AU1657000A

AU1657000A - Method for preparing halogenated copolymers, resulting halogenated copolymers and use thereof

Info

Publication number: AU1657000A
Application number: AU16570/00A
Authority: AU
Inventors: Bernard Guenaire; Yves Vanderveken
Original assignee: Solvay SA
Current assignee: Solvay SA
Priority date: 1998-12-02
Filing date: 1999-11-30
Publication date: 2000-06-19
Also published as: CN1333789A; BE1012318A3; CA2353715A1; BR9915891A; EP1141052A1; JP2002531603A; WO2000032659A1; RU2001117853A

Description

WO 00/32659 PCT/EP99/09370 Process for preparing halogenated copolymers, halogenated copolymers obtained and use thereof The invention relates to a process for 5 preparing halogenated copolymers, to the halogenated copolymers obtained, to their use for preparing extruded articles and to the extruded articles obtained. Generally, copolymers of vinylidene chloride 10 and of vinyl chloride are prepared by an aqueous dispersion polymerization process in which all of the two monomers is introduced at the start of the polymerization. This process has the drawback of giving rise to relatively poor degrees of conversion of the 15 monomers. The copolymers obtained by this process have the drawback of being highly heterogeneous in terms of monomer distribution. Moreover, these copolymers have a relatively low heat stability and limited flexibility. 20 Furthermore, these copolymers have a strong tendency to bond, which results in considerable deposits of degraded materials on the die used during the implementation. These copolymers moreover have the great drawback of having a high melting point, which 25 involves relatively high implementation temperatures. One subject of the present invention is a process which is particularly suitable for preparing halogenated copolymers which do not have the drawbacks presented by the processes of the prior art. 30 A subject of the invention is also halogenated copolymers which do not have the drawbacks of the copolymers of the prior art. A subject of the invention is also the use of these halogenated copolymers. 35 A subject of the invention is also the articles obtained from the copolymers according to the invention. REPLACEMENT SHEET (RULE 26) - 2 To this end, the invention relates firstly to a process for preparing halogenated copolymers by copolymerization of at least two monomers, in which the copolymerization is carried out in aqueous dispersion 5 with a subsequent injection of a fraction of at least one of the monomers. For the purposes of the present invention, the expression "subsequent injection" is intended to denote that a fraction of at least one of the monomers is 10 introduced a certain time after the start of the polymerization. The time at which the subsequent injection is started is usually the time when the initiation of the polymerization is complete. Usually, the subsequent 15 injection is started between 10 and 60 minutes after the start of the polymerization. Generally, the subsequent injection is started at least 10 minutes, preferably at least 15 minutes, particularly preferably at least 20 minutes and most particularly preferably at 20 least 25 minutes after the start of the polymerization. Usually, the subsequent injection is started not more than 60 minutes, preferably not more than 50 minutes, particularly preferably not more than 45 minutes and most particularly preferably not more than 25 40 minutes after the start of the polymerization. Generally, the fraction subsequently injected may be injected in total in a single portion or in fractions or continuously. It is preferably injected continuously. 30 The period of time during which the subsequent injection takes place generally ranges from 60 to 600 minutes. Generally, the period of time during which the subsequent injection takes place is at least 60 minutes, preferably at least 100 minutes and 35 particularly preferably at least 150 minutes. Generally, the period of time during which the subsequent injection takes place is not more than REPLACEMENT SHEET (RULE 26) - 3 600 minutes, preferably not more than 500 minutes and particularly preferably not more than 400 minutes. For the purposes of the present invention, the expression "injection of a fraction of at least one of 5 the monomers" is intended to denote that at least one of the monomers involved in the copolymerization is partially subsequently injected. One of the monomers involved in the copolymerization or several of them may thus be partially subsequently injected. 10 In the process according to the invention, a fraction of a halogenated monomer is preferably subsequently injected. In a particularly preferred manner, a fraction of the main halogenated monomer of the halogenated copolymers is subsequently injected. 