Particulate polymeric materials and their production

A dispersion is formed of aqueous polymer particles in a non-aqueous liquid and a stabiliser is covalently reacted on to the particles.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to the formation of polymeric particles (ie 
particles having an external surface of organic polymer) which give 
improved stability when dispersed in a liquid. 
2. Description of the Related Art 
Processes are described in PCT/GB96/03233 for forming particulate 
compositions comprising particles having a hydrophilic core within a shell 
comprising a membrane comprising an association product of (a) an 
interfacial condensation product (IFC) formed by reaction in a non-aqueous 
liquid between a first IFC reactant having at least two first condensation 
groups and the second IFC reactant having at least two second condensation 
groups and (b) an amphipathic polymeric stabiliser which will concentrate 
at the interface between oil and water and which has recurring hydrophobic 
groups and recurring reactive hydrophilic groups which associate with the 
second condensation groups. After formation in the non-aqueous liquid, the 
particles are dispersed in liquid electrolyte. 
It is explained in that application that the association may comprise a 
condensation reaction and, in particular, condensation may occur when the 
stabiliser is a copolymer of an ethylenically unsaturated carboxylic 
anhydride such as maleic anhydride and the second condensation groups are 
amino groups. It is also explained, however, that the association 
preferably comprises forming an internal, ring-formed salt between the 
adjacent carboxylic groups of a stabiliser formed from a monomer such as 
maleic acid or maleic anhydride with an IFC reactant which is a polyamine. 
We have found that the best performance is generally achieved when the 
formation of the IFC shell does depend on the use of a polycarboxylic 
stabiliser which is in hydrolysed acid form rather than anhydride form, 
and this is probably due to the fact that internal salt formation occurs 
and that covalent reaction between the amine and the carboxylic acid 
groups does not occur during normal processing. 
We have also found that when particles are made in this way, the resultant 
particles sometimes have less dispersion-stability than is desirable, 
especially when they are subsequently dispersed in an aqueous electrolyte 
solution (such as a liquid detergent concentrate). 
We have found that, when developing these unpublished processes, it is 
difficult simultaneously to optimise the shell formation and the stability 
of the particles in the final liquid dispersion. We believe that this may 
arise because of there being different requirements for optimum shell 
formation and for optimum stability, and because of the differences in the 
continuous phase. We believe that optimum shell formation may often be 
promoted by some degree of ionic association between the stabiliser and 
IFC reactant groups, but we believe that materials which are optimum for 
undergoing this ionic association may give less satisfactory stability in 
the final dispersion. Conversely, materials which may give optimum 
stability in the final dispersion appear to give less adequate shell 
formation. 
Our object, arising out of this unpublished work, is to try to obtain a 
better combination of properties during manufacture and during long term 
storage in the electrolyte. 
As regards information which has been published, it is well known to 
stabilise a dispersion of particles in a liquid (for instance a 
non-aqueous liquid) by including in the dispersion an amphipathic 
polymeric stabiliser, that is to say a stabiliser formed from hydrophobic 
groups and hydrophilic (generally ionic) groups. When, as is common, the 
stabiliser is used for stabilising hydrophilic polymer particles in a 
hydrophobic environment, the hydrophilic units in the polymer are 
attracted to the polymer particles and the stabiliser thereby becomes 
attached to the polymer particles. The mechanism in many instances may be 
ionic but other types of physical adsorption may be utilised. 
A difficulty with this type of stabiliser is that its performance 
properties are significantly influenced by the nature of the liquid in 
which the particles are dispersed. If that liquid is changed then the 
stabiliser may become much less effective. For instance the stabiliser may 
be effective when the particles are dispersed in a non-aqueous liquid but 
may be much less effective or wholly ineffective when the continuous phase 
(the first liquid) of the initial dispersion is changed to a different 
continuous phase (a second liquid). This change may be brought about by a 
solvent swap techniques as described in WO94/25560 or it may be brought 
about by dispersing the initial dispersion into the second liquid. 
Particular problems arise when the second liquid contains electrolyte. 
It would therefore be desirable to be able to improve the self-stabilising 
properties of polymer particles so that they have the potential to have 
improved stability even though the continuous phase may be changed from a 
first (usually non-aqueous) liquid to a different, second, liquid (which 
is usually aqueous electrolyte). 
Stabilisers for different dispersions are known from, for instance, 
GB-A-1,198,052, GB-A-1,231,614, GB-A-1,268,692, GB-A-2,207,681, 
AU-A-455,165, U.S. Pat. No. 3,580,880, U.S. Pat. No. 3,875,262, 
EP-A-707,018 and EP-A-719,085. 
BRIEF SUMMARY OF THE INVENTION 
According to the invention, we provide a process comprising forming a 
dispersion in a first non-aqueous liquid of aqueous polymer particles 
having an outer surface which includes reactive groups, and covalently 
reacting a reactive stabiliser material with some of the reactive groups 
and thereby forming a dispersion of the particles with the stabiliser 
material covalently bonded on to the outer surface of the particles. 
DETAILED DESCRIPTION OF THE INVENTION 
By saying that we covalently react the stabiliser material with some of the 
reactive groups, we mean that there is sufficient covalent bonding between 
the stabiliser material and the reactive groups to ensure that the 
stabiliser is attached to the particles by sufficient covalent bonding to 
hold the stabiliser material in place despite reasonable changes in the 
continuous phase in which the particles may be dispersed. For instance the 
stabiliser material should remain in place, and give a stabilising effect, 
even though the continuous phase may change from a first non-aqueous, 
predominantly hydrocarbon, liquid to the second liquid, which may be a 
relatively high electrolyte liquid. There can additionally be some ionic 
bonding or other forms of association but there must be sufficient 
covalent bonding to dominate the performance of the particles when the 
continuous phase is changed. 
The number of reactive groups which remain unreacted after covalently 
reacting the stabiliser material on to the particles is often unimportant 
but in practice there will always be some reactive groups that do not 
react covalently with the stabiliser. For instance some of the reactive 
groups will be prevented from reacting because of steric hindrance between 
the stabiliser and the particle surface. Some of the reactive groups will 
be prevented from reacting covalently because they may react in another 
manner, for instance forming an ionic complex. In practice some of the 
reactive groups may remain unreacted because there is a stoichiometric 
excess of reactive groups on the polymer particles over groups on the 
stabiliser that can react with them. 
The particles may be relatively large particles such that they can be 
separated from the continuous liquid phase and utilised as, for instance, 
powder. Thus, for instance, they may have a size above 30 .mu.m, for 
instance in the range 100 to 100 .mu.m. For instance the invention can be 
useful when such particles are being processed or transported in a 
continuous phase of a second liquid different from the first liquid. The 
invention can minimise aggregation or other instability problems that 
might otherwise occur despite keeping the dispersion of coarse particles 
in the continuous phase stirred to prevent sedimentation. 
Preferably however, the invention is applied to the production of particles 
which have a size at least 90% by weight below 30 .mu.m, preferably below 
10 or 20 .mu.m, and in particular to the production of particles which are 
provided as a substantially stable dispersion in a liquid. The invention 
reduces or eliminates the risk of the particles aggregating and/or 
sedimenting, both at low concentrations (e.g., down to 0.1% by weight) and 
at higher concentrations (e.g., 5% or even much higher such as 30% or 50% 
in some liquids). 
Generally the process comprises the additional step of providing the 
particles as a dispersion in a second liquid before or (usually) after the 
covalent reaction, wherein the covalently bonded stabiliser on the 
particles promotes the stability of the dispersion in the second liquid. 
Thus, by the invention, a substantially stable dispersion of the particles 
may be formed in a first liquid and then these particles may be dispersed 
in a second liquid in which the dispersion would have been less stable if 
the covalent bonding of the invention had not been applied. In particular, 
by the invention the dispersion in the second liquid is preferably more 
stable than if the same stabiliser material is simply mixed into the final 
dispersion of particles in the second liquid, without the covalent 
reaction. Generally the covalent reaction is conducted in the first, 
non-aqueous, liquid and the resultant self-stabilised particles are 
dispersed in the second liquid. However, if desired the first liquid may 
be exchanged with another non-aqueous liquid (or some other liquid such a 
surfactant) before the covalent reaction or even before adding the 
stabiliser. 
The second liquid is an electrolyte. It is usually an aqueous liquid or is 
a water miscible liquid, and generally it contains at least 0.5% by weight 
electrolyte, often at least 3% and generally at least 5% up to, for 
instance, 30% or 50% by weight electrolyte. The electrolyte may be 
inorganic or organic and monomeric or polymeric. Preferably the 
electrolyte includes anionic or cationic surfactant, most preferably 
anionic surfactant. Accordingly the second liquid may be an aqueous or 
non-aqueous liquid detergent concentrate. 
The change of the continuous phase from the first liquid to the second 
liquid can be conducted in various ways. For instance it can be achieved 
by adding the second liquid and distilling off the first liquid (for 
instance as described in WO94/25560). This "solvent swap" technique may be 
conducted so as to put the particles into the second liquid in which the 
self-stabilising properties are required, or this product may itself be 
dispersed in the second liquid so as to disperse the particles in the 
second liquid. For instance the particles may initially be formed in a 
hydrocarbon which is the first liquid, this continuous phase may then be 
changed to a non-ionic surfactant, glycol or other water miscible organic 
liquid, and this water miscible liquid can be the second liquid or, 
alternatively, the dispersion in this water miscible liquid can then be 
mixed into the final second liquid in which the particles are to be 
substantially self-stabilising. The stabiliser which is to react with the 
polymer is usually reacted with the polymer while in the first liquid, but 
the reaction may be deferred until the particles are in the second liquid, 
or in a water miscible liquid. 
The dispersion in the water miscible liquid may be mixed into a second 
liquid having a high electrolyte concentration. Alternatively the 
dispersion in the first liquid may be mixed direct into the aqueous 
electrolyte. 
The dispersion in first non-aqueous liquid of the particles may be made by 
dispersing preformed aqueous polymer particles in the liquid or may be 
made by forming the particles in that liquid as a dispersion. The 
particles are polymeric, that is to say their outer surface is polymeric, 
and also includes the reactive groups. 
The particles may be formed of a matrix of a polymer which carries the 
reactive groups and which, for instance, extends throughout the particles. 
For instance the particles may be aqueous polymer particles made by 
polymerising droplets of aqueous monomer or monomer blend while dispersed 
in a first non-aqueous liquid (for instance by reverse phase 
polymerisation in a non-aqueous liquid) or the particles may be made by 
dispersing in a liquid (often a non-aqueous liquid) polymeric material in 
liquid form and converting it to solid particles. For instance the 
polymeric material may be introduced as a solution in water or as an 
emulsion in water and the resultant aqueous polymer particles of solution 
or emulsion may then be converted to solid form, for instance by 
distilling or otherwise removing the water from the dispersion of those 
particles in the first liquid. The particles may contain an active 
ingredient dispersed throughout the matrix. 
As an example, the particles may be formed of a polymer of acrylic acid, 
hydroxy ethyl acrylate or a glycidyl acrylate, optionally copolymerised 
with other water soluble monomer such as acrylamide, so that the particles 
are then formed of an addition polymer having free carboxylic, hydroxyl or 
epoxy groups, which then serve as the reactive groups. 
It is often preferred that the particles should have a shell-core 
configuration wherein the core contains an active ingredient and the shell 
is formed of a polymer carrying the reactive groups. The core may include 
a matrix polymer or may consist solely of reactive ingredient, and 
optionally a non-polymeric carrier or diluent. 
The shell may be formed by any convenient technique. It may be formed by, 
for instance, coacervation of one or more polymers, wherein at least one 
of the polymers in the coacervate carries reactive groups. For instance 
polymers that are used for coacervation may consist of or include polymers 
carrying the carboxylic groups such as polyacrylic acid or natural 
polymers such as carboxy methyl cellulose. 
Preferably, however, the shell is formed by interfacial condensation (IFC). 
Suitable combinations of materials for forming the shell by IFC are 
described in U.S. application Ser. No. 08/860,564 which is incorporated 
herein by reference. Any of these may be used in the invention. Such 
methods produce aqueous polymer particles, having a hydrophilic core. 
The reactive groups on the polymer particles can be epoxide or hydroxyl 
groups (in which even the covalent bond will be an ether). They can be 
carboxylic groups (free acid, water soluble salt, anhydride or acid 
halide) in which event the covalent linkage can be an ester or amide 
linkage. Preferably, however, the reactive groups are amino groups in 
which event the covalent linkage is preferably an amide linkage, formed by 
reaction between these amino groups and carboxylic groups which can be 
covalently bonded with them. 
Although covalent bonding can be achieved between carboxylic free acid, 
salt or halide groups and amino groups, the covalent reaction generally 
occurs much more easily if the carboxylic groups are in the form of 
anhydride groups and thus preferably the reactive groups are amino groups 
and the stabiliser provides dicarboxylic anhydride groups. 
We believe that one reason why some existing stabiliser systems are less 
effective in, for instance, aqueous electrolytes is that the reactive 
groups on many of the particles that are under consideration are ionisable 
(for instance being cationic or anionic) and the stabiliser is usually 
counterionic so that the attraction between the stabiliser and the 
particle is primarily ionic. This ionic attraction can be displaced by, 
for instance, changes in the electrolyte concentration. 
In the invention, it is preferred that the reactive groups on the polymer 
are ionisable and the stabiliser is a counterionic material or a 
derivative (such as an anhydride) of a counterionic material and which is 
now covalently bonded to the particles in contrast to being ionically 
attached, as in prior processes. 
The stabiliser material can be a monomeric material which achieves the 
self-stabilising effect merely by covalently blocking sufficient of the 
ionisable reactive groups on the polymer particles that the stabilising 
effecting is not significantly altered by moderate changes in electrolyte 
concentrate. For instance, amino reactive groups on the particles would 
normally be ionisable, but if they are reacted with a monomeric anhydride 
or acid halide they are covalently blocked and so cannot ionise. This 
prevention of ionisation is, in some environments, sufficient to maintain 
self-stabilising properties when the continuous phase is changed. 
Accordingly the invention includes processes in which the stabilising 
material is a monomeric anhydride or acid halide such as acetic anhydride, 
acetyl chloride, maleic anhydride or succinic anhydride and which is 
covalently reacted on to polymer particles having free amino groups so as 
to form amide groups. When these particles carrying amide groups are 
dispersed into a detergent or other electrolyte liquid, optionally in the 
presence of additional polymeric stabiliser which is unreactive with the 
particles, the particles are self stabilising. 
By this we mean that improved stability is obtainable compared to the 
stability that is achieved when the same particles are dispersed into the 
same liquid (in the presence of the same extra stabiliser if that is used) 
but without the prior reaction with the anhydride or acid halide. 
Preferably, however, the stabilising material which is used in the 
invention is a reactive copolymer of hydrophilic monomer units and 
hydrophobic monomer units, i.e., it is an amphipathic polymer. The 
hydrophilic units are attracted to the aqueous polymer particles and the 
hydrophobic units are attracted to the non-aqueous liquid. The amount of 
water in the particles may be above 10% by weight of the particles but may 
be considerably less provided the polymer or the core is hydrophilic. 
Suitable hydrophobic monomers and hydrophilic monomers and their amounts 
(except for the groups which are to react) are given in PCT/GB96/03233. 
The hydrophilic monomer units should provide groups which will react 
covalently with the reactive groups on the particles. Preferably the 
stabiliser is a copolymer of dicarboxylic anhydride monomer units and the 
reactive groups on the particles are amino groups. 
The preferred aspects of the invention are those in which the dispersion in 
the first liquid is formed by IFC polymerisation in the presence of a 
first stabiliser which is a copolymer of hydrophobic units with 
hydrophilic units which preferably include dicarboxylic units and wherein 
the dicarboxylic units (if present) are in the hydrolysed form (free acid, 
acid salt or acid halide) and a second stabiliser is reacted with amino 
groups from the IFC polymerisation and the second stabiliser is a 
copolymer of hydrophobic monomer units with hydrophilic monomer units 
which include dicarboxylic acid units and wherein the dicarboxylic units 
include anhydride groups, whereby they will enter into covalent amide 
formation with the amino groups. Other stabilisers which have hydrophilic 
monomer units which can react covalently with the amino groups may be 
used. 
In PCT/GB96/03233 we described a process in which IFC particles containing 
amine groups are made in the presence of one such stabiliser, either free 
dicarboxylic acid or anhydride, and preferably the present invention does 
not include such an IFC process using, as the sole stabiliser, such a 
polymer which is hydrolysed (so that all the dicarboxylic acid groups are 
free acid or salt form) or mainly unhydrolysed anhydride, mainly meaning 
preferably above 80%. 
We can obtain useful results using a polymer which is partially hydrolysed 
eg 20-80% anhydride and 80-20% dicarboxylic acid or acid salt, preferably 
30-80% dicarboxylic acid. 
We have now found that best results are achieved by using a combination of 
stabilisers (generally amphipathic stabilisers) wherein the first will 
predominantly enter into ionic association with the amino IFC reactant (so 
as to promote shell formation) and the other will enter into covalent 
reaction with the amino groups, so as to bond stabiliser to the surface of 
the particles and so as to block some or all of the ionisable amino 
groups. The first may have free dicarboxylic acid groups without 
anhydride, and the second may have anhydride groups. 
Good results are also obtained when the amount of anhydride monomer units 
is low, e.g., 1 to 10% by weight of the monomers or when 1 to 10% glycidyl 
monomer units are included instead of the anhydride units. 
The remaining hydrophilic units in the stabiliser can be mono- or di- 
carboxylic acid monomer units and/or hydroxyalkyl monomer units, generally 
to provide 10 to 30 mole % ionic or other hydrophilic units, with the 
balance being hydrophobic (see PCT/GB96/03233). Suitable hydrophobic 
groups include fatty (C8-24) alkyl acrylates or methacrylates, C1-4 alkyl 
acrylates or methacrylates and styrenes. 
The second carboxylic stabiliser, or other stabilising material which is to 
react with the reactive groups, may be added at any time such that it 
achieves the desired effect and blocks the ionisable groups in the final 
particles. For instance the particles may be formed initially with the 
reactive groups on them (optionally in the presence of a polymeric 
stabiliser) and then the stabilising material may be reacted covalently on 
to the particles having the reactive groups. Thus the particles may be 
formed in the presence of one stabiliser (which is unreactive) and then 
the reactive stabiliser is added and reacted on to the particles. As 
another example, the stabiliser which is to react with the reactive groups 
may be added before the formation of the particles is completed. 
The stabiliser which is to be covalently reacted on to the reactive groups 
may be incorporated before the interfacial condensation reaction is 
started. For instance both a dicarboxylic acid stabiliser and a 
dicarboxylic anhydride stabiliser may be present before the IFC is 
initiated. For instance the stabiliser which is to promote wall formation 
(e.g., the dicarboxylic acid stabiliser) may be present during the 
emulsification of the aqueous core phase into a non-aqueous liquid, and 
the stabiliser which is to react covalently with amino or other reactive 
groups is then added, for instance with the other IFC reactant. 
Irrespective of when the various materials are added, the process of the 
invention preferably includes a reaction stage at the end of the particle 
formation (or subsequently) in order to allow the reaction which forms the 
covalent linkages. For instance the dispersion may be left to react at 
ambient temperature for, for instance 3 to 48 hours, but preferably the 
reaction is driven by heating, e.g., to 30 to 90.degree. C., preferably 
35.degree. C. to 60.degree. C. or 70.degree. C., for 1 to 18 hours, e.g., 
3 to 16 hours at 35-55.degree. C. 
The addition of the reactive stabiliser material is often made after the 
particles have been made in the first liquid, e.g., after the 
polymerisation of monomers or after the IFC shell formation is 
substantially complete. 
