Tin-free catalyst for the crosslinking process of silane-grafted polyolefins

Abstract

Use of a tin-free catalyst based on indium (III) coordination compounds with β-diketone ligands for the water-crosslinking of polymers grafted or copolymerized by silane technology.

Description

[0001] DESCIPTION

[0002] Tin- free catalyst for the crosslinking process of silane-grafted polyolefins"

[0003] The present invention relates to the use of a tin- free catalyst in the crosslinking process of silane-grafted polyolefins .

[0004] In particular, the present invention relates to the use of a class of indium ( I I I ) -based catalysts for the water- induced crosslinking of polyolefins via silane technology .

[0005] As is known, polyolefins ( PCs ) constitute the most commercially important family of high-tonnage thermoplastic polymers . Polyolefins can be extruded into various products such as cables , pipes and films . The conversion of the more or less linear structure of PCs into a three-dimensional structure can be achieved through crosslinking . Chemical crosslinking dramatically improves many properties of polyolefins , such as thermomechanical properties , chemical and stress-cracking resistance , and additionally imparts new functional properties , such as shape-memory behavior .

[0006] Among crosslinking methods , the most widely employed are peroxide crosslinking, irradiation crosslinking, and silane crosslinking. Extensive studies have been devoted to the crosslinking of a wide range of polyolefins, particularly polyethylene. Among these methodologies, water-crosslinking via silane technology is widely adopted owing to ease of processing, low material cost, low capital investment requirements, and favorable properties of the finished materials .

[0007] Water-crosslinking of polymers grafted or copolymerized with silanes to produce filled or unfilled polymeric composite materials, particularly polyethylene (PE) and its copolymers, involves at least two stages (Figure 1) , which may also occur consecutively depending on the method used. In the first stage, a mono-unsaturated organoalkoxysilane, such as vinylalkoxysilane ( vinylmethyldimethoxysilane, vinyltriethoxysilane, vinyltrimethoxysilane, etc.) , is grafted onto polyethylene through its vinyl groups via a peroxide-initiated radical reaction. In a second stage, the resulting silane-functionalized polymer composite is compounded with a hydrolysis and condensation catalyst (typically an organotin compound) and can be extruded into cable or pipe form, which is subsequently crosslinked by moisture exposure (water-crosslinking) .

[0008] It is likewise possible to obtain a molded or extruded product based on a thermoplastic polymer via a single-step process . In this case , the method essentially consists in reacting the thermoplastic polymer in a heated screw extruder with the addition of a mixture comprising a mono-unsaturated organoalkoxysilane , such as vinyltrialkoxysilane , a free- radical initiator and a hydrolys is / condensation catalyst , such as an organotin compound . The product is then molded or extruded and subsequently crosslinked by moisture exposure , e . g . , in a water bath . In any case , water-crosslinking occurs through hydrolysis and condensation reactions of alkoxysilane groups grafted onto the polyolefin .

[0009] For example , hydrolysable unsaturated alkoxysilanes such as 3-methacryloxypropyltrimethoxysilane (MTMS ) or vinyltrimethoxysilane (VTMS ) are grafted onto polyolefins by a radical reaction .

[0010] The grafting reaction of the alkoxysilane onto the polyolefin ( #-Si-OR) is followed by hydrolysis of the alkoxysilane ( #-Si-OH) and therefore by the formation of siloxane linkages ( #-Si-O-Si-# ) via condensation .

[0011] In these reactions , known as water-crosslinking, a water molecule acts as the crosslinking agent .

[0012] Based on the possibility of performing the two stages of silane crosslinking either separately or together, two processes are known in the art , respectively described in US3646155 (Sioplas® process) and US4117195 (Monosil® process) .

[0013] In both known processes, further additives and / or fillers may be included, such as pigments, antioxidants, metal deactivators, UV stabilizers, dyes, other processing aids such as flame retardants, or other fillers imparting mechanical reinforcement or flame-retardant properties.

[0014] The water-crosslinking reaction of alkoxysilanes proceeds generally very slowly without a catalyst. Catalysts are therefore required to promote both hydrolysis and condensation reactions, in order to reduce crosslinking time and obtain fully crosslinked materials.

