EP4341307A1

EP4341307A1 - Organic peroxide emulsion

Info

Publication number: EP4341307A1
Application number: EP21830451.7A
Authority: EP
Inventors: Markus Brandhorst; Jürgen Lohr
Original assignee: Arkema France SA
Current assignee: Arkema France SA
Priority date: 2021-05-20
Filing date: 2021-11-24
Publication date: 2024-03-27
Also published as: BR112023024165A2; CO2023015465A2; CN117730104A

Abstract

The invention relates to an organic peroxide emulsion containing at least one organic peroxide, at least one emulsifier comprising at least one non-ionic surfactant including at least one fatty chain and having an HLB value of 18 or less, at least one antifreeze having a dynamic viscosity at 20°C from 40 mPa.s to 100 mPa.s, and water. The invention also relates to a method for preparing such an emulsion, to the use of such an emulsion for the polymerization or copolymerization of one or more ethylenically unsaturated monomers, and to a halogenated vinyl polymer obtained by the use of such an emulsion.

Description

Organic peroxide emulsion Field of the invention The present invention relates to organic peroxide emulsions, to a process for their preparation and to the use thereof for the polymerization or copolymerization of one or more ethylenically unsaturated monomers. . The invention also relates to a halogenated vinyl polymer prepared in the presence of such emulsions. TECHNICAL BACKGROUND Organic peroxides, in liquid or solid form, are commonly used as polymerization initiators for ethylenically unsaturated monomers for the synthesis of different types of polymers. However, their implementation frequently poses a number of problems. Indeed, organic peroxides most often constitute highly unstable species because they decompose relatively easily under the action of a low input of heat, mechanical energy (friction or impact) or incompatible contaminants. Thus, in the event of an uncontrolled rise in their storage temperature, certain organic peroxides can undergo self-accelerating exothermic decomposition which can lead to fires and/or violent explosions. Furthermore, under these conditions, some of these organic peroxides can release combustible vapors liable to react with any source of ignition, which can drastically increase, or even accelerate, the risks of a violent explosion. As a result, it is important to take adequate precautionary measures in terms of safety when storing and transporting organic peroxides. In order to overcome these drawbacks, organic peroxides are in particular packaged in the form of aqueous emulsions comprising antifreezes. Thus the presence of water makes it possible both to absorb and to dissipate the energy generated in the event of exothermic decompositions of the organic peroxides, while the antifreeze has the role of maintaining the emulsion in the form liquid, at temperatures below -10°C, generally below -15°C, which makes it possible to limit the risks of involuntary exothermic decomposition of the organic peroxides. Aqueous emulsions generally also contain an emulsifier having the advantage of lowering the interfacial tension between the aqueous phase and the organic peroxide in order to facilitate its dispersion in the form of droplets and to maintain the size of the latter over time. Indeed, over time, the peroxide droplets can sediment, form a cream, or undergo Ostwald ripening, or can agglomerate between them causing an increase in their average size and their maximum size which can lead , in some cases, to a total or partial phase separation and, consequently, to an overall destabilization of the emulsion. In view of the foregoing, the aqueous emulsions of organic peroxide must therefore be stable for safety reasons not only during their production but also during a relatively long period corresponding to their transport and their storage before being used as polymerization initiators. To do this, as indicated above, the droplets of organic peroxide must mainly present a mean size and a maximum size that are small and stable over time. Thus, the peroxide droplets of an organic peroxide emulsion must have a low average size and, preferably, a homogeneous size distribution, and be stable over time, preferably over a period of at least six months. In particular, the maximum diameter of these droplets should very preferably not be less than 20 μm. Moreover, in addition to the safety considerations due to the destabilization phenomenon described above, it is essential to obtain homogeneous emulsions with small droplet size also for considerations of quality and efficiency of the polymerization process. Indeed, the use of an inhomogeneous organic peroxide emulsion or with a droplet size that is too large as a polymerization initiator in a vinyl monomer emulsion or suspension can produce inhomogeneity in the final product. This inhomogeneity is generally characterized by poorly gelled polymer particles during processing in the molten state (“fish eyes”, hard grains). However, the presence of hard grains opacifies the polymer material. These stability considerations are thus very important for applications where the transparency of the final product is imperative, in particular for medical applications. In addition, the use of inhomogeneous organic peroxide emulsions, that is to say having a significant difference in organic peroxide concentration distributed between the upper part and the lower part of the aqueous phase, can also generate differences unpredictable initiator concentration in the polymerization reactor. A difference in initiator concentration in the polymerization reactor can pose a problem of polymerization time. Too low a concentration reduces the productivity of the reactor since the polymerization time is extended, and can have an impact on the quality of the polymer. Too high a concentration leads to a very high release of energy by the polymerization and therefore poses a problem of evacuation of this energy. The temperature of the polymerization reactor will then have to be controlled by the various means of cooling, such as the double jacket, refrigerated counter-blades or a condenser, or else, in the absence of good control of the temperature, the operation of polymerization must be stopped. In addition, the steps of unloading the emulsion into intermediate storage silos, pumping and introducing an organic peroxide emulsion into a polymerization reactor are important steps for the quality of the polymer obtained, the reliability of the polymerization process and productivity. These handling steps must be carried out in a short time. To do this, it is important that the peroxide emulsion has a low viscosity so that the flow of the emulsion is facilitated. Thus, an organic peroxide emulsion must advantageously have a flowability measured by a consistometric cutting technique of less than or equal to 200 seconds (measured for example according to the DIN 53211 standard, with a diameter of the viscosity cup of 4 mm and a temperature of 5°C). Different organic peroxide emulsions have been developed. However, there is a real need to provide an organic peroxide emulsion that remains stable and relatively homogeneous over a long period of time and that allows the droplet size to be kept small. Summary of the invention The invention relates firstly to an emulsion of organic peroxide comprising: - at least one organic peroxide; – at least one emulsifier comprising at least one nonionic surfactant comprising at least one fatty chain and having an HLB of less than or equal to 18; – at least one antifreeze having a dynamic viscosity at 20°C ranging from 40 mPa.s to 100 mPa.s; – from 0 to 1% polyvinyl acetate – water and in which, when said emulsion comprises at least one alcohol chosen from the group consisting of methanol, ethanol, ethylene glycol and diethylene glycol, the latter is present in a mass ratio strictly less than 1, preferably in a ratio less than 0.9, even more preferably less than 0.7 and even more preferably less than 0.5 with respect to said at least one antifreeze having a viscosity dynamic at 20°C ranging from 40 mPa.to 100 mPa.s. In embodiments, the emulsion consists of the at least one organic peroxide, the at least one emulsifier, the at least one antifreeze, water optionally an organic solvent, and optionally one or more selected additives from the group consisting of antifoaming agents, chain transfer agents, chain extenders, pH regulating agents, plasticizers, and mixtures thereof, said emulsion not being one of the excluded compositions above. In embodiments, the at least one antifreeze is an alcohol, preferably chosen from the group consisting of diols and mixtures thereof. In embodiments, the at least one antifreeze is selected from the group consisting of propane-1,2-diol, propane-1,3-diol, triethylene glycol and mixtures thereof, preferably is propane-1,2-diol. In embodiments, the at least one antifreeze comprises, preferably consists of, a mixture of propane-1,2-diol and 2-propanol, preferably the mass ratio of propane-1,2-diol to 2- propanol being strictly greater than 1. In embodiments, the mass ratio of propane-1,2-diol relative to 2-propanol is strictly greater than 1 and less than 4, preferably is strictly greater than 1 and less than 2. In embodiments, the at least one antifreeze is present in an amount of 10 to 40 wt%, preferably 15 to 25 wt%, more preferably 17 to 22 wt%, based on the weight total of the emulsion. In embodiments, the at least one organic peroxide is selected from the group consisting of peroxydicarbonates, peroxyesters, diacyl peroxides and combinations thereof. In embodiments, the at least one organic peroxide is selected from the group consisting of tert-amyl peroxypivalate, tert-butyl peroxypivalate, tert-butyl peroxyneodecanoate, tert-amyl peroxyneodecanoate, 3-hydroxy-1, 1-dimethylbutyl peroxyneodecanoate, cumyl peroxyneodecanoate, di-sec-butyl peroxydicarbonate, di(2-ethylhexyl) peroxydicarbonate, di(3,5,5-trimethylhexanoyl) peroxide, and mixtures thereof. In embodiments, the at least one organic peroxide is present in a content ranging from 40 to 80% by weight, preferably ranging from 44 to 65% by weight, more preferably ranging from 45 to 60% by weight, relative to the total weight of the emulsion. In embodiments, the at least one nonionic surfactant is chosen from the group consisting of oxyalkylenated fatty alcohols, oxyalkylenated fatty acids, oxyalkylenated vegetable or animal oils, polysorbates, sorbitan esters, alkyl glucosides, oxyalkylenated alkyl glucosides and mixtures thereof. Preferably, the emulsion according to the invention is not: - a composition consisting of: 50% by weight of di-sec-butyl peroxydicarbonate, 1.44% by weight of ethoxylated castor oil with a rate of average ethoxylation of 31 and 21.4% by weight of propane-1,2-diol, the balance being water; - a composition consisting of: 50% by weight of di-sec-butyl peroxydicarbonate, 1.5% by weight of ethoxylated castor oil with an average ethoxylation rate of 20 and 21.4% by weight of propane- 1,2-diol, the balance being water; - a composition consisting