Di-sec-butyl peroxydicarbonate emulsion

Abstract

The invention relates to an organic peroxide emulsion containing at least one organic peroxide comprising di-sec-butyl peroxydicarbonate, at least one emulsifier, at least one antifreeze and water; said emulsion being free of methanol and ethanol. The invention also relates to a method for preparing such an emulsion, the use of such an emulsion for the polymerization or copolymerization of one or more ethylenically unsaturated monomers, and a halogenated vinyl polymer obtained by the use of such an emulsion.

Description

Field of the inventionThe present invention relates to a di-sec-butyl peroxydicarbonate emulsion freeof methanol and ethanol, to a process for preparing same and to the use thereof for thepolymerization or copolymerization of one or more ethylenically unsaturatedmonomers. The invention also relates to a halogenated vinyl polymer prepared in thepresence of such an emulsion.Technical backgroundOrganic peroxides, in liquid or solid form, are commonly used aspolymerization initiators for ethylenically unsaturated monomers for the synthesis ofvarious types of polymers.However, their use frequently presents a certain number of problems.Specifically, organic peroxides usually constitute highly unstable species since theydecompose relatively easily under the action of a slight input of heat, of mechanicalenergy (friction or impact) or of incompatible contaminants. Thus, in the event of anuncontrolled elevation of their storage temperature, certain organic peroxides canundergo an autoaccelerated exothermic decomposition which can result in fires and / orviolent explosions. In addition, under these conditions, some of these organicperoxides can release combustible vapors that are capable of reacting with any sourceof ignition which can drastically increase, or even accelerate, the risks of violentexplosion. As a result, it is important to take appropriate precautionary measures interms of safety during the storage and transportation of organic peroxides.In order to overcome these drawbacks, organic peroxides are notably packagedin the form of aqueous emulsions comprising antifreezes. Thus, the presence of watermakes it possible both to absorb and to dissipate the energy generated in the event ofexothermic decompositions of organic peroxides, while the role of the antifreeze is tokeep the emulsion in liquid form, at temperatures of less than -10°C, generally of lessthan -15°C, which makes it possible to limit the risks of an involuntary exothermicdecomposition of organic peroxides.The aqueous emulsions generally also contain an emulsifier having theadvantage of lowering the interfacial tension between the aqueous phase and theorganic peroxide for the purpose of facilitating the dispersion of the peroxide in theform of droplets and of maintaining the size of said droplets over time. Specifically,over time, the peroxide droplets may sediment, form a cream, or undergo Ostwaldripening, or may agglomerate together, bringing about an increase in their mean sizeand in their maximum size which can result, in certain cases, in total or partial phaseseparation and consequently in an overall destabilization of the emulsion.In view of the above, aqueous organic peroxide emulsions must therefore bestable for safety reasons not only during their production but also for a relatively longperiod of time during their transportation and storage before being used aspolymerization initiators. For this purpose, as mentioned above, the organic peroxidedroplets must be mainly have small average and maximum sizes.Thus, the peroxide droplets of an organic peroxide emulsion should have a lowaverage size and preferably a homogeneous size distribution, and should be stable overtime, preferably over a period of at least three months. In particular, the maximumdiameter of these droplets should very preferably not exceed 20 μm.Moreover, in addition to the safety considerations due to the destabilizationphenomenon described above, it is essential to obtain homogeneous emulsions with asmall droplet size also for considerations of quality and efficiency of thepolymerization process. The reason for this is that the use of a non-homogeneousorganic peroxide emulsion or an emulsion with an excessively large droplet size aspolymerization initiator in an emulsion or suspension of vinyl monomer may produceinhomogeneity in the final product. This inhomogeneity is generally characterized bypolymer particles that are poorly gelled during implementation in molten form ("fisheyes", hard grains). Now, the presence of hard grains opacifies the polymer material.These stability considerations are thus very important for applications in which thetransparency of the final product is imperative, notably for medical applications.Furthermore, the use of non-homogeneous organic peroxide emulsions, i.e.emulsions having a significant difference in organic peroxide concentration distributedbetween the upper and lower part of the aqueous phase, can also give rise tounpredictable differences in initiator concentration in the polymerization reactor. Adifference in initiator concentration in the polymerization reactor can cause a problemregarding the polymerization time. A concentration that is too low reduces theproductivity of the reactor since the polymerization time is extended, and can have animpact on the quality of the polymer. A concentration that is too high causes a verysubstantial release of energy by the polymerization and thus poses the problem ofevacuating this energy. The temperature of the polymerization reactor must then becontrolled by the various cooling means, such as the jacket, refrigerated counter-bladesor a condenser, or else, if the temperature is not well controlled, the polymerizationoperation must be stopped.In addition, the steps of discharging the emulsion in intermediate storage silos,of pumping and of introduction of an organic peroxide emulsion into a polymerizationreactor are steps that are important for the quality of the polymer obtained, thereliability of the polymerization process and the productivity. These handling stepsmust be performed in a short time. To do this, it is important for the peroxide emulsionto have a low viscosity so that the flow of the emulsion is facilitated.Thus, an organic peroxide emulsion should advantageously have a flowabilitymeasured by a consistometric cup technique of less than or equal to 200 seconds(measured, for example, according to the standard DIN 53211, with a viscosity cupdiameter of 4 mm and a temperature of 5°C).Various organic peroxide emulsions have been developed.For example, WO 99 / 31194 describes organic peroxide emulsions comprisingan antifreeze and a chlorinated paraffin and optionally nonionic surfactants andprotective colloidal agents.WO 00 / 42078 relates to peroxide emulsions comprising a copolymer of an α,β-unsaturated dicarboxylic acid and a C8-C24 α-olefin whose acid groups are esterifiedwith an ethoxylated alcohol and also an ethoxylated fatty alcohol with an HLB ofgreater than 16.US 5 369 197 describes organic peroxide emulsions comprising a protectivecolloidal agent, such as a polyvinyl alcohol or xanthan gum and an alcohol, inparticular methanol, ethanol or ethylene glycol.JP H0676445 relates to peroxide emulsions comprising an antifreeze, anonionic surfactant and / or a protective colloidal agent and alkali metal ions, alkaline-earth metal ions and hydrogen ions.GB 2083374 relates to aqueous emulsions comprising an organic peroxide, analcohol with a molecular mass of less than 100 and an emulsifier comprising apolyvinyl alcohol.FR 2995905 relates to aqueous organic peroxide emulsions not containing aprotective colloidal agent, comprising as emulsifier