DERIVATIVES OF ALKYL-SUBSTITUTED 4-HYDROXY-METHYL-PIPERIDINE AND USE THEREOF AS STABILIZERS

Abstract: Derivatives of 4-hydroxy-methyl-piperidine having general formula: wherein: R₁, R₂, R₃ and R₄ may be alkyl or may form, with the carbon they are bound to, a cycloalkyl group or the group with R₆, R₇, R₈ and R₉ being hydrogen or alkyl; R₅ may be H, alkyl, aryl, alkenyl, etc.; Y may be an organic or inorganic group or atom having a valence from 1 to 4 and n is an integer from 1 to 4. The use of the derivatives of the alkyl-substituted 4-hydroxy-methyl-piperidine of formula (I) as stabilizers of polymeric substances, and polymeric compositions stabil­ ized with said piperdine derivatives. This invention relates to new derivatives of alkyl-­ substituted 4-hydroxy-methyl-piperidine, to the use thereof as stabilizers of polymeric substances usually subject to worsening owing to thermal and/or photo-oxidation, and to the polymeric compositions stabilized with said derivatives.

Description: As it is known, heat, oxygen and light, especially the actinic radiation in the short wavelength ultraviolet range, have an adverse effect on the appearance and the properties of organic polymers. For example, polyesters, which are usually colorless, turn yellow when exposed to sunlight. Analogously, the oxidation rate of polyolefins when exposed to air is strongly increased in the presence of ultraviolet light. Polystyrene gets yellow and brittle, with corresponding loss of its desirable properties, when exposed to actinic light, etc. The same degradation and alteration effects of the mechanical properties occur when the polymeric materials are subjected to heat-treatments, for example during their transformation into formed articles, such as films, fibers and the like. In order to stabilize the polymeric materials and to maintain the properties thereof unchanged, it is usual practice to add thereto one or more stabilizers, the function of which is just that of counteracting the susceptibility of such materials to oxidative and thermal degradation. A particular type of stabilizers which has been employed very successfully is represented by the sterically hindered amines (HALS) and in particular the derivatives of alkylsubstituted piperidine. The hindered amines based on alkyl-substituted piperidine, although being excellent stabilizers for polymeric substances in general, do not afford satisfactory results with all polymeric substances and in all technological uses. In fact, the known stabilizers show the drawback of not possessing all those parameters and technical characteristics necessary for all technological applications, such as low volatility, resistance to migration, thermal stability, insolubility in water, etc. US-A-3937711, among many others, mentions 2,2,6,6-tetraalkyl-4-hydroxyethyl piperidine derivatives as possible stabilizers for polymers. It is an object of the present invention to improve the properties of the known alkyl-substituted piperidine stabilizers. It has now been found that this and still further objects are achieved by derivatives of alkyl-substituted 4-hydroxy-methyl-piperidine having general formula: wherein: R₁, R₂, R₃ and R₄, the same or different, are each an alkyl group containing from 1 to 6 carbon atoms; or R₁ and R₂ and/or R₃ and R₄, together with the carbon atoms to which they are bound, represent a cycloalkyl group or a group of formula: in which R₆, R₇, R₈ and R₉, the same or different, represent a hydrogen atom or an alkyl group containing 1 to 6 carbon atoms and R₅ has the meaning defined below; R₅ represents a hydrogen atom, an alkyl group, an alkenyl group, an alkoxyalkyl group, an aralkyl group, optionally carrying one or more substituents on the aryl radical, a 2,3-epoxypropyl group, a group of formula -CH₂-COOR₁₀, in which R₁₀ is an alkyl group, an alkenyl group, a phenyl group, an aralkyl group or a cyclohexyl group; an aliphatic acyl group or a group of formula -COOR₁₃ in which R₁₃ is an alkyl group, a benzyl group or a phenyl group; a group of formula: in which R₁₁ is a hydrogen atom, a methyl group, an ethyl group or a phenyl group and R₁₂ is a hydrogen atom, an alkyl-substituted piperidyl group optionally also having a hydroxy group on the ring, an acyl group or a group of formula: in which Z and Z¹, the same or different, represent hydrogen, -NR₁₄R₁₅, -O-R₁₆ or -S-R₁₇ in which R₁₄, R₁₅, R₁₆ and R₁₇ may be hydrogen, an alkyl radical containing 1 to 18 carbon atoms or an alkyl-substituted piperidyl group of formula: or R₁₄ and R₁₅ together with the N atom form a ring which may optionally contain other heteroatoms; Y represents an organic or inorganic group or atom, except hydrogen, having a valence ranging from 1 to 4 which does not adversely affect the polymer-stabilization activity; and n is an integer ranging from 1 to 4, depending on the valence of Y. According to the present invention it has also been found that the derivatives of alkyl-substituted 4-hydroxymethyl-piperidine having general formula (I), either alone or in admixture with other known stabilizers, can effectively stabilize a wide range of polymers against photo-and thermal degradation and, furthermore, are highly compatible with the polymers, in particular with polyolefins. When R₁, R₂, R₃ or R₄ in the above formula (I) represent alkyl groups, said alkyl groups preferably contain from 1 to 4 carbon atoms, such as, e.g., methyl, ethyl, propyl, isopropyl, butyl or isobutyl, the methyl group being particularly preferred. R₁ and R₂ and/or R₃ and R₄, along with the carbon atom to which they are bound, may also represent a cycloalkyl group containing from 5 to 7 carbon atoms, such as, e.g., cyclopentyl, cyclohexyl, cycloheptyl, etc., or an alkyl-substituted piperidyl group, such as for example: When R₅ is an alkyl group, it may contain from 1 to 8 carbon atoms. In practice, it is preferable that the alkyl group contains from 1 to 4 carbon atoms and among these, the methyl group is particularly preferred. When R₅ is an alkenyl group, it may contain from 3 to 6 carbon atoms, such as e.g., the allyl group, the, 2-butenyl group or the 2-hexenyl group; alkenyl groups containing 3 or 4 carbon atoms are preferred and the allyl group is particularly preferred. When R₅ is an alkoxyalkyl group, it may be an alkoxyalkyl group containing 1 to 3 carbon atoms in the alkyl chain and from 1 to 18 carbon atoms in the alkoxy radical. Examples of alkoxyalkyl groups are: methoxymethyl, ethoxymethyl, 2-butoxyethyl, 3-butoxypropyl, 2-octoxyethyl and 2-octadecyloxyethyl. Among the alkoxyalkyl groups those containing a total of 2 to 6 carbon atoms are preferred. When R₅ is an aralkyl group, it preferably contains 7 or 8 carbon atoms and may be unsubstituted or contain up to 3 substituents in the aryl radical. Chlorine atoms, alkyl groups with 1 to 4 carbon atoms, alkoxy groups with 1 to 8 carbon atoms or hydroxy groups may be used as substituents. Typical examples of aralkyl groups are: benzyl, p-chlorobenzyl, o-chlorobenzyl, m-chlorobenzyl, o-methylbenzyl, m-methylbenzyl, p-methylbenzyl, p-isopropylbenzyl, p-tert-butylbenzyl, p-methoxybenzyl, p-butoxybenzyl, p-octoxybenzyl, 4-hydroxy-3,5-ditert-butylbenzyl, etc.. When R₅ is a group of formula -CH₂-COOR₁₀, R₁₀ may represent: an alkyl group containing preferably from 1 to 18 carbon atoms, such as methyl, ethyl, isopropyl, butyl, isobutyl, tert -butyl, isopentyl, octyl, dodecyl, octadecyl, etc.; an alkenyl group preferably containing from 3 to 6 carbon atoms, such as allyl, 2-butenyl, 2-hexyl, etc.; a phenyl group; an aralkyl group, preferably containing 7 or 8 carbon atoms, or a cyclohexyl group. Alkyl groups containing 1 to 4 carbon atoms are the preferred groups R₁₀. When R₅ represents the group R₁₁ represents a hydrogen atom, a methyl group or a phenyl group and R₁₂ represents a hydrogen atom, an acyl group, for example an aliphatic, araliphatic, aromatic or alicyclic group, an alkyl-substituted piperidyl group (optionally also having a hydroxy group on the ring) such as: or a triazine group, such as: in which Z and Z', the same or different from each other, represent hydrogen, -NR₁₄R₁₅, -O-R₁₆ or -S-R₁₇ in which R₁₄, R₁₅, R₁₆ and R₁₇ may be hydrogen, an alkyl radical containing from 1 to 18 carbon atoms or an alkyl-substituted piperidyl group such as: or R₁₄ and R₁₅ together with the N atom form a ring which optionally contains other heteroatoms, such as: When R₁₂ is an acyl group, it preferably has the formula -COR₁₈ in which R₁₈ is an alkyl group with 1 to 18 carbon atoms; an alkenyl group with 2 to 4 carbon atoms; a phenyl group, optionally substituted with up to 3 substituents, equal or different from each other and selected from chlorine, alkyl with 1 to 4 carbon atoms, alkoxy with 1 to 8 carbon atoms and hydroxy; an aralkyl group with 7 or 8 carbon atoms, the aryl radical of which may optionally be substituted with up to 3 substituents, the same or different from one another and selected from chlorine, alkyl with 1 to 4 carbon atoms, alkoxy with 1 to 6 carbon atoms and hydroxy; a styryl group, or a cyclohexyl group. Examples of radicals R₁₈ are: methyl, ethyl, propyl, butyl, heptyl, 1-ethyl-pentyl, nonyl, undecyl, heptadecyl, vinyl, 1-propenyl, 2-methy-1-propenyl, 1-butenyl, phenyl, o-chlorophenyl, m-chlorophenyl, 2,4-di-chlorophenyl, o-methylphenyl, p-methylphenyl, m-methylphenyl, p-isopropylphenyl, p-tert -butylphenyl, p-methoxyphenyl, p-ethoxyphenyl, p-butoxyphenyl, 3,4,5-trimethoxyphenyl, o-hydroxyphenyl, 4-hydroxy-3,5-di-tert -butylphenyl, benzyl, p-methylbenzyl and 4-hydroxy-3,5-di-tert-butylphenyl. Particularly preferred are the groups of formula -CH₂-CH₂-O-R₁₂, in which R₁₂ has one of the meanings given above. When R₅ is an aliphatic acyl group, it preferably contains up to 4 carbon atoms and is a saturated or unsaturated acyl group, such as, e.g., formyl, acetyl, acrylyl or crotonyl. When R₅ is a group of formula -COOR₁₃, R₁₃ is an alkyl group, preferably with 1 to 8 carbon atoms, such as methyl, ethyl, isobutyl, heptyl; a benzyl group or a phenyl group. In general Y may represent a hydrocarbon residue which may be non-substituted or substituted, a residue derived from an organic or inorganic acid, a heterocyclic group and a group comprising a phosphorus, boron or silicon atom. The following groups are preferred: When n = 1, Y preferably represents an acyl-aliphatic, aryl-aliphatic, alicyclic, aromatic or heterocyclic group; particularly preferred groups Y are acyl groups containing up to 18 carbon atoms and, even more specifically, groups of formula -COR₁₉ in which R₁₉ represents a hydrogen atom; an alkyl group with 1 to 17 carbon atoms (such as methyl, ethyl, propyl, isopropyl, butyl, tert -butyl, pentyl, isopentyl, 1-ethylpentyl, nonyl, undecyl, pentadecyl, etc.); an alkenyl group with 2 to 5 carbon atoms, such as vinyl, 1-propenyl, 2-methyl-1-propenyl, isopropenyl, or 1,3-pentadienyl; an alkynyl group with 2 or 3 carbon atoms, such as ethynyl or propynyl; phenyl, optionally substituted with up to 3 substituents, the same or different from each other, such as chlorine, alkyl with 1 to 4 carbon atoms, alkoxy with 1 to 8 carbon atoms, hydroxy or nitro (such as, for example, phenyl, o-chlorophenyl, m-chlorophenyl, p-chlorophenyl, o-methylphenyl, m-methylphenyl, p-methylphenyl, p-isopropylphenyl, p-tert-butylphenyl, m-methoxyphenyl, p-methoxyphenyl, p-octoxyphenyl, o-hydroxyphenyl, 2-hydroxy-3-methylphenyl, 4-hydroxy-3,5-di-tert-butylphenyl, m-nitrophenyl, etc.); naphthyl; styryl; an aralkyl group with 7 or 8 carbon atoms, optionally substituted with up to 3 identical or different substituents, such as chlorine, alkyl with 1 to 4 carbon atoms, alkoxy with 1 to 8 carbon atoms or hydroxy (such as benzyl, phenethyl, 4-hydroxy-3,5-di-tert-butylbenzyl or 4-hydroxy-3,5-di-tert-butylphenethyl); phenoxymethyl; cyclohexyl; 2-pyridyl, 3-pyridyl; 4-pyridyl; 2-furyl; a group of formula -CO-R₂₀-COOH, in which R₂₀ is an alkylene group preferably containing from 1 to 10 carbon atoms, the chain of which can be interrupted by an oxygen or sulphur atom; or metal salts thereof in which the metal may be, for example, barium, nickel, manganese, calcium, zinc, iron, sodium, cobalt or tin; or lower alkyl esters thereof in which the alkyl chain contains from 1 to 4 carbon atoms, such as the methyl, ethyl, propyl, butyl esters, etc.; a radical obtained by removing a hydroxy group of a phosphorus-containing acid, for example a radical of phosphoric acid, of phosphonic acid, or phosphorous acid, either unsubstituted or substituted, such as the radicals a group of formula: in which R₂₁ is hydrogen; an alkyl group containing 1 to 4 carbon atoms; an aralkyl group preferably containing 7 or 8 carbon atoms; or a phenyl group; and R₂₂ is an alkyl group containing from 1 to 18 carbon atoms, an aryl group preferably containing 6 to 10 carbon atoms, optionally substituted by one or more chlorine atoms and/or alkyl groups with from 1 to 4 carbon atoms such as,for example,phenyl, o-chlorophenyl, p-chlorophenyl, o-, m- and p-toluyl, alpha-naphthyl or beta-naphthyl; an aralkyl group containing 7 or 8 carbon atoms, or a cyclohexyl group; alternatively, R₂₁ and R₂₂, together with the nitrogen atom to which they are bound, represent a piperidine group, a 1-pyrrolidinyl group or a morpholine group; among these groups, those having the formula -CO-NH-R₂₂ in which R₂₂ is the same as specified hereinbefore, are particularly preferred; an alkyl group preferably containing from 1 to 18 carbon atoms, such as methyl, ethyl, butyl, octyl, dodecyl or octadecyl; an alkenyl group preferably containing from 3 to 6 carbon atoms, such as allyl, 2-butenyl, methallyl or 2-hexenyl; an aralkyl group with from 7 to 9 carbon atoms and optionally carrying up to 3 substituents on the aryl radical, such as alkyl with 1 to 4 carbon atoms and/or hydroxy, (for example, benzyl, p-methylbenzyl, p-isopropylbenzyl, 4-hydroxy-3,5-di-tert -butylbenzyl or 3-(4-hydroxy-3,5-di-tert -butylphenyl)-propyl); a cyclohexyl group; or a group of formula in which R₂₃ is a hydrogen atom, a C₁₋₆ alkyl group (particularly methyl) or a phenyl group and R₂₄ is an alkyl group containing preferably from 1 to 8 carbon atoms. When n = 2, Y preferably represents an aliphatic, araliphatic, aromatic, alicyclic or heterocyclic diacyl group containing up to 22 carbon atoms, preferably a group of formula -CO-(R₂₅) m -CO-in which m may be 0 or 1 and R₂₅ is a linear or branched alkylene group with 1 to 20 carbon atoms, optionally containing as substituent the alkylbenzyl or hydroxy-alkylbenzyl group (additionally, the chain may be interrupted by a sulphur or oxygen atom); phenylene, cyclohexylene, 2,4-pyridindiyl, 2,5-pyridindiyl or thiophendiyl; a carbonyl group; a group obtained by removing the two hydroxyl groups of an acid containing phosphorus, in particular a group of formula: in which R₂₆ represents a hydrogen atom, an alkyl group with preferably from 1 to 4 carbon atoms, a phenyl or benzyl group, optionally substituted such as 4-hydroxy-3,5-di-tert-butylbenzyl); a group of formula: a group of formula: in which R₂₁ has the same meaning as above and R₂₇ represents an alkylene group preferably containing from 2 to 10 carbon atoms; an optionally substituted arylene group having preferably from 6 to 10 carbon atoms (such as o-phenylene, m-phenylene, p-phenylene, 2,4-toluidene, 1,5-naphthylene, etc.), a xylylene group, a cyclohexylene group (such as 1,4-cyclohexylene), a group of formula: in which R₂₈ may be an oxygen atom of an alkylene group containing from 1 to 4 carbon atoms; a group of formula: in which R₂₉ may be a hydrogen atom of a methyl group; a group of formula: (such as methylene-di-4,1-cyclohexene), or a group of formula: such as,for example,1,3-cyclohexylene-dimethylene, etc.;(among the groups comprised by this formula, those of formula -CO-NH-R₂₇-NH-CO- in which R₂₇ is as defined hereinbefore are particularly preferred); an alkylene group containing up to 10 carbon atoms and preferably from 2 to 6 carbon atoms, such as ethylene, tetramethylene, hexamethylene, etc.; an alkenylenegroup containing from 4 to 10 carbon atoms; or a xylylene group, such as o-xylylene, m-xylylene, p-xylylene, etc. When n = 3 , Y may be selected from the following radicals: When n = 4 , Y may be: or Derivatives of alkyl-substituted 4-hydroxy-piperidine which are particularly preferred are those of general formula: in which R₅ is a hydrogen atom, a methyl group, a benzyl group, a 2,3-epoxypropyl group or a group of formula -CH₂-CH₂-O-R₁₂ in which R₁₂ is hydrogen or an alkyl group with from 2 to 18 carbon atoms or a benzoyl group; n = 1, 2 or 3; and when n = 1 Y represents a group of formula -CO-R₁₉ in which R₁₉ represents an alkyl group with from 1 to 17 carbon atoms, phenyl, optionally substituted by up to 3 alkyl radicals with 1 to 4 carbon atoms and/or hydroxy, or 4-hydroxy-3,5-di-tert -butylphenethyl; or a group of formula -CO-NH-R₂₂ in which R₂₂ represents an alkyl group with 1 to 18 carbon atoms, phenyl or cyclohexyl; when n = 2 Y represents a group of formula -CO-(R₂₅) m -CO- in which m is 0 or 1 and R₂₅ represents an alkylene group with 1 to 10 carbon atoms, the group -CH₂-CH₂-S-CH₂-CH₂- or a phenylene group; or a group of formula -CO-NH-R₂₇-NH-CO-, in which R₂₇ represents hexamethylene, 2,4-toluylene or methylene-di-p-phenylene; when n = 3 Y represents Particularly preferred compounds are those in which n = 1 and Y represents a group of formula -CO-R₁₉; or n = 2 and Y represents a group of formula -CO-R₂₅-CO-, R₁₉ and R₂₅ having the meanings defined hereinbefore. A non-limitative list of derivatives of alkyl-substituted 4-hydroxy-methyl-piperidines is given hereinbelow, and the numbers of the corresponding products will be used to identify them also in the examples. (2) (2,2,6,6-tetramethyl)-4-methyl piperidine acetate; (3) (2,2,6,6-tetramethyl)-4-methyl piperidine palmitate; (4) (2,2,6,6-tetramethyl)-4-methyl piperidine ethylhexanoate; (5) (2,2,6,6-tetramethyl)-4-methyl piperidine stearate; (6) (2,2,6,6-tetramethyl)-4-methyl piperidine acrylate; (7) (2,2,6,6-tetramethyl)-4-methyl piperidine crotonate; (8) (2,2,6,6-tetramethyl)-4-methyl piperidine methacrylate; (9) (2,2,6,6-tetramethyl)-4-methyl piperidine tetrolate; (10) (2,2,6,6-tetramethyl)-4-methyl piperidine benzoate; (11) (2,2,6,6-tetramethyl)-4-methyl piperidine p-tertbutylbenzoate; (12) (2,2,6,6-tetramethyl)-4-methyl piperidine p-methoxybenzoate; (13) (2,2,6,6-tetramethyl)-4-methyl piperidine salicylate; (14) (2,2,6,6-tetramethyl)-4-methyl piperidine p-chlorobenzoate; (15) (2,2,6,6-tetramethyl)-4-methyl piperidine naphthalene-1-carboxylate; (16) (2,2,6,6-tetramethyl)-4-methyl piperidine phenyl acetate; (17) (2,2,6,6-tetramethyl)-4-methyl piperidine β-(4-hydroxy-3,5-di-tert-butylphenyl)-propionate; (18) (2,2,6,6-tetramethyl)-4-methyl piperidine cinnamate; (19) (2,2,6,6-tetramethyl)-4-methyl piperidine cyclohexancarboxylate; (20) (2,2,6,6-tetramethyl)-4-methyl piperidine methyl salicylate; (21) (2,2,6,6-tetramethyl)-4-methyl piperidine methylphthalate; (23) (1,2,2,6,6-pentamethyl)-4-methyl-piperidine stearate; (24) (1,2,2,6,6-pentamethyl)-4-methyl piperidine benzoate; (25) (1,2,2,6,6-pentamethyl)-4-methyl piperidine m-toluate; (26) (1,2,2,6,6-pentamethyl)-4-methyl piperidine p-octyloxybenzoate; (27) (1,2,2,6,6-pentamethyl)-4-methyl piperidine β-(4-hydroxy-3,5-di-tert-butylphenyl)propionate; (28) (1-butyl-2,2,6,6-tetramethyl)-4-methyl piperidine hexanoate; (29) (1-allyl-2,2,6,6-tetramethyl)-4-methyl piperidine stearate; (30) (1-allyl-2,2,6,6-tetramethyl)-4-methyl piperidine crotonate; (31) (1-allyl-2,2,6,6-tetramethyl)-4-methyl piperidine benzoate; (32) (1-benzyl-2,2,6,6-tetramethyl)-4-methyl piperidine acetate; (33) (1-benzyl-2,2,6,6-tetramethyl)-4-methyl piperidine stearate; (34) (1-benzyl-2,2,6,6-tetramethyl)-4-methyl piperidine crotonate; (35) (1-benzyl-2,2,6,6-tetramethyl)-4-methyl piperidine benzoate; (36) [1-(2,3-epoxypropyl)-2,2,6,6 -tetramethyl]-4-methyl piperidine stearate; (37) [1-(2,3-epoxypropyl)-2,2,6,6-tetramethyl]-4-methyl piperidine benzoate; (39) [1-(2-hydroxyethyl)-2,2,6,6-tetramethyl]-4-methyl piperidine benzoate; (40) [1-(2-hydroxypropyl)-2,2,6,6-tetramethyl]-4-methyl piperidine benzoate; (41) [1-(2-hydroxy-2-phenylethyl)2,2,6,6-tetramethyl]-4-methyl piperidine p-tert-butylbenzoate; (42) [1-(2-acetoxymethyl)-2,2,6,6-tetramethyl]-4-methyl piperidine benzoate; (43) [1-(2-stearoyloxyethyl)-2,2,6,6-tetramethyl]-4-methyl piperidine stearate; (44) 1-{2[β-(4-hydroxy-3,5-di-tert-butylphenyl)propionyloxy]ethyl}-2,2,6,6-tetramethyl-4-methyl piperidine β-(4-hydroxy-3,5-di-tert-butyl phenyl)propionate; (45) [1-(2-palmitoxyethyl)-2,2,6,6-tetramethyl]-4-methyl piperidine palmitate; (46) [1-(2-acetoxypropyl)-2,2,6,6-tetramethyl]-4-methyl piperidine benzoate; (47) [1-(2-acetoxy-2-phenylethyl)-2,2,6,6-tetramethyl]-4-methyl piperidine butyrate; ` (48) (1-ethoxymethyl-2,2,6,6-tetramethyl)-4-methyl piperidine benzoate; (49) (1-butoxyethyl-2,2,6,6-tetramethyl)-4-methyl piperidine butyrate; (50) (1-formyl-2,2,6,6-tetramethyl)-4-methyl piperidine