Note: Descriptions are shown in the official language in which they were submitted.
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MANUFACTURE OF POLYMER DISPERSIO~S A~DCOATING COMPOSITIONS DERIVED FROM THEM.
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 polymer-
isation processes, a characteristic of which is that
,, ,., ,, - .
~.~6~S
-- 2
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 mainten-
ance 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. m is second
type of polymer dispersion is most frequently obtained
by means of a so-called non-aqueous dispersion poly-
merisation 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 cansequence becomes anchored thereto.
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A full treatment of the subject of non-aqueous
dispersions is to be found in "Dispersion Polymer-
isation 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 commer-
cial 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 composit-
ions, since the use of water as a carrying liquidavoids 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 fcund extensive use in the formul-
ation of coating compositions, but they neverthelessfall short of being wholly satisfactory for that
purpose. Although, in these dispersions, some measure
of steric stabilisation ce 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-soluble surfact-
ants 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
~1 t ;'~S
-- 4 --
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.
Accoraing 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 10C higher than the glass transit-
ion temperature as hereinafter defined of the polymer
which is formed, in the presence in the aqueous
medium as steric stabiliser of a block or graft co-
polymer which contains in the molecule a polymeric
component of one type which is solvatable by the
aqueous medium and a polymeric component of another
type which is not solvatable by the aqueous medium
and is capable of becoming associated with the polymer
particles formed, the aqueous medium being a mixture
comprising (a) at least 300~0 by weight of water and
(b) not more than 70/0 by weight of a second constit-
uent which is miscible with water, the nature and
.r-;~G~S
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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 through-
out 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 2~h 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 plast-
iciser for the polymer is not added as such, the
"environmental" Tg of the polymer under the conditions
obtained during polymerisation may be somewhat lower
than the bulk Tg value referred ~o above, owing to
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some plasticisation of the polymer by residual
monomer or other constituents of the polymerisation
mixture. m us it may be possible in practice 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 a~d
error, it is more convenient under these conditions
to choose the temperature of polymerisation by refer- -
ence to the bulk Tg value. The Tg of a bulk polymer,
or of a deliberately 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 approp-
riate. ~lternati~ely, Tg values can be calculated,from a knowledge of the monomer composition of the
polymer, by ~nown 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 co-
polymer, 4 C; for a 80:20 methyl methacrylate/2-ethyl-
hexyl acrylate copolymer, 41C; for a homopolymer of
ethyl acrylate, -22 C; for a homopolymer of methyl
methacrylate plasticised in the ratio 60:40 with a
neopentyl glycol/butyl alcohol adipate poiyester plast-
iciser, 55 C. Any of these polymer compositions can
be successfully prepared in the form of an aqueous
-- 7
latex by the process of the invention at the polymer-
isation temperatures in the range 70-90C 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,
~utyl methacrylate, lauryl methacrylate, ethyl acryl-
ate, butyl acrylate, hexyl acrylate, n-octylacrylate,
2-ethylhexyl acrylate, nonyl acrylate, lauryl acryl-
ate and cetostearyl acrylate, the hydroxyalkyl esters
of the same acids such as 2-hydroxyethyl acrylate,
2-hydroxyethyl methacrylate and 2-hydroxypropyl meth-
acrylate, 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. ~et other comonomers which may.~e:used in
conjunction with any of the foregoing.monome~s include
dialkyl maleates, dialkyl itacona.tes, dialkyl methyl-
ene-malonates, i~oprene and ~utadiene.
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
S
-- 8 --
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.
S Preferably, the temperature of polymeris-
ation of the monomer or monomers is at least 20 C,
more preferably at least 30C, higher than the glass
transition temperature of the polymer which is formed.
In general, polymerisation temperatures in the range
30-80C 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 disper-
sion, 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 propor-
tion 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 -
90C, 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
OI water.
In practice, there may be some interaction
between these variables; for example, the freedom of
g
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 constit-
uent 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 constit-
uent of the aqueous medium is sufficiently volatila to
permit refluxing at the polymerisation temperature,
that constituent can usually, if desired, be stripped
off by distillation when polymerisation is complete.
~n contrast, a water-misci~le 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 ~lways be the major
S
-- 10 --
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 polymer-
isation mixture which it is desired to màintain 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 constit-
ute 30-7~/0 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. ~thanol is
somewhat less preferred than methanol because its
greater effectiveness as a chain terminator in the
polymerisation process may ma~e it difficult to
obtain a disperse polymer of high molecular weight,
S
and also because it is a more active solvent for
many polymers than is methanol. ~evertheless, 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, bu~anol, 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 ths 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 60C.
Steric stabilisation of the polymer particles
produced in the process is achieved by the presence in
the polymerisation mixture of the block or graft co-
~5 polymer. As already stated, this copolymer containsin the molecule one type of polymeric component which
is solvatable by the aqueous medium; by "solvatable"
we mean that, if that component were an independent
molecule rather than part of the graft copolymer, it
would actually be soluble in that medium. By virtue
of this solvatable character, the polymer chains of
this component consequently adopt an extended config-
uration in that medium so as to form a steric barrier
~l'``'~ti~S
- 12 -
around the particles. ~he copolymer also contains
another type of polymeric component which is not
solvatable by the aqueous medium and is capable of
becoming associated with the polymer particles. the
steric barrier being thereby anchored to the surface
of the particles.
~ he block or graft copolymer stabiliser may
be introduced into the polymerisation mixture in a
number of different ways. Firstly, i~ may be introduced
as a fully pre-formed material, prepared in a separate
operation. Secondly, it may be formed in situ during
the polymerisation by introducing into the reaction
miXture, before polymerisation begins, a "stabiliser
precursor" compound comprising in its molecule a poly-
meric component which is solvatable by the aqueousmedium and an unsaturated grouping which is capable
of copolymerising with the monomer or monomers being
polymerised. Thirdly, it may be formed, again in situ,
by introducing into the reaction mixture before poly-
merisation begins a simple polymer of molecular weightat least 1000 which is soluble in the aqueous medium
and which contains in the molecule hydrogen atoms
which are abstractable by free radicals under the
conditions of polymerisation and are in consequence
capable of promoting grafting on to the said polymer
of the monomer or monomers being polymerised.
When a pre-formed block or graft copolymer
stabiliser is employed, the solvatable polymeric com-
ponent thereof is, as stated above, derived from a
water-soluble polymer. Examples of such polymers
include non-ionic polymers such a~ the polyethylene
glycols and their monoal~yl ethers, poly(ethylene
oxide) - poly(propylene oxide) copolymers containing
6~5
- 13 -
at least 40% of ethylene oxide and their monoalkyl
ethers, polyvinylpyrrolidone, polyacrylamide, poly-
methacrylamide and polyvinyl alcohol. Preferably
the molecular weight of this component is at least
1000 and more preferably at least 2000. The preferred
solvatable components are those derived from poly-
ethylene glycols, or their monoalkyl ethers, of
molecular weight in the range 2000-4000.
The second component of the block or graft
copolymer, which is capable of associating with the
disperse particles, can in the simplest case be of
identical or similar chemical composition to the
disperse polymer itself, which by definition is
insoluble in (and therefore not solvated by) the
aqueous medium. Such a polymeric component will have
an inherent tendency to associate with the disperse
polymer. However, any polymer which satisfies the
more general requirement of non-solvatability by the
aqueous medium is suitable as the second component.