a nonionic surfactant, and also anantifreeze, preferably a mixture of methanol and propane-1,2-diol.FR 2995906 describes an aqueous organic peroxide emulsion in which theemulsifying agent is a colloidal agent consisting of a polyvinyl acetate having a degreeof hydrolysis of greater than 80%.In the particular case of di-sec-butyl peroxydicarbonate, an additional problemmust be taken into account, that of the compatibility of the organic peroxide with theantifreeze.Indeed, at the present time, the alcohols most commonly used as antifreezes inorganic peroxide emulsions are methanol and ethanol. However, it has been found thatthese alcohols induce phase separation of the emulsion and decomposition of the di-sec-butyl peroxydicarbonate, when they are placed in contact therewith, leading to adeterioration of the emulsion. This incompatibility between di-sec-butylperoxydicarbonate and methanol and ethanol is specific to this peroxide and is notobserved with other peroxides, including other peroxydicarbonates.In addition, di-sec-butyl peroxydicarbonate has the specificity, relative to othercommonly used organic peroxides, of having a density of greater than 1 g / cm3 (at15°C). In emulsion, it therefore tends to sediment, unlike other commonly used organicperoxides, which tend to float. Di-sec-butyl peroxydicarbonate thus has a specificbehavior in emulsion that is very different from that of other commonly used organicperoxides.There is thus a real need to provide a di-sec-butyl peroxydicarbonate emulsionwhich can maintain a low maximum and average droplet size, and which remainsstable and homogeneous over a long period of time.Summary of the inventionThe invention relates firstly to an organic peroxide emulsion comprising:- at least one organic peroxide comprising di-sec-butyl peroxydicarbonate;- at least one emulsifier;- at least one antifreeze; and- water;said emulsion being free of methanol and ethanol.In certain embodiments, the at least one antifreeze is an alcohol, preferablychosen from the group consisting of monoalcohols, diols, triols and mixtures thereof.In certain embodiments, the at least one antifreeze is chosen from the groupconsisting of ethylene glycol, 2-propanol, 1-propanol, propane-1,2-diol, propane-1,3-diol, glycerol, butan-1-ol, butan-2-ol, butan-1,3-diol, butan-1,4-diol, diethyleneglycol, triethylene glycol and mixtures thereof.In certain embodiments, the at least one antifreeze comprises, preferablyconsists of, propane-1,2-diol.In certain embodiments, the at least one antifreeze is present in an amount offrom 10% to 40% by weight, preferably from 15% to 25% by weight, relative to thetotal weight of the emulsion.In certain embodiments, the at least one organic peroxide consists of di-secbutyl peroxydicarbonate.In certain embodiments, the di-sec-butyl peroxydicarbonate is present in anamount of from 30% to 80% by weight, preferably from 40% to 60% by weight, morepreferentially from 45% to 60% by weight, relative to the total weight of the emulsion.In certain embodiments, the at least one emulsifier comprises a nonionicsurfactant, preferably chosen from the group consisting of oxyalkylenated fattyalcohols, oxyalkylenated fatty acids, oxyalkylenated plant or animal oils, polysorbates,sorbitan esters, non-oxyalkylenated alkyl glucosides, oxyalkylenated alkyl glucosidesand mixtures thereof.In certain embodiments, the at least one emulsifier comprises at least oneprotective colloidal agent, preferably at least one polyvinyl alcohol and / or hydrolyzedpolyvinyl acetate.In certain embodiments, the at least one emulsifier consists of at least oneprotective colloidal agent, preferably at least one polyvinyl alcohol and / or hydrolyzedpolyvinyl acetate.In certain embodiments, the emulsion is free of polyvinyl alcohol and ofhydrolyzed polyvinyl acetate.The invention also relates to a process for preparing an emulsion as describedabove, comprising the following steps:- mixing the at least one organic peroxide, the at least one emulsifier, the atleast one antifreeze and water; and- emulsifying the mixture.The invention also relates to the use of an emulsion as described above for thepolymerization or copolymerization of one or more ethylenically unsaturatedmonomers, in particular vinyl monomers, preferably halogenated vinyl monomers, andmore preferentially vinyl chloride.The invention also relates to a halogenated vinyl polymer obtained bypolymerization of at least one ethylenically unsaturated monomer in the presence ofan emulsion as described above.The present invention meets the need expressed above. More particularly, itprovides an emulsion comprising di-sec-butyl peroxydicarbonate which is stable andhomogeneous over a long period of time and which retains a small average droplet sizeand a small maximum droplet size. The emulsion according to the invention can thusbe transported and stored over long periods in total safety. In addition, the emulsionaccording to the invention meets the required conditions in terms of viscosity and flowtime. Furthermore, the emulsion according to the invention allows the production of apolymer, when it used for the polymerization of ethylenically unsaturated monomers,having a low content of hard grains.This is achieved by virtue of the presence, in the emulsion, of an antifreezecombined with the absence of both ethanol and methanol. Indeed, as indicated above,it was found that the presence of methanol or ethanol in a di-sec-butylperoxydicarbonate emulsion resulted in decomposition of this peroxide and anunstable emulsion. Surprisingly, it was found that emulsions comprising an antifreezebut free of ethanol and methanol remained stable and homogeneous over a long periodof time, had a suitable viscosity, and had droplets that remained of small size.Detailed descriptionThe invention is now described in greater detail and in a nonlimiting mannerin the description that follows.In the present text, unless expressly indicated otherwise, all the percentages(%) shown are percentages by weight.In the present text, the amounts indicated for a given species may apply to thatspecies according to all its definitions (as mentioned in the present text), including themore restricted definitions.EmulsionThe invention relates firstly to an organic peroxide emulsion. The emulsionaccording to the invention is an aqueous emulsion, i.e. it comprises water. Preferably,the water is demineralized or deionized water.Particularly preferably, the emulsion is an oil-in-water type emulsion.The emulsion according to the invention comprises at least one organicperoxide. The at least one organic peroxide comprises di-sec-butyl peroxydicarbonate.This peroxide is sold, for example, under the trade name Luperox 225 by Arkema.Advantageously, the at least one organic peroxide may consist of di-sec-butylperoxydicarbonate. Di-sec-butyl peroxydicarbonate is then the only peroxide in theemulsion.Alternatively, the at least one peroxide may comprise di-sec-butylperoxydicarbonate as a mixture with at least a second organic peroxide. The emulsionaccording to the invention may comprise a mixture of two organic peroxides, or morethan two organic peroxides, provided that one of the organic peroxides is di-sec-butylperoxydicarbonate.The at least one second peroxide is preferably chosen from peroxydicarbonates,peroxyesters, and / or diacyl peroxides.Among the peroxydicarbonates, the preferred peroxides are diethylperoxydicarbonate, diisopropyl peroxydicarbonate, di-n-propyl peroxydi-carbonate, din-butyl peroxydicarbonate, diisobutyl peroxydicarbonate, di-tert-butylperoxydicarbonate, bis(3-methoxybutyl) peroxydicarbonate, dineopentylperoxydicarbonate, bis[2-(2-methoxyethoxy)ethyl] peroxydicarbonate, bis(3-methoxy-3-methylbutyl) peroxydicarbonate, bis(2-ethoxyethyl) peroxydicarbonate,bis(2-ethylhexyl) peroxydicarbonate, and