CA2050305A1 - Sterically stabilized aqueous polymer dispersions - Google Patents

Abstract

ABSTRACT

Sterically stabilized aqueous polymer dispersions based on ethylenically unsaturated monomers polymerized by a free radical method and a graft polymer as protective colloid are made available by grafting the essentially hydrophobic ethylenically unsaturated monomers such as alkyl esters of acrylic acid or methacrylic acid onto the essentially water-soluble or water-dispersible polymeric protective colloid precursor by a radical method using a graft initiator, and then polymerizing ethylenically unsaturated monomers capable of free radical polymeriza-tion in an aqueous medium in the presence of the protec-tive colloid thus obtained by emulsion polymerization in the presence of a conventional free radical-forming initiator. Protective colloid precursors preferably used are polysaccharides and polymers of ethylenically unsatu-rated monomers, such as polyvinylpyrrolidone and polyvinyl alcohol in particular. The aqueous polymer dispersions, which can be processed even at room temperature, are suit-able as the base for paints or coatings.

Description

2 ~ ~ 0 3 ~ L7 ~TERI~AI,~Y ~TABILIZ~D AQUEOU~ POLYMB~ DI~PERSXO~

This invention relates to sterically stabilized aqueous dispersions of polymers based on free radical-polymerized ethylenically u]nsaturated monomers, their preparation, and their use as film-formers, for example for producing coatings.
Polymer dispersions usually have the advantage over polymer solutions in that they permit the use of polymer preparations with astonishingly high solids con-tent with a relatively small proportion of solvents (dispersion medium), but nevertheless with relatively low rocessing viscosities. The smaller proportion of solvent necessary with them is desirable with regard to air pollution requirements.
Increasingly more stringent air pollution regula-tions and cost considerations have finally led to develop-ments in which organic solvents are largely eliminated, whether as solvent or dispersant, and environmentally harmless and more economical water is used instead.
Aqueous polymer dispersions have been described repeatedly and are being used increa~ingly even where the end product, coatings for example, must meet high specifi-cations.
The problem of stability of aqueous polymer ~5 dispersions has played a central role in their market introduction. In general, the dispersion particles coagulated after relatively short shelf lives and settled out. Polymer dispersions stable in storage which show useful shelf lives can now be made available. It became a question in particular of matching the usually anionic emulsifier to the protective colloid or the so-called internal stabilizer in a suitable way, which was done more or less empirically. Of course, useful results are ordinarily obtained here when the emulsifier, the protec-tive colloid, and the internal stabilizer all have rela-tively strongly polarized to ionic groups. Therefore, the stabili7ation in this case qepends especially on the electrostatic repulsion of like polar charges on the

3 ~ ~

dispersion particle surfaces. Naturally, such stabilized dispersion systems therefore have the following two serious drawbacks: .
- They are very sensitive from the stability 5standpoint to added electrolyte.
- Finished products made from them such as paint films are relatively unstable to external aqueous effects.
The latter drawback is evidently caused by the fact that completely homogeneous films do not develop 10after the preparation of these aqueous polymer disper-sions, for example, and after evaporation of the disper-sion medium, but instead a heterogeneous honeycomb struc-ture caused by inadequate coalescence and determined by the dispersion particles is retained. The originally 15stabilizing polar to ionic groups of emulsifier, prot~c-tive colloid, and internal stabilizer are concentrated in the interfaces of these honeycombs, and polar substances of low molecular weight such as water can then di~fuse along these hydrophilic interfacial structures and thus 20make the coating useless. The particular emulsifiers used can also migrate along these honeycomb surfaces either to the surface of the coating (sweating) or to the substrate.
In the former case, the surface acquires an unwanted stickiness; in the latter case, a loss of adhesion is found.
Thus, there is a need for stable aqueous polymer dispersions that do not have these drawb~cks. The result-ing problem is solved by the invention by sterically stabili~ed emulsifier-free aqueous dispersions of polymers 30based on free radical-polymerized ethylenically unsat-urated monomers and a protective colloid, which are ; characterized by the facts that (1) the dispersions are essentially free of organic solvents, 35(2) the protective colloid consists essentially of an essentially saturated water-soluble or water-disper-sible poly~er grafted by a free radical method with 3 ~ ~

essentially hydrophobic chains based on ethylenically unsaturated monomers, and (3) the protective colloid contains essentially no ionic groups.
Stable dispersions are thus made available that have essentially no ionic groups at the interfaces between dispersion particles and aqueous medium, and whose stabi-lization depends on steric effects alone.
A process for the preparation of sterically stabilized aqueous dispersions of polymers based on Pthylenically unsaturated monomers is also described in U.S. Patent 4,453,261. According to this publication, the stPrically stabilizing auxiliary can be any grafted polymer, among other things. This paper also states that the preparation of the graft polymers preferably involves only a polymerization of ethylenically unsaturated mono-mers, with a long-chained hydrophilic monomer and a short-chained hydrophobic monomer leading to a hydrophobic main chain with hydrophilic side chains. The preparation of the protective colloids pursuant to the invention is a very different matter: this involves grafting in the narrower sense, in which reactive centers are formed on a saturated polymer chain by radical formation, and finally hydrophobic side chains are formed on a hydrophilic main chain.
Accordingly, the side chains of the preferred protective colloids pursuant to U.S. Patent 4,453,261 are aligned toward the aqueous phase, while those of the protective colloids pursuant to this invention are orient-ed into the interior of the dispersion particles. Thus, substantially different dispersion particle structures prevail, and organic, water-compatible solvents such as those according to U.S. Patent 4,453,261 do not necessari-ly have to be added to the disp~rsions pursuant to this invention in accordance with the stabilization principle to obtain stable dispersions or to process them furkher, for example into usable coating films. Quite evidently, the considerable amounts of solvent in the dispersicns according to U.S. Patent 4,453,261 are needed for this, to increase the mobility of the polymérs in the dispersion particles by swelling them, and thus to achieve adequate dispersion stability but also adequate coalescence of the particles during film formation. On the other hand, the hydrophobic side chains aligned toward th~ interior of the particles in the dispersion particles pursuant to the invention perform this function of the solvent, 50 that additional coalescence aids are not needed.
The sterically stabilized aqueous polymer disper--Oions pursuant to the invention therefore meet the maximum requirement for environmentally harmless coating systems as completely free of solvents as possible considerably more advantageously and with less compromise.
Hydrophilic polymers grafted with acrylate mono mers as protective colloids for the emulsion polymeriza-tion of ethylenically unsaturated monomers are also described by Japanese Disclosure 55-161,806. In this case, starch products modified by grafting function as protective colloids. These protective colloids are intended to permit the preparation by emulsion polymeriza-tion of useful aqueous polymer dispersion~ based not only on a few selected ethylenically unsaturated monomers, but a substantially broadened spectrum of monomers. In contrast to the hydrophobic monomers grafted on pursuant to this invention, however, the grafted monomers according to Jap. Kokai 55-161,806 are hydrophilic acrylates that conform to the general chemical formula given there.
Consequently, the side chains formed by grafting these hydrophilic monomers onto the starch chain are oriented in the dispersion toward the aqueous phase, just as in the case of the protective colloids according to U.S. Patent

