Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
1997-09-11
2003-02-04
Lipman, Bernard (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C526S201000
Reexamination Certificate
active
06515065
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to the polymerization of unsaturated monomers in aqueous medium and, more particularly, to protective colloids for such polymerization processes. The protective colloids according to the invention are water-soluble nonionic polyurethanes produced from polyiso-cyanates, water-soluble polyalkylene glycols with an ethylene glycol content of at least 70% by weight and branched alcohols containing at least three hydroxyl groups which are characterized by a certain ratio of water-soluble polyalkylene glycols to polyhydric branched alcohols.
Protective colloids are mainly used in suspension, emulsion and dispersion polymerization. Suspension polymerizations are polymerizations of water-insoluble monomers in water, the polymerization reactions taking place in monomer droplets where they are initiated by oil-soluble initiators. The water-insoluble monomers are suspended in water in the form of numerous small monomer droplets by addition of a suspending agent. Emulsion polymerizations are generally radical polymerizations of water-insoluble monomers emulsified in water. In emulsion polymerizations, in contrast to suspension polymerizations, the polymerization reaction does not take place in monomer droplets, but in micelles or latex particles which are produced by addition of interfacially active substances (emulsifiers, detergents, soaps). There are also emulsion polymerizations which take place in the absence of an emulsifier, although their exact reaction mechanism is not yet known. Dispersion polymerizations are emulsion polymerizations “in reverse” where an aqueous phase is dispersed in an organic phase.
In the polymerization processes listed above, the function of protective colloids is to stabilize the polymer dispersions during and after polymerization of the monomers. This is done by adsorption of the protective colloids to the surface of the polymer particles which results in steric hindrance so that the polymer particles are prevented from coagulating. Conventional protective colloids are water-soluble partly and fully hydrolyzed polyvinyl acetates with various polyvinyl alcohol contents which, in addition, are available in various molecular weights. The higher the molecular weight of the polyvinyl acetate/polyvinyl alcohols, the higher the viscosities to which the dispersions of polymers or polymer particles can be adjusted.
Other known protective colloids are polyvinyl pyrrolidone, cellulose ethers, starch and cellulose. These known protective colloids perform entirely satisfactorily although the resistance of the final polymer dispersions to freezing and thawing is in need of improvement where polyvinyl acetate/polyvinyl alcohol is added as the protective colloid.
However, since protective colloids remain in the polymer, the properties of the polymer can be adversely affected by the known protective colloids. For example, polymer films based on emulsion polymers of vinyl acetate are always very hard and, in addition, sensitive to alkalis and water where the conventional protective colloids are used. It would be desirable if the polymer films in question could have improved resistance to water and alkalis and, in addition, could be far more flexible so that the need for external plasticizers could be reduced or eliminated altogether.
2. Discussion of Related Art
It is known from WO 94113726 that water-soluble polyurethanes produced from diisocyanates, a water-soluble polyethylene glycol and optionally a hydrophobic diol can be used as protective colloids in emulsion polymerization. Where these water-soluble polyurethanes are used as protective colloids in emulsion polymerization, stable dispersions of polyvinyl acetate or the copolymer of vinyl acetate and maleic acid dibutyl ester are obtained. In addition, films obtained from these dispersions are relatively flexible and water-resistant.
The disadvantage of the polyurethanes known from WO 94/13726 is that a certain viscosity can only be more or less adjusted in the polymer dispersions produced with these polyurethanes.
However, there is a demand among manufacturers of polymer dispersions for protective colloids on the lines of polyvinyl acetate/polyvinyl alcohol where the viscosities of the polymer dispersions can be adjusted as required by varying the molecular weights of the protective colloids.
EP-B-334 032 describes oligourethanes which have a branched molecular structure and which are terminated by hydrophilic groups. The hydrophilic groups are preferably ionic groups, such as carboxylate or quaternary ammonium groups. These oligourethanes are produced from polyisocyanates, hydrophobic polyhydric polyols and monofunctional compounds containing hydrophilic groups of the type described above. They may be used as emulsifiers in emulsion polymerization.
The problem addressed by the present invention was to provide protective colloids which, through variation of their chemical structure, would be capable of adjusting polymer dispersions to the required viscosities. In addition, the films obtainable from the polymer dispersions would show improved resistance to water and alkalis and would also be relatively flexible so as to reduce or eliminate the need for external plasticizers. The protective colloids would of course also provide for stable dispersions of the polymers as reflected above all in increased resistance to freezing and thawing.
DESCRIPTION OF THE INVENTION
According to the invention, this problem has been solved by water-soluble nonionic polyurethanes as protective colloids for the polymerization of olefinically unsaturated monomers in aqueous medium, characterized in that the water-soluble nonionic polyurethanes have been produced by reaction of
a) organic polyisocyanates with
b) water-soluble polyalkylene glycols containing at least 70% by weight of ethylene glycol units and with
c) polyhydric branched alcohols containing at least three hydroxyl groups per molecule, the equivalent ratio of b) to c) being in the range from 1:0.01 to 1:10.
“Nonionic” in the context of the present invention means that the polyurethane does not contain any ionic groups as emulsifying groups, i.e. does not contain any carboxylate, sulfonate, phosphonate or ammonium groups. Rather is the dispersibility of the polyurethane attributable to the presence of the water-soluble polyalkylene glycols which contain at least 70% by weight of ethylene glycol units, based on polyalkylene glycols, and preferably at least 80% by weight of ethylene glycol units. In the context of the invention, the polyalkylene glycols are “water-soluble” providing more than 10 g remain dissolved in 100 g of water for more than 6 months at 20° C.
Ethylene glycol units correspond to the formula —[CH
2
—CH
2
—O]
n
—, where n is the degree of oligomerization.
Suitable water-soluble polyalkylene glycols are polyethylene glycols produced by polyaddition of ethylene oxide to water or to ethylene glycol as the starter molecule and also polyaddition products of ethylene oxide with other low molecular weight diols, such as butanediol, hexanediol or 4,4′-dihydroxydiphenyl propane. Several water-soluble polyethylene glycols differing in their average molecular weight may also be used. Copolymers of ethylene oxide and propylene oxide are also suitable providing the content of ethylene glycol units is at least 70% by weight, based on copolymer, and preferably at least 80% by weight.
Water-soluble polyethylene glycols with an average molecular weight in the range from 500 to 100,000, preferably in the range from 1,000 to 20,000 and more particularly in the range from 3,000 to 12,000 are particularly preferred.
It is crucial to the invention that branched alcohols containing at least three hydroxyl groups per molecule are used as an additional polyol component for the production of the polyurethanes. The equivalent ratio of the polyalkylene glycols described above to the branched alcohols containing three hydroxyl groups is another particularly important factor.
Preferred bra
Baumann Carsten
Feustel Dieter
Huebner Norbert
Drach John E.
Henkel Kommanditgesellschaft auf Aktien
Lipman Bernard
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