Manufacture of aqueous polymer dispersions and coating compositions derived from them

Sterically stabilized aqueous polymer dispersions of at least 20% solids content are made by free radical-initiated polymerization of monomers in an aqueous medium at a temperature at least 10.degree. C. higher than the glass transition temperature of the polymer to be formed, in the presence of a compound which is soluble in the aqueous medium and contains in the molecule a polymeric component of molecular weight at least 1000 which is solvatable by the aqueous medium and an unsaturated grouping which can copolymerize with the monomers, the conditions being such that there is at no time present a separate monomer phase. The dispersions are useful as a basis of improved coating compositions.

This invention relates to the production of dispersions of polymer 
particles in aqueous liquid media in which the particles are stabilised 
against gross flocculation. More particularly, it relates to producing 
dispersions in which the stabilisation of the particles is achieved 
substantially by means of a steric mechanism. The invention also relates 
to coating compositions derived from dispersions so made. 
By "gross flocculation" is meant herein a state in which, even at low 
solids contents, the dispersions contain many multi-particle aggregates. 
Polymer dispersions are well known in which the particles of polymer are 
stably dispersed in water or an aqueous medium (in which by definition the 
polymer is insoluble), the stability of the particles being achieved at 
least to a major extent by the presence on the surface of the particles of 
electrical charges whereby repulsive forces are generated which counteract 
the natural tendency of the particles to attract one another. Such 
dispersions are the products of the so-called emulsion polymerisation 
processes, a characteristic of which is that the monomer being 
polymerised, as well as the polymer which is formed, is insoluble in the 
aqueous medium. The initiation of the polymerisation, and the maintenance 
of a fine emulsion of the monomer in the aqueous medium, are effected by 
ionisable species which are dissolved in the aqueous phase. 
Other polymer dispersions are well known in which the particles of polymer 
are stably dispersed in a non-aqueous organic liquid medium (in which 
again the polymer is insoluble), and in which the particles are stabilised 
exclusively by means of their having attached to their surfaces polymeric 
chains of a nature such as to be inherently soluble in the non-aqueous 
medium; in this way there is formed around each particle a steric barrier 
of solvated and extended polymer chains which supplies the repulsive force 
necessary to prevent adjacent particles coming into contact with each 
other. The charge-stabilisation mechanism previously referred to is in 
general not applicable to non-aqueous liquid systems. This second type of 
polymer dispersion is most frequently obtained by means of a so-called 
non-aqueous dispersion polymerisation process, which has the 
characteristic that, whilst the polymer ultimately formed is insoluble in 
the non-aqueous liquid, the monomer being polymerised is actually soluble 
therein. The polymerisation is carried out in the presence of a steric 
stabiliser which is an amphipathic molecule incorporating one component 
which is inherently soluble in the liquid medium and another component 
which has an affinity for the surface of the polymer particles as they 
form and which in consequence becomes anchored thereto. A full treatment 
of the subject of non-aqueous dispersions is to be found in "Dispersion 
Polymerisation in Organic Media", ed. K. E. J. Barrett (John Wiley, 1975), 
and there are many published patent specifications relating to it, for 
example British Specifications Nos. 941,305; 1,052,241; 1,122,397; 
1,123,611; 1,143,404; 1,231,614. 
Whilst for many purposes the production of stable polymer dispersions in 
non-aqueous organic liquid media is of considerable technical and 
commercial importance, there are nevertheless advantages in being able to 
obtain comparable dispersions in water or aqueous media. This is 
particularly true where the dispersions are intended for use in coating 
compositions, since the use of water as a carrying liquid avoids the 
problems of pollution associated with the evaporation of volatile organic 
liquids. The known aqueous polymer dispersions of the kind referred to 
above have indeed found extensive use in the formulation of coating 
compositions, but they nevertheless fall short of being wholly 
satisfactory for that purpose. Although, in these dispersions, some 
measure of steric stabilisation of the disperse phase particles may 
operate, as the result of the use of non-ionic surfactants or protective 
colloids, the fact that stabilisation is chiefly brought about by the use 
of low molecular weight, water-insoluble surfactants can lead to problems 
of various kinds, notably water-sensitivity of the derived film. Attempts 
have previously been made to prepare aqueous dispersions in which the 
polymer particles are wholly stabilised by a steric mechanism analogous to 
that which operates in non-aqueous dispersions. These attempts, however, 
have not been successful; in particular, it has not proved possible to 
achieve adequate stability of the particles against flocculation except 
where the polymer content of the dispersion was so low as to render it of 
little value for the formulation of coating compositions. 
We have now, however, found a process whereby sterically stabilised 
dispersions of polymers in aqueous media, having high polymer contents and 
hence being suitable for use in coating compositions, may be 
satisfactorily prepared. 
According to the present invention there is provided a process for the 
production of a sterically stabilised dispersion of polymer particles of a 
size in the range 0.01 to 10 microns in an aqueous medium, the process 
comprising the free radical-initiated polymerisation in the aqueous medium 
of one or more ethylenically unsaturated monomers at a temperature which 
is at least 10.degree. C. higher than the glass transition temperature as 
hereinafter defined of the polymer which is formed, in the presence of a 
stabiliser precursor compound which is soluble in the aqueous medium and 
which contains in the molecule a polymeric component of molecular weight 
1000 which is solvatable by the aqueous medium and an unsaturated grouping 
which is capable of copolymerising with the said monomer or monomers, the 
aqueous medium being a mixture comprising (a) at least 30% by weight of 
water and (b) not more than 70% by weight of a second constituent which is 
miscible with water, the nature and proportion of the second constituent 
being such that the mixture as a whole is capable of dissolving the 
monomer or monomers being polymerised to the extent of at least 3% by 
weight but is a non-solvent for the polymer formed, the concentration of 
free monomer in the polymerisation mixture being maintained throughout the 
process at a level such that at no time does the free monomer form a 
separate phase and the total amount of monomer polymerised being such that 
the resulting dispersion contains at least 20% by weight of polymer. 
The second constituent of the aqueous medium may be a single substance or 
it may be a water-miscible mixture of two or more substances. Preferably 
the aqueous medium is capable of dissolving the monomer or monomers to the 
extent of at least 10% by weight. 
By "glass transition temperature" (Tg) we mean the temperature at which the 
polymer which is produced in the process of the invention passes from the 
glassy state to the rubbery state, or vice versa. The Tg value in question 
will normally be that of the bulk polymer as 100% material, but in a case 
where, as subsequently described, a plasticising substance is deliberately 
added to the polymerisation mixture for the purpose of reducing the 
effective Tg of the polymer, the Tg value for the purposes of the 
invention is that of the plasticised polymer. Even where a plasticiser for 
the polymer is not added as such, the "environmental" Tg of the polymer 
under the conditions obtained during polymerisation may be somewhat lower 
then the bulk Tg value referreed to above, owing to some plasticisation of 
the polymer by residual monomer or other constituents of the 
polymerisation mixture. Thus it may be possible in practive to operate 
with a somewhat lower minimum polymerisation temperature than that 
indicated by the bulk Tg value. However, the effect of such fortuitous 
plasticisation on the Tg value is difficult to predict and, whilst it can 
in principle be determined by simple trial and error, it is more 
convenient under these conditions to choose the temperature of 
polymerisation by reference to the bulk Tg value. The Tg of a bulk 
polymer, or of a deliverately plasticised polymer may be determined for 
the present purposes, by experimental methods which are well known to 
those skilled in the art, upon polymer of the same composition as that 
which is to be formed in the process of the invention but obtained by some 
other route, for example by polymerisation of the monomers in bulk or in 
solution, with subsequent addition of plasticiser where appropriate. 
Alternatively, Tg values can be calculated, from a knowledge of the 
monomer composition of the polymer, by known methods. 
