Emulsion polymers and paint formulated therewith

ICI viscosity of a paint is improved by incorporating into the paint an acrylic polymer emulsion or latex made with the use of a water soluble chain transfer agent, preferably one that comprises both sulfur functionality and hydroxyl functionality. A preferred chain transfer agent is monothioglycerol.

BACKGROUND 
The present invention relates to latex paints, to polymeric emulsions or 
latexes useful as binders for latex paints, and to processes for making 
such emulsions. 
Latex paints are mixtures of many ingredients. Typical ingredients include 
coalescing aids, thickening aids, dispersing aids, defoamers, biocides, 
pigments, and binders. The large number of ingredients makes it difficult 
to formulate latex paints. In addition, optional ingredients are also 
employed in latex paints to enhance various paint properties. For example, 
rheology modifiers are often employed to enhance the flow and leveling and 
film build characteristics of a paint. 
Flow and leveling is an indication of a paint's ability to form a smooth 
surface devoid of brush marks, roller marks, or other film thickness 
irregularities upon application of the paint to a surface. Film build 
relates to the thickness of a paint film that can be applied in one coat. 
It is an indication of a paint's hiding power, that is, an indication of 
how well one coat of the paint conceals a surface. 
The viscosity of a pigmented paint usually decreases with increased shear 
rate, an effect called shear thinning. The relationship is non-linear and 
is difficult to predict with precision because it is affected by the many 
different ingredients and processing techniques employed in formulating 
paints. During application of a paint, for example by brushing, rolling, 
or spraying, flow is vigorous and shear rates are correspondingly high, on 
the order of 1000 to 10000 sec.sup.-1 or more. As a result of shear 
thinning, the viscosity of the paint is low, on the order of 0.1 to 10 
poise. Once the paint has been applied, continued flow within the film 
from leveling, sag, or slump is slow and shear rates are correspondingly 
low, on the order of 0.001 to 1 sec.sup.1. At such low shear rates, the 
viscosity of the paint can be as high as 100 to 1000 poises or more. 
The paint properties of film build and flow and leveling are not mutually 
opposed, but it is difficult to achieve both to a desirable degree in a 
single paint formulation. For acceptable film build, shear thinning must 
be limited, so that the paint has sufficiently high viscosity, under the 
high shear rate conditions that prevail in the wet paint film at the point 
of application, to form a desirably thick film on the substrate. For 
example, a paint must have a high enough viscosity under brushing 
conditions that a paint film of the desired thickness will adhere to the 
surface as the brush moves past. However, for acceptable flow and 
leveling, it is necessary to avoid excessively high viscosity in the wet 
paint film under the low shear rate conditions that prevail immediately 
after the paint is applied. Otherwise, brush marks and other 
irregularities will remain to mar the appearance of the dried paint film. 
After a paint has been applied to a surface, the wet film must have a low 
enough viscosity that the forces attributable to surface tension can cause 
the paint to flow from thicker to thinner regions of the film to achieve 
the desired leveling, or uniform film thickness. At the same time, the 
viscosity must not be so low that the film will sag, slump, or drain 
excessively on vertical or slanted surfaces under the force of gravity. 
Flow and leveling is a property of the paint and is determined by complex 
interactions among the various ingredients. The low shear viscosity of the 
polymer emulsion used in the paint is a contributing factor in flow and 
leveling and also affects other characteristics of the paint, such as its 
behavior during formulation, flow through pipes, brush loading, and the 
like. In general, it is desirable to keep the viscosity of the emulsion 
itself fairly low to allow for flexibility in the formulation of paints 
having the desired flow characteristics. For example, if the emulsion 
viscosity is too high, it may be harder to formulate a paint having 
acceptable flow and leveling. 
Emulsion polymerization is a widely used process for making polymer 
emulsions or latexes. The polymer emulsion is made, for example, by 
charging the monomeric ingredients, water, and a surfactant into a 
reaction vessel, emulsifying the monomers, purging the reaction vessel 
with an inert gas to remove oxygen, and heating the reaction vessel to the 
reaction temperature. An initiator is then added to the reaction vessel, 
and the reaction is continued for about 2 to about 4 hours. After the 
reaction is completed, the reaction vessel is cooled. This synthesis 
yields an aqueous polymeric composition comprising polymer particles 
suspended or dispersed in water. 
Chain transfer agents can be added to the reaction vessel to lower the 
molecular weight of the resulting polymer. For latexes that are used as 
conventional surface coatings, it is usually desirable to maximize 
molecular weight, and so chain transfer agents are not used. However, when 
it is desirable to produce a polymer emulsion having lower viscosity, or 
where shorter chain length is desired for other reasons, minor proportions 
of chain transfer agents can be used. 
SUMMARY OF THE INVENTION 
The present invention provides an acrylic latex paint which is capable of 
exhibiting enhanced film build without the use of a rheology modifier. The 
latex paint comprises an acrylic polymer latex specially made in 
accordance with this invention to improve the film build of the paint. 
The latex, comprising water and a substantially water-insoluble acrylic 
polymer, is formed by reacting at least one monomer, usually a plurality 
of monomers. At least a portion of the polymerization is conducted in the 
presence of a chain transfer agent. Surprisingly, the use of a chain 
transfer agent in accordance with this invention produces an acrylic 
polymer latex that improves the film build of a paint comprising the 
latex, regardless of the effect that the chain transfer agent has on the 
viscosity of the latex itself. 
Preferably, the chain transfer agent and a portion of the monomer are delay 
added to the reaction vessel. The term "delay added" is a term of art that 
means ingredients are added after at least a portion of the polymerization 
reaction has occurred. The chain transfer agent is desirably at least 
slightly soluble in water. The chain transfer agent is preferably an alkyl 
mercaptan. More preferably, the chain transfer is an alkyl mercaptan 
having hydroxyl functionality, such as monothioglycerol. 
The invention also encompasses a composition formed by drying the latex 
paint as well as an article having at least a portion of its surface 
coated with the composition. 
The present invention is thus directed to (a) a polymer emulsion or latex 
comprising water and a substantially water insoluble acrylic polymer, (b) 
a process for making the latex, (c) a paint containing the latex, (d) a 
composition formed by drying the paint, and (e) an article having a 
portion of its surface coated with the dried paint. 
DETAILED DESCRIPTION OF THE INVENTION 
In accordance with this invention, an acrylic polymer emulsion is prepared 
in an emulsion polymerization process. A monomer feed comprising at least 
one acrylate monomer, usually a mixture of acrylate monomers, is 
emulsified in water, usually with a surfactant, and is polymerized in a 
reaction zone in the presence of a polymerization catalyst and a chain 
transfer agent. The monomer feed comprises more than about 50 phm, 
preferably at least about 75 phm, even more preferably at least about 90 
phm, of an acrylate monomer or mixture of acrylate monomers. The 
abbreviation "phm" means parts per hundred parts, by weight, of the total 
polymerizable monomer used in preparation of the polymer emulsion. 
The acrylate monomers can be represented by the formula I 
##STR1## 
wherein R.sub.1 is selected from the group consisting of hydrogen, alkyl 
and halo-substituted alkyl groups having 1 to about 6 carbon atoms, and 
halogen, notably chlorine, with hydrogen and unsubstituted alkyl groups 
preferred; and R.sub.2 is a monovalent organic radical containing up to 
about 18 carbon atoms. R.sub.2 can be a substituted or unsubstituted 
alkyl, cycloalkyl, alkylaryl, or arylalkyl group, the alkyl groups 
typically having from 1 to about 12 carbon atoms, the cycloalkyl groups 
having from 5 to 8 carbon atoms in the ring, and the arylalkyl and 
alkylaryl groups typically having from 6 to about 18 carbon atoms. The 
organic radicals may bear substituents such as halogen, amino, alkoxy, and 
hydroxyl groups. Alkyl esters of acrylic acid and methacrylic acid having 
1 to about 8 carbon atoms in the alkyl group are preferred. 
Examples of suitable acrylate monomers include, but are not limited to, 
methyl acrylate, methyl methacrylate, 2-phenoxyethyl acrylate, norbornenyl 
acrylate, dicyclopentenyl acrylate, cyclohexyl acrylate, 2-tolyloxyethyl 
acrylate, isopropyl methacrylate, ethyl acrylate, methyl 
alphachloroacrylate, beta-dimethylaminoethyl methacrylate, ethyl 
methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, cyclohexyl 
methacrylate, hexyl methacrylate, 2-methylcyclohexyl methacrylate, 
beta-bromoethyl methacrylate, benzyl methacrylate, phenyl methacrylate, 
neopentyl methacrylate, butyl methacrylate, hexyl acrylate, dodecyl 
acrylate, 3-methyl-1-butyl acrylate, -ethoxyethyl acrylate, phenyl 
acrylate, butoxyethoxyethyl acrylate, 2-methoxyethyl acrylate, octyl 
acrylate, isodecyl acrylate, dichloroisopropyl acrylate, butyl 
chloroacrylate, lauryl chloroacrylate, and the like. Preferred are lower 
alkyl acrylates and methacrylates in which the alkyl group has from 1 to 
about 8 carbon atoms, more preferably from 1 to about 4 carbon atoms, such 
as methyl acrylate, methyl methacrylate, ethyl acrylate, n-propyl 
acrylate, isopropyl methacrylate, n-butyl methacrylate, and t-butyl 
acrylate. The acrylate monomers are usually employed in amounts of more 
than about 50 phm, preferably at least about 75 phm, more preferably at 
least about 90 phm, and even at least about 95 phm. Combinations of 
acrylate monomers are usually used to achieve desired properties. For 
exterior paint, a combination of butyl acrylate and methyl methacrylate in 
amounts of from about 50 to about 60 phm and from about 35 to about 45 
phm, respectively, is highly preferred. 