Examples of second polymeric components include
polymers and copolymers derived from methyl meth-
acrylate, ethyl acrylate, butyl acrylate, styrene,
tert-butylstyrene, vinyl toluene, vinyl acetate and
acrylonitrile; there may also be incorporated
together with one or more of these monomers a function-
al monomer such as acrylic acid, methacrylic acid,
2-hydroxyethyl methacrylate and 2-hydroxyisopropyl
methacrylate.
The pre-formed block or graft copolymer may
range in structure from simple block copolymers of
the AB, ABA or BAB types, where A and B represent the
solvatable and non-solvatable components respectively,
through multiple block copolymers of the ABABAB
6~5
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types, to "comb" type graft copolymers of the
structure AnB, in which a plurality of the solvatable
A components are attached at intervals to a polymer
backbone constituting the hydrophobic, associatable
B component. Preferably the copolymer is of this
last-mentioned, "comb" type and has a slight weight
excess of the solvatable components A over the non-
solvatable components B, for example in a ratio of
from 1.1 : l. to 2 : 1. It is also preferred that,
in this type of copolymer, the value of n, i.e. the
number of A components which are attached to each B
component, should be in the range 3-10.
The molecular weight of each solvatable A
component is, as already stated, at least 1000 and
preferably at least 2000; the molecular weight of each
non-solvated B component is preferably at least 1000.
Moreover, it is preferred that the total molecular
weight of the copolymer should be at least 5000.
The block or graft copolymer may be made
by any of the methods which are well known in the art.
Thus the solvatable component may be prepared first
and then copolymerised with the appropriate monomers
so as to give rise to the non-solvatable, associating
component in situ, or the non-solvatable component
may be prepared first and the solvatable component
then prepared in situ. Alternatively, the individual
components can both be prepared separately and then
be covalently linked to one another through the medium
of suitable mutually reactive groups. Thus, for example,
in the preparation of the preferred "comb" type graft
copolymers, a water-soluble polymer suitable as the A
component, such as the mono-methyl ether of a poly-
~26~5
5 --
ethylene glycol of molecular weight 1000 to 2000, canbe converted to the acrylic or methacrylic ester, and
this intermediate product can then be subjected to
free radical-initiated copolymerisation with other
5 unsaturated monomers such as styrene, ethyl acrylate
or methyl methacrylate, in order to build up an
appropriate non-solvatable polymer backbone constit-
uting the B component from which are pendant a
plurality of the A component side chains. Another
suitable type of addition copolymer may be made by
means of ionic polymerisation methods, for example by
preparing a "living" polystyrene block and then
reacting this with ethylene oxide in order to build
up a poly-(oxyethylene) block attached thereto.
If desired, the non-solvatable component of
the block or graft copolymer employed as stabiliser
may contain groupings which are capable of reacting
with the monomer or monomers which are being polymerised
in the process of the invention. By this means, the
stabiliser becomes covalently linked to the disperse
polymer and the stability of the latter towards
flocculation may be enhanced. Suitable reactive group-
ings include ethylenically unsaturated groupings
which can copolymerise with the monomer, or functional
groups which can react under the conditions of polymer-
isation with complementary functional groups in the
monomer, e.g. epoxide groups which can react with a
hydroxylic monomer such as 2-hydroxyethyl methacrylate.
Methods of introducing such reactive groupings into
the copolymer molecule will be apparent to those
skilled in the art; for example, in the preparation
of a "comb" type graft copolymer as outlined above,
:~ ~ ~` ~6tj5
- 16 -
the unsaturated monomers with which the intermediateacrylic or methacrylic ester of polyethylene glycol
is copolymerised may include an epoxide group-contain-
ing monomer, such as glycidyl acrylate or glycidyl
methacrylate. In this way, the non-solvatable polymer
backbone of the copolymer which is built up will be
caused to contain pendant glycidyl groups. The latter
may be utilised directly to react with a main monomer
containing a functional group, such as a hydroxyl
group, during the polymerisation process of the
invention. Alternatively, the graft copolymer contain-
ing the glycidyl groups may be reacted further with
an ethylenically unsaturated acid, such as acrylic
acid or methacrylic acid, whereby there are introduced
into the non-solvatable component of the copolymer
double bonds which can copolymerise with the main
monomer or monomers during the polymerisation process.
Where the block or graft copolym~r contains
reactive groupings as just described, it is preferred
that there should be present on average of from 1 to
20 such groupings in each copolymer molecule.
In British Specification ~o. 1,544,335
there is described a process for polymerising an
ethylenically unsaturated monomer in water in the
presence of a catalyst and also in the presence of a
block copolymer dispersion stabiliser having certain
defined characteristics. Amongst the advantages that
are stated to be achieved by this process, as compared
with other polymerisation techniques, are high polymer
solids contents of the dispersions obtained and the
avoidance of the use of any organic diluents in the
polymerisation step. It is evident, however, that the
- 17 -
process in question has in common with both conven-
tional aqueous suspension and conventional aqueous
emulsion polymerisation techniques that there is
present in the reaction mixture, for the greater
part of the process, unpolymerised monomer as a
separate, distinct liquid phase. ~otwithstanding a
general statement in the said specification that the
polymer particles of the dispersions obtained are in
the colloidal size range of 0.1 to lO microns, none
of the examples therein gives any information bearing
out this statement; on the contrary, several of those
examples indicate clearly that the particles obtained
are considerably larger than colloidal size. Thus it
is not a characteristic of the process in question
that it yields fluid dispersions of polymer in an
aqueous medium in which the particles of polymer are
of colloidal size and are ~terically stabilised
against flocculation. It may also be noted that, by
way of further distinction between the present
invention and the process described in British
Specification ~o. l,544,335, it is not essential
that the copolymer stabiliser used in the process of
the present invention should contain groupings which
are capable of reacting with the monomer or monomers
being polymerised.
The proportion of pre-formed bloc~ or graft
copolymer stabiliser which is added to the polymer-
isation 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
~s ~6S
- 18 -
found by simple experiment. However, for generalguidance it may be stated that the proportion in
question will usually lie in the range 0. 5 ~ 20%~
and more especially 2-1~/o by weight of the disperse
polymer content of the dispersion being made. Prefer-
ably, the stabiliser is introduced along with the
monomers, as explained below.
When the copolymer stabiliser is produced
in situ during the polymerisation, according to the
secvnd alternative method referred to above, from a
copolymerisable precursor compound, the precursor
employed is a water-soluble derivative of a water-
of molecular weight at least 1000
soluble polymer/which contains in the molecule an
unsaturated grouping which can copolymerise with the
monomer or monomers being polymerised.