By way of illustration, the following bulk Tg values may be quoted (ratios 
stated are by weight): for a 50:50 methyl methacrylate/butyl acrylate 
copolymer, 4.degree. C.; for a 80:20 methyl methacrylate/2-ethylhexyl 
acrylate copolymer, 41.degree. C.; for a homopolymer of ethyl acrylate, 
-22.degree. C.; for a homopolymer of methyl methacrylate plasticised in 
the ratio 60:40 with a neopentyl glycol/butyl alcohol adipate polyester 
plasticiser, 55.degree. C. Any of these polymer compositions can be 
successfully prepared in the form of an aqueous latex by the process of 
the invention at the polymerisation temperatures in the range 
70.degree.-90.degree. C. which are normally employed for the 
polymerisation of acrylic monomers in the presence of an azo initiator. 
Ethylenically unsaturated monomers which may be used in the process of the 
invention include in particular the acrylic monomers, that is to say 
acrylic acid or methacrylic acid and their alkyl esters such as methyl 
methacrylate, ethyl methacrylate, butyl methacrylate, lauryl methacrylate, 
ethyl acrylate, butyl acrylate, hexyl acrylate, n-octylacrylate, 
2-ethylhexyl acrylate, nonyl acrylate, lauryl acrylate and cetostearyl 
acrylate, the hydroxyalkyl esters of the same acids such as 2-hydroxyethyl 
acrylate, 2-hydroxyethyl methacrylate and 2-hydroxypropyl methacrylate, 
and the nitriles and amides of the same acids such as acrylonitrile, 
methacrylonitrile, acrylamide and methacrylamide. Other monomers which may 
be used, either alone or in admixture with these acrylic monomers, include 
vinyl aromatic compounds such as styrene and vinyl toluene, vinyl esters 
of organic and inorganic acids such as vinyl acetate, vinyl propionate, 
vinyl chloride and vinylidene chloride. Yet other comonomers which may be 
used in conjunction with any of the foregoing monomers include dialkyl 
maleates, dialkyl itaconates, dialkyl methylene-malonates, isoprene and 
butadiene. 
Where it is desired that the latex polymer should be of the cross-linkable 
or thermosetting type, the monomers from which it is derived will normally 
include a proportion of at least one monomer carrying a reactive group, 
such as one of the hydroxy monomers mentioned above or an N-(alkoxy-alkyl) 
derivative of acrylamide, e.g. N-(n-butoxymethyl) acrylamide, or a monomer 
carrying an epoxy group, such as glycidyl methacrylate. 
Preferably, the temperature of polymerisation of the monomer or monomers is 
at least 20.degree. C., more preferably at least 30.degree. C., higher 
than the glass transition temperature of the polymer which is formed. In 
general, polymerisation temperatures in the range 30.degree.-80.degree. C. 
are convenient. 
Thus, in principle, the temperature at which the polymerisation is carried 
out will be determined first and foremost with reference to the Tg value 
of the polymer which it is proposed to produce in dispersion, and, having 
decided upon that temperature, one will then proceed to choose an 
appropriate composition for the aqueous medium in which the process is to 
be conducted. In order to help the maintaining of a constant 
polymerisation temperature, it is preferred to arrange that the aqueous 
medium can boil under reflux at that temperature, and the nature and 
proportion of the water-miscible second constituent of the mixture will 
then be selected with this object in mind. Having regard to the fact that, 
for many of the monomers likely to be used in the process, an effective 
polymerisation temperature will lie in the range 70.degree.-90.degree. C., 
the second constituent of the aqueous medium, or a constituent thereof, 
will usually require to be a liquid of boiling point significantly lower 
than that of water. 
In practice, there may be some interaction between these variables; for 
example, the freedom of choice of composition of the aqueous medium to 
suit a particular operating temperature may be restricted by the need to 
find a water-miscible second constituent which does not have a strong 
solvent action on the polymer which is formed, otherwise the aqueous 
medium as a whole may not be a non-solvent for the polymer and there may 
be significant production of polymer in solution rather than in 
dispersion. In the case where the aqueous medium contains a relatively 
volatile water-miscible liquid, the available range of formulations may be 
increased by including therein a further water-soluble constituent which 
does not boil below the boiling temperature of water; such a further 
constituent may be either a solid or a liquid, capable of assisting the 
achievement of the necessary solvent/non-solvent characteristics in the 
aqueous medium. It will be desirable, however, to retain a sufficient 
proportion of the lower-boiling constituent to permit refluxing of the 
polymerisation mixture. Another factor to be borne in mind is the 
desirability or otherwise of the continuous phase of the final dispersion 
permanently containing materials other than water only. Where the 
water-miscible liquid constituent of the aqueous medium is sufficiently 
volatile to permit refluxing at the polymerisation temperature, that 
constituent can usually, if desired, be stripped off by distillation when 
polymerisation is complete. In contrast, a water-miscible constituent of 
higher boiling point may not be removable from the continuous phase in 
this way. 
The use of the term "aqueous medium" herein does not imply that water 
should always be the major constituent of the medium in which the 
polymerisation is carried out; in many cases, the water-miscible 
constituent or constituents may predominate in the mixture. In practice, 
as high a proportion of water as possible is employed, consistent with the 
aqueous medium being capable of dissolving the monomer being polymerised 
at least to the extent necessary to avoid the existence of a separate 
monomer phase, and at the same time being a non-solvent for the polymer 
produced. Evidently the degree of solvency for the monomer which the 
aqueous medium is required to possess will depend upon the concentration 
of free monomer in the polymerisation mixture which it is desired to 
maintain during the process, which in turn will depend upon the rate at 
which it is desired that the polymerisation should proceed. In practice, 
water will most usually constitute 30-70% by weight of the aqueous medium. 
Substances which are suitable for use as the water-miscible constituent of 
the aqueous medium include in particular the lower aliphatic alcohols; the 
preferred member of this class is methanol, but ethanol is also very 
suitable. Water-methanol mixtures can be prepared having boiling points 
which lie both in the optimum polymerisation temperature range and 
sufficiently above the polymer glass transition temperatures for the 
process of the invention to be carried out satisfactorily in such mixtures 
with a variety of acrylic or vinyl monomers. Ethanol is somewhat less 
preferred than methanol because its greater effectiveness as a chain 
terminator in the polymerisation process may make it difficult to obtain a 
disperse polymer of high molecular weight, and also because it is a more 
active solvent for many polymers than is methanol. Nevertheless, ethanol 
is useful where the monomer mixture to be polymerised contains an 
appreciable proportion of styrene. In the case of polymers derived from 
acrylic or methacrylic esters of higher alcohols, e.g. lauryl 
methacrylate, a suitable water-miscible constituent is acetonitrile. 
Suitable water-miscible substances having a boiling point above that of 
water include, for example, butanol, 2-methoxyethanol, 2-ethoxyethanol, 
ethylene glycol, diethylene glycol and tetraethylene glycol. In general, 
the proportion of such substances which it is possible to use in the 
aqueous medium will be relatively low because they tend to be effective 
solvents for many polymers. 
Although simple experimentation may sometimes be called for, the 
formulation of a suitable aqueous medium which meets the various 
requirements set out above does not present any serious difficulty in the 
majority of cases, especially if the Tg of the polymer to be formed does 
not exceed 60.degree. C. 
Steric stabilisation of the polymer particles produced in the process is 
effected as the result of the presence in the polymerisation mixture of 
the compound comprising a solvatable polymeric component and a 
copolymerisable unsaturated grouping. It is believed that the 
copolymerisation of this compound with a minor proportion of the monomer 
or monomers being polymerised leads to the production of an amphipathic 
graft copolymer which is the actual stabilising species. Accordingly the 
compound in question is referred to herein as the "precursor" for the 
graft copolymer stabiliser. The graft copolymer stabiliser is a molecule 
containing two components of differing characteristics. The first 
component is a polymer chain of molecular weight at least 1000 derived 
from the precursor which is solvated by the aqueous medium by virtue of 
the fact that, when in the form of an independent molecule, it is actually 
soluble in that medium. The second component is another polymer chain 
which is similar in chemical composition to the disperse polymer being 
formed in the process and which is, like that polymer, not solvated by 
(i.e. per se insoluble in) the aqueous medium; this component becomes 
associated with, or anchored to, the particles of disperse polymer, whilst 
the chains of the solvated component assume an extended configuration in 
the environment of the aqueous medium and thereby build a steric barrier 
around each particle which overcomes the natural tendency of adjacent 
particles to flocculate. 
The solvatable polymeric component will, as stated above, be derived from a 
water-soluble polymer, examples of which include non-ionic polymers such 
as the polyethylene glycols and their monoalkyl ethers, poly(ethylene 
oxide)--poly(propylene oxide) block copolymers and their monoalkyl ethers, 
and polyvinylpyrrolidone. Preferably the molecular weight of this 
component is at least 1500 and more preferably at least 2000. The 
preferred solvatable components are those derived from polyethylene 
glycols, or their monoalkyl ethers, of molecular weight in the range 
2000-4000. The precursors which are introduced into the polymerisation 
mixture are derivatives of such water-soluble polymers containing a 
copolymerisable unsaturated grouping, which in the case of the 
polyethylene glycols, or their ethers, may conveniently be esters of these 
substances with copolymerisable unsaturated acids, for example methacrylic 
acid, itaconic acid or maleic acid. Esterification of the glycol, or ether 
thereof, may be effected by an ester-interchange reaction with a lower 
alkylester of the unsaturated acid, for example with methyl methacrylate; 
alternatively the glycol or its ether may be reacted with a suitable acid 
chloride, for example methacrylyl chloride, in the presence of a hydrogen 
chloride acceptor. Yet again, the glycol or its ether may be reacted 
directly with the unsaturated acid to give the ester, or with its 
anhydride to form a half-ester. Other suitable precursors may be obtained 
by reacting a carboxyl group-terminated polyvinylpyrrolidone (see, British 
Specification No. 1,096,912) with glycidyl methacrylate. Yet other 
suitable precursors may be obtained by the procedure described in our 
copending application Ser. No. 101,265 filed Dec. 7, 1979, that is to say 
by reacting a water-soluble polyalkylene glycol or its monoalkyl ether 
with a cyclic aliphatic carboxylic anhydride and then reacting the 
resulting half-ester with an epoxy compound containing a polymerisable 
double bond. For example, the monoethyl ether of a polyethylene glycol is 
reacted with succinic anhydride and the product then condensed with 
glycidyl methacrylate to give a precursor containing a terminal vinyl 
grouping. As explained in the co-pending application referred to, this 
method of making a precursor is convenient because it avoids the necessity 
of removing any by-products or excess reagents, which could interfere with 
the subsequent use of the precursor, that arises with most of the other 
methods discussed above. 
The proportion of stabiliser precursor which is added to the polymerisation 
mixture will vary to some extent according to the particular disperse 
polymer which is involved and the disperse particle size which it is 
desired that the resulting dispersion should have, and the optimum 
proportion in any individual case can readily be found by simple 
experiment. However, for general guidance it may be stated that the 
proportion in question will usually lie in the range 0.5-20%, and more 
especially 2-10%, by weight of the disperse polymer content of the 
dispersion being made. Preferably, the precursor is introduced along with 
the monomers, as explained below. 
The process of the invention will usually require the presence in the 
polymerisation mixture of a suitable catalyst or initiator capable of 
producing free radicals. Suitable substances for this purpose are those 
catalysts or initiators well known for use in the polymerisation of 
acrylic or vinyl monomers which are soluble in the monomers, in particular 
azo compounds such as azo diisobutyronitrile and 4,4-azobis(4-cyanovaleric 
acid), or peroxy compounds such as benzoyl peroxide, lauroyl peroxide and 
diisopropyl peroxydicarbonate. To some extent, the choice of initiator can 
influence the temperature at which the polymerisation is carried out and 
thus may constitute a further factor to be considered in deciding the 
overall composition of the polymerisation mixture as discussed above. 
However, azo compounds are generally to be preferred over peroxy compounds 
in view of the tendency of the latter to promote random grafting of the 
monomers on to the solvated component of the precursor. The amount of 
catalyst or initiator used will normally lie in the range 0.5% to 2% of 
the weight of monomer, and here also the addition is preferably made along 
with the monomers being polymerised. 
There may also be present during the polymerisation process a chain 
transfer agent which, unlike the catalyst or initiator, is soluble in the 
aqueous medium. An example of a suitable agent is thioglycollic acid. The 
chain transfer agent may be used in an amount of from 0.1% to 2% of the 
weight of monomer. The effect of the chain transfer agent is to regulate 
the molecular weight of the disperse polymer and ultimately to reduce the 
proportion of finer particles in the disperse phase, thus increasing the 
average particle size. 
In carrying out the process of the invention, it is preferred to introduce 
the monomer or monomers gradually into the aqueous medium, rather than to 
add the total monomer charge all at once. This procedure may in fact be 
essential in many cases if the condition is to be satisfied that at no 
time during the polymerisation should there be present a separate monomer 
phase. Where two or more monomers are involved, these may be pre-mixed 
before being fed into the aqueous medium. A particularly preferred 
procedure, whereby improved control of particle size of the disperse 
polymer is achieved, is to add initially to the aqueous medium a small 
portion, not exceeding 20% by weight, of the total monomer charge, 
together with an appropriate amount of initiator and the whole or the 
greater part of the stabiliser precursor required. This initial charge, 
which may be added all at once provided that the aqueous medium is capable 
of dissolving it completely, is allowed to polymerise first; the reaction 
mixture is initially clear and homogeneous, but subsequently becomes 
opalescent as a very fine "seed" dispersion of polymer is formed. 
Following this, the main portion of the monomer charge, containing 
initiator and the remainder, if any, of the precursor, is fed in steadily 
at a rate sufficient to maintain an acceptable speed of polymerisation but 
not such as to cause monomer to form a separate phase in the polymerising 
mixture. Where the polymerisation is carried out at the reflux temperature 
of the aqueous medium, it is preferred to arrange for this main monomer 
feed to mix with the returning distillate so that it is well diluted 
before it enters the reaction zone; this distillate will normally be rich 
in the second, water-miscible constituent of the aqueous medium and will 
be a good solvent for the monomer being introduced. The rate of monomer 
feed is preferably such that the monomer is diluted with at least its own 
volume of returning distillate. It may be desirable in some cases to 
reserve a portion of the monomer charge for final addition to the 
polymerising mixture without further precursor being present. 
In the case where the process of the invention is performed, as described 
above, by gradual "feed" of monomer to a preformed "seed" dispersion of 
polymer, it is possible to form the "seed" particles from monomer 
different from the main monomer which is subsequently introduced in the 
"feed" stage. Such "seed" monomer does not need to satisfy the requirement 
hereinbefore stated that the polymerisation temperature should be at least 
10.degree. C. higher than the glass transition temperature of the polymer 
(viz. the "seed" polymer) which is formed. Thus, essentially any monomer 
may be used in the "seed" stage so long as it does not amount to more than 
20% of the aggregate of its own weight and the weight of the main monomer, 
does not form a separate phase in the reaction mixture and gives rise to a 
polymer which is insoluble in the aqueous medium. For example, where the 
main disperse polymer is to be derived from a mixture of methyl 
methacrylate and 2-ethylhexyl acrylate (Tg of polymer, approximately 
-10.degree. C.; polymerisation temperature, 76.degree.-80.degree. C.), it 
is possible to employ methyl methacrylate alone (Tg of polymer, 
105.degree. C.) in a "seed" stage; the main monomers are then introduced 
in the "feed" stage to give rise to the main disperse polymer. It is, 
however, to be understood that, in a "seed-feed" procedure as just 
described, the "feed" stage must always be conducted in accordance with 
the definition of the process of the invention hereinabove given. 
Other substances which may be added to the polymerisation mixture include, 
as already mentioned, a plasticiser for the disperse polymer, where it is 
desired that the latter should be softer than the unmodified polymer. The 
addition of plasticiser may, indeed, render it possible to apply the 
process of the invention to certain monomers where it would otherwise 
fail. For example, the homopolymer of methyl methacrylate has a Tg of 
105.degree. C. and it is practically impossible to operate the present 
process with methyl methacrylate as the sole monomer so as to produce a 
stable latex; however, by the addition of plasticiser the Tg can be 
brought down to a level where the process can successfully be carried out. 
Suitable plasticisers are any of those which are well known in the art for 
use with the particular polymer in question; they may either soluble or 
insoluble in the aqueous medium. Conveniently the plasticiser may be added 
to the polymerisation mixture along with the monomer or monomers. 
By the process of the invention, aqueous polymer dispersions may readily be 
made which have disperse phase contents in the range 40-60% by weight, and 
even as high as 70% by weight, and which are effectively stabilised 
against flocculation or aggregation of the disperse polymer. The polymer 
particles may vary considerably in size, a normal range of variation being 
from 0.05 to 5 microns; within this broad range, the particles in any 
individual dispersion will usually show a distribution of sizes, in which 
the largest particles may be up to ten times the diameter of the smallest. 
Such dispersions are especially suitable as the basis of water-borne 
coating compositions, having a number of advantages for this purpose over 
conventional, charge-stabilised dispersions made by aqueous emulsion 
polymerisation procedure. Thus the dispersions made according to the 
invention are stable towards gross flocculation of the disperse phase over 
the whole range of pH, whereas known dispersions are stable only over 
limited pH ranges; they are also stable in the presence of polyvalent 
ions, which is not usually the case with ionically stabilised dispersions, 
and show improved freeze-thaw stability. All these features greatly 
facilitate the formulation of coating compositions from the dispersions. 
Furthermore, the coating compositions themselves show greatly improved 
flow and film integration properties as compared with compositions based 
on conventional dispersions. 
The coating compositions incorporating dispersions made according to the 
invention may be of either the thermosetting type or the thermoplastic 
type, depending upon whether or not the disperse polymer contains any 
reactive groupings which can bring about cross-linking, either with or 
without the addition of a cross-linking agent such as a 
melamine-formaldehyde resin (which may be, but is not necessarily, 
water-soluble), in a heat treatment step subsequent to the application of 
the composition to a substrate. If desired, an external cross-linking 
agent can be introduced into the dispersion by adding it to the aqueous 
medium prior to polymerisation of the monomers from which the disperse 
polymer is formed, provided that the agent in question does not undergo 
any reaction under the conditions of polymerisation (which will normally 
be true of, for example, an amino resin at the temperature at which many 
acrylic or vinyl monomers are polymerised). Other desirable additives to a 
coating composition based on the dispersions, which may also be introduced 
at the polymerisation stage, are reactive silicon compounds capable of 
reacting with hydroxyl groups in the disperse polymer, whereby the polymer 
is enabled to produce a coating of enhanced durability; such a compound 
is, for example, the intermediate QP8-5314 marketed to Dow Corning Inc. 
The actual procedure of making polymer dispersions according to the 
invention is more straightforward in certain respects than the 
conventional emulsion polymerisation techniques, in particular that the pH 
of the polymerisation mixture is not critical, nor is the speed at which 
it is stirred; also the possibility of carrying out the polymerisation 
under reflux makes the maintenance of a steady reaction temperature much 
simpler.

The invention is illustrated but not limited by the following Examples, in 
which parts and percentages are by weight. 
EXAMPLE 1 
Preparation of latex of a thermosetting-type polymer having a theoretical 
Tg of 10.degree. C., in 39:61 water/methanol mixture at reflux temperature 
To a 2-liter flask fitted with stirrer, thermometer, inert gas inlet and 
reflux condenser with provision for feeding ingredients into the returning 
distillate there was charged: 
______________________________________ 
Charge A 
______________________________________ 
Distilled water 315 g 
Methanol 500 g 
______________________________________ 
There was then added the following mixture: 
______________________________________ 
Charge B 
______________________________________ 
Methyl methacrylate 26 g 
Butyl acrylate 24 g 
Stabiliser precursor 
(as described below) 17.5 g 
Azodiisobutyronitrile 
1.0 g 
______________________________________ 
The contents of the flask were then heated at reflux temperature 
(73.degree. C.) for 30 minutes to form a seed dispersion of polymer. There 
was then commenced the dropwise feed into the returning distillate of the 
following mixture: 
______________________________________ 
Charge C 
______________________________________ 
Methyl methacrylate 210 g 
Butyl acrylate 165 g 
N-Butoxymethyl acrylamide 
44 g 
(60% solution in 3:1 
butanol/xylene) 
Methacrylic acid 11 g 
Stabiliser precursor 14.5 g 
(as described below) 
Azidiisobutyronitrile 6.7 g 
______________________________________ 
The addition of Charge C occupied 3 hours. When this was complete, there 
was added in the same manner, over a period of 45 minutes, the following 
mixture: 
______________________________________ 
Charge D 
______________________________________ 
Methyl methacrylate 45 g 
Butyl acrylate 34 g 
N-Butoxymethylacrylamide 
11 g 
(60% solution in 3:1 
butanol/xylene) 
Methacrylic acid 2.7 g 
Azodiisobutyronitrile 1.3 g 
______________________________________ 
One half-hour after this final feed was complete, there was added Charge E 
consisting of a further 0.8 g of azidiisobutyronitrile (dissolved in about 
10 g of the distillate returning from the reflux condenser). Heating was 
thereafter maintained at reflux temperature for a further 30 minutes, and 
alcohol was finally removed by distillation to give a stable latex of 54% 
solids content. The disperse polymer had the composition methyl 
methacrylate 51%, butyl acrylate 40.5%, N-butoxymethylacrylamide 6% and 
methacrylic acid 2.5%; it had a molecular weight of about 140,000 and a Tg 
of 10.degree. C. The disperse phase particles ranged in size from 0.1 to 
1.0 micron. The stabiliser precursor used in this preparation was the 
methacrylic acid ester of the monomethylether of polyethylene glycol, 
mol.wt. 2000, prepared by the action of methacrylyl chloride upon the 
hydroxy compound in the presence of a hydrogen chloride acceptor. The 
proportion of the precursor used was 5.5% of the non-volatile content of 
the latex. 
EXAMPLE 2 
Preparation of latex of thermosetting-type polymer having a theoretical Tg 
of 14.degree. C., in 40:60 water/ethanol mixture under reflux 
To a flask fitted as described in Example 1 there was charged: 
______________________________________ 
Charge A 
______________________________________ 
Distilled water 330 g 
Ethanol 480 g 
______________________________________ 
followed by: 
______________________________________ 
Charge B 
______________________________________ 
Styrene 15 g 
Methyl methacrylate 11 g 
Butyl methacrylate 14 g 
2-Ethylhexyl acrylate 12 g 
Stabiliser precursor 3.5 g 
(as described below) 
Azodiisobutyronitrile 1 g 
______________________________________ 
The contents of the flask were heated at reflux temperature (76.degree. C.) 
for 30 minutes to form a seed polymer dispersion. There was then added a 
further 15 g of the stabiliser precursor (Charge C). Immediately after 
this there was begun the dropwise feeding, over a period of 2 hours and 
into the returning distillate, of the following mixture: 
______________________________________ 
Charge D 
______________________________________ 
Styrene 74 g 
Methyl methacrylate 53 g 
Butyl methacrylate 74 g 
2-Ethylhexyl acrylate 63 g 
2-Hydroxypropyl methacrylate 
32 g 
Stabiliser precursor 4.5 g 
(as described below) 
Azodiisobutyronitrile 6 g 
______________________________________ 
This was followed by a dropwise feed over a similar period of time of an 
exactly similar mixture except for omission of the stabiliser precursor 
(Charge E). Finally, 30 minutes after completion of this last addition, a 
further lg of azodiisobutyronitrile (Charge F) was introduced and the 
mixture maintained at reflux temperature for 1 hour more. The product was 
then strippd of alcohol by distillation to give a stable latex of solids 
content 54%. 