[0015] In water-crosslinking of alkoxysilanes, dibutyltin dilaurate (DBTL) and dioctyltin dilaurate (DOTL) , which are organotin compounds (OTCs) , represent highly efficient catalysts. Bis ( acyl ) dialkyltins effectively catalyze silanol hydrolysis and condensation owing to their strong oxophilicity and pronounced Lewis acidity. The presence of lipophilic organic groups, such as n-butyl and n-octyl, enhances their solubility in the non-polar polysiloxane matrix, while hydrolysable ester groups enable facile catalyst activation by ambient moisture. However, OTCs exhibit high toxicity even at low exposure levels, not only in marine invertebrates but also in mammals and other animals, and are potentially carcinogenic.

[0016] Therefore, OTCs are not suitable for all applications, such as food-contact films or medical uses.

[0017] After nearly 20 years of widespread use of tributyltins (TBTs) in antifouling paints, TBTs were restricted in Japan in 1990 due to their high toxicity towards marine organisms. In 2003, the ban was adopted in Europe and subsequently in all Member States of the United Nations Marine Environment Protection Committee (MEPC) .

[0018] Although dibutyltins (DBTs) are comparatively less toxic than TBTs, countries including Japan, Germany, Denmark and Sweden have adopted regulations limiting the use of organotin stabilizers due to their potential risks to humans and the environment.

[0019] In Europe, DBTs are now classified as CMR-2 agents (carcinogenic, mutagenic or toxic for reproduction) , meaning that since 2012, products intended for the general public may not contain dibutyltin compounds above 0.1% tin (w / w) . On January 19, 2021, the European Chemicals Agency (ECHA) announced the addition of several organotin compounds to the candidate list of substances of very high concern (SVHC) under REACH. This group includes dioctyltin dilaurate and other organotin compounds used as polymer additives, identified as reproductive toxicants.

[0020] Therefore, replacing OTCs with environmentally friendly catalysts for water-crosslinking is of great importance.

[0021] A publication by Sharma R. K. et al., entitled "A highly efficient synthesis of oxindoles using a functionalized silica gel as support for indium(III) acetylacetonate catalyst in an aqueous-acetonitrile medium", Journal of Molecular Catalysis A: Chemical, is also known, which describes the use, as a heterogeneous catalyst in the synthesis of oxindole derivatives, of the species referred to as In (acac)3-APSG. This species is obtained by covalently anchoring the indium (III) acetylacetonate complex (or tris ( acetylacetonato ) indium ( I I I ) ) to aminopropyl- functionalized silica gel (APSG) , which in turn is obtained by modifying silica gel with 3-aminopropyltriethoxysilane . Specifically, the In (acac)3-APSG catalyst was tested in the synthesis of oxindole derivatives, namely 3,3- di (heteroaryl ) oxindoles , produced via electrophilic substitution of indoles with various isatins in an aqueous- acetonitrile medium. The chemical nature of the In (acac)3- APSG catalyst is more clearly illustrated in Figure 1 of the cited patent document. This figure clearly shows that the covalent anchoring of the indium (III) acetylacetonate complex (In (acac)3) to aminopropylsilica modifies the properties of the indium(III) acetylacetonate complex, with a chemical transformation of one of the three acetylacetonate (acac) ligands resulting from the conversion of a carbonyl group into a propylimino group. The In (acac)3complex is merely the precursor of the heterogeneous catalyst referred to by the authors as In (acac)3-APSG, which is chemically and correctly formulable as In (acac)2(CH3COC=N- (CH2)3-silica) , i.e., the derivative of a bis (acetylacetonate) indium(III) complex. Furthermore, as shown in Figure 2 of the cited patent document, the catalyst in question is used in the synthesis of oxindoles, which bears no chemical relation to the water-crosslinking reaction for the crosslinking of silane-grafted polyolefins, the specific technical field of the present invention.

