Abstract: An aqueous dispersion containing a vinylidene chloride polymer (P1) containing vinylidene chloride in a proportion of at least 50% by weight, and at least one random, alternating or gradient copolymer (C1) having: a) at least one monomer unit (m1) carrying at least one phosphonate group —PO(OH)(OR1) with R1 being a hydrogen atom or an alkyl radical comprising from 1 to 11 carbon atoms, and b) monomer units (m2) which represent at least 50% by weight of the copolymer (C1), derived from at least one monomer (M2) chosen from styrene, maleic anhydride, itaconic acid and the (meth)acrylic monomers corresponding to the general formula CH2=CR2R3 in which R2 and R3 are described herein, copolymer (C1) not containing monomer units derived from vinylidene chloride.

Abstract: A water- and oil-repellent includes, as an active ingredient, a fluorine-containing copolymer including as a copolymer unit (A) at least one of perfluoroalkylalkyl acrylates and corresponding methacrylates, (B) benzyl acrylate or benzyl methacrylate represented by the general formula: CnF2n+1CmH2mOCOCR?CH2 (wherein R represents a hydrogen atom or a methyl group; n represents 4, 5, or 6; and m represents 1, 2, 3, or 4), (C) a fluorine-free polymerizable monomer other than benzyl acrylate and benzyl methacrylate, and (D) a cross-linkable group-containing polymerizable monomer.

Abstract: To provide a copolymer which can impart sufficient dynamic water repellency, after air-drying water repellency and friction durability to a surface of an article, and which has low impact on the environment, a method for producing the same, a water repellent composition and an article excellent in dynamic water repellency, after air-drying water repellency and friction durability.

Abstract: A water- and oil-repellent comprising an aqueous dispersion of a fluorine-containing copolymer including as a copolymerization unit (a) a perfluoroalkylalkyl (meth)acrylate represented by the general formula CnF2n+1CmH2mOCOCR?CH2 (wherein R represents hydrogen atom or methyl group; n represents 4, 5, or 6; and m represents 1, 2, 3, or 4), (b) benzyl (meth)acrylate, (c) a fluorine-free polymerizable monomer other than benzyl (meth)acrylate, and (d) a cross-linkable group-containing polymerizable monomer; and a blocked isocyanate added to the aqueous dispersion in a weight ratio of 0.05 to 3.0 to the weight of the solid content of the aqueous dispersion.

Abstract: A water- and oil-repellent includes, as an active ingredient, a fluorine-containing copolymer including as a copolymer unit (A) at least one of perfluoroalkylalkyl acrylates and corresponding methacrylates, (B) benzyl acrylate or benzyl methacrylate represented by the general formula: CnF2n+1CmH2mOCOCR?CH2 (wherein R represents a hydrogen atom or a methyl group; n represents 4, 5, or 6; and m represents 1, 2, 3, or 4), (C) a fluorine-free polymerizable monomer other than benzyl acrylate and benzyl methacrylate, and (D) a cross-linkable group-containing polymerizable monomer.

Abstract: Process for preparing a seed latex of a methyl methacrylate polymer (PMMA) by radical polymerization in aqueous emulsion of methyl methacrylate and optionally at least one comonomer. Process for preparing a chlorinated vinyl polymer latex by radical polymerization in aqueous emulsion of at least one chlorinated vinyl monomer, according to which the polymerization takes place in the presence of at most 3% by weight, expressed relative to the total weight of the monomers, of the PMMA seed latex.

Abstract: Copolymers which are composed of at least 4 monomers, including (meth)acrylate compounds containing perfluoroalkyl groups, are suitable for the treatment of fiber materials. The copolymers are usually used here in the form of aqueous dispersions. The fiber materials are in particular fabrics, for example made of polyolefin. Treatment with the copolymers imparts to them oil- and water-repellent properties and also repellent properties toward low molecular weight alcohols.

Abstract: Process of controlled free-radical polymerization in aqueous dispersion for the preparation of a block copolymer at least one block of which is a block of a halogenated polymer using molecular iodine and at least one oxidant whose solubility in water is at least 10 g/l for the synthesis of the first block of the block copolymer.

Abstract: Copolymers which are composed of at least 4 monomers, including (meth)acrylate compounds containing perfluoroalkyl groups, are suitable for the treatment of fiber materials. The copolymers are usually used here in the form of aqueous dispersions. The fiber materials are in particular fabrics, for example made of polyolefin. Treatment with the copolymers imparts to them oil- and water-repellent properties and also repellent properties toward low molecular weight alcohols.

