Note: Descriptions are shown in the official language in which they were submitted.
10~9~77
This invention relates to concentrated, fluid dis-
persions of amphipathic copolymer aggregates in hemi-solvent
liquids, more particularly to a process for converting such
dispersions into homogeneous solids without the intervention of
arly chemical change.
In our Canadian Patent No. 908892, issued on ~ugust 29,
1972 there is described and claimed a process of preparing in
a hemi-solvent a dispersion of substantially spherical aggregates
. of an amphipathic copolymer which contains at least 5% by
weight of each of two types of polymeric component of mole-
cular weight at least 500 whieh have different solubility
charaeteristies. The process comprises heating the amphipathie
copolymer in the presence of the hemi-solvent to a temperature
above the environmental glass transition temperature (the ; ~:
"environmental Tg") of the polymeric ccmponent of the copoly-
mer which is insoluble in the hemi-solvent, the proportion
of copolymer which is heated with the hemi-solvent being such - :
that on cooling to a temperature below the environmental Ty
of the insoluble component the final mixture of eopolymer and :.
20 . hemi-solvent is completely miscible with added hemi-solvent ~ :~
liquid which is a good solvent for the polymerie component which ::
; is solu~le ln the hemi-solvent present in the final mixture. :~
The dispersions so obtained are proposed in Patent
No. 908892 for use in the formulation of eoating compositions
` because of their generally low viscosity, due, it is believed,
to the existence of the amphipathic copolymer in the dis-
I persions in the form of stable, approximately spherical
-, aggregates, in which the polymeric components which are insoluble
in the hemi-solvent medium cluster together to form a core, this
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core being surrounded by the associated soluble polymeric
componen-ts o~ the copolymer. The dispersions are particularly
suitable for use in coating compositions when the aggregated
insoluble components of the copolymer are at temperatures below
their environmental Tg, that is to say, when they are in the
solid or glassy state, since under these conditions it is
believed that the aggregates are not in equilibrium with
individual copolymer molecules in the hemi-solvent, in the
manner of micelles, but have stable, permanent identities.
It is an essential condition that, in preparing these dis-
persions by heating the two constituents together at a temper-
ature above the environmental Tg of the insoluble components,
a certain critical concentration of copolymer in hemi-solvent
is not exceeded. If this concentration is exceeded above
the environmental Tg, the mixture of copolymer and hemi-
solvent, on cooling to below that temperature, no longer
appears miscible with added hemi-solvent, such addition re-
sulting instead in the formation of separate phases so that
the product is useless as a constituent of a coating composition.
It is believed that under these conditions the insoluble com-
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ponents are not aggregated to form the cores of identifiable,
stable particles but are grossly entangled. It is, however,
disclosed in Patent No. 908892 that dispersions having a:
concentration of copolymer in hemi-solvent which is above
the critical concentration just referred to can be produced
by preparing a dispersion of concentration below the critical
value in the manner described above, and then removing part of
the hemi-solvent, for example, by distillation, provided that
during the distillation or other treatment the li~uid phase
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1~49177
remains a hemi-solvent and the temperature is not allowed to
rise above the environmental Tg of the insoluble components.
Such a concentrated dispersion also contains the amphipathic
copolymer in spherical aggregate form and, like the relatively
more dilute dispersions discussed previously, is comparatively
low in viscosity.
We have now found that certain of these concentrated
dispersions are very suitable for use in the formulation of
casting or potting compositions, by virtue of the fact that
they may be converted into solid materials by a simple heat
treatment involving no chemical change.
- According to the present invention we provide a pro- -
cess for converting into a homogeneous solid mass a concentrated
fluid dispersion of spherical aggregates of an amphipathic block
or graft copolymer in a hemi-solvent as hereinafter defined,
the process comprising the steps of (i) heating the concen~
trated dispersion, without significant change in the concentra-
' - tion of the copolymer in the hemi-solvent, to a temperature
above the environmental glass transition temperature o the
20 components of the copolymer which are insoluble in the hemi- -
solvent and ~ subsequently cooling the resulting fluid
composition to a temperature below the said transition temper-
ature.
By an amphipathic copolymer we mean a block or grat - .
copolymer as defined in Patent No. 908892, that is to say a
block or graft copolymer comprising at least two polymeric ~.
~-. components of molecular weight at least 500, the said compo-
nents having such differences in their chemical nature that they
differ significantly from each other in their solubility charac-
teristics.