[0022] The patent document KR 2024 0127251A is also known, which describes an innovative method for producing nanometric composite fibers based on organosilicon compounds (such as organosilsesquioxanes ) and metals, using the electrospinning technique. These fibers combine the properties of organic materials (flexibility, stability) and inorganic materials (thermal resistance, catalytic properties) , making them suitable for advanced applications such as catalysts, sensors, batteries, and filters. The document refers to the use of various materials or compositions, in particular derivatives of organosilicon compounds such as phenyltrimethoxysilane (PTMS) or vinyltriethoxysilane (VTMS) , having a 3D structure and functional groups (e.g., -OH, -NH2) . To prepare the electrospinning solution, solvents such as DMF, THF, acetone, etc., are mentioned. Among the metals employed, particular mention is made of Ti, Zr, Ag, Cu, Er, and more than 20 metals spanning alkali metals, transition metals and rare earth elements, including Li, Cs, Be, Mg, Ca, Ba, Sr, Al, Ga, In, Ge, Sn, Pb, As, Sb, Pr, Cd, and Yb, in their most common oxidation states and in the form of metallic precursors, including several acetylacetonates . In this context, indium is included among the metals used to modify the properties of the fibers and is introduced in the form of indium(III) acetylacetonate (In(acac)3) , synthesized from indium nitrate (In(NO3)3) , or indium neodecanoate (In(ND)3) , obtained from indium nitrate and neodecanoic acid. Indium is chosen for its electrical conductivity (useful for electronics or solar cell applications) , thermal stability (suitable for high-temperature treatments up to 1500 °C) , and chemical compatibility with the organosilicon matrix. The document proposes a scalable method for producing hybrid nanometric fibers with customizable properties suitable for high-tech industries. The use of metal precursors and the optimization of electrospinning and heat-treatment parameters make it a promising solution for industrial applications. In any case, it is clear that indium(III) acetylacetonate (In(acac)3) is cited in said patent document for a use and context which have no chemical correlation with the water-crosslinking reaction, namely the crosslinking of silane-grafted polyolefins through the known Monosil® or Sioplas® processes, which constitute the specific technical field of the present invention.

[0023] Furthermore, patent document WO 2014 / 017598 Al describes a curable organopolysiloxane composition employing a novel condensation catalyst, and discloses a curable (i.e., hardenable) organopolysiloxane composition comprising an organopolysiloxane having two or more hydroxyl groups and / or two or more hydrolysable groups per molecule (said groups being bonded to silicon atoms) , and at least one organic indium compound selected from chelated complexes, alkoxides, and salts of fatty acids of indium. The document addresses the problem of providing a new hardenable composition based on organopolysiloxanes (technically known as modified silicones) by using an innovative condensation catalyst based on organic indium compounds, which improves the solubility of indium in the polysiloxane and enhances catalytic efficiency compared to traditional catalysts (e.g., tin, zirconium, or gallium compounds) . The composition comprises: an organopolysiloxane having at least two hydroxyl (-0H) and / or hydrolysable groups per molecule, bonded to silicon atoms; an organic indium catalyst selected from chelated complexes (e.g., tris ( acetylacetonato ) indium ( I I I ) ) , alkoxides (e.g., triisopropoxyindium) , or carboxylate salts (e.g., indium 2- ethylhexanoate ) . The principal applications of the organopolysiloxanes described in the document include: LED sealing and other semiconductor devices; optical coatings (e.g., lenses, waveguides) ; adhesive materials for electronic components. Therefore, the document does not interfere with the technical solution proposed by the present invention .

[0024] Finally, patent document CA2921828A1 describes a tin- free composition used for the crosslinking of thermoplastic polyolefins via the Monosil® process. The document discloses a chemical composition for the Monosil® process comprising: 1) caprylic acid (H3C (CH2)6COOH) (5-60 wt%) ; 2) monounsaturated organofunctional alkoxysilanes of general formula A-SiR2x(OR1)3-x, where A is an olefinic group, R1independently represents a linear or branched hydrocarbon group containing 1 to 4 carbon atoms, and R2represents a methyl group; 3) a free-radical generator (e.g., organic peroxides) ; 4) optional components (e.g., stabilizers, antioxidants) . The composition is used to crosslink thermoplastic polyolefins (e.g., polyethylene, polypropylene) in the absence of tin, thus avoiding the toxicity associated with traditional tin-based catalysts (e.g., dibutyltin dilaurate, DBTL) . The technical context relates to conventional methods (e.g., Sioplas® and Monosil® processes) that employ tin catalysts or sulfonic acids, which are toxic or malodorous. Caprylic acid is identified as an efficient and non-toxic alternative, with high solubility in alkoxysilanes and stability at low temperatures (e.g., 6 °C) . The document does not in any way disclose the use of indium-based catalysts or indium compounds for the crosslinking of thermoplastic polyolefins. Rather, it focuses exclusively on tin-free systems, proposing caprylic acid as an alternative to traditional tin-based catalysts (e.g., dibutyltin dilaurate, DBTL) , aromatic sulfonic acids (e.g., Ambicat™) , and other metals (such as titanium, zinc, cobalt, etc . ) .