Abstract: Polymer composition comprising: 1) a polymer (P1) comprising at least 50% by weight of monomeric units derived from an ethylenically unsaturated monomer (M1), and 2) at least one co-oligomer (O1) comprising at least: a) a component (A) comprising at least one monomeric unit identical to that derived from the monomer (M1) on which the polymer (P1) is based, and b) a component (B) comprising at least one monomeric unit (m2), derived from an ethylenically unsaturated monomer, carrying at least one group chosen from the following groups: —CaH2a+1 with a between 6 and 30; —(CH2)b—CcF2c+1 with b between 1 and 11 and c greater than or equal to 5; —(CH2)d—(Si(CH3)2—O)e—Si(CH3)3 with d between 1 and 11 and e between 1 and 1000; —COOH; —SO3H, and the phosphonate groups —PO(OH)(OR1) with R1 being a hydrogen atom or an alkyl radical containing from 1 to 11 carbon atoms.

Abstract: A copolymer composition comprising monomers copolymerized in the following percentages by weight: (a) from about 20% to about 95% of a monomer, or mixture of monomers, of formula (I): CnF2n+1(CH2)x[(CF2CF2)y(CH2CH2)z]m-L-C(O)—C(R)?CH2??(I) wherein R is H, Cl, F or CH3, L is O, S, NH, S—(CH2)rO, S—(CH2)rNH, OC(O)NH—CH2CH2O, NHC(O)NHCH2CH2O, S—(CH2)rOC(O)NHCH2CH2O, or S(CH2)rNHC(O)NHCH2CH2O, and (b) from about 5% to about 80% of at least one of: (i) an alkyl (meth)acrylate monomer having a linear, branched or cyclic alkyl group of from about 6 to about 18 carbons; or (II) a monomer of formula (II) (R2)2N—R3—O—C(O)—C(R)?CH2??(II) wherein R is H, Cl, F or CH3, each R2 is independently a C1 to C4 alkyl; and R3 is a divalent linear or branched C1 to C4 alkylene; and wherein the nitrogen is from about 40% to 100% salinized; or (iii) a mixture thereof.

Abstract: The invention includes a copolymer of vinylidene chloride with at least one monounsaturated comonomer and at least one branching monomer in an amount sufficient to increase molecular weight over that of a polymer prepared using the same process and same monomers in the same relative amounts except without the branching monomer, but preferably the branching monomer is present in a quantity not sufficient to result in measurable crosslinking as determined by solubility in tetrahydrofuran at up to 83° C. The invention includes a process for making the polymer and processes for forming the copolymer or compositions thereof as well as articles comprising the copolymer and compositions thereof. The copolymer exhibits improved bubble stability and is particularly useful for processes in which the copolymer is at least partially oriented in formation such as blow molding, formation of monofilament fiber and film blowing.

Abstract: A polymer substrate having a weight loss of less than about 1% based on an initial weight at a temperature ranging from about 420° C. to about 600° C., a method for forming the polymer substrate, a display device including the polymer substrate, and a method for manufacturing the display device. The method for forming the polymer substrate includes preparing the polymer layer and performing an annealing process to the polymer layer at a temperature greater than about 350° C.

Abstract: Disclosed are free-radical retrograde precipitation processes to product a radicalized polymer or copolymer. A process includes form an admixture of a monomer, a solvent, and a free-radical-forming agent to initiate the polymerization at a temperature above the lower critical solution temperature of the mixture. Polymer radicals are precipitated to form micron-sized or nano-sized particulates. The admixture is cooled to stop the polymerization. The radicalized polymer radical may be mixed with a monomer to form a second radicalized copolymer.

Abstract: A process for the purification of a vinyl chloride polymer containing a compound of a heavy metal by: (a) dissolving the PVC in a solvent; (b) treating the solution with at least one additive capable of adsorbing or of forming a complex with the compound of the heavy metal; (c) centrifuging the treated solution to precipitate the adsorbed or complexed compound of the heavy metal; and (d) separating the precipitate from the PVC solution.

Abstract: Method for recovering a polymer from a liquid medium (1) substantially containing the polymer and a solvent for the latter, wherein: (a) this liquid medium (1) is injected into a reactor (2) containing a stirred substantially monophase liquid mixture comprising a major fraction by weight of a non-solvent and a minor fraction by weight of a solvent, the mixture having a composition and temperature such that the polymer precipitates therefrom progressively; (b) the polymer is recovered in the form of particles in suspension (5) in a liquid rich in non-solvent; (c) the polymer particles (9) are separated from the liquid.

Abstract: The present invention concerns a controlled structure copolymer comprising at least two different parts, a first part A, amphoteric or zwitterionic, including anionic or potentially anionic units, and cationic or potentially cationic units, or zwitterionic units, and another part B, non amphoteric or zwitterionic. Said copolymer further exhibits a high potential for adaptation, through variation in its composition, in order to improve or modify the properties of compositions in which it is introduced.

Abstract: An organotellurium compound of the formula (1) is useful as a living radical polymerization initiator and makes possible precision control of molecular weights and molecular weight distributions under mild conditions wherein R1 is C1-C8 alkyl, R2 and R3 are each a hydrogen atom or C1-C8 alkyl, and R4 is aryl, substituted aryl, aromatic heterocyclic group, hydroxycarbonyl or cyano.

Abstract: A polymer extender composition comprising monomers copolymerized in the following percentages by weight: (a) from about 5% to about 90% of a monomer of the formula I: R1—OC(O)—C(R)?CH2??(I) (b) from about 5% to about 85% of vinylidene chloride, vinyl chloride, vinyl acetate, or a mixture thereof, (c) from about 0.5% to about 3% of a monomer of the formula II: HO—CH2—NH—C(O)—C(R)?CH2??(II) (d) from about 0.5% to about 3% of a monomer of the formula III HO—CH2CH2—OC(O)—C(R)?CH2??(III) and (e) from about 1% to about 5% of a monomer of the formula IV: H—(OCH2CH2)m—O—C(O)—C(R)?CH2??(IV) (f) from 0% to about 25% of methyl methacrylate, vinylbenzyl chloride, styrene or a mixture thereof, wherein each R is independently H or CH3; R1 is a linear or branched or cyclic alkyl chain having from about 4 to about 18 carbon atoms, and m is 2 to about 10.

Abstract: The invention includes a copolymer of vinylidene chloride with at least one monounsaturated comonomer and at least one branching monomer in an amount sufficient to increase molecular weight over that of a polymer prepared using the same process and same monomers in the same relative amounts except without the branching monomer, but preferably the branching monomer is present in a quantity not sufficient to result in measurable crosslinking as determined by solubility in tetrahydrofuran at up to 83° C. The invention includes a process for making the polymer and processes for forming the copolymer or compositions thereof as well as articles comprising the copolymer and compositions thereof. The copolymer exhibits improved bubble stability and is particularly useful for processes in which the copolymer is at least partially oriented in formation such as blow molding, formation of monofilament fiber and film blowing.

Abstract: Acrylic polymers are made by the living radical polymerization of acrylic monomers utilizing organo halide initiators with either metal-free or metal catalysts. Moreover, block copolymers of vinyl halide monomers and acrylic monomers are described by generally polymerizing either the vinyl halide monomers or acrylic monomers utilizing an organo halide initiator in the presence of either a metal catalyst or a metal-free catalyst and subsequently polymerizing thereon the remaining type of monomer.

Abstract: An organotellurium compound of the formula (1) is useful as a living radical polymerization initiator and makes possible precision control of molecular weights and molecular weight distributions under mild conditions wherein R1 is C1-C8 alkyl, R2 and R3 are each a hydrogen atom or C1-C8 alkyl, and R4 is aryl, substituted aryl, aromatic heterocyclic group, hydroxycarbonyl or cyano.

Abstract: The present invention is directed to a free radical control agent of the structural formula: wherein R1 is a divalent alkyl group of 1 to 12 carbon atoms, R2 and R3 are each independently hydrogen or an alkyl group of 1 to 12 carbon atoms, and R4 is —OH or —COOH, with the proviso that the total carbon atoms of R1, R2, and R3 is no greater than 12; and wherein Y represents a functional group that is capable of activating a vinylic carbon toward free radical addition.

Abstract: The present invention is directed to a free radical control agent of the structural formula: wherein R1 is a divalent alkyl group of 1 to 12 carbon atoms, R2 and R3 are each independently hydrogen or an alkyl group of 1 to 12 carbon atoms, and R4 is —OH or —COOH, with the proviso that the total carbon atoms of R1, R2, and R3 is no greater than 12; and wherein Y represents a functional group that is capable of activating a vinylic carbon toward free radical addition.