15 For the purposes of the present invention, the expression "halogenated copolymers" is intended to denote the copolymers obtained by aqueous-dispersion free-radical polymerization of a halogenated monomer, which is the main monomer, with one or more monomers 20 copolymerizable therewith. For the purposes of the present invention, the expression "main halogenated monomer" is intended to denote the halogenated monomer which is present in the resulting halogenated copolymers in a proportion of at 25 least 50% by weight. For the purposes of the present invention, the expression "halogenated monomer" is intended to denote any free-radical-polymerizable monomer containing terminal olefinic unsaturation and substituted with at 30 least one halogen atom. Preferably, these monomers are chosen from substituted ethylene and propylene derivatives and contain only two or three carbon atoms, respectively. As non-limiting examples of such monomers, mention may be made of vinyl chloride, 35 vinylidene chloride, vinyl bromide, vinylidene bromide, vinyl fluoride, vinylidene fluoride, trifluoroethylene, REPLACEMENT SHEET (RULE 26) - 4 tetrafluoroethylene, chlorotrifluoroethylene and hexafluoropropylene. Among the monomers that are copolymerizable with the halogenated monomer, mention may be made, in a 5 non-limiting manner, of halogenated monomers of different nature, vinyl esters such as, for example, vinyl acetate, vinyl ethers, acrylic acids, esters and amides, methacrylic acids, esters and amides, styrene, styrene derivatives, butadiene, olefins such as, for 10 example, ethylene and propylene, itaconic acid and maleic anhydride. The process for preparing halogenated copolymers according to the invention is particularly useful for preparing copolymers containing chlorine and 15 most particularly useful for preparing vinylidene chloride copolymers. For the purposes of the present invention, the expression "copolymers containing chlorine" is intended to denote copolymers obtained by aqueous-dispersion 20 free-radical polymerization of a monomer containing chlorine such as, for example, vinyl chloride and vinylidene chloride, with one or more monomers that are copolymerizable therewith. In this case, the monomer containing chlorine is the main halogenated monomer, 25 i.e. the monomer which is present in the resulting copolymers in a proportion of at least 50% by weight. Among the monomers that are copolymerizable with the monomer containing chlorine, mention may be made, in a non-limiting manner, of monomers containing 30 chlorine of different nature, vinyl esters such as, for example, vinyl acetate, vinyl ethers, acrylic acids, esters and amides, methacrylic acids, esters and amides, styrene, styrene derivatives, butadiene, olefins such as, for example, ethylene and propylene, 35 itaconic acid and maleic anhydride. For the purpose of the present invention, the expression "vinylidene chloride copolymers" is intended REPLACEMENT SHEET (RULE 26) - 5 to denote copolymers of vinylidene chloride with one or more monomers that are copolymerizable therewith. In this case, the vinylidene chloride is the main halogenated monomer, i.e. the monomer which is present 5 in the resulting copolymers in a proportion of at least 50% by weight. Among the monomers that are copolymerizable with vinylidene chloride, mention may be made, in a non-limiting manner, of vinyl chloride, vinyl esters 10 such as, for example, vinyl acetate, vinyl ethers, acrylic acids, esters and amides, methacrylic acids, esters and amides, styrene, styrene derivatives, butadiene, olefins such as, for example, ethylene and propylene, itaconic acid and maleic anhydride. 15 In general, the weight ratio, for a monomer of which a fraction is subsequently injected, between the fraction subsequently injected and the total amount introduced during the polymerization ranges from 20% to 80%. 20 In general, the weight ratio, for a monomer of which a fraction is subsequently injected, between the fraction subsequently injected and the total amount introduced during the polymerization is greater than or equal to 20%, preferably greater than or equal to 30% 25 and particularly preferably greater than or equal to 40%. In general, the weight ratio, for a monomer of which a fraction is subsequently injected, between the fraction subsequently injected and the total amount 30 introduced during the polymerization is less than or equal to 80%, preferably less than or equal to 70% and particularly preferably less than or equal to 60%. A weight ratio, for a monomer of which a fraction is subsequently injected, between the fraction 35 subsequently injected and the total amount introduced during the polymerization ranging from 40% to 60% gives good results. REPLACEMENT SHEET (RULE 26) - 6 The process for preparing halogenated copolymers according to the invention is particularly suitable for use in preparing copolymers of vinylidene chloride and of vinyl chloride and also for preparing 5 copolymers of vinylidene chloride with vinyl chloride and at least one (meth)acrylic monomer corresponding to the general formula:

CH

2 =CRiR 2 in which R 1 is chosen from hydrogen and a methyl 10 radical and R 2 is chosen from a -CN radical and a

-CO-OR

3 radical in which R 3 is chosen from hydrogen, alkyl radicals containing from 1 to 18 carbon atoms, alkoxyalkyl radicals containing a total of from 1 to 10 carbon atoms and radicals -NR 4

R

5 in which R 4 and R 5 are 15 chosen from hydrogen and an alkyl radical containing from 1 to 10 carbon atoms. For the purposes of the present invention, the expression "at least one (meth)acrylic monomer" is intended to denote that the vinylidene chloride 20 copolymers may contain one or more (meth)acrylic monomer(s), denoted hereinbelow as (meth)acrylic monomer. The (meth)acrylic monomer is preferably chosen from acrylic and methacrylic esters containing from 1 25 to 8 carbon atoms and particularly preferably from acrylic and methacrylic esters containing from 1 to 6 carbon atoms. Examples of such acrylic and methacrylic esters that are particularly preferred are methyl acrylate, 30 methyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, n-butyl acrylate, n-butyl methacrylate, isobutyl acrylate, isobutyl methacrylate, t-butyl acrylate t-butyl methacrylate, n-pentyl acrylate, n-pentyl 35 methacrylate, isoamyl acrylate, isoamyl methacrylate, n-hexyl acrylate, n-hexyl methacrylate, 2-methylpentyl acrylate and 2-methylpentyl methacrylate. REPLACEMENT SHEET (RULE 26) - 7 The (meth)acrylic monomer is most particularly preferably selected from acrylic and methacrylic esters containing from 1 to 4 carbon atoms. Examples of such acrylic and methacrylic esters 5 that are most particularly preferred are methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, n-butyl acrylate, n-butyl methacrylate, isobutyl acrylate, isobutyl methacrylate, t-butyl acrylate and 10 t-butyl methacrylate. In this case, vinylidene chloride is the main monomer. The vinylidene chloride is generally present in the resulting copolymers in a proportion of at least 50% by weight. 15 In general, the amount of vinylidene chloride in the vinylidene chloride copolymers ranges from 50% to 95% by weight, preferably from 60% to 95% by weight and particularly preferably from 70% to 95% by weight. In general, the amount of vinyl chloride in the 20 vinylidene chloride copolymers ranges from 3% to 50% by weight, preferably from 3% to 40% by weight and particularly preferably from 4.25% to 30% by weight. In general, the amount of the (meth)acrylic monomer in the vinylidene chloride copolymers ranges 25 from 0% to 20% by weight, preferably from 0% to 13% by weight and particularly preferably from 0% to 4.5% by weight. Generally, the total amount of vinyl chloride may be introduced either into the polymerization 30 charge, or subsequently, or a fraction of the total amount may be introduced into the polymerization charge and the other fraction may be introduced subsequently. Preferably, the total amount of the vinyl chloride is introduced initially into the polymerization charge. 35 Generally, the total amount of the (meth)acrylic monomer may be introduced either into the polymerization charge, or subsequently, or a fraction REPLACEMENT SHEET (RULE 26) - 8 of the total amount may be introduced into the polymerization charge and the other fraction may be introduced subsequently. Preferably, a fraction of the (meth)acrylic monomer is subsequently injected. 5 Generally, the fraction of the (meth)acrylic monomer injected subsequently is injected at the same time and under the same conditions as the vinylidene chloride. The time at which the subsequent injection is started is usually the time when the initiation of the 10 polymerization is complete. Usually, the subsequent injection is started between 10 and 60 minutes after the start of the polymerization. Generally, the subsequent injection is started at least 10 minutes, preferably at least 15 minutes, particularly preferably 15 at least 20 minutes and most particularly preferably at least 25 minutes after the start of the polymerization. Usually, the subsequent injection is started not more than 60 minutes, preferably not more than 50 minutes, particularly preferably not more than 20 45 minutes and most particularly preferably not more than 40 minutes after the start of the polymerization. Generally, the fraction subsequently injected may be injected in total in a single portion or in fractions or continuously. It is preferably injected 25 continuously. The period of time over which the subsequent injection takes place generally ranges from 60 to 600 minutes. Generally, the period of time over which the subsequent injection takes place is at least 60 30 minutes, preferably at least 100 minutes and particularly preferably at least 150 minutes. Generally, the period of time over which the subsequent injection takes place is not more than 600 minutes, preferably not more than 500 minutes and particularly 35 preferably not more than 400 minutes. In general, the weight ratio for the (meth)acrylic monomer between the fraction injected REPLACEMENT SHEET (RULE 26) - 9 subsequently and the total amount introduced during the polymerization ranges from 20% to 80%. In general, the weight ratio for the (meth)acrylic monomer between the fraction injected 5 subsequently and the total amount introduced during the polymerization is greater than or equal to 20%, preferably greater than or equal to 30% and particularly preferably greater than or equal to 40%. In general, the weight ratio for the 10 (meth)acrylic monomer between the fraction injected and the total amount introduced during the polymerization is less than or equal to 80%, preferably less than or equal to 70% and particularly preferably less than or equal to 60%.] A weight ratio for the (meth)acrylic 15 monomer between the fraction injected subsequently and the total amount introduced during the polymerization ranging from 40% to 60% gives good results. For the purposes of the present invention, the expression "aqueous-dispersion copolymerization" is 20 intended to denote aqueous-suspension free-radical copolymerization and also aqueous-emulsion free-radical copolymerization. For the purposes of the present invention, the expression "aqueous-suspension free-radical 25 copolymerization" is intended to denote any free radical copolymerization process which is carried out in aqueous medium in the presence of oleosoluble free radical initiators and dispersants. For the purposes of the present 30 invention, the