WO2000047633A2

WO2000047633A2 - Emulsion polymerisation of ethylenically-unsaturated monomers in the presence of phosphorylated cellulose

Info

Publication number: WO2000047633A2
Application number: PCT/EP2000/001050
Authority: WO
Inventors: Karel Hindrik Van Streun
Original assignee: Akzo Nobel N.V.
Priority date: 1999-02-09
Filing date: 2000-02-09
Publication date: 2000-08-17
Also published as: AU2803600A; WO2000047633A3

Abstract

Proposed is a process for the emulsion polymerisation of ethylenically-unsaturated monomers such as vinyl esters, monovinyl aromatic compounds, (meth)acrylic acid and/or derivatives thereof in the presence of a stabilising amount of water-soluble phosphorylated cellulose obtained by dissolving cellulose in a phosphoric acid-containing solvent to give a solution of which 94-100 wt. % is composed of the constituents cellulose, phosphoric acid and/or its anhydrides, and water. The relative viscosity, θrel, of the phosphorylated cellulose is preferably < 2.5 (measured at 25 °C in a concentration of 0.3g phosphorylated cellulose/100ml cueen), while the content of cellulose-bound phosphorus is in the range of 3 to 20, preferably 4 to 8 wt. %. In the obtained latex dispersions a biodegradable polymer (cellulose phosphate) is coupled to a non-biodegradable polymer of vinyl esters, styrene, acrylates and/or methacrylates. These dispersions have a very high salt solutions stability and a high storage stability and because of their good adhesive power they are pre-eminently suited to be used for the preparation of latex paints. What is special about this system is that a biodegradable polymer (cellulose phosphate) is coupled to a non-biodegradable polymer of ethylenically-unsaturated monomers such as vinyl esters, monovinyl aromatic compounds (meth)acrylic acid and/or derivatives thereof.

Description

Emulsion polymerisation of ethylenically-unsaturated monomers in the presence of phosphorylated cellulose

The invention pertains to a process for the emulsion polymerisation of ethylenically-unsaturated monomers in the presence of a stabilising amount of a water-soluble cellulose derivative.

A process of the aforesaid type was earlier described in WO 96/14357. Said document lists a large number of water-soluble cellulose derivatives which all result in the percentage of coarse particles due to the occurrence of side reactions in the emulsion polymerisation process being reduced. The coating industry is mentioned as the principal field of application for the dispersions described in this document. Key requirements to be met by paints are good storage stability and the capacity to adhere properly to the substrate to be coated. Equally relevant is the painted substrate's weather resistance. Especially when the substrate is a metal surface susceptible to corrosion, it is of the essence that the paint to be applied to it should have anticorrosive properties. Although it is possible using the known dispersions to obtain paints which show excellent adhesion to the substrate and also provide good protection to surfaces susceptible to corrosion, there is a constant need for further improvement of the known paints in these respects.

The invention now provides a process for the emulsion polymerisation of ethylenically-unsaturated monomers where no or only a very small amount of by-product in the form of coarse particles or grit is obtained and by means of which paints with significantly enhanced properties can be achieved.

The invention consists in that in a process of the known type mentioned in the opening paragraph the cellulose derivative employed is a water-soluble phosphorylated cellulose obtained by dissolving cellulose in a phosphoric acid- containing solvent to give a solution of which 94-100 wt.% is composed of the constituents cellulose, phosphoric acid and/or its anhydrides, and water. It should be noted that the preparation of a water-soluble phosphorylated cellulose by dissolving cellulose in a phosphoric acid-containing solvent to obtain a solution of which 94-100 wt.% is composed of the constituents cellulose, phosphoric acid and/or its anhydrides, and water is known as such from WO 97/30090. However, no mention whatsoever is made there of the potential use of the described water-soluble phosphorylated cellulose as stabiliser in the emulsion polymerisation of ethylenically-unsaturated monomers. A wide range of mono-ethylenically unsaturated monomers may be used for carrying out the invented process. Very good results are obtained when the ethylenically-unsaturated monomers are selected from the group of vinyl esters, monovinyl aromatic compounds, (meth)acrylic acid and/or derivatives thereof. Examples of suitable monomers include (meth)acrylic acid and derivatives thereof, such as esters and amides, vinyl esters, vinyl ethers, monovinyl aromatic compounds, vinyl and vinylidene halides, N-vinyl pyrrolidone, ethylene, propylene, or greater alpha-olefins, allyl amines, allyl esters of saturated monocarboxylic acids, and amides thereof.

Suitable esters of (meth)acrylic acid include (cyclo)alkyl(meth)acrylates having 1-12 carbon atoms in the (cyclo)alkyl group, such as methyl(meth)acrylate, octyl(meth)acrylate, isobornyl(meth)acrylate, dodecyl(meth)acrylate, and cyclohexyl(meth)acrylate. Suitable monovinyl aromatic compounds include styrene, vinyl toluene, α-methyl styrene, and vinyl naphthalene. Suitable substituted (meth)acrylate compounds include (meth)acrylamide, (meth)acrylonitrile, N-methylol (meth)acrylamide, and N-alkyl

(meth)acrylamides. Suitable vinyl compounds include vinyl chloride and vinylidene chloride. Suitable vinyl esters include vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl valerate, vinyl caproate and vinyl versatate. Suitable vinyl ethers include methylvinyl ether, ethylvinyl ether and n- butylvinyl ether. In addition, use may be made in small quantities of di-, tri- or polyunsaturated compounds having at least 2 ethylenically-unsaturated groups, such as butadiene-1 ,3, vinylesters of polycarboxylic acids such as maleic acid, adipic acid, or trimellitic acid; (meth)acrylic esters of di-, tri- or polyvalent polyols, including polyester polyols and polyether polyόls. As examples of suitable polyols may be mentioned ethylene glycol, propylene glycol, diethylene glycol, tetramethylene diol, neopentyl glycol, hexamethylene diol; cyclohexane diol, bis-(4-hydroxycyclohexyl)methane, glycerol, trimethylol ethane, trimethylol propane, tri(2-hydroxyethyl)isocyanurate, and pentaerythritol. These esters may optionally contain a hydroxyl group.

The term phosphoric acid in this patent application refers to all inorganic acids of phosphorus and/or mixtures thereof. Orthophosphoric acid (H₃PO ) is the acid of pentavalent phosphorus. Its anhydrous equivalent, i.e. the anhydride, is phosphorus pentoxide (P₂O₅). In addition to orthophosphoric acid and phosphorus pentoxide there is, depending on the amount of water in the system, a series of acids of pentavalent phosphorus with a water-binding capacity in between those of phosphorus pentoxide and orthophosphoric acid, such as tetrapolyphosphoric acid (H₆P₄O₁₃, PPA).

In addition to water, phosphoric acid and its anhydrides, and cellulose and/or reaction products of phosphoric acid and cellulose, other substances may be present in the solution when preparing phosphorylated cellulose. The solution can be prepared by mixing constituents classifiable into four groups: cellulose, water, inorganic acids of phosphorus including their anhydrides, and other constituents. These "other constituents" may be substances which benefit the processability of the cellulose solution, solvents other than phosphoric acid, or adjuvants (additives), e.g., to counter cellulose decomposition as much as possible, or dyes and the like.

It was found that, in general, very favourable results are obtained when the relative viscosity, η_reι, of the phosphorylated cellulose is < 2.5 (measured at 25°C in a concentration of 0.3 g phosphorylated cellulose /100 ml cueen). When the η_reι has a value of more than 2.5, solubility problems may arise. This was also found to be the case when the phosphorus content is less than 3 wt.%, particularly with a higher η_re|. For practical reasons the phosphorus content is general bound to a maximum of 20 wt.%. Optimum results have been obtained so far with the phosphorylated cellulose having an η_reι of less than 2.0 and more preferably less than 1.5 and the content of cellulose-bound phosphorus being in the range of 4 to 8 wt.%.

When carrying out the emulsion polymerisation, generally favourable results were obtained when the amount of phosphorylated cellulose corresponded to a weight percentage in the range of 0.05 to 5, calculated on the overall amount of monomers. Optimum results were obtained using a weight percentage in the range of 0.1 to 3.

If so desired, a quantity of a different water-soluble cellulose derivative with a molecular weight < 75 000 may also be present during the emulsion polymerisation. As examples may be mentioned carboxymethyl cellulose and derivatives thereof with a degree of substitution of at least 0.7, hydroxyethyl cellulose, ethyl hydroxyethyl cellulose, methyl cellulose, methyl hydroxypropyl cellulose, hydroxypropyl cellulose, polyacrylic acid and its alkali salts, ethoxylated starch derivatives, water-soluble starch, gelatin, water-soluble alginates, casein, agar, wholly and partially hydrolysed polyvinyl alcohol, polyacrylamide, poly(vinyl pyrrolidone), and poly(methyl vinyl ether-maleic anhydride).