The disperse polymer had the composition styrene 25%, methyl methacrylate 
18%, butyl methacrylate 25%, 2-ethylhexyl acrylate 22% and 2-hydroxypropyl 
methacrylate 10%; and a theoretical Tg of 14.degree. C. The particle size 
range of the disperse phase was 0.1-1.0 micron. The stabiliser precursor 
used in this preparation was the methacrylic acid ester of the monomethyl 
ether of polyethylene glycol, mol.wt. 2200, and the proportion of 
precursor used amounted to 3.4% of the non-volatile content of the latex. 
EXAMPLE 3 
Preparation of latex of thermoplastic-type polymer of Tg 4.degree. C., in a 
39:61 mixture of water and methanol under reflux 
The procedure of Example 1 was repeated, but substituting for the Charges 
A-E there described the following: 
______________________________________ 
Charge A 
Distilled water 315 g 
Methanol 500 g 
Charge B 
Methyl Methacrylate 25 g 
Butyl acrylate 25 g 
Stabiliser precursor (as 
described below) 18 g 
Asodiisobutyronitrile 
1 g 
Charge C 
Methyl methacrylate 206 g 
Butyl acrylate 206 g 
Stabiliser precursor (as 
described below) 10 g 
Azodiisobutyronitrile 
6.7 g 
Charge D 
Methyl methacrylate 44 g 
Butyl acrylate 44 g 
Azodiisobutyronitrile 
1.3 g 
Charge E 
Azodiisobutyronitrile 
0.8 g 
______________________________________ 
There was thus obtained a stable, 41% solids latex of a 50:50 methyl 
methacrylate/butyl acrylate copolymer having a Tg of 3.degree. C. The 
solids content could be raised without adversely affecting the stability 
of the latex by removing alcohol by distillation. The stabiliser precursor 
used in this procedure was the methacrylic acid ester of the monomethyl 
ether of polyethylene glycol, mol.wt. 2000 and the proportion used 
amounted to 4.8% of the non-volatile content of the latex. 
EXAMPLE 4 
Preparation of a latex of a thermoplastic polymer having a Tg of 41.degree. 
C., in a 52:48 water/ethanol mixture under reflux. 
The procedure described in Example 2 was repeated, but substituting for the 
Charges A-E there described the following: 
______________________________________ 
Charge A 
Distilled water 420 g 
Ethanol 390 g 
Charge B 
Methyl methacrylate 40 g 
2-Ethylhexyl acrylate 
10 g 
Stabiliser precursor(as 
described below) 7 g 
Azodiisobutyronitrile 
1 g 
Charge C 
Stabiliser precursor(as 
described below) 23 g 
Charge D 
Methyl methacrylate 320 g 
2-Ethylhexyl acrylate 
80 g 
Stabiliser precursor(as 
described below) 14 g 
Azodiisobutyronitrile 
8 g 
Charge E 
Methyl methacrylate 160 g 
2-Ethylhexyl acrylate 
40 g 
Azodiisobutyronitrile 
4 g 
Charge F 
Azodiisobutyronitrile 
1 g 
______________________________________ 
The reflux temperature of the aqueous medium was 80.degree. C. 
The product was a stable, 46% solids latex of a 80:20 copolymer of methyl 
methacrylate and 2-ethylhexyl acrylate, having a theoretical Tg value of 
41.degree. C. The stabiliser precursor used was the same as that described 
in Example 1 and the proportion used was 6.3% based on the non-volatile 
content of the latex. 
EXAMPLE 5 
Preparation of a latex of a thermosetting-type polymer of Tg 14.degree. C., 
in an 51:26:23 mixture of water/methanol/ethanol under reflux. 
To a flask fitted as described in Example 1 there was charged: 
______________________________________ 
Charge A 
Distilled water 320 g 
Methanol 165 g 
Ethanol 140 g 
followed by 
Charge B 
Methyl methacrylate 25 g 
Ethyl acrylate 28 g 
Butyl acrylate 5 g 
Stabiliser precursor (as 
described below) 18.4 g 
Azodiisobutyronitrile 
1.3 g 
______________________________________ 
The contents of the flask were heated at reflux temperature (77.degree. C.) 
for 30 minutes, to form a seed polymer dispersion. There was then 
commenced the dropwise feeding, over a period of 4 hours and into the 
returning distillate, of the following mixture: 
______________________________________ 
Charge C 
______________________________________ 
Methyl methacrylate 225 g 
Ethyl acrylate 244 g 
Butyl acrylate 43 g 
2-Hydroxypropyl methacrylate 
33.5 g 
N-Butoxymethylacrylamide 
56 g 
(60% solution in 3:1 
butanol/xylene) 
Stabiliser precursor (as 
14 g 
described below) 
Azodiisobutyronitrile 8.5 g 
______________________________________ 
When addition of Charge C was complete, the reflux temperature was 
maintained for 30 minutes, then a further 1 g of azodiisobutyronitrile 
(Charge D) was added and the same temperature maintained for a further 1 
hour. Alcohols were then removed from the batch by distillation, to give a 
stable, 50.5% solids latex of a polymer having the composition methyl 
methacrylate 39%, ethyl acrylate 43%, butyl acrylate 8%, 
N-butoxymethylacrylamide 5% and 2-hydroxypropyl methacrylate 5%, with a 
theoretical Tg value of 14.degree. C. The particle size range of the 
disperse phase was 0.1-1.7 microns. The stabiliser precursor used in this 
preparation was the product of reacting 1 mole of polyethylene glycol, 
mol.wt. 4000 with 2 moles of methacrylyl chloride, and the amount used was 
4.8% based on the non-volatile content of the latex. 
EXAMPLE 6 
Preparation of latex of a thermoplastic-type homopolymer of Tg -22.degree. 
C., in a 51:26:23 mixture of water/methanol/ethanol under reflux. 
The procedure described in Example 5 was repeated, but substituting for 
Charges A-D there described the following: 
______________________________________ 
Charge A 
Distilled water 320 g 
Methanol 165 g 
Ethanol 140 g 
Charge B 
Ethyl acrylate 58 g 
Stabiliser precursor (as 
20 g 
described below) 
Azodiisobutyronitrile 
1.3 g 
Charge C 
Ethyl acrylate 579 g 
Stabiliser precursor (as 
14 g 
described below) 
Azodiisobutyronitrile 
8.5 g 
Charge D 
Azodiisobutyronitrile 
1 g 
______________________________________ 
The product was a stable, 51.5% solids latex of ethyl acrylate homopolymer 
having a theoretical Tg of -22.degree. C. The stabiliser precursor used in 
this preparation was the product of successively reacting the monomethyl 
ether of polyethylene glycol mol.wt. 2000 (1 mole) with succinic anhydride 
(1 mole) and then with glycidyl methacrylate (1 mole) as described in our 
co-pending application Ser. No. 101,265, file Dec. 7, 1979. The amount of 
the precursor used was 5% based on the non-volatile content of the latex. 
EXAMPLE 7 
Preparation of a latex of a thermosetting-type polymer of Tg 6.degree. C., 
in a 39:39:22 mixture of water/methanol/ethanol under reflux 
The procedure of Example 1 was repeated, but substituting for Charges A-E 
there described the following: 
______________________________________ 
Charge A 
Distilled water 315 g 
Methanol 315 g 
Ethanol 185 g 
Charge B 
Styrene 14 g 
Methyl methacrylate 13 g 
Butyl acrylate 23 g 
Stabiliser presursor (as 
13 g 
described below) 
Azodiisobutyronitrile 1 g 
Charge C 
Styrene 110 g 
Methyl methacrylate 102 g 
Butyl acrylate 178 g 
N-Butoxymethylacrylamide 
39 g 
(60% solution in 3:1 
butanol/xylene) 
Methacrylic acid 4.5 g 
Stabiliser presursor 6.5 g 
Azodiisobutyronitrile 6 g 
Charge D 
Styrene 22 g 
Methyl methacrylate 20 g 
Butyl acrylate 35 g 
N-Butoxymethylacrylamide 
7 g 
(60% solution in 3:1 
butanol/xylene) 
Methacrylic acid 1 g 
Azodiisobutyronitrile 1.3 g 
Charge E 
Azodiisobytyronitrile 1 g 
______________________________________ 
The reflux temperature of the aqueous medium was 76.degree. C. The product 
was a stable, 40% solids content latex of a polymer having the composition 
styrene 26%, methyl methacrylate 25%, butyl acrylate 43%, 
N-butoxymethylacrylamide 5% and methacrylic acid 1%, and having a 
theoretical Tg value of 6.degree. C. The stabiliser precursor used in this 
preparation was the same as that employed in Example 1 and was used in an 
amount of 3.4% based on the non-volatile content of the latex. The 
particle size range of the disperse phase was 0.1-2 microns. 
EXAMPLE 8 
The procedure of Example 7 was repeated, but replacing the stabiliser 
precursor there referred to by an equal weight of the maleic acid 
half-ester of the monomethyl ether of polyethylene glycol, mol. wt. 2000. 
The product was again a stable polymer latex, but with a somewhat coarser 
particle size range, namely 0.5-6 microns. 
EXAMPLE 9 
Preparation of a latex of a thermosetting-type polymer of Tg 10.degree. C., 
in a 39:61 mixture of water and methanol 
The procedure of Example 1 was repeated, but substituting for Charges A-E 
there described the following: 
______________________________________ 
Charge A 
Distilled water 315 g 
Methanol 500 g 
Charge B 
Methyl methacrylate 26 g 
Butyl acrylate 24 g 
Stabiliser precursor (as 
20 g 
described below) 
Azodiisobutyronitrile 1 g 
Charge C 
Methyl methacrylate 210 g 
Butyl acrylate 165 g 
N-Butoxymethylacrylamide 
44 g 
(60% solution in 3:1 
butanol/xylene) 
Methacrylic acid 11 g 
Stabiliser precursor (as 
18 g 
described below) 
Azodiisobutyronitrile 6.7 g 
Charge D 
Methyl methacrylate 45 g 
Butyl acrylate 34 g 
N-butoxymethylacrylamide 
11 g 
(60% solution in 3:1 
butanol/xylene) 
Methacrylic acid 2.7 g 
Azodiisobutyronitrile 1.3 g 
Charge E 
Azodiisobutyronitrile 0.8 g 
______________________________________ 
The product was a 41% solids stable latex of a polymer having the same 
composition and characteristics as that of Example 1. The stabiliser 
precursor used in this preparation was the glycidyl methacrylate adduct of 
a carboxyl group-terminated polyvinylpyrrolidone of mol.wt. 30,000, made 
by polymerising vinylpyrrolidone in water in the presence of 
4,4-azobis(4-cyanovaleric acid) as initiator and thioglycollic acid as 
chain transfer agent. The amount of the stabiliser precursor used was 6.5% 
based on the non-volatile content of the latex. 
EXAMPLE 10 
Preparation of latex of thermosetting-type polymer of Tg 18.degree. C., in 
50:50 water/2-methoxyethanol, not under reflux conditions 
To a 500-ml flask fitted with stirrer, thermometer, dropping funnel and 
inert gas feed, there was charged: 
______________________________________ 
Distilled water 80 g 
2-Methoxyethanol 80 g 
______________________________________ 
The charge was heated to 85.degree.-90.degree. C. and the following mixture 
was then added dropwise over a period of 3 hours: 
______________________________________ 
Styrene 75 g 
Ethyl acrylate 75 g 
Butyl acrylate 15 g 
2-Hydroxypropylmethacrylate 
18 g 
Stabiliser precursor 29 g 
Azodiisobutyronitrile 3 g 
______________________________________ 
When the addition was complete, the temperature was maintained at 
85.degree.-90.degree. C. for 30 minutes, then a further 0.3 g of 
azodiisobutyronitrile was added and heating continued at the same 
temperature for 1 hour more. The product was a stable, 57% solids latex of 
a polymer having the composition styrene 41%, ethyl acrylate 41%, butyl 
acrylate 8% and 2-hydroxypropyl methacrylate 10%, and having a theoretical 
Tg value of 18.degree. C. The particle size range was 0.1-1 micron. The 
stabiliser precursor used in this preparation was the same as that 
described in Example 6 and was employed in an amount of 13.7% based on the 
non-volatile content of the latex. 
EXAMPLE 11 
Preparation of latex of plasticised polymethyl methacrylate in 50:25:25 
water/methanol/ethanol mixture under reflux 
The procedure described in Example 5 was repeated, but substituting for 
Charges A-D there described the following: 
______________________________________ 
Charge A 
Distilled water 247 g 
Methanol 127 g 
Ethanol 127 g 
Charge B 
Methyl methacrylate 27 g 
Polyester plasticiser (as 
17 g 
described below) 
Stabiliser presursor (as 
15 g 
described below) 
Azodiisobutyronitrile 
1 g 
Charge C 
Methyl methacrylate 271 g 
Polyester plasticiser (as 
171 g 
described below) 
Stabiliser precursor (as 
11 g 
described below) 
Azodiisobutyronitrile 
6 g 
Charge D 
Azodiisobutyronitrile 
1 g 
______________________________________ 
The refluxing temperature of the water/methanol/ethanol mixture was 
76.degree. C. The product was a stable, 50% solids latex of polymethyl 
methacrylate/polyester plasticiser in the ratio 60:40, having a Tg of 
55.degree. C. as compared with a Tg of 105.degree. C. for unplasticised 
polymethyl methacrylate. The polyester plasticiser used was the product of 
condensing together neopentyl glycol (0.67 mole), adipic acid (1 mole) and 
benzyl alcohol (0.67 mole). The stabiliser precursor used was the same as 
that employed in Example 1, and was present in an amount of 5.5% based on 
the non-volatile content of the latex. 
Comparative Example A 
Attempted preparation of unplasticised polymethyl methacrylate 
The procedure of Example 11 was repeated, but omitting the polyester 
plasticiser. The latex produced during the early stages of addition of 
Charge C was much coarser than that of Example 11, and the disperse phase 
completely flocculated when addition had proceeded to a stage 
corresponding to a latex non-volatile content of about 15%. 
EXAMPLE 12 
Use of a chain transfer agent soluble in the aqueous medium 
The product of Example 5 was repeated, with the addition of 0.6 g of 
thioglycollic acid to Charge B and of 6 g of the same substance to Charge 
C (amounting in total to 1% of the monomers being polymerised). 
The product was a stable latex of somewhat coarser particle size than that 
of Example 5, namely 0.5-8 microns; thus the maximum particle size was 
increased by the use of the chain transfer agent. 
Comparative Examples B and C 
The procedure of Example 5 was repeated, but replacing the bis(methacrylic 
ester) of polyethylene glycol, mol.wt. 4000 that was there used as the 
stabiliser precursor by a similar amount of the analogous bis-ester of 
polyethylene glycol, mol.wt. 1000. 