expression "aqueous-emulsion free radical copolymerization" is intended to denote any free-radical copolymerization process which is carried out in aqueous medium in the presence of free-radical initiators and emulsifiers. This definition 35 specifically encompasses the "conventional" aqueous emulsion copolymerization in which water-soluble free radical initiators are used, and also microsuspension REPLACEMENT SHEET (RULE 26) - 10 copolymerization, also known as homogenized aqueous dispersion copolymerization, in which oleosoluble initiators are used and an emulsion of droplets of monomers is prepared by means of vigorous mechanical 5 stirring in the presence of emulsifiers. The process according to the invention is particularly suitable for preparing halogenated copolymers by "conventional" aqueous-emulsion copolymerization which is carried out under the 10 conditions known to those skilled in the art. Thus, the copolymerization is carried out using water-soluble initiators and emulsifiers, which are present in amounts known to those skilled in the art. Examples of emulsifiers which may be mentioned 15 include anionic emulsifiers and nonionic emulsifiers. Among the anionic emulsifiers which may be mentioned, in a non-limiting manner, are paraffin sulphonates, alkyl sulphates, alkyl sulphonates, alkylaryl mono- or disulphonates and alkyl sulphosuccinates. Among the 20 nonionic emulsifiers which may be mentioned, in a non limiting manner, are alkyl- or alkylarylethoxylated derivatives. Examples of water-soluble initiators which may be mentioned include water-soluble peroxides such as 25 ammonium or alkali metal persulphates, hydrogen peroxide, perborates and t-butyl hydroperoxide, which are used alone or in combination with a reducing agent. The invention also relates to halogenated copolymers which are homogeneous in terms of monomer 30 distribution. For the purposes of the present invention, the expression "copolymers which are homogeneous in terms of monomer distribution" means that the copolymers are characterized by a homogeneous distribution of the 35 monomers in the polymer chain. The homogeneous distribution of the monomers in the polymer chain may generally be demonstrated by REPLACEMENT SHEET (RULE 26) - 11 analytical techniques. Among these, mention may be made of the determination of the mechanical loss by dynamic analysis and 'H NMR spectrometry. The copolymers according to the invention are 5 also characterized by a melting point, determined by differential thermal analysis, of less than or equal to 1700C, preferably less than or equal to 1550C, particularly preferably less than or equal to 1400C and most particularly preferably less than or equal to 10 1200C. For the purposes of the present invention, the expression "halogenated copolymers" is intended to denote the copolymers obtained by aqueous-dispersion free-radical polymerization of a halogenated monomer, 15 referred to as the main halogenated monomer, with one or more monomers that are copolymerizable therewith. For the purposes of the present invention, the expression "main halogenated monomer" is intended to denote the halogenated monomer which is present in the 20 resulting halogenated copolymers in a proportion of at least 50% by weight. For the purposes of the present invention, the expression "halogenated monomer" is intended to denote any free-radical-polymerizable monomer containing 25 terminal olefinic unsaturation and substituted with at least one halogen. Preferably, these monomers are chosen from substituted ethylene and propylene derivatives and contain only two or three carbon atoms, respectively. Non-limiting examples of such monomers 30 which may be mentioned include vinyl chloride, vinylidene chloride, vinyl bromide, vinylidene bromide, vinyl fluoride, vinylidene fluoride, trifluoroethylene, tetrafluoroethylene, chlorotrifluoroethylene and hexa fluoropropylene. 35 Among the monomers that are copolymerizable with the halogenated monomer, mention may be made, in a non-limiting manner, of halogenated monomers of REPLACEMENT SHEET (RULE 26) - 12 different nature, vinyl esters such as, for example, vinyl acetate, vinyl ethers, acrylic acids, esters and amides, methacrylic acids, esters and amides, styrene, styrene derivatives, butadiene, olefins such as, for 5 example, ethylene and propylene, itaconic acid and maleic anhydride. The halogenated copolymers are preferably copolymers containing chlorine and more preferably vinylidene chloride copolymers. 10 For the purposes of the present invention, the expression "copolymers containing chlorine" is intended to denote the copolymers obtained by aqueous-dispersion free-radical polymerization of a monomer containing chlorine such as, for example, vinyl chloride and 15 vinylidene chloride, with one or more monomers that are copolymerizable therewith. The monomer containing chlorine is in this case the main monomer, i.e. the one which is present in the resulting copolymers in a proportion of at least 50% by weight. 20 Among the monomers that are copolymerizable with the monomer containing chlorine, mention may be made, in a non-limiting manner, of monomers containing chlorine of different nature, vinyl esters such as, for example, vinyl acetate, vinyl ethers, acrylic acids, 25 esters and amides, methacrylic acids, esters and amides, styrene, styrene derivatives, butadiene, olefins such as, for example, ethylene and propylene, itaconic acid and maleic anhydride. For the purposes of the present invention, the 30 expression "vinylidene chloride copolymers" is intended to denote copolymers of vinylidene chloride with one or more monomers that are copolymerizable therewith. In this case, the vinylidene chloride is the main monomer, i.e. the monomer which is present in the resulting 35 copolymers in a proportion of at least 50% by weight. Among the monomers that are copolymerizable with vinylidene chloride, mention may be made, in a REPLACEMENT SHEET (RULE 26) - 13 non-limiting manner, of vinyl chloride, vinyl esters such as, for example, vinyl acetate, vinyl ethers, acrylic acids, esters and aides, methacrylic acids, esters and amides, styrene, styrene derivatives, 5 butadiene, olefins such as, for example, ethylene and propylene, itaconic acid and maleic anhydride. The copolymers that are particularly preferred are copolymers of vinylidene chloride with vinyl chloride and optionally at least one (meth)acrylic 10 monomer corresponding to the general formula:

CH

2

=CR

1

R

2 in which Ri is chosen from hydrogen and a methyl radical and R 2 is chosen from a -CN radical and a

-CO-OR

3 radical in which R 3 is chosen from hydrogen, 15 alkyl radicals containing from 1 to 18 carbon atoms, alkoxyalkyl radicals containing a total of from 1 to 10 carbon atoms and radicals -NR 4 RS in which R 4 and R 5 are chosen from hydrogen and an alkyl radical containing from 1 to 10 carbon atoms. 20 For the purposes of the present invention, the expression "optionally at least one (meth)acrylic monomer" is intended to denote that the copolymers of vinylidene chloride with vinyl chloride may or may not contain at least one (meth)acrylic monomer. 25 For the purposes of the present invention, the expression "at least one (meth)acrylic monomer" is intended to denote that the vinylidene chloride copolymers may contain one or more (meth) acrylic monomer(s), referred to hereinbelow as (meth)acrylic 30 monomer. The (meth)acrylic monomer is preferably chosen from acrylic and methacrylic esters containing from 1 to 8 carbon atoms and particularly preferably from acrylic and methacrylic esters containing from 1 to 6 35 carbon atoms. Examples of such acrylic and methacrylic esters that are particularly preferred are methyl acrylate, REPLACEMENT SHEET (RULE 26) - 14 methyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, n-butyl acrylate, n-butyl methacrylate, isobutyl acrylate, isobutyl methacrylate, t-butyl acrylate 5 t-butyl methacrylate, n-pentyl acrylate, n-pentyl methacrylate, isoamyl acrylate, isoamyl methacrylate, n-hexyl acrylate, n-hexyl methacrylate, 2-methylpentyl acrylate and 2-methylpentyl methacrylate. The (meth)acrylic monomer is most particularly 10 preferably selected from acrylic and methacrylic esters containing from 1 to 4 carbon atoms. Examples of such acrylic and methacrylic esters that are most particularly preferred are methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl 15 methacrylate, propyl acrylate, propyl methacrylate, n-butyl acrylate, n-butyl methacrylate, isobutyl acrylate, isobutyl methacrylate, t-butyl acrylate and t-butyl methacrylate. In this case, vinylidene chloride is the main 20 monomer. The vinylidene chloride is generally present in the resulting copolymers in a proportion of at least 50% by weight. In general, the amount of vinylidene chloride in the vinylidene chloride copolymers ranges from 50% 25 to 95% by weight, preferably from 60% to 95% by weight and particularly preferably from 70% to 95% by weight. In general, the amount of vinyl chloride in the vinylidene chloride copolymers ranges from 3% to 50% by weight, preferably from 3% to 40% by weight and 30 particularly preferably from 4.25% to 30% by weight. In general, the amount of the (meth)acrylic monomer in the vinylidene chloride and vinyl chloride copolymers and in the vinylidene chloride copolymers ranges from 0% to 20% by weight, preferably from 3% to 35 13% by weight and particularly preferably from 0% to 4.5% by weight. REPLACEMENT SHEET (RULE 26) - 15 The invention also relates to the halogenated copolymers obtained by the process according to the invention. The invention also relates to the use of the 5 halogenated copolymers according to the invention to produce extruded articles, for example bioriented or blown monolayer or multilayer barrier films, monolayer or multilayer tubes, monolayer or multilayer sheets and sheets prepared by extrusion layering on polymeric 10 substrates (polyvinyl chloride, polyethylene terephthalate or polypropylene) or on paper. The invention also relates to extruded articles manufactured with the halogenated copolymers according to the invention. These articles are usually used in 15 the food-wrapping field and in the medical field (for example for pharmaceutical blister packs). The process according to the invention has the advantage of allowing higher degrees of conversion of monomers than the processes of the prior art. 20 The copolymers according to the invention have the advantage over the copolymers of the prior art of being homogeneous in terms of monomer distribution. The copolymers according to the invention are characterized, unexpectedly, by a melting point which 25 is markedly lower than that of the copolymers of the prior art for the same monomer content. By virtue of this property, the copolymers may be used at lower temperature and do not require the addition of stabilizer when implemented. By virtue of their low 30 melting point, the copolymers according to the invention have the advantage of being able to be co extruded with other low-melting polymers (ethylene/vinyl acetate copolymers, ethylene/methyl acrylate copolymers and polyamide copolymers) to 35 produce extruded articles. Moreover, the copolymers according to the invention are characterized by improved heat stability REPLACEMENT SHEET (RULE 26) - 16 and improved flexibility and they show no problem of bonding when