According to the invention, preference is given to a process in which at least 10 wt.% of the water-soluble cellulose is phosphorylated cellulose. In addition to the aforesaid cellulose derivatives, during the emulsion polymerisation there may also be present 0,01 to about 4 wt.% of a surface-active compound, calculated on the overall amount of monomer present.

Suitable surface-active compounds according to the present invention preferably belong to the group of anionic and non-ionic compounds. The suitable anionic emulsifiers include: potassium laurate, potassium stearate, potassium oleate, sodium decyl sulphate, sodium dodecyl sulphate, sodium dodecyl benzene sulphonate, and sodium rosinate. As examples of non-ionic emulsifiers may be mentioned: linear and branched alkyl polyethylene glycol and alkylaryl polyethylene glycol, polypropylene glycol ethers and thio ethers, alkyl phenoxypoly(ethyleneoxy)ethanols, such as the adduct of 1 mole of nonylphenol and 5-12 moles of ethylene oxide, or the ammonium salt of said adduct's sulphate.

In general, the emulsion polymerisation is carried out at a temperature between room temperature and 120°C, preferably at a temperature from 45 to 95°C, in the presence of conventional radical initiators in the usual amounts. The suitable radical initiators include: ammonium persulphate, sodium persulphate, potassium persulphate, di-n-butyl peroxydicarbonate, t-butyl perpivalate, t-butyl hydroperoxide, dibenzoyl peroxide, 2,2'-azobisisobutyro-nitrile, and 2,2'-azobis- 2-methylbutyronitrile. Alternatively, the emulsion polymerisation can be carried out in the presence of a redox catalyst, such as a combination of potassium persulphate and sodium disulphite. The amount of initiator employed in the polymerisation reaction generally corresponds to 0.1 to 5 wt.% of the overall amount of monomers. Preference is given to an amount of from 0.3 to 1.0 wt.%. Optionally, a chain length regulator, such as n-octyl mercaptan, dodecyl mercaptan, and 3-mercaptopropionic acid, may be employed.

The emulsion polymerisation can be carried out in a batchwise as well as a semi-batchwise and a continuous process. Preference is given to the use of a process where the monomers are added stepwise and the initiator is dosed either continuously or stepwise. Alternatively, the polymerisation can be carried out under high shearing stress, which means that it can be carried out in a closed circuit reactor. At the start of the reaction 0 to 40 wt.%, preferably about 5 to about 15 wt.%, of the ethylenically unsaturated monomer or mixture of monomers is charged. When there is continuous dosing, the polymerisation reaction generally is continued for 2 to 5 hours.

On conclusion of the emulsion polymerisation a latex system of particulate polymer particles in a continuous aqueous phase is obtained. What is special about this system is that a portion of these particles is formed by a biodegradable polymer (cellulose phosphate) coupled to a non-biodegradable polymer of vinyl esters, styrene, acrylates and/or methacrylates. The size of the latex particles in that case generally ranges from 50 to 500 nanometres, preferably from 100 to 400 nm. The latex is free of coarse ingredients such as grit. The latex system obtained by emulsion polymerisation according to the present invention is exceptionally stable, even in the presence of a salt and resistant to high shearing forces. It was further found that fillers and pigments can be dispersed without the aid of a dispersant. This is not only attractive from an economic point of view, it also has technical advantages in that the absence of a dispersant usually is attended with reduced foaming. The latices obtained in this manner are pre-eminently suitable for incorporation into a large number of coating compositions. An additional advantage of this is good adhesion to pigment particles. The invention will be elucidated with reference to the following examples. It goes without saying that these are exemplified embodiments only and the scope of the invention is not limited thereto.

The values given in the examples for the relative viscosity, η_reι, and the phosphorus content were determined as follows:

Determination of ηmt and [η]

The relative viscosity, η_reι, of the phosphorylated cellulose was determined with the aid of an Ubbelohde type 1 (k=0.01). To this end the cellulose specimens to be measured were dried in vacuo for 16 hours at 50°C after neutralisation, or the amount of water in the copper II ethylene diamine/water mixture was corrected to take into account the water in the cellulose. In this way an 0.3 wt.% of cellulose-containing solution was made using a copper II ethylene diamine/water mixture (1/1). The resulting solution had its viscosity ratio (vise, rat. or η_reι) determined, and from this the limiting viscosity [η] was determined in accordance with the formula: _ _ vise, rat - 1 „_nn

[η] = x 100 c + (k x c x (visc.rat.-1))

wherein c = cellulose concentration of the solution (g/dl) and k = constant = 0.25

Determination of phosphoms content

The content of cellulose-bound phosphorus can be measured as described in

WO 96/06208.