Abstract: Radical polymerization process for the preparation of halogenated polymers employing one or more ethylenically unsaturated monomers, at least one of which is chosen from halogenated monomers, molecular iodine and one or more radical-generating agents chosen from diazo compounds, peroxides and dialkyl diphenylalkanes Radical polymerization process for the preparation, starting from the halogenated polymers prepared by the process as described above, of block copolymers, at least one block of which is a halogenated polymer block. Halogenated polymers which have a number-average molecular mass Mn of greater than 1.0×104 and an Mz/Mw ratio of less than 1.65. Block copolymers, at least one block of which is a block of halogenated polymer identical to the halogenated polymers described above. Block copolymers comprising at least one halogenated polymer block which have a number-average molecular mass Mn of greater than 1.5×104 and a polydispersity index Mw/Mn of less than 1.60.

Abstract: Radical polymerization process for the preparation of halogenated polymers and block copolymers. Halogenated polymers and block copolymers.

Abstract: These compounds contain an oxetane functionality and a cinnamyl functionality. The oxetane functionality is homopolymerizable in reactions that can undergo cationic or anionic ring opening, and the cinnamyl functionality is polymerizable with compounds such as electron acceptor compounds. The dual functionality allows for dual cure processing. The generic structure of such compounds is in which R is a methyl or ethyl group, X and Y independently are a direct bond, or an ether, ester, or carbamate group, and Q is a divalent hydrocarbon (which may contain heteroatoms of N, O, or S), provided that X and Y will not both be direct bonds in the same molecule.

Abstract: The instant invention relates to multifunctional alkoxyamines based on polyalkylpiperidines, polyalkylpiperazinones and polyalkylmorpholinones and their use as polymerization regulatros/initiators. Further subjects of the invention are a polymerizable composition comprising an ethylenically unsaturated monomer or oligomer and the alkoxyamine compound as well as a process for polymerization and a process for preparation of the compounds.

Abstract: Superabsorbent polymers having reduced levels of residual monomer are produced using a peroxodisulfate salt.

Abstract: Provided is a polymer scale deposition-preventive agent. It includes (A) a condensation reaction product of an aldehyde compound and a hydroxynaphthalene compound and (B) a soluble methoxyl group-substituted cellulose ether. The agent is formed into a film having an adequate polymer scale deposition-preventive property in a single-step application. The time for the application process is shortened to improve productivity. Polymer scales can be prevented from adhering to the inner wall surfaces of the polymerization vessel even if a plenty number of batches for polymerization are repeated.

Abstract: A polymer scale preventive agent for use in the polymerization of a monomer containing an ethylenic double bond is provided. The agent includes (A) a condensation reaction product obtained by reacting an aldehyde compound and a hydroxynaphthalene-based compound in the presence of a reducing agent, and (B) a polymer compound containing a nitrogen atom. This agent is capable of forming a coating with satisfactory scale prevention properties on inner wall surfaces of a polymerization vessel with a single-stage application, enabling the production process time to be shortened and the productivity and quality of polymeric products improved.

Abstract: A process for the preparation of polyvinyl chloride (PVC) with controlled molecular weight and molecular weight distribution is disclosed. The polymerization reaction can be initiated by various organic halide initiators in conjunction with a metal catalyst and an optional ligand in organic solvents or water and in the presence of an optional comonomer. The polymerization process provides PVC with a controlled molecular weight and narrow molecular weight distribution. The chlorine containing polymers compositions are useful as, among others, viscosity modifiers, impact modifiers and compatibilizers.

Abstract: The instant invention relates to multifunctional alkoxyamines based on polyalkylpiperidines, polyalkylpiperazinones and polyalkylmorpholinones and their use as polymerization regulatros/initiators. Further subjects of the invention are a polymerizable composition comprising an ethylenically unsaturated monomer or oligomer and the alkoxyamine compound as well as a process for polymerization and a process for preparation of the compounds.

Abstract: The present invention pertains to a process for controlled free radical polymerization or copolymerization of vinyl chloride at a temperature between 40° C. and 95° C., at a pressure between 5 and 30 bar in the presence of a stable free nitroxyl radical.