of: 50% by weight of di-sec-butyl peroxydicarbonate, 1.5% by weight of ethoxylated castor oil with an average ethoxylation rate of 20, 21.4% by weight of propane- 1,2-diol and 3% 3-hydroxy-1,1-dimethylbutyl peroxyneodecanoate, balance water - an emulsion consisting of: 50% by weight di-sec-butyl peroxydicarbonate, 1.5% by weight of castor oil ethoxylated with an average ethoxylation level of 20 ^, 21.4% by weight of propane-1,2-diol and 11.5% of 3-hydroxy-1,1-dimethylbutyl peroxyneodecanoate, the balance being water. The invention also relates to a method for preparing an emulsion as described above, comprising a step of mixing the at least one organic peroxide, the at least one emulsifier, the at least one antifreeze and the water ; and optionally, a step of emulsifying the mixture. The invention also relates to the use of an emulsion as described above, for the polymerization or the copolymerization of one or more ethylenically unsaturated monomers, in particular vinyl monomers, preferably halogenated, and more preferably chloride of vinyl. The invention also relates to a halogenated vinyl polymer obtained by polymerization of at least one ethylenically unsaturated monomer in the presence of an emulsion as described above. The present invention makes it possible to meet the need expressed above. More specifically, it provides a homogeneous and stable organic peroxide emulsion over time, in which the average and maximum droplet sizes remain as small as possible, thus being able to be transported and stored over long periods of time in complete safety, and respecting the required conditions. in terms of viscosity and flow time of the emulsion. In addition, the emulsion according to the invention makes it possible to obtain a polymer, when it is used for the polymerization of ethylenically unsaturated monomers, having a low content of hard grains. Surprisingly, it has been discovered that emulsions with low (or even zero) contents of ethanol, methanol and protective colloid agent, in combination with the use of an emulsifier and a particular antifreeze, allow obtaining small droplets and remained stable and homogeneous over a long period of time, with an adapted viscosity. Detailed Description The invention is now described in more detail and in a non-limiting manner in the description which follows. In the present text, unless otherwise expressly indicated, all the percentages (%) indicated are percentages by weight relative to the total weight of the emulsion. In this text, the quantities indicated for a given species can apply to this species according to all its definitions (as mentioned in this text), including the more restricted definitions. Emulsion The invention relates firstly to an emulsion of organic peroxide. The emulsion according to the invention is an aqueous emulsion, that is to say it comprises water. Preferably, the water is demineralized or deionized water. Particularly preferably, the emulsion is an emulsion of the oil-in-water type. The emulsion according to the invention comprises at least one organic peroxide. The organic peroxide is preferably chosen from peroxydicarbonates, peroxyesters and/or diacyl peroxides. Among the peroxydicarbonates, the preferred peroxides are di-ethyl peroxydicarbonate, di-iso-propyl peroxydicarbonate, di-n-propyl peroxydicarbonate, di-sec-butyl peroxydicarbonate, di-n-butyl peroxydicarbonate , di-iso-butyl peroxydicarbonate, di-tert-butyl peroxydicarbonate, di-(3-methoxybutyl) peroxydicarbonate, di-neopentyl peroxydicarbonate, bis[2-(2-methoxyethoxy)ethyl peroxydicarbonate ], di-(3-methoxy-3-methylbutyl)peroxydicarbonate, di-(2-ethoxyethyl)peroxydicarbonate, di-2-ethylhexylperoxydicarbonate, and mixtures thereof. Among the peroxyesters, the preferred peroxides are tert-amyl peroxypivalate, tert-butyl peroxypivalate, tert-butyl peroxyneodecanoate, tert-amyl peroxyneodecanoate, tert-butyl peroxy isobutyrate, cumyl peroxyneodecanoate, cumyl peroxyneodecanoate, 2 ,4,4 trimethylpenty peroxyneodecanoate, tert-butyl peroxy n-heptanoate, cumylperoxy n-heptanoate, tert-amyl peroxy n-heptanoate, tert-butyl peroxy n-octanoate, tert-amyl peroxy n-octanoate tert -butyl peroxyneoheptanoate, tert-amyl peroxy 2-ethylhexanoate, tert-butyl peroxy 2-ethylhexanoate, 1,1,3,3-tetramethyl butyl-peroxy-2 ethylhexanoate, hydroxyperoxyesters and mixtures thereof. As hydroxyperoxyesters that can be used in the emulsion according to the invention, mention may be made of 4-hydroxy-2-methylpentylperoxyneodecanoate, 4-hydroxy-2-methylpentylperoxy-(2-ethylhexanoate), 4-hydroxy-2-methylpentylperoxy -2-phenylbutyrate, 4-hydroxy-2-methylpentylperoxy-2- phenoxypropionate, 4-hydroxy-2-methylpentylperoxy-(2-butyloctanoate), 4-hydroxy-2-methylpentylperoxyneotridecanoate, 4-hydroxy-2- methylhexylperoxyneodecanoate , 5-hydroxy-1,3,3-trimethylcyclohexylperoxyneodecanoate, 4-hydroxy-2,6-dimethyl-2,6-di(neohexanoylperoxy)heptane, 4-hydroxy-2,6-dimethyl-2,6- di(neodecanoylperoxy)heptane, 3-hydroxy-1,1 dimethylbutylperoxy 2-ethylhexanoate, 3-hydroxy-1,1 dimethylbutylperoxyneodecanoate and mixtures thereof. Among the diacyl peroxides, the preferred peroxides are chosen from the group consisting of diisobutyryl peroxide, di(2-ethylbutanoyl) peroxide, di(3,5,5-trimethylhexanoyl) peroxide, di( 2-ethylhexanoyl), as well as asymmetric peroxides such as isobutyroyl octanoyl peroxide, isobutyroyl decanoyl peroxide, isobutyroyl lauroyl peroxide, 2-ethylbutanoyl decanoyl peroxide, 2-ethylhexanoyl lauroyl peroxide, and mixtures thereof. In a particularly preferred manner, the organic peroxide is chosen from the group consisting of tert-butyl peroxyneodecanoate, for example sold under the name Luperox® 10 by Arkema, 3-hydroxy-1,1 dimethylbutyl peroxyneodecanoate, for example sold under the trade name Luperox® 610 by Arkema, cumyl peroxyneodecanoate, for example sold under the name Luperox® 188 by Arkema, di-sec-butyl peroxydicarbonate, for example sold under the trade name Luperox® 225 by Arkema, di(2 - ethylhexyl), for example sold under the trade name Luperox® 223 by Arkema, tert-amyl peroxyneodecanoate, for example sold under the name Luperox® 546 by Arkema, tert-butyl peroxypivalate, for example sold under the name Luperox® 11 by Arkema, tert-amyl peroxypivalate, for example sold under the name Luperox® 554 by Arkema, di(3,5,5-trimethylhexanoyl) peroxide, for example sold under the d designation Luperox® 219 by Arkema and mixtures thereof. Preferably said organic peroxide is di(2-ethylhexyl) peroxydicarbonate. The emulsion according to the invention can comprise a mixture of two or more organic peroxides, in particular as described above. Alternatively, the emulsion according to the invention can comprise a single organic peroxide, in particular a single organic peroxide as described above. In a particular embodiment, the emulsion according to the invention does not comprise di-sec-butyl peroxydicarbonate. Preferably, the emulsion according to the invention comprises the at least one organic peroxide in a content ranging from 40 to 80% by weight, preferably ranging from 44 to 65% by weight, more preferably ranging from 45 to 60% by weight, relative to the total weight of the emulsion. Preferably, when the emulsion comprises several organic peroxides, the total content of these ranges from 40 to 80% by weight, preferably ranging from 44 to 65% by weight, more preferably ranges from 45 to 60% by weight. , relative to the total weight of the emulsion. The organic peroxide(s) according to the invention advantageously have a half-life temperature at one hour, measured in trichlorethylene, of less than or equal to 90°C, preferably less than 80°C. In addition, the organic peroxide(s) in the emulsion according to the invention advantageously have a storage temperature below 0°C. The organic peroxide(s) are advantageously liquid at the storage temperature, preferably at a storage temperature below 0° C., measured at atmospheric pressure. The emulsion according to the invention comprises at least one antifreeze. The antifreeze makes it possible to prevent the formation of gels when the emulsion is transported and/or stored cold, that is to say conventionally in an environment whose temperatures are below 0°C. The antifreeze according to the invention has a dynamic viscosity at 20° C. ranging from 40 to 100 mPa.s. The dynamic viscosity at 20° C. of the antifreeze can be measured according to the DIN 53019 standard with an apparatus of the Viscotester Haake VT550 type, for a shear rate of 100 s ⁻¹ . The use of an antifreeze having such a dynamic viscosity makes it possible to obtain emulsions having a sufficiently low viscosity to be compatible with an application in polymerization. Preferably, the at least one antifreeze included in the emulsion according to the invention consists of at least one antifreeze having a dynamic viscosity at 20° C. ranging from 40 to 100 mPa.s. The dynamic viscosity at 20° C. of the antifreeze is more preferably less than or equal to 90 mPa.s, preferably less than or equal to 80 mPa.s, preferably less than or equal to 70 mPa.s, preferably less than or equal to 60 mPa.s and even more preferably 55 mPa.s, The antifreeze according to the invention has a dynamic viscosity at 20° C. greater than or equal to 40 mPa .s. The use of an antifreeze having such a dynamic viscosity makes it possible to limit the mobility of the droplets of the emulsion and therefore to increase the stability of the emulsion. It also makes it possible to obtain droplets with a smaller average size. In particular, the antifreeze can have a dynamic viscosity at 20° C. of 40 to 55 mPa.s. The antifreeze is preferably an alcohol. Thus, the antifreeze can be any alcohol that is soluble in water at the storage temperature, for example at a temperature of 0° C., respecting the dynamic viscosity conditions mentioned above. By "water-soluble alcohol" is meant a solubility greater than 1% in water at 0°C. The amount of antifreeze in the water can be measured by gas chromatography. More particularly, the antifreeze can advantageously be a diol. Preferably, the antifreeze is chosen from the group consisting of propane-1,2-diol (dynamic viscosity at 20°C of 45 mPa.s), propane-1,3-diol (dynamic viscosity at 20°C of 52 mPa.s) and triethylene glycol (dynamic viscosity at 20° C. of 48 mPa.s) and mixtures thereof, these mixtures comprising at least two of the antifreezes listed above. More preferably, the antifreeze is propane-1,2-diol. According to advantageous embodiments, the antifreeze is propane-1,2-diol, optionally mixed with one or more antifreezes, preferably such than mentioned above. More advantageously, the antifreeze consists of propane-1,2-diol. According to other advantageous embodiments, the antifreeze comprises a mixture of propane-1,2-diol and 2-propanol, optionally mixed with one or more antifreezes, preferably as mentioned above. More advantageously, the antifreeze consists of a mixture of propane-1,2-diol and 2-propanol. Compared to the use of propane-1,2-diol alone, the use of a mixture of propane-1,2-diol and 2-propanol makes it possible to reduce