A PROCESS FOR PREPARING THERMICALLY STABLE OLEFINIC POLYMERS

Abstract: Olefinic polymers thermically stable are obtained by addition during polymerization of compounds of monomeric or oligomeric type, containing in the molecule one or more steric hindered piperidinic groups having formula: wherein R₁, R₂ = C₁-C₄ alkyl radicals or rings of tetramethylpiper­ idine or together they form with the piperidinic carbon atom they are bound to a C₅-C₁₀ cycloalkylic group. R₃, R₄ = C₁-C₁₈ alkyl groups or together they form with the carbon atom they are bound to a C₅-C₁₀ cyclo-alkylic group. R₅÷R₉, Z=H or an organic radical preferably a C₁-C₁₈ alkyl, C₃-C₁₂ alkenyl, C₇-C₁₈ aralkyl radical.

Description: The present invention relates to a process for carrying out the thermal stabilization of olefinic polymers and, in particular, of polypropylene, polyethylene and elastomeric copolymers of propylene with ethylene optionally containing diene monomers, directly in polymerization phase. Attempts in this way have been made in the past, using the most usual thermal stabilizing agents. According to U.S. patent 3.477.991 alkylphenols are added to the polymerization mixture, carried out by means of TiCl₃ and Al-alkyls, to achieve a polymer already thermically stabilized. According to European patent application 3836, the stabilization of polyethylene, produced by means of chromium catalysts, is obtained by addition during polymerization of antioxidizers of phenolic type. The direct stabilization during polymerization is of particular interest in the case of the recent processes for the production of polyolefines by means of high yield catalysts which can be marketed without granulation, and therefore they cannot be stabilized by means of the usual methods that just foresee a granulation stage. The use of compounds of phenolic type in the propylene polymerization by means of supported stereospecific catalysts does not lead, however, to satisfactory results as either it has a negative influence on the catalyst performances and causes a yellowing of the polymer or it gives rise to undesired effects on the polymer morphology. The yellowing due to some phenolic compunds occurs also when the product is dried from the slurry at the end of the polymerization. Now the applicant has found surprisingly that olefinic polymers, for instance polypropylene, polyethylene,and elastomeric copolymers propylene/ethylene/(diene), can be obtained already in the stabilized state, without incurring the typical drawbacks caused by the phenolic compounds by using as stabilizing agents (to be added, either at the start or during or in the final phase of the polymerization, to the polymerization slurry, before the monomer separation), one or more compounds containing in the molecule one or more steric hindered piperidinic groups having the following general formula wherein: R₁,R₂ may be alkyl radicals containing from 1 to 4 carbon atoms, or rings of 2,2,6,6-tetramethylpiperidine or together they can form with the piperidinic carbon atom they are bound to a cycloalkyl group containing from 5 to 10 carbon atoms. R₃,R₄= alkyl radicals containing from 1 to 18 carbon atoms or together they form with the piperidinic carbon atom they are bound to a cycloalkylic group containing from 5 to 10 carbon atoms, R₅.R₆,R₇,R₈,R₉,Z = hydrogen or an organic radical preferably a C₁-C₁₈ alkyl, C₃-C₁₂ alkenyl, C₇-C₁₈ aralkyl radical. Compounds containing in the molecule groups having aforesaid formula (I) utilizable for the purpose of the present invention may be represented by the formulas (II) to (XXXI) specified below. They can be: (A) oligomeric products and/or (B) monomeric products containing in the molecule one or more piperidinic rings of the general formula (I), optionally substituted and bound to each other. n = a whole number ranging between 2 and 100, R₁, R₂, R₃, R₄, Z have the meaning as defined for structure (I), R₅, R₆, R₇, R₈, R₉ have the same meaning as in formula (I), A = a bivalent organic radical, preferably an alkylene radical containing from 1 to 12 carbon atoms or a group containing one or more ester or amidic function, W = a direct chemical bond or a bivalent organic radical, preferably a C₁ - C₁₂ alkylene radical, radical (wherein R = H or a C₁ - C₁₈ alkyl radical), or - O -, Y = a direct chemical bond or a bivalent organic radical of aliphatic, cycloaliphatic, aromatic or heterocyclic type, containing N or O, S, P atoms in the chain or in the heterocyclic ring. The compounds of formula (II) are known from US-A-4104248, wherein n, A, Y, R₁, R₂,R₃, R₄,R₅,R₆ , R₇, R₈, R₉ have the meanings as defined for structures (II) and (III). wherein : Z, R₁, R₂, R₃, R₄, R₅, R₆. R 7 , R₈ have the meaning indicated for structure (I), A has the same meaning as in formulas (II) and (III). The compounds of formula (III), (IV) and (V) are known from US-A-4233410. wherein: R₁, R₂, R₃, R₄ have the value assigned for formula (I), R = an alkyl, alkenyl or phenyl radical, n = a whole number ranging between 1 and 3, extremes included, and Z has the same meaning as in formula (I). The compounds of formula (VI) are known and can be prepared according to what is described in GB-A-1502557. wherein: R₁ = hydrogen or methyl radical Z = hydrogen or a C₁-C₁₂ alkyl; C₃-C₈ alkenyl; C₇-C₁₁ aralkyl; cyanomethyl or C₂-C₄ acyl radical R₃ = a C₁-C₁₈ alkylene; C₂-C₁₈ oxalkylene, C₂-C₈ alkenylene radical R₄ = a C₁-C₄ alkyl radical. Compounds of this formula are described in US-A-4461898. Among the compounds utilizable for the purpose of the present invention those products are also comprised in whose molecule rings of 1,3,5-triazine and substituted piperidinic rings are contemporaneously present and optionally the products containing in the molecule one or more unsaturated chains of olephinic type as well. Among them compounds are comprised that may be represented with the following general formulas: wherein: Q = a bivalent organic group, for instance an alkylene, phenylene group or group having formula R₁ = a substitued piperidylaminic group R = H, a C₁-C₁₈ alkyl radical; or a monovalent organic radical, for instance a substituted piperidinic group. y = 1 or zero x,m = 1,2 or 3 n = 2 or 3 Compound of such general formula are described for instance in US-A-4.433.145. wherein: R = a C₁-C₈ alkylene radical. Compounds of general formula (IX) are described for instance in European patent application No.101.411. wherein: R = a C₃-C₆ oxyalkenyl, or a C₃₋C₆ aminoalkenyl or di-(C₃-C₆ alkelyl) amino group; R₂ = H, a C₁-C₈ alkyl or benzil radical; R₃, R₄, independently, may be a C₁-C₈ alkyl, benzil or phenyl-ethyl radical; or they form together with the carbon atom they are bound to a C₅-C₁₀ cycloalkyl group; Z = H, a C₂-C₃ hydroxyalkyl, C₁-C₈ alkyl or hydroxyl radical; Q = -O-, or group; R₆ = H, or a C₁-C₁₈ alkyl or group; Y and Y' equal or different, may be -O-, or group X = a C₂-C₁₂ alkylene radical wherein the alkylenic chain may be interrupted by a Q group, as defined hereinbefore or by a thio group, or X may be a C₅-C₁₀ cycloalkylenic, or C₆-C₁₂ arylenic or C₈-C₁₄ aralkylenic group. Compounds having formula (X) are described in U.S.patent No. 4435555. wherein: R₁, R₃, R₄, R₆ equal to or different from each other, may be hydrogen or a C₁-C₁₂ alkyl; C₂-C₆ hydroxyalkyl; C₃-C₁₂ alkenyl ; C₅-C₁₂ cycloalkenyl; C₆-C₁₂ substituted or non-substituted aryl; C₇-C₁₂ substituted or non-substituted aralkyl group; R₂, R₅ equal or different, may be: a C₂-C₁₂ alkylene, C₄-C₁₂ iminodialkylene or oxadialkylene; C₅-C₁₂ cycloalkelyne; C₆-C₁₂ arylene; C₇-C₁₂ aralkylene radical; X is >O, >S, >N-R7, in which R7 is hydrogen, C₁-C₁₈-alkyl, C₃-C₁₈-alkenyl, C₅-C₁₈-cycloalkyl, substituted or unsubstituted C₆-C₁₈-aryl, substituted or unsubstituted C₇-C₁₈-aralkyl, an -R₈-Y radical, in which R₈ is C₂-C₆-alkylene and Y is-O-R₉ or R₉ being hydrogen or C₁-C₁₈-alkyl and R₁₀ and R₁₁, which may be identical or different, being C₁-C₆-alkyl, 2,2,6,6-tetramethyl-piperid-4-yl or 1,2,2,6,6-pentamethylpirid-4-yl, or R₇ is a radical of the formula (II) in which n is zero or 1, r is zero, 1, 2 or 3, R₁₂ is hydrogen, C₁-C₁₂-alkyl, C₃-C₁₂-alkenyl or -alkynyl, substituted or unsubstituted C₇-C₁₂-aralkyl, C₁-C₁₂-acyl, 2,3-epoxypropyl or in which R₁₃ is hydrogen, methyl, ethyl or phenyl and R₁₄ is hydrogen, C₁-C₁₂-alkyl, C₃-C₁₂-alkenyl, C₇-C₁₂-aralkyl or C₁-C₁₂-acyl, or R₇ is a radical of the formula (III) in which R₁₅ is hydrogen, C₁-C₈-alkoxy, C₃-C₈-alkenyloxy or benzyloxy and R₁₃ is as defined above; n = zero or 1 r = zero or 1,2 or 3. The compounds of formula (XI) are described , for instance, in US-A-4.442.250. W = a C₁-C₂₀ alkoxyl, or group; R, R₁ = equal or different, may be hydrogen or a C₁-C₁₈ alkyl radical; R₂ = hydrogen, a C₁-C₁₈ alkyl or benzyl radical; R₃, R₄, equal or different, are a C₁-C₁₈ alkyl, benzyl, phenylethyl