Abstract: Fluorine-modified comb polymers based on acryloyldimethyltaurine The invention provides water-soluble or water-swellable copolymers obtainable by free-radical copolymerization of

Abstract: A polymeric material containing a halogen-containing polymer such as PVC, an inorganic hydroxide and, an acrylic material is described. The presence of the inorganic hydroxide provides a material of superior weathering resistance as compared to materials comprising halogen-containing polymers which do not contain hydroxide.

Abstract: Compounds comprising a peroxide and a curable blend by peroxidic way, consisting essentially of hydrocarbon elastomers containing at least an acrylic monomer, and of unsaturated fluorinated elastomers obtained by dehydro halogenation of fluorinated VDF-based elastomers, said fluorinated elastomers having in the polymer chain at least 5% by moles of hydrogenated C1 groups of the type —CH2— and/or —CH3, the amount of unsaturated fluorinated elastomer in the elastomeric blend being comprised from 1 to 99% by weight.

Abstract: A production process for a vinyl-based polymer is provided. The production process comprises a step for polymerizing a vinyl-based monomer by a radical reaction within an aqueous medium in a polymerization vessel, and a step for supplying a reaction inhibitor with a melting point of no more than 40° C. from a reaction inhibitor supply tank to the polymerization vessel via a reaction inhibitor supply pipe. The reaction inhibitor supply tank and the reaction inhibitor supply pipe are heated, and the reaction inhibitor is added to the polymerization vessel in a liquid state with a viscosity of no more than 200 mPa·s. The reaction inhibitor can be added to the polymerization mixture without the use of an organic solvent even at low temperatures, and problems such as the solidification of the reaction inhibitor inside the supply tank or piping, and subsequent blocking of the piping do not occur.

Abstract: A production process for a vinyl-based polymer is provided. The production process comprises a step for polymerizing a vinyl-based monomer by a radical reaction within an aqueous medium in a polymerization vessel, and a step for supplying a reaction inhibitor with a melting point of no more than 40° C. from a reaction inhibitor supply tank to the polymerization vessel via a reaction inhibitor supply pipe. The reaction inhibitor supply tank and the reaction inhibitor supply pipe are heated, and the reaction inhibitor is added to the polymerization vessel in a liquid state with a viscosity of no more than 200 mPa·s. The reaction inhibitor can be added to the polymerization mixture without the use of an organic solvent even at low temperatures, and problems such as the solidification of the reaction inhibitor inside the supply tank or piping, and subsequent blocking of the piping do not occur.

Abstract: A process for producing a vinyl chloride polymer, the process including the steps of charging into a polymerization vessel, vinyl chloride or a monomer mixture containing vinyl chloride, water, and other materials necessary for polymerization, and polymerizing in an aqueous medium the vinyl chloride or the monomer mixture. An antioxidant is added to a mixture of materials before polymerization, or to a polymerization reaction mixture during polymerization or after polymerization. The antioxidant is added in the state of an aqueous dispersion and by means of a uniaxial eccentric screw pump. The aqueous antioxidant dispersion can be added at a constant rate and stably, without causing any block-up of the interior of the pump even when the polymerization vessel is held at a high internal pressure. Hence, vinyl chloride polymers having less uneven plasticizer absorption and having good anti-initial discoloration properties and thermal stability can be produced stably.

Abstract: A living polymerization process for preparation of poly(vinyl chloride) (PVC) with controlled molecular weight and molecular weight distribution is described. The polymerization reaction can be initiated by various polyhalocarbon initiators in conjunction with non-metallic reducing single electron transfer reagents as catalysts and accelerated by electron shuttles. The process occurs at room temperature in water or water-organic solvent medium. The polymerization provides PVC with a controlled molecular weight and narrow molecular weight distribution. The halogen containing polymer compositions are useful as, among others, viscosity modifiers, impact modifiers and compatibilizers.

Abstract: A reshapable hair styling composition comprising heterogeneous (meth)acrylic copolymer particles, said particles being the same or different and comprising at least one (meth)acrylic copolymer comprising: (a) units derived from at least one monomer chosen from (meth)acrylate esters of branched and straight chain alkyl alcohols, (b) units derived from at least one monomer chosen from (meth)acrylate esters of saturated and unsaturated cyclic alcohols containing 6 to 20 carbon atoms, (c) optionally units derived from at least one monomer chosen from hydrophilic monomers, and (d) optionally units derived from at least one monomer other than (a), (b), and (c) monomers, wherein said composition provides a reshapable effect.