the viscosity of the emulsion. Compared to the use of 2-propanol alone, the use of a mixture of propane-1,2-diol and 2-propanol makes it possible to increase the stability of the emulsion. The mass ratio of propane-1,2-diol relative to 2-propanol is preferably strictly greater than 1, preferably is strictly greater than 1 and less than 4, preferably is strictly greater than 1 and less than 2. When the emulsion according to the invention comprises an alcohol chosen from the group consisting of methanol, ethanol, ethylene glycol and diethylene glycol, the latter is present in a mass ratio strictly less than 1, preferably in a ratio less than 0.9, even more preferably less than 0.7 and even more preferably less than 0.5 with respect to said at least one antifreeze having a dynamic viscosity at 20°C ranging from 40 mPa.to 100 mPa.s, In one embodiment, when the emulsion according to the invention comprises an alcohol having a dynamic viscosity at 20°C strictly less than 40 mPa. s or strictly greater than 100 mPa.s, the latter is present in a mass ratio strictly less than 1, preferably in a ratio less than 0.9, more preferably less than 0.7 and more preferably less than 0.5 compared to said at least one ant igel having a dynamic viscosity at 20° C. ranging from 40 mPa.to 100 mPa.s. In particular, when the emulsion according to the invention comprises an alcohol different from propane-1,2-diol, propane-1,3-diol and triethylene glycol, said alcohol is present in a mass ratio strictly less than 1 of preferably in a ratio of less than 0.9, even more preferably less than 0.7 and even more preferably less than 0.5 with respect to said at least one antifreeze chosen from the group consisting of propane-1,2-diol, propane- 1,3-diol of triethylene glycol. When the emulsion comprises two or more antifreezes having a dynamic viscosity at 20° C. ranging from 40 mPa·s to 100 mPa·s, then the ratio is calculated with respect to the total weight of said antifreezes. Similarly, when the emulsion comprises two or more alcohols chosen from the group consisting of methanol, ethanol, ethylene glycol and diethylene glycol, then the ratio is calculated with respect to the total weight of said alcohols. Likewise, when the emulsion comprises two or more alcohols having a dynamic viscosity at 20° C. strictly less than 40 mPa.s or strictly greater than 100 mPa.s, then the ratio is calculated with respect to the total weight of said alcohols. Preferably, the emulsion according to the invention comprises less than 5% by weight, preferably less than 2% by weight, more preferably less than 1% by weight, more preferably less than 0.4% by weight and more preferably is free of ethanol. Preferably, the emulsion according to the invention comprises less than 5% by weight, preferably less than 2% by weight, more preferably less than 1% by weight, more preferably less than 0.4% by weight and more preferably is free of methanol. In a particularly preferred embodiment, the emulsion according to the invention is free of methanol and ethanol. Preferably, the emulsion according to the invention comprises less than 5% by weight, preferably less than 2% by weight, more preferably less than 1% by weight, and more preferably is free of ethylene glycol. Preferably, the emulsion according to the invention comprises less than 5% by weight, preferably less than 2% by weight, more preferably less than 1% by weight, and more preferably is free of diethylene glycol. Preferably, the at least one antifreeze of the emulsion according to the invention consists of one or more antifreezes as defined above, particularly preferably the antifreeze consists of propane-1,2-diol. The antifreeze is preferably present in the emulsion according to the invention in a content less than or equal to 40% by weight (relative to the total weight of the emulsion), preferably less than or equal to 25% by weight, of preferably still less than or equal to 22% by weight, relative to the total weight of the emulsion. Such antifreeze contents allow the aqueous phase to remain in liquid form up to temperatures below or equal to -20°C, preferably up to temperatures below or equal to -25°C. Thus, the person skilled in the art is able to establish the quantity of antifreeze necessary to maintain the aqueous phase in liquid form at the storage temperature. More particularly, the antifreeze can be present in the emulsion in an amount of 10 to 40% by weight, preferably 15 to 25% by weight, more preferably 17 to 22% by weight, relative to the total weight emulsion. Preferably, the quantity of antifreeze present in the emulsion comprises both the quantity of antifreeze according to the invention and the quantity of any other antifreeze present in the emulsion. The emulsion according to the invention comprises at least one emulsifier. Preferably, the emulsifier according to the invention has easy biodegradability. The qualification of the biodegradability of the emulsifier can be determined by the OECD 301 method and more particularly by the OECD 301 B method by release of carbon dioxide. The emulsifier comprises, or is (that is to say, consists of), one (or more) nonionic surfactant(s) comprising at least one fatty chain and having an HLB of less than or equal to 18. By “fatty chain”, is meant an aliphatic carbon chain optionally comprising hydroxyl branches and comprising at least 6 carbon atoms, preferably from 6 to 60 carbon atoms, more preferably from 6 to 20 carbon atoms. The nonionic surfactant may or may not be oxyalkylenated. Preferably, the nonionic surfactant comprises, or is, an oxyalkylenated or non-oxyalkylenated nonionic surfactant chosen from the group consisting of fatty alcohols, fatty acids, sorbitan esters, alkyl glucosides, vegetable or animal oils (hydrogenated or not) and mixtures thereof. The mixtures of nonionic surfactants used in the invention can be mixtures of nonionic oxyalkylenated surfactants only, or mixtures of nonionic nonionic oxyalkylenated surfactants only, or mixtures of nonionic oxyalkylenated surfactants and nonionic nonoxyalkylenated surfactants. Advantageously, the nonionic surfactant comprises, or is, a nonionic surfactant chosen from the group consisting of oxyalkylenated fatty alcohols, oxyalkylenated fatty acids, oxyalkylenated vegetable or animal oils, polysorbates, sorbitan esters, non-oxyalkylenated alkyl glucosides , oxyalkylenated alkyl glucosides and mixtures thereof. The oxyalkylenated units are more particularly oxyethylene units (that is to say ethylene oxide groups), oxypropylene units (that is to say propylene oxide groups), or a combination of units oxyethylenated units and oxypropylene units, preferably the oxyalkylenated units are oxyethylenated units or a combination of oxyethylenated units and oxypropylene units. Thus, the nonionic surfactant is preferably chosen from the group consisting of fatty alcohols having oxyethylenated units and optionally oxypropylene units, fatty acids having oxyethylenated units and optionally oxypropylene units, vegetable or animal oils, optionally hydrogenated, having oxyethylenated units and optionally oxypropylene units, polysorbates, sorbitan esters, alkyl glucosides having oxyethylenated units and optionally oxypropylene units and mixtures thereof. The oxyethylenated (i.e. ethylene oxide groups) and oxypropylene (i.e. propylene oxide groups) units can be distributed randomly or in a block. The number of moles of ethylene and/or propylene oxide preferably varies from 1 to 250, more preferably from 2 to 100, even more preferably from 2 to 50 and more particularly from 2 to 40. Preferably, the number of moles of ethylene oxide in the emulsifier varies from 2 to 40. By "fatty alcohol" is meant within the meaning of the present invention an alcohol comprising at least 6, preferably at least 8, carbon atoms, of more preferably a C ₈ -C ₄₀ alcohol, preferably a C ₈ -C ₂₀ alcohol. Among the fatty alcohols which can be used in the invention, mention may be made in particular of 2-octyl dodecanol, decanol, lauryl alcohol, oleocetyl alcohol, isodecanol, capric alcohol, oxo isotridecanol, alcohol cetostearic alcohol, eleostearic alcohol, caprylic alcohol, myristic alcohol, hexadecanoic or palmitic alcohol, stearic alcohol, eicosanoic or arachidic alcohol, behenic alcohol, oleic alcohol, eicosenoic alcohol or gadoleic alcohol, docosenoic alcohol, ricinoleic alcohol, linoleic alcohol, linolenic alcohol or mixtures thereof. Preferably, the nonionic surfactant is chosen from the group consisting of oxyalkylenated fatty alcohols and is preferably chosen from octyl dodecanol, decanol, lauryl alcohol, oleocetyl alcohol, isodecanol, capric alcohol , oxo isotridecanol alcohol, cetostearic alcohol, eleostearic alcohol, caprylic alcohol, myristic alcohol, hexadecanoic or palmitic alcohol, stearic alcohol, eicosanoic or arachidic alcohol, behenic alcohol , oleic alcohol, eicosenoic or gadoleic alcohol, docosenoic alcohol, ricinoleic alcohol, linoleic alcohol or linolenic alcohol, oxyalkylenated, preferably oxyethylenated and/or oxypropylene, and more preferably oxyethylenated and optionally oxypropylene . The more preferred fatty alcohols in the context of the invention are oleocetyl alcohol, hexadecanoic or palmitic alcohol, stearic alcohol, oleic alcohol, linoleic alcohol or mixtures thereof, and so even more preferred are the oxyalkylenated versions, preferably oxyethylenated and/or oxypropylene, and more preferably oxyethylenated and optionally oxypropylene, thereof. More preferably, the nonionic surfactant is an oxyalkylenated fatty alcohol chosen from the group consisting of oxyethylenated linoleic alcohol, oxyethylenated oleocetyl alcohol, oxyethylenated hexadecanoic or palmitic alcohol, oxyethylenated stearic alcohol, oxyethylenated oleyl alcohol and their mixtures. The fatty alcohols mentioned above may optionally be oxypropylene to a minor extent. Preferably, the oxyalkylenated vegetable/animal oils (hydrogenated or not) are in particular derivatives of ethoxylated mono-, di- and triglycerides and comprise a complex mixture of ethoxylated glycerol linked or not to one or more chains of fatty acids (them themselves ethoxylated or not), fatty acids ethoxylated on the acid function and/or on the hydroxyl function carried by the fatty acid chain, as well as variable proportions of fatty acids, glycerol and mono-, di - or triglycerides of fatty acids. By “fatty acid”, is meant within the meaning of the present invention an acid or a mixture of acids comprising at least 6 carbon atoms, preferably from 6 to 40 carbon atoms, more preferably from 8 to 20 carbon atoms. The oxyalkylenated vegetable/animal oils (hydrogenated or not) that can be used in the invention are preferably chosen from the group consisting of optionally hydrogenated, oxyethylenated (or ethoxylated) vegetable oils. The optionally hydrogenated, oxyethylenated vegetable oils are preferably chosen from the group consisting of ethoxylated castor oil and ethoxylated hydrogenated castor oil comprising from 5 to 40 moles of ethylene oxide per mole of ricinoleic acid. Mention may also be made of ethoxylated oils derived from copra, palm, palm kernel, olive, peanut, rapeseed, soybean, sunflower, walnut, hazelnut, coconut, poppy, safflower, flax, perilla, oïtica, and/or chinawood. Mention may also be made, as vegetable/animal oils which can be used according to the invention as an emulsifier, of ethoxylated fats based on oils of tallow, crude or refined tall, whale, herring and/or sardines. All of these ethoxylated glyceride derivatives are characterized in that they comprise mixtures of ethoxylated mono-, di- or triglycerides as well as ethoxylated derivatives of fatty acids and of the corresponding glycerol. These fatty acids are in particular saturated or unsaturated fatty acids derived from caproic, caprylic, capric, lauric, myristic, palmitic, stearic, arachic, behenic, myristoleic, palmitoleic, oleic, ricinoleic, erucic, linoleic, linolenic, eleostearic, licanic, gadoleic, and/or erneic acids. Some unsaturated fatty acids are or are not hydrogenated as in the case of ethoxylated castor oil where the ricinoleic group has or has not been partially or totally hydrogenated. In embodiments, the nonionic surfactant according to the invention may comprise, or be, one or more fatty acids, preferably oxyalkylenated, more preferably oxyethylenated and optionally oxypropylene, these fatty acids possibly being chosen from those listed above . Advantageously, the nonionic surfactant can comprise, or be, a nonionic surfactant chosen from the group consisting of vegetable or animal oils (hydrogenated or not) oxyalkylenated. More preferentially, the nonionic surfactant can comprise, or be, a nonionic surfactant chosen from the group consisting of vegetable oils, optionally hydrogenated, oxyethylenated and optionally oxypropylene. Preferably again, the nonionic surfactant can comprise, or be, a nonionic surfactant chosen from the group consisting of ethoxylated vegetable oils, optionally hydrogenated, comprising from 5 to 40 moles of ethylene oxide, in particular oil of ethoxylated castor oil and ethoxylated hydrogenated castor oil containing from 20 to 40 moles of ethylene oxide. Even more preferentially, the nonionic surfactant can comprise, or be, ethoxylated castor oil comprising from 20 to 40 moles of ethylene oxide. Advantageously, the nonionic surfactant may comprise, or be, one (or more) non-ethoxylated sorbitan ester(s) and/or one (or more) ethoxylated sorbitan ester(s). In the present text, the ethoxylated sorbitan esters are also called “polysorbates”, the term “sorbitan ester” designating in the present text the non-ethoxylated sorbitan esters, unless expressly indicated otherwise. Preferably, the unethoxylated sorbitan ester is selected from the group consisting of sorbitan monostearate, sorbitan tristearate, sorbitan monolaurate, sorbitan trilaurate, sorbitan monooleate, sorbitan trioleate, sorbitan, sorbitan tripalmitate and combinations thereof. Sorbitan monooleate is available under the trade name Span 80® (from Croda). Preferably, the ethoxylated sorbitan ester (or polysorbate) comprises between 3 and 40 ethylene oxide groups, preferably between 5 and 20 ethylene oxide groups. Preferably, the ethoxylated sorbitan ester is selected from the group consisting of ethoxylated sorbitan monostearate, ethoxylated sorbitan tristearate, ethoxylated sorbitan monolaurate, ethoxylated sorbitan trilaurate, ethoxylated sorbitan monooleate, sorbitan trioleate ethoxylated sorbitan monopalmitate, ethoxylated sorbitan tripalmitate and combinations thereof. Sorbitan Monooleate 20 EO (i.e. with an average of 20 ethylene oxide groups) is available as SURFALINE SE80® (from Arkema) or Tween 80® (from Croda). The nonionic surfactant can comprise, or be, one (or more) alkyl glucoside(s). As alkyl glucoside which can be used in the invention, mention may be made of capryl glucoside, caprylyl glucoside, lauryl glucoside, coco glucoside, hexyl glucoside, isooctyl glucoside, decyl glucoside, and/or undecyl glucoside. These alkyl glucosides can be oxyalkylenated or not (and more particularly ethoxylated or not). The emulsion may comprise a combination of at least two nonionic surfactants, in particular each of which may independently be as described above. Preferably, the combination of the at least two nonionic surfactants comprises a non-ethoxylated sorbitan as defined above and an ethoxylated sorbitan comprising between 5 and 20 ethylene oxide groups, as described above. The nonionic surfactant can advantageously have a molar mass less than or equal to 10,000 g/mol. Preferably again, the molar mass of the nonionic surfactant is less than or equal to 5000 g/mol, even more preferably less than or equal to 2000 g/mol. The probability that the nonionic surfactant has good biodegradability is higher when its molar mass is within the ranges below. Preferably, the at least one emulsifier of the emulsion according to the invention consists of at least one nonionic surfactant comprising at least one fatty chain, having an HLB of less than or equal to 18 and having a molar mass in the ranges mentioned. above. The nonionic surfactant according to the invention has an HLB (for “Hydrophilic-Lipophilic Balance”, or hydrophilic/lipophilic balance) less than or equal to 18, preferably less than or equal to 17, more preferably less than or equal to 16.5, and more preferably less than or equal to 16.2. In embodiments, the nonionic surfactant (when the emulsifier comprises a single nonionic surfactant) or the mixture of nonionic surfactants (when the emulsifier comprises several nonionic surfactants) has an HLB of less than or equal to 15.5 , preferably less than or equal to 15. The term “HLB” or “HLB value” means the hydrophilic-lipophilic balance which makes it possible to assess the solubility of an emulsifier in water. Preferably, the HLB is determined according to the method proposed by Griffin (Journal of the Society of Cosmetic Chemists, 5(4), (1954), 249-256). The HLB of a combination of at least two emulsifiers can be calculated from the mass ratio of said emulsifiers. The emulsifier may be present in the emulsion according to the invention in an amount ranging from 0.1 to 10% by weight, preferably from 0.2 to 5% by weight, preferably from 0.5 to 2.5 % by weight, and more preferably from 0.6 to 2% by weight, and more preferably strictly greater than 1% and strictly less than 2% by weight relative to the total weight of the emulsion. The nonionic surfactant as described above can also be present in the emulsion in the quantities mentioned above. The emulsion according to the invention may also comprise one or more additives intended to provide the final composition with particular properties/characteristics. These additives will ideally be present for the final polymerization or copolymerization. The additive can be chosen from the group consisting of antifoaming agents, chain transfer agents, chain extenders, pH regulating agents, plasticizers and mixtures thereof. The additive(s) are preferably present in an amount of 0.1 to 10% by weight, preferably 1 to 5% by weight, relative to the total weight of the emulsion. Preferably, the emulsion according to the invention comprises one or more plasticizers, preferably chosen from the group consisting of aliphatic esters, such as for example phthalates, adipates, benzoates, hydrogenated derivatives of these molecules and mixtures of these. In particular, the plasticizer can be diisononylcyclohexane, di-isononyl cyclohexane dicarboxylate, and their mixture. The plasticizer(s) may be present in the emulsion in an amount of 1 to 5% by weight relative to the total weight of the emulsion. Preferably, the emulsion according to the invention comprises from 0 to 1% by weight, preferably from 0 to 0.5% by weight, more preferably from 0 to 0.1% by weight of polyvinyl acetate, in particular partially hydrolyzed polyvinyl acetate, based on the total weight of the emulsion. Preferably, the emulsion according to the invention is free of partially hydrolyzed polyvinyl acetate, in particular is free of polyvinyl acetate and even more preferably is free of protective colloid agent. Within the meaning of the present invention, the term "protective colloid agent" means the group consisting of polyvinyl alcohol, polyvinyl acetate and in particular partially hydrolyzed polyvinyl acetate, cellulose esters and xanthan gums . The absence of protective colloid agent in the emulsion makes it possible in particular to reduce the preparation time of the emulsion at the industrial level, because the protective colloid agent (in particular polyvinyl acetate) which is in solid form requires a step prior dissolution, and to minimize the risks associated with handling powders. Furthermore, the presence in the emulsion of a protective colloid agent can increase the viscosity of the emulsion, which can be undesirable for certain applications. Preferably, the emulsion according to the invention comprises from 0 to 2% by weight of chlorinated paraffin, preferably from 0 to 1% by weight, even more preferably the emulsion according to the invention is devoid of chlorinated paraffin. The low content, or even the absence of chlorinated paraffin makes it possible, when the emulsion is used for the polymerization of ethylenically unsaturated monomers, to produce a polymer that is more respectful of the environment. Preferably, the emulsion according to the invention comprises from 0 to 0.05% by weight, preferably does not contain copolymers of α-olefins and dicarboxylic acids, partially esterified with an ethoxylated alcohol such as Dapral® GE202, also called Ketjenlube ® 522. In one particular embodiment, the emulsion according to the invention does not include any lubricant. Within the meaning of the present invention, the term “lubricant” is understood to mean a substance interposed between two surfaces in relative motion in order to reduce their friction. Advantageously, the emulsion according to the invention can consist essentially of, or consist of, the at least one organic peroxide, the at least at least one emulsifier, the at least one antifreeze, water and optionally one or more additives as described above, said emulsion preferably not being one of the compositions excluded above. By "the emulsion consists essentially of constituents", it is meant that all of these constituents represent at least 90% by weight, preferably at least 95% by weight, more preferably at least 98% by weight of the total weight of the 'emulsion. The expression "consists of" does not exclude the presence of impurities present in trace amounts in the emulsion (for example, in an amount less than or equal to 1% by weight relative to the total weight of the emulsion), for example impurities brought with the organic peroxide. Thus, in embodiments, the emulsion according to the invention may comprise an organic solvent, in an amount less than or equal to 1% by weight relative to the total weight of the emulsion. The emulsion according to the invention may comprise an organic solvent, preferably a non-chlorinated organic solvent, for example in an amount less than or equal to 