Process for preparing stabilized polymer dispersion

Abstract: Stabilized polymer dispersions in which the principal polymer contains a core component of acrylic polymers and stabilizer components which are polymers of ethylenically unsaturated monomers and which are grafted to the core component at the stabilizer ends, can be prepared using a catalytic chain transfer agent containing Co⁺².

Description: Technical Field This invention relates to a process for preparing a stabilized polymer dispersion. It is more particularly directed to a process for preparing a dispersion of a polymer having an acrylic polymer core component and a polymeric stabilizer component, in which the stabilizer component is prepared using a cobalt catalytic chain transfer agent. Background and Summary of the Invention The stabilized polymeric dispersions prepared according to this invention are described in a general way in U.S. Patent 4,746,714 to Spinelli, Scopazzi and Antonelli. While those dispersions function very well for their intended purpose, the method described for their preparation provides no convenient way for incorporating living functional groups, especially hydroxyl groups, on the chains of the stabilizer polymer molecules. These functional groups confer certain advantages when the polymer system is to be cross-linked with melamines or isocyanates. It has now been found that such groups can be easily incorporated on the stabilizer polymer molecules, in any number, if one uses a cobalt catalytic chain transfer agent in the polymer's preparation. WO 87/03605 describes a process for the free radical polymerization of unsaturated monomers utilizing cobalt 2+ or cobalt 3+ chelate complexes, for instance bis[µ-[(2,3-butanedione dioximato)(2-)O:O']-tetrafluorodiborato (2-)-N,N',N'',N'''](methanol)cobalt(II), as chain transfer agents. Neither the use of a cobalt 2+ chelate complex with water as a ligand nor the copolymerization of a macro-monomer with a vinylic monomer in an organic liquid being a non-solvent for the core polymer is disclosed in WO 87/03605. Detailed Description The polymers of the dispersions prepared according to the invention are described in U.S. Patent 4,746,714, previously mentioned. The polymers described there have core components of acrylic polymers and substantially linear acrylic polymeric stabilizer components, each having a terminal polymerizable functional group, which are grafted to the core component at one end of the chain. Illustrative of monomers which can be used to prepare the core components are those shown in the '714 patent, column 3, line 55, to column 4, line 25. Isocyanate, silane and amine functional monomers can also be used. Preferred for use in the process of the invention are methyl methacrylate, hydroxyethyl methacrylate, methacrylic acid, methyl acrylate, styrene and glycidyl methacrylate. The monomers used to prepare the stabilizer component according to the invention can be any of the conventional polymerizable ethylenically unsaturated monomers. Preferred for use are butyl methacrylate, isobutyl methacrylate, 2-ethylhexyl methacrylate, hydroxyethyl methacrylate, methyl methacrylate, glycidyl methacrylate, itaconic acid or anhydride, maleic acid or anhydride, styrene, isocyanatoethyl methacrylate, benzene 1-(1-isocyanato-1-methyl ethyl)-3,4(1-methyl ethenyl), methacrylic acid, acrylic acid, silanes and amines. The ratio of monomer units in the final polymer is a matter of choice, as will be understood by those skilled in this art. The catalytic chain transfer agent used in the process of the invention are diaquabis(borondifluorodimethylglyoximato)cobaltate (II) and diaquabis(borondifluorodiphenylglyoximato)cobaltate (II) (see U.S. Patents 4,680,352 and 4,722984). The chain transfer agents are used at concentrations of 5-150 ppm based on monomers. The process is run in two steps, the second of which can be run immediately after the first but which is ordinarily run after a pause for analysis and to permit more efficient use of the reactor. In step one, a mixture of stabilizer monomers and organic liquid is heated, preferably to reflux temperature for ease of control, and to it is added the catalytic chain transfer agent of choice, additional monomer(s) and solvent, and the usual amount of a conventional polymerization initiator such as azo- or peroxide initiators. The reaction is run, with additions of monomers and initiator as needed, until the desired stabilizer component is obtained having a M W of 5000-12000). In step two, an organic liquid which is a solvent for the stabilizer component but a non-solvent for the core component is added to the product of step one. "Solvent" and "non-solvent" are being used in the conventional sense, as will be understood by those skilled in the polymer art. Illustrative of organic liquids which can be used are aromatic- and aliphatic hydrocarbons such as heptane and VM&P naphtha. Mixtures of liquids can also be used. The stabilizer/liquid ratio is of secondary importance, but is usually in the range 1/2 to 1/4 (weight). The resulting mixture is again heated, preferably to reflux temperature for better control and to it are added the core monomers and a conventional initiator such as one of those previously mentioned, in the usual amount. Polymerization is continued, with additions of liquid and initiator as needed, until it is complete, as determined by periodic sampling and analysis. The dispersions prepared according to the process of the invention can be used to modify the rheology and/or the physical properties of conventional coating compositions at concentrations of 1-80%, preferably 10-40%, by weight of the total composition. Examples In the examples, all parts are by weight unless indicated otherwise. Example 1 Part A To a reaction vessel were charged Toluene 827.2 parts n-butyl methacrylate 447.9 2-Ethylhexyl methacrylate 588.9 3-methacryloxypropyltrimethoxysilane (A-174) 108.1 This mixture was brought to reflux temperature, held there under nitrogen with stirring, and to it was then added, over a ten-minute period, a solution of 1,1'-azobis(cyclohexanecarbonitrile) (initiator) 1.14 parts Diaquabis(borondifluorodimethylglyoximato)-cobaltate(II) 0.023 n-butyl methacrylate 80.7 Toluene 42.1 The reaction mixture was then held at reflux temperature, with stirring, and to it was added, over a 60-minute period, a mixture of n-butyl methacrylate 209.0 2-ethylhexyl methacrylate 271.6 A-174 (described above) 63.6 Initiator 1.95 This was followed immediately by the addition of a solution of n-butyl methacrylate 209.0 parts 2-ethylhexyl methacrylate 304.9 A-174 (described above) 63.0 Initiator 2.12 Toluene 84.4 over a 180-minute period while maintaining reflux temperature. The reaction mixture was then held at reflux temperature, with stirring, for 30 minutes after which time was added, over a 60-minute period, a mixture of Toluene 105.9 parts Initiator 0.5 This reaction mixture was held at reflux temperature for 60 minutes, and toluene (246.3 parts) was then added to it and the mixture cooled. The resulting solution, 64.2% solids, contained the stabilizer component 2-EHMA/BMA/A-174 50/40/10. Part B To a reaction vessel were charged Product of (A) 265.0 parts Heptane 396.0 This mixture was brought to reflux temperature and to it were then added 0.6 parts of t-butyl peroctoate. The mixture was then held at reflux temperature and to it were immediately and simultaneously added, over a 210-minute period, (1) A solution of Methyl methacrylate 207.9 parts Methyl acrylate 103.9 Styrene 62.4 A-174 41.6 Heptane 19.3 Product of A 128.8 and (2) A solution of Heptane 67.7 t-butyl peroctoate 6.2 The resulting mixture was held at reflux temperature for 45 minutes, and to it was then added, over a 30-minute period, at reflux, a solution of Heptane 24.7 parts t-butyl peroctoate 4.1 This was again held at reflux temperature for 60 minutes, and 119.7 parts of solvent were boiled off to give a dispersion containing 55% solids. The composition of the principal polymer in the resulting product was BMA/2-EHMA/A-174/MMA/MA/STY 14.4/18.8/9.9/31.6/15.8/9.5 Example 2 Part A To a reaction vessel were charged Toluene 853.5 parts Isobutyl methacrylate 495.2 2-ethylhexyl methacrylate 434.2 Hydroxyethyl methacrylate 151.5 The mixture was brought to reflux temperature (129°C), held there under nitrogen with stirring, and to it was then added, over a 10-minute period, a solution of Diaquabis(borondifluorodimethylglyoximato)-cobaltate II 0.033 parts 1,1'-azobis(cyclohexanecarbonitrile) (initiator) 1.0 Hydroxyethyl methacrylate 36.6 Toluene 38.0 The reaction mixture was held at reflux temperature with stirring and to it was added, over a 240-minute period, a mixture of Isobutyl methacrylate 353.1 parts 