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
has the same general characteristics as those of the
pre-formed block or graft copolymer referred to
earlier. The water-soluble polymer frDm which the
precursor is derived may be any of those polymers
which have been described above in connection with
the pre-formed bloc~ or graft copolymer. The preferred
water-soluble polymers are again the polyethylene
glycols, or their monoalkyl ethers, of molecular
weight in the range 2000-4000. In the case where the
precursor is an unsaturated derivative of a polyethyl-
ene glycol, or its monoalXyl ether, it may conven-
iently be an ester thereof with a copolymerisable
unsaturated acid, for example methacrylic acid,
Z~5
-- 19 --
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 meth-
acrylate; alternatively the glycol or its ether maybe 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 polyvinylpyrrol-
idone (see, British Specification ~o. 1,0~6,912) with
glycidyl methacrylate. Yet other suitable precursors
may be obtained by the procedure described in our
United States Patent No. 4273888 which issued June 16, 1981 that
is to say by reacting a water-soluble polyaIkylene
glycol or its monoalkyl ether with a cyclic aliphatic
carboxylic a~hydride and then reacting the resulting
half-ester with an epoxy compound containing a poly-
merisable 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 conver.ient 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.
~,
s
-- 20 ~
As in the case of the use of a pre-formed
stabiliser, the proportion of stabiliser precursor
which is added to the polymerisation mixture will
vary according to the particular circumstances, but
the optimum proportion can readily be found by
experiment. In most instances, this will lie in the
range 0.5 - 20%~ and more especially 2 - 10~ by
weight of the disperse polymer content of the disper-
sion being made. Preferably, the precursor is intro-
duced along with the monomers, as explained below.
In the third method outlined above, thecopolymer stabiliser is produced in situ by including
in the polymerisation mixture a simple polymer of
molecular weight at least 1000 which is soluble in
the aqueous medium and which contains in the molecule
atoms of hydrogen which are abstractable under the
conditions of polymerisation so as to give rise to
polymer grafting. The simple polymer may ~e either
linear or branched and either homopolymeric or co-
polymeric in nature, but it is "simple" in the sensethat all polymeric components of the molecule are
soluble in the aqueous medium (as contrasted with an
amphipathic block or graft copolymer of the kind
which acts as the actual stabilising species in the
process). In practice, any water-soluble polymer is
suitable, since all such polymers contain some
potentially abstractable hydrogen atoms, but preferred
polymers include polyvinyl pyrrolidone, polyvinyl
alcohol, hydroxyalkylcelluloses, in particular
hydroxyethyl cellulose, polyacrylamide, polymeth-
acrylamide, water-solu~le polyalkylene oxides
including poly(ethylene oxide) and random copolymers
- 21 -
of ethylene oxide with propylene oxide containing at
least 40% of ethylene oxide, and monoalkyl ethers of
such polyaLkylene oxides. Other suitable polymers
include water-soluble nitrogen resins, such as water-
soluble melamine-formaldehyde condensates. Advantage-
ously, the soluble polymer may contain in the
molecule deliberately introduced groups which are
especially susceptible to abstraction of hydrogen by
a neighbouring free radical. Such groups include
mercapto-, sec-butyl, cyanomethyl and (CH3)2 ~ CH2-
groups and examples of suitable water-soluble polymers
containing these include copolymers of vinylpyrroli-
done with minor proportions of dimethylaminoethyl
methacrylate, sec-butyl methacrylate or vinyl cyano-
~5 acetate.
As with the pre-formed copolymer stabiliser
or the copolymerisable stabiliser precursor, the
proportion of soluble simple polymer 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,
but, as before, the optimum proportion in any
individual case can readily be found by simple
experiment. Typical proportions are in the range 0.5 -
20%~ and more especially 5 - 10%~ by weight of the
disperse polymer content of the dispersion being made.
Preferably, the soluble polymer is introduced along
with the monomers, as explained below.
It may assist, in achieving a high degree
of grafting of the soluble simple polymer during the
polymerisation process, if the soluble polymer is
~15;~ 5
- 22 -
pre-activated, prior to its being introduced into
the polymerisation mixture. This may be done by
heating it, preferably dissolved in some of the
aqueous medium to be used subsequently, together with
the polymerisation initiator at a temperature in the
range 65to 120C for a period of from 5 minutes to
1 hour; the conditions chosen should, of course, be
such as not to cause the soluble polymer to undergo
significant degradation, cross-linking or other
deleterious changes.
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 catalystsor initiators well known
for use in the polymerisation of acrylic or vinyl
monomers which are soluble in the monomers. Suitable
initiators include peroxy compounds such as benzoyl
peroxide, lauroyl peroxide and diisopropyl peroxy-
dicarbonate, and azo compounds such as azodiisobutyro-
nitrile and 4,4-azobis(4-cyanovaleric acid). 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. The
type of initiator chosen may also vary according to
the mode in which the copolymer stabilise~ is intro- -
duced into the polymerisation mixture. When a pre-
formed block or graft copolymer is employed, it isgenerally preferred to use azo compounds rather than
peroxy compounds in view of the tendency of the
- 23 -
latter to promote random grafting of the monomers
on to the copolymer, which could result in impair-
ment of the stabilising properties of the copolymer.
The same is true when a copolymerisable precursor
for production of the copolymer stabiliser in situ
is used. In contrast, where the copolymer is to be
formed in situ from a soluble polymer containing
abstractable hydrogen atoms, the above-mentioned
characteristic of peroxy compounds is advantageous
and this type of initiator is therefore then to be
preferred, although azo compounds may also be used
in certain cases. 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 poly-
merised.
mere may also be present during the poly-
merisation 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 increas-
ing the average particle size. It is, however,
preferred not to use a chain transfer agent when the
copolymer stabiliser is to be generated from a
soluble polymer having abstractable hydrogen atoms.
In carrying out the process of the invention,
it is preferred to introduce the monomer or monomers
~ic~5
- 24 -
gradually into the aqueous medium, rather than toadd 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
0 of the disperse polymer is achieved, is to add
not exceedinq 20~ by weight,
initially to the aqueous medium a small portion,/ of
the total monomer charge, together with an approp-
riate amount of initiator and the whole or the
greater part of the necessary copolymer stabiliser,
lS precursor or soluble polymer, as the case may be.
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.
In the case where the copolymer stabiliser is to be
generated in situ from a soluble polymer containing
abstractable hydrogen atoms, it is desirable that
the whole of the soluble polymer should be added
along with this initial charge of monomer. Subsequen-
tly, the main portion of the monomer charge,
containing further initiator and the remainder, if
any, of the stabiliser or precursor, is fed in
steadily at a rate sufficient to maintain an accept-
able speed of polymerisation but not such as to
cause monomer to form a separate phase in the poly-
- ~5 -
merising 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 stabiliser
or precursor being present.
In the case where the process of the inven-
tion 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 require-
ment hereinbefore stated that the polymerisation temp-
erature should be at least 10 C higher than the glass
transition temperature of the polymer (viz. the "seed"
polymer) which is formed. Thus, essentially any mono-
mer 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
- 26 -
polymer is to be derived from a mixture of methyl
methacrylate and 2-ethylhexyl acrylate (Tg of polymer,
approximately -10C; polymerisation temperature, 76 -
80 C), it is possible to employ methyl methacrylate
alone tTg of polymer, 105C) 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 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 be 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
6~S
- 27 -
polymer dispersions may readily be made which have
disperse phase contents in the range 40-60% by weight,
and even as high as 700/0 by weight, and which are
effectively stabilised against flocculation or aggre-
gation of the disperse polymer. The polymer particlesmay 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 disper-
sion 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 w~ole range of pH, whereas
known dispersions are stable only over limited pH
ranges; they are also stable in the presence of poly-
valent 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 comp-
ositions themselves show greatly improved flow and
film integration properties as compared with compos-
itions based on conventional dispersions.