20% by weight relative to the total weight of the emulsion. By "organic solvent" is meant in the present text organic solvents having a solubility in water of less than 1% by weight at 0°C. The emulsion according to the invention can consist essentially of, or consist of, the at least one organic peroxide, the at least one emulsifier, the at least one antifreeze, water, a non-chlorinated organic solvent ( preferably in an amount less than or equal to 20% by weight relative to the total weight of the emulsion) and optionally one or more additives as described above. The emulsion according to the invention can consist essentially of, or consist of, the at least one organic peroxide, the at least one emulsifier, the at least one antifreeze and water (the emulsion preferably being devoid of methanol, ethanol and polyvinyl alcohol). Preferably, the emulsion according to the invention has a flowability (or flow time) at 5° C., measured by a consistometric cutting technique, of less than or equal to 200 seconds, more preferably less than or equal to 170 seconds, and even more advantageously less than or equal to 100 seconds. Flowability can be measured according to DIN 53211, with a viscosity cup diameter of 4 mm and a temperature of 5°C. In a particularly advantageous manner, the emulsion according to the invention has an average droplet size of less than or equal to 10 μm, preferably less than or equal to 4 μm. Advantageously, the emulsion according to the invention has a maximum droplet size less than or equal to 20 μm, more preferably less than or equal to 15 μm. Droplet size (mean and maximum) can be determined by conventional means using the light diffraction technique. Measurements can be made using a Malvern Master Sizer 2000 ^® device at room temperature. More advantageously, the emulsion according to the invention exhibits the droplet sizes mentioned above during the storage period, for example during a period of at least six months. Preferably, the concentration of organic peroxide in the emulsion is homogeneous. By “homogeneous concentration”, it is meant that the difference between the peroxide concentrations (in mass percentage) at the top and at the bottom of the emulsion is less than 3%, preferably less than 2%. The concentration of the organic peroxide is measured by HPLC on a sample taken at the top of the emulsion and another at the bottom of the emulsion. More advantageously, the emulsion according to the invention is homogeneous during the storage period, for example during a period of at least six months. Another object of the invention is an organic peroxide emulsion comprising (or essentially consisting of, or consisting of): - at least one organic peroxide; – at least one emulsifier comprising at least one nonionic surfactant comprising at least one fatty chain and having an HLB of less than or equal to 18; – at least one antifreeze chosen from the group consisting of propane-1,2-diol, propane-1,3-diol, triethylene glycol and mixtures thereof; - some water ; - optionally one or more additives chosen from the group consisting of anti-foaming agents, chain transfer agents, chain extenders, pH regulating agents, plasticizers and mixtures thereof; – optionally an organic solvent; and – when said emulsion comprises at least one alcohol chosen from the group consisting of methanol, ethanol, ethylene glycol and diethylene glycol, the latter is present in a mass ratio strictly less than 1 with respect to said at least an antifreeze having a dynamic viscosity at 20° C. ranging from 40 mPa·s to 100 mPa·s preferably, said emulsion not being one of the compositions excluded above. . According to another aspect, the invention relates to an emulsion comprising (or consisting essentially of, or consisting of): - at least one organic peroxide; – at least one emulsifier comprising a nonionic surfactant having a molar mass less than or equal to 10,000 g/mol or a combination of two or more nonionic surfactants having a molar mass less than or equal to 10,000 g/mol, in which the non-ionic surfactant ionic or the combination of nonionic surfactants have an HLB of less than or equal to 15; – at least one antifreeze having a dynamic viscosity at 20°C ranging from 40 mPa.s to 100 mPa.s; - some water ; - optionally one or more additives chosen from the group consisting of anti-foaming agents, chain transfer agents, chain extenders, pH regulating agents, plasticizers and mixtures thereof; and - optionally an organic solvent; when said emulsion comprises at least one alcohol chosen from the group consisting of methanol, ethanol, ethylene glycol and diethylene glycol, the latter is present in a mass ratio strictly less than 1 with respect to said at least one antifreeze having a dynamic viscosity at 20° C. ranging from 40 mPa·s to 100 mPa·s, preferably, said emulsion not being one of the compositions excluded above. The at least one emulsifier may consist of a nonionic surfactant having a molar mass less than or equal to 10000 g/mol or a combination of two or more nonionic surfactants each having a molar mass less than or equal to 10000 g/mol, the nonionic surfactant or the combination of nonionic surfactants having an HLB of less than or equal to 15. According to this aspect, the invention provides a homogeneous and stable organic peroxide emulsion over time, having an average and maximum droplet size which remains small . In addition, the emulsion has a viscosity and a sufficiently low flow time and leads, when it is used for the polymerization of ethylenically unsaturated monomers, to a polymer having a low content of hard grains. This is accomplished by the combination of a particular emulsifier (comprising one or more nonionic surfactants having a molar mass and an HLB specific) and a particular antifreeze (having a specific dynamic viscosity at 20°C). According to this aspect, the organic peroxide, the emulsifier, the antifreeze, the water, the additives, and their amounts, can be as described above (unless expressly stated otherwise). The organic solvent may be present in an amount less than or equal to 20% by weight relative to the total weight of the emulsion. The flowability at 5°C, the size of the droplets and the homogeneity of the emulsion can also be as described above. According to this second aspect, the emulsion may comprise a chlorinated solvent. Yet another object of the invention lies in an emulsion comprising (or consisting essentially of, or consisting of): - at least one organic peroxide; – at least one emulsifier comprising a nonionic surfactant having a molar mass less than or equal to 10,000 g/mol or a combination of two or more nonionic surfactants having a molar mass less than or equal to 10,000 g/mol, in which the non-ionic surfactant ionic or the combination of nonionic surfactants have an HLB of less than or equal to 15; – at least one antifreeze chosen from the group consisting of propane-1,2-diol, propane-1,3-diol, triethylene glycol and mixtures thereof; - some water ; - optionally one or more additives chosen from the group consisting of anti-foaming agents, chain transfer agents, chain extenders, pH regulating agents, plasticizers and mixtures thereof; and - optionally an organic solvent; when said emulsion comprises at least one alcohol chosen from the group consisting of methanol, ethanol, ethylene glycol and diethylene glycol, the latter is present in a mass ratio strictly less than 1 with respect to said at least one antifreeze having a dynamic viscosity at 20° C. ranging from 40 mPa·s to 100 mPa·s preferably, said emulsion not being one of the compositions excluded above. The organic peroxide, emulsifier, antifreeze, water, additives, and their amounts, may be as described above (unless expressly stated otherwise). The characteristics of the emulsion can be as described above. Preferably, the emulsion as defined above is not: - a composition consisting of 50% by weight of di-sec-butyl peroxydicarbonate, 1.44% by weight of ethoxylated castor oil with a rate average ethoxylation of 31 and 21.4% by weight of propane-1,2-diol, the balance being water; - a composition consisting of 50% by weight of di-sec-butyl peroxydicarbonate, 1.5% by weight of ethoxylated castor oil with an average ethoxylation rate of 20 and 21.4% by weight of propane-1 ,2-diol, the balance being water; - a composition consisting of 50% by weight of di-sec-butyl peroxydicarbonate, 1.5% by weight of ethoxylated castor oil with an average ethoxylation rate of 20.21.4% by weight of propane-1 ,2-diol and 3% 3-hydroxy-1,1-dimethylbutyl peroxyneodecanoate, the balance being water; - a composition consisting of 50% by weight of di-sec-butyl peroxydicarbonate, 1.5% by weight of ethoxylated castor oil with an average ethoxylation rate of 20.21.4% by weight of propane-1 ,2-diol and 11.5% 3-hydroxy-1,1-dimethylbutyl peroxyneodecanoate, the balance being water. Preferably, in addition to the 4 compositions listed above, the emulsion as defined above is also not: - an emulsion consisting of 59.9% by weight of di(2-ethylhexyl) peroxydicarbonate, 20.6% by weight of propane-1,2-diol and 0.6% by weight of polyvinyl acetate with a hydrolysis rate of 72.5% by mole, 0.30% by weight of alcohol in C16-C18 ethoxylate comprising an average ethoxylation rate of 25, the remainder being water; - an emulsion consisting of 50.1% by weight of di-sec-butyl peroxydicarbonate, 1.6% by weight of nonionic surfactant, mono/di-ester of unsaturated C16–C18 glycerol comprising a medium ethoxylation rate of 15 units and 21.4% by weight of propane-1,2-diol, the balance being water. Preferably, the emulsion as defined above is not: - an emulsion consisting of 50% by weight of di-sec-butyl peroxydicarbonate, 1.44% by weight of ethoxylated castor oil and 21.4% by weight of propane-1,2-diol, the remainder being the water ; - an emulsion consisting of 50% by weight of di-sec-butyl peroxydicarbonate, 1.5% by weight of ethoxylated castor oil and 21.4% by weight of propane-1,2-diol, the remainder being the water; - an emulsion consisting of 50% by weight of di-sec-butyl peroxydicarbonate, 1.5% by weight of ethoxylated castor oil, 21.4% by weight of propane-1,2-diol and 3% by weight 3-hydroxy-1,1-dimethylbutyl peroxyneodecanoate, the balance being water; - an emulsion consisting of 50% by weight of di-sec-butyl peroxydicarbonate, 1.5% by weight of ethoxylated castor oil, 21.4% by weight of propane-1,2-diol and 11.5% by weight of 3-hydroxy-1,1-dimethylbutyl peroxyneodecanoate, the balance being water. Preferably, in addition to the 4 emulsions listed above, the emulsion as defined above is also not: - an emulsion consisting of 59.9% by weight of di(2-ethylhexyl) peroxydicarbonate, 20.6% by weight of propane-1,2-diol and 0.6% by weight of polyvinyl acetate, 0.30% by weight of C16-C18 alcohol, the remainder being water; - an emulsion consisting of 50.1% by weight of di-sec-butyl peroxydicarbonate, 1.6% by weight of nonionic surfactant, mono/di-ester of glycerol C16–C18 and 21.4% by weight of propane-1,2-diol, the balance being water. Still preferably, the emulsion as defined above is not: - an emulsion comprising 49 to 51% by weight of di-sec-butyl peroxydicarbonate, 1.4% to 1.5% by weight of ethoxylated castor oil and 21% to 22% by weight propane-1,2-diol; - an emulsion comprising 49 to 51% by weight of di-sec-butyl peroxydicarbonate, 1.4% to 1.6% by weight of ethoxylated castor oil and 21% to 22% by weight of propane-1,2 -diol; - an emulsion comprising 49 to 51% by weight of di-sec-butyl peroxydicarbonate, 1.4% to 1.6% by weight of ethoxylated castor oil, 21% to 22% by weight of propane-1,2 -diol and from 2% to 4% by weight of 3-hydroxy-1,1-dimethylbutyl peroxyneodecanoate; - an emulsion comprising 49 to 51% by weight of di-sec-butyl peroxydicarbonate, 1.4% to 1.6% by weight of ethoxylated castor oil, 21% to 22% by weight of propane-1,2 -diol and 11% to 12% by weight of 3-hydroxy-1,1-dimethylbutyl peroxyneodecanoate. Preferably, in addition to the 4 emulsions listed above, the emulsion as defined above is also not: - an emulsion comprising 59% to 61% by weight of di(2-ethylhexyl) peroxydicarbonate, 20% to 21% by weight of propane-1,2-diol and 0.4% to 0.8% by weight of polyvinyl acetate, 0.2% to 0.4% by weight of C16- alcohol C18; - an emulsion comprising 49% to 51% by weight of di-sec-butyl peroxydicarbonate, 1% to 2% by weight of nonionic surfactant, C16–C18 and C18 glycerol mono/di-ester and 21% to 22% by weight of propane-1,2-diol. Preparation of the emulsion The invention also relates to a process for preparing the emulsion according to the invention. The preparation process according to the invention comprises a step of mixing the at least one organic peroxide, the at least one emulsifier, the at least one antifreeze and water as defined above. This step may also include the above mixing with other constituents of the emulsion when the emulsion includes them, for example mixing with one or more additives (such as one or more plasticizers, etc.) as described in the previous section. The mixing can be carried out in one step (the constituents all being added to the mixture simultaneously) or in several steps (a premixing of certain constituents being first carried out before the addition of other constituents). The method may also comprise a step of emulsifying the mixture. The steps of mixing the constituents of the emulsion and of emulsifying can be simultaneous. Alternatively, the emulsification step can be carried out successively to a first step of mixing the constituents of the emulsion. The emulsion according to the invention can be prepared by dispersing at least the emulsifier and the antifreeze as well as optionally one or more additives, in water to obtain a homogeneous aqueous phase then by adding one or more organic peroxides to said aqueous phase, the whole then being emulsified during an emulsification step. Alternatively, the emulsifier or one or more of the emulsifiers can be dissolved in the organic peroxide(s) before being added to the aqueous phase. The steps mentioned above can be performed in the particular order indicated above, or in a different order. The temperature at which the emulsion is prepared is not critical but it must be sufficiently reduced to avoid a high rate of decomposition of the organic peroxide, the result of which would be a loss of titer. The chosen temperature depends on the organic peroxide. Preferably, the mixing step and/or the emulsifying step are carried out at a temperature below 5°C and even more preferably below -5°C. Mixing and emulsifying at such temperatures makes it possible to limit the premature degradation of the organic peroxide. Even more preferably, the mixing step and/or the emulsifying step are carried out at a temperature of between -15 and 10°C, preferably from -10 to 5°C. Preferably, the mixing and emulsifying steps are carried out at the same temperature, preferably within the ranges mentioned above. To prepare the aqueous emulsion, preferably deionized water or distilled water is used. The emulsification step of the process according to the invention is preferably carried out with a mixer with a high shear rate in order to best divide and/or homogenize the peroxide in the aqueous phase. By way of example, mention may be made of mechanically rotating paddle and anchor stirrers, propeller stirrers, i.e. one or more stirrers mounted on a common shaft, turbine stirrers, i.e. that is to say those comprising fixed baffles on the mixing tank or in a position adjacent to the agitating members. Colloid mills and homogenizers can also be used. According to a variant of the process according to the invention, it is possible to use an ultrasonic mixer or a rotor-stator mixer for the emulsification. Following the preparation of the emulsion, the steps of pumping and introducing the emulsions into a polymerization reactor must usually be done as quickly as possible. Thus the peroxide emulsions should advantageously have a low viscosity. Thus, the emulsions of organic peroxides according to the invention preferably have a range of dynamic viscosity, at -10° C. and at a shear rate of 100 s ^-1 , less than or equal to 850 mPa.s, preferably even less or equal to 700 mPa.s, more preferably less than or equal to 500 mPa.s, just after production (the viscosity measurements are measured for example according to the DIN 53019 standard with a Viscotester Haake VT550 type device, at -10°C and for a shear rate of 100 s ^-1 ). Their flowability measured by a consistometric cutting technique is advantageously less than or equal to 200 seconds, more preferably less than or equal to 170 seconds, and even more advantageously less than or equal to 100 seconds (measured for example according to the DIN 53211 standard, with a diameter viscosity cup of 4 mm and a temperature of 5°C). Use The present invention also relates to the use of an emulsion as described above, for the polymerization or the copolymerization of one or more ethylenically unsaturated monomers, in particular of one or more vinyl monomers, preferably halogenated, and more preferably vinyl chloride. As examples of ethylenically unsaturated monomers which can be used in the invention, 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 group consisting of vinyl halide monomers (that is to say halogenated vinyl monomers), and more preferably the ethylenically unsaturated monomers are vinyl chloride. The invention also relates to a process for preparing a halogenated vinyl polymer comprising a stage of polymerization or copolymerization of one or more ethylenically unsaturated monomers in the presence of an emulsion as described above. The ethylenically unsaturated monomers can be as described above and are more preferably vinyl chloride. The halogenated vinyl polymer prepared is preferably a poly(vinyl chloride). Polymerization of the ethylenically unsaturated monomer(s), preferably polymerization of the vinyl chloride monomer, has advantageously takes place in suspension, preferably at an initiation temperature ranging from 45°C to 70°C. The emulsion can be added directly to the polymerization reactor or be premixed with other organic peroxides, water, polyvinyl alcohol and/or other additives before introducing this mixture into the polymerization reactor. Polymer Another object of the present invention relates to a halogenated vinyl polymer obtained (or capable of being obtained) by polymerization of at least one ethylenically unsaturated monomer, as described above, in the presence of the emulsion according to invention as described above. The polymerization can be as described in the previous section. Preferably, the invention relates to a poly(vinyl chloride) obtained (or capable of being obtained) by polymerization of vinyl chloride in the presence of the emulsion according to the invention. The invention also relates to a halogenated vinyl polymer obtained (or capable of being obtained) by a preparation process as described above. Such halogenated vinyl polymers have the advantage of having a low content of hard grains. The level of hard grains can be determined as described in the article by O. Leachs, in Kunststoffe, Vol.50(4), 1960 pp 227-234. Examples The following examples illustrate the invention without limiting it. Example 1 The following emulsions were prepared (the amounts indicated in the tables below are expressed as percentage by mass relative to the total weight of the emulsion): [Table 1] [Table 2] Qsp 100 = quantity sufficient to reach 100% of the weight of the emulsion. The nature of the compounds used is indicated below: – Luperox® 10: tert-butyl peroxyneodecanoate; – Luperox® 610: 3-hydroxy 1,1-dimethylbutyl peroxyneodecanoate; – Luperox® 225: di-sec-butyl peroxydicarbonate; – Span® 80: nonionic surfactant sorbitan monooleate (HLB: 4.3); – Tween® 80: nonionic surfactant, polyethoxylated sorbitan monooleate (HLB: 15.0); – Surfaline LG15: nonionic surfactant, mono/diester of glycerol, C16–C18 and C18 unsaturated, polyethoxylated (15 units); – PVA: polyvinyl acetate with a hydrolysis rate of 72.5 mol% (Alcotex 72.5). Emulsions 1, 4, 5, 7 and 9 correspond to emulsions according to the invention, emulsions 2, 3, 6 and 8 are comparative emulsions. The emulsions were prepared as described below. In the reactor, the aqueous phase containing the emulsifier(s) (with the exception of Span® 80), the antifreeze and the water was stirred between 500 and 1000 revolutions per minute (rpm) with a propeller stirrer (IKA RW 20) equipped with an anchor rod, and maintained at -5°C (Celsius) for 5 minutes. The Span® 80 was added at -5°C with stirring to the organic peroxide and this mixture was stirred for 5 minutes. The organic peroxides (with Span® 80 if necessary) were added gradually to the reactor containing the aqueous phase. Stirring was maintained for three minutes at 2000 rpm. The assembly was then vigorously stirred using an “Ultraturrax type S-25N 18G” for two minutes at 9500 rpm, then stirred using a blade at 1000 rpm for one minute. Each emulsion is made on 200 grams in total. The emulsions were then transferred to a plastic container, the container was closed and the emulsions were stored at -20°C for the indicated time. The average and maximum droplet sizes, by volume, over a 6-month period, as well as the concentration of organic peroxide at the top and bottom of the aqueous phase of the emulsion (in percentage by weight, relative to the total weight of the aqueous phase) were determined, as shown below. The average droplet size as well as the maximum droplet size are determined by conventional means using the light diffraction technique. Measurements are made using a Malvern Master Sizer 2000® device at room temperature. The average droplet size is 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 surface of the emulsion) and a sample from the bottom of the emulsion (taken from the first centimeter from from the bottom of the emulsion) were taken and then analyzed to determine the concentration of organic peroxide. Organic peroxide concentrations in the aqueous phase were determined on a Waters H-class UPLC with an accuracy of ±1%. The results are presented in the tables below. [Table 3]