2-ethylhexyl methacrylate 414.0 Hydroxyethyl methacrylate 213.8 Toluene 76.3 The reaction mixture was then held at reflux temperature with stirring for 30 minutes, after which time was added, over a 60-minute period, a mixture of Toluene 227.9 parts Initiator 0.9 The reaction mixture was further held at reflux temperature for 60 minutes and then cooled. The resulting solution, 63.6% solids, contained the stabilizer component 2-EHMA/IBMA/HEMA 40/40/20. Part B To a reaction vessel were charged Product of A 639.2 parts Isopropanol 44.0 Petroleum naphtha 62.8 Heptane 790.6 Xylol 99.1 The mixture was brought to reflux temperature (92°C) and to it were added 1.6 parts of t-butyl peroctoate. The reaction mixture was held at reflux temperature and to it were immediately and simultaneously added, over a 210-minute period, (1) a solution of Methacrylic acid 42.2 parts Hydroxyethylacrylate 264.7 Methyl methacrylate 370.3 Methyl acrylate 190.6 Styrene 158.9 Glycidyl methacrylate 32.2 Xylol 49.1 Product of A 320.9 and (2) a solution of Petroleum naphtha 157.0 parts Butanol 27.9 t-butyl peroctoate 15.9 The reaction mixture was then held at reflux temperature for 45 minutes and to it was then added, over a 30-minute period, at reflux, a solution of Butanol 62.8 parts t-butyl peroctoate 10.4 The reaction mixture was held at reflux temperature for a further 60 minutes, at which time 304.8 parts of solvent were boiled off, to give a dispersion containing 55% solids. The composition of the principal polymer in the resulting product was IBMA/2-EHMA/HEMA/MMA/MA/S/MAA/GMA 29.7/29.7/12.8/13/6.7/5.5/1.5/1.1 The pentacyanocobaltates (II) and diaquabis(borondifluorodiphenylglyoximato)cobaltate (II) can replace the diaquabis(borondifluorodimethylglyoximato)cobaltate (II) catalytic chain transfer agent in the foregoing procedures, in equivalent amounts, with substantially the same result.

Claims: A process for preparing a stabilized polymer dispersion in an organic liquid in which dispersion the polymer comprises (a') a plurality of stabilizer components with M w of 5 000 - 12 000 which are polymers of ethylenically unsaturated monomers, and (b') a core component composed of polystyrene and/or acrylic polymers and/or acrylic copolymers with styrene as comonomer; substantially all of the stabilizer components being grafted to the core component at one of the stabilizer ends, the process comprising the following steps (a) preparing the stabilizer component by polymerizing one or more ethylenically unsaturated monomers, at least one of said monomers containing a functional group, using diaquabis(borondifluorodimethyl- glyoximato)cobaltate (II) or diaquabis(borondifluorodiphenylglyoximato)cobaltate (II) in an amount of 5 to 150 ppm, and then (b) preparing the core component by polymerizing one or more acrylic monomers and/or styrene while they are in contact with stabilizer components, steps (a) and (b) being conducted in an organic liquid which is a solvent for the stabilizer components but a non-solvent for the core component. The process of claim 1 in which the monomers used in (a) are butyl methacrylate, isobutyl methacrylate, 2-ethylhexyl methacrylate, hydroxyethyl methacrylate, methyl methacrylate, glycidyl methacrylate, styrene, methacrylic acid, acrylic acid, itaconic acid or anhydride, maleic acid or anhydride, or 3-methacryloxypropyl-trimethoxysilane. The process of claims 1 or 2 in which the monomers used in (b) are methyl methacrylate, hydroxyethyl methacrylate, methacrylic acid, styrene, glycidyl methacrylate or 3-methacryloxypropyl-trimethoxysilane. A process according to claim 1 in which the monomers used in (a) are butyl methacrylate, isobutyl methacrylate, 2-ethylhexyl methacrylate, hydroxyethyl methacrylate, methyl methacrylate, glycidyl methacrylate, styrene, methacrylic acid, acrylic acid, itaconic acid or anhydride, maleic acid or anhydride, or 3-methacryloxypropyl-trimethoxysilane, and the monomers used in (b) are methyl methacrylate, hydroxyethyl methacrylate, methacrylic acid, styrene, glycidyl methacrylate or 3-methacryloxypropyl-trimethoxysilane.

Inventors: ANTONELLI JOSEPH ALBERT, DOHERTY MARK MATTHEW, SCOPAZZI CHRISTOPHER, ANTONELLI, JOSEPH ALBERT, DOHERTY, MARK MATTHEW, SCOPAZZI, CHRISTOPHER
Applicants: DU PONT, E.I. DU PONT DE NEMOURS AND COMPANY
Application year: 1991
Main classification: C08F265
IPC codes: C08F2, C08F265, C08F290