implemented. The examples which follow are intended to illustrate the invention without, however, limiting its 5 scope. Example 1 (in accordance with the invention) Preparation of a halogenated copolymer 21.7 litres of demineralized water are first introduced into a 40-litre reactor fitted with a 10 stirrer of impeller type. 112 g of sodium dodecylbenzene sulphonate, 5.6 kg of vinylidene chloride and 4 kg of vinyl chloride are then introduced with stirring at 120 rpm. The reactor temperature is then raised to 40 0 C. When the temperature reaches 40 0 C, 15 0.96 g of hydrogen peroxide and 6.4 g of erythorbic acid are added. Thirty minutes later, 6.4 kg of vinylidene chloride are then added over a period of about 300 minutes. Starting from the time at which these 6.4 kg of vinylidene chloride are introduced, 20 4.42 g of erythorbic acid and 1.15 g of hydrogen peroxide are introduced in parallel and continuously over the same period of 300 minutes. Six hours forty five minutes after the start of the polymerization, the reactor is returned to atmospheric pressure and placed 25 under vacuum for 3 hours at 45OC. It is then cooled to room temperature. The degree of conversion is 93.5%. Twenty litres of demineralized water are then added to the aqueous dispersion obtained. 22.4 litres of a 0.2 g/l solution of aluminium 30 sulphate are introduced into a 150-litre container fitted with a stirrer of impeller type. The container is then stirred at about 200 rpm and the temperature is adjusted to 10-14 0 C. All of the dilute aqueous dispersion obtained is then added over about 30 35 minutes, along with 5 litres of a solution containing 2.1 g/l of aluminium sulphate. The temperature of the container is then brought to 70 0 C and maintained for 90 REPLACEMENT SHEET (RULE 26) - 17 minutes. The container is then cooled to room temperature. A slurry is thus obtained. This slurry is then dried in two steps. The first step consists of a liquid/solid separation in an Escher Wyss@ system to 5 form a cake. The second step consists in drying the cake in a fluidized bed of Munster type with an inlet air temperature of about 60 0 C. A halogenated copolymer with a volatile material content of less than 0.3% is obtained. The volatile material content is determined 10 by measuring the loss of mass of the sample after a residence time of 45 minutes in a ventilated oven maintained at 120 0 C. Example 2 (in accordance with the invention) Properties of the halogenated copolymer 15 Various properties of the halogenated copolymer obtained in Example 1 were measured. Among these are the relative viscosity, the melting point, the modulus of elasticity under tension. The relative viscosity is measured using an 20 Ubbelohde viscometer with a constant K of about 0.003, at a temperature of 20 0 C. The solvent used is tetrahydrofuran. The concentration of the solution of the halogenated copolymer in tetrahydrofuran is 10 g/l. The melting point is measured using a Perkin 25 Elmer® differential thermal analysis machine. 18 mg of resin are used and the heating rate is 10 0 C/minute. The modulus of elasticity under tension is measured according to ISO standard 527 on a 30 ym non bioriented extruded monosheet. 30 The values of relative viscosity, melting point and modulus of elasticity under tension measured for the halogenated copolymer obtained in Example 1 are summarized in Table I. The halogenated copolymer obtained in Example 1 35 was also analysed using an EplexorD dynamic analyser. Measurements were taken in tensile mode on cast mono sheets 30 Am thick of the copolymer obtained in REPLACEMENT SHEET (RULE 26) - 18 Example 1. The temperature ramp is 2 0 C/minute between -60 0 C and 80 0 C. The values observed for the mechanical loss tan 8 as a function of temperature for the copolymer obtained in Example 1 are represented in 5 Figure 1 by triangles. The mechanical loss tan 6 is represented on the y-axis and the temperature (OC) is represented on the x-axis. The halogenated copolymer obtained in Example 1 was also analysed by 1H NMR spectrometry using a 10 DPX 300 NMR spectrometer. Measurements were taken on a solution of the halogenated copolymer in hexachloro butadiene. The spectrum obtained is shown in Figure 2 (the scale indicated shows the chemical shifts in ppm). From the analysis of this spectrum, it is seen 15 that the line assigned to the CH 2 groups of the vinyl chloride-vinyl chloride sequence (identified as A-A hereinbelow) between 1.8 and 2.5 ppm is of very low intensity compared with that corresponding to the CH 2 groups of the vinylidene chloride-vinyl chloride 20 sequences (identified as B-A hereinbelow) and vinyl chloride-vinylidene chloride (identified as A-B hereinbelow) between 2.5 and 3.25 ppm and that corresponding to the CH 2 groups of the vinylidene chloride-vinylidene chloride sequences (identified as 25 B-B hereinbelow) between 3.25 and 4.1 ppm. By integrating these lines, it may be calculated that the mole fraction of the various sequences is 7% for the A-A sequences, 39% for the A-B and B-A sequences and 54% for the B-B sequences. 