group; Gi and G 2 , the same or different, represent a hydrogen atom; a methyl group; or they jointly represent an oxygen atom. The stabilizing mixtures for organic polymers according to claim 1, wherein the compounds belonging to the group of sterically hindered amines (d) are selected from compounds (a')-(h') which comprise at least one group having general formula (XXIII) or (XXIV) according to claim 6. The stabilizing mixtures for organic polymers according to claim 7, wherein the compounds belonging to the group of sterically hindered amines (d) are selected from compounds (a') having general formula (XXV) : wherein n is a number ranging from 1 to 4 , extremes included; G and G x , independently, represent a hydrogen atom or a methyl ; Gn represents a hydrogen atom, 0" , a hydroxyl group, an NO group, a -CH 2 CN group, a Ci-Cia alkyl group, a C 3 -Ca alkenyl group, a C 3 -C 8 alkinyl group, a C -Cι 2 arylalkyl group, a Cχ~ Cis alkoxyl group, a Cs-Cs cycloalkoxyl group, a C -C 9 phenylalkoxyl group, a Ci-Cβ alkanoyl group, a C3-C5 alkenoyl group, a Ci-Cis alkanoyloxyl group, a benzy- loxyl group, a glycidyl group, an OGn' group, wherein Gn' represents a linear or branched Ci-Cio alkyl group; a -CH 2 CH(OH)-Z group wherein Z repre- sents a hydrogen atom, a methyl, or a phenyl, Gn preferably being hydrogen, a C1-C4 alkyl group, an allyl, a benzyl, an acetyl or an acryloyl; Gι 2 , when n is 1, represents a hydrogen atom, a Ci-Cia alkyl group, said alkyl group optionally containing one or more oxygen atoms, a cyanoethyl group, a benzyl, a glycidyl group, a monovalent radical of a carboxylic acid, of a carbamic acid or of an acid containing phosphorous, aliphatic, cycloaliphatic or arylaliphatic, unsaturated or aromatic, or a monovalent silyl radical, preferably a radical of an aliphatic carboxylic acid having from 2 to 18 carbon atoms, of a cycloaliphatic carboxylic acid having from 7 to 15 carbon atoms, of an α, β-unsaturated carboxylic acid having from 3 to 5 carbon atoms, of an aromatic car- boxylic acid having from 7 to 15 carbon atoms, said carboxylic acids optionally substituted in the aliphatic, cycloaliphatic or aromatic part, with 1-3 -COOZι 2 groups, wherein Z i2 represents a hydrogen atom, a Cι-C 20 alkyl group, a C 3 -Cι 2 alkenyl group, a C5-C-7 cycloalkyl group, a phenyl or a benzyl; Gι 2 , when n is 2, represents a C 2 -C 12 alkylene group, a C4~Cι 2 alkenylene group, a xylylene group, a divalent radical of a dicarboxylic acid, of a dicarbamic acid or of an acid containing phosphorous, aliphatic, cy- cloaliphatic, arylaliphatic or aromatic, or a divalent silyl radical, preferably a radical of an aliphatic dicarboxylic acid having from 2 to 36 carbon atoms, of a cycloaliphatic or aromatic dicarboxylic acid having from 8 to 14 carbon atoms, of an ali- phatic, cycloaliphatic or aromatic dicarbamic acid, having from 8 to 14 carbon atoms, said dicarboxylic , acids optionally substituted in the aliphatic, cycloaliphatic or aromatic part, with 1 or 2 -COOZ i2 groups wherein Z i2 has the same meanings defined above; Gι 2 , when n is 3, represents a trivalent radical of an aliphatic, cycloaliphatic or aromatic tricarboxylic acid, optionally substituted in the aliphatic, cycloaliphatic or aromatic part, with a - COOZι 2 group wherein Zι 2 has the same meanings de- fined above, or of an aromatic tricarbamic acid or of an acid containing phosphorous, or it represents a trivalent silyl radical; Gι 2 , when n is 4, is a tetravalent radical of an aliphatic, cycloaliphatic or aromatic tetracarboxylic acid. The stabilizing mixtures according to claim 7, wherein the compounds belonging to the group of sterically hindered amines (d) are selected from compounds ( r ) having general formula (XXVI) : wherein n is 1 or 2 ; G, Gi and Gn have the same meanings described above under claim 8 ; G i3 represents a hydrogen atom, a Cι~Cι 2 alkyl group, a C 2 -Cs hydroxyalkyl group, a C 5 -C 7 cycloalkyl group, a C -C 8 arylalkyl group, a C 2 -Cιs alkanoyl group, a C3-C5 alkenoyl group, a benzoyl group, or a group having the following general formula : wherein G, G l7 Gn have the same meanings defined above under claim 8; G 1 4, when n is 1, represents a hydrogen atom, a Ci-Cis alkyl group, a C3-C8 alkenyl group, a C 5 -C 7 cycloalkyl group, a C 1 -C4 alkyl group substituted with a hydroxyl group, with a cyano group, with an alkoxycarbonyl group or with a carbamide group, a glycidyl group, a group having the formula -CH 2 -CH(OH) -Z or a group having the formula -CONH-Z wherein Z represents a hydrogen atom, a methyl or a phenyl; G 14 , when n is 2, represents a C 2 -Cι 2 alkylene group, a Cδ-Cι 2 arylene group, a xylylene group, a group of formula -CH 2 -CH (OH) -CH 2 - or a group having the formula -CH 2 -CH(OH) -CH 2 -0-D-0- wherein D represents a C 2 -Cιo alkylene group, a Cβ~ C 1 5 arylene group, a C 6 -Cι 2 cycloalkylene group; or, on the condition that G13 does not represent an alkanoyl group, an alkenoyl group or a benzoyl group, G 14 can also represent a 1-oxo- (C 2 -Cι 2 ) -alkylene group, a divalent radical of a dicarboxylic acid or of a dicarbamic acid, aliphatic, cycloaliphatic or aromatic, or also a -CO- group; or, when n is 1, G13 and G 1 considered jointly, can also represent a divalent radical of a 1,2- or 1, 3-dicarboxylic acid, aliphatic, cycloaliphatic or aromatic. 10. The stabilizing mixtures according to claim 7, wherein the compounds belonging to the group of sterically hindered amines (d) are selected from compounds (c') having general formula (XXVII): (XXVII) wherein n is 1 or 2; G, Gi and Gn have the same meanings described above under claim 8; Gis, when n is 1, represents a C 2 -C8 alkylene or hydroxyalkylene group, or a C 4 -C 22 acyloxyalkylene group, and, when n is 2, it is a (-CH 2 ) 2 C (CH 2 -) 2 group. 11. The stabilizing mixtures according to claim 7, wherein the compounds belonging to the group of sterically hindered amines (d) are selected from compounds (d') having general formula (XXVI11A) , (XXVIIIB) and (XXVIIIC) , the compounds having general formula (XXVIIIC) being preferred: 7 (XXVIIIA) (XXVIIIB) 7 (XXVIIIC) wherein n is 1 or 2, G, Gi and Gn have the same meanings defined above under claim 8; Giε represents a hydrogen atom, a C1-C 12 alkyl group, an allyl group, a benzyl, a glycidyl group or a C 2 -Ce alk- oxyalkyl group; Gι 7 , when n is 1, represents a hydrogen atom, a C1-C12 alkyl group, a C3-C5 alkenyl group, a C 7 -C 9 arylalkyl group, a C5-O7 cycloalkyl group, a C 2 -C 4 hydroxyalkyl group, a C 2 -C 6 alkoxyal- kyl group, a Cβ-Cio aryl group, a glycidyl group, or a group having the formula - (CH 2 ) p -COO-Q or - (CH 2 ) P -0-CO-Q wherein p is 1 or 2 and Q represents a C 1 -C4 alkyl group or a phenyl; G i7 , when n is 2, represents a C2-C12 alkylene group, a C4-C12 alkenylene group, a C6-C 12 arylene group, a group having the formula: -CH 2 -CH (OH) -CH 2 -0-D-0-CH 2 -CH (OH) -CH 2 - wherein D represents a C 2 -Cι 0 alkylene group, a C 6 - L5 arylene group, a C6~Ci 2 cycloalkylene group, or a group having the formula: -CH 2 CH(OZ')CH 2 - (OCH 2 -CH(OZ')CH 2 ) 2 wherein Z' represents a hydrogen atom, a Ci-Ciβ alkyl group, an allyl, a benzyl, or a C2-C12 alkanoyl group or a benzoyl; Ti and T 2 each independently represent a hydrogen atom, a Ci-Cis alkyl group, a Cε-Cio aryl group, a C-C 9 arylalkyl group, said groups optionally substituted with a halogen atom or with a C1-C4 alkyl group; or T x and T 2 considered jointly with the carbon atom to which they are bound, form a C5- C14 cyloalkane ring. The stabilizing mixtures according to claim 7, wherein the compounds belonging to the group of sterically hindered amines (d) are selected from compounds (e') having general formula (XXIX): wherein n is 1 or 2, and Gis represents a group having one of the following formulae: wherein G and Gn have the same meanings defined above under claim 8; Gi and G 2 represent a hydrogen atom, a methyl, or, considered jointly, they form a substituent =0, E represents -0- or -NG 1 3-; A represents a C 2 -C 6 alkylene group or a -(CH 2 ) 3 -0- group; x is 0 or 1; Gι 3 represents a hydrogen atom, a C1-C12 alkyl group, a C2-C5 hydroxyalkyl group, a C 5 -Cη cycloalkyl