mixtures thereof.Among the peroxyesters, the preferred peroxides are tert-amyl peroxypivalate,tert-butyl peroxypivalate, tert-butyl peroxyneodecanoate, tert-amylperoxyneodecanoate, tert-butyl peroxyisobutyrate, cumyl peroxyneodecanoate, cumylperoxyneoheptanoate, 2,4,4-trimethylpentyl peroxyneodecanoate, tert-butyl peroxy-n-heptanoate, cumyl peroxy-n-heptanoate, tert-amyl peroxy-n-heptanoate, tert-butylperoxyneoheptanoate, tert-amyl peroxy-2-ethylhexanoate, tert-butyl peroxy-2-ethylhexanoate, 1,1,3,3-tetramethylbutyl peroxy-2-ethylhexanoate, hydroxyperoxyesters and mixtures thereof.As hydroxyperoxyesters that may be used in the emulsion according to theinvention, mention may be made of 4-hydroxy-2-methylpentyl peroxyneodecanoate,4-hydroxy-2-methylpentyl peroxy-(2-ethylhexanoate), 4-hydroxy-2-methylpentylperoxy-2-phenylbutyrate, 4-hydroxy-2-methylpentyl peroxy-2-phenoxypropionate, 4-hydroxy-2-methylpentyl peroxy-(2-butyloctanoate), 4-hydroxy-2-methylpentylperoxyneotridecanoate, 4-hydroxy-2-methylhexyl peroxyneodecanoate, 5-hydroxy-1,3,3-trimethylcyclohexyl peroxyneodecanoate, 4-hydroxy-2,6-dimethyl-2,6-bis(neohexanoylperoxy)heptane, 4-hydroxy-2,6-dimethyl-2,6-bis(neodecanoylperoxy)heptane, 3-hydroxy-1,1-dimethylbutyl peroxy-2-ethylhexanoate, 3-hydroxy-1,1-dimethylbutyl peroxyneodecanoate and mixturesthereof.Among the diacyl peroxides, the preferred peroxides are chosen from the groupconsisting of diisobutyryl peroxide, diheptanoyl peroxide, bis(2-ethylbutanoyl)peroxide, bis(3,5,5-trimethylhexanoyl) peroxide, bis(2-ethylhexanoyl) peroxide, andalso asymmetric peroxides such as isobutyroyl octanoyl peroxide, isobutyroyldecanoyl peroxide, isobutyroyl lauroyl peroxide, 2-ethylbutanoyl decanoyl peroxide,2-ethylhexanoyl lauroyl peroxide, and mixtures thereof.More preferentially, the second organic peroxide is chosen from the groupconsisting of tert-butyl peroxyneodecanoate, for example sold under the nameLuperox 10 by Arkema, 3-hydroxy-1,1-dimethylbutyl peroxyneodecanoate, forexample sold under the trade name Luperox 610 by Arkema, cumylperoxyneodecanoate, for example sold under the name Luperox 188 by Arkema,bis(2-ethylhexyl) peroxydicarbonate, for example sold under the trade nameLuperox 223 by Arkema, tert-amyl peroxyneodecanoate, for example sold under thename Luperox 546 by Arkema, tert-butyl peroxypivalate, for example sold under thename Luperox 11 by Arkema, tert-amyl peroxypivalate, for example sold under thename Luperox 554 by Arkema, bis(3,5,5-trimethylhexanoyl) peroxide, for examplesold under the name Luperox 219 by Arkema, and mixtures thereof.When the emulsion comprises more than two peroxides, each of the peroxidesother than di-sec-butyl peroxydicarbonate may be as described above.The second organic peroxide(s) according to the invention advantageouslyhave a one-hour half-life temperature, measured in trichloroethylene, of less than orequal to 90°C, preferably less than 80°C.Furthermore, the second organic peroxide(s) in the emulsion according to theinvention advantageously have a storage temperature below 0°C.The second organic peroxide(s) are advantageously liquid at the storagetemperature, preferably at a storage temperature below 0°C, measured at atmosphericpressure.Preferably, the emulsion according to the invention comprises the at least oneorganic peroxide in an amount of from 30% to 80% by weight, preferably from 40%to 60% by weight, more preferentially from 45% to 60% by weight, relative to the totalweight of the emulsion. In particular the amount of peroxide, relative to the totalweight of the emulsion, may be from 30% to 35% by weight, or from 35% to 40% byweight, or from 40% to 45%, or from 45% to 50%, or from 50% to 55%, or from 55%to 60%, or from 60% to 65%, or from 65% to 70%, or from 70% to 75%, or from 75%to 80% by weight.Advantageously, di-sec-butyl peroxydicarbonate is present in the emulsion inan amount of from 30% to 80% by weight, preferably from 40% to 60% by weight,more preferentially from 45% to 60% by weight, relative to the total weight of theemulsion. Notably, the amount of di-sec-butyl peroxydicarbonate in the emulsion maybe from 30% to 35% by weight, or from 35% to 40% by weight, or from 40% to 45%,or from 45% to 50%, or from 50% to 55%, or from 55% to 60%, or from 60% to 65%,or from 65% to 70%, or from 70% to 75%, or from 75% to 80%, by weight, relativeto the total weight of the emulsion.The emulsion according to the invention comprises at least one antifreeze. Theantifreeze prevents the formation of gels when the emulsion is transported and / orstored cold, i.e. conventionally in an environment with temperatures below 0°C.The antifreeze is preferably an alcohol. Thus, the antifreeze may be any alcoholthat is water-soluble at the storage temperature, for example at a temperature of 0°C.The term "water-soluble alcohol" means a solubility of more than 1% in water at 0°C.The amount of antifreeze in water can be measured by gas chromatography.More particularly, the antifreeze may advantageously be a monoalcohol, a dioland / or a triol.Preferably, the antifreeze is chosen from the group consisting of ethyleneglycol, 2-propanol, 1-propanol, propane-1,2-diol, propane-1,3-diol, glycerol, butan-1-ol, butan-2-ol, butan-1,3-diol, butan-1,4-diol, diethylene glycol, triethylene glycol, andmixtures thereof, these mixtures comprising at least two of the antifreezes listedpreviously. The mixtures of antifreezes may comprise two or more antifreezes asmentioned above, preferably two.Particularly advantageously, the antifreeze is propane-1,2-diol, optionally as amixture with one, or more, antifreezes, preferably as mentioned above. Moreadvantageously, the antifreeze consists of propane-1,2-diol.The emulsion according to the invention is free of ethanol and free of methanol.The antifreeze is preferably present in the emulsion according to the inventionin a content of less than or equal to 40% by weight (relative to the total weight of theemulsion), preferably less than or equal to 25% by weight, more preferably less thanor equal to 22% by weight, relative to the total weight of the emulsion. Such antifreezecontents allow the aqueous phase to remain in liquid form down to temperatures ofless than or equal to -20°C, preferably down to temperatures of less than or equal to -25°C.More particularly, the antifreeze may be present in the emulsion in an amountof from 10% to 40% by weight, preferably from 15% to 25% by weight, relative to thetotal weight of the emulsion. In certain embodiments, the emulsion comprises from10% to 15% by weight, or from 15% to 20% by weight, or from 20% to 25% by weight,or from 25% to 30% by weight, or from 30% to 35% by weight, or from 35% to 40%by weight, of antifreeze, relative to the total weight of the emulsion.The emulsion according to the invention comprises at least one emulsifier.Preferably, the emulsifier according to the invention is readily biodegradable.The qualification of the biodegradability of the emulsifier may be determined by theOECD 301 method and more particularly by the OECD 301 B method by release ofcarbon dioxide.Preferably, the emulsifier comprises, or is (i.e. consists of), a nonionicsurfactant. Thus, the emulsion according to the invention may comprise at least onenonionic surfactant.Even more preferably, the emulsifier comprises, or is, an oxyalkylenated ornon-oxyalkylenated nonionic surfactant chosen from the group consisting of fattyalcohols, fatty acids, sorbitan esters, plant or animal oils (hydrogenated or non-hydrogenated), alkyl glucosides and mixtures thereof. The nonionic surfactantmixtures used in the invention may be mixtures of oxyalkylenated nonionic surfactantsonly, or mixtures of non-oxyalkylenated nonionic surfactants only, or mixtures ofoxyalkylenated nonionic surfactants and non-oxyalkylenated nonionic surfactants.In certain embodiments, the nonionic surfactant may comprise, or be, one ormore poly(ethylene oxide) block copolymers and poly(propylene oxide) blockcopolymers, optionally in combination with one or more other nonionic surfactants,for example as described in the present text.Advantageously, the emulsifier comprises, or is, a nonionic surfactant chosenfrom the group consisting of oxyalkylenated fatty alcohols, oxyalkylenated fatty acids,polysorbates, sorbitan esters, oxyalkylenated plant or animal oils, non-oxyalkylenatedalkyl glucosides, oxyalkylenated alkyl glucosides, and mixtures thereof.The oxyalkylene units are more particularly oxyethylene units (i.e. ethyleneoxide groups), oxypropylene units (i.e. propylene oxide groups), or a combination ofoxyethylene units and oxypropylene units; preferably, the oxyalkylene units areoxyethylene units or a combination of oxyethylene units and oxypropylene units.Thus, the nonionic surfactant is preferably chosen from the group consisting offatty alcohols containing oxyethylene units and optionally oxypropylene units, fattyacids containing oxyethylene units and optionally oxypropylene units, polysorbates,sorbitan esters, plant or animal oils, which are optionally hydrogenated, containingoxyethylene units and optionally oxypropylene units, alkyl glucosides containingoxyethylene units and optionally oxypropylene units, and mixtures thereof.The oxyethylene units (i.e. ethylene oxide groups) and oxypropylene units (i.e.propylene oxide groups) may be randomly distributed or in block form.The number of moles of ethylene oxide and / or propylene oxide preferablyranges from 1 to 250, more preferentially from 2 to 100, even more preferentially from2 to 50 and more particularly from 2 to 20.Preferably, the number of moles of ethylene oxide in the emulsifier ranges from2 to 20.For the purposes of the present invention, the term "fatty alcohol" means analcohol containing at least 6, preferably at least 8, carbon atoms, more preferably a C8-C40 alcohol, preferentially a C8-C20 alcohol.Among the fatty alcohols that may be used in the invention, mention maynotably be made of 2-octyldodecanol, decanol, lauryl alcohol, oleocetyl alcohol,isodecanol, capryl alcohol, oxoisotridecanol, cetostearyl alcohol, eleostearyl alcohol,caprylyl alcohol, myristyl alcohol, hexadecyl or palmityl alcohol, stearyl alcohol,eicosanyl or arachidyl alcohol, behenyl alcohol, oleyl alcohol, eicosenyl or gadoleylalcohol, docosenyl alcohol, ricinoleyl alcohol, linoleyl alcohol, linolenyl alcohol ormixtures thereof.Preferably, the nonionic surfactant is chosen from the group consisting ofoxyalkylenated fatty alcohols and is preferably chosen from octyldodecanol, decanol,lauryl alcohol, oleocetyl alcohol, isodecanol, capryl alcohol, oxoisotridecanol,cetostearyl alcohol, eleostearyl alcohol, caprylyl alcohol, myristyl alcohol, hexadecylor palmityl alcohol, stearyl alcohol, eicosanyl or arachidyl alcohol, behenyl alcohol,oleyl alcohol, eicosenyl or gadoleyl alcohol, docosenyl alcohol, ricinoleyl alcohol,linoleyl alcohol or linolenyl alcohol, which are oxyalkylenated, preferablyoxyethylenated and / or oxypropylenated, and more preferentially oxyethylenated andoptionally oxypropylenated.The fatty alcohols that are more preferred in the context of the invention areoleocetyl alcohol, hexadecyl or palmityl alcohol, stearyl alcohol, oleyl alcohol, linoleylalcohol or mixtures thereof, and even more preferred are the oxyalkylenated,preferably oxyethylenated and / or oxypropylenated, and more preferablyoxyethylenated and optionally oxypropylenated versions thereof.More preferably, the nonionic surfactant is an oxyalkylenated fatty alcoholchosen from the group consisting of oxyethylenated linoleyl alcohol, oxyethylenatedoleocetyl alcohol, oxyethylenated hexadecyl or palmityl alcohol, oxyethylenatedstearyl alcohol, oxyethylenated oleyl alcohol, and mixtures thereof.The abovementioned fatty alcohols may optionally be oxypropylenated to aminor extent.Preferably, the oxyalkylenated plant / animal oils (hydrogenated or non-hydrogenated) are in particular derivatives of ethoxylated mono-, di- and triglyceridesand comprise a complex mixture of ethoxylated glycerol optionally linked to one ormore fatty acid chains (which are themselves ethoxylated or not), fatty acidsethoxylated on the acid function and / or on the hydroxyl function borne the fatty acidchain, and also variable proportions of fatty acids, glycerol and fatty acid mono-, dior triglycerides.For the purposes of the present invention, the term "fatty acid" means an acidor a mixture of acids comprising at least 6 carbon atoms, preferably from 6 to 40 carbonatoms, more preferentially from 8 to 20 carbon atoms.The oxyalkylenated plant / animal oils (hydrogenated or non-hydrogenated) thatmay be used in the invention are preferably chosen from the group consisting ofoptionally hydrogenated, oxyethylenated (or ethoxylated) plant oils.The optionally hydrogenated, oxyethylenated plant oils are preferably chosenfrom the group consisting of ethoxylated castor oil and ethoxylated hydrogenatedcastor oil comprising from 5 to 40 mol of ethylene oxide per mole of ricinoleic acid.Mention may also be made of ethoxylated oils derived from coconut kernel oil, palmoil, palm kernel oil, olive oil, groundnut oil, rapeseed oil, soybean oil, sunflower oil,walnut oil, hazelnut oil, coconut oil, poppy oil, safflower oil, linseed oil, perilla oil,oitica oil, and / or Chinese wood oil.As plant / animal oils that may be used according to the invention as emulsifiers,mention may also be made of ethoxylated fats based on tallow oil, crude or refined talloil, whale oil, herring oil and / or sardine oil. All these ethoxylated glyceride derivativesare characterized in that they include mixtures of ethoxylated mono-, di- ortriglycerides and also corresponding ethoxylated derivatives of fatty acids and ofglycerol. These fatty acids are notably saturated or unsaturated fatty acids derived fromcaproic acid, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearicacid, arachic acid, behenic acid, myristoleic acid, palmitoleic acid, oleic acid,ricinoleic acid, erucic acid, linoleic acid, linolenic acid, eleostearic acid, licanic acid,gadoleic acid, and / or erneic acid. Some unsaturated fatty acids may or may not behydrogenated as in the case of ethoxylated castor oil in which the ricinoleic group mayor may not have been partially or fully hydrogenated.In certain embodiments, the emulsifier according to the invention maycomprise, or be, one or more fatty acids, which are preferably oxyalkylenated, morepreferably oxyethylenated and optionally oxypropylenated, these fatty acids beingselectable from those listed above.Advantageously, the emulsifier may comprise, or be, a nonionic surfactantchosen from the group consisting of oxyalkylenated plant or animal oils (hydrogenatedor non-hydrogenated).More preferentially, the emulsifier may comprise, or be, a nonionic surfactantchosen from the group consisting of plant oils, which are optionally hydrogenated,oxyethylenated and optionally oxypropylenated.More preferentially, the emulsifier may comprise, or be, a nonionic surfactantchosen from the group consisting of ethoxylated, optionally hydrogenated plant oilsincluding from 5 to 40 mol of ethylene oxide, in particular ethoxylated castor oil andethoxylated hydrogenated castor oil including from 20 to 40 mol of ethylene oxide.Even more preferentially, the emulsifier may comprise, or be, ethoxylatedcastor oil including from 20 to 40 mol of ethylene oxide.Advantageously, the emulsifier may comprise, or be, one or more non-ethoxylated