The coating compositions incorporating
dispersions made according to the invention may be
of either the thermosetting or the thermoplastic type,
depending upon whether or not the disperse polymer
~_ ~,?~tj5
- 28 -
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 tWhich may be, but is not necessarily, water-
soluble), in a heat treatment step subsequent to theapplication 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 o~
enhanced durability; such a compound is, for example,
the intermediate QP8-5314 marketed by Dow Corning,Inc.
The actual procedure of making polymer
dispersions according to the invention is more
straightforward in certain respects than the conven-
tional 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
11~2~s
- 29 -
by the following Examples, in which parts and per-
centages are by weight.
EXAMPLES 1 - 4
These Examples illustrate the preparation
according to the invention of aqueous polymer disper-
sions utilising pre-formed graft copolymer stabilisers.
A. PreParation of Graft CoPolYmer Stabilisers
A mixture of methoxy(polyethylene glycol),
molecular weight about 2000 (2000 parts), toluene
(800 parts), pyridine (800 parts), and 2:4 dimethyl-
6-tert-butylphenol (1.5 parts) was heated to reflux
under a nitrogen blan~et, and any water being azeo-
troped was removed. This being accomplished, meth-
acrylic anhydride (188 parts), was added and the temp-
erature of the mixture was maintained at a~out 90 C
for three hours. On cooling, a granular mass was
formed and a large excess o a medium boiling point
aliphatic hydrocarbon was added to complete the prec-
ipitation. (The actual choice of aliphatic hydro-
carbon was not important). The product was filteredoff, washed with aliphatic hydrocarbon (boiling
range 60-80C) and dried under vacuum. The product
was essen~ially the methacryla~e ester of methoxy
(polyethylene glycol), containing little or no
unreacted material.
A similar result was obtained if the pyrid-
ine was replaced by 2:6-lutidine and the methacrylic
anhydride was replaced by methacrylyl chloride (128
parts), a warm filtration step being incorporated at
the end of the reaction period to remove lutidine
hydrochloride.
A mixture of the methoxy(polyethylene glycol)
- 30 -
methacrylate thus prepared and the appropriate other
monomers in the desired ratio as indicated in detail
in the Examples below, the total quantity of monomers
in each case being 300 parts, azo diisobutyronitrile
(3.8 parts), toluene (202 parts), ethanol (202 parts),
and water (45 parts) was refluxed for 2~ hours. A
further quantity of azodiisobutyronitrile (2.2 parts)
was added and the mixture was refluxed for a further
2 hours. The product was a 4~ solution of the desired
copolymer.
EXAMPLE 1
PreParation of latex of a thermoPlastic-tYpe
polymer havinq a theoretical Tq of 4C, in 4:1 water/
ethanol mixture at reflux temPerature.
In this Example there was first prepared a
"seed" dispersion of a copolymer of methyl methacryl-
ate and butyl acrylate by polymerisation of the
monomers in a water-ethanol mixture in the presence
of methoxy(polyethylene glycol) methacrylate function-
ing as a "precursor" for a steric stabiliser. A disp-
ersion polymerisation of methyl methacrylate and butyl
acrylate was then carried out according to the process
of the invention, in the presence of the seed disper-
sion and of a pre-formed graft copolymer.
A mixture of methoxy(polyethylene oxide)
methacrylate (3.7 parts), prepared by the method
described above and having a molecular weight of
about 2000, ethanol (12.5 parts), methyl methacrylate
(3.7 parts), butyl acrylate (3.7 parts), and azodi-
isobutyronitrile (0.15 part) was added slowly over a
6~iS
- 31 -
1 hour period to a refluxing mixture of water (340
parts) and ethanol (85 parts). This resulting mixture
was refluxed for a further hour, giving a composition
which was opalescent in appearance. To this composit-
ion at reflux temperature (84C) was added slowly
during 2.5 hours a mixture of methyl methacrylate
(100 parts), butyl acrylate (100 parts), azodiiso-
butyronitrile (3 parts) and a 11.6% solution of a
graft copolymer I, (206 parts). The mixture was heated
for one hour more to give a 27% solids content polymer
dispersion with a particle size in the range 0.05-0.5~.
The Tg of the main copolymer was 4 C.
The graft copolymer I was prepared by the
general method described above from the methacrylate
of methoxy(polyethylene oxide) (molecular weight 2000),
methyl methacrylate and butyl acrylate in the weight
ratios 5:3:2, the molecular weight of the acrylic
portion being about 10,000. The solution of copolymer
was diluted with ethanol to the stated concentration.
COMPARATIVE EXAMPLE A
The procedure described in Example 1 was
repeated, but with the mixture of methyl methacrylate
(100 parts) and butyl acrylate (100 parts) used in
the main polymerisation being replaced by methyl
methacrylate alone (200 parts). The composition
finally obtained in this way contained coarse, flocc-
ulated granules of polymer. In this case, the main
polymer had a Tg of 110 C, which was above the poly-
merisation temperature of 84C; this illustrates the
necessity, according to the invention, of the polymer-
isation temperature being higher than the Tg of the
polymer being formed, if a stable, non-flocculated
~ 5
- 32 -
dispersion is to be obtained.
EXAMPLE 2
The procedure described in Example 1
was repeated, excepting that the solution of graft
copolymer I was replaced by a 13.2% solution of a
graft copolymer II (182 parts). The resulting polymer
dispersion had a solids content of 27% and contained
particles in the size range 0.05 - 0.5 ~.
The graft copolymer II was prepared by the
method described above from the methacrylate of
methoxy (polyethylene oxide) (molecular weight 2000),
methyl methacrylate in the ratio of 1:1 by weight,
the acrylic portion having a molecular weight of
about 10,000. The solution of copolymer was diluted
with ethanol to the required concentration.
COMPARATIVE EXAMPLE B
The procedure described in Example 2 was
repeated, excepting that the mixture of methyl meth-
acrylate (100 parts) and butyl acrylate (100 parts)
used in the main feed was replaced by methyl methacryl-
ate alone (200 parts). Again, as in Comparative
Example A, the Tg of the resulting polymer was greater
than the polymerisation temperature; a granular,
flocculated product was o~tained.
EXAMPLE 3
Preparation of latex of a thermoPlastic-
tyPe PolYmer havinq a theoretical Tq of 4 C, in 4:1
water/ethanol mixture at reflux temPerature.
,
~15~6~5
- 33 -
In this Example, the general procedure of
Examples 1 and 2 was followed, but the "seed" disper-
sion initially prepared was of a homopolymer of methyl
methacrylate; a pre-formed graft copolymer stabiliser
was used both in the making of the seed dispersion
and in the main polymerisation, according to the
process of the invention.
A mixture of a 37% solution of graft co-
polymer II in ethanol (8 parts), methyl methacrylate
(30 parts) and azodiisobutyronitrile (0.5 part) was
added to water (455 parts) and ethanol (114 parts).