4,453,261; this results in the same way in dispersions ; stabilized differently from those pursuant to this inven-tion (see discussions of this US Patent).
The object of Jap. Xokai 55-161,806 also differs from this invention in particular by the presence of emulsifiers that carry ionic charges in addition, while 2~3~

- 5 according to the invention, just such emulsifiers are avoided for the reasons mentioned above. It can therefore not be expected that such dispersions containing emulsi~i-ers are sufficiently stable to electrolyte, or that film~
resulting from them are stable to aqueous media. Nothing beyond the storage stability of these polyacrylate disper-sions is mentioned in Jap. Kokai 55-161,806 regarding their properties and use. The experimental examples specified in the Jap. Kokai also prove not to be feasible:
the grafted starch products A to C prepared by the in-s~-ructions given there did not lead to stable dispersions either by emulsion polymerization of ethylhexyl acrylate according to the instructions of this Jap. Kokai or by a method of emulsion polymeri~ation pursuant to this inven-tion.
It was extremely surprising that stable disper-sions can actually be obtained with protective colloids pursuant to the invention even without the presence of the emulsifier, especially the ionic emulsifier that is apparently indispensable in emulsion polymerizations as a prerequisite for resultant stable dispersions.
It should be pointed out explicitly at this point that the term "emulsifier" is intended to mean convention-al emulsion stabilizers with surface-active properties, but not such stabilizers with the effect of thickeners, which in the present case are separately called protective colloids (cf. Classification of Emulsifiers in "Rompps Chemie-Lexikon," 8th Edition, 1981, Page 1126).
The protectivs colloids that sterically stabilize the aqueous polymer dispersions pursu~nt to the invention are formed by grafting from protective colloid precursors, which can be water-soluble or water-aispersible natural or synthetic polymers. Examples of such protective colloid precursors preferred pursuant to the invention are poly-saccharides and polymers of ethylenically unsaturatedmonomers.
The naturally occurring, unmodified poly-saccharides can be used preferably. Preferred naturally ?,~3~

occurring polysaccharides or natural products containing them are those from the group of poly--~-glucoses such as starches, amyloses, amylopectins, dextrins, dextrans, and pullulans, from the group of ]polygalactoses such as gum arabic, agar agar, tragacanth, carrageenin, and pectins, and from the group of polymannoses such as carubin, tara gum, algin, alginic acid, and guar ~galactomannoge).
of the polymers of ethylenically unsaturated monomers, polyvinyl compounds prove to be especially suitable as protective colloid precursors, and of these, polyvinylpyrrolidone and polyvinyl alcohol in particular.
Such polymers that have a polymer weight of 10,000 to 5,000,000 and especially from 50,000 to 500,000 are preferred as protective colloid precursors.
Useful essentially hydrophobic ethylenically unsaturated monomers that can be grafted onto the protec-tive colloid precursors with the formation of hydrophobic side chains are those that can bP added onto the radical-activated centers of the saturated polymer.
Such monomers suitable for grafting in particular are those chosen from the group of alkyl esters of acrylic acid or methacxylic acid, benzyl methacrylate, dialkyl esters of itaconic acid, maleic acid, or fumaric acid, acrylonitrile or methacrylonitrile, styrene~ or styrene compounds substituted by alkyl groups with 1 to 4 carbon atoms or by a chlorine atom, and vinyl esters of aliphatic carboxylic acids with 2 to 1 carbon atoms. The alkyl groups of the esters and substituted styrene compounds mentioned can be straight-chained or branched. ~he graft monomers mentioned can be grafted either alone or mixed.
However, the free unsaturated acids, especially acrylic acid or methacrylic acid, acrylamide or methacrylamide, as well as hydroxyalkyl acrylates or methacrylates can also be used advantageously in small proportions mixed with one or more of 1:he aforementioned monomers.
of the mentioned alkyl esters of acrylic acid and methacrylic acid and the mentioned dialkyl esters of ethylenically unsaturated dicarboxylic acids, those with 1 ~.
: . .

3 ~ ~

to 18 carbon atoms and particularly with 1 to ~ carbon atoms in the alkyl group are preferred. Other preferred graft monomers are the monomers acrylonitrile, styrene, vinyltoluene, t-butylstyrene, vinyl acetate, or vinyl propionate.
In most cases, the monomers that make up the grafted side chains are also mon~mers that participate in the structure of the rest of t]he dispersion polymer~
PreEerred protective colloids are also those in which the average length of the grafted side chains amounts to 10 to 100 monomer units and those in which the average number of grafted side chains is 50 to 1,000 per main chain of protective colloid.
The polymer weight of the grafted polymers is no longer measurable because it is too high for the polymers to be able to be dissolved.
No addition of conventional emulsifiers is neces-sary for the preparation of the desired stable polymer dispersions pursuant to the invention, and even a small proportion of protective colloid is usually sufficient.
Useful stabilities are thus achieved in many cases even with protective colloids that represent a fraction of protective colloid precursor of less than 1 wt.% based on the total weight of the ethylenically unsaturated monomer needed to construct the graft polymer and the emulsion polymer. The upper limit for this proportion of protec-tive colloid precursor can vary within wide limits, but the proportion chosen will not be too high if possible for economic reasons, or with a view to the desired resistance of the resulting paint film to aqueous media; however, it can definitely be 20 wt.%. A particularly preferred range for the fraction of protective colloid is between 1 and 10 wt.% based on the weight of nonvolatile fractions of the polymer dispersion. A fraction of protective colloid precursor of 0.2 to 20 wt. % is preferred, and from 1 to 10 wt.% is especially preferred, based in each case on the total weight of monomers in the side chains of the graft polymer and in the emulsion polymer.