sorbitan esters and / or one or more ethoxylated sorbitan esters. In thepresent text, ethoxylated sorbitan esters are also referred to as "polysorbates", the term"sorbitan ester" denoting in the present text non-ethoxylated sorbitan esters, unlessexpressly indicated otherwise.Preferably, the non-ethoxylated sorbitan ester is chosen from the groupconsisting of sorbitan monostearate, sorbitan tristearate, sorbitan monolaurate,sorbitan trilaurate, sorbitan monooleate, sorbitan trioleate, sorbitan monopalmitate andsorbitan tripalmitate and combinations thereof.Sorbitan monooleate is available under the brand name Span 80 (fromCroda).Preferably, the ethoxylated sorbitan ester (or polysorbate) comprises between3 and 40 ethylene oxide groups, preferably between 5 and 20 ethylene oxide groups.Preferably, the ethoxylated sorbitan ester is chosen from the group consistingof ethoxylated sorbitan monostearate, ethoxylated sorbitan tristearate, ethoxylatedsorbitan monolaurate, ethoxylated sorbitan trilaurate, ethoxylated sorbitanmonooleate, ethoxylated sorbitan trioleate, ethoxylated sorbitan monopalmitate,ethoxylated sorbitan tripalmitate and combinations thereof.Sorbitan monooleate 20 OE (i.e. containing 20 ethylene oxide groups) isavailable under the brand name Surfaline SE80 (from Arkema) or Tween 80 (fromCroda).The emulsifier may comprise, or be, one or more alkyl glucosides. As alkylglucosides that may be used in the invention, mention may be made of caprylglucoside, caprylyl glucoside, lauryl glucoside, cocoyl glucoside, hexyl glucoside,isooctyl glucoside, decyl glucoside and / or undecyl glucoside. These alkyl glucosidesmay or may not be oxyalkylenated (and more particularly ethoxylated or nonethoxylated).The emulsion may comprise a combination of at least two emulsifiers, inparticular each of which may independently be as described above.Preferably, the combination of the at least two emulsifiers comprises a non-ethoxylated sorbitan as defined above and an ethoxylated sorbitan comprising between5 and 20 ethylene oxide groups, as described above.In addition or as an alternative to the use of one or more nonionic surfactants(for example as described above), the emulsion according to the invention maycomprise, as emulsifier, at least one protective colloidal agent. Protective colloidalagents are emulsifiers that are well known to those skilled in the art. For the purposesof the present invention, they refer to the group consisting of polyvinyl alcohol,polyvinyl acetate and notably partially hydrolyzed polyvinyl acetate, cellulose estersand xanthan gums.Thus, preferably, the protective colloidal agent in the emulsion according tothe invention is chosen from the group consisting of polyvinyl alcohols, partiallyhydrolyzed polyvinyl acetates, cellulose esters, xanthan gums and mixtures thereof.The hydrolyzed polyvinyl acetate is preferably hydrolyzed to a degree of from 5 mol%to 85 mol%, preferably from 5 mol% to 75 mol%.The at least one emulsifier of the emulsion according to the invention mayconsist of at least one protective colloidal agent.More particularly, the emulsion according to the invention may comprise, asthe at least one emulsifier, at least one polyvinyl alcohol and / or at least one hydrolyzedpolyvinyl acetate, optionally in combination with one or more surfactants, in particularone or more nonionic surfactants as described above. The at least one emulsifier of theemulsion according to the invention may consist of at least one polyvinyl alcoholand / or at least one hydrolyzed polyvinyl acetate, optionally in combination with oneor more surfactants, in particular one or more nonionic surfactants as described above.The emulsifier according to the invention may consist of at least one nonionicsurfactant, in particular at least one nonionic surfactant as described above, andoptionally at least one protective colloidal agent.The emulsifier according to the invention may consist of at least one protectivecolloidal agent and optionally at least one nonionic surfactant, in particular at least onenonionic surfactant as described above.Alternatively, the emulsion according to the invention may be free of polyvinylalcohol. The emulsion according to the invention may be free of partially hydrolyzedpolyvinyl acetate, and may more particularly be free of polyvinyl acetate.More particularly, the emulsion according to the invention may be free ofprotective colloidal agent. This notably makes it possible to reduce the time for theindustrial preparation of the emulsion, since the protective colloidal agent (notablypolyvinyl acetate) which is in solid form requires a prior dissolution step, and makesit possible to minimize the risks associated with the handling of powders. Furthermore,the presence in the emulsion of a colloidal protective agent may increase the viscosityof the emulsion, which may be undesirable for certain applications.The emulsion according to the invention may be free of cellulose ester, moreparticularly cellulose derivatives. The emulsion may be free of xanthan gum.The emulsifier may be present in the emulsion according to the invention in anamount ranging from 0.1% to 10% by weight, preferably from 0.5% to 5% by weight,relative to the total weight of the emulsion. In particular, the emulsion may comprisethe emulsifier in an amount of from 0.1% to 0.5% by weight, or from 0.5% to 1% byweight, or from 1% to 2% by weight, or from 2% to 3% by weight, or from 3% to 4%by weight, or from 4% to 5% by weight, or from 5% to 6% by weight, or from 6% to7% by weight, or from 7% to 8% by weight, or from 8% to 9% by weight, or from 9%to 10% by weight, relative to the total weight of the emulsion.The emulsion according to the invention may comprise the at least one nonionicsurfactant in an amount of from 0.1% to 10% by weight, preferably from 0.5% to 5%by weight, relative to the total weight of the emulsion. In particular, the emulsion maycomprise the nonionic surfactant in an amount of from 0.1% to 0.5% by weight, orfrom 0.5% to 1% by weight, or from 1% to 2% by weight, or from 2% to 3% by weight,or from 3% to 4% by weight, or from 4% to 5% by weight, or from 5% to 6% byweight, or from 6% to 7% by weight, or from 7% to 8% by weight, or from 8% to 9%by weight, or from 9% to 10% by weight, relative to the total weight of the emulsion.The emulsion according to the invention may comprise the at least oneprotective colloidal agent in an amount of from 0.1% to 10% by weight, preferablyfrom 0.5% to 5% by weight, relative to the total weight of the emulsion. In particular,the emulsion may comprise the nonionic surfactant in an amount of from 0.1% to 0.5%by weight, or from 0.5% to 1% by weight, or from 1% to 2% by weight, or from 2%to 3% by weight, or from 3% to 4% by weight, or from 4% to 5% by weight, or from5% to 6% by weight, or from 6% to 7% by weight, or from 7% to 8% by weight, orfrom 8% to 9% by weight, or from 9% to 10% by weight, relative to the total weightof the emulsion.The emulsion according to the invention may also comprise one or moreadditives intended to give the final composition particular properties / characteristics.These additives will ideally be present for the final polymerization orcopolymerization.The additive may be chosen from the group consisting of antifoams, chain-transfer agents, chain extenders, pH regulators, plasticizers and mixtures thereof.The additive(s) are preferably in an amount of from 0.1% to 10% by weight,preferably from 1% to 5% by weight, relative to the total weight of the emulsion.Preferably, the emulsion according to the invention comprises one or moreplasticizers, preferably chosen from the group consisting of aliphatic esters, forinstance phthalates, adipates, benzoates, hydrogenated derivatives of these