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A hemi-solvent liquid. is defined as a liquid or
mixture of liquids which is a good solvent for one polymeric
component and a non-sol~ent or precipitant for another
polymeric component of an amphipathic copolymer By a good
solvent we mean a solvent which is better than a theta solvent,
the nature of a theta solvent being discussed in "Polymer
Handbook" (Ed. Brandrup and Immergut, Interscience 1966) For
the purposes of the present invention, amphiphatic copolymers
are further defined as being copolymers in which the weight
ratio of the components insoluble in a given hemi-solvent to
the components soluble in that hemi-solvent is not less than
50:50. :
By a concentrated, fluid dispersion of an amphipathic
block or graft copolymer in a hemi-solvent is meant in the
present context a dispersion wherein the concentration of the
copolymer in the hemi-solvent is not less than 20% by weight
. and is such that when the dispersion is heated.without ~` :
significant loss of hemi-solvent to a temperature above the
environmental glass transition temperature of the insoluble
~omponents of the copolymer and is subsequently cooled to a
temperature below the said transition temperature, the ~:
dispersion is transformed into a homogeneous, solid mass. .
The term environmental glass transition temperature" .:
used herein (abbreviated to "environmental Tg") means ~e
. temperature at which the insol~bLe component of the copolymer
passes from the glassy to the non-glassy state, or vice versa,
~ in the environment constituted by the hemi-solvent with which
; it is in contact. In general, the environmental Tg will be
substantially below the Tg as normally determined for the
material of the insol.uble components on samples of pure high
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molecular weight bulk polymer. This is because (1) the
hemi-solvent liquid may contain minor proportions of liquid,
which, alone, would be a good solvent for the insoluble com-
ponents; (2) in many cases the molecular weight of ~he insoluble
components is relatively :Low; and (3) the soluble components
of the copolymer are also present. Normally the environmental
Tg of the material of the insoluble components measured in bulk
should be at least 20C, and preferably at least 50C, above
the maximum ambient temperature to which the dispersion will
be subjected during storage. Exact determination of the envi-
ronmental Tg may be carried out on polymer of the same molecular
weight and composition as the insoluble polymeric components
present in the amphipathic copolymer. This polymer must have
been equilibrated in the relevant hemi~solvent environment. The
determination may be made by differential thermal analysis or
similar wellknown techniques.
As is explained in the specification of Patent No.
908,892, relatively low concentration dispersion of amphipathic
copolymer in hemi-solvent are fluid at temperatures both above
and below the environmental ~g of the insoluble components. In
contrast, as will be understood from the foregoing description,
analogous compositions of concentration above the critical value
are fluid dispersions above the environmental Tg and are homo-
geneous solids below that temperature. The exact minimum value
of the concentration which is required in order that the present
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to another, according to its structure and molecular weight, and ~ -~
also varies with the particular hemi-solvent employed. The
higher the molecular weight and the higher the weight fraction
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of the insoluble component, the lower will be this limiting
concentration. When the molecular weight of the amphipathic
copolymer is of the order of 10,000 and. the proportion of
soluble component approaches the upper limit of 50% o~ the total
weight of the molecules, the limiting concentration may be as
high as 50%. In the case of copolymers having a molecular
weight of several thousands and having a ratio of insoluble
to soluble components of 3:1, the limiting concentration may
be in the region of 20%. :
In view of the foregoing considerations, it is
preferred that the copolymer dispersions used in the process :
of the invention should have a weight ratio of insoluble
components to soluble components of the amphipathic copolymer
of at least 67:33. It is also preferred that the total
molecular weight of the copolymer should.not exceed 200,000.
However,for any particular combination of amphipathic copolymer
- and hemi-solvent, the minimum concentration of copolymer
required to give the benefits of the present invention is .
readily established by means of a series of simple tests. ::.
It is further preferred that ~he weight ratio of
insoluble to soluble components in the amphipathic copolymer
should not be greater than 80:20.
The amphipathic copolymer, when prepared, should be ~.
as free as possible from any ungrafted polymer species insoluble
in the hemi-solvent en~ironment.
'I In selecting suitable hemi-solvents to be used
with any given amphipathic copolymer, it is necessary to
appreciate that the difference in solubility of the two
components will generally derive from differences in polarity~
Therefore, the principle to be observed is that "like dissolves
like"; that is polar polymeric components are dissolved by
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liquids of similar polarity, or a highly polarizable liquid,
while non-polar polymeric components are solvated by non-
polar liquids. Those liquids which will or will not dissolve
polymeric components of given polarity are well known to
those skilled in the art and are illustrated for example in
British Patent Specificatio~ ~o~ 1,052,241 and in page IV~ -~
185-234 of "Polymer Handbook" (Ed. Brandrup and Immergut,
Interscience 1966).