2~30~

Practically all monomers whose use has already been described or is feasible in homopolymerization or copolymerization by emulsion polymerization in aqueous medium are suitable as ethylenically unsaturated monomers that constitute the ~asis for the polymers of the aqueous dispersions pursuant to the invention. Reference may be made to the appropriate literature in this regard, for example HOELSCHER, "Dispersions of Synthetic High Poly-mers", Part I, Springer-Verlag 1969, or H. WARSON, "The Application of Synthetic Resin Emulsions", Benn Limited, ~ondon 1972. Many of these monomers can be polymerized only to homopolymers or only to copolymers in such emul-sion polymerization. The nature and proportion o~ the particular comonomers in particular af~ect the feasibility of copolymerization by emulsion polymerization and the stability of the resulting dispersions. Limitations in this regard, however, can be found from the state of the art. The monomers chosen also depend on the resulting polymer glass transition temperatures with a view to the intended field of use, on which information is available without difficulty to one skilled in the art. Since the preparation of coatings is under discussion especially as a possible field of use for dispersions pursuant to the invention, and film formation plays a central role in the field of coating preparation, monomers or monomer combina-tions that lead to polymers with glass transition tempera-turss that adequately satisfy the requirement~ of film-forming temperatures in the resulting paint film will primarily be selected.
The following ethylenically unsaturated monomers capable of radical polymerization are suitable examples of constituents of the dispersion polymers pursuant to the invention: alkyl esters of acrylic acid such as methyl acrylate, ethyl acrylate, butyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, decyl acrylate and dodecyl acry-late, benzyl acrylate, alkyl esters of meth-acrylic acid such as methyl methacrylate, ethyl methacrylate and butyl methacrylate, dialkyl esters of itaconic acid, 2~5~Q~
g methylene-malonic acid, maleic acid and fumaric acid, for example diethyl maleate and diethyl fumarate, acryloni-trile, methacrylonitrile, ~c:rylamide, methacrylamide, styrene, substituted styrene compounds such as vinyltoluene, chlorostyrene, and t-butylstyrene, vinyl esters of saturated straight-chained or branched carboxyl-ic acids such as vinyl acetate, vinyl propionate, viny~
laurate, or vinyl versatate, vinyl ethers such as vinyl isobutyl ether, vinyl chloride, vinylidene chloride, chloroprene, isoprene, butadiene, ethylene, propylene, 2-butene and ~-olefins with 4 to 12 carbon atoms, stil-bene, alkyl esters of crotonic acid and cinnamic acid, and allyl ethers or mixtures of these monomers.
In the same way, these monomers, like the graft monomers, can be the free unsaturated acid components of the aforementioned esters, acrylamide or methacrylamide, and hydroxyalkyl acrylates or methacrylates, in relatively small proportions in each case mixed with one or more of the aforementioned monomers.
Preferred ethylenically unsaturated monomers are those from the group consisting of alkyl esters of acrylic acid or methacrylic acid, the dialkyl esters s,~ itaconic acid, maleic acid, or fumaric acid, acrylonitrile or methacrylonitrile, styrene, or styrene compounds substi-tuted by alkyl groups with 1 to 4 carbon atoms or by a chlorine atom, vinyl esters of aliphatic carboxyli~ acids with 2 to 12 carbon atoms, or mixtures of these. The alkyl groups of the esters and of the substituted styrene compounds of these preferred monomers can be either straight-chained or branched. Coatings with high quality standards, for example with regard to appearance, mechan-ical properties, and resistance to extremely varied external ef~ects are generally obtained especially with such polymers based on acrylic and methacrylic compounds alone or in combination with styrene compounds and/or vinyl esters, so that dispersion polymers basPd on these monomers in particular were examined closely in the context of this invention. Of these monomers, the alkyl 2~03~

esters of acrylic acid and methacrylic acid with 1 to 18 carbon atoms, and especially 1 to 8 carbon atoms, acrylo-nitrile, acrylamide, methacrylamide, styrene, me~hyl-styrene, t-butylstyrene, chlorostyrene, vinyl acetate, and vinyl propionate or their mixtures are especially pre-ferred.
~ he object of this inv,ention is also a process for the preparation of sterically stabilized emulsifier-free aqueous polymer dispersions that is characterized by the fact that one or more ethylenically unsaturated monomers capable of radical polymerization is/are emulsion polymer-ized in an aqueous medium essentially free of organic solvents in the presence of a protective colloid and a conventional free radical-forming initi.ator, with the protective colloid consisting essentially of (a) an essentially saturated water-soluble or water-dispersible polymer grafted by a free radical method with (b) essen-tially hydrophobic chains based on one or more ethylen-ically unsaturated monomers, and containing essentially no ionic groups.
An advantageous process for the preparation of sterically stabili.zed emulsifier-free aqueous polymer dispersions is characterized hy the fact that a protective colloid containing essentially no ionic groups is ~irst prepared by free radical grafting of ~a) essentially hydrophobic chains based on one or more ethylenically unsaturated monomers onto (b) an essentially saturated water-soluble or water-dispersible polymer in an aqueous medium essentially free of organic solvents in the pres-ence of a conventional graEting initiator, and then in thepresence essentially of this protective colloid, one or ~ more ethylenically unsaturated monomers capable of radical : polymerization islare emulsion polymerized in an aqueous medium essentially free of organic solvents in the pres-ence of a free radical-forming initiator.
The grafting reaction of ethylenically unsaturated monomers and polymers with activated, graftable hydrogen bonds, known for itself, is described, for example, in :: - ' 2 ~ J ~ 3 ~ ~

"Houben Weyl, Methods of Organic Chemistry", Volume E20 (1987).
In the same way, details of emulsion polymeriza-tion can be found in the pertinent literature, for example "Houben-Weyl, Methods o~ Organic Chemistry", ~olume E20, or HOELSCHER, "Dispersions of Synthetic High Polymers", Part I, Springer-Verlag 1969.
-It is preferred to use 0.5 to 20 wt.%, and espe-cially 1 to 10 wt.% of the ungrafted protective colloid 10 precursor in the process pursuant to the invention for the preparation of polymer dispersions, each based on the total weight of the ethylenically unsaturated monomer needed for the graft and emulsion polymerizations.
It is recommended that the protective colloid precursor first be prepared by stirring in water at room temperature for several hours, and then activated by adding a portion of the graft initiator at process temper-ature. The graft polymerization can then be carried out by metering in the ethylenically unsaturated monomers and - 20 the remaining quàntity of graft initiator.
The process of the invention can advantayeously be - - -carried out in such a way that the protective colloid is -prepared by grafting and the sterically stabilized polymer dispersion is prepared by emulsion polymerization of the 25ethylenically unsaturated monomers in direct succession in the same reaction batch without prior isolation of the graft polymer. A two-step process is then superfluous;
the graft polymerization and emulsion polymerization can be carried out in one reaction vessel.
30In another advantageous form of embodiment, the preparation of the polymer dispersions in a one step procedure can be accomplished hy carrying out the grafting of the protective colloid precursor by means of the graft initiator until the monomer conversion becomes stagnant, 35and then i~mediately changing over to preparation of tha dispersion by emulsion polymerization by adding an initia--tor for conventional polymerization. It is well known that the graft polymerization does not proceed to complete 2~3~3~'~