Preferably, the monomer feed includes at least one acrylate monomer wherein 
R.sub.2 is a hydroxyalky group having up to about 8 carbon atoms, such as 
2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl 
acrylate, 3-hydroxypropyl acrylate, 1-hydroxypropyl methacrylate, 
2-hydroxypropyl methacrylate, 3-hydroxpropyl methacrylate, 1-hydroxybutyl 
acrylate, and 2-hydroxyhexyl methacrylate. Hydroxypropyl methacrylates are 
preferred. The hydroxyalkyl monomers are generally used in proportions of 
from about 0.1 to about 10 phm, preferably from about 0.5 to about 5 phm, 
and more preferably from about 1 to about 3 phm. 
Preferably, the monomer feed also includes at least one ethylenically 
unsaturated carboxylic acid monomer that is copolymerizable with the 
acrylate monomers in the feed. Examples of these are acrylic acid; 
methacrylic acid; alpha-haloacrylic acids such as chloroacrylic acid; 
itaconic acid; maleic acid; and fumaric acid. Acrylic acid is preferred 
for increasing the high shear viscosity of a paint made with the resulting 
polymer emulsion. Methacrylic acid is more preferred because it improves 
the high shear viscosity of paint without unduly increasing the low shear 
viscosity of the polymer emulsion itself. The acid monomers are usually 
included in amounts of from about 0.1 to about 10 phm, more preferably 
from about 0.5 to 5 phm, and most preferably from about 2 to about 5 phm. 
It is also advantageous to include in the monomer feed at least one wet 
adhesion promoter such as a ureido-containing monomer, a 
cyanoacetoxy-containing monomer, an acetoacetoxy-containing monomer, 
hydroxymethyl diacetone acrylamide, and mixtures thereof. The wet adhesion 
promoter is usually employed in proportions of from about 0.1 to about 5 
phm, preferably from about 0.5 to about 2 phm. 
The ureido-containing monomers contain a ureido group of the formula V: 
##STR2## 
Exemplary ureido-containing monomers include, but are not limited to, 
2-ureido-ethyl acrylate, 2-ureido-ethyl methacrylate, 2-ureido-ethyl 
acrylamide, 2-ureido-ethyl methacrylamide, 
1-[2-(3-allyloxy-2-hydroxypropylamino)ethyl]-imidazolidin-2-one. Mixtures 
of ureido-containing monomers can be used. A commercially available 
ureido-containing monomer is 
1-[2-(3-allyloxy-2-hydroxy-propylamino)ethyl]-imidazolidin-2-one which is 
commercially known as Sipomer WAM brand monomer available from Alcolac. 
Cyanoacetoxy-containing monomers and acetoacetoxy-containing monomers have 
the formulas VI and VII, respectively, 
##STR3## 
wherein R.sub.10 is selected from the group consisting of hydrogen and 
halogen, R.sub.11 is selected from the group consisting of hydrogen, halo, 
thio, and monovalent organic radicals, R.sub.12 is a divalent radical, and 
R.sub.13 is selected from the group consisting of hydrogen and monovalent 
organic radicals. As used throughout the specification and claims, the 
term "organic radical" means any group containing at least one carbon 
atom, and the term "inorganic radical" means any group devoid of carbon 
atoms. 
Preferably, R.sub.10 is hydrogen, R.sub.11 is hydrogen or an alkyl radical 
having up to about 10 carbon atoms, R.sub.12 is a cyclic or acyclic 
organic radical containing up to about 40 carbon atoms, and R.sub.13 is an 
acyclic organic radical containing up to about 15 carbon atoms. More 
preferably, R.sub.12 is an acyclic radical containing up to about 20 atoms 
in length, with any and all side groups each being up to about 6 atoms in 
length, and R.sub.13 is hydrogen or an alkyl group containing up to about 
7 carbon atoms. R.sub.12 is most preferably alkylene and alkoxylene groups 
containing up to about 10 carbon atoms, and R.sub.13 is most preferably 
methyl. While acetoacetoxyethyl methacrylate, cyanoacetoxyethyl 
methacrylate, and allylacetoacetate are reported in the literature, and 
while acetoacetoxyethyl methacrylate and allylacetoacetate are 
commercially available, acetoacetoxyethyl methacrylate is the preferred 
acetoxy-containing monomer. 
In the most preferred embodiment of this invention, a combination of 
polymerizable monomers is used, which comprises at least three different 
acrylate monomers, at least one of which is a hydroxyalkyl acrylate 
monomer, at least one ethylenically unsaturated carboxylic acid monomer, 
and at least one ureido-containing wet adhesion promoter. The two acrylate 
monomers together are present in a proportion of from about 90 to about 97 
phm; most preferred are butyl acrylate and methyl methacrylate in 
proportions of from about 50 to about 60 phm and from about 35 to about 45 
phm respectively. The hydroxyalkyl acrylate is used in amounts of from 
about 1 to about 4 phm; most preferred is hydroxypropyl methacrylate in a 
proportion of about 1.5 to about 3 phm. The acid monomer is used in 
proportions of from about 1 to about 5 phm; most preferred is methacrylic 
acid in a proportion of about 2 to about 4 phm. The ureido-containing wet 
adhesion promoter is used in proportions of from about 0.5 to about 2 phm; 
most preferred is 
1-[2-(3-allyloxy-2-hydroxy-propylamino)ethyl]-imidazolidin-2-one in a 
proportion of about 0.7 to 0.9 phm. 