However, there is also a simpler way of determining the phosphorus content of cellulose products. To this end the cellulose product is tabletted after being dried in vacuo for some 15 hours at 50°C. Using an X-ray fluorescent emission spectrometer (e.g., a Philips PW 1400 with chromium tube, line: Kα, 50 kV,

50 mA, GE crystal, angle: 141.025, counting time: 50 s) the tablet's X-ray fluorescence intensity of phosphorus is then measured. By calibrating the spectrometer using tablets with a known phosphorus content, the measured intensity can be converted to the phosphorus content of the specimen in a simple manner known to the skilled person.

Example Into a 1 -litre four-neck flask equipped with a glass stirrer, a thermocouple, and a dropping funnel (in which there was 50% of the initiator solution composed of 1.27 parts of ammonium persulphate and 77.90 parts of water) was charged a mixture composed of 311.62 g of water, 2.12 g of phosphorylated cellulose (η_reι = 1.45 and content of cellulose-bound phosphorus = 4.6 wt.%), 9,80 g nonylphenol ether (containing 30 ethylene oxide units), 10.46 g lauryl ether sulphate, and 1.27 g NaHCO₃. A vacuum was applied to the reactor, which was then flushed with nitrogen three times. Next, the reactor was heated to 60°C, after which 10% of the mixture of monomers composed of 289.16 parts of vinyl acetate and 96.39 parts of vinyl versatate was added, followed by the initiator solution present in the dropping funnel. After the temperature had risen to 70°C, the heating of the reaction mixture was continued at 80°C. The remaining monomers mixture was dosed over a period of 2 hours and 45 minutes. The feeding of the initiator solution was continued for a further 15 minutes, followed by halting of the polymerisation after 1 hour. The reaction mixture did not contain any grit.

The percentage of solid ingredients in the reaction mixture was determined by heating 1 g of latex at 140°C for 45 minutes. The percentage of solid ingredients in this example was determined to be 49.3, the mean particle size, determined with the aid of capillary hydrodynamic fractionation (CHDF), was 158 nanometres (nm).

Example I

In a manner analogous to that indicated in Example I three latices B, C, and D were prepared. In the preparation of latex B use was made of 85 parts by weight (pbw) of vinyl acetate and 15 pbw of butyl acrylate.

In the preparation of latex C use was made of 49.7 pbw of methyl methacrylate,

49.7 pbw of butyl acrylate, and 0.6 pbw of methacrylic acid.

The preparation of latex D was identical with that of latex C, with the proviso that instead of phosphorylated cellulose, hydroxyethyl cellulose (Natrosol 250

LR^® ex Hercules) was used as stabiliser.

Latices B en C did not contain any grit; the solids content of both was determined to be 49.1%, while the mean particle size was determined to be 203 and 109 nm, respectively. The preparation of latex D had to be halted after 50 minutes due to excessive coagulation and high viscosity.

Example I I

Into a 1-litre four-neck flask equipped with a glass stirrer, a thermocouple, and a dropping funnel (which contained 50% of the initiator solution composed of 1.18 parts of ammonium persulphate and 65.2 parts of water) was charged a mixture composed of 334.8 g of water, 3.94 g of phosphorylated cellulose (η_reι = 1.29 and content of cellulose-bound phosphorus = 6.6 wt.%), and 1.3 g of sodium bicarbonate. A vacuum was applied to the reactor, which was flushed with nitrogen. After this procedure had been repeated twice, the reactor was heated to 85°C. The initiator solution was added in one go. Next, the monomers mixture composed of 172.2 g of methyl methacrylate, 172.2 g of butyl acrylate, and 49.2 g of styrene was dosed together with the remaining initiator solution in 3 hours at 85°C. After 1 hour of after-reaction the dispersion was cooled to room temperature and filtered through a stainless steel 250 mesh filter. The solids content of said latex (latex E) was 49.9%. The particle size, determined by means of capillary hydrodynamic fractionation (CHDF), was 353 nm. The obtained latex was very monodisperse.