butyrate; (51) (1-acetyl-2,2,6,6-tetramethyl)-4-methyl piperidine benzoate; (52) (2,2,6,6-tetramethyl)-4-methyl piperidine methyl carbamate; (53) (2,2,6,6-tetramethyl)-4-methyl piperidine octadecyl carbamate; (54) (2,2,6,6-tetramethyl)-4-methyl piperidine carbanilate; (55) (2,2,6,6-tetramethyl)-4-methyl piperidine p-chlorocarbanilate; (56) (2,2,6,6-tetramethyl)-4-methyl piperidine 1-naphthalene carbamate; (57) (2,2,6,6-tetramethyl)-4-methyl piperidine cyclohexane carbamate; (58) (2,2,6,6-tetramethyl)-4-methyl piperidine piperidine-1-carboxylate; (59) (2,2,6,6-tetramethyl)-4-methyl piperidine pyrrolidine-1-carboxylate; (60) (1,2,2,6,6-pentamethyl)-4-methyl piperidine methylcarbamate; (61) (1,2,2,6,6-pentamethyl)-4-methyl piperidine carbanilate; (62) (1-butyl-2,2,6,6-tetramethyl)-4-methyl piperidine methyl carbamate; (63) (1-benzyl-2,2,6,6-tetramethyl)-4-methyl piperidine methyl carbamate; (64) [1-(2-hydroxyethyl)-2,2,6,6-tetramethyl]-4-methyl piperidine cyclohexane carbamate; (65) [1-(2-acetonyl ethyl)-2,2,6,6-tetramethyl]-4-methyl piperidine methyl carbamate; (66) (2,2,6,6-tetramethyl)-4-methoxymethyl piperidine; (67) 4-butoxymethyl-(2,2,6,6-tetramethyl) piperidine; (68) 4-octadecyloxymethyl-(2,2,6,6-tetramethyl) piperidine; (69) [(2,2,6,6-tetramethyl-4-hydroxy)-4-piperidine methoxyl (2,2,6,6-tetramethyl)-4-methylpiperidine; (70) β-[(2,2,6,6- tetramethyl)-4-piperidine methoxy] ethyl acrylate; (71) (1,2,2,6,6-pentamethyl)-4-methoxymethyl piperidine; (72) 4-benzyloxymethyl-(1,2,2,6,6-pentamethyl)-piperidine; (73) 1-allyl-2,2,6,6-tetramethyl-4-allyloxymethyl piperidine; (74) 1-(2-hydroxymethyl)-4-methoxymethyl (2,2,6,6-tetramethyl) piperidine; (75) 1-(2-acetoxyethyl)-4-methoxymethyl (2,2,6,6-tetramethyl) piperidine; (76) bis-(2,2,6,6-tetramethyl)-4-methyl piperidine carbonate; (77) bis-(2,2,6,6-tetramethyl)-4-methyl piperidine oxalate; (78) bis-(2,2,6,6-tetramethyl)-4-methyl piperidine succinate; (79) bis-(2,2,6,6-tetramethyl)-4-methyl piperidine adipate; (80) bis-(2,2,6,6-tetramethyl)-4-methyl piperidine sebacate; (81) bis-(2,2,6,6-tetramethyl)-4-methyl piperidine (3,5-di-tert-butyl-4- hydroxy) benzyl, n-butyl malonate; (82) bis-(2,2,6,6-tetramethyl)-4-methyl piperidine diethyl malonate; (83) bis-(2,2,6,6-tetramethyl)-4-methyl piperidine fumarate (84) bis-(2,2,6,6-tetramethyl)-4-methyl piperidine terephthalate; (85) bis-(2,2,6,6-tetramethyl)-4-methyl piperidine cyclohexane 1,4-dicarboxylate; (86) bis-(2,2,6,6-tetramethyl)-4-methyl piperidine phenyl phosphonate; (87) bis-(1,2,2,6,6-pentamethyl)-4-methyl piperidine adipate; (88) bis-(1,2,2,6,6-pentamethyl)-4-methyl piperidine sebacate; (89) bis-(1,2,2,6,6-pentamethyl)-4-methyl piperidine terephthalate; (90) mono-(1,2,2,6,6-pentamethyl)-4-methyl piperidine succinate; (91) mono-(1,2,2,6,6-pentamethyl)-4-methyl piperidine 3,4,5,6-tetrahydrophthalate; (92) mono-(2,2,6,6-tetramethyl)-4-methyl piperidine maleate; (93) nickel di-[3,4,5,6-tetrahydrophthalate of mono-(1,2,2,6,6-pentamethyl)-4-methyl piperidine]; (94) calcium di-[adipate of mono-(1,2,2,6,6-pentamethyl) -4-methyl piperidine]; (95) zinc di-[succinate of mono-(2,2,6,6-tetramethyl)-4-methyl piperidine]; (96) barium di-[succinate of mono-(2,2,6,6-tetramethyl)-4-methyl piperidine]; (97) nickel di-[maleate of mono-(2,2,6,6-tetramethyl)-4-methyl piperidine]; (98) nickel di-[succinate of mono-(1,2,2,6,6-pentamethyl)-4-methyl piperidine]; (99) bis{[1(2,3-epoxypropyl) 2,2,6,6-tetramethyl]-4-methyl piperidine} isophthalate; (100) bis [(1-benzyl-2,2,6,6-tetramethyl)-4-methyl piperidine] sebacate; (101) bis {[1-(-acetoxyethyl) 2,2,6,6-tetramethyl]-4-methyl piperidine} sebacate; (102) bis [(2,2,6,6-tetramethyl)-4-methyl piperidine] hexamethylene-di-carbamate; (103) bis [(2,2,6,6-tetramethyl)-4-methyl piperidine] toluene-2,4-di-carbamate; (104) bis [(2,2,6,6-tetramethyl)-4-methyl piperidine] naphthalene-1,5-di-carbamate; (105) bis [(2,2,6,6-tetramethyl)-4-methyl piperidine] (oxy-di-p-phenylene)di-carbamate; (106) bis [(2,2,6,6-tetramethyl)-4-methyl piperidine] (methylene-di-p-phenylene) di-carbamate; (107) bis [(2,2,6,6-tetramethyl)-4-methyl piperidine] (methylene-di-4,1-cyclohexylene)-di-carbamate; (108) bis [(1,2,2,6,6-pentamethyl)-4-methyl piperidine] hexamethylene-di-carbamate; (109) bis [(1,2,2,6,6-pentamethyl)-4-methyl piperidine] methylene-di-p-phenylene-di-carbamate; (110) 1,2-bis [(2,2,6,6-tetramethyl)-4-piperidine methoxy] ethane; (111) 1,4-bis [(2,2,6,6-tetramethyl)-4-piperidine methoxy] butane; (112) 1,4-bis [(2,2,6,6-tetramethyl)-4-piperidine methoxy] butene; (113) 1,6-bis [(2,2,6,6-tetramethyl)-4-piperidine methoxy] hexane; (114) 1,4-bis [(2,2,6,6-tetramethyl)-4-piperidine methoxy] methylbenzene; (115) 1,3-bis {[(1,2,2,6,6-pentamethyl)-4-piperidine methoxy] methyl} benzene; (116) 1,6-bis {[1-(2-stearoyloxyethyl) 2,2,6,6-tetramethyl]-4-piperidine methoxy} hexane; (117) the compound: (118) tris [(2,2,6,6-tetramethyl)-4-methyl piperidine] trimellitate; (119) tris [(2,2,6,6-tetramethyl)-4-methyl piperidine] trimesate; (120) tris [(2,2,6,6-tetramethyl)-4-methyl piperidine] tricarballylate; (121) tris [(2,2,6,6-tetramethyl)-4-methyl piperidine] phosphite; (122) tris [(2,2,6,6-tetramethyl)-4-methyl piperidine] phosphate; (123) tris [(1,2,2,6,6-pentamethyl)-4-methyl piperidine] trimellitate; (124) tris [(1,2,2,6,6-pentamethyl)-4-methyl piperidine] phosphite; (125) tetrakis [(2,2,6,6-tetramethyl)-4-methyl piperidine] pyromellitate; (126) tetrakis [(1,2,2,6,6-pentamethyl)-4-methyl piperidine] pyromellitate; (127) (2,5-dioxa-1-phospholan-1-yloxy)-[(2,2,6,6-tetramethyl)-4-methyl piperidine]; (128) (4,4-dimethyl-2,6-dioxa-1-phospholan-1-yloxy)[(2,2,6,6-tetramethyl)-4-methyl piperidine]; (129) O-ethyl,O-[(2,2,6,6-tetramethyl)-4-methyl piperidine] benzyl phosphonate; (130) O,O'-bis [(2,2,6,6-tetramethyl)-4-methyl piperidine] phosphonate; (131) O,O'-bis [(2,2,6,6-tetramethyl)-4-methyl piperidine] benzyl phosphonate; (132) O,O'-bis-[(2,2,6,6-tetramethyl)-4-methyl piperidine] 4-hydroxy-3,5-di-tert-butyl benzyl phosphonate; (133) 3,9-bis-[(2,2,6,6-tetramethyl)-4-methoxy piperidine]-2,4,8,10-tetraoxa-3,9-di-phospha-spyro-[5,5] undecane. The compound prepared in Example 1 below is described in Khim.Get.Soed. 1976 No. 7, pages 927-34 (E.I. Levkoeva, L.N. Iachontov), but it is not stated therein that said compound might be useful as stabilizer for polymers. The derivatives of 4-hydroxy-methyl-piperidine (I) are preparable according to conventional methods by means of the processes indicated hereinbelow. Method A The compounds of formula (I) where Y is hydrogen, (not compounds according to the invention but useful starting materials) are preparable by reduction of a compound of formula (III) where R₁, R₂, R₃, R₄ and R₅ are defined as hereinbefore, by means of a reducing agent such as lithium or aluminum hydride with hydrogen and a catalyst such as the nickel Raney. Method B The compounds of formula (I), wherein Y is an acyl group, a diacyl group, a carbonyl group, a group obtained by removing one or two hydroxy groups from a phosphorus-containing acid or a group of formula are obtainable by reacting a compound of formula: (wherein R₁, R₂, R₃, R₄ and R₅ are defined as hereinbefore) with a reactive derivative of the acid corresponding to group Y, for example with a halide or a lower alcohol ester. Method C The compounds of formula (I) in which Y represents an alkyl, alkenyl, aralkyl group, a cyclohexyl group, an alkylene group, an alkenyl group or a xylylene group are preparable by reacting a compound of formula (IV), as already defined, with a halide of group Y. Method D The compounds of formula (I) wherein Y represents one of the groups -CONHR₂₂ or -CONHR₂₇NH-CO- can be prepared by reacting a compound of formula (IV), as already defined, with an isocyanate of formula R₂₂NCO or OCN-R₂₇-NCO. Method E The compounds of formula (I), wherein Y represents one of the groups are preparable by reacting a compound of formula (IV), as already defined, with the carbamoyl chloride obtained by reacting phosgene and an amine of the type Method F The compounds of formula (I) in which Y represents the group -CO-R₂₀-COOH are preparable by reacting the compound of formula (IV), as already defined, with an anhydride of formula: The esters and the salts of this group can be easily prepared according to conventional methods. Method G The compounds of formula (I) wherein Y represents a group can be prepared by reacting a compound of formula (IV), as already defined, with a compound of formula R₂₃-C≡C-COOR₂₄. Method H The compounds of formula (I) where Y represents a group of formula are preparable by reacting a compound of formula (IV), as already defined, with a compound of formula: When R₅ is a group other than hydrogen, it can be introduced into the compound prior to or after the introduction of Y, by treating a compound of formula I, II, III or IV, where R₅ is the hydrogen atom, according to one of the following methods. Method J The compounds of formula I, II, III or IV, in which R₅ represents an alkyl group, an alkenyl group, an alkoxyalkyl group, an aralkyl group, a 2,3-epoxypropyl group, the group -CH₂-COO-R₁₀, the group an aliphatic acyl group or the group -COOR₁₃ (R₁₀, R₁₁, R₁₂, R₁₃ and R₁₄ are the same as defined hereinbefore), are easy to prepare by reacting the corresponding compounds in which R₅ is a hydrogen atom with a halide of the group R₅. Method K The compounds of formula I, II, III or IV, in which R₅ represents the group (R₁₁ being defined as hereinbefore) can be prepared by reacting the corresponding compounds in which R₅ is hydrogen with an epoxide, such as ethylene oxide, propylene oxide or styrene oxide. The resulting compounds can be acylated to obtain the corresponding acylated compounds. Method L The compounds of formula I, II, III or IV, in which R₅ represents a methyl group, are preparable according to the Leuckart-Wallach reaction, i.e., by reacting the corresponding compound in which R₅ represents hydrogen with formic acid and formaldehyde. Method M The compounds of formula I, II, III or IV in which R₅ represents a formyl group can be prepared by reacting a corresponding compound in which R₅ is hydrogen, with ethyl orthoformate, in the presence of an acidic catalyst. The compounds of formula III, which represent the starting substances for preparing the derivatives of 4-hydroxymethyl-piperidine having general formula (I), utilized in the polymeric compositions according to the present invention, can be prepared according to the teachings of US-A-4,400,513. The derivatives of 4-hydroxy-methyl piperidine having general formula (I) are useful to stabilize polymers, in particular synthetic polymers, against photo- and thermal degradation. Examples of polymers which can be stabilized according to the present invention are: polymers of olefins and of dienes, such as homopolymers of olefins and dienes (e.g., low density polyethylene, high density polyethylene and cross-linked polyethylene, polypropylene, polyisobutene, polymethylbutene-1, polymethylpentene-1, polyisoprene, polybutadiene), mixtures of such homopolymers or copolymers (for example, ethylene-propylene copolymers, propylene-butene-1 copolymers, or terpolymers of ethylene, propylene and dienes, such as hexadiene, dicyclopentadiene), etc.; styrene polymers, such as polystyrene, copolymers of styrene and α-methylstyrene with acrylonitrile, methyl methacrylate, acrylic esters, and styrene polymers modified with elastomers, grafted styrene polymers, etc.; halogenated vinyl and vinylidene polymers, such as: polyvinylchloride, polyvinylidenechloride, polyvinylfluoride, polychloroprene, vinyl chloride/vinylidene chloride copolymers, vinyl chloride/vinyl acetate copolymers, vinylidene chloride/vinyl acetate copolymers; etc.; polymers derived from α,β-unsaturated acids, such as polyacrylates, polymethacrylates, polyacrylonitrile, polyacrylic amides; polymers derived from alcohols and from unsaturated amines and acylated or acetal derivatives thereof, such as polyvinyl alcohol, polyvinyl acetate, polyallyl melamine and copolymers thereof with other ethylenically unsaturated monomers; epoxide polymers; polyacetals; polyurethanes and polyureas; polycarbamates; polysulphones; polyamides and copolyamides; polyesters; cross-linked polymers, derived from aldehydes and from phenols, from ureas or from melamines; alkyd resins; unsaturated polyester resins; natural polymers, such as cellulose, rubber, proteins or chemically modified analogues thereof (e.g., cellulose acetate), etc. The proportion of 4-hydroxy-methyl-piperidine of formula (I) necessary to effectively stabilize the polymers depends on various factors, such as the type and properties of the polymer, the use for which it is intended, the simultaneous presence of other stabilizers. Generally, suitable amounts range from 0.01 to 5% by weight of stabilizer, based on the polymer. In particular, the preferred amount ranges from 0.02 to 1% for the polymers of olefins, dienes and styrene, from 0.02 to 0.5% for the polymers of vinyl and vinylidene halides, from 0.02 to 2% for polyurethanes and polyamides. Optionally, two or more stabilizers having general formula (I) can be utilized. The derivatives of 4-hydroxymethyl piperidine of formula (I) utilized as stabilizers in the polymeric compositions according to this invention can be easily incorporated into the polymers to be stabilized, according to conventional operating methods, e.g., the stabilizers can be mixed with the polymer in the form of a dry powder, or a stabilizer solution or suspension or emulsion can be admixed with a polymer solution or suspension or emulsion. The derivatives of the alkyl-substituted 4-hydroxymethyl-piperidine of formula (I) can be employed either alone or in admixture with other known additives such as antioxidants, UV-ray absorbers, pigments, fillers, basic nitrogen containing polycondensates, stabilizers and the like. Examples of such additives are oxybenzotriazoles, oxobenzophenones, Ni stabilizers, metal soaps, phenolic antioxidants, phosphites, phosphinites, thioesters, hydroquinone derivatives, triazinic compounds, acylamino-phenols, benzyl-phosphates, sterically hindered phenols, such as 4,4'-bis-butylidene-bis-(2-6-di-tert-butyl-phenol); triazino-phenol compounds, etc. Such additives can be utilized along with the compounds having formula (I), according to the present invention, in a weight ratio ranging from 0.5:1 to 3:1. For a better understanding of the present invention and as aid for practicing the same, a few illustrative preferred examples are given in the following. In the examples, all parts refer to the weight, unless otherwise specified. EXAMPLE 1 (Reference example) Preparation of 2,2,6,6-tetramethyl-4-hydroxymethyl-piperidine 134.4 g of 2,2,6,6-tetramethyl piperidyl-4-spirooxirane (0.8 moles) in 500 ml of ethanol and 15 g of Ni/Raney were placed in a steel autoclave equipped with a magnetic stirrer. Hydrogen was introduced up to a pressure of 5 MPa (50 atm) and the temperature was brought to 120°C. The reaction mixture was maintained at the indicated temperature for 6 hours, then it was cooled down, the catalyst was filtered off, the solvent was evaporated and the residue was placed in an oven under vacuum at 100°C/0.13 kPa (1 mm Hg) of residual pressure. There were obtained 125 g of product having a melting point of 172-174°C and a gas-chromatographic purity (on a Supelco ® column SP 1000) higher than 99%. The yield was 91.4%. The desired product was characterized by N.M.R. and I.R. analyses. EXAMPLE 2 Preparation of bis (2,2,6,6-tetramethyl)-4-methyl-piperidine adipate (compounds No. 79) Into a flask there were introduced 20.5 g of 2,2,6,6-tetramethyl-4-hydroxymethyl piperidine of Example 1 (0.12 moles), 10.45 of methyl adipate (0.06 moles) and 0.5 g of LiOH in 100 ml of xylene. The temperature inside the flask was brought to 140°C and at the top of a rectification column the methyl alcohol resulting from the reaction distilled. Once the theoretical amount of alcohol had been distilled, the whole mixture was brought to dryness by distilling xylene under vacuum. CH₂Cl₂ and water were added to the residue and the resulting organic layer was separated from the aqueous layer. The dried organic layer was evaporated from the solvent and the residue was diluted again with hot acetone. There were obtained 25 g of title product having a M.P. of 97-98°C, which product was identified by means of N.M.R. and I.R. EXAMPLES 3 TO 12 By operating under the same conditions as described in Example 2, the following products were prepared: EXAMPLE 13 Preparation of 1-(2-stearoyloxyethyl)-2,2,6,6-tetramethyl-4-methyl piperidine stearate (compound No. 43) 9.8 g of 1-(2-hydroxyethyl)-2,2,6,6-tetramethyl-4-hydroxymethyl piperidine (0.045 mole) were added to 28.7 g of methyl stearate (0.09 mole) in the presence of 0.5 g of LiOH. The mixture was heated to 140°C in a nitrogen atmosphere and was maintained under stirring until the formation of the resulting methyl alcohol was complete. The reaction mass was diluted again with CH₂Cl₂ and washed with H₂O. After removal of solvent from the organic layer, the residue was crystallized from acetone. 29 g of product having a melting point of 50-52°C were obtained. The product was identified by its I.R. and N.M.R. spectra. EXAMPLE 14 By operating according to Example 13, [1-(2-palmitoxyethyl)-2,2,6,6-tetramethyl] piperidine palmitate (compound No. 45) was prepared. The product was liquid. EXAMPLE 15 Preparation of mono-(1,2,2,6,6-pentamethyl-4-methyl piperidine succinate) (compound No. 90) 62 g of 1,2,2,6,6-pentamethyl-4-hydroxymethyl piperidine (0.335 mole) and 33.5 g of succinic anhydride (0.335 mole) were dissolved in 300 ml of benzene and the solution was brought to the reflux temperature of the solvent. After half an hour, the reaction mixture was cooled down and the precipitate was filtered, yielding 85 g of title compound having a M.P. of 186-189°C. EXAMPLES 16 AND 17 By operating according to the procedure of Example 15, there were prepared mono-(1,2,2,6,6-pentamethyl)-4-methyl piperidine-3,4,5,6-tetrahydrophthalate, having a M.P. of 182-185°C (compound No. 91); and mono-(2,2,6,6-tetramethyl)-4-methyl piperidine maleate, having a M.P. of 245-248°C (compound No. 92). EXAMPLE 18 Preparation of nickel di-[mono (1,2,2,6,6-pentamethyl)-4-methyl piperidine succinate] (compound No. 98) 14.27 g of compound No. 90 of Example 15 (0.05 mole) were dissolved in 50 ml of methanol. To the resulting solution there were added 2.8 g of KOH (0.05 mole) and, dropwise within half an hour, 5.94 g of NiCl₂.6H₂O, dissolved in 20 ml of methanol. After completion of the addition the temperature was raised to solvent reflux for 2 hours. The mixture was then cooled down and the KCl which had formed was filtered. The solvent was evaporated and the residue was diluted with benzene. The insoluble portion was filtered and the solution was evaporated to dryness. The residual green solid product had a M.P. of 149-154°C and, subjected to elemental analysis, revealed a Ni content of 9.4% (theoretical value = 9.36% for the desired product). EXAMPLE 19 By operating under the same conditions as in Example 18, nickel di-[3,4,5,6-tetrahydrophthalate of mono-(1,2,2,6,6-pentamethyl)-4-methyl piperidine] (compound No. 93) was prepared, which was a green solid having a M.P. of 154-157°C. EXAMPLE 20 Preparation of bis-[(1,2,2,6,6-pentamethyl)-4-methyl piperidine] hexamethylene di-carbamate (compound No. 108) Into a flask there were introduced 19.8 g (0.107 mole) of 1,2,2,6,6-pentamethyl-piperidyl-4-spiro-oxirane in 100 ml of ethyl acetate, and to the solution there were added under stirring 9 g (0.0535 mole) of hexamethylene diisocyanate dissolved in 50 ml of ethyl acetate. Stirring was continued for 4 hours while raising the temperature up to solvent reflux. The solvent was evaporated under vacuum and the residue was diluted with acetonitrile. Thus the solid title compound having a melting point of 48 to 50°C was obtained. EXAMPLE 21 Preparation of (compound No. 117). 23 g of 1,2,2,6,6-pentamethyl-piperidyl-4-spiro-oxirane (0.126 mole) were reacted with 12.9 g of 1-(2-hydroxyethyl)-2,2,6,6-tetramethyl-4-hydroxymethyl piperidine (0.06 mole) at 140°C for 3 hours in the presence of 0.5 g of KOH. The reaction mass was then diluted with CH₂Cl₂ and washed with water. From the dried organic layer the solvent was evaporated and the residue was diluted with acetone. There were obtained 30 g of title product having a M.P. of 124-126°C. EXAMPLE 22 By operating as in Example 21, [(2,2,6,6-tetramethyl-4-hydroxy)-4-piperidinemethoxy] (2,2,6,6-tetramethyl)-4-methyl piperidine of formula was prepared (compound No. 69). White solid having a melting point of 65-67°C. EXAMPLE 23 Preparation of 1,6-bis-[(2,2,6,6-tetramethyl)-4-piperidinemethoxy]hexane (compound No. 113) 34.2 g (0.2 mole) of the compound of Example 1 were dissolved in 200 ml of xylene. Under stirring, 4.6 g of sodium metal (0.2 g.a.) were gradually added to the solution. Successively, there were dropwise added to the solution 33.8 g of di-iodohexane (0.1 mole). The mixture was heated to solvent reflux which was maintained for 8 hours. Water was added and from the organic layer, after separation and drying, the solvent was evaporated. The residue was crystallized from acetone. 32 g of the title compound, a solid product having a melting point of 69-70°C, were obtained. EXAMPLE 24 By operating under the conditions described in Example 23, 1,4-bis [(2,2,6,6-tetramethyl)-4-piperidine methoxy] butane (compound No. 111) was prepared. The product obtained was solid and had a M.P. of 68-69°C. EXAMPLE 25 Preparation of 3,9-bis-[(2,2,6,6,-tetramethyl)-4-methoxy piperidine]-2,4,8,10-tetraoxa-3,9-di-phospha-spiro-[5,5]undecane (compound No. 133) 18.52 g of the compound of Example 1 (0.1083 mole) were dissolved in 150 ml of xylene. To the resulting solution there were gradually added, under stirring, 2.55 g of sodium metal (0.11 g.a.) and, successively, 13.25 g of 3,9-di-chloro (2,4,8,10-tetraoxa-3,9-diphospha)spiro[5,5]undecane (0.05 mole). The mixture was heated to solvent reflux for 8 hours. Thereafter water was added and the organic layer was separated and dried and the solvent was evaporated. The residue was diluted with hexane and was crystallized. 20 g of title compound having a melting point of 99-101°C were obtained. EXAMPLE 26 Stabilization tests To 300 g of non-stabilized polypropylene having an instrinsic viscosity, measured at 130°C in tetralin, of 162 ml/g, a residue of 96.5% after extraction with heptane and an ash content of 80 ppm, there were added 200 ml of chloroform containing, dissolved therein, one of the compounds reported in the table below. The amount of added compound was 0.5% by weight, based on polypropylene. The mixture was stirred for about 6 hours at room temperature in a rotary evaporator, then it was dried at 50°C/1.3 Pa (0.01 mm Hg) for 1 hour. The resulting stabilized powder was extruded in a Brabender extruder at 220°C and granulated. The granules were transformed to films having a uniform thickness of 50-60 µm. On the films thus obtained there was determined the photo-oxidative stability, defined as the time required to obtain rupture of the film, by one bending by 180°, after exposure to Zenotest 1200 under the following conditions: black panel temperature: 43 ± 2°C relative humidity: 50 ± 5% alternate exposure. The obtained results were:

Claims: Derivatives of alkyl-substituted 4-hydroxy-methyl piperidine having general formula: wherein: R₁, R₂, R₃ and R₄, the same or different, are each an alkyl group containing from 1 to 6 carbon atoms; or R₁ and R₂ and/or R₃ and R₄, together with the carbon atoms to which they are bound, represent a cycloalkyl group or a group of formula: in which R₆, R₇, R₈ and R₉, the same or different, represent a hydrogen atom or an alkyl group containing 1 to 6 carbon atoms and R₅ has the meaning defined below; R₅ represents a hydrogen atom, an alkyl group, an alkenyl group, an alkoxyalkyl group, an aralkyl group optionally carrying one or more substituents on the aryl radical, a 2,3-epoxypropyl group, a group of formula -CH₂-COOR₁₀ in which R₁₀ is an alkyl group, an alkenyl group, a phenyl group, an aralkyl group or a cyclohexyl group; an aliphatic acyl group or a group of formula -COOR₁₃ in which R₁₃ is an alkyl group, a benzyl group or a phenyl group; a group of formula: in which R₁₁ is a hydrogen atom, a methyl group, an ethyl group or a phenyl group and R₁₂ is a hydrogen atom, an alkyl-substituted piperidyl group optionally also having a hydroxy group on the ring, an acyl group or a group of formula: in which Z and Z', the same or different, represent hydrogen, -NR₁₄R₁₅, -O-R₁₆ or -S-R₁₇ in which R₁₄, R₁₅, R₁₆ and R₁₇ may be hydrogen, an alkyl radical containing 1 to 18 carbon atoms or an alkyl-substituted piperidyl group of formula: or R₁₄ and R₁₅ together with the N atom form a ring which may optionally contain other heteroatoms; Y represents an organic or inorganic group or atom, except hydrogen, having a valence ranging from 1 to 4, which does not adversely affect the polymer-stabilization activity; and n is an integer ranging from 1 to 4, depending on the valence of Y. Derivatives of alkyl-substituted 4-hydroxy-methyl piperidine according to claim 1, in which each of R₁, R₂, R₃ and R₄ is an alkyl group containing from 1 to 4 carbon atoms. Derivatives of alkyl-substituted 4-hydroxy-methyl piperidine according to claim 1, in which R₁ and R₂ and/or R₃ and R₄, together with the carbon atoms to which they are bound, represent a cycloalkyl group containing from 5 to 7 carbon atoms, or a group of formula: Derivatives of alkyl-substituted 4-hydroxy-methyl piperidine according to one or more of the claims 1-3, in which R₅ is selected from the following groups: alkyl containing 1 to 4 carbon atoms; alkenyl containing 3 to 6 carbon atoms; alkoxy-alkyl containing 1 to 3 carbon atoms in the alkyl chain and 1 to 18 carbon atoms in the alkoxy chain; aralkyl containing 7 or 8 carbon atoms, optionally substituted in the aryl radical by up to 3 substituents selected from chlorine atoms, alkyl groups containing 1 to 4 carbon atoms, alkoxy groups containing 1 to 8 carbon atoms and hydroxy groups; a group of formula -CH₂COOR₁₀ in which R₁₀ is an alkyl group containing 1 to 18 carbon atoms, an alkenyl group containing 3 to 6 carbon atoms, phenyl, an aralkyl group containing 7 or 8 carbon atoms or a cyclohexyl group; a group of formula -COOR₁₃ in which R₁₃ represents an alkyl group, e.g. containing 1 to 8 carbon atoms, a benzyl group or a phenyl group; and a group of formula in which R₁₁ is hydrogen, methyl or phenyl and R₁₂ is a hydrogen atom, a group of formula in which Z and Z' , the same or different, represent hydrogen, -MR₁₄R₁₅, -O-R₁₆ or -S-R₁₇ in which R₁₄, R₁₅, R₁₆ and R₁₇ may be hydrogen, an alkyl radical containing 1 to 18 carbon atoms or an alkyl-substituted piperidyl group of formula: or R₁₄ and R₁₅ together with the N atom form a ring which optionally contains other heteroatoms, e.g. or R₁₂ represents an acyl group-COR₁₈ in which R₁₈ represents an alkyl group containing 1 to 18 carbon atoms, an alkenyl group with 2 to 4 carbon atoms; a phenyl group optionally substituted by up to 3 substituents, the same or different from one another and selected from chlorine, alkyl with 1 to 4 carbon atoms, alkoxy with 1 to 8 carbon atoms and hydroxy; an aralkyl group with 7 or 8 carbon atoms the aryl radical of which may optionally be substituted by up to 3 substituents, the same or different from one another and selected from chlorine, alkyl with 1 to 4 carbon atoms, alkoxy with 1 to 8 carbon atoms and hydroxy; a styryl group, or a cyclohexyl group. Derivatives of alkyl-substituted 4-hydroxy-methyl piperidine according to one or more of the claims 1-4, in which Y is a hydrocarbon radical, a substituted hydrocarbon radical, a radical derived from an organic or inorganic acid, a heterocyclic group, a group comprising a phosphorus atom, a boron atom or a silicon atom. Derivatives of alkyl-substituted 4-hydroxy-methyl piperidine according to claim 5, in which Y represents: when n = 1 an aliphatic, acyl-aliphatic, arylaliphatic, alicyclic, aromatic or heterocyclic group and preferably an acyl group containing up to 18 carbon atoms and, particularly, a group of formula -COR₁₉ in which R₁₉ represents a hydrogen atom, an alkyl group with 1 to 17 carbon atoms; an alkenyl group with 2 to 5 carbon atoms; an alkynyl group with 2 or 3 carbon atoms; a phenyl group, optionally substituted with up to 3 substituents, the same or different from each other and selected from chlorine, alkyl with 1 to 4 carbon atoms, alkoxy with 1 to 8 carbon atoms, hydroxy or nitro; a naphthyl group; a styryl group; an aralkyl group with 7 or 8 carbon atoms, optionally substituted with up to 3 identical or different substituents selected from chlorine, alkyl with 1 to 4 carbon atoms, alkoxy with 1 to 8 carbon atoms or hydroxy; a phenoxymethyl group, a cyclohexyl group, a 2-pyridyl group; a 3-pyridyl group; a 4-pyridyl group; a 2-furyl group; a group of formula -CO-R₂₀-COOH, in which R₂₀ represents an alkylene group, preferably containing 1 to 10 carbon atoms, the chain of which can be interrupted by an oxygen or sulphur atom; or a metal salt thereof, in which the metal is selected from barium, nickel, manganese, calcium, zinc, iron, sodium, cobalt and tin; or a C₁₋₄-alkyl ester thereof; a radical resulting from the removal of a hydroxy group of a phosphorus acid, preferably phosphoric acid, phosphonic acid or phosphorous acid, either simple or substituted and selected from, e.g., a group of formula: in which R₂₁ represents hydrogen, an alkyl group containing 1 to 4 carbon atoms, an aralkyl group containing 7 or 8 carbon atoms or a phenyl group; and R₂₂ represents an alkyl group containing 1 to 18 carbon atoms, an aryl group containing from 6 to 10 carbon atoms, optionally substituted by one or more chlorine atoms and/or alkyl groups with 1 to 4 carbon atoms, an aralkyl group containing 7 or 8 carbon atoms or a cyclohexyl group; or R₂₁ and R₂₂, together and with the nitrogen atom to which they are bound, form a piperidinyl group, a 1-pyrrolidinyl group or a morpholinyl group; an alkyl group containing 1 to 18 carbon atoms; an alkenyl group containing 3 to 6 carbon atoms; an aralkyl group with 7 to 9 carbon atoms, optionally carrying up to 3 substituents in the aryl radical, said substituents being selected from alkyl with 1 to 4 carbon atoms and/or hydroxy; a cyclohexyl group; or a group of formula: in which R₂₃ represents a hydrogen atom, a C₁₋₆-alkyl group, particularly methyl, or a phenyl group and R₂₄ represents an alkyl group containing 1 to 8 carbon atoms; when n = 2 an aliphatic, araliphatic, aromatic, alicyclic or heterocyclic diacyl group containing up to 22 carbon atoms; phenylene; cyclohexylene; 2,4-pyridindiyl;2,5-pyridindiyl, or thiophendiyl; a carbonyl group; a group obtained by removing two hydroxyl groups of an acid containing phosphorus, preferably having the formula: in which R₂₆ represents a hydrogen atom, an alkyl group with 1 to 4 carbon atoms, a phenyl or benzyl group, optionally substituted; a group of formula: a group of formula: in which R₂₁ has the same meaning as defined above and R₂₇ represents an alkylene group containing 2 to 10 carbon atoms, an optionally substituted arylene group having 6 to 10 carbon atoms, a xylylene group, a cyclohexylene group; a group of formula: in which R₂₈ may be an oxygen atom or an alkylene group containing 1 to 4 carbon atoms; a group of formula: in which R₂₉ may be a hydrogen atom or a methyl group; a group of formula: a group of formula: an alkylene group containing up to 10 carbon atoms; an alkenylene group containing from 4 to 10 carbon atoms or a xylylene group; when n = 3 when n = 4 Derivatives of alkyl-substituted 4-hydroxy-methyl piperidine according to claim 1, having general formula: in which R₅ represents a hydrogen atom, a methyl group, a benzyl group, a 2,3-epoxypropyl group or a group of formula -CH₂-CH₂-O-R₁₂ in which R₁₂ is hydrogen or an alkyl group with 2 to 18 carbon atoms or a benzoyl group; n = 1, 2 or 3; and when n = 1 Y represents a group of formula -CO-R₁₉ in which R₁₉ represents an alkyl group with 1 to 17 carbon atoms, phenyl, optionally substituted by up to 3 alkyl radicals containing 1 to 4 carbon atoms and/or hydroxy or 4-hydroxy-3,5-di-tert-butyl-phenethyl; or a group of formula -CO-NH-R₂₂ in which R₂₂ represents an alkyl group with 1 to 18 carbon atoms, phenyl or cyclohexyl; when n = 2 Y represents a group of formula -CO-(R₂₅) m -CO- in which m is 0 or 1 and R₂₅ represents an alkylene group with 1 to 10 carbon atoms, the group -CH₂-CH₂-S-CH₂-CH₂- or a phenylene group; a group of formula -CO-NH-R₂₇-NH-CO-, in which R₂₇ represents hexamethylene, 2,4-toluylene or methylene-di-p-phenylene; when n = 3 Y represents Derivatives of alkyl-substituted 4-hydroxy-methyl piperidine according to claim 7, in which in general formula (II) n = 1 and Y represents a group of formula -CO-R₁₉; or n = 2 and Y represents a group of formula -CO-R₂₅-CO-, with R₁₉ and R₂₅ having the same meanings as defined above. Use of the derivatives according to claim 1 as stabilizers for polymers. Polymeric compositions stabilized against photo-and thermal degradation, containing a stabilizer according to any one of the claims 1-8. Stabilized polymeric compositions according to claim 10 in which the stabilizer having general formula (I) is present in an amount of from 0.01 to 5% by weight, based on the polymer. Stabilized polymeric compositions according to any one of claims 10 and 11, in which the polymeric substance is a polymer derived from olefins or dienes; a styrene polymer; a halogenated vinyl or vinylidene polymer; a polymer derived from α,β-unsaturated acids; a polyurethane or a polyamide. Stabilized polymeric compositions according to one or more of the claims 10-12, in which the derivative of general formula (I) is utilized in combination with other conventionally used stabilizing additives, e.g. selected from anti-oxidants, ultraviolet-ray absorbers, pigments, fillers, basic nitrogen-containing polycondensates, different and similar stabilizers. Stabilized polymeric compositions according to claim 13, in which the other additives are employed together with the derivative of general formula (I) in a weight ratio of from 0.5:1 to 3:1. Derivatives according to claim 6, in which n in formula (I) is 1 and Y is an acyl group containing up to 18 carbon atoms. Derivatives according to claim 6 in which in formula (I) n is 2 and Y is a group of formula -CO(R₂₅) m -CO- in which m is O or 1 and R₂₅ is a linear or branched alkylene radical containing up to 20 carbon atoms which may contain an alkylbenzyl or hydroxyalkyl benzyl group and may be interrupted by an oxygen or sulfur atom.

Inventors: DI BATTISTA, PIERO, NUCIDA, GILBERTO
Applicants: AUSIMONT S.R.L.
Application year: 1985
Main classification: C07D211
IPC codes: C08L1, C08K5, C08L101, C08L27, C07D211, C08L67, C08L21, C07F9, C08L33, C08L77, C08L7, C08L23