The resulting latex was very coarse during the early stages of 
polymerisation of the monomers and the disperse phase became unstable, 
depositing on the walls of the flask and on the stirrer, when a 
non-volatile content of about 15% had been reached. 
A similar result was obtained when the original stabiliser precursor of 
Example 5 was replaced by the methacrylic acid ester of polyethylene 
glycol, mol.wt. 750. 
EXAMPLES 13-14 
The procedure of Example 5 was repeated, using as initiator, in place of 
azodiisobutyronitrile, equal amounts of 4,4-azobis(4-cyanovaleric acid) or 
lauroyl peroxide, respectively. 
Similar results to those of Example 5 were obtained. The azo initiator led 
to the production of a slightly finer particle size range than was 
recorded in that Example, namely 0.1-1 micron, while the peroxy initiator 
gave a somewhat coarser range, namely 0.3-4 microns. 
EXAMPLE 15 
Preparation of latex of thermosetting-type polymer modified by a reactive 
silicon compound 
To a 2-liter flask fitted as described in Example 1 there was charged the 
following: 
______________________________________ 
Charge A 
______________________________________ 
Distilled water 215 g 
Methanol 112 g 
Ethanol 95 g 
______________________________________ 
To this was added the following mixture: 
______________________________________ 
Charge B 
______________________________________ 
Methyl methacrylate 12 g 
Butyl methacrylate 5 g 
Ethyl acrylate 12 g 
Butyl acrylate 4 g 
Stabiliser precursor (as 
8 g 
described in Example 1) 
Azodiisobutyronitrile 
0.9 g 
______________________________________ 
and the batch was heated for 30 minutes at reflux temperature (76.degree. 
C.) to form a seed dispersion of polymer. There was then begun the 
dropwise addition, into the returning distillate, of the following 
mixture: 
______________________________________ 
Charge C 
______________________________________ 
Methyl methacrylate 112 g 
Butyl methacrylate 51 g 
Ethyl acrylate 112 g 
Butyl acrylate 48 g 
2-Hydroxypropyl methacrylate 
21 g 
N-butoxymethylacrylamide 
24 g 
(60% solution in 3:1 
butanol/xylene) 
Stabiliser precursor (as 
10 g 
described in Example 1) 
Azodiisobutyronitrile 5 g 
______________________________________ 
Three-quarters of Charge C was added over a period of 4 hours: there was 
then added to the remaining one-quarter of Charge C the following Charge 
D, and the mixture was fed dropwise into the returning distillate over a 
period of 11/2 hours: 
______________________________________ 
Charge D 
______________________________________ 
Silicone intermidiate QP8-5314 
180 g 
(ex. Dow Corning Inc.) 
N-Butoxymethylacrylamide 
12 g 
(60% solution as above) 
______________________________________ 
After this last addition was completed, the batch was heated at reflux 
temperature for a further 30 minutes, after which there was added (Charge 
E) 1 g of azodiisobutyronitrile. Following a final period of 1 hour at 
reflux temperature, the batch was vacuum stripped to give a 58% solids 
stable dispersion of polymer having the composition methyl methacrylate 
31%, butyl methacrylate 14%, ethyl acrylate 31%, butyl acrylate 13%, 
2-hydroxypropyl methacrylate 5.5% and N-butoxymethylacrylamide 5.5%, the 
polymer being modified to the extent of 20% by reaction of the silicone 
intermediate with the hydroxyl groups present. The Tg of the acrylic 
polymer was 7.degree. C. 
EXAMPLE 16 
Preparation of latex of thermosetting-type polymer containing an amino 
resin as cross-linking agent 
To a 1-liter flask fitted with stirrer, thermometer, condenser, dropping 
funnel and inert gas feed, there was charged: 
______________________________________ 
Charge A 
______________________________________ 
Distilled water 40 g 
Diethylene glycol 34 g 
Tetraethylene glycol 7 g 
Methylated melamine/ 54 g 
formaldehyde resin 
("Cymel" 301* ex. Cyanamid) 
______________________________________ 
*"Cymel" is a Registered Trade Mark. 
The contents of the flask were heated to 90.degree. C. and there was then 
added dropwise, over a period of 3 hours, the following: 
______________________________________ 
Charge B 
______________________________________ 
Styrene 95 g 
Ethyl acrylate 50 g 
2-Ethylhexyl acrylate 15 g 
2-Hydroxyisopropyl 
methacrylate 16 g 
Ethanol 25 g 
Stabiliser precursor (as 
described below) 25 g 
Azodiisobutyronitrile 3.3 g 
______________________________________ 
The batch was heated at 90.degree. C. for 30 minutes after this addition 
was completed and there was then added (Charge C) 0.5 g of 
azodiisobutyronitrile. Finally, heating was continued for a further 1 hour 
at the same temperature. The product was a stable, 72% solids latex of 
polymer having the composition styrene 54%, ethyl acrylate 28%, 
2-ethylhexyl acrylate 9% and 2-hydroxyisopropyl methacrylate 9%. The 
theoretical Tg of the polymer was 26.degree. C. The stabiliser precursor 
used in this preparation was the same as that described in Example 1 and 
was present in an amount of 11.6% based on the non-volatile content of the 
latex. 
Comparative Example D 
Attempted preparation of latex, using peroxide initiator, at a 
polymerisation temperature less than 10.degree. above the Tg of the 
polymer in 39:61 water/methanol 
An attempt was made to repeat the procedure of Example 1, but with the 
Charges A-E there described replaced by the following charges, and 
operating under reduced pressure so that the temperature of reflux was 
50.degree. C. only: 
______________________________________ 
Charge A 
Distilled water 245 g 
Methanol 389 g 
Stabiliser precursor (as 
14.7 g 
described below) 
Charge B 
Methyl methacrylate 28.3 g 
Butyl acrylate 10.4 g 
Bis(4-t-buytlcyclohexyl- 
0.7 g 
peroxydicarbonate) 
Charge C 
Methyl methacrylate 234 g 
Butyl acrylate 86.4 g 
Stabiliser precursor (as 
12.4 g 
described below) 
Bis(4-t-butylcyclohexyl- 
5.0 g 
peroxydicarbonate) 
Charge D 
Methyl methacrylate 50.3 g 
Butyl acrylate 18.5 g 
Bis(4-t-butylcyclohexyl)- 
1 g 
peroxydicarbonate 
Charge E 
Bis(4-t-butylcyclohexyl)- 
peroxydicarbonate 0.62 g 
______________________________________ 
Charges A and B heated together to 55.degree. C., and vacuum was then 
applied to the system so as to achieve a reflux temperature of 50.degree. 
C. This temperature was held for 30 minutes in order to form a seed 
dispersion, after which Charge C was slowly fed in. The experiment was 
abandoned after this feed has been continued for only 30 minutes; the 
dispersion had an unsatisfactory appearance from the beginning and by the 
end of this period a thick mass of polymer had separated out from the 
aqueous medium. 
The composition of the polymer which it was attempted to prepare was methyl 
methacrylate 73%, butyl acrylate 27%, the theoretical Tg of this polymer 
was 43.degree. C. 
The stabiliser precursor used in this experiment was the methacrylic acid 
ester of the monomethyl ether of polyethylene glycol, mol.wt. 1600. 