The resulting clear solution was heated to reflux
temperature and was maintained at that temperature
for 30 minutes, during which time a fine particle size,
low solids dispersion was formed. The dispersion was
maintained at the ref lux temperature (about 80C), and
a mixture of methyl methacrylate (149 parts), butyl
acrylate (149 parts), a 37% solution of graft co-
polymer II in ethanol (80 parts) and azodiisobutyro-
nitrile (8.9 parts) was added over 1.5 hours and,
while still at reflux temperature during the sub-
sequent 1.5 hours, a further mixture was added of
methyl methacrylate (149 parts), butyl acrylate (149
parts), a 37% solution of graft copolymer II in
ethanol (64.4 parts) and azodiisobutyronitrile (8.9
parts). Refluxing was continued for 0.25 hour longer
to give a fine particle size polymer dispersion
(0.06 - 0.5 ~) with a solids content of about 40%.
The Tg of the resulting polymer was 4 C.
EXAMPLE 4
This Example illustrates a procedure
6tjS
-- 34 --
generally similar to that of Example 3, but both
the seed polymer and the polymer formed during the
main polymerisation are of more complex monomer
composition than those of the previous Example.
To a mixture of distilled water (320 parts),
methanol (165 parts) and ethanol (140 parts) at 30 C,
was added a mixture of methyl methacrylate (25 parts),
ethyl acrylate (28 parts), butyl acrylate (5 parts),
40/0 solution of graft copolymer II made as described
above (60 parts) and azodiisobutyronitrile (1.3
parts). The combined mixture was heated at reflux
temperature (70-80 C) for 30 minutes in order to
form a seed dispersion. There was then fed into this
dispersion, over a period of 3 hours and into the
returning distillate, a pre-formed mixture of methyl
methacrylate (225 parts), ethyl acrylate (244 parts),
butyl acrylate (43 parts), 2-hydroxypropyl methacryl-
ate (33.5 parts),N-butoxymethylacrylamide (6~/o sol-
ution in butanol) (56 parts), 400/0 solution of graft
copolymer II made as described above (80 parts) and
azodiisobutyronitrile (8.5 parts). When this addition
was complete, a further 1 part of azodiisobutyro-
nitrile was introduced; after 20 minutes more at
reflux temperature, a still further 1 part of azo-
diisobutyronitrile was added, and the reaction
mixture was finally heated at reflux temperature
for 20 minutes longer. The product was a stable dis-
persion of polymer of Tg 14 C; the solids content
was 550~0. The dispersion did not deposit any sediment
on standing for many days.
-- 35 --
EXAMPLES S - 20
These Examples illustrate the preparation
according to the invention, of aqueous polymer dis-
persions, utilising copolymerisable stabiliser pre-
cursors.
EX~MPLE S
PreParation of latex of a thermosettinq-
tYpe polymer havina a theoretical Ta of 10 C, in
39:61 water/methanol mixture at reflux temPerature~
To a 2-litre flask fitted with stirrer,
thermometer, inert gas inlet and reflux condenser
with provision for feeding ingredients into the
returning distillate there was charged:
Charae A
Distilled water 315 g
Methanol S00 g
There was then added the following mixture:
Charae B
Methyl methacrylate 26 g
Butyl acrylate 24 g
Stabiliser precursor 17.S g
(as de~cribed below~
Azodiisobutyronitrile l.0 g
The contents of the flask were then heated at reflux
temperature (73 C) for 30 minutes to form a seed
2S dispersion of polymer. m ere was then commenced the
dropwise feed into the returning distillate of the
following mixture:
6~5
- 36 -
Charqe C
Methyl methacrylate 210 g
Butyl acrylate 165 g
N-Butoxymethyl acrylamide44 g
(60~o solution in 3:1
butanol/xylene)
Methacrylic acid ll g
Stabiliser precursor14.5 g
(as described below)
Azodiisobutyronitrile6. 7 g
The addition of Charge C occupied 3 hours. When this
was complete, there was added in the same manner,
10 over a period of 45 minutes, the following mixture:
Charqe D
Methyl methacrylate 45 g
Butyl acrylate 34 g
N-Butoxymethylacrylamide11 g
(60~/o solution in 3:1
butanol/xylene)
Methacrylic acid 2.7 g
Azodiisobutyronitrile1.3 g
One half-hour after this final feed was complete,
there was added Charge E consisting of a further
0.8g of azodiisobutyronitrile (dissolved in about lOg
of the distillate returning from the reflux condenser).
Heating was thereafter maintained at reflux temperat-
ure 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 composit-
ion methyl methacrylate 51%, butyl acrylate 40.5%,
~-butoxymethylacrylamide 6% and methacrylic acid 2.5%;
it had a molecular weight of about 140,000 and a Tg
of 10C. The disperse phase particles ranged in size
-~15,4~i~5
- 37 -
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 6
Preparation of latex of thermosettinq-tYPe
PolYmer havinq a theoretical Tq of 14C, in 40:60
water/ethanol mixture under reflux.
To a flask fitted as described in Example 5
there was charged:
Charqe A
Distilled water 330 g
Ethanol 480 g
followed by:
Charqe 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
m e contents of the flas~ were heated at reflux temper-
ature (76C) for 30 minutes to form a seed polymer
dispersion. There was then added a further 15g of the
stabiliser precursor tCharge C~. Immediately after
this there was begun~ the dropwise feeding, over a
~.~5Z665
- 38 -
period of 2 hours and into the returning distillate,
of the following mixture:
Charqe 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 stripped 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 methacryl-
ate 25%, 2-ethylhexyl acrylate 22% and 2-hydroxy-
propyl methacrylate 10%, and a theoretical Tg of 14 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.
- 39 -
EXAMPLE 7
Preparation of latex of thermoPlastic-tYPe
polYmer of Tq 4C, in a 39:61 mixture of water and
methanol under reflux.
The procedure of Example 5 was repeated,
5 but substituting for the Charges A-E there described
the following:
Charqe A
Distilled water 315 g
Methanol 500 g
Charqe B
Methyl Methacrylate 25 g
Butyl acrylate 25 g
Stabiliser precursor (as
described below) 18 g
Asodiisobutyronitrile 1 g
Charqe C
Methyl methacrylate 206 g
Butyl acrylate 206 g
Stabiliser precursor (as
described below) 10 g
Azodiisobutyronitrile6.7 g
Charqe D
Methyl methacrylate 44 g
Butyl acrylate 44 g
Azodiisobutyronitrile1.3 g
Charqe ~
Azodiisobutyronitrile0.8 g
There was thus,obtained a stable, 41%
solids latex of a 50:50 methyl methacrylate/butyl
acrylate copolymer having a Tg of 3 C. The solids
content could be raised without adversely affecting
~15~6~5
- 40 -
the stability of the latex by removing alcohol bydistillation. The stabiliser precursor used in this
procedure was the methacrylic acid ester of the mono-
methyl ether of polyethylene glycol, mol.wt. 2000 and
the proportion used amounted to 4.8% of the non-
volatile content of the latex.
EXAMPLE 8
Preparation of a latex of a thermoPlastic
PolYmer havinq a Tq of 41Cj in a 52:48 water/ethanol
mixture under reflux.