For example, non-polar liquids such as aliphatic or
cyclo-aliphatic hydrocarbons or long chain alcohols will
dissolve non-polar polymeric components such as:
copolymers of ethylene and copolymers of propylene;
polymers of vinyl stearate;
polymers of an ester of along chain alcohol with
acrylic or methacrylic acid;
polyesters derived from a long chain hydroxy
carboxylic acid;
but will not dissolve polar polymeric components such as:
polymers of an ester of a short chain alcohol with
acrylic or methacrylic acid;
polyesters of a short chain hydroxy carboxylic acid;
polyvinyl chloride;
polyacrylonitrile.
Conversely, polar liquids will not dissolve non-
polar polymeric components such as those listad above, but
they will dissolve polar polymeric components such as those
listed above.
The preparation of graft or block copolymers from
such polymeric components is well known to those skilled in
the art and reference may be made to British Patent
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Specification No. 1,122,397 and to "Graft Copolymers" (Battaerd .
and Tregear, Interscience 1967) and "Copolymerisation" (Ham,
Interscience 1964).
When the amphipathic copolymer is a graft copolymer,
it is preferred that it should be of the type in which a ¦
polymeric backbone has grafted on to it a plurality of
polymeric side-chains, and that the backbone should constitute
the insoluble component of the copolymer an~ the side chains
the soluble components. Where the amp~ipathic copolymer is a
10 block copolymer, it may be advantageous in certain cases if .
it is of the ABA type, where the A blocks constitute the
soluble components and the B`block the insoluble component
As already indicated, the concentrated dispersions
used in the process o~ the invention ma~ be prepared by (i)
heating an amphipathic block or gra~t copolymer as herein- .
before defined with a hemi-solvent as hereinbefore defined to
a temperature above the environmental Tg of the polymeric
components o the copolymer which are insoluble in the hemi-
solvent, the proportion of hemi-solvent to copolymer employed
20 being such that the resulting ~luid composition on cooling to - .
a temperature below the said environmental Tg forms a stable,
fluid precursor dispersion of substan~ially spherical
: ag~regates o~ the copolymer, and (ii) xemoving from the said
precursor dispersion at a temperature below the environmental
Tg a su~icient proportion o hemi sol.vant to give a dispersion
having a copolymer concentration which is not less than 20% by ~.
weight and is such that when th~ said concentrated _ .
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dispersion is heated without significant loss of hemi-solvent
to a temperature above the environmental Tg and is subsequently
cooled to a temperature below the environmental Ty, the disper-
sion is transformed into a homogeneous, solid mass.
Preferably the removal of part of the hemi-solvent
from the precursor dispersion first obtalned, in order to pro-
vide the final, concentrated dispersion, is carried out by
distillation, if necessary under reduced pressure so that the
hemi-solvent can be volatilised without the environmental Tg
of the insoluble components being exceeded. It is, however,
essential to ensure that, as such volatile constituents of the
dispersion are removed, the remaining li~uid phase of the dis-
persion must still be a hemi-solvent for the amphipathic copoly-
mer.
The temperature to which the amphipathic copolymer is
initially heated with the hemi-solvent may be only just above
that at which the insoluble components cease to be in the glassy
form. However, the rate at which the copolymer becomes dispersed
in the hemi-solvent depends upon the extent to which the temper-
ature used exceeds the environmental Tg of the insoluble compo-
nents and it is, therefore, preferred that the copolymer is
heated to a temperature of up to 100C above the environmental Tg.
With reference to the foregoing discussion of the in-
, fluence of temperature and concentration upon the nature of
compositions comprising an amphipathic copolymer and a hemi-
solvent, and also to the discussion in Patent ~o. 908,892, it
may be surmised that, in preparing the concentrated dispersions
to be used in the process of the invention, the fact that the
removal of part of the hemi-solvent from the relatively -~
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dilute precursor dispersion is performed at a temperature at
which the insoluble components of the copolymer are in the
glassy state means that the microparticles o~ copolymer present
have no possibility of re-arranging their structure into that
which they would otherwise possess under the conditions of
relatively high concentration, namely a structure which is
not one of essentially spherical particles but is believed, as
already stated, to be a disordered arrangement in which the
insoluble components may be grossly entangled with one another.
HoweverD as soon as the concentrated dispersion is heated to
a temperature above the environmental Tg in step (i) of ~he
present process, such a re-arrangement of structure can occur
because ofthe mobility of the insoluble components. On cooling
below the environmental Tg, in step (ii) of the process, the
postulated disordered, entangled structure persists and the
composition becomes an apparently homogeneous, solid mass. It
retains this form indefinitely, so long as the lower temperature
is maintained, even in prolonged contact with added hemi-
solvent.
