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...
Patent
1998-10-28
2000-12-12
Wu, David W.
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...
526 72, 526 87, C08F 222
Patent
active
061600490
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a process for preparing an aqueous polymer dispersion by free-radically initiated polymerization of free-radically polymerizable compounds whose individual solubility in water under the conditions (pressure, temperature) of the free-radically initiated polymerization is at least 0.001% by weight, based on the respective saturated aqueous solution (compounds I), whose disperse polymer particles comprise, in addition to the compounds I, at least one compound II whose solubility in water under the conditions (pressure, temperature) of the free-radically initiated polymerization is less than 0.001% by weight, based on the respective saturated aqueous solution, and in which process a mixture consisting of a portion of the compounds I and of the at least one compound II is used to produce an aqueous oil (disperse phase)-in-water(continuous phase) emulsion I whose disperse phase consists predominantly of droplets with a diameter .ltoreq.500 nm, and in which at least a portion of the aqueous emulsion I is supplied to the polymerization vessel in the course of continuing free-radical polymerization.
Aqueous polymer dispersions are fluid systems whose disperse phase in an aqueous dispersion medium comprises polymer particles which are in stable disperse distribution. The diameter of the polymer particles is predominantly within the range of, in general, from 0.01 to 5 .mu.m and, in many cases, from 0.01 to 1 .mu.m.
Like polymer solutions when the solvent is evaporated, aqueous polymer dispersions have the property, when the aqueous dispersion medium is evaporated, of forming polymer films, which is why aqueous polymer dispersions are much employed as binders, for example for paints or for leather-coating compositions.
Aqueous polymer dispersions are usually prepared by free-radical aqueous macroemulsion polymerization of free-radically polymerizable compounds, the latter normally comprising--with the exception of any minor amounts of molecular weight regulators additionally employed--monomers containing at least one ethylenically unsaturated group (often referred to below just as monomers for short).
In this procedure the monomers that are to be polymerized, and also any molecular weight regulators additionally used, are emulsified in the aqueous medium without any relatively great effort, for example by means of customary stirring, and, with the addition of free-radical polymerization initiators which dissolve in the aqueous medium, are subjected to polymerization. The term emulsion as used here denotes that a system of two mutually insoluble or only sparingly soluble liquids is present in which the liquids are in a state of more or less fine dispersion. The liquid which is present in excess is termed the continuous or external phase, and the liquid dispersed as droplets in the discontinuous phase is termed the disperse phase. The term aqueous emulsion, then, is generally used to refer to an emulsion in which the aqueous phase constitutes the continuous phase. The preparation of an emulsion normally requires the addition of emulsifiers (Ullmanns Encyklopadie der technischen Chemie, Vol. 10, 4th Edition, Verlag Chemie, Weinheim (1975), p. 449) which prevent the direct combination of two liquid droplets in the disperse distribution that happen to collide. The prefix "macro" expresses the fact that the aqueous monomer emulsion is one whose disperse phase consists, as a result of the low dispersion effort, predominantly of droplets with a diameter .gtoreq.1000 nm.
An essential feature of the free-radical aqueous macroemulsion polymerization, then, is that each of the monomers that are to be polymerized has a certain level of solubility in water under the conditions (pressure, temperature) of the free-radical aqueous macroemulsion polymerization. Thus the polymerization initiator dissolved in the external aqueous phase of the aqueous macromonomer emulsion has available to it, in the same external aqueous phase, a large number of dissolved monomers as coreactants. Above a critical chain l
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Kroner Hubertus
Machtle Walter
Mathauer Klemens
McKee Graham Edmund
BASF - Aktiengesellschaft
Egwim Kelechi C.
Wu David W.
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