The procedure described in Example 6 was
repeated, but substituting for the Charges A-E there
described the following:
Charqe A
Distilled water 420 g
Ethanol 390 g
Charae B
Methyl methacrylate 40 g
2-Ethylhexyl acrylate 10 g
Stabiliser precursor (as
descr~bed below) 7 g
Azodiisobutyronitrile 1 g
Charqe C
Stabiliser precursor (as
described below) 23 g
Charqe D
Methyl methacrylate 320 g
2-Ethylhexyl acrylate 80 g
Stabiliser precursor (as
described below) 14 g
Azodiisobutyronitrile 8 g
iS
- 41 -
Charqe E
Methyl methacrylate 160 g
2-Ethylhexyl acrylate 40 g
Azodiisobutyronitrile 4 g
5 Charqe F
Azodiisobutyronitrile 1 g
The reflux temperature of the aqueous medium was 80 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 41C. The ~tabiliser precursor used was the same
as t~at described in Example 5 and the proportion
used was 6.3% based on the non-volatile content of
the latex.
EXAMPLE 9
Preparation of a latex of a thermosettinq-
tYPe PolYmer of Tq 14 C, in an 51:26:23 mixture of
water/methanol/ethanol under reflux.
To a flask fitted as described in Example 5
there was charged:
Charqe A
Distilled water 320 g
Methanol 165 g
Ethanol 140 g
followed by
Charqe B
Methyl methacrylate 25 g
Ethyl acrylate 28 g
Butyl acrylate 5 g
Stabiliser precursor (as
described below) 18.4 g
Azodiisobutyronitrile1.3 g
- ~2 -
The contents of the flask were heated at
reflux temperature (77C) for 30 minutes, to form a
seed polymer dispersion. There was then commenced
the dropwise feeding, over a period of 4 hours and
5 into the returning distillate, of the following
mixture:
Charae C
Methyl methacrylate 225 g
Ethyl acrylate 244 g
Butyl acrylate 43 g
2-Hydroxypropyl methacrylate 33.5 g
N-Butoxymethylacrylamide 56 g
(60h solution in 3:1
butanol/xylene)
Stabiliser precursor (as 14 g
described below)
Azodiisobutyronitrile 8. ~ g
15 When addition of Charge C was complete, the reflux
temperature was maintained for 30 minutes, then a
further lg 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 39/0, ethyl acrylate 43%, butyl
acrylate 8%~ ~-butoxymethylacrylamide 5% and 2-hydroxy-
propyl methacrylate 5%, with a theoretical Tg value of
14C. 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~/o
based on the non-volatile content of the latex.
6~i5
- 43 -
EX~MPT ~ 10
Preparation of latex of a thermoplastic-
type homopolYmer of Tq -22 C, in a 51:26:23 mixture
of water/methanol/ethanol under reflux.
The procedure described in Example 9 was
repeated, but substituting for Charges A-D there
described the foilowing:
Charae A
Distilled water 320 g
Methanol 165 g
Ethanol 140 g
Char~e B
Ethyl acrylate 58 g
Stabiliser precursor (as 20 g
described below)
Azodiisobutyronitrile 1.3 g
Charqe C
Ethyl acrylate 579 g
Stabiliser precursor (as 14 g
described below)
Azodiisobutyronitrile 8~5 g
20 Charqe D
Azodiisobutyronitrile 1 g
The product was a stable, 51.5% solids latex of ethyl
acrylate homopolymer having a theoretical Tg of -22 C.
The sta~iliser 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 metnacrylate (1 mole) as descrlbed in our
aforesaid United States Patent No. 4273888. Ihe
amount of the precursor used was 5% based on the non-
volatile content of the latex.
E~
Z6~S
-- 44 --
EXAMPLE 11
PreParation of a latex of a thermosettinq-
tYPe Polymer of Tq 6 C~ in a 39:39:22 mixture of
water/methanol/ethanol under reflux.
The procedure of Example 5 was repeated,
but substituting for Charges A-E there described the
following:
Charqe A
Distilled water 315 g
Methanol 315 g
Ethanol 185 g
Charqe B
Styrene 14 g
Methyl methacrylate 13 g
Butyl acrylate 23 g
Stabiliser precursor (as13 g
described ~elow')
Azodiisobutyronitrile 1 g
Charqe C
Styrene 110 g
Methyl methacrylate 102 g
Butyl acrylate 178 g
~-Butoxymethylacrylamide 39 g
(60% solution in 3:1
butanol/xylene)
Methacrylic acid 4. 5 g
Stabiliser precursor 6.5 g
Azodiisobutyronitrile 6 g
Charcre D
Styrene 22 g
Methyl methacrylate 20 g
Butyl acrylate 35 g
~-Butoxymethylacrylamide 7 g
(600/o solution in 3:1
butanol/xylene)
ll~;f. ~itjS
- 45 -
Methacrylic acid 1 g
Azodiisobutyronitrile 1.3 g
Charqe E
Azodiisobutyronitrile 1 g
The reflux temperature of the aqueous medium was 76C.The product was a stable, 4~/0 solids content latex of
a polymer having the composition styrene 26%, methyl
methacrylate 25%, butyl acrylate 43%, ~-butoxymethyl-
acrylamide 5% and methacrylic acid 1%, and having a
theoretical Tg value of 6C. The stabiliser precursor
used in this preparation was the same as that employed
in Example 5 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 12
The procedure of Example 11 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 13
PreParation of a latex of a thermosettinq-
tYPe PolYmer of Tq 10C, in a 39:61 mixture of water
and methanol.
The procedure of Example 5 was repeated, but
substituting for Charges A-E there described the
following:
.L 1'~ 5
~ 46 ~
Charqe A
Distilled water 315 g
Methanol 500 g
Charqe B
Methyl methacrylate 26 g
B~tyl acrylate. 24 g
Stabiliser precursor (as20 g
described below)
Azodiisobutyronitrile 1 g
Charqe C
Methyl methacrylate 210 g
Butyl acrylate 165 g
N-Butoxymethylacrylamide 44
(~/0 solution in 3:1
butanol/xylene)
Methacrylic acid 11 g
Stabiliser precursor (as18 g
described below)
Azodiisobutyronitrile 6.7 g
Charqe 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
Charqe E
Azodiisobutyronitrile 0.8 g
The product was a 41% solids stable latex of a polymer
2~ having the same composition and characteristics as
that of Example 5. The stabiliser precursor used in
this preparation was the glycidyl methacrylate adduct
of a carboxyl group-terminated polyvinylpyrrolidone
;5
- 47 -
of mol.wt. 30,000, made by polymerising vinylpyrrolid-
one in water in the presence of 4,4-azobis(4-cyanoval-
eric 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.
EXAMæLE 14
PreParation of latex of thermosettin~-tYPe
olYmer of T~ 18 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 85-90 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-Hydroxypropylmethacrylate18 g
Stabiliser precursor 29 g
Azodiisobutyronitrile 3 g
25 When the addition was complete, the temperature was
maintained at 85-gO C for 30 minutes, then a further
0.3g 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
S
-- 48 --
of 18 C. The particle size range was 0.1 - l micron.
The stabiliser precursor used in this preparation was
the same as that described in Example 10 and was
employed in an amount of 13.7% based on the non-
5 volatile content of the latex.
EX~MPLE 15
-
Pret~aration of latex of ~lasticised PolY-
methYl methacrYlate in 50:25:25 water/methanol/et~anol
mixture under reflux.
The procedure described in Example 9 was
repeated, but substituting for Charges A-D there
described the following:
Charqe A
Distilled water 247 g
Methanol 127 g
Ethanol .127 g
Charqe B
Methyl methacrylate 27 g
Polyester plasticiser (as 17 g
described below)
Stabiliser precursor (as 15 g
described below
Azodiisobutyronitrile 1 g
Charqe C
Methyl methacrylate 271 g
Polyester plasticiser (as 171 g
described below)
Stabiliser precursor (as 11 g
described below)
Azodiisobutyronitrile 6 g
Charcte D
Azodiisobutyronitrile l g
~`of~S
- 49 -
The refluxing temperature of the water/methanol/
ethanol mixture was 76 C.
The product was a stable, 500~ solids latex of poly-
methyl methacrylate/polyester plasticiser in the
ratio 60:40, having a Tg of 55C as compared with a
Tg of 105 C for unplasticised polymethyl methacrylate.
The polyester plasticiser used was ~he 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 5, and was present in an amount
of 5.5% based on the non-volatile content of the latex.
comParative ExamPle C
AttemPted preparation of unPlasticised poly-
methYl methacrYlate.
The procedure of Example 15 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 15,
and the disperse phase completely flocculated when
addition had proceeded to a stage corresponding to
a latex non-volatile content of about 15%.
EXAMPLE 16
Use of a chain transfer aqent soluble in
the a~ueous medium.
The product of Example 9 was repeated, with
the addition of 0.6g of thioglycollic acid to Charge ~
and of 6g of the same substance to Charge C (amounting
in total to 1% of the monomers being polymerised).
S
- 5Q -
The product was a stable latex of somewhat
coarser particle size than that of Example 9, namely
0.5 - 8 microns; thus the maximum particle size was
increased by the use of the chain transfer agent.
ComParative Examples D and E
The procedure of Example 9 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 qtirrer, when a non-
volatile content of about 15% had been reached.
A similar result was obtained when the
original stabiliser precursor of Example 9 was
replaced by the methacrylic acid ester of polyethyl-
ene glycol, mol.wt. 750.
EXAMPLES 17 - 18
The procedure of Example 9 was repeated,
using as initiator, in place of azodiisobutyronitrile,
equal amounts of 4,4-azobist4-cyanovaleric acid) or
lauroyl peroxide, respectively.
Similar results to those of Example 9 were
obtained. The azo initiator led to the production of
a sl-ghtly finer particle size range than was record-
ed in that Example, namely 0.1 - 1 micron, while the
peroxy initiator gave a somewhat coarser range,
;S
-- 51 --
namely 0.3 - 4 microns.
EXAMPLE 19
PreParation of latex of thermosettinq-tYPe
~olYmer modified bY a reactive silicon comPound.
To a 2-litre flask fitted as described in
Example 5 there was charged the following:
Charqe A
Distilled water 215 g
Methanol 112 g
Ethanol 95 g
To this was added the following mixture:
Charqe 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 5)
Azodiisobutyronitrile 0.9 g
and the batch was heated for 30 minutes at reflux
temperature (76 C) to form a seed dispersion of
polymer.. There was then begun the dropwise addition,
into the returning distillate, of the following
mixture:
Charqe C
Methyl methacrylate 112 g
Butyl methacrylate 51 g
Ethyl acrylate 112 g
Butyl acrylate 48 g
2-~ydroxypropyl methacrylate 21 g
6~5
- 52 -
~-Butoxymethylacrylamide 24 g
(60h solution in 3:1
butanol/xylene)
Stabiliser precursor (as10 g
described in Example 5)
Azodiisobutyronitrile 5 g
Three-guarters 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 dist-
illate over a period of l~ hours:
Charqe D
Silicone intermediate QP8-5314 180 g
(ex. Dow Corning Inc.)
~-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 É) lg of
azodiisobutyronitrile. Following a final period of
l hour at reflux temperàture, 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 ~-butoxymethylacrylamide 5.5%, the polymer being
modified to the extent of 20% by reaction of the
silicone intermediate with the hydroxyl groups
present. Thc Tg of the acrylic polymer was 7 C.
EXAMPLE 20
Preparation of latex of thermosettinq-tYPe
polymer containinq an amino resin as cross-linkinq
aqent.
To a l-litre flask fitted with stirrer,
- S3 -
thermometer, condenser, dropping funnel and inert
gas feed, there was charged:
Charae A
Distilled water 40 g
Diethylene glycol 34 g
Tetraethylene glycol 7 g
Methylated melamine/
formaldehyde resin 54 g
("Cymel" 301* ex. Cyanamid)
* "Cymel" is a Registered Trade Mar~.
10 The contents of the flask were heated to 90 C and
there was then added dropwise, over a period of 3
hours, the following:
Charqe B
Styrene 95 g
Ethyl acrylate 50 g
2-Ethylhexyl acrylate 15 g
2-Hydroxyisopropyl
methacrylate 16 g
Ethanol 25 g
Stabiliser precursor (as
descr~bed below) 25 g
Azodiisobutyronitrile 3.3 g
The batch was heated at 90C for 30 minutes after
this addition was completed and there was then added
(Charge C) 0.5g 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 2~%, 2-ethylhexyl acrylate 9% and
2-hydr~xyisopropyl methacrylate 9%. m e theoretical
Tg of the polymer was 26 C. The stabiliser precursor
used in this preparaticn was the same as that
.,
.
i6S
- 54 -
described in Example 5 and was present in an amount
of 11.6% based on the non-volatile content of the
latex.
ComParative Example F
Attempted PreParation of latex, usinq
~eroxide initiator, at a PolYmerisation temperature
less than 10 above the Tq of the PolYmer in 39:61
water/methanol.
An attempt was made to repeat the procedure
of Example 5, 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
50C only:-
Charqe A
Distilled water 245 g
Methanol 389 g
Stabiliser precursor (as
described below) 14.7 g
Charqe B
Methyl methacrylate 28.3 g
Butyl acrylate 10.4 g
Bis(4-t-butylcyclohexyl- 0.7 g
peroxydicarbonate)
Charqe C
Methyl methacrylate 234 g
3utyl acrylate 86.4 g
Stabiliser precursor (as12.4 g
described below)
Bis(4-t-butylcyclohexyl- 5.0 g
peroxydicarbonate)
Charae D
Methyl methacrylate 50.3 g
Butyl acrylate 18.5 g
i65
- 55 -
Bis(4-t-butylcyclohexyl)-
peroxydicarbonate 1 g
Charqe E
Bis(4-t-butylcyclohexyl)-
peroxydicarbonate 0.62 g
Charges A and B heated together to 55 C, and vacuum
was then applied to the system so as to achieve a
reflux temperature of 50C. 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 had 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 43C.
The stabiliser precursor used in this
experiment was the methacrylic acid ester of the
monomethyl ether of polyethylene glycol, mol.wt. 1600.