Example IV Latex F was prepared in a manner analogous to that indicated in Example 111, with the proviso that the amount of phosphorylated cellulose was halved. The solids content was determined to be 49.1%. The particle size, determined by means of CHDF, was 395 nm. The obtained latex was very monodisperse.

Example V (Comparative example)

Latex G was prepared in a manner analogous to that indicated in Example III, with the proviso that this time, instead of phosphorylated cellulose, the same quantity by weight of carboxymethyl cellulose (Ambergum 3021^® ex Hercules) was employed. The obtained latex contained so much grit that it proved impossible to determine the particle size using CHDF.

The preparation of latex H was analogous to that of latex G, with the proviso that this time the amount of carboxymethyl cellulose (Ambergum 3021^® ex Hercules) was doubled. The particle size of the largest fraction, determined by means of CHDF, was 543 nm, while there was also a fraction having a particle size up to 900 nm. The solids content was determined to be 49.2%. Example VI (Comparative example)

Latex I was prepared in a manner analogous to that indicated in Example IV, with the proviso that instead of phosphorylated cellulose, this time use was made of the same quantity by weight of a low-molecular weight surface-active substance (Perlankrol EP36^® ex Acros).

The solids content was determined to be 49.6%. The particle size, determined by means of CHDF, was 343 nm.

Example V I Latices E through I had their salt stability measured by mixing 1 part of latex with 1 part of salt solution and then visually assessing the stability of this mixture.

The outcome of this test was that the stability of latex I was very poor: after being mixed with a 1 M NaCI solution the latex was unstable. All latices E through H were stable even after being mixed with a solution of a 1 M MgCI₂ solution in water.

Claims

1. A process for the emulsion polymerisation of ethylenically-unsaturated monomers in the presence of a stabilising amount of a water-soluble cellulose derivative, characterised in that the cellulose derivative is a water-soluble phosphorylated cellulose obtained by dissolving cellulose in a phosphoric acid-containing solvent to give a solution of which 94-100 wt.% is composed of the constituents cellulose, phosphoric acid and/or its anhydrides, and water.

2. A process according to claim 1 , characterised in that the ethylenically- unsaturated monomers are selected from the group of vinyl esters, monovinyl aromatic compounds, (meth)acrylic acid and/or derivatives thereof.

3. A process according to claim 1 , characterised in that the relative viscosity, η_reι, of the phosphorylated cellulose is < 2.5 (measured at 25°C in a concentration of 0.3 g phosphorylated cellulose /100 ml cueen) and the content of cellulose-bound phosphorus is in the range of 3 to 20 wt.%.

4. A process according to claim 3, characterised in that the relative viscosity, η_reι, of the phosphorylated cellulose is < 2.0 and the content of cellulose-bound phosphorus is in the range of 4 to 8 wt.%.

5. A process according to one or more of the preceding claims, characterised in that the amount of phosphorylated cellulose corresponds to a percentage by weight in the range of 0.05 to 5, calculated on the overall amount of monomers.

6. A process according to one or more of claims 1-4, characterised in that the amount of phosphorylated cellulose corresponds to a percentage by weight in the range of 0.1 to 3, calculated on the overall amount of monomers.

7. A process according to one or more of the preceding claims, characterised in that the polymerisation takes place in the presence of sodium, potassium and/or ammonium persulphate as radical initiator.

8. A process according to one or more of the preceding claims, characterised in that in addition to the water-soluble phosphorylated cellulose another amount of water-soluble cellulose derivative with a molecular weight < 75 000 is present, which is selected from the group of carboxymethyl cellulose and derivatives thereof with a degree of substitution of at least 0.7, hydroxyethyl cellulose, ethyl hydroxyethyl cellulose, methyl cellulose, methyl hydroxypropyl cellulose, hydroxypropyl cellulose, polyacrylic acid and the alkali salts thereof, ethoxylated starch derivatives, water-soluble starch, gelatin, water- soluble alginates, casein, agar, wholly and partially hydrolysed polyvinyl alcohol, polyacrylamide, (vinyl pyrrolidone), and poly(methyl vinylether- maleic anhydride).

9. A process according to claim 8, characterised in that the amount of water-soluble phosphorylated cellulose is at least 10% of the overall amount of water-soluble cellulose.

10. A process according to one or more of the preceding claims, characterised in that in addition 0.01 to about 4 wt.% of a surface-active compound, calculated on the overall amount of monomer, is present.

11. A latex obtained using a process according to one or more of the preceding claims, characterised in that the obtained polymer comprises particles with a mean particle size of 50 to 500 nm.