Comparative Example E 
Attempted preparation of latex, using azo initiator, at a polymerisation 
temperature less than 10.degree. above the Tg of the polymer, in 39:61 
water/methanol 
An attempt was made to repeat the procedure of Example 1, but with the 
Charges A-E there described replaced by the following charges, and 
operating under reduced pressure so that the temperature of reflux was 
55.degree. C. only: 
______________________________________ 
Charge A 
Distilled water 245 g 
Methanol 389 g 
Stabiliser precursor (as 
described in Comparative 
Example D) 14.7 g 
Charge B 
Methyl methacrylate 29.3 g 
Butyl acrylate 9.7 g 
2,2-azobis(2,4-dimethyl- 
valeronitrile) 0.7 g 
Charge C 
Methyl methacrylate 240.6 g 
Butyl acrylate 79.8 g 
Stabiliser precursor (as 
12.4 g 
described in Comparative 
Example D) 
2,2-azobis(2,4-dimethyl- 
5.0 g 
valeronitrile) 
Charge D 
Methyl methacrylate 51.5 g 
Butyl acrylate 17 g 
2,2-azobis(2,4-dimethyl- 
1.0 g 
valeronitrile) 
Charge E 
2,2-azobis(2,4-dimethyl- 
0.62 g 
valeronitrile) 
______________________________________ 
Charges A and B were heated together to 60.degree. C., and vacuum was then 
applied to the system so as to achieve a reflux temperature of 
54.degree.-55.degree. C. This temperature was held for 30 minutes in order 
to form a seed dispersion, after which Charge C was slowly fed in over a 
period of 3 hours. The initial seed dispersion appeared to be of good 
quality, but as the feeding in of Charge C progressed, "bits" were seen to 
form and by the end of the feed these had aggregated to form large lumps 
of polymer. The experiment was then abandoned. 
The composition of the polymer which it was attempted to prepare was methyl 
methacrylate 75%, butyl acrylate 25%; the theoretical Tg of this polymer 
was 46.degree. C. 
EXAMPLE 17 
This Example illustrates the preparation of a water-borne, medium-gloss 
non-crosslinking acrylic primer coating composition from one of the 
latices described above. 
A. Preparation of Polymer Latex 
A latex was prepared, by the method generally described in Example 7, of a 
copolymer having the composition styrene/methyl methacrylate/butyl 
acrylate/N-Butoxymethylacrylamide/methacrylic acid 26/25/43/5/1, the latex 
having a non-volatile content of 46.8%. 
B. Preparation of Pigment Millbase 
A mixture of titanium dioxide (44 g: "Kronos" RN 45 (Registered Trade 
Mark), strontium chromate (18.5 g), blanc fixe (76.5 g), china clay (45 g: 
Grade D) and the polymer latex described in (A) above (304 g) was ground 
overnight in quater-gallon capacity ball mill using 1050 g of quarter-inch 
steatite balls. 
C. Preparation and Application of Paint Composition 
The millbase prepared as in (B) above (488 parts) was blended with a 
further 200 parts of the latex prepared as in (A). The primer paint so 
obtained was applied to panels of hot-dip galvanised steel pretreated with 
"Bonderite" 1303 (Registered Trade Mark) by means of a wire-wound 
applicator bar so as to give a dry film thickness of 5 microns. The 
coating was stoved in an oven for less than 1 minute so as to attain a 
metal peak temperature of 193.degree.-199.degree. C.; there was then 
applied over the coating a commercially available ionically stabilised 
water-borne acrylic top-coat. When subjected to the humidity test of B.S. 
3900, the performance of the panels after 500 hours was equal to that of 
similar panels prepared with a non-aqueous epoxy primer which is in wide 
commercial use. In the salt spray test of A.S.T.M. B117-64, a similar 
results was obtained. 
EXAMPLE 18 
This Example illustrates the preparation of a high gloss paint from one of 
the polymer latices described above. 
A. Preparation of Polymer Latices 
Two latices were prepared by the general method described in Example 2, 
Latex (i) had the polymer composition styrene 39.7%, ethyl acrylate 53.2%, 
N-butoxymethylacrylamide 5.9% and methacrylic acid 1.2%, and a solids 
content of 44%. Latex (ii) had the polymer composition styrene 25.1%, 
ethyl acrylate 67.7%, N-butoxymethylacrylamide 5.9% and methacrylic acid 
1.2%, and a solids content of 46.9%. 
B. Preparation of Millbase 
A mixture of 135 g of titanium dioxide pigment ("Runa" RH 472: Registered 
Trade Mark of Laporte Industries Limited) and 302 g of the polymer latex 
described in (A) was ground for 24 hours in a quarter-gallon ball mill 
with a charge of 1050 g of quarter-inch steatite balls. A fluid dispersion 
was obtained having a particle size of less than 5 microns as measured on 
a Hegman gauge. There was incorporated into this millbase 6.6% by weight 
of a water-miscible hexamethoxymethylmelamine. 
C. Preparation and Application of Paint 
The blend of millbase and melamine-formaldehyde resin as prepared in (B) 
(13.5 parts) was mixed with the latex (ii) described above (18 parts). The 
paint so obtained was catalysed by addition of 0.08 part of p-toluene 
sulphonic acid and was then applied to pretreated aluminium by means of a 
wire-wound applicator bar and stoved in an oven for less than 1 minute so 
as to attain a metal peak temperature of 193.degree.-199.degree. C. The 
coating which resulted had the following excellent characteristics: 
______________________________________ 
Gloss (60.degree. meter) 88% 
Hardness (pencil test) H 
Reverse Impact (lb/sq.in) 
80 
Bend Test 1T 
______________________________________ 
EXAMPLE 19 
This Example illustrates the preparation of an unpigmented finish suitable 
for spray application to an automobile body previously treated with a 
pigmented basecoat. 
A. Preparation of Polymer Latex 
A latex was prepared, according to the general method described in Example 
2, of a polymer having the composition styrene 25%, methyl methacrylate 
18%, butyl methacrylate 24%, 2-ethylhexyl acrylate 21%, hydroxyisopropyl 
methacrylate 10% and dimethylaminoethyl methacrylate 2%; the latex had a 
solids content of 52%. 
B. Preparation of Paint 
The latex described in (A) (164 parts), a melamine-formaldehyde resin 
("Beetle" BE 670) (12.5 parts) and water (40 parts) were mixed and 
p-toluene sulphonic acid (1 part) was added. The finish so obtained, which 
had a viscosity of 33 secs. (B.S. B3 cup at 25.degree. C.) and a solids 
content of 45%, was sprayed on to an automobile panel, already coated with 
a basecoat, using a Binks 19 spray gun with suction feed and 65 p.s.i. air 
pressure. The film produced on the substrate was free from sagging and 
other defects. It was dried at room temperature for 1 hour, baked for 30 
minutes at 80.degree. C. and then for a further 30 minutes at 150.degree. 
C. The film had a thickness of 50 microns, a gloss of 90% (20.degree. 
meter) and a Knoop hardness of 6.4-7.4. It was free from defects. 
EXAMPLE 20 
This Example illustrates the preparation of a finish which is capable of 
being cured at moderate temperatures and which is therefore suitable for 
applications in the Industrial market. 
A latex was prepared by the general method of Example 5 of a polymer having 
the composition methyl methacrylate 39.2%, ethyl acrylate 42.7%, butyl 
acrylate 7.5%, hydroxyisopropyl methacrylate 5.3% and 
N-butoxymethylacrylamide 5.3%; the latex had a solids content of 50.1%. 
This latex (14.8 parts) was blended with a melamine-formaldehyde resin 
("Beetle" BE 670) (0.5 part) and the blend was catalysed by the addition 
of 0.05 part of p-toluene sulphonic acid: 
The paint thus obtained was applied by wire-wound applicator bar to 
aluminium panels, which were then subjected to various curing schedules as 
shown in the table below: the degree of cure achieved in each case was 
then determined by measuring the percentage by weight of the film which 
remained undissolved after extraction with boiling acetone for 2 hours in 
a Soxhlet apparatus. 
______________________________________ 
Curing Schedule % Cure 
______________________________________ 
30 mins. at 150.degree. C. 
97 
30 mins. at 120.degree. C. 
99.2 
30 mins. at 100.degree. C. 
96.6 
30 mins. at 80.degree. C. 
92.8 
10 mins. at 150.degree. C. 
95.6 
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