[0025] In recent years, increasing efforts have been devoted to the development of environmentally friendly alternatives. Currently, there are mainly three classes of catalytic systems: i) acid catalysts, including Bronsted acids (such as aromatic sulfonic acids, phosphoric acids, and carboxylic acids) and Lewis acids; ii) basic catalysts containing nitrogen (including amines, amidines, and imines) or phosphorus (including organophosphorus compounds, phosphazenes, and phosphoranes ) ; iii) hybrid acid / base catalysts and boron-based catalysts.

[0026] However, the tin-free catalytic systems currently in use often suffer from poor compatibility with the polymer, exhibit lower efficiency compared to classical organotin catalysts, display activity that varies depending on the nature of the polyolefin substrate, and face additional limitations arising from interactions with additives commonly incorporated into polymer compounds (flameretardant agents, antioxidants, etc.) .

[0027] Moreover, in the current state of the art, only organotin catalysts (OTCs) are capable of maintaining catalytic activity under the particularly harsh conditions imposed by the presence of inorganic flame-retardant fillers such as aluminum hydroxide (Al (OH)3, ATH) and magnesium hydroxide (Mg(OH)2, MDH) . In particular, such additives are typically used in the production of electrical or optical- fiber cables at loadings of 50-65 wt% in order to meet regulatory requirements for obtaining, depending on the application, the IEC 60332-1 / IEC 60332-3 classifications ( flame propagation resistance ) , EN 50575 ( reaction to fire for construction cables ) and UL 1685 / UL 1581 ( cable flame spread and smoke tests in the United States and Canada ) . It is therefore evident that there exists a technical problem of providing a catalyst for the water-crosslinking reaction that is both ef fective , even in the presence of flameretardant fillers , and environmentally benign .

[0028] The purpose of the present invention is to provide a catalyst , or rather a class of innovative and environmentally friendly catalysts , for catalyzing the water-crosslinking reaction of polymers grafted or copolymeri zed through silane technology .

[0029] A further obj ective of the present invention is to provide a tin- free catalyst for the crosslinking of silane- grafted polyolefins which, in addition to solving the problem of replacing the conventional organotin compounds ( OTCs ) currently in use and therefore overcoming the issues associated with their high toxicity, also of fers the advantage of being compatible with the additives and / or fillers normally incorporated into the polymer compound .

[0030] A key aspect of the invention lies in the fact that indium ( I I I ) acetylacetonate-based catalysts are capable o f maintaining catalytic activity ( comparable to or greater than that of conventional OTCs ) under the particularly harsh conditions imposed by the presence of inorganic flameretardant fillers such as aluminum hydroxide (Al (OH)3, ATH) and magnesium hydroxide (Mg(OH)2, MDH) , as well as metal deactivators and antioxidants.

[0031] This latter aspect is of fundamental importance for understanding the innovative nature of the invention. Indeed, as discussed above, due to the toxic effects of organotin catalysts, increasing efforts have been devoted in recent years to the development of catalytic systems that are both effective and environmentally friendly.

[0032] According to the present invention, an indium(III) - based catalyst is proposed, and in particular coordination compounds of indium (III) with p-diketone ligands, for the water-crosslinking of polyolefins via silane technology, whether by the Sioplas® method or the Monosil® method.

[0033] The catalysts according to the present invention are advantageously compatible with the additives and / or fillers normally incorporated into the compound and exhibit catalytic activity comparable to that of OTCs, without the specific restrictions imposed by ECHA.

[0034] Furthermore, the catalysts of the present invention are compatible with the additives normally incorporated into the compound and exhibit synergistic activity with flame- retardant additives , decomposing at high temperatures to form the inert species In2O3.

[0035] The purpose of the present invention is to provide a catalyst , usable in a Monosil® or Sioplas® process , for the crosslinking of silane-grafted polyolefins , having characteristics such as to overcome the limitations that still af fect the systems and compositions known from the prior art .

[0036] According to the present invention, the use of a catalyst as defined in claim 1 is proposed .

[0037] For a better understanding of the present invention, a preferred embodiment is now described, purely by way of nonlimiting example , with reference to the accompanying drawings , wherein :

[0038] - Figure 1 illustrates the water-crosslinking process for the production of silane-grafted POs , wherein Phase 1 comprises the incorporation of the silane into the polymer, either by grafting vinylsilane onto the polymer backbone or by copolymeri zing vinylsilane with ethylene in the polymeri zation reactor, whi le Phase 2 involves crosslinking in the presence of water, generally catalyzed by tin compounds or other suitable catalysts ; according to the invention, this second phase may be controlled and carried out either during the extrusion process (one-step process) or after extrusion (two-step process) .