30 Example 3 (not in accordance with the invention) Preparation of a halogenated copolymer 21.7 litres of demineralized water are first introduced into a 40-litre reactor fitted with a stirrer of impeller type. 112 g of sodium 35 dodecylbenzene sulphonate, 11 296 g of vinylidene chloride and 4 704 g of vinyl chloride are then introduced with stirring at 120 rpm. The reactor REPLACEMENT SHEET (RULE 26) - 19 temperature is then raised to 40 0 C. When the temperature reaches 40 0 C, 5.12 g of erythorbic acid and 0.8 g of hydrogen peroxide are added. Thirty minutes later, over a period of about 390 minutes, 1.248 g of 5 hydrogen peroxide and 4.784 g of erythorbic acid are injected continuously. Seven hours after the start of the polymerization, the reactor is returned to atmospheric pressure and placed under vacuum for 3 hours at 45 0 C. It is then cooled to room temperature. 10 The degree of conversion is 85%. 17.3 litres of demineralized water are then added. 20 litres of a 0.2 g/l solution of aluminium sulphate are introduced into a 150-litre container fitted with a stirrer of impeller type. The container 15 is then stirred at about 200 rpm and the temperature is adjusted to 10-14 0 C. All of the dilute aqueous dispersion obtained is then added over about 30 minutes, along with 5 litres of a solution containing 1.9 g/l of aluminium sulphate. The 20 temperature of the container is then brought to 70 0 C and maintained for 90 minutes. The container is then cooled to room temperature. A slurry is thus obtained. This slurry is then dried in two steps. The first step consists of a liquid/solid separation in an Escher 25 Wyss" system to form a cake. The second step consists in drying the cake in a fluidized bed of Minster type with an inlet-air temperature of about 60 0 C. A halogenated copolymer with a volatile material content of less than 0.3% is obtained. The volatile material 30 content is determined by measuring the loss of mass of the sample after a residence time of 45 minutes in a ventilated oven maintained at 120 0 C. Example 4 (not in accordance with the invention) Properties of the halogenated copolymer 35 The relative viscosity, melting point and modulus of elasticity under tension of the halogenated REPLACEMENT SHEET (RULE 26) - 20 copolymer obtained in Example 3 were measured in the same way as in Example 2. The results of these various measurements are summarized in Table I. 5 The halogenated copolymer obtained in Example 3 was analysed using an Eplexor0 dynamic analyser in the same way as in Example 2. The values observed for the mechanical loss tan 8 as a function of the temperature for the copolymer obtained in Example 3 are represented 10 in Figure 1 by squares. The mechanical loss tan 8 is shown on the y-axis and the temperature (OC) is shown on the x-axis. The copolymer obtained in Example 3 was analysed by 'H NMR spectrometry in the same way as in 15 Example 2. The spectrum obtained is shown in Figure 3 (the scale indicated shows the chemical shifts in ppm). From the analysis of this spectrum, it is seen that the line assigned to the CH 2 groups of the A-A sequence between 1.8 and 2.5 ppm is of appreciable 20 intensity compared with that corresponding to the CH2 groups of the B-A and A-B sequences between 2.5 and 3.25 ppm and that corresponding to the CH 2 groups of the B-B sequences between 3.25 and 4.1 ppm. By integrating these lines, it may be 25 calculated that the mole fraction of the various sequences is 16% for the A-A sequences, 38% for the A-B and B-A sequences and 46% for the B-B sequences. TABLE I Example Relative Melting Modulus of elasticity viscosity point (OC) under tension (MPa) 2 1.52 108 245 4 1.58 143 439 From the comparison of the results given in 30 Table I, it is seen that despite a larger content of vinylidene chloride, the copolymer according to the invention has a markedly lower melting point and REPLACEMENT SHEET (RULE 26) - 21 significantly higher flexibility than the copolymer obtained according to the prior art. Moreover, Figure 1 shows that the copolymer according to the invention is characterized by a 5 mechanical loss peak which is markedly narrower than the copolymer according to the prior art, which reflects a greater homogeneity in terms of monomer distribution for the copolymer according to the invention. 10 Furthermore, from the comparison of the 1H NMR spectrometry results, it is seen that the copolymer according to the invention is characterized by a mole fraction of A-A sequences (vinyl chloride-vinyl chloride) which is much smaller than that calculated 15 for the copolymer obtained according to the prior art. This reflects a greater homogeneity in terms of monomer distribution for the copolymer according to the invention. REPLACEMENT SHEET (RULE 26)

Claims

1. Process for preparing halogenated copolymers by 5 copolymerization of at least two monomers, characterized in that the copolymerization is carried out in aqueous dispersion with a subsequent injection of a fraction of at least one of the monomers.

2. Process for preparing halogenated copolymers 10 according to Claim 1, characterized in that a fraction of a halogenated monomer is subsequently injected.

3. Process for preparing halogenated copolymers according to either of Claims 1 and 2, characterized in that a fraction of the main halogenated monomer of the 15 halogenated copolymers is subsequently injected.

4. Process for preparing halogenated copolymers according to Claim 3, characterized in that the main halogenated monomer is a monomer containing chlorine.

5. Process for preparing halogenated copolymers 20 according to either of Claims 3 and 4, characterized in that the main halogenated monomer is vinylidene chloride.

6. Process for preparing halogenated copolymers according to any one of Claims 1 to 5, characterized in 25 that, for a monomer of which a fraction is subsequently injected, the weight ratio between the fraction subsequently injected and the total amount introduced during the copolymerization ranges from 20% to 80%.

7. Process for preparing halogenated copolymers 30 according to any one of Claims 1 to 6, characterized in that, for a monomer of which a fraction is subsequently injected, the weight ratio between the fraction subsequently injected and the total amount introduced during the copolymerization ranges from 40% to 60%. 35

8. Process for preparing halogenated copolymers according to any one of Claims 1 to 7, characterized in that it is applied to the preparation of copolymers of REPLACEMENT SHEET (RULE 26) - 23 vinylidene chloride and of vinyl chloride and copolymers of vinylidene chloride with vinyl chloride and at least one (meth)acrylic monomer corresponding to the general formula: 5 CH 2 =CRiR 2 in which Ri is chosen from hydrogen and a methyl radical and R 2 is chosen from a -CN radical and a -CO-OR 3 radical in which R 3 is chosen from hydrogen, alkyl radicals containing from 1 to 18 carbon atoms, 10 alkoxyalkyl radicals containing a total of from 1 to 10 carbon atoms and radicals -NR 4 R 5 in which R 4 and R 5 are chosen from hydrogen and an alkyl radical containing from 1 to 10 carbon atoms.

9. Process for preparing halogenated copolymers 15 according to Claim 8, characterized in that the (meth)acrylic monomer is chosen from acrylic and methacrylic esters containing from 1 to 8 carbon atoms.

10. Process for preparing halogenated copolymers according to either of Claims 8 and 9, characterized in 20 that the total amount of the vinyl chloride is introduced initially into the polymerization charge.

11. Process for preparing halogenated copolymers according to any one of Claims 8 to 10, characterized in that a fraction of the (meth)acrylic monomer is 25 subsequently injected.

12. Process for preparing halogenated copolymers according to any one of Claims 1 to 11, characterized in that it is applied to the preparation of halogenated copolymers by aqueous-emulsion copolymerization. 30

13. Halogenated copolymers, characterized in that they are homogeneous in terms of monomer distribution.

14. Halogenated copolymers according to Claim 13, characterized in that they have a melting point, determined by differential thermal analysis, of less 35 than or equal to 170oC. REPLACEMENT SHEET (RULE 26) - 24

15. Halogenated copolymers according to either of Claims 13 and 14, characterized in that they are copolymers containing chlorine.

16. Halogenated copolymers according to any one of 5 Claims 13 to 15, characterized in that they are vinylidene chloride copolymers.

17. Halogenated copolymers according to any one of Claims 13 to 16, characterized in that they are copolymers of vinylidene chloride with vinyl chloride 10 and optionally at least one (meth)acrylic monomer corresponding to the general formula: CH 2 =CRiR2 in which R 1 is chosen from hydrogen and a methyl radical and R 2 is chosen from a -CN radical and a 15 -CO-OR 3 radical in which R 3 is chosen from hydrogen, alkyl radicals containing from 1 to 18 carbon atoms, alkoxyalkyl radicals containing a total of from 1 to 10 carbon atoms and radicals -NR 4 R 5 in which R 4 and R 5 are chosen from hydrogen and an alkyl radical containing 20 from 1 to 10 carbon atoms.

18. Halogenated copolymers according to Claim 17, characterized in that the (meth)acrylic monomer is chosen from acrylic and methacrylic esters containing from 1 to 8 carbon atoms. 25

19. Use of the halogenated copolymers according to any one of Claims 13 to 18, to produce extruded articles.

20. Extruded articles, characterized in that they are manufactured with the halogenated copolymers 30 according to any one of Claims 13 to 18. REPLACEMENT SHEET (RULE 26)