The invention also includes novel polymeric particles which are 
self-stabilised and which have an outer surface which includes reactive 
groups wherein a polymer stabiliser has been covalently bonded on to the 
particles. Preferably the covalent bond between each particle and the 
stabiliser is an amide bond formed between reactive amino groups on the 
particles and dicarboxylic anhydride groups on the stabiliser. 
An active ingredient may be present in the polymer particles, generally in 
the matrix polymer when the particles are formed of a polymer matrix, or 
in the core of a shell core particle. It can be any active ingredient 
which is useful for the eventual use of the particles. For instance it can 
be an agricultural active ingredient such as a herbicide, insecticide, or 
pesticide. It may be a fragrance, it may be a pharmaceutical or it may be 
a biologically produced material of any type. For instance it may be an 
enzyme. 
The following are examples.

EXAMPLE 1 
This example shows that the microcapsules obtained in Example 1 of 
PCT/GB96/03233 when using hydrolysed maleic acid copolymer stabiliser can 
be post treated to improve the capsules from aggregating in liquid 
detergent formulations. 
Acetic anhydride (2.5 parts) was added to 50 parts of microcapsules 
dispersion in surfactant (Capsules A) under stirring. The mixture formed 
was allowed to react for 1 hour at room temperature (20.degree. C.) to 
give Capsules B. 
The capsules A and B were separately dosed into commercial heavy duty 
liquid detergents at 0.10 KNPU/g protease activity. Each one of the 
detergent mixtures was placed in an oven at 40.degree. C. and subjected to 
the accelerated storage test. 
After 24 hours, the detergent mixture containing Capsules A had aggregated 
and settled to the bottom of the container. The acetic anhydride treated 
microcapsules (Capsule B) remained dispersed and showed no signs of 
instability. After, further 3 days at 40.degree. C., Capsules B showed 
formation of fine aggregates. 
EXAMPLE 2 
Microcapsules were prepared according to Example 1 of PCT/GB96/03233 except 
that an oil-soluble stabiliser having a proportion (about 25%) of 
unhydrolysed (maleic anhydride) groups in the stabilising polymer was 
employed instead of the fully hydrolysed version. 
The resulting capsules (Capsules C) were dosed in liquid detergent at 0.10 
KNPU/g enzyme activity and placed in an oven at 40.degree. C. Also, a 
comparative detergent mixture was made with Capsules A (Example 1 of 
PCT/GB96/03233). Capsules A aggregated and settled to the bottom of the 
container after 1 day storage. Capsules C remain dispersed and showed no 
signs of instability after 1, 4 and 7 days storage. 
EXAMPLE 3 
A dispersion of microcapsules was prepared as in Example 1 of 
PCT/GB96/03233 using a polymeric stabiliser in which the hydrophilic 
groups are hydrolysed to maleic acid groups. The dispersion was then 
treated as in that Example first to dehydrate the dispersion to provide 
anhydrous particles in hydrocarbon, then to exchange the hydrocarbon with 
a non-ionic surfactant to provide an anhydrous dispersion in non-ionic 
surfactant, and then to mix this dispersion into a heavy duty liquid 
detergent at 0.10 KNPU/g enzyme activity. 
When an addition of the same polymeric stabiliser, but in the unhydrolysed, 
anhydride form, was made to the wet or dry dispersion in hydrocarbon or 
the dispersion in non-aqueous liquid, it was found that storage stability 
was improved compared to the process without the addition of this extra, 
anhydride, stabiliser. 
EXAMPLE 4 
The dispersion in hydrocarbon in Example 3, before dehydration, has added 
to it a solution in hydrocarbon of reactive copolymer stabiliser formed 
from (by weight) 65% stearyl methacrylate, 17.5% styrene, 15% maleic acid 
and 2.5% maleic anhydride, or from 55% stearyl methacrylate, 33% methyl 
methacrylate, 10% methacrylic acid and 2% glycidyl methacrylate. The 
resultant dispersion was, in each instance, stirred overnight at 
40.degree. C. to allow covalent reaction to occur between the stabiliser 
and the IFC shell.