moleculesand mixtures thereof. In particular, the plasticizer may be diisononylcyclohexane,diisononyl cyclohexanedicarboxylate, and a mixture thereof. The plasticizer(s) may bepresent in the emulsion in an amount of from 1% to 5% by weight relative to the totalweight of the emulsion.Advantageously, the emulsion according to the invention may consistessentially of, or consist of, the at least one organic peroxide, the at least oneemulsifier, the at least one antifreeze, water and optionally one or more additives asdescribed above. The term "the emulsion consists essentially of constituents" meansthat the total amount of these constituents represents at least 90% by weight, preferablyat least 95% by weight, more preferentially at least 98% by weight of the total weightof the emulsion. The expression "consists of" does not exclude the presence ofimpurities present in trace amounts in the emulsion (for example, in an amount of lessthan or equal to 1% by weight relative to the total weight of the emulsion), for exampleimpurities introduced with the organic peroxide. Thus, in certain embodiments, theemulsion according to the invention may comprise an organic solvent, in an amountof less than or equal to 1% by weight relative to the total weight of the emulsion.In other embodiments, the emulsion according to the invention may comprisean organic solvent, for example in an amount of less than or equal to 20% by weightrelative to the total weight of the emulsion. In the present text, the term "organicsolvent" means organic solvents which have a solubility in water of less than 1% byweight at 0°C. The emulsion according to the invention may consist essentially of, orconsist of, the at least one organic peroxide, the at least one emulsifier, the at least oneantifreeze, water, an organic solvent (preferably in an amount of less than or equal to20% by weight relative to the total weight of the emulsion) and optionally one or moreadditives as described above.The emulsion according to the invention may consist essentially of, or consistof, the at least one organic peroxide, the at least one emulsifier, the at least oneantifreeze and water (the emulsion being free of methanol and ethanol).Preferably, the emulsion according to the invention has a flowability (or flowtime) at 5°C, measured via a consistometric cup technique, of less than or equal to 200seconds, more preferentially less than or equal to 150 seconds, and even moreadvantageously less than or equal to 100 seconds. The flowability may be measuredaccording to the standard DIN 53211, with a viscosity cup diameter of 4 mm and atemperature of 5°C.Particularly advantageously, the emulsion according to the invention has anaverage droplet size of less than or equal to 10 μm, preferably less than or equal to 7μm and more particularly advantageously less than or equal to 6 μm. Advantageously,the emulsion according to the invention has a maximum droplet size of less than orequal to 20 μm, more preferentially less than or equal to 18 μm, and even moreadvantageously less than or equal to 15 μm. The droplet size (average and maximum)may be determined via conventional means using the light scattering technique. Themeasurements may be taken using a Malvern Master Sizer 2000 device at roomtemperature.More advantageously, the emulsion according to the invention has theabovementioned droplet sizes during the storage period, for example for a period of atleast three months.Preferably, the concentration of organic peroxide in the emulsion ishomogeneous. The term "homogeneous concentration" means that the differencebetween the concentrations of peroxide (as mass percentages) at the top and bottom ofthe emulsion is less than 3%. The organic peroxide concentration is measured byHPLC on a sample taken from the top of the emulsion and another from the bottom ofthe emulsion.More advantageously, the emulsion according to the invention is homogeneousduring the storage period, for example for a period of at least three months.Preparation of the emulsionThe invention also relates to a process for preparing the emulsion according tothe invention.The preparation process according to the invention comprises a step of mixingthe at least one organic peroxide, the at least one emulsifier, the at least one antifreezeand water. This step may also comprise the above mixing with other constituents ofthe emulsion when the emulsion comprises them, for example mixing with one or moreadditives (such as one or more plasticizers, etc.) as described in the previous section.The mixing may be performed in one step (the constituents all being added to themixture simultaneously) or in several steps (a premix of some constituents first beingmade, followed by the addition of other constituents).The process also comprises a step of emulsifying the mixture. The steps ofmixing of the constituents of the emulsion and of emulsifying may be simultaneous.Alternatively, the emulsifying step may be performed successively to a first step ofmixing the constituents of the emulsion.The emulsion according to the invention may be prepared by dispersing at leastthe emulsifier and the antifreeze, and also optionally one or more additives, in waterso as to obtain a homogeneous aqueous phase, then by adding one or more organicperoxides to said aqueous phase, the whole being then emulsified in the course of anemulsification step at a temperature preferably below 5°C, so as to limit prematuredegradation of the peroxide, and more preferably below -5°C. Alternatively, theemulsifier or one or more of the emulsifiers may be dissolved in the organicperoxide(s) before being added to the aqueous phase.The abovementioned steps may be performed in the particular order indicatedabove, or in a different order.The temperature at which the emulsion is prepared is not critical, but it mustbe sufficiently low to avoid a high rate of decomposition of the organic peroxide,which would result in a loss of titer. The temperature chosen depends on the organicperoxide. It is, for example, between 15 and 10°C, preferably from -10 to 5°C.Preferably, the mixing and emulsifying steps are performed at the same temperature,preferably within the ranges mentioned above.Deionized water or distilled water is preferably used to prepare the aqueousemulsion.The emulsifying step of the process according to the invention is preferablyperformed with a high-shear mixer to optimally divide and / or homogenize theperoxide in the aqueous phase. Examples that may be mentioned include mechanicallyrotating blade and anchor agitators, impeller agitators, i.e. one or more agitatorsmounted on a common shaft, turbine agitators, i.e. those including baffles attached tothe mixing vessel or adjacent to the agitator members. Colloidal mills andhomogenizers may also be used.According to one variant of the process according to the invention, anultrasonic mixer or a rotor-stator mixer may be used for the emulsification.Following the preparation of the emulsion, the steps of pumping andintroducing the emulsions into a polymerization reactor should generally be performedas quickly as possible. Accordingly, the peroxide emulsions should advantageouslyhave a low viscosity. Thus, the organic peroxide emulsions according to the inventionpreferably have a dynamic viscosity range, at -10°C and at a shear rate of 100 s-1, ofless than or equal to 850 mPa.s, more preferably less than or equal to 700 mPa. s, morepreferentially less than or equal to 500 mPa.s, immediately after production (theviscosities are measured, for example, according to the standard DIN 53019 withapparatus of the Haake VT550 Viscotester type, at -10°C and for a shear rate of 100 s1).Their flowability, measured by means of a consistometric cup technique, isadvantageously