REDOX POLYMERIZATION PROCESS

Abstract: A process for emulsion polymerization comprising the steps of reacting together a polymerization initiator, a reductor, and a polymerizable species, with the proviso that the polymerization initiator is not a hydroperoxide, characterized in that the polymerization initiator and the reductor are reacted together to provide a free radical moiety of the initiator, whereupon this free radical moiety initiates polymerization of the polymerizable species, this step being carried out at an initial cold start temperature, whereafter the temperature is increased to follow a temperature profile to a final preselected polymerization temperature.

Description: REDOX POLYMERIZATION PROCESS The present invention relates to a process for emulsion polymerization, to the polymers obtainable by such a process, and to their uses. The production of water based resins, for example by means of emulsion polymerization techniques, is earned out thermally with inorganic persulfates. A problem with thermal polymerization is the process time, which leads to a less than desirable reactor output. An object of the present invention is to provide an alternative polymerization process which aims to improve the process time. The first aspect of the present invention provides a process according to claim 1. Since the polymerization process according to the present invention provides a free radical initiator moiety by means of a redox reaction instead of by thermal decomposition, the polymerization can be earned out with a so-called "cold start", which involves the process time being reduced and the reactor output per unit time being increased. A redox polymerization is known for tertiary butyl hydroperoxide "Trigonox A- W70". The inventors have shown, however, that a redox polymerization utilizing other organic peroxides provides unexpectedly good results. The inventors have shown that polymerization can start at a lower initial temperature, which means that because of the longer "heating-up" time necessary in thermal polymerization, the polymerization time can be reduced utilizing the process of the current invention. The inventors have furthermore demonstrated that the process according to the present invention enables a polymer with a very low residual monomer level to be obtained, whilst, with respect to thermal polymerization, the amount of initiator used can be reduced. Good results have been achieved under the conditions as defined in claims 2-6. The polymerization initiator is most preferably a substantially non-water-soluble initiator, such as defined in claim 7 or 8, since these non-water-soluble initiators yield an unexpectedly high efficiency in polymerization. This higher efficiency results in shorter polymerization times and in polymer resins with improved properties. The higher efficiency of the organic peroxides is expressed by the low level of residual monomers and by the low molecular weights (Mw/Mn) of the polymers formed. Furthermore, the conductivity of the resins initiated with the organic peroxide/redox system is lower than for corresponding resins that were initiated by persulfates. The reductor of the redox system preferably is chosen from the following group: sodium formaldehyde sulfoxylate (SFS), sodium bisulfite, Ascorbic acid (vitamin C), aldehydes, for example glutaraldehyde, sodium metabisulfite, sodium dithionate, and sugars, wherein the reductor most preferably is sodium formaldehyde sulfoxide. The polymerizable species preferably is chosen from the following group: acrylonitrile, acrylic acid, methyl acrylate, ethyl acrylate, butyl acrylate, 2- ethylhexyl acrylate, methoxyethyl acrylate, dimethyl aminoacrylate, methacrylic acid, methyl methacrylate, ethyl methacrylate, butyl methacrylate, isobutyl methacrylate, 2-ethylhexyl methacrylate, lauryl methacrylate, stearic methacrylate, dimethyl aminomethacrylate, allyl methacrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, acrylamide, methacrylamide, glycidyl acrylate, vinyl ester of versatic acid, styrene, para-methyl styrene, vinyl acetate, alpha-methyl styrene, wherein the polymerizable species most preferably comprises vinyl acetate and/or the vinyl ester of versatic acid. Further preferred process conditions are detailed in claims 11-15. The polymerization is earned out in a conventional emulsion, for example in a mixture of anionic and non-ionic surfactants such as Witconate (sodium alpha- olefin sulfonate) and Syntopon (ethoxylated nonylphenol); however, other emulsifiers or mixtures are also possible. This emulsifier solution preferably is a mixture of nonionic and anionic emulsifiers and most preferably is selected from the group consisting essentially of: - long-chain aliphatic carboxylates (ionic) - alkylbenzene sulfonates (ionic) - alkyl sulphates (ionic) - dialkylsulphosuccinate (ionic) - ethoxylated alcohols (nonionic) - ethoxylated alkyl phenols (nonionic) - ethoxylated amine or amides (nonionic). A second aspect of the present invention provides a polymer obtainable according to this process. The invention will now be further elucidated by way of the following examples. Examples 1-6 are comparative examples and Examples 7-12 are examples according to the present invention using a redox system. Examples 3, 4, 6, 8-12 were subjected to a temperature profile increasing from an initial temperature to a final temperature, i.e. subjected to a so-called "cold-start", and Example 7 was earned out at constant temperature. Procedure of preparation The polymerization in all the examples was carried out in a 0.25 L glass reactor with a stirrer under nitrogen. A seed was prepared first by adding 10% of the reactive components at polymerization temperature. The preparation of the seed was carried out as follows: The reactor was filled with buffered (NaAc/HAc) emulsifier solution (Witconate/Syntopon), prepared with oxygen-free deionized water. At the polymerization temperature 10% of the pre-emulsion containing soaps (Witconate and Syntopon), monomers, and, in the case of the redox system according to the present invention, also reductor and catalyst, were added. In addition the solution or pre-emulsion of the initiator was added to achieve control over the accurate dosing of the initiator. After a polymerization time of 30 minutes the remaining monomers, pre-emulsion, and initiator solution were dosed in 2.5 hours. In Examples 3, 4, 6, 8-12 the temperature was increased to the final temperature in the same period, following a temperature profile. The final temperature was maintained for 1 hour. The composition of the buffered soap solution used was as follows: NaAC.3aq 0.25 g (sodium acetate) HAc 0.11 g (acetic acid) H 2 O 30.3 g Witconate 0.38 g (soap) Syntopon 0.38 g (soap) Example 1 Thermal system The temperature was kept at 70' °C during the polymerization. The composition of the used pre-emulsior i was: Witconate 1.28 g Syntopon 1.28 g H 2 O 34.43 g Vac (vinyl acetate) 52.5 g (monomer) VEOVA (vinyl ester of versatic acid) 22.5 g (monomer) The initiator solution was composed of 4.18 mmoles ammonium/sodium or potassium persulfate in 25 g H 2 O. The total process time including the time needed for heating up the reactor contents to 70°C before polymerization amounted to 5.5 hours. Examples 2, 5, 7 The temperature was kept at 70°C (Examples 2, 5) and 20°C (Example 7), respectively. The composition of the used pre-emulsions was as follows: Witconate 1.28 g Syntopon 1.28 g H 2 O 34.43 g Peroxide 1.04-4.18 mmoles as mentioned in the examples Vac (vinyl acetate) 52.5 g (monomer) VEOVA (vinyl ester of 22.5 g (monomer) versatic acid) The reductor SFS (sodium formaldehyde sulfoxyde: 0.65 g) and the catalyst (FeSO 4 16.7 mg) were dissolved in 25 g H 2 O. The total process time was 4 hours. Examples 3. 4. 6. 8-12 The polymerization temperature was kept at 20°C for the first 30 minutes to prepare a seed. The temperature was then increased by 20°C/hour to 70°C following a temperature profile. It is noted that other starting temperatures and temperature programmes can be used, either for initiating polymerization or for initiating and completing polymerization. In all the examples the residual monomers were determined by gas chromatography (GC). The molecular weight of the prepared polymers was determined by gel permeation chromatography (GPC) with polystyrene for calibration. The conversion/solids content was determined by standard procedure. The viscosity was determined using a Brookfield digital viscometer. The results are shown in Table 1. Examples 13-24 Procedure of preparation The polymerization in all examples was carried out in a 0.25 L glass reactor with a stirrer under nitrogen. A seed was prepared first by adding 10% of the reactive components at polymerization temperature. The preparation of the seed was carried out as follows: The reactor was filled with the emulsifier solution (sodium lauryl sulfate in water) prepared with