[Table 4]

It is found that emulsion No. 1 according to the invention is more stable than comparative emulsion No. 2 comprising ethanol which gives rise to demixing after 2 months of storage. In addition, the mean and maximum size of the droplets of emulsion No. 1 according to the invention remain low over a period of at least 6 months. Compared to comparative emulsion no. 3 which contains ethanol, emulsions no. 4 and 5 according to the invention are stable over a period of at least 6 months, with an average and maximum size of the droplets remaining low over this whole period. On the other hand, a demixing of comparative emulsion No. 3 is observed after a period of only 3 weeks. In addition, the emulsions according to the invention Nos. 1 and 5 have similar concentrations of organic peroxide at the top and at the bottom of the aqueous phase after 6 months: they remained homogeneous during this period. Comparative emulsion No. 8 comprising ethanol undergoes demixing from 2 hours after its preparation, while emulsions No. 7 and 9 according to the invention remain stable over a period of time greater than 6 months while maintaining a low mean and maximum droplet size. In addition, these emulsions Nos. 7 and 9 remained homogeneous after 6 months, the concentrations of organic peroxide at the top and at the bottom of the aqueous phase being similar. The organic peroxide droplets therefore sedimented little or not at all. In addition, compared to comparative emulsion No. 6 comprising a hydrolyzed polyvinyl acetate, emulsions No. 7 and 9 have a much lower average and maximum droplet size from 2 months. Example 2 The following emulsions were prepared (the amounts indicated in the table below are expressed as percentage by weight relative to the total weight of the emulsion): [Table 5] Qsp 100 = quantity sufficient to reach 100% of the weight of the emulsion. The nature of the compounds used is indicated below: – Luperox® 223: di(2-ethylhexyl) peroxydicarbonate – Surfaline R20: nonionic surfactant, ethoxylated castor oil (20EO) (HLB: 9.6). Emulsions 11, 13 and 14 correspond to emulsions according to the invention, emulsions 10 and 12 are comparative emulsions. The emulsions were prepared as described in Example _1. The average and maximum droplet sizes, by volume, were determined after the production of the emulsions and after 2 months of storage, as indicated in Example 1. The results are presented in the table below. [Table 6] It is found that the emulsions according to the invention, nos. 11, 13 and 14, are stable over a period of at least two months. The emulsions according to the invention no. 11, 13 and 14 have an average size and a maximum size of droplets that are smaller than the comparative emulsions comprising methanol (emulsions no. 10 and 12), whether it is just after the preparation of the emulsion or after two months.