less than or equal to 200 seconds, more preferentially less than or equalto 170 seconds, and even more advantageously less than or equal to 100 seconds(measured, for example, according to the standard DIN 53211, with a viscosity cupdiameter of 4 mm and a temperature of 5°C).The average droplet size of the emulsion is preferably less than or equal to 10μm, more preferably less than or equal to 7 μm and more particularly advantageouslyless than or equal to 6 μm. Advantageously, the maximum droplet size of the emulsionis less than or equal to 20 μm, more preferentially less than or equal to 18 μm, andeven more advantageously less than or equal to 15 μm. The droplet size (average andmaximum) may be determined via conventional means using the light scatteringtechnique and the measurements may be taken using a Malvern Master Sizer 2000device at room temperature.UseThe present invention also relates to the use of the emulsion as described abovefor the polymerization or copolymerization of one or more ethylenically unsaturatedmonomers, in particular of one or more vinyl monomers, preferably halogenated vinylmonomers, and more preferentially vinyl chloride.As examples of ethylenically unsaturated monomers that may be used in theinvention, mention may be made of acrylates, vinyl esters, vinyl halide monomers,vinyl ethers, butadiene and / or aromatic vinyl compounds such as styrene.Preferably, the ethylenically unsaturated monomers are chosen from the groupconsisting of vinyl halide monomers (i.e. halogenated vinyl monomers), and morepreferentially the ethylenically unsaturated monomers are vinyl chloride.The invention also relates to a process for preparing a halogenated vinylpolymer, comprising a step of polymerization or copolymerization of one or moreethylenically unsaturated monomers in the presence of an emulsion as describedabove. The ethylenically unsaturated monomers may be as described above and aremore preferentially vinyl chloride. The halogenated vinyl polymer prepared ispreferably a poly(vinyl chloride).The polymerization of the ethylenically unsaturated monomer(s), preferablythe polymerization of the vinyl chloride monomer, advantageously takes place insuspension, preferably at an initiation temperature ranging from 45°C to 70°C.The emulsion may be added directly to the polymerization reactor or may bepremixed with other organic peroxides, water, polyvinyl alcohol and / or other additivesprior to introducing this mixture into the polymerization reactor.PolymerAnother subject of the present invention relates to a halogenated vinyl polymerobtained (or which may be obtained) by polymerization of at least one ethylenicallyunsaturated monomer, as described above, in the presence of the emulsion accordingto the invention as described above. The polymerization may be as described in thepreceding section.Preferably, the invention relates to a poly(vinyl chloride) obtained (or whichmay be obtained) by polymerization of vinyl chloride in the presence of the emulsionaccording to the invention.The invention also relates to a halogenated vinyl polymer obtained (or whichmay be obtained) via a preparation process as described above.Such halogenated vinyl polymers have the advantage of having a low hardgrain content. The hard grain content may be determined as described in the article byO. Leachs, in Kunststoffe, Vol. 50(4), 1960 pages 227-234.ExamplesThe examples that follow illustrate the invention without limiting it.The following emulsions were prepared (the amounts indicated in the tablesbelow are expressed as mass percentages relative to the total weight of the emulsion):[Table 1][Table 2]qs 100 = quantity sufficient to reach 100% of the weight of the emulsion.The nature of the compounds used is indicated below:- Luperox 225: di-sec-butyl peroxydicarbonate;- Surfaline LG15: nonionic surfactant, unsaturated C16-C18 and C18 glycerolmono- / diester, polyethoxylated (15 units);- PVA: polyvinyl acetate with a degree of hydrolysis of 72.5 mol% (Alcotex72.5).Emulsions 7, 8 and 9 correspond to emulsions according to the invention, andemulsions 1, 2, 3, 4, 5, 6 and 10 are comparative emulsions.The emulsions were prepared as described below.The aqueous phase containing the emulsifier, antifreeze and water was stirredat between 500 and 1000 revolutions per minute (rpm) and maintained at -5°C(Celsius).The organic peroxides were added gradually to the reactor containing thismixture. Stirring was continued for three minutes at 2000 rpm. The whole was thenstirred vigorously with an "Ultra-Turrax S-25N 18G" blender for two minutes (exceptfor emulsion No. 8, which was stirred for six minutes) at 9500 rpm, then stirred witha paddle at 1000 rpm for one minute. Each emulsification is made on 200 g in total.The emulsions were then transferred into a plastic container, the container wasclosed and the emulsions were stored at -20°C for the time indicated.The flow time at 5°C (viscosity cup at 5°C), the average and maximum dropletsizes, by volume, over a period of 6 months, and also the concentration of organicperoxide at the top and bottom of the aqueous phase of the emulsion (as weightpercentages relative to the total weight of the aqueous phase) were determined, asindicated below.The flow time measurements are taken using consistometric cups according tothe standard DIN 53211 (viscosity cup diameter: 4 mm), which is well known to thoseskilled in the art. The measurement is taken on 100 g of emulsion after conditioning at+5°C. The flow time measurements are expressed in seconds and the accuracy is ±10%of the indicated value.The average droplet size and the maximum droplet size are determined viaconventional means using the light scattering technique. The measurements are takenusing a Malvern Mastersizer 2000 device at room temperature. The average dropletsize and the maximum droplet size are given with an accuracy of ± 0.5 μm(micrometer).After 6 months of storage at -20°C, a sample from the top of the emulsion(taken from the first centimeter below the emulsion surface) and a sample from thebottom of the emulsion (taken from the first centimeter from the bottom of theemulsion) were taken and analyzed to determine the organic peroxide concentration.The concentrations of organic peroxide in the aqueous phase were determined on aWaters H-class UPLC machine with an accuracy of ± 1%.The results are presented in the tables below.[Table 3][Table 4]It is seen that emulsions 7 and 8 according to the invention are more stable thanemulsions 1 to 6. Indeed, the latter undergo demixing after only 1 or 2 months ofstorage, whereas emulsions 7 and 8 remain stable over a period of at least 6 months.The appearance of pressure in the container of emulsions 1 to 6 is also observed, whichis a sign of decomposition of the Luperox 225. In addition, the average droplet size ofemulsions 7 and 8 remains small over a period of at least 6 months. Furthermore, after6 months, the concentrations of organic peroxide at the top and bottom of the aqueousphase of emulsions 7 and 8 are similar: emulsions 7 and 8 are still homogeneous after6 months of storage.Emulsion 9 according to the invention is also more stable than the comparativeemulsion 10, for which phase separation is observed as early as 2 hours after itspreparation. On the other hand, emulsion 9 according to the invention maintains itsstability over a period of at least 6 months and retains a low average and maximumdroplet size over this period. In addition, after 6 months, emulsion 9 has remainedhomogeneous, the concentrations of organic peroxide at the top and bottom of theaqueous phase being similar.The viscosity cup values of the emulsions according to the invention arerelatively low and are suitable for a polymerization application.