Abstract: Water-soluble polymers having a water-soluble backbone and side units having in water a lower critical solution temperature, LCST, the polymers being obtainable by free-radical precipitation polymerization of water-soluble monomers and of macromonomers comprising a unit with an LCST whose heat-induced demixing temperature in aqueous solution is from 5 to 40° C. for a concentration by mass in water of 1% of the said unit. Also described is a process for preparing these polymers by free-radical precipitation polymerization, and aqueous compositions containing these polymers and the use of these polymers and compositions, especially in cosmetics, for the cleansing and/or making up and/or care and/or antisun protection of keratin materials.

Abstract: A process for producing a vinyl chloride polymer is provided. This process includes polymerizing vinyl chloride or a monomer mixture containing vinyl chloride in an aqueous medium in a polymerization vessel fitted with a reflux condenser. This process is characterized by starting to add (A) an anti-foam agent, and (B) a partially saponified polyvinyl alcohol with an average degree of polymerization of 100 to 500 and a saponification degree of 75 to 85 mole %, to a reaction mixture during the operation of said reflux condenser, and continuing the addition of (A) and (B) until recovery of unreacted monomers from said polymerization vessel is completed. According to the process, it is possible to prevent the polymer slurry from foaming, rising, or scattering during polymerization or recovery of unreacted monomers.

Abstract: A graft copolymer composition and the preparation of the composition by living radical polymerization is disclosed. The polymerization reaction can be initiated at active chlorine sites on the poly(vinyl chloride) backbone in conjunction with a transition metal catalyst and an optional ligand. The graft copolymers are useful as, among others, compatibilizers for blends and alloys, as high heat distortion temperature poly(vinyl chloride) materials, as impact modifiers, and permanently plasticized materials.

Abstract: Copolymers of ethylene and alpha olefins that have been formed by a polymerization reaction in the presence of a single site catalyst, such as a metallocene, are used as a film or as a layer in multiple layer films, including molecularly oriented and irradiated heat shrinkable films. Novel blends of the copolymers with other polymeric materials are disclosed and used as a film or a layer in a film particularly in molecularly oriented and heat shrinkable films. Bags made from the multiple layer films are especially useful for shrink packaging primal cuts of meat. Processes for the formation of flexible films and packages made therefrom are also disclosed.

Abstract: The subject invention is directed to new and novel copolymers having long chain branches formed from ethylene and at least one vinyl alicyclic monomer, to solution polymerization using certain unstrained bridged metallocene catalyst which has been found capable of forming said copolymers and to packaging material formed therefrom.

Abstract: A polymerization process for the preparation of (meth)acrylate containing homopolymers or block copolymers comprises heating a mixture of a free radical initiator, a stable free radical agent, and a polymerizable monomer compound to form a thermoplastic resin or resins with a narrow polydispersity. The stable free radical agent is a piperazinone or morpholone based nitroxide or any adducts thereof.

Abstract: Disclosed is a method of polymerizing vinyl chloride or vinylidene chloride monomer. A mixture is prepared of (1) a monomer selected from the group consisting of vinyl chloride, vinylidene chloride, and mixtures thereof with up to about 20 wt % of a comonomer, (2) supercritical carbon dioxide, subcritical carbon dioxide, or liquid carbon dioxide in a weight ratio to the monomer of about 0.5 to about 5; and (3) about 0.1 to about 1 phr of a free radical initiator that is soluble in said supercritical carbon dioxide or a solution of said a free radical initiator in a solvent that is miscible with the carbon dioxide. The mixture is heated to a temperature of about 40 to about 70° C. to polymerize the monomer.

Abstract: This process is characterized in that at least one of the said monomers is polymerized or copolymerized in bulk, solution, emulsion or suspension at a temperature which may be as low as 0.degree. C., in the presence of an initiator system comprising at least one radical-generator compound other than an arenesulphonyl chloride; and at least one catalyst consisting of a metal complex represented by the following formula (I): Ma.sub.a (L).sub.n in which: M represents Ni, Pd or Pt; A represents a halogen or a pseudohalide; the groups L are ligands of the metal M, which are chosen independently from those containing at least one from among N, P, As, Sb, and Bi, it being possible for at least two of these ligands to be connected together by one or more divalent radicals; a is an integer from 1 to 5; n is an integer from 1 to 4; with 4.ltoreq.a+n.ltoreq.6, a+n representing the coordination number of the complex.