conversion of the monomers; with polysaccharides aa the grafting substrate, it frequently stagnates even a~ter conversion of only 25 to 30%, dep~nding on the monomer.
This unreacted monomer can be ]eft in -the reaction mixtur~
for carrying out the emulsion polymerization. However, it can also be removed ~rom the mixture before changing over to emulsion polymerization, for example by vacuum distil-lation. This is done especia:Lly when the graft monomers and the monomer constituents of the emulsion polymer ar~
lo not to be the same. To avoid the work oE separating the monomer, it is thus advantageous to prepare polymer dispersions in which the graft monomers can be a constitu-ent of the emulsion polymer at the same time.
The ethylenically unsaturated monomers in the process of the invention can be used alone or mixed. When using monomer mixtures, the different monomers can be metered or added in at the same time. However, the different monomers can also be introduced at different times, both for the graft reaction and for the emulsion polymerization, by which the properties of the resulting dispersions can be varied to some extent. For example, the particular polymerization can be initiated with a monomer Ml or a monomer mixture consisting primarily of Ml, and completed with a monomer M2 or a mixture consisting primarily of monomer M2, during which the monomer ratio can be varied continuously (so-called power feed)~
The graft initiator desirable in the particular case, its quantity and nature, and the method of its addition in many cases depend on the graft substrate.
Salts of polyvalent metals and~or peroxides are usually used. Examples of very suitable graft initiators are salts of tetravalent cerium.
Con~entional initiators for emulsion polymeriza-tion are radical-formers such as inorganic peroxides, for example hydrogen peroxide or persulfates, organic perox-ides, for example t-butyl, cumyl, or lauroyl peroxide, or azo compounds, for example azobisisobutyro~nitrile, and can be used in combination with chain regulators, for .

2~3 example mercapto compounds, and other conventional poly-merization aids.
Initiators and auxiliaries are used in conven~
tional amounts.
The process of the invention for the preparation of aqueous, sterically stabilized polymer dispersions is preferably carried out in the range of 40 to lDOC, and 55 to 90oC is especially preferred, both in the graft poly-merization step and in the emulsion polymerization. Above the upper temperature limits a poor grafting e~ficiency can be expected; the polymerization proceeds too rapidly and problems can arise in process control. Below the preferred temperature limits the polymerization proceeds too slowly and monomer conversion is no longer guaranteed.
When a relatively low polymerization temperature is compulsory for certain reasons, a redox initiator system can be used in a known way. The polymeriæation tempera-ture chosen also depends on the particular monomers to be polymerized; it should not be below the ~lass transition temperature of the resulting polymers.
It was also surprising that not only are stable dispersions obtained pursuant to the invention, but that these stable dispersions actually do not have the draw-backs of dispersions o~ the state of the art described initially, and furthermore, they are distinguished by other desirable practical properties.
The dispersions pursuant to the invention prove to be table to strong electrolytes, for example salts of polyvalent cations. Addition of iron(III) chloride/calcium chloride led to no precipitation at all.
It was also found that the dispersions are miscible with strongly alkaline waterglass without precipitation. Thus, processing dispersions pursuant to the invention together with auxiliaries to be added depending on the application, particularly polar auxiliaries, presents no difficulties.
Above all, the di~persions can also be piqmented.
The solids content, i.e., the proportion of nonvolatilP constituents, in the dispersions pursuant to - 14 - ~3~3~
the invention is advantageously in t~le range o~ ~o to 60 wt.% based on the total weight of the particular disp~r-sion. There are limits with regard to the flow beha~ior of the dispersions at higher proportions. However, a solids fraction up to 70% is definitely possible, particu-larly when the dispersions have an appropriately favorable dis tribution of particle diameters.
The viscosity of the dispersions pursuant to the invention is in a low range desirable for further process-ing. I-t depends partly on the pH range of the dispersion medium, but especially on the solids content of the dispersion, i.e., on the fraction of non-volatile constit-uents. The standard method for preparing dispersions in the context of the studies pursuant to the invention assumes a solids content of about 50 wt.% and leads to acidic dispersions, with viscosities in the desirable low range of 18 to 100 mPa-s usually being obtained, and frequently also above 100 mPa-s and up to 500 mPa s~
Dispersions pursuant to the invention can therefore be used with conventional application techniques.
The average diameters of the individual particles of dispersions prepared within the scope of the studies of the invention vary in the range of 250 to 2000 nm. These average particle diameters can readily be varied in the dispersion system of the invention by appropriate polymer-ization technique. Since the particlP size and particle size distribution are well known to have a determining effect on a number of practical properties such as flow behavior, ability to penetrate into porous substrates, coalescence behavior, and density, as well as smoothness or gloss of resulting film surfaces, it is desirable to adjust the average particle size and particle size distri-bution in one direction or another. For example, to obtain glossy, smooth film surfaces, dispersions with the smallest possible average particle diameters and favorable distribution of larger and smaller particles are used.
The ready variability of particle size and particle size distribution in sterically stabilized dispersions pursuant ~ 15 ~ 3~
to the invention, which therefore permit the prepara n of dispersions "tailor-made" to some extent depending on ~the practical specifications can be illustrated with J Figures 1 and 2. These relate to copolymer dispersions based on the monomer composition (parts by weight) 48 methyl methacrylate - 48 butyl acrylate - 1 mathacryl-amide - 1 methacrylic acid with guar gum as protective colloid precursor according to the standard formula, versus the proportion by weight o~ guar gum (Fig. 1) or guar/Ce(IV) sulfate (Fig. 2), and versus the fraction of the Ce(IV) sulfate in the starting batch (Fig. 2).
It is clear from these Figures that wlth a con-stant proportion of graft initiator (Fig. 1; 1 wt.%) having a very small proportion of protecti~e colloid precursor, the average particle diameter at first is relatively large and its distribution is very broad, ~ut with an increasing proportion, very small average diame-ters are then obtained with extremely narrow distribution, and finally with a further increased proportion (> 2 wt.%) a trend is seen toward bimodal distribution. The bimodality is particularly striking with a very narrow distribution at both particle sizes when the proportion of Ce(IV) is raised at the same time as the proportion of protective colloid precursor (Figures 2b). As ~hown by Figs. 2a and 2b, curves on the right, the distribution of the amount of graft initiator between starting batch and added portion also has a crucial effect on the size distribution and modality. Therefore, according to the distribution curves of Figures 1 and 2, it is very sur-prising that under certain conditions very narrow distri-butions of particle diameters sometimes result, so that they can even be described as practically monodisperse systems, since polymer dispersions usually have more or less wide~;pread particle diameters and practically mono-disper~e dispersions can be prepared in only few cases by the state of the art; and in these cases only with very special simplified systems, particularly o~
homopolymers, usually styrene.

Films with smooth sur~aces can be prepared easily from the sterically stabilized dispersions pursuant to the invention. It i5 very beneficial and surprising that ~ilm formation and ~ilm drying (hardening throughout) occur relatively rapidly ~ven at roo~ temperature in many cases.
Usually, extensive drying throughout occurs after e~en a few hours.
Paint films obtained from dispersions pursuant to the invention prove to he essentially stable to the action of water for 24 hours (water test) in contrast to films from comparable dispersions not sterically stabilized.
Dispersions pursuant to the invention are therefore suitable as the base for paints or coatings, especially those for exterior use.
Their processibility even at room temperature makes them interesting for the do-it-yourself sector and artist's paints.
In cases in which dispersions in the context of the invention at room temperature lead to films that are insufficiently cured and therefore inadequately rasistant, improvements can be achieved even with slightly elevated drying temperature, for example even at 50C. Dispersions pursuant to the invention can also be processed as a thermosetting system, for example combined with blocked polyisocyanates or melamine resins. Appropriate tests with melamine resins of the CymelR type (Cymel 325 and Cymel 327) with curing temperatures above 80OC, especially between 90 and 130C, and a cure time of only 30 minutes, led to pendulum hardnesses increased by 50 to ~00%, and increased strengths. Yellowing can sometimes be found above 100C in films ~rom dispersions free of melamine resin based on grafted cellulose; corresponding disper-sions containing melamine resin do not show this yellow-ing. The dispersions applied with the melamine resins also led to coatings with excellent adhesion to plastic substrates, for example polybutylene terephthalate.
It is obvious that the requirements for qualita-tively very high-grade paints cannot be met at the same 2 ~ V~3 time that the maximum requirements with reyard to environ-mental harmlessness and occupational health are complied with pursuant to the invention, and therefore, for the mentioned benefits achieved, a certain compromise has to be made in the coating quality, for example in the visual impression. On the other hand, by appropriate steps familiar to one skilled in the art, the paint quality can be optimized in the particular direction desired when an acceptable compromise with environmental harmlessness and occupational health below the maximum requirement justi-fies this. For example, certain paint properties can be improved by small additions of volatile organic solvent~
as film-forming aids within the scope of the invention.
Experiment~l Part Standard Formula for the PreParation of Aqueous Polymer Dispersions Pursuant to the Invention.
If not otherwise indicated, the procedure is as follows:
10 g of protective colloid precursor is dispersed or dissolved in 400 g of distilled water under nitrogen in a 1-liter flask with stirrer, reflux condenser, nitrogen supply line, and metering device. The mixture is stirred at room temperature for several hours if dispersions are present, for example up to 10 hours in the case of poly-saccharides as a precursor. It is then heated to 70C, 1g of Ce(IV) sulfate dissolved in 70 g of water is then added, and the mixture is stirred for 1 hour at 70C. 490 g of ethylenically unsaturated monomers is then fed in from a metering device, and at the same time 4 g of Ce~IV) sulfate dissolved in 30 g of water is fed in from another metering device over a period of 1 hour.
After an additional reaction time o~ 1 hour at 70C, 5 g of ammonium persulfate dissolved in 20 g of water is finally metered in over a period of 10 minutes.
The content:s of the flask are kept at 70C for 1 hour longer and then cooled.

2~3~

The solids content of the aqueous sterically stabilized polymer dispersion thus obtained with 100%
conversion o-E monomers has to be 49.3 wt.%.
If not otherwise indicated, guar flour (food quality) from the Roth Co., Xarlsruhe is used as the protective colloid precursor, and a mixture of the follow-ing composition is used as the ethylenically unsaturated monomers: 240 g methyl methacrylatel240 g butyl acry-late/5 g methacrylamide/5 g methacrylic acid.
_stinq the Aaueous Polymer I)is~Esions Pursuant to the Tnvention.
Solids content/conversion:
To determine the monomer conversion, the fraction of nonvolatile dispersion constituents is determined by drying the dispersion at 150C to constant weight, and this is compared with the figures calculated for 100%
conversion.
Viscosity:
The dynamic viscosity of the polymer dispersions was determined at 20C in a rotary viscosimeter ("Viskotester VTI' 180 from the Haake Co.).
Storage stability:
For this purpose, the dispersions were stored at room temperature or in a so-called fast test at 50C, and the storage time was recorded after which the particular dispersion had noticeably coagulated, and the coagulate could no longer be stirred up. In the fast test, the dispersions that had not settled out or could still be : stirred up after 30 days were graded as outstandingly stable.
Electrolyte stability:
25 ml of the dispersion to be tested was diluted to 100 ml and titrated with a saturated solution of ~erric chloride and calcium chloride (1:1 ratio by weight~. A
polymer dispersion was judged to be stable to electrolyte when no coagulation of the dispersion had yet occurred when 25 ml of salt solution was consumed.
Particle size:

: .