radical , or they form with the carbon atom they are bound to, a C₅-C₁₀ cycloalkyl group; Z = hydrogen or a C₂-C₃ hydroxyalkyl, C₁-C₁₈ alkyl, hydroxyl radical; Q = a C₂-C₂₀ linear or branched alkylene, C₅-C₁₀ cycloalkylene, C₆-C₁₂ arylene, C₈-C₁₄ aralkylene radical; Y = hydrogen or a C₁-C₂₀ alkyl group, or a group of formula: X = halo, C₁-C₈ alkylamino, di(C₁-C₈) alkylamino, pyrrolidyl, or morpholino n = a whole number comprised between 1 and 3, extremes included, m = a whole number greater than 1. Such compounds are described in US-A-4386177. wherein: R₁, R₂, R₃, R₄, R₅ equal or different, may be: a C₁-C₁₈ alkyl; C₅-C₁₂ cycloalkyl; C₇-C₁₄ aralkyl radical; or a group having formula (XIV): or a radical having formula or formula R₆ = hydrogen or a C₁-C₅ alkyl radical R₇,R₈, equal or different, a hydrogen or a C₁-C₁₈ alkyl, C₅-C₁₂ cycloalkyl; C₇-C₁₄ phenylalkyl radical; m and n , equal or different, are whole numbers ranging between 2 and 6; p = a whole number ranging between 0 and 3, extremes included; X = a radical having formula: wherein R₁₀ and R₁₁, equal or different, are hydrogen or a C₁-C₁₈ alkyl radical, optionally substituted by hydroxyl, alkoxyl, C₁-C₄ dialkylamino groups, or they are C₅-C₁₂ cycloalkyl groups, or phenyl groups, substituted by C₁-C₁₈ alkyl radicals; R₉ = hydrogen, or a C₁-C₁₈ alkyl, C₅-C₁₂ cycloalkyl, C₇-C₁₄ aralkyl group or a group having formula (XIV). The compounds of such formula (XIII) are described in US-A-4376836. wherein: Z = hydrogen, or a C₁-C₁₈ alkyl; C₃-C₁₂ alkenyl; C₃-C₅ alkynyl; C₃-C₁₈ alkoxyalkyl group; C₂-C₄ hydroxyalkyl group, optionally substituted by phenyl or phenoxy groups; a C₇-C₁₈ aralkyl group; R₄ = hydrogen or methyl radical R₂ = hydrogen, or cyano, phenylic, azidic, hydrazidic group or -OR₅, -SR₅, group R₅ = hydrogen, or a C₁-C₁₈ alkyl, C₃-C₁₂ alkenyl, C₃-C₁₈ alkoxyalkyl, C₅-C₁₂ cycloalkyl, C₇-C₁₈ aralkyl, C₆-C₁₀ aryl group; R₆, R₇, equal or different, may be hydrogen, a C₁-C₂₃ alkyl, C₃-C₁₈ alkenyl, C₃-C₅ alkynyl, C₂-C₄ hydroxyalkyl, C₂-C₅ cyanoalkyl, C₅-C₁₂ cycloalkyl, C₇-C₁₈ aralkyl, C₆₋C₁₆ aryl group; R₁ = hydrogen, or a C₁-C₂₃ alkyl, C₃-C₁₂ cycloalkyl, C₇₋C₁₈ aralkyl, C₆-C₁₀ aryl group; X = a C₂-C₆ alkylene group Q = hydrogen, or a C₁-C₂₄ aryl group or group having formula: P = a halogen atom, or group, or hydroxyl, or a -OMe group, wherein Me is an alkaline or alkaline-earth metal having valence 1 or 2, or or group wherein: R₈ = Q, or C₁-C₂₃ alkyl, C₃-C₁₂ cycloalkyl, C₇-C₁₈ aralkyl, the aryl group being in particular a C₆-C₁₀ aryl group, Y = -O-, or -S-, or m = a whole number between 0 and 4, extremes included n = a whole number between 1 and 3, extremes included p = a whole number between 0 and 3, extremes included q = 0, 1 or 2 r = 0,1, 2 or 3 whereas the sum r + q cannot be over value 3. The compounds of formula (XV) are described in US-A- 4315859. wherein: Z = hydrogen, a C₁-C₁₂ alkyl, C₃-C₇ alkenyl, C₇-C₁₁ phenylalkyl- cyanomethyl, C₂-C₁₈ alkanoil, C₃-C₁₈ alkenoyl, -CON(R)₂(R₃) or -CH₂-CH(R₄)-OH group; R₂ = a C₁-C₁₂ alkyl, allyl, cyclohexyl, benzyl, phenyl, or a C₇-C₁₂ alkylphenylradical; R₃ = hydrogen, a C₁-C₁₂ alkyl, allyl or benzyl radical; R₂ and R₃, together with the nitrogen atom they are bound to, may form a heterocyclic ring having 5-6 members; R₄ = hydrogen, a C₁-C₁₂ alkyl, phenyl, C₂-C₁₃ alkoxymethyl or phenoxymethyl radical; X = a bivalent group having formula -O-; -N(R₅)-; -NH-(CH₂)₂-O-; -NH(CH₂)₃-O-; or -N(R₅)-R₇-N(R₆)-; R₅ = hydrogen, a C₁-C₁₂ alkyl, C₃-C₇ alkenyl, cyclohexyl, C₃-C₁₂ alkoxyalkyl, C₅-C₁₂ alkenoxyalkyl, C₄-C₁₂ dialkylaminoalkyl, benzyl radical, or -CH₂-CH(R₄)-OH group, or a group having formula or Y = a bivalent group having formula -O- or -NR₆- R₆ = hydrogen, a C₁-C₁₂ alkyl, C₃-C₇ alkenyl, cyclohexyl radical or a group -CH₂-CH(R₄)-OH or a group R₇ = a C₁₋C₁₂ alkylene, whose chain may be interrupted by 1,2 or 3 -O- or-N(R₆)- groups, or R₇ may be a C₆-C₁₄ cycloalkylene group or cycloalkylendialkylene group A and B, equal to or different from each other, may be: (a) group, wherein: R₈ = a C₁-C₁₂ alkyl, C₃-C₇ alkenyl, C₃-C₁₂ alkoxyalkyl, C₄-C₁₂ dialkylaminoalkyl, cyclohexyl, benzyl, phenyl, C₇-C₁₂ alkylphenyl radical; R₉ = a C₁-C₁₂ alkyl, C₃-C₇ alkenyl, C₅-C₈ cycloalkyl, C₃-C₁₂ alkoxyalkyl C₅-C₁₂ alkenoxyalkyl C₄-C₁₂ dialkylaminoalkyl radical, a -CH₂-CH(R₄)-OH group, a phenyl, C₇-C₁₂ alkylphenyl, C₇-C₁₁ phenylalkyl radical; R₁₀ = hydrogen, a C₁-C₁₂ alkyl, C₃-C₇ alkenyl, C₅-C₈ cycloalkyl, C₃-C₁₂ alkoxyalkyl, C₅-C₁₂ alkenoxyalkyl, C₄-C₁₂ dialkylaminoalkyl, C₂-C₁₂ alkanoyl, C₃-C₁₂ alkenoyl radical, a -CH₂-CH(R₄)-OH group, a C₇-C₁₁ phenylakkyl radical, or R₉ and R₁₀ together with the nitrogen atom they are bound to, form a heterocyclic ring with 5 or 6 members; or (b) a group having formula: with the general condition that at least one of the groups Z , R₂, R₃, R₄, R₅, R₆, R₈, R₉, R₁₀ represents an alkenyl or alkenoyl group. The compounds having general formula XVI are described in European patent application EP-A-0101411 wherein m = 2,3 or 4, Z = a radical having valence m, such as a C₂-C₁₂ alkylene, C₄-C₈ alkenylene, xylilene radical, -CH₂-CH(OH)-CH₂ group; or a -CH(OH)-CH₂-; group wherein X = a radical or -OOC-R₁₃-COO- radical wherein R₁₂ and R₁₃ are bivalent aliphatic, cycloaliphatic, aromatic or araliphatic radicals, K = a trivalent aliphatic or heterocyclic group; Y = a tetravalent aliphatic group; Q = a bivalent group having formula -O-, or -N(R₁₄)-, wherein R₁₄ = hydrogen, a C₁-C₁₂ alkyl, C₃-C₇ alkenyl, cyclohexyl, C₂-C₄ hydroxyalkyl, C₃-C₁₂ alkoxyalkyl, C₅-C₁₂ alkenoxyalkyl, C₄-C₁₂ dialkylaminoalkyl, benzyl radical. A and B have the meaning expressed in formula XVI, under the condition that the molecule contains at least an alkenyl or alkenoyl group wherein: n = a whole number ranging between 2 and 20, extremes included Y = a group having formula R₈-O- or (R₉) (R₁₀) N-, wherein R₈ and R₉ are C₃-C₇ alkenyl groups. W = a bivalent group having formula -O- or wherein R₁₆ = hydrogen, or a C₁-C₁₂ alkyl, C₃-C₇ alkenyl, cyclohexyl, benzyl radical, or a group having formula and wherein Z, R₇ and R₁₀ have the meaning expressed for formul XVI wherein: Z has the meaning expressed in formula XVI Q has the meaning expressed in formula XVII Y has the meaning expressed in formula XVIII R₁₇ is the radical, having valence p, of a polyol or of a polyamine p = 2,3 or 4. The compounds having formula XVII, XVIII, XIX are described in European patent application EP-A-0101411. wherein: -OR₅; -SR₅ group; or group. R₁ may be a C₁-C₁₈ alkyl; C₅-C₁₂ cycloalkyl; C₇-C₁₁ aralkyl radical; a C₃-C₁₂ alkyl radical, whose chain is interrupted by -O- or by -N(R₆)- groups; a C₂-C₆ carboxyalkyl, C₃-C₁₂ alkoxycarboxalkyl radical; or an -A-O-Q group, wherein A = methylene, ethylene or trimethylene, and Q = a phenyl radical, non-substituted or mono, bi or trisubstituted by C₁-C₄ alkyl radicals; or Q is a group having formula Z = hydrogen, a C₁-C₄ alkyl, benzyl, allyl, acetyl, acryloyl, oxyl radical, a -CH₂-CH(R₇)OH group or a or a -CH₂CN group. R₃, R₄ equal or different, are a C₁-C₁₈ alkyl; C₅-C₁₂ cycloalkyl; C₇-C₁₁ aralkyl radical; a C₃-C₁₂ alkyl radical, whose chain is interrupted by -O- or groups; C₂-C₄ hydroxyalkyl; C₃-C₁₅ acyloxyalkyl; C₂-C₆ carboxyalkyl; C₃-C₁₂ alkoxycarbonylalkyl groups and furthermore R₄ may be hydrogen, whereas R₃ and R₄ may form, with the nitrogen atom they are bound to, a heterocyclic ring. R₅ = a C₁-C₁₈ alkyl; C₃-C₁₂ alkenyl; C₅-C₁₂ cycloalkyl; C₇-C₁₁ aralkyl radical; a C₃-C₁₂ alkyl radical, whose chain is interrupted by an -O- or group. R₆ = a C₁-C₄ alkyl radical R₇ = a methyl, ethyl or phenyl radical The compounds of formula (XX) are described in European patent application EP-A-0107615. wherein: Z = hydrogen or methyl radical R₂ = hydrogen, a C₁-C₁₈ alkanoyl radical, or 3-(3,5-di-t. butyl-4-hydroxyphenyl) propionyle group n = 1 or 2, therefore: when n = 1: X = a C₁-C₁₈ alkyl, benzyl, -CH₂-CH₂-OR₂ group Y = hydrogen, or a group having formula or having formula whereas, when n = 2 X = a C₂-C₆ alkylene group, a xylilene group or a group having formula: wherein m = a whole number ranging between 1 and 4, extremes included, Q = a group having formula (XXIII) Y = hydrogen, or a group having formula XXII. The compounds of formula XXI are described in European patent application EP-A-0022080. Preferred compounds, comprised in general formula (II), fall within restricted formulas of the following type: wherein: n = a whole number ranging between 2 and 20 or radical wherein R₁ = an alkyl radical containing from 1 to 10 carbon atoms and preferably -C(CH₃)₂-CH₂-C(CH₃)₃ radical. wherein n = a whole number comprised between 2 and 20, included. Preferred compounds comprised in general formula (III) fall within the following restricted formulas: wherein n = a whole number comprised between 2 and 20, extremes included. wherein n = a whole number ranging between 2 and 20, extremes in cluded. Preferred compounds comprised in general formula (IV) present a formula of the following type: wherein n is a whole number comprised between 2 and 20, extremes included. Preferred compounds of formula (V) are comprised in the formulas of type: Preferred compounds of formula (VI) are comprised in the following formula of type: K = H or a halogen atom or a C₁-C₄ alkyl radical. Preferred compounds of general formula (VIII) present formulas of type: wherein: R₁ = hydrogen, or a C₁-C₁₈ alkyl radical, or a monovalent organic radical, for instance a substituted piperidinic group. R₂ = hydrogen, a C₁-C₁₈ alkyl radical or another monovalent organic radical, for instance: -(CH₂) n -Y (wherein n = a whole number comprised between 1 and 12, Y = a -OH or -OR group or a group, wherein R = a C₁-C₁₈ alkyl radical; R' = a C₁-C₂ alkyl radical. As mentioned above, the compounds belonging to classes A and B described herein before, may be used for the purposes of the present invention, by addition to the polymer slurry, before the drying of the same, or, and preferably, before or during the polymerization of the olefinic monomer or monomers, carried out by means of catalysts prepared by reaction of an Al-alkyl compound with a solid component selected from a product comprising a Titanium compound and a magnesium halide, and a product formed by a tetravalent titanium compound which is supported onto a trivalent titanium halide having a surface area greater than 50 m²/g. In particular said polymerization is carried out by means of stereospecific catalysts for the polymerization of alphaolefins and comprising the reaction product of an Al-alkyl compound with catalytic components comprising a Ti compound, in particular TiCl₄, and an electron-donor compound, supported on a Mg halide in the active form. Mg halide in the active form is characterized by a X-ray spectrum wherein the reflections of highest intensity, which appear in the halide spectrum of usual type are replaced by halos. Catalysts of such type are described in U.S. patents No. 4.107.413, 4.107.414, 4.226.741 and 4.298.718. Peculiar characteristics of the supported catalysts, endowed with higher stereospecifity and activity in the alpha-olefins polymerization is the one to be prepared with methods which lead to the formation of components comprising the Ti compound on magnesium halide, which do not contain or contain, only in small percentages, Ti compounds heat-extractable by means of hot heptane and of TiCl₄. The preparation of these catalysts is generally carried out under conditions in which the solid comprising the magnesium halide in the active form is reacted in suspension in the Ti compound; the excess of Ti compound is then removed by filtration at temperatures at which no Ti compound, extractable by means of hot heptane and of TiCl₄ at 80° C, remains on the solid; then the solid is washed repeatedly with hydrocarbonic solvents in order to remove any trace of soluble compound of Ti. According to other methods, Mg halide, electron-donor compound and Ti compound optionally in the presence of coadjuvant agents for the grinding are co-pulverized till magnesium halide is activated, namely till, in the x-ray spectrum of Mg halide, halos appeared in place of the lines of highest intensity appearing in the spectrum of magnesium halide of usual type. The solid is then subjected to a heat-treatment with a hydrocarbonic solution of a halogenated hydrocarbonic compound and the liquid phase is separated by heat-filtration in order to remove the soluble compounds. Finally the solid is further washed with an aliphatic hydrocarbon. Examples of these methods are described in European patent applications No. 004789 and No.0004791. According to another method described in U.S.patent No. 4.146.502, the solid catalytic component obtained by cogrinding both of a Mg halide and of an electron-donor compound and by subsequent treatment with an excess of TiCl₄ under heat is further treated in suspension in a halogenated hydro-carbonic solvent separated from the liquid phase and finally washed repeatedly with a hydrocarbonic solvent. By carrying out the addition of the aforesaid piperidinic compounds during the polymerization and in the case of a polymerization carried out in a discontinuous way, the stabilizing agent can be introduced into the reactor before