Optional ethylenically unsaturated polymerizable monomers can also be 
present in the monomer feed. These include, but are not limited to, 
ethylene; vinyl monomers; acrylamides; alkenyl aromatics; alkadienes; and 
mixtures thereof. These optional monomers are used in proportions of less 
than about 50 phm, usually less than about 20 phm, and preferably less 
than about 10 phm. 
Typical vinyl monomers include, but are not limited to, vinyl halides, 
vinylidene halides, acrylonitrile, and vinyl esters such as vinyl acetate, 
vinyl propionate, vinyl butyrate, vinyl valerate, vinyl benzoate, and 
vinyl versatate. 
The acrylamide monomers generally have the formula 
##STR4## 
wherein R.sub.3 is selected from the group consisting of hydrogen, alkyl 
groups containing 1 to about 6 carbon atoms, and halo-substituted alkyl 
groups containing 1 to about 6 carbon atoms, and R4 and R5 are each an 
alkyl group independently containing up to about 18 carbon atoms. 
Preferably, R.sub.3 is selected from the group containing hydrogen and 
methyl, and R.sub.4 and R.sub.5 are each an alkyl group independently 
containing up to about 8 carbon atoms. 
As used in the specification and claims, "alkenyl aromatic monomers" are 
defined as any organic compound containing at least one aromatic ring and 
at least one aliphatic-containing moiety having alkenyl unsaturation. 
Preferred alkenyl aromatic monomers are represented by the formula III 
##STR5## 
wherein X is an aliphatic radical containing at least one alkenyl bond, Y 
is a substituent on the aromatic ring, and n is the number of Y 
substituents on the ring, n being an integer from 0 to 5. Generally, X 
comprises at least 2 carbon atoms, but usually no more than about 6, and 
preferably no more than about 3 carbon atoms. X is preferably a 
substituted or unsubstituted alkenyl group. Preferred alkenyl group 
substituents are halogen radicals, e.g., chloride. However, the most 
preferred alkenyl group is unsubstituted, i.e., a hydrocarbon, and 
contains only one olefinic unsaturation. Ethylene is the most preferred X. 
Y is an organic or inorganic radical. When n is 2 or more, Y can be the 
same or different. If organic, Y generally contains from 1 to about 15 
carbon atoms and, preferably, is an aliphatic radical. Even more 
preferably, Y is a saturated aliphatic radical. If inorganic, Y is 
preferably a halogen. Exemplary Y substituents include halo and cyano 
radicals and substituted and unsubstituted alkyl radicals of 1 to about 10 
carbon atoms. Preferred Y substituents are chloride and unsubstituted 
alkyl groups of 1 to about 6 carbon atoms. Y is more preferably a chloride 
radical and C.sub.1 to about C.sub.4 unsubstituted alkyl radicals. 
Illustrative alkenyl aromatic monomers include styrene, p-methyl styrene, 
methyl styrene, o,p-dimethyl styrene, o,p-diethyl styrene, 
p-chlorostyrene, isopropyl styrene, t-butyl styrene, o-methyl-p-isopropyl 
styrene, o,p-dichlorostyrene, and mixture thereof. Due to its commercial 
availability and low cost, styrene is the preferred alkenyl aromatic 
monomer. 
Exemplary alkadiene monomers have the formula IV 
##STR6## 
wherein R.sub.6, R.sub.7, R.sub.8, and R.sub.9 are each independently 
selected from the group consisting of hydrogen, halogen, and alkyl 
radicals containing 1 to about 2 carbon atoms. Commercially available 
alkadiene monomers include butadiene, isoprene, 1,3-pentadiene, 2-ethyl 
butadiene, and 4-methyl-1,3-pentadiene. The preferred alkadiene monomer is 
butadiene. 
Chain transfer agents useful in the practice of this invention are at least 
slightly soluble in the aqueous polymerization medium under polymerization 
conditions. The phrase "at least slightly soluble" as used in the 
specification and the claims means more soluble than n-dodecyl mercaptan. 