In converting the concentrated, fluid dispersion to
a solid product according to the process hereinabove de~ined,
it is preferred that the dispersion should be heated to a
temperature which is very appreciably above the environmental
Tg of the insoluble components of the copolymer, for example
at least 100C. above that temperature. In general, this
preferred temperature of heating will be higher than the
temperature to which the amphipathic copolymer and hemi-solvent ;~
are heated in the initial preparation of the relatively dilute
precursor dispersion. This preference is based on the fact
that the greater the difference between the environmental Tg
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177
and the temperature at which conversion to the disordered
struc-ture is e~fected, the greater is the rigidity and
strength of the solid mass obtained on cooling. This effect
is believed to be attributable to the existence of a
higher energy barrier towards transition, from the ordered,
essentially spherical aggregated structure of the copolymer
molecules to the disordered, entangled structure than that
which operates in the reverse transition.
~s a matter of convenience, the temperature to
which the concentrated, fluid dispersion is heated in order
to convert it to a solid product may be chosen to be at least
100C above the Tg for the bulk polymer of which the in-
soluble components of the copolymer consist~ rather than as
stated above. Since the environmental Tg of the insoluble
components will, as explained earlier, always be lower than
the bulk Tg of these components, a heating temperature so chosen
will be amply adequate to effect the desired transition between
the ordered and the disordered structures Provided this
preferred form of the process is carried out, therefore, the
experimental determination of the environmental Tg of the
insoluble components can be replaced by the rather more
straightorward determination of the corresponding bulk Tg,
for example by differential scanning calorimetry, where that
information i9 not already available from published data.
From the foregoing description it will be evident ~
that the present invention provides a means of rapidly trans- -
forming low viscosity fluids which are permanently stable when
kept at normal temperatures, by a simple heating and cooling
process, into homogeneous solid masses without any change
whatever in their chemical composition. The process of
the invention is, therefore, admirably suitable for
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casting and potting techniques, ~or example t~e encapsulation
and protection of electronic equipment and other articles of
a delicate nature. The absence of any chemical r~action from
the process means that there is no risk of attack upon the
articles being so treated by reactive chemical species, nor
is there any risk of local overheating due to exothermic
effects. In carrying out such casting or encapsulating
operations, some form of containing mould will normally be
employed and two alternative methods are available. In the
first method, the concentrated fluid dispersion is poured
into the mould(in which any article to be encapsulated has
already been placed) at ambient temperature; the mould and
contents are then heated to a temperature above the environmental
: Tg and subsequently allowed to cool. In the second method, the ..
concentrated fluid dispersion is separately heated to above
the environmental Tg and is then poured into the mould and
allowed to cool. Where other considerations permit, the first
method is to be preferred since the viscosity of the concentrated
dispersion at ambient temperature is mormally lower than that
20 of the same composition at a temperature above the environmental -
Tg, due to the disordered structure of the latter. If the
.~ second method is to be employed, it is desirable to heat the :
dispersion to a higher temperature than is employed in the
~irst method, in order to offset this viscosity increase
The invention is illustrated by the following
Examples, in which parts and percentages are by weight unless
otherwise stated~ '
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EXAMPLE 1
In this Example there was employed an amphipathic
graft copolymer prepared in known manner having a backbone
of poly(methyl methacrylate) and side chains of poly~12-hydroxy-
stearic acid) in a weight ratio of 75/25 respectively. The
molecular weight of the copolymer was approximately 56,000 and
of the side chains approximately 1700. Hence the average
number of side chains per molecule was 8. The bulk Tg of
the backbone was about 100C.
To a gelatinous solid consisting of 40 parts of
the above graft copolymer mixed with 60 paxts of high-boiling
aliphatic hydrocarbon, which contained large irregular
aggregates, were added 280 parts of medium-boiling aliphatic
hydrocarbon(boiling point approximately 160C). Both hydro-
carbons were hemi-solvents for the copolymer. The temperature
of the mixture was raised to 160C. and maintained at that
temperature for one hour with stirring to form a dispersion of
aggregates in hydrocarbon in which t~e poly-(hydroxystearic
acid) component was soluble. The dispersion was allowed to
~0 cool to 80C. to form micro,-particles. A~ this stage,
the polymer concentration was 11%. The dispersion was
concentrated by removing medium-boiling aliphatic hydrocarbon
by distillation under reduced pressure at temperatures below
80C. (i,eO below the environmental Tg of the poly(methyl
methacrylate) backbone~.
The resