Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2001-10-01
2004-06-08
Egwim, Kelechi C. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S100000, C524S800000
Reexamination Certificate
active
06747102
ABSTRACT:
The present invention relates to a process for free radical-initiated aqueous emulsion polymerization for the preparation of an aqueous polymer dispersion, in which at least one chemical compound (monomer) having at least one ethylenically unsaturated group is dispersed in an aqueous medium and polymerized by means of at least one free radical polymerization initiator in the presence of at least one organometallic compound.
Controlled polymerization reactions open up the possibility of synthesizing polymers having a specific molecular structure, defined molecular weight and low polydispersity and thus establishing a specific property profile of said polymers. In the last 40 years, a large number of methods which were essentially based on anionic and cationic mechanisms have been developed for this purpose (cf. O. W. Webster in Science 1991, 251, pages 887 to 893).
Compared with the ionic polymerization variants free radical polymerization reactions have the fundamental advantage that they can be carried out with a larger number of commercially important monomers and moreover can be effected by mass, solution, suspension and emulsion polymerization. However, attempts to find suitable catalysts for controlled free radical polymerization reactions have for a long time been unsuccessful.
It recently became known that N-oxyl radicals may be suitable for controlling free radical-initiated polymerization reactions of ethylenically unsaturated monomers. In this context, reference may be made, for example, to U.S. Pat. No. 4,581,429, EP-A 735 052, WO 94/11412, U.S. Pat. No. 5,322,912, U.S. Pat. No. 5,412,047 and GB 1 124 009.
The fact that organic metal complexes, too, are capable of controlling free radical polymerization processes is described by Wayland et al. in J. Am. Chem. Soc. 1994, 116, pages 7943 to 7944, for the controlled free radical solution polymerization of arylates using specific cobalt-porphyrin complexes, by way of example.
U.S. Pat. No. 5,312,871 discloses the use of a catalyst system for the controlled polymerization of ethylenically unsaturated monomers, consisting of an alkyl- or aryl-metal compound, an organic ligand and a stable radical. EP-A 841 346 discloses specific cobalt, rhodium and iridium complexes for controlling free radical polymerization reactions of ethylenically unsaturated monomers.
Application WO 87/03605 discloses the preparation of oligomeric compounds. The oligomers are prepared by free radical polymerization of ethylenically unsaturated monomers using specific transition metal catalysts. The preparation of aqueous polymer dispersions by means of free radical-initiated aqueous emulsion polymerization is, however, not disclosed.
Research Disclosure, December 1998, 416, pages 1595 to 1604, describes the controlling effect of specific porphyrin-, phthalocyanine- and salen-iron complexes in the solution and mass polymerization of styrene. In addition to the azobisisobutyronitrile used as free radical initiator, substituted alkyl bromides are used as polymerization initiator. The porphyrin-, phthalocyanine- or salen-iron complexes are always present in less than the molar stoichiometric amount relative to the substituted alkyl bromide used as a free radical polymerization initiator. Free radical aqueous emulsion polymerizations are not included.
In a corresponding manner, EP-A 714 416 discloses the use of specific cobalt complexes with tetradentate nitrogen ligands for controlling free radical polymerization reactions both in solution and in emulsion. The free radical initiators used are, exclusively, substituted aliphatic azo compounds.
U.S. Pat. No. 5,763,548 likewise discloses a process for controlled free radical polymerization, in which the controlling effect of organometallic compounds is employed.
WO 98/50436 describes the controlling effect of specific cobalt-oxime/boron fluoride complexes in free radical-initiated aqueous emulsion polymerization. Characteristic of the disclosed process is that hydrophobic solvents, for example higher alkanes or fatty alcohols for taking up the cobalt complex, are required in addition to the monomers.
Makino et al. disclose, in Polymer Preprints Vol. 39, March 1998, 288 and 289 (Am. Chem. Soc.; Polymer Chemistry Division), a process for the controlled free radical aqueous emulsion polymerization of ethyl methacrylate. The polymerization initiator used is ethyl 2-bromoisobutanoate. Furthermore, the emulsion polymerization is carried out in the presence of a relatively water-soluble copper(I)-bispyridyl complex. The molar ratio of the polymerization initiator used to the water-soluble copper(I)-bispyridyl complex is 1:1. The dispersant used is sodium dodecyl sulfate.
According to Matyjaszewski et al., Macromolecules 1998, 31, 5951 to 5954, the results obtained by Makino et al. are unsatisfactory. This is because, on the one hand, the copper(I)-bispyridyl complex is said to have much too high a water solubility and in addition the combination Cu
2+
/SO
4
2−
is said to be completely disadvantageous for a controlling effect. Matyjaszewski et al. therefore recommend using nonionic polyethylene glycol oleyl ethers as dispersants and water-insoluble copper(I)-dialkylbispyridyl complexes as organometallic compounds.
In view of the above prior art, it is an object of the present invention to provide a process for controlled free radical aqueous emulsion polymerization, in which organometallic compounds other than those in the processes of the prior art exercise the controlling effect and which, in particular in the presence of sodium dodecyl sulfate as a dispersant, results in satisfactory control and furthermore does not require the presence of a hydrophobic organic solvent and requires no special polymerization initiators.
We have found that this object is achieved by a process for free radical-initiated aqueous emulsion polymerization for the preparation of an aqueous polymer dispersion, in which at least one monomer having at least one ethylenically unsaturated group is dispersed in an aqueous medium and polymerized by means of at least one free radical polymerization initiator in the presence of at least one organometallic compound, wherein the at least one organometallic compound on the one hand has the following structural feature of the formula I,
where:
Me
is a metal ion,
—.—.—
is a covalent bond or a monoatomic to triatomic covalent,
bridging chain, the atoms bonded to the chain members not
being included, and
—
is a covalent bond to a neighboring atom,
and, on the otherhand, is such that at 20° C. and 1 bar (absolute) its solubility in acidic, basic and/or neutral water is greater than its solubility in styrene.
The procedure for a free radical-initiated aqueous emulsion polymerization of monomers having at least one ethylenically unsaturated group has often been described in the past and is therefore sufficiently well known to a person skilled in the art [cf. for example Encyclopedia of Polymer Science and Engineering, Vol. 8, page 659 et seq. (1987); D. C. Blackley, in High Polymer Latices, Vol. 1, page 35 et seq. (1966); H. Warson, The Applications of Synthetic Resin Emulsions, page 246 et seq., Chapter 5 (1972); D. Diederich, Chemie in unserer Zeit 24, page 135 to 142 (1990); Emulsion Polymerization, Interscience Publishers, New York (1965); DE-A 40 03 422 and Dispersionen synthetischer Hochpolymerer, F. Hölscher, Springer-Verlag, Berlin (1969)]. It is usually carried out by dispersing the at least one monomer, frequently in the presence of dispersants, in an aqueous medium and polymerizing it by means of a free radical polymerization initiator. The novel process differs from the procedure only in the additional presence of at least one organometallic compound which has the structural feature of formula I.
Monomers having at least one ethylenically unsaturated group which are suitable for the novel process include in particular monomers capable of free radical polymerization in a simple manner, for example ethylene, vinylaromatic monomers such as styrene, &agr;-methyl styrene, o
Christie David
Claverie Jerome
Kanagasabapathy Saba
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