Claims

Claims 1. Organic peroxide emulsion comprising: - at least one organic peroxide; – at least one emulsifier comprising at least one nonionic surfactant comprising at least one fatty chain and having an HLB of less than or equal to 18; – at least one antifreeze having a dynamic viscosity at 20°C ranging from 40 mPa.s to 100 mPa.s; and – from 0 to 1% polyvinyl acetate – water and in which, when said emulsion comprises at least one alcohol chosen from the group consisting of methanol, ethanol, ethylene glycol and diethylene glycol , the latter is present in a mass ratio strictly less than 1, preferably in a ratio less than 0.9, even more preferably less than 0.7 and even more preferably less than 0.5 with respect to said at least one antifreeze having a dynamic viscosity at 20°C ranging from 40 mPa.to 100 mPa.s.

2. Emulsion according to claim 1, consisting of the at least one organic peroxide, the at least one emulsifier, the at least one antifreeze, water and optionally one or more additives chosen from the group consisting of agents anti-foaming agents, chain transfer agents, chain extenders, pH regulating agents, plasticizers and mixtures thereof.

3. Emulsion according to one of Claims 1 or 2, in which the at least one antifreeze is an alcohol, preferably chosen from the group consisting of diols and mixtures thereof.

4. Emulsion according to one of claims 1 to 3, in which the at least one antifreeze is chosen from the group consisting of propane-1,2-diol, propane-1,3-diol, triethylene glycol and mixtures thereof, preferably is propane-1,2-diol.

5. Emulsion according to one of claims 1 to 4, in which the at least one antifreeze comprises, preferably consists of, a mixture of propane-1,2-diol and 2-propanol, preferably the mass ratio of propane-1,2-diol compared to 2-propanol is strictly greater than 1.

6. Emulsion according to claim 6, in which the mass ratio of propane-1,2-diol relative to 2-propanol is strictly greater than 1 and less than 4, preferably is strictly greater than 1 and less than 2.

7. Emulsion according to one of claims 1 to 6, in which the at least one antifreeze is present in an amount of 10 to 40% by weight, preferably 15 to 25% by weight, more preferably 17 to 22% by weight, relative to the total weight of the emulsion.

8. Emulsion according to one of claims 1 to 7, in which the at least one organic peroxide is chosen from the group consisting of peroxydicarbonates, peroxyesters, diacyl peroxides and combinations thereof.

9. Emulsion according to one of claims 1 to 8, in which the at least one organic peroxide is chosen from the group consisting of tert-amyl peroxypivalate, tert-butyl peroxypivalate, tert-butyl peroxyneodecanoate, tert-amyl peroxyneodecanoate, 3-hydroxy-1,1 dimethylbutyl peroxyneodecanoate, cumyl peroxyneodecanoate, di-sec-butyl peroxydicarbonate, di(2-ethylhexyl) peroxydicarbonate, di(3,5,5-trimethylhexanoyl) peroxide, and mixtures thereof.

10. Emulsion according to one of claims 1 to 9, in which the at least one organic peroxide is present in a content ranging from 40 to 80% by weight, preferably ranging from 44 to 65% by weight, more preferably ranging from 45 to 60% by weight, relative to the total weight of the emulsion.

11. Emulsion according to one of claims 1 to 9, in which the at least one nonionic surfactant is chosen from the group consisting of oxyalkylenated fatty alcohols, oxyalkylenated fatty acids, oxyalkylenated vegetable or animal oils, polysorbates, sorbitan esters, alkyl glucosides, oxyalkylenated alkyl glucosides and mixtures thereof.

12. Emulsion according to any one of the preceding claims, said emulsion not being: - a composition consisting of 50% by weight of di-sec-butyl peroxydicarbonate, 1.44% by weight of castor oil ethoxylated with an average ethoxylation rate of 31 and 21.4% by weight of propane-1,2-diol, the remainder being water; - a composition consisting of 50% by weight of di-sec-butyl peroxydicarbonate, 1.5% by weight of ethoxylated castor oil with an average ethoxylation rate of 20 and 21.4% by weight of propane-1 ,2-diol, the balance being water; - a composition consisting of 50% by weight of di-sec-butyl peroxydicarbonate, 1.5% by weight of ethoxylated castor oil with an average ethoxylation rate of 20.21.4% by weight of propane-1 ,2-diol and 3% 3-hydroxy-1,1-dimethylbutyl peroxyneodecanoate, the balance being water; - a composition consisting of 50% by weight of di-sec-butyl peroxydicarbonate, 1.5% by weight of ethoxylated castor oil with an average ethoxylation rate of 20.21.4% by weight of propane-1 ,2-diol and 11.5% 3-hydroxy-1,1-dimethylbutyl peroxyneodecanoate, the balance being water.

13. Process for preparing an emulsion according to one of claims 1 to 12, comprising a step of mixing the at least one organic peroxide, the at least one emulsifier, the at least one antifreeze and water ; and optionally, a step of emulsifying the mixture.

14. Use of the emulsion according to one of claims 1 to 12, for the polymerization or copolymerization of one or more ethylenically unsaturated monomers, in particular vinyl monomers, preferably halogenated, and more preferably vinyl chloride.

15. Halogenated vinyl polymer obtained by polymerization of at least one ethylenically unsaturated monomer in the presence of the emulsion according to one of claims 1 to 12.