The chain transfer agent is preferably at least 50 percent more soluble, 
more preferably at least 100 percent more soluble, than n-dodecyl 
mercaptan in the polymerization medium under polymerization conditions, 
e.g., temperature, pH, and the like. The chain transfer agents can usually 
be selected from aliphatic mercaptans having from 1 to about 4 carbon 
atoms; aliphatic halides, preferably chlorides, having 1 to about 3 carbon 
atoms; aliphatic alcohols having 1 hydroxyl group and from 1 to about 6 
carbon atoms; and aliphatic alcohols having 2 or more hydroxyl groups and 
2 to about 10 carbon atoms or more. Specific examples of these include, 
but are not limited to, methyl mercaptan, ethyl mercaptan, n-propyl 
mercaptan, isopropyl mercaptan, n-butyl mercaptan, sec-butyl mercaptan, 
t-butyl mercaptan, and butyl-1,4-dimercaptan; carbon tetrachloride, 
chloroform, trichlorobromomethane, chloroethane, fluoroethane, 
chlorofluoroethane, and trichloroethylene; methanol, ethanol, ethylene 
glycol, 1-propanol, 1,3-propanediol, glycerol, vinylglycol, 
1,4-butanediol, but-1-en-3-ol, 1-pentanol, 2-pentanol, t-amyl alcohol, 
1,2,3-hexanetriol, 1,2,5-hexanetriol, and 1,10-decanediol. Also useful are 
aliphatic mercaptans having carboxylic acid functionality, such as 
thioglycolic acid (mercaptoacetic acid), thiodiglycolic acid, and 
thiomalic acid (mercaptosuccinic acid); and aliphatic sulfides, such as 
diallyl sulfide, diethenyl sulfide, and diethyl sulfide. 
Preferred chain transfer agents have both sulfur functionality active for 
chain transfer and oxygen functionality capable of participating in 
hydrogen-bonding interactions. These can be represented by the formula 
VIII 
EQU R.sub.14 --S--R.sub.15 (VIII) 
wherein R.sub.14 and R.sub.15 are independently selected from (a) 
straight-chain or branched aliphatic radicals having at least 1 hydroxyl 
group, preferably 2 or more hydroxyl groups, and from 2 to about 6, 
preferably 2 to about 4 carbon atoms, and (b) aliphatic radicals having at 
least 1 hydroxyl group, at least 2 carbon atoms, and at least 1 ether 
oxygen. R.sub.15 can also be, and preferably is, hydrogen. Specific 
examples of R.sub.14 and R.sub.15 include, but are not limited to, 
1-hydroxyethyl, 1-hydroxypropyl, 1,2-dihydroxypropyl, 2-hydroxybutyl, 
1,3-dihydroxypentyl, 1,2,3-trihydroxyhexyl, 1,2,5-trihydroxyhexyl, 
HOCH.sub.2 CH.sub.2 OCH.sub.2 --, and HOCH.sub.2 CH.sub.2 OCH.sub.2 
CH.sub.2 --. R.sub.14 and R.sub.15 can be even larger carbon chain 
radicals having many hydroxyl groups; hydroxy-terminated polyether 
radicals derived from polyethylene glycols, polypropylene glycols, 
polyethylene oxides, polypropylene oxides, and the like; and polyhydric 
polyether radicals derived from, for example, polyglycerols. Highly 
preferred for their high chain transfer activity, low cost, commercial 
availability, and high sulfur to hydroxyl ratio are monothioglycerol 
(including 1-monothioglycerol, 2-monothioglycerol, and mixtures thereof), 
and 2-mercaptoethanol; particularly preferred is monothioglycerol. 
The chain transfer agents can be used in proportions of from about 0.01 to 
about 10 phm, depending on their molecular weight and the level of chain 
transfer activity desired. Usually, they can be used in amounts of from 
about 0.01 to about 5 phm, and preferably from about 0.01 to about 2 phm. 
Monothioglycerol is most preferably used in proportions of from about 0.01 
to about 1 phm. 
One effect of chain transfer agents in polymerization reactions is to lower 
the average molecular weight and to change the molecular weight 
distribution of the polymer. When chain transfer agents are used, they 
participate directly in the polymerization reaction and thus become 
incorporated into the product polymer as terminal groups. A portion of a 
chain transfer agent molecule may terminate the growing end of a polymer 
chain, or it may react with monomer to begin the growth of a new chain. 
For example, when a chain transfer agent of formula VIII is used, at least 
a portion of the R.sub.14 and R.sub.15 groups become attached as terminal 
groups on polymer molecules. The sulfur in the mercaptan group or the 
organic sulfide is more active for chain transfer than the hydroxyl group, 
so that when R.sub.14 or R.sub.15 (other than hydrogen) reacts with 
polymer or monomer, it bonds through the sulfur, and hydroxyl-terminated 
polymer molecules are produced. Some of these polymer molecules can have 
sufficiently low molecular weight that they remain water soluble. Without 
intending to be bound by any particular theory, it is believed that such 
water soluble, low molecular weight, hydroxyl-terminated polymers or 
oligomers can interact with the substantially water insoluble polymer 
particles in the emulsion or latex to increase the high shear (ICI) 
viscosity of a paint comprising such an emulsion, thus improving the film 
build of the paint. 
The polymer emulsion is made, for example, by charging the monomeric 
ingredients, water, and a surfactant (when employed) into a reaction 
vessel, purging the reaction vessel with an inert gas, e.g., nitrogen, to 
remove essentially all the oxygen from the reactor vessel, and heating the 
reactor vessel to the reaction temperature, e.g. from about 80.degree. to 
about 100.degree. C. When the reactor vessel reaches the desired reaction 
temperature, an initiator and a chain transfer agent are then added to the 
reaction vessel, and the reaction is continued for about 2 to about 4 
hours. After the reaction is completed, the reactor vessel is cooled. This 
synthesis yields an aqueous polymeric composition comprising polymer 
particles suspended or dispersed in water. 
Typical initiators include thermally generated free radical sources such as 
persulfates, perphosphates, and hydrogen peroxide. Generally, the 
initiator is employed in a concentration of about 0.5 to about 2 phm, and 
preferably in a concentration of about 0.75 to about 1.25 phm. 
Anionic, nonionic, and amphoteric surfactants can be employed in the 
polymer synthesis process. Exemplary anionic, nonionic, and amphoteric 
surfactants are Siponate A246L brand surfactant available from Alcolac, 
polyoxyethylene alkyl phenol surfactants, and N,N-biscarboxyethyl 
lauramine, respectively. A preferred nonionic surfactant is an 
alkylphenoxy poly(oxyethylene)ethanol having a hydrophilic-lipophilic 
balance of about 13, which is sold as Igepal CO-630 brand surfactant. 
Usually, an initial charge comprising water, a buffer (preferably a 
carbonate or bicarbonate such as ammonium carbonate), at least one 
surfactant (e.g., anionic and nonionic surfactants), and a minor 
proportion, from about 1 to about 10 percent, of the monomeric 
ingredients, that is, the monomer feed, is placed in the reaction vessel, 
purged, and heated. An initiator system is then added to the reactor. The 
initiator system can be the above described thermally generated free 
radical sources or a redox system containing an oxidizing agent (e.g., 
hydrogen peroxide) and a reducing agent (e.g., sodium metabisulfite or 
erythorbic acid). An aqueous polymer dispersion is formed. The remainder 
of the monomeric ingredients, usually pre-emulsified with surfactant in 
water, and an additional amount of the initiator system are then 
simultaneous fed into the reactor by separate feed streams. After all the 
monomer and initiator have been added to the reactor, the reaction is 
continued for about 15 minutes to about 1 hour and post-addition 
ingredients are then added to the reactor to reduce any residual monomer 
concentration. The monomer feed can be a single mixture of all monomeric 
ingredients or it can be two or more mixtures that can be added 
separately, either simultaneously or at different times. When all 
ingredients have been added, the reaction is continued to completion, and 
the vessel is cooled. 
The chain transfer agent can be introduced into the reaction vessel in one 
portion at the beginning of the polymerization reaction or at some later 
time during the polymerization. Preferably, the chain transfer agent is 
delay added to the reaction vessel after a substantial portion, at least 
about 25 percent, preferably at least about 50 percent, of the time 
allotted for the polymerization has passed, so that a substantial portion 
of the monomer feed has been polymerized before the chain transfer agent 
is introduced into the reaction vessel. Usually, it is preferable to add 
the chain transfer agent in portions or in a continuous flow during the 
addition of the monomer feed. 
The chain transfer agent can be incorporated into the monomer feed. It can 
be included in the initial monomer feed mixture, so that it is present in 
the reaction vessel at or near the beginning of the polymerization and is 
continually added with the monomeric ingredients until all of the monomer 
feed has been added. The chain transfer agent is preferably delay added to 
the remaining monomer feed after a substantial proportion of the initial 
monomer feed mixture, at least about 25 percent, preferably about 50 
percent, has been introduced into the reaction vessel. 
The polymer emulsion thus produced can have a low shear viscosity of about 
100 to about 16,500 cps measured with a Brookfield viscometer at about 
25.degree. C. and about 50 sec.sup.-1 shear rate. Delayed addition of the 
chain transfer agent as described above is useful when a polymer emulsion 
having lower low shear viscosity are desired. Preferably, the polymer 
emulsion has a low shear viscosity from about 100 to about 1000 centipoise 
(cps), more preferably from about 200 to about 500 cps, measured at about 
25.degree. C. and about 50 sec.sup.-1 shear rate. 
The polymer emulsion of the present invention is most preferably employed 
in a paint. Usually, paints have a solids content of at least about 40 
percent by volume, and more typically about 50 to about 65 percent by 
volume. Generally, the paint comprises the polymer emulsion, a pigment, 
and a carrier, e.g., water. In addition, the paint also typically 
comprises a coalescing aid, a thickening aid, a dispersing aid, a 
defoamer, and a biocide. 
In addition, a paint comprising a polymer emulsion of this invention 
typically has a high shear viscosity of about 0.5 to about 5.0 poises 
measured with an ICI cone and plate viscometer according to the 
manufacturer's instructions (about 25.degree. C. and about 12,000 
sec.sup.-1 shear rate, or cone speed of about 20 rev/min). Preferably, the 
paint has a high shear viscosity from about 0.5 to about 3.0 poises, more 
preferably from about 1.0 to about 1.6 poises. 