ComParatlve ExamPle G
Attempted PreParation of latex, usinq azo
initiator, at a polYmerisation temPerature less than
above the Tq of the Polymer~ in 39:61 water/
methanol.
An attempt was made to repeat the procedure
of Example 5, 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 C only:
6tj5
- 56 -
Charae A
Distilled water 245 g
Methanol 389 g
Stabiliser precursor (as
described in Comparative
Example F) 14.7 g
5 Charqe B
Methyl methacrylate 29.3 g
Butyl acrylate 9.7 g
2,2-azobis(2,4-dimethyl-
valeronitrile) 0.7 g
Charae C
Methyl methacrylate 240.6 g
Butyl acrylate 79.8 g
Stabiliser precursor (as
described in Comparative
Example F~ 12.4 g
2,2-azobis(2,4-dimethyl-
valeronitrile) 5.0 g
Charqe D
Methyl methacrylate 51.5 g
Butyl acrylate 17 g
2,2-azobis(2,4-dimethyl-
valeronitrile) 1.0 g
Charqe E
2,2-azobis(2,4-dimethyl-
valeronitrile) 0.62 g
Charges A and B were heated together to 60C, and
vacuum was then applied to the system so as to achieve
a reflux temperature of 54-55C. 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 ~y the end
s
_ 57 -
of the feed these had aggregated to form large lumps
of polymer. The experiment was then abandoned.
m e composition of the polymer which it was
attempted to prepare was methyl methacrylate 75%,
butyl acrylate 25%; the theoretical Tg of this
polymer was 46C.
EXAMPLE 21 - 23
These Examples illustrate the preparation
according to the invention of dispersions of a
thermoplastic-type polymer having a theoretical Tg
of about 0C, in a 37:32 ethanol/water mixture at
reflux temperature where the stabiliser is derived
from a water-soluble simple polymer containing
abstractable hydrogen atoms.
EXAMPLE 21
A solution of 49.9 parts of polyvinyl
pyrrolidone of molecular weight 40,000 (Brand K30
257/72E, manufactured by G.A.F.) in 370 parts ethanol
was mixed with 320 parts of water, 2 parts of benzoyl
peroxide, 30.6 parts of methyl methacrylate and 29.4
parts of 2-ethylhexylacrylate and the clear solution
was then heated to reflux temperature (76 - 80 C).
Refluxing was maintained for 15 minutes, at which
stage the mixture was opalescent or milky in
appearance. Refluxing was continued and over the
next 2.5 hours a mixture of 228.9 parts of methyl
methacrylate, 210.1 parts of 2-ethylhexyl acrylate
and 4.3 parts of benzoyl peroxide was added dropwise
to the mixture via the returning refluxing distillate.
Refluxing was continued for a further hour. At
this stage the solids content of the dispersion was
~5.5% (a small loss of solvent occurred during the
~_~tt~ 5
- 58 -
polymerisation). Distillation was then commenced
and 200 parts of aqueous aicoholic distillate was
removed, yielding a fine particle size (0.2 - 0.6
micron)dispersion,of solids content 55.1% and
viscosity 10 poise, of copolymer of Tg about 0C.
EXAMPLE 22
The procedure described in Example 21 was
repeated, except that 10 parts of polyvinyl alcohol
of molecular weight 29,400 (Gohsenol GL05 148/77Q,
manufactured by Nippon Gohsei) were used instead of
the 10 parts of polyvinyl pyrrolidone. At the end
of the polymerisation, the solids content of the
dispersion was 45.3%. After removing 253 parts of
a~ueous alcoholic distillate, the solids content was
60.7% and the fine particle size dispersion (0.2 - 2.0
microns) had a viscosity greater than 15 poise.
EXAMPLE 23
The procedure of Example 21 was repeated
but with the 10 parts of polyvinyl pyrrolidone
replaced by 10 parts of hydroxyethyl cellulose
(Cellosize WP0 Q~ manufactured by Union Carbide).
This yielded a dispersion which at the end of the
polymerisation had a solids content of 44.6% and a
particle size range of (0.2 - 8.0 microns). In
this case the dispersion was very viscous (viscosity
greater than 15 poise) and none of the diluent was
distilled off.
"Gohsenol" and "Cellosize" are Registsred
Trade Mar~s.
EX~MPLE 24
This Example illustrates the preparation
of a water-borne, medium gloss non-crosslinXing
~L5;~i6S
- 59 -
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 11, of a copolymer
having the composition styrene/methyl methacrylate/
butyl acrylate/~-Butoxymethylacrylamide/methacrylic
acid 26/25/43/5/1, the latex having a non-volatile
content of 46.8%.
B. Pre~aration of Piament Millbase
A mixture of titanium dioxide (44 g:
"Kronos" R~ 45 (Registered Trade Mark), strontium
chromate (18.5 g), blanc fixe (76.5 g), china clay
(~5 g: Grade D) and the polymer latex described in
(A) above (304 g) was ground overnight in 4-gallon
capacity ball mill using 1050 g of 4-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 thic~ness 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 - 199C: 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
. . .
:
-:, .
s
- 60 -
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 result was
obtained.
EXAMPLE 25
This Example illustrates the preparation of
a high gloss paint from one of the polymer latices
described above.
A. Pre~aration of PolYmer Latices
Two latices were prepared by the general
method described in Example 6. 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. Pre~aration of Millbase
A mixture of 135 g of titanium dioxide
pigment ("Runa" RH 472: Registered Trade Mar~ of
Laporte Industries Limited) and 302.8 g of the
polymer latex described in (A) was ground for 24
hours in a 4-gallon ball mill with a charge of 1050 g
of 4-inch steatite balls. A ~luid dispersion was
obtained having a particle size of less than 5 microns
as measured on a Hegman gauge. m ere was
incorporated into this millbase 6.6% by weight of a
water-miscible hexamethoxymethylmelamine.
665
- 61 -
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
S 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 - 199 ~. The coating which
resulted had the following excellent characteristics:
Gloss (60 meter) 88%
Hardness (pencil test) H
Reverse impact (lb/sq in) 80
Bend test lT
EXAMPLE 26
This Example i-llustrates 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 6, of a polymer
having the composition styrene 25%, methyl
methacrylate 18%, butyl methacrylate 24%, 2-ethyl-
hexyl acrylate 21%, hydroxyisopropyl methacryiate
10% and dimethylaminoethyl methacrylate 2%; the
latex had a solids conten~ of 52%.
B. PreParation of Paint
The laiex described in (A) (164 parts), a
melamine-formaldehyde resin (~Beetle~BE 670)
(12.5 parts) and water (40 parts) were mixed and
s
- 62 -
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 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 80C and then for
a further 30 minutes at 150C. The film had a
thickness of 50 microns, a gloss of 90% (20 meter)
and a Knoop hardness of 6.4 - 7.4. It was free
from defects.
EXAMPLE 27
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 9 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 su~jected to various curing
schedules as shown in the table below: the degree
s
- 63 -
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 ¦ ~0 Cure
30 mins. at 150C
30 mins. at 120C 99.2
30 mins. at 100C 96.6
30 mins. at 80C 92.8
10 mins. at 150C 95.6