oxygen-free deionized water. At the starting polymerization temperature 10% of the pre-emulsion containing soap, monomers, and in the case of the redox system, also reductor and catalyst, were added. In addition the solution or pre-emulsion of the initiator was added to achieve control over the accurate dosing of the initiator. After a polymerization time of 30 minutes the remaining monomers, pre-emulsion, and initiator solution were dosed in 2.5 hours. The temperature was increased to the final temperature in the same period, following a temperature profile. The final temperature was maintained for 1 hour. The composition of the soap solution was as follows: 0.10 g sodium lauryl sulfate (emulsifier) 25.0 ml deionized water Pre-emulsion: 1.60 g sodium lauryl sulfate 30 ml deionized water 70 g monomer mixture (butylacrylate / styrene / methacrylic acid = 6/4/0.1) including the initiator (1.04 meq), if not water-soluble. The reductor SFS (sodium formaldehyde sulfoxylate 0.16 g) and the catalyst (Fe"SO 4 2.8 mg) were dissolved in 10 ml water. The molar ratio oxidator: reductor: Fe = 1 : 1 : 0.01 The results are shown in Tables 2 and 3. Table 1 Table 2 Emulsion: Theoretical solids content: VeoVa10/VAc-emulsions: 44% Reductant: SFS/Fe(ll) Ox : SFS : Fe = 1 : 1 : 0.01 n.a. = not applicable n.d. = not detected Table 3 Emulsion: Theoretical solids content: STY/BA MA-emulsions:46% Reductant: SFS/Fe(ll) Ox : SFS : Fe = 1 : 1 : 0.01 n.a. = not applicable n.d. = not detected Styrene/butyl acrylate/methacrylic acid : 4/6/0.1 Tx C = tert-butyl peroxybenzoate Tx 22 = 1 ,1 di(tert-butylperoxy)cyclohexane Tx 117 = tert-butylperoxy-2-ethylhexyl carbonate Laurox = di-lauroyl peroxide Results As reference the emulsion copolymerization of vinylacetate and VeoVa with potassium persulfate at 70°C was used (thermal conditions). The results show low residual monomer levels for the non-water-soluble organic peroxides (peroxyesters) under redox conditions. As the efficiency of the non-water-soluble peroxyesters such as Trigonox C was much higher than that of the water-soluble persulfates and hydroperoxides, the levels of addition could be lowered to 20-40% of the original milli-equivalents of initiator used. Due to lower amounts of initiator and reductor, a higher value for pH and lower values for the conductivity were obtained. The prepared polymer had molecular weights (Mw/Mn) comparable with those of the reference copolymer of VeoVa/VAc. The peroxyesters such as Trigonox 21 gave a high conversion of monomers at ambient temperature. The invention is not limited to the above description; rather, the requested rights are determined by the following claims.

Claims: CLAIMS 1. A process for emulsion polymerization comprising the steps of reacting together a polymerization initiator, a reductor, and a polymerizable species, with the proviso that the polymerization initiator is not a hydroperoxide, characterized in that the polymerization initiator and the reductor are reacted together to provide a free radical moiety of the initiator, whereupon this free radical moiety initiates polymerization of the polymerizable species, this step being carried out at an initial cold start temperature, whereafter the temperature is increased to follow a temperature profile to a final preselected polymerization temperature. 2. Process according to claim 1 carried out at an initial temperature of up to 70°C, for example carried out at an initial temperature of up to 50°C and preferably of up to 35°C. 3. Process according to claim 1 or 2 carried out at an initial temperature lying in the range of +10° to 35°C, preferably in the range of 15° to 25°C. 4. Process according to any one of the preceding claims wherein the initial temperature is maintained for a predetermined length of time, for example up to 2 hours, preferably up to 1 hour, most preferably up to half an hour. 5. Process according to any one of the preceding claims wherein the temperature is increased subsequent to the initial temperature maintenance period to follow a temperature profile to a final polymerization temperature, preferably up to a final polymerization temperature of at the most 90°C, and wherein the final polymerization temperature preferably lies in the range of 50-80°C and most preferably is 70°C or less. 6. Process according to claim 5 wherein the initial temperature is increased incrementally per pre-selected time period, preferably by about 20°C per hour. 7. Process according to claim 