group; G i9 has the same meanings as Gis or it represents one of the following groups: -NG 2 ιG 22 , -OG23, -NHCH 2 0G 23 , or -N(CH 2 OG 23 ) 2; G20, when n is 1, has the same meanings as Gι 8 , or Gι 9 , if n is 2, represents an -E-B-E- group wherein B represents a C2-C8 alkylene group optionally interrupted by 1 or 2 -N(G 2 ι)- groups; G 2 ι represents a C1-C12 alkyl group, a cyclohexyl group, a benzyl, a C1-C4 hydroxyalkyl group, or a group having the following general formula: G 22 represents a C -C 12 alkyl group, a cyclohexyl group, a benzyl, a C1-C 4 hydroxyalkyl group; G23 represents a hydrogen atom, a C1-C12 alkyl group, a phenyl , or, G 2 ι and G 22 , considered j ointly, represent a C 4 -C5 alkylene or oxyalkylene group, such as : -CH 2 CH 2 ^ O -CH 2 CH 2 or a group having the formula : G 2 ι is a gr 13. The stabilizing mixtures according to claim 7, wherein the compounds belonging to the group of sterically hindered amines (d) are selected from oligomeric or polymeric compounds (f) whose recurrent structural unit contains a 2, 2, 6, 6-tetramethylpiperidine radical, in particular polyesters, polyethers, polyamides, polyamines, polyurethanes, polyureas, polyaminotriazines, poly (meth) acrylates, poly (meth) acrylamides, and their copolymers containing said radical. 14. The stabilizing mixtures according to claim 7, wherein the compounds belonging to the group of sterically hindered amines (d) are selected from compounds (g') having general formula (XXXIV): 4 (XXXIV) wherein n is 1 or 2, G and Gn have the same meanings defined above under claim 8 and Gι 4 has the same meanings described above under claim 9, on the condition that G 14 can never represent the group -CONH-Z or the group -CH 2 -CH(OH) -CH 2 -0-D-0. 15, The stabilizing mixtures according to claim 7, wherein the compounds belonging to the group of sterically hindered amines (d) are selected from compounds (h 1 ) having general formula (XXXV): wherein R represents a Ci-Cio alkyl group, a Cs-Cι 2 cycloalkyl group optionally substituted with a C1-C4 alkyl group, a phenyl optionally substituted with a C1-C10 alkyl group; R 2 represents a C3-C 1 0 alkylene group; R 3 represents a hydrogen atom, a Ci-Cβ alkyl group, 0", a -CH 2 CN group, a C3-C6 alkenyl group, a C-C 9 phenylalkyl group optionally substituted in the phenyl radical with a C1-C4 alkyl group, a Ci-Ca acyl group, an -OR' 3 group wherein R' 3 represents a C1-C10 alkyl group; and n is a number ranging from 1 to 50, extremes included. 16. Polymeric compositions containing an organic polymer and an effective quantity of one of the stabilizing mixtures according to any of the previous claims. 17. The polymeric compositions according to claim 16, wherein the stabilizing mixtures are used in a combination with other stabilizers. 18. End-products obtained from the processing of the polymeric compositions according to claim 16 or 17. 19. A method for stabilizing organic polymers against degradation caused by oxygen, heat and/or light, which comprises the addition or application to said organic polymers of the stabilizing mixtures according to any of the claims from 1 to 15. 20. The use of 3-pyrazolidinones having general formula (I) or (II) according to claim 2, as process stabilizers for organic polymers. 21. Polymeric compositions containing an organic polymer and an effective quantity of at least one 3- pyrazolidinone having general formula (I) or (II) according to claim 2. 22. The polymeric compositions according to claim 21, wherein the 3-pyrazolidinones having general formula (I) or (II) are used in a combination with other stabilizers. 23. End-products obtained from the processing of the polymeric compositions according to claim 21 or 22.

Inventors: BROUSSARD FABIO, GIRELLI DANIELE, MALATESTA VINCENZO, BROUSSARD, FABIO, GIRELLI, DANIELE, MALATESTA, VINCENZO
Applicants: BROUSSARD FABIO, GIRELLI DANIELE, GREAT LAKES CHEMICAL EUROP, MALATESTA VINCENZO, BROUSSARD, FABIO, GIRELLI, DANIELE, GREAT LAKES CHEMICAL (EUROPE) GMBH, MALATESTA, VINCENZO
Application year: 2001
Main classification: C08K5
IPC codes: C08K5