2Q~ 3~

The average diameters of the dispersion particles were determinPd by turbidity measurement.
The distribution curves for the particle diameters were determined by transmission electron microscopy (Phillips TEM instrument) with automatic image analysis system (Quantimet instrument), with the particle specimens being solidified with vsmium tetroxide and sputtered with carbon.
Film formation/curing:
To evaluate the film-forming properties and the curing of the resultant coating films of dispersions pursuant to the invention, they were coated on glass plates and formed on them into wet films 150 ~m thick with a deep-drawing coil. The curing process with drying at room temperature and also at 50C was evaluated by measur-ing the film hardness after 4 hours, 1 day, 15 days, and 30 days.
The film formation was evaluated qualitatively by visual impression (smoothness and homogeneity of the film surface, transparency of the film).
The films from mixtures of dispersions pursuant to the invention with melamine resin were baked in the standard tests for 30 minutes at 100 and 120C. These mixtures in the standard tests consisted o~ 100 g disper-sion and 25 g Cymel 325 or Cymel 327 (Cyanamid Co.) Film hardness:
The hardness of the films on the glass plates was determined as the Koenig pendulum haraness ~DIN 53157).
Water test:
To determine the water resistance of the films, a swab thoroughly saturated with tap water was placed on the film on the glass plate and covered with a watch glass.
After standing for 24 hours at room temperature, the appearance of the film was evaluated tfilms not resistant to water turn cloudy white). Films cured for 1 day at room temperature and at 50C, and also films cured for an additional :29 days at room temperature were evaluated.

2~3Q~

Experimental Exam~les 1 to 6 and Comparison Example Stable aqueous polymer dispersions were prepared with the following commercial colloid precursors ,by the standard formula given on Page 22:
1. Guar (guar flour from the Roth Co., Karlsruhe) 2. Water-soluble starch 3. Gum arabic (commercial) 4. Olibanum (commercial) 5. Dextran (commercial)

6. Polyvinylpyrrolidone (Type PVP-K15 from the GAF Co.) The ethylenically unsaturated monomers used were 490 g of a mixture of methyl methacrylate (49 wt.%), butyl acrylate (49 wt.%), methacrylamide (1 wt.%), and meth~
acrylic acid (1 wt.%).
The following procedure was used ~o prepare a comparison dispersion not sterically stabilized:
4.0 g of Natrosol 250 LS (hydroxyethylcellulose from the Hercules Co. as protective colloid), 12.0 g of Triton X
165 (nonionic emulsifier from the Rohm & Haas Co.~, and 9.0 g of sodium lauryl sulfate were dissolved in the 1-liter flask equipped as described in the standard formula, and heated to 70~C. The ~ollowing three mixtures were also prepared:
1) Monomer mixture as in experimental examples 1 to 6; plus 4 g of t-dodecyl mercaptan as chain reyulator 2) 4.0 g ammonium persulfate in 60 ml of water 3) 4.0 g sodium bisulfite in 60 ml of water 10% of each of these three mixtures was added to the contsnts of the flask heated to 70-C, and allowed to react for 20 minutes (seed). The remaining 90% of each of the three mixtures was then metered into the flasX at 70C
over a period of 2 hours at the same time from separate metering dlevices. The contents of the flask wer~ then kept at 70"C for 2 hours longer and then cooled.
Important properties of the polymer dispersion~
thus obt~i,ned and of paint films resulting from them are compiled in Table 1.

3 @ ~

Hiyh conversion of the ethylenically unsaturated monomers (2 99%~ was achieved in all cases. The disper-sions show a pH in the acidic range, and in spite o~ their high solids co~tent they show 21 low viscosity suitable for processing into paints. The stability of the dispersions on room temperature storage and the average diameters oE
the disperslon particles turn out to be relatively differ-ent ~epending on the protective colloid pre-cursor used.
Electron microscope photographs of the sterically stabilized dispersions show particles of relatively uniform large size which agglomerate only slightly. The particle size distribution can be determined very easily from such photographs. On the other hand, the particles of conventiona dispersions not sterically stabilized tend to agglomerate severely while taking electron microscope photographs, as they did in the case of the present comparison experiment, so that it is practically impossi-ble to determine the averagP particle diameters and their distribution in this way.
In contrast to the dispersion from ths comparison experiment, which was not sterically stabilized, the sterically stabilized dispersions of experiments 1 to 6 prove to be stable to electrolyte additions.
The figures shown in Table la for the pendulum hardness of paint films from the dispersions after 4 hours and 1 day of drying at room temperature and 50C, and an additional 29 days of drying at room temperature, show that extensive hardening throughout has occurred even after a few hours, and that in most cases the hardnesses reached after 1 day rise no further, or only insignifi-cantly. In most cases, the hardnesses reached at 50C are higher than those reached at room temperature. The more desirable film formation with 50~C drying can also be seen in the appearance of the resulting paint films: films dried at 50C are almost clear, while the films dried at room temperature generally stay whike. In contrast to paint films from the dispersion not sterically stabilized (comparison experiment), those from sterically stabilized 3 ~ j - 2~ -dispersions are predominantly resistant to the action o~
water for 24 hours (experiments 1, 2, 5, and 6).
Ex~erimental Examples 7 to 11 Stable polymer disperslions with 490 g of various monomer compositions (as speciEied in Table 2) and 10 g of guar as protective colloid precursor (2% based on the weight of monomers ~ precursor) were prepared by the - standard formula. The conversion and properties o~ the dispersions are shown in Table 2. In the case of experi-ment 8a with vinyl acetate as comonomer, the acidic dispersion was neutralized after pol~merization (pH 7.5) to prevent the acid hydrolysis of the acetyl group. The - dispersions of experiments 8a and 8b proved to be very viscous. Repetitions o~ them but with the solids content being adjusted to about 40 wt.% instead of about 49 wt.%
- led to lower-viscosity dispersions (with almost 100%
monomer conversion):
8a 480 mPa-s; 8b 570 mPa-s.
- All of the dispersions are stable to the addition of electrolyte. Paint films dried either at room tempera-ture or at 50C proved to be resistant to water in the 24-- hour test.
Experimental Examples 12 to 18 - Polymer dispersions with the monomer composition - 25 consisting of methyl methacrylate (49 wt.~), butyl acry-late (49 wt.%~, methacrylamide (1 wt.%), and methacrylic acid (1 wt.%) were prepared by the standard formula with - different proportions of guar as protective colloid precursor, as shown in Table 3. With a proportion of 10 - 30 wt.% or more of guar, the dispersions already become very - viscous. To obtain dispersions with usable viscosity but nevertheless with this high proportion of guar, thP solids contents of the dispersions had to be set lower, i.e., a correspondingly lower monomer-water ratio had to b~ used from the start. In dispersion 17 (10% guar) the solids content is thus 42 wt.%, and in dispersion 18 (15% guar) -it is 26 w~.%.