6 wherein the initiator is selected from the group consisting essentially of: diisobutanoyl peroxide, cumyl peroxyneodecanoate, 2,4,4-trimethylpentyl-2-peroxyneodecanoate, tert- amyl peroxyneodecanoate, bis(4-tert-butylcyclohexyl)peroxydicarbonate, bis(-ethylhexyl)peroxydicarbonate, tert-butyl peroxyneodecanoate, dibutyl peroxydicarbonate, dicetyl peroxydicarbonate, dimyristyl peroxy- dicarbonate, tert-amyl peroxypivalate, tert-butyl peroxypivalate, bis(3,5,5- trimethylhexanoyl) peroxide, dilauroyl peroxide, didecanoyl peroxide, 2,5"- bis(2-ethylhexanoylperoxy)-2,5-dimethylhexane, tert-amyl peroxy-2- ethylhexanoate, dibenzoyl peroxide, tert-butyl peroxy-2-ethylhexanoate, tert-butyl peroxydiethylacetate, 1 ,4-bis(tert-butylperoxycarbo)cyclohexane, tert-butyl peroxyisobutanoate, 1 ,1-bis(tert-butylperoxy)-3,3,5- trimethylcyclohexane, 1 ,1-bis(tert-butylperoxy)cyclohexane, tert-butyl peroxy-3,5-trimethylhexanoate, 2,2-bis(tert-butylperoxy)butane, tert- butylperoxy isopropyl carbonate, tert-butylperoxy 2-ethylhexyl carbonate, tert-butyl peroxyacetate, tert-butyl peroxybenzoate, di-tert-amyl peroxide, dicumyl peroxide, bis(tert-butylperoxyisopropyl)benzene, 2,5-bis(tert- butylperoxy)-2,5-dimethylhexane, tert-butyl cumyl peroxide, 2,5-bis(tert- butylperoxy)-2,5-dimethyl-3-hexyne, and di-tert-butyl peroxide. 8. Process according to claim 7 wherein the initiator is substantially non- water-soluble and is selected from the group consisting essentially of: - alifatic and aromatic peroxyesters, preferably tert-butyl peroxy-2- ethylhexanoate (Trigonox 21), tert-amyl peroxy-2-ethylhexanoate, tert- butyl peroxybenzoate (Trigonox C), tert-amyl peroxybenzoate, tert-butyl peroxyacetate, tert-butyl peroxy-3,5-trimethylhexanoate, tert-butyl peroxyisobutanoate, tert-butyl peroxydiethylacetate, tert-butyl peroxypivalate; - peroxycarbonates, preferably tert-butyl peroxyisopropyl carbonate (Trigonox BPIC), and tert-butyl peroxy-2-ethyl hexyl carbonate Trigonox 117). . Process according to any one of the preceding claims wherein the reductor is chosen from the group consisting essentially of: sodium formaldehyde sulfoxylate (SFS), sodium bisulfite, Ascorbic acid (vitamin C), aldehydes, for example glutaraldehyde, sodium metabisulfite, sodium dithionate, and sugars. 10. Process according to any one of the preceding claims wherein the polymerizable species is selected from the group consisting essentially of: acrylonitrile, acrylic acid, methyl acrylate, ethyl acrylate, butyl acrylate, 2- ethylhexyl acrylate, methoxyethyl acrylate, dimethyl aminoacrylate, methacrylic acid, methyl methacrylate, ethyl methacrylate, butyl methacrylate, isobutyl methacrylate, 2-ethylhexyl methacrylate, lauryl methacrylate, stearic methacrylate, dimethyl aminomethacrylate, allyl methacrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2- hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, acrylamide, methacrylamide, glycidyl acrylate, vinyl ester of versatic acid, styrene, para- methyl styrene, vinyl acetate, alpha-methyl styrene. 11. Process according to any one of the preceding claims caπied out in the presence of a catalyst, said catalyst preferably being a water-soluble salt derived from a transition metal, and most preferably being selected from the group consisting essentially of Fe 2+ , Co 3+ , Cu\ and Ce 3+ . 12. Process according to any one of the preceding claims wherein the initiator s and the reductor are provided in the following ratios 10:1 to 1:5, preferably 4:1 to 1:2. 13. Process according to any one of the preceding claims wherein the ratio of catalyst: oxidator is about 0-0.1 on a molar basis. 0 14. A polymer obtainable according to the process of any one of the preceding claims. 15. Polymer according to claim 14 having one or more of the following s characteristics: - a conductivity lower than about 5, - a low residual monomer level, - a particle size of less than about 220 nm, preferably less than 200 nm. 0 16. Use of a polymer according to claims 14 and/or 15 in coatings and/or adhesives.

Inventors: MALTHA ANNEMARIEKE, VAN SWIETEN ANDREAS PETRUS, WAANDERS PETRUS PAULUS, MALTHA, ANNEMARIEKE, VAN SWIETEN, ANDREAS, PETRUS, WAANDERS, PETRUS, PAULUS
Applicants: AKZO NOBEL NV, MALTHA ANNEMARIEKE, SWIETEN ANDREAS PETRUS VAN, WAANDERS PETRUS PAULUS, AKZO NOBEL N.V., MALTHA, ANNEMARIEKE, VAN SWIETEN, ANDREAS, PETRUS, WAANDERS, PETRUS, PAULUS
Application year: 1999
Main classification: C08F4
IPC codes: C08F2, C08F4, C09D5, C09D201, C09J201