Claims

1. An organic peroxide emulsion comprising: - at least one organic peroxide comprising di-sec-butyl peroxydicarbonate; - at least one emulsifier; - at least one antifreeze; and - water; said emulsion being free of methanol and ethanol.

2. The emulsion as claimed in claim 1, in which the at least one antifreeze is an alcohol, preferably chosen from the group consisting of monoalcohols, diols, triols and mixtures thereof.

3. The emulsion as claimed in claim 1 or 2, in which the at least one antifreeze is chosen from the group consisting of ethylene glycol, 2- propanol, 1-propanol, propane-1,2-diol, propane-1,3-diol, glycerol, butan-1-ol, butan-2-ol, butan-1,3-diol, butan-1,4-diol, diethylene glycol, triethylene glycol and mixtures thereof.

4. The emulsion as claimed in one of claims 1 to 3, in which the at least one antifreeze comprises, preferably consists of, propane-1,2-diol.

5. The emulsion as claimed in one of claims 1 to 4, in which the at least one antifreeze is present in an amount of from 10% to 40% by weight, preferably from 15% to 25% by weight, relative to the total weight of the emulsion.

6. The emulsion as claimed in one of claims 1 to 5, in which the at least one organic peroxide consists of di-sec-butyl peroxydicarbonate.

7. The emulsion as claimed in one of claims 1 to 6, in which the di-sec- butyl peroxydicarbonate is present in an amount of from 30% to 80% by weight, preferably from 40% to 60% by weight, more preferentially from 45% to 60% by weight, relative to the total weight of the emulsion.

8. The emulsion as claimed in one of claims 1 to 7, in which the at least one emulsifier comprises a nonionic surfactant, preferably chosen from the group consisting of oxyalkylenated fatty alcohols, oxyalkylenated fatty acids, oxyalkylenated plant or animal oils, polysorbates, sorbitan esters, non-oxyalkylenated alkyl glucosides, oxyalkylenated alkyl glucosides and mixtures thereof.

9. The emulsion as claimed in one of claims 1 to 8, in which the at least one emulsifier comprises at least one protective colloidal agent, preferably at least one polyvinyl alcohol and / or hydrolyzed polyvinyl acetate.

10. The emulsion as claimed in one of claims 1 to 7 or 9, in which the at least one emulsifier consists of at least one protective colloidal agent, preferably at least one polyvinyl alcohol and / or hydrolyzed polyvinyl acetate.

11. The emulsion as claimed in one of claims 1 to 8, which is free of polyvinyl alcohol and of hydrolyzed polyvinyl acetate.

12. A process for preparing an emulsion as claimed in one of claims 1 to 11, comprising the following steps: - mixing the at least one organic peroxide, the at least one emulsifier, the at least one antifreeze and water; and - emulsifying the mixture.

13. The use of the emulsion as claimed in one of claims 1 to 11, for the polymerization or copolymerization of one or more ethylenically unsaturated monomers, in particular vinyl monomers, preferably halogenated vinyl monomers, and more preferentially vinyl chloride.

14. A halogenated vinyl polymer obtained by polymerization of at least one ethylenically unsaturated monomer in the presence of the emulsion as claimed in one of claims 1 to 11.