or together with the components of the catalytic system or successively when the polymerization has already started. In the continuous systems it can be fed into the reactor together with the catalyst or separately. In the case of more reactors in series it can be fed into anyone of them. Therefore object of the present invention is a process for preparing olefinic polymers thermically stable consisting in adding into the polymerization medium of the monomers before, during or after the polymerization or to the polymer before the drying of same or before the removal of the monomer, one or more compounds containing at least a piperidinic group sterically hindered. The amount of compound that may be added either into the polymerization medium or, alternatively, to the polymer before the drying of same ranges between 0,01 and 1% by weight referred to the polymer and preferably between 0,05 and 0,5%. The olefine polymers to which the process of the present invention is applied comprise crystalline homo- and copolymers such as the linear high- and low-density polyethylene, polypropylene, polybutene and amorphous polymers such as the elastomeric ethylene-propylene copolymers, possibly containing diene monomers. In particular, the process is applied to isotactic, or prevailingly, isotactic polypropylene, to the crystalline propylene-ethylene copolymers containing prevailingly amounts of propylene and further to high impact polypropylene. The following examples will illustrate the invention without limiting it. Examples 1-6 relate to the use of the catalytic system prepared according to the process described in example 3 of Italian patent No.1054410 and purpose to show the effectiveness of the different piperidinic compounds used as stabilizing agents. Examples 7-9 have the same aim but they relate to the catalytic system prepared according to the process described in examples 30-34 of issued European patent application No. 45977. Example 10 shows that the stabilizing agent can be fed together with the catalyst (in the preceding examples on the contrary it is fed when the polymerization is half-way). Examples 11-12 and 13 show the negative effect on the isotacticity index of the polymer when the usual catalytic system is used, based on TiCl₃/DEAC. Examples 14-16 exhibit the drawbacks due to the phenolic stabilizing agents. Example 17 is useful for comparing by using the same additive the stabilization carried out according to the invention and according to the traditional method. Examples 18-21 relate to the preparation of copolymers of ethylene with propylene and butene-1, respectively, in the presence or absence of the stabilizing agents according to the present invention. All the numeric data are reported on Table (I). EXAMPLE 1 (of comparison) 5 mmoles of Al (i-Bu)₃ and 1,67 mmoles of methyl para-toluate were introduced into 50 ml of hexane. After 5 minutes at room temperature one introduced the amount specified in the Table of a catalytic component prepared according to the process described in Italian patent No.1054410 in example 3. 2,25 l of hydrogen and 0,9 kg of propylene were introduced into a steel autoclave having a capacity of 3 l, equipped with stirrer and thermostat, and the temperature was brought to 70°C. Then one introduced the catalytic mixture prepared as described herein before. After two hours the stirring was stopped and the residual propylene was quickly degassed. The obtained polymer was treated for 10 minutes with steam at 100°C, then dried in an oven at 50°C in a nitrogen flow. The following measures were carried out on the polymer according to standard methods isotacticity index by extraction with hot n-heptane intrinsic viscosity in tetrachloroethylene at 135°C resistance against oxidization (T.O. 150°C) in an oven at 150°C (Method ASTM D-3012) induction time to the oxidization at 180°C (Ox. I.T.180°C) (D.B.Marshall et al. Polym.Eng. & Sci., 13 (6), 415 (1973)). The result reported on Table,showed that the polymer was wholly free from resistance to thermoxidization. EXAMPLES 2 - 6 One worked as in example 1 with the difference that after 1 hour from the polymerization start the stabilizing agents indicated in the Table and in the specified amount were introduced into the autoclave in the form of a solution or of a suspension in 50 ml of hexane. The results reported on the Table showed that the polymer had no particular colouring and had a high thermal stability. Moreover the performances of the catalyst did not turn out to be at all altered. EXAMPLE 7 (of comparison) One worked as in example 1, with the difference that a catalyst was used, prepared according to the method of issued European patent application No. 45977, examples 30-34, together with 5 mmoles of AlEt₃ and 0.25 mmoles of phenyltriethoxysilane. In this case as well, the obtained polymer had no thermal stability. EXAMPLES 8 - 9 One worked as in example 7 with the difference that after 1 hour from the polymerization start the specified amounts of the stabilizing agents indicated on the Table were introduced into the autoclave. One obtained polymers free from colouring and endowed with a high thermal stability whereas the catalyst performances did not turn out to be damaged. EXAMPLE 10 One worked as in examples 2-6 with the difference that the stabilizing agent was introduced into the autoclave together with the catalyst. From the comparison with example 2 one deduced that such modification did not change the final result. EXAMPLE 11 (of comparison) One worked as in example 1 using, however, as activated catalyst TiCl₃.0.33 AlCl₃ and 10 mmoles of AlEt₂Cl as co-catalyst. A polymer was obtained wholly free from thermal stability. EXAMPLES 12-13 One worked as in example 11 with the difference that the stabilizing agent in the amount indicated on the Table was introduced into the autoclave together with the catalyst. From the comparison with example 11 one remarked that with this catalytic system the addition of the stabilizing agent lowers in an unacceptable degree the isotacticity index of the polymer. EXAMPLES 14-16 One worked as in examples 2-6 while using, however, the stabilizing agents of phenolic type as indicated on the Table. The obtained results showed that such stabilizing agents although they had been added in a lower amount with respect to the piperidinic ones steric hindered either they interferred on the catalytic performances (ex.14) or imparted an undesired colouring to the polymer (ex.15 and 16) and therefore they could not be used for the desired purpose. EXAMPLE 17 (of reference) The example relates to a polymer stabilized with the traditional method, namely by adding the additive during the granulation stage. By comparing examples 2,8 and 10 with example 17 we were able to conclude that a stabilization carried out with the process object of the present invention gave a result at least equal to the one carried out with the traditional method. EXAMPLE 18 (comparative test) Into a stainless steel autoclave having a capacity of 2.5 l equipped with a stirrer and a thermoregulating device there was introduced at room temperature and in an isobutane stream a catalytic mixture consisting of 0,6 g of (Et)₃Al and of 8,8 mg of a catalyst prepared according to example 5 of Italian Patent No.1,078,995 along with 2o ml of hexane. 350 g of isobutane were then introduced and the temperature was quickly brought to 65°C. H₂ was added up to a pressure of 12.5 kg/cm² gauge, then 300 g of butene-1 were added and at last the total pressure was brough to 25 kg/cm² gauge with ethylene. The autoclave was maintained at 65°C and 25 kg/cm² gauge during two hours by continuously replenishing the consumed ethylene and butene-1. After 2 hours, stirring was stopped and the monomer mixture as well as the solvent were allowed to quickly evaporate. The resulting slurry was treated with steam at 100°C during 10 minutes whereafter it was dried at 70°C in a nitrogen stream. Obtained were 220 g of a copolymer containing 8,2% by weight of butene and 91,8% by weight of ethylene such polymer being charaterized as is apparent from the values reported in the Table by a very low resistance to thermo-oxidation. EXAMPLE 19 It was operated as in example 15 with the exception that in the present case 10 ml of hexane containing 0,32 g of CHIMASSORB 944 were injected into the autoclave under an ethylene pressure after a 1-hour polymerization. At the end of the test there were obtained from 8,6 g of catalyst 207 g of copolymer at 6,5% by weight of butene containing 1540 ppm of stabilizer and endowed with a much higher resistance to thermo-oxidation than in the preceding case as is apparent from the values reported in the Table. EXAMPLE 20 (comparative test) Into the same autoclave utilized in the preceding examples 18 and 19 there were