[0039] - Figure 2 shows the chemical formula of the catalyst according to the invention.

[0040] In particular, the invention comprises a catalyst for the water-crosslinking reaction of polymers grafted or copolymerized via silane technology, of general formula In (R1COCR2COR3)3, characterized by the presence of indium (III) and a p-diketone ligand (R1COCR2COR3) .

[0041] The structural formula of the catalyst according to the invention is shown in Figure 2:

[0042] According to one aspect of the invention, such complexes may be obtained, with a high degree of purity, by metathesis reaction between a low-toxicity and environmentally compatible indium(III) salt, such as commercially available indium(III) acetate, and the appropriate p-diketone; or, for example, by reacting indium (III) bromide with the sodium salt, or another alkali-metal salt, of the appropriate p- diketone .

[0043] The p-diketone ligands are characterized by the presence of substituents R1and R3, which may independently be alkyl or aryl groups , identical or di f ferent , linear , branched, or cyclic, optionally substituted, and having from 1 to 20 carbon atoms . For the entire class of compounds , the R2group may be a hydrogen atom, or an alkyl or aryl group, substituted or unsubstituted, having from 1 to 20 carbon atoms .

[0044] The present invention also relates to a production process , as well as molded or extruded articles or products obtainable therefrom, based on polymers in which the catalyst according to the invention is reacted with at least one polymer grafted or copolymeri zed with silanes via the Monosil® or Sioplas® method .

[0045] The Applicant has carried out experimental tests in support of the characteristics and catalytic activity of the above-described indium-based species in the speci fic reaction .

[0046] In particular, the chemical species evaluated for their ability to catalyze the water-crosslinking reaction of silane-grafted polyolefins were synthesi zed and / or characteri zed at the Inorganic Chemistry Laboratory of the ChIP Research Center ( Chemistry Interdisciplinary Proj ect ) of the University of Camerino . Subsequently, their catalytic activity was evaluated at the laboratories of Fainplast S . r . l . in Ascoli Piceno . In particular, the catalytic behavior of the chemical species described according to the present invention was compared with that of dioctyltin dilaurate ( DOTL ) , which is the catalyst currently employed in industry for the watercrosslinking of silane-grafted compounds by the Sioplas® or Monosil® process .

[0047] Speci fically, within the Sioplas® process , the method used involves preparing a mixture consisting of a polyolefin- based compound grafted with silanes , containing inorganic flame-retardant fillers such as aluminum hydroxide (Al ( OH)3, ATH) and magnesium hydroxide (Mg ( OH)2, MDH) , together with a catalyst masterbatch containing the active species . In this context , catalyst masterbatch refers to a mixture comprising the active species at high concentration and a polymeric carrier compatible with the silane-modi f led product .

[0048] The mixture is obtained using a Plastograph EC Brabender universal torque rheometer, at a set temperature of 150 ° C and with a total mixing time of 4 minutes .

[0049] The resulting mixture , referred to as the "masterbatch sheet" is molded into a square plate with dimensions of 150 mm per side and 1 mm thickness . From this plate , dog-bone specimens are then die-cut for performing tests to determine the degree of crosslinking . The procedure used to verify the crosslinking of the materials obtained as described above is the Hot Set Test.

[0050] The Hot Set Test is the method described in TEC Standard 60811-507, which is generally applied to crosslinkable compounds used for insulating and sheathing materials, under the following conditions:

[0051] • Test temperature: (200 ± 3) °C

[0052] • Applied load: (20 ± 0.5) N / cm2

[0053] The test is considered passed when the following conditions are met:

[0054] • Maximum elongation under load: 175%

[0055] • Maximum permanent elongation: 15%

[0056] Crosslinking is performed by immersing the specimens in water at 95 °C. The degree of crosslinking is monitored at intervals of 1, 2, 3, 4, 6, 8, 24 and 48 hours, removing the dog-bone specimen from the water bath and subjecting it to the Hot Set Test under the conditions described above. Typically, for hot-water curing times longer than 4 hours, the specimens are dried in an oven at 95 °C for 45 minutes to remove absorbed water.

[0057] Specifically, the sample obtained by blending the silane-grafted EVA-based compound containing ATH as flameretardant filler, designated HEX 500P, with 0.75% of a catalyst masterbatch designated CAT 1296TF, containing 8% of the active species, passes the Hot Set Test after 3 hours of curing in water at 95 °C, providing the following results:

[0058] • Maximum elongation under load: 50%

[0059] • Maximum permanent elongation: 0%

[0060] Such behavior is fully comparable to that of the "standard" tin-based active species.