2 ~ 5 The dispersions proved to be stable also in the test for electrolyte ~tability. The variation of the particle size distribution o~ the dispersions with in-creasing guar fraction shown in Figure 2 i5 conspicuous:
dispersions with less than 1 wt.% guar show a broad particl~ size distribution. V,ery narrow distributions are then recorded with 1 wt.% and 1.5 wt.%, which become increasingly broader with higher proportions, and finally become bimodal with 4 wt.% guar or more. Dispersions with 10 to 15 wt.% guar, on the other hand, are monomodal again and show relatively small and very uniform particle diameters, with the uniformity becoming so conspicuous that automatic image analysis was dispensed with.
Experimental Examples 19 to 27 The effect of the Ce(IV) sulfate ~raction and of the time of its addition in the polymerization process on the properties of the polymer dispersions was examined by these experiments. It proved to be desirable to increase the proportion of guar also with increasing proportion of Ce(IV) sulfate. The experimental conditions and disper-sion properties are shown in Table 4. If not otherwise indicated in th~ table, the procedure followed the stan-dard formula. "Starting" Ce(IV) sulfate means the propor-tion that is added before metering in the monomers (20 wt.% according to the standard formula), and "metered"
Ce(IV) sulfate means the fraction that is metered in at the same time as the monomers (but from a different metering device)(80 wt.~ according to the standard form~-la).
A desirable property picture can be found from the data in the table. Only in the case of a very small proportion of Ce(IV) sulfate (which is used only at the start) according to experiments 19 and 20, are relatively high-viscosity dispersions obtained, with very high monomer conversion, to be sure, which remain stable only for 13 days of storage at 50C.

2 ~ 5 Dispersion stability to added electrolyte and film stability to the action o~ water for 24 hours are good in all cases.
The effect of the graft initiator on -the size distribution of dispersion particles is conspicuous, as shown by Fiyure 2 for experiments 21 to 24 (increasing bimodality with increasing Ce(IV) sulfate/guar proportion, and increasing proportion of Ce(IV) sulfate in the start-ing batch). 1 Experimental Exam~les 28 and 29 These experiments relate to the preparation of polymer dispersions by the standard formula, but at temperatures 10C below (experiment 28~ and 10C above (experiment 29) the standard temperature of 70C. Disper-sions are obtained with a property picturP like that ofdispersions prepared at 70C. On the other hand, polymer-ization at 60C leads to a conversion of only 88% of the monomers; n~vertheless, the conversion can he increased to 98.2% if 1.5 wt.% ammonium persulfate is used in departure from the standard formula (instead of 1 wt.%) and the polymerization is carried out for 3 hours (instead of 2 hours).
Experimental Examples 30 to 33 These experiments relate to the preparation of stable polymer dispersions with variations of the monomer infeed by metering in one of the two main monomers, butyl acrylate and methyl methacrylate, at the beginning of the metering in excess, and the other in excess at the end of addition~ or the reverse. The procedure here was the same as in the standard formula, but at the beginning of the monomer feed, the conventional metering device contains only one of these main monomers, while the other monomer is added slowly at the same time to this metering device over the same metering time of 1 hour. This procedure is an attempt to form a high-butyl acrylate graft polymer and a high-methyl methacrylate main polymer, or conversely a high-methyl methacrylate graft polymer and a high-butyl acrylate main polymer.

2~3~
- ~5 -These experiments are summarized in Table 5. No significant changes from the comparable standard experi-ments (experiments 21 and 23) were found in the basic properties evaluated for these~ polymer dispersions. The dispersions are stable to electrolyte addition, and paint films prepared from them are resistant to the action of water (water test~.
Experimental Examples 34 to 36 In these experiments, the polymer disper6ions were prepared by first forming a graft polymer as usual, but then with polymerization to form the main polymer occur-ring only with the other monomers being metered in.
The procedure in the case of experiment 34 was to meter in only two-thirds of the total monomer mixture for 1 hour when preparing the graft polymer by the standard formula (2 wt.% guar, 2 wt.% Ce(IV) sulfate~, and then after 1 hour of continued reaction, to change over to the main polymerization with ammonium persulfate by metering in th~ ammonium persulfate solution and the remaining third of the monomer mixture separately and at the same time, over a period of 1 hour.
In the case of experiments 35 and 36 the procedure was the same as in the standard formula (2 wt.% guar, 2 wt.% Ce(IV) sul~ate) until the end of the continued reaction after the graft polymerization; then, however, the monomers that did not react in the graft polymeriza-tion were removed by distillation. After heating the aqueous dispersion of the graft polymer with a solids content of 16 wt.% to 70C, another monomer mixture and an aqueous ammonium persulfate solution were fed into it separately and simultaneously over a period of 1 hour.
The amount of monomer mixture was chosen so that a disper-sion was present at the end of the polymerization with the usual solids content of 49 wt.%. The proportion of ammonium pe.rsulfate was 1 wt.% as usual, based on the weight of the added monomers. In the case o~ experiment 35, the monomer mixture contained 55 wt.~ methyl methacry-late, 43 wt.% butyl acrylate, 1 wt.% methacrylamide, and l 2 ~

wt.% methacrylic acid, and in the case of experiment 36, it contained 27.5 wt.% methyl methacrylate, 43 wt.% butyl acrylate, 27.5 wt.% styrene, 1 wt.% methacrylamide, and 1 wt.% methacrylic acid.
The stable polymer dispersions 34 to 36 thus obtained showed no significant changes with regard to the evaluated basic properties from other comparable polymer dispersions pursuant to the invention. Their electrolyte stability and the resistance of corresponding paint films to the action of water are good. A particularly narrow distribution of dispersion particle diameters was fvund in the dispersion from experiment 34, so that in this case we can speak practically of a monodisperse system.
ExPerimental Example 37 This example relates to the curing of polymer dispersions pursuant to the invention in the presence of melamine resins. The dispersions from experiments 15, 19, 24, 30, and 33 and the melamine resins Cymel 3~5 and Cymel 327 (Cyanamid Co.) were used for this. In each case, 100 g of dispersion and 25 g of the melamine resin were mixed together. The paint films prepared from these were cured for 30 minutes at 100C. The resulting film hardnesses are shown in Table 6 and are compared with the hardnesses of films free of melamine resin dried at room temperature.
Table 6 for comparison also contains the hardnesses o*
films cured at 100C without melamine resin.

Claims (21)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. Sterically stabilized emulsifier-free aqueous dispersions of polymers based on ethylenically unsaturated monomers polymerized by a free radical method and a protective colloid, characterized by the fact that (1) the dispersions are essentially free of organic solvents, (2) the protective colloid consists essen-tially of an essentially saturated water-soluble or water-dispersible polymer grafted with essentially hydrophobic chains based on ethylenically unsaturated monomers by a free radical method, and (3) the protective colloid contains essen-tially no ionic groups.