With respect to low shear viscosity, the paint typically has a low shear 
viscosity of about 65 to about 110 Krebs units measured at about 
25.degree. C., and preferably about 80 to about 100 Krebs units measured 
at about 25.degree. C. 
The paint is applied to at least a portion of a surface of a substrate and, 
when dried, forms a film.

EXAMPLES 
In the following examples, Example 1 describes the preparation of polymer 
latex without the use of any chain transfer agent. Examples 2, 3, and 4 
describe the preparation of polymer latexes in accordance with this 
invention. Example 5 relates to the use of a chain transfer agent, dodecyl 
mercaptan, that is outside the scope of this invention. Example 1A through 
5A describe the preparation of paints comprising the polymer latexes of 
Examples 1 through 5. 
EXAMPLE 1 
Preparation of Polymer Latex Without Chain Transfer Agent 
A polymer emulsion or latex was prepared by introducing a reactor charge of 
water (about 241 g) and ammonium carbonate (about 2.6 g) to a reaction 
vessel. A monomer feed pre-emulsion was prepared, containing water (about 
152 g), Siponate A-246L brand alkylaryl sulfonate-type anionic surfactant 
(about 16 g, 40% active), Igepal CO-630 brand alkylphenoxy 
poly(oxyethylene)ethanol-type nonionic surfactant (about 16 g), butyl 
acrylate (about 353 g), methyl methacrylate (about 253 g), and 
hydroxypropyl methacrylate (about 13 g). The reactor was heated to about 
82.degree. C. while purging the reactor with nitrogen. About 26 ml of the 
monomer feed was added to the reactor. The mixture was stirred for about 5 
minutes, and a first initiator solution of sodium persulfate (1.33 g) 
dissolved in water (26.3 g) was added all at once to the reactor. A second 
initiator solution containing sodium persulfate (about 1.5 g) dissolved in 
water (about 41.9 g) was prepared. About 15 minutes after the first 
initiator was added, addition of the remaining monomer feed and the second 
initiator solution was begun at flow rates of about 53.2 ml/15 min and 2.4 
ml/15 min respectively. Thirty minutes later, addition of a solution of 
Sipomer WAM brand ureido-containing monomer (about 4.9 g) in water (about 
38.3 g) was begun at a flow rate of about 3.1 ml/15 min. Addition of the 
monomer feed took about 4 hours. When about half the monomer feed had been 
added to the reaction vessel, methacrylic acid (about 22 g) was mixed with 
the then remaining monomer feed, which continued to flow into the vessel. 
Second initiator addition continued about 30 minutes after all the monomer 
feed had been added. The reaction vessel was then cooled to about 
72.degree. C. To remove residual monomer, t-butyl hydroperoxide (about 1.2 
g in about 6 ml of water) was added in one portion and about 0.4 g of 
sodium erythorbate in about 9 ml of water was added over a period of about 
1 hour. The reaction mixture was cooled and the pH adjusted to about 8.0 
to about 8.3 with ammonia. 
EXAMPLE 2 
MTG (0.03 phm) 
The procedure of Example 1 was followed exactly, except that about 0.19 g 
(about 0.03 phm) of the chain transfer agent monothioglycerol (MTG) was 
added to the monomer feed pre-emulsion before any of the monomer feed was 
charged to the reaction vessel. 
EXAMPLE 3 
MTG Delay Add (0.03 phm) 
The procedure of Example 1 was followed, except that after about half the 
monomer feed had been added to the reaction vessel, about 0.19 g (about 
0.03 phm) of MTG was mixed with the remaining monomer feed, which 
continued to flow into the reaction vessel. 
EXAMPLE 4 
MTG (0.1 phm) 
The procedure of Example 2 was followed, except that about 0.64 g (about 
0.1 phm) of MTG was used. 
EXAMPLE 5 
Dodecyl Mercaptan Delay Add (0.04 phm) 
The procedure of Example 3 was followed, except that about 0.04 phm of 
dodecyl mercaptan was used instead of the MTG. 
EXAMPLES 1A-5A 
Preparation of Paints 
Five flat white exterior paints (having a PVC content of about 44) were 
each prepared using the emulsion polymer latexes of Examples 1 through 5 
by combining water, Aquathix brand polycarboxylate thickener, Triton N-101 
brand surfactant, Polywet ND-2 brand dispersing aid, AMP-95 brand 
aminomethylpropanol base, ethylene glycol, Colloid 681-F brand defoamer, 
Nuosept 95 brand and Nopcocide N-96 brand biocides, Tronox CR-800 brand 
titanium dioxide, 325 mesh mica extender, Duramite brand calcium carbonate 
extender, and Nytal 300 brand talc extender in the proportions set forth 
in Table I below. 