[0061] Among the various species tested, the composition containing from 0.001 to 1 wt% of indium(III) 2,4- pentanedionate — the simplest chemical species within the class of In (R1COCR2COR3)3complexes described in Figure 2, with R1= CH3, R2= H and R3= CH3, commercially available under CAS No. 14405-45-9 — was used as a reference active species, whose catalytic efficacy was evaluated by means of the Hot Set Test. This complex exhibited excellent silane crosslinking (water-crosslinking) catalytic properties when tested on the EVA-based silane-modif led compound containing inorganic flame-retardant fillers, specifically designated HEX 500, with Hot Set Test results comparable to those obtained using DOTL. This active species is compatible with the additives and / or fillers incorporated into the compound and is chemically stable under standard environmental conditions. Based on the chemical and structural properties of In (III) p-diketone complexes, it is reasonable to assume that the catalytic behavior described for indium(III) 2,4- pentanedionate can be extended to the entire series of complexes described in Figure 2 , as defined in the appended claims .

[0062] Advantageously, the use of the In ( acac )3-based catalyst for the crosslinking of silane-grafted polyolefins not only replaces the conventional organotin compounds ( OTCs ) currently in use , thereby eliminating the issues associated with their high toxicity and the speci fic restrictions imposed by the European Chemicals Agency (ECHA) , but also proves to be compatible with the additives and / or fillers normally incorporated into the polymer compound .

[0063] Advantageously, indium ( I I I ) acetylacetonate-based catalysts are capable of maintaining catalytic activity ( comparable to or greater than that of conventional OTCs ) under the particularly harsh conditions imposed by the presence of inorganic flame-retardant fillers such as aluminum hydroxide (A1 ( OH)3, ATH) and magnesium hydroxide (Mg ( OH)2, MDH) , as well as metal deactivators and antioxidants .

[0064] Therefore , the use of the catalyst according to the invention makes it possible to avoid the use of tin compounds , known to be hazardous and toxic, in processes involving the crosslinking of silane-modi f led polymers , whether or not containing flame-retardant fillers , thereby providing a non-toxic and ef fective alternative catalyst .

[0065] Advantageously, the catalyst according to the invention can be employed in crosslinking processes that are well- established and industrially relevant .

[0066] Finally, it is clear that modi fications and variations may be made to the catalyst and to its use , as described and illustrated herein, without thereby departing from the scope of protection of the present invention as defined in the appended claims .

Claims

CLAIMS1. Use of a tin-free compound, based on indium(III) coordination compounds with p-diketone ligands, as a catalyst for the water-crosslinking reaction of polymers grafted or copolymerized via silane technology, wherein said compound has the general formula In (R1C0CR2C0R3)3, wherein :R1and R3are alkyl or aryl groups, identical or different, linear, branched or cyclic, optionally substituted, and having from 1 to 20 carbon atoms;R2is a hydrogen atom or an alkyl or aryl group, substituted or unsubstituted, having from 1 to 20 carbon atoms .

2. Use according to claim 1, wherein said compound has the structural formula:

3. Use of a compound having the general formula In (R1C0CR2C0R3)3, wherein:R1and R3are alkyl or aryl groups, identical or different, linear, branched or cyclic, optionally substituted, and having from 1 to 20 carbon atoms;R2is a hydrogen atom or an alkyl or aryl group, substituted or unsubstituted, having from 1 to 20 carbon atoms ; as a catalyst for a water-crosslinking reaction of polymers containing hydrolysable silane groups , wherein said polymers are previously obtained by grafting or copolymeri zing a vinylsilane onto a thermoplastic polyolefin, and crosslinking occurs by exposing the solid or semi-molten polymers to humidity under ambient or controlled conditions , with the formation of crosslinking siloxane bonds between polymer chains .4 . Process for producing molded or extruded polymeric products , comprising a reaction step between the compound of general formula In (R1C0CR2C0R3)3, wherein :R1and R3are alkyl or aryl groups , identical or di f ferent , linear, branched or cyclic, optionally substituted, and having from 1 to 20 carbon atoms ;R2is a hydrogen atom or an alkyl or aryl group, substituted or unsubstituted, having from 1 to 20 carbon atoms ; and at least one polymer grafted or copolymeri zed with silanes .

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