2. Dispersions pursuant to Claim 1, character-ized by the fact that the water-soluble or water-dis-persible natural or synthetic polymers are those from the group of modified or unmodified polysaccharides or the polymers from ethylenically unsaturated monomers.

3. Dispersions pursuant to Claim 2, character-ized by the fact that the polysaccharide is a naturally occurring unmodified polysaccharide.

4. Dispersions pursuant to Claims 2 or 3, characterized by the fact that the polysaccharide is a poly-.alpha.-glucose, a polygalactose, or a polymannose.

5. Dispersions pursuant to Claim 2, character-ized by the fact that the polymer of ethylenically unsatu-rated monomers is a polyvinyl compound and preferably polyvinylpyrrolidone and polyvinyl alcohol.

6. Dispersions pursuant to one or more of the Claims 1 to 5, characterized by the fact that the water-soluble or water-dispersible polymers constituting the protective colloid precursor have a polymer weight of 10,000 to 5,000,000 and especially from 50,000 to 500,000.

7. Dispersions pursuant to one or more of the Claims 1 to 6, characterized by the fact that the essen-tially hydrophobic ethylenically unsaturated monomers grafted onto the polymeric protective colloid precursor are chosen from the group consisting of alkyl esters of acrylic and/or methacrylic acid, benzyl methacrylate, the dialkyl esters of itaconic acid, maleic acid and/or fumaric acid, acrylonitrile and/or methacrylonitrile, styrene and/or styrene compounds substituted by alkyl groups with 1 to 4 carbon atoms or by a chlorine atom, vinyl esters of aliphatic carboxylic acids with 2 to 12 carbon atoms, or mixtures of these monomers.

8. Dispersions pursuant to Claim 7, character-ized by the fact that the alcoholic component in the alkyl esters and dialkyl esters mentioned has 1 to 18 carbon atoms and preferably 1-8 carbon atoms.

9. Dispersions pursuant to Claim 7, charac-terized by the fact that the substituted styrene compounds are vinyltoluene, t-butylstyrene, and the vinyl esters are vinyl acetate or vinyl propionate.

10. Dispersions pursuant to one or more of the Claims 1 to 9, characterized by the fact that the average length of the grafted side chains in the protective colloid corresponds to 10 to 100 monomer units.

11. Dispersions pursuant to one or more of the Claims 1 to 10 characterized by the fact that the average number of grafted side chains is in the range of 50 to 1,000 per protective colloid main chain.

12. Dispersions pursuant to one or more of the Claims 1 to 11, characterized by the fact that the pro-portion of protective colloid precursor is 0.5 to 20 wt.%
and preferably 1 to 10 wt.%, based in each case on the total weight of monomers in the side chains of the graft polymers and in the emulsion polymer.

13. Dispersions pursuant to one or more of the Claims 1 to 12, characterized by the fact that the ethyl-enically unsaturated monomers polymerized by a free radical method that constitute the basis of the polymers in the aqueous dispersions are monomers from the group consisting of alkyl esters of acrylic and/or methacrylic acid, dialkyl esters of itaconic acid, maleic acid and/or fumaric acid, acrylonitrile and/or methacrylonitrile, styrene and/or styrene compounds substituted by alkyl groups with 1 to 4 carbon atoms or by a chlorine atom, vinyl esters of aliphatic carboxylic acids with 2 to 12 carbon atoms, or mixtures of these monomers.

14. Dispersions pursuant to Claim 13, character-ized by the fact that the ethylenically unsaturated mono-mers are alkyl esters and dialkyl esters with 1 to 8 carbon atoms in the alcoholic component, vinyltoluene, t-butylstyrene, chlorostyrene, vinyl acetate, vinyl propionate, and/or vinyl laurate.

15. Process for preparing sterically stabilized emulsifier-free aqueous polymer dispersions, characterized by the fact that one or more ethylenically unsaturated monomers capable of free radical polymerization are emulsion polymerized in an aqueous medium essentially free of organic solvents in the presence of a protective colloid and a conventional free radical-forming initiator, with the protective colloid consisting essentially of (b) an essentially saturated water-soluble or water-dispers-ible polymer grafted with (a) essentially hydrophobic chains based on one or more ethylenically unsaturated monomers by a free radical method, and containing essen-tially no ionic groups.

16. Process for preparing sterically stabilized emulsifier-free aqueous polymer dispersions, characterized by the fact that a protective colloid containing essen-tially no ionic groups is first prepared by free radical grafting (a) essentially hydrophobic chains based on one or more ethylenically unsaturated monomers onto (b) essentially saturated water-soluble or water-dispersible polymers in an aqueous medium essentially free of organic solvents in the presence of a conventional graft initia-tor, and then one or more ethylenically unsaturated monomers capable of free radical polymerization are emul sion polymerized essentially in the presence of this protective colloid in an aqueous medium essentially free of organic solvents in the presence of a free radical-forming initiator.

17. Process for preparing aqueous polymer disper-sions pursuant to Claim 15 or 16, characterized by the fact that 0.5 to 20 wt.% and preferably 1 to 10 wt.% of the ungrafted protective colloid precursor, based in each case on the total weight of monomers in the side chains of the graft polymers and in the emulsion polymer, is used.

18. Process for preparing aqueous polymer disper-sions pursuant to Claim 15 or 16, characterized by the fact that the preparation of the protective colloid by grafting and the preparation of the sterically stabilized polymer dispersions by emulsion polymerization of ethylen-ically unsaturated monomers are carried out in immediate succession in the same reaction batch without prior isolation of the graft polymer.

19. Process pursuant to Claim 18, characterized by the fact that the grafting of the protective colloid precursor is carried out by means of the graft initiator until monomer conversion becomes stagnant, and a change is then made directly to the preparation of the dispersion by emulsion polymerization by adding an initiator for the conventional polymerization.

20. Process for preparing aqueous polymer disper-sions pursuant to one or more of the Claims 15 to 19, characterized by the fact that both the graft polymeriza-tion for the preparation of the protective colloid and the emulsion polymerization for the preparation of the polymer dispersions are carried out at temperatures in the range of 40 to 100°C and preferably in the range of 55 to 90°C.

21. Use of aqueous polymer dispersions pursuant to one or more of the Claims 1 to 20 to prepare coatings.