TABLE I 
______________________________________ 
Standard Paste 
Material Weight, g Volume, ml 
______________________________________ 
Water 2030.9 2031.0 
Aquathix 30.5 22.8 
AMP-95 20.3 20.3 
TritonN-101 20.3 20.3 
Polywet ND-2 50.8 48.2 
Ethylene Glycol 188.9 169.3 
Colloid 681-F 10.2 11.8 
Nuosept 95 20.3 22.0 
Nopcocide N-96 50.8 27.1 
Cr-800 (TiO.sub.2) 
2538.6 604.2 
325 Mesh Mica 253.9 97.3 
Duramite 1523.2 562.8 
Nytal 300 761.6 274.2 
______________________________________ 
The material combination listed in Table I was ground at a high speed to a 
National Standard rating of about 4. Next, Texanol brand coalescing aid, 
Colloid 681-F brand defoamer, and 55% testing acrylic emulsion polymer 
latex were added to the ground mixture in the proportions stated in Table 
II below. 
Each paint had the physical properties set forth in Table III. 
TABLE II 
______________________________________ 
Standard Paint Formula 
Weight, g 
______________________________________ 
Standard Paste 60.56 
Texanol 1.64 
Colloid 681-F 0.16 
55% Testing Latex 31.08 
Water 6.55 
Total Weight 100.00 g 
Total Volume 70.00 ml 
______________________________________ 
TABLE III 
______________________________________ 
Physical Properties 
______________________________________ 
Viscosity, KU 83-92 
Density 11.9 lbs/gal 
P.V.C. 43.7% 
% Solids 
By Weight 58.1% 
By Volume 40.6% 
pH 8.4 +/- 0.5 
______________________________________ 
The Brookfield (Bfd) viscosity of each polymer latex of Examples 1 through 
5 was measured in centipoises on a Brookfield viscometer according to 
manufacturer's instructions (about 25.degree. C. and about 50 sec.sup.-1 
shear rate). The ICI viscosity of each corresponding paint of Example 1A 
through 5A was measured in poises at about 25.degree. C. and about 12,000 
sec.sup.-1. The results are presented in Table 
TABLE VI 
______________________________________ 
Viscosities 
Examples 
1 2 3 4 5 
1A 2A 3A 4A 5A 
______________________________________ 
Latex, Bfd 
875 1650 270 16800 195 
Paint, ICI 
1.0 1.4 1.5 2.0 1.1 
______________________________________ 
Examples 1 and 1A are the reference polymer latex and the standard paint 
made therewith, respectively. In Example 2, about 0.03 phm of 
monothioglycerol (MTG) was included in the monomer feed. The ICI viscosity 
of the corresponding paint 2A was about 40 percent higher than the 
reference, and the Brookfield viscosity of the latex was still acceptable. 
In Example 3, the same amount of MTG was delay added after half the monomer 
feed had been introduced into the reaction vessel. Note that the ICI 
viscosity of the paint 3A was about 50 percent higher than the reference 
while at the same time the Brookfield viscosity of the parent latex 3 was 
almost 70 percent lower than the viscosity of the reference latex. 
In Example 4, a higher amount of MTG (about 0.1 phm) was used, and it was 
added to the monomer feed at the beginning, so that MTG was present in the 
reaction vessel from the start of the polymerization reaction. The ICI 
viscosity of the paint was about 100 percent higher than the reference 
value, and the Brookfield viscosity of the latex was over 19 times as high 
as the reference. Latexes of lower viscosity are usually preferred for 
paint making, but they can be useful where a viscous latex is desired. 
Example 5 relates to the use of dodecyl mercaptan, a widely used chain 
transfer agent different from those useful in the practice of this 
invention. The amount used (about 0.04 phm) corresponds to about 0.02 phm 
of MTG based on equivalent numbers of mercaptan groups. If dodecyl 
mercaptan were comparable to MTG, a paint made with the latex of Example 5 
would be expected to have an ICI viscosity of about 1.3. Assuming a 
measurement error of about +/-0.05 poise in measuring ICI viscosity, the 
figure of 1.1 poise for the ICI viscosity of paint 5A is not significantly 
different from the reference ICI viscosity of 1.0 poise. 
Although the present invention has been described in considerable detail 
with reference to certain preferred embodiments thereof, other variations 
are possible. Therefore, the spirit and scope of the appended claims 
should not necessarily be limited to the description of the preferred 
embodiments contained herein. 
The term "Standard Paint Formula" as used in the specification and the 
claims means the paint used in Examples 1A-5A; that is, the paint 
specified in Tables I, II, and III and the associated procedure. The 
"Testing Latex," adjusted to a nominal 55 percent solids content, is 
incorporated into the Standard Paint Formula as described and the 
properties of the paint are measured. When a polymer emulsion made with 
the use of a chain transfer agent in accordance with this invention is 
incorporated into the Standard Paint Formula, the resulting paint exhibits 
a higher high shear (ICI) viscosity, measured at about 25.degree. C. and 
about 12,000 sec.sup.-1, than a paint resulting from the incorporation 
into the Standard Paint Formula in like proportion of a polymer emulsion 
identically made but without the use of the chain transfer agent.