introduced at room temperature and in a gaseous propylene flow 1,1 g of (i-C₄H₉)₃Al dissolved in 25 ml of hexane. Subsequently, 750 g of propylene were added, the temperature was quickly brought to 40°C and ethylene was fed till reaching a total pressure of 18,8 kg/cm² gauge. Now a suspension consisting of 50 ml of hexane and 5,3 mg of the same catalyst used in example 18 was introduced under an ethylene pressure into the autoclave. The autoclave was maintained at 40°C and 18,8 kg/cm² g during 1 hour while continuously replenishing the consumed ethylene. At last, following the procedure of example 18, there were obtained 160 g of a rubber-like polymer having a composition consisting for 55.4% by weight of ethylene and for 44.6% by weight of propylene and exhibiting an inherent viscosity equal to 4,05 dl/g. The yield was of 30.2 kg of polymer/g of catalyst. As it results from the data in the Table, the resistance to thermo-oxidation of the polymer is very low. EXAMPLE 21 It was operated as in example 20 with the exception that in this case 30 minutes after the polymerization beginning 10 ml of hexane containing 0,39 g of CHIMASSORB 905 were introduced into the autoclave under ethylene pressure. At the end of the test there were obtained from 5 mg of catalyst 140 g of a copolymer having a composition consisting for 55,5% by weight of ethylene and for the remaining 44,5% by weight of propylene and exhibiting an inherent viscosity equal to 4.2 dl/g. The yield was of 28 kg of polymer/g of catalyst. The polymer contains 2860 ppm of the stabilizing compound and, as it results from the Table, it has a much higher resistance to thermo-oxidation than the polymer of example 2o.

Claims: A process for the manufacture of thermally stable olefinic polymers which polymers are obtained by means of catalysts prepared by reaction of an Al-alkyl compound with a solid component selected from a product comprising a titanium compound and a magnesium halide and a product formed by a tetravalent titanium compound which is supported onto a trivalent titanium halide having a surface area greater than 50 m²/g, which process comprises adding to the polymerization slurry during the polymerization or at the end of the polymerization a compound containing in the molecule one or more steric hindered piperidinic groups that are represented by the following general formula wherein: R₁,R₂ may be alkyl radicals containing from 1 to 4 carbon atoms or rings of 2,2,6,6-tetramethylpiperidine or together they may form with the piperidinic carbon atom they are bound to a cycloalkyl group containing from 5 to 10 carbon atoms, R₃,R₄ = alkyl radicals containing from 1 to 18 carbon atoms or together, they form with the piperidinic carbon atom they are bound to a cycloalkyl group containing from 5 to 10 carbon atoms, R₅, R₆, R₇, R₈, R₉, Z = hydrogen or an organic radical, preferably a C₁-C₁₈alkyl, C₃-C₁₂ alkenyl, C₇-C₁₈ aralkyl radical, phenolic compounds being excluded. A process according to claim 1 wherein the compound containing in the molecule one or more steric hindered piperidinic groups is an oligomeric product. A process according to claim 1 wherein the compound containing one or more steric hindered piperidinic groups is a monomeric product wherein the piperidinic rings optionally may be substituted and bound to each other. A process according to claim 1 wherein the compound containing steric hindered piperidinic groups is added to the monomer or to the mixture of monomers at the start or during the polymerization. A process according to claim 1 wherein the compound containing steric hindered piperidinic groups is added to the polymer slurry before separating the non-reacted monomer. A process according to one or more of the preceding claims wherein the compound containing steric hindered piperidinic groups is added in an amount ranging between 0,01 and 1% by weight, referred to the polymer. A process according to claim 1 wherein the olefinic polymers are obtained by means of stereospecific catalysts comprising the reaction product of an Al-alkyl compound with catalytic components comprising a titanium compound and an electron-donor compound supported on a magnesium halide in the active form.

Inventors: NORISTI, LUCIANO, SEVINI, FRANCO
Applicants: HIMONT INCORPORATED
Application year: 1986
Main classification: C08F2
IPC codes: C08K5, C08F4, C08F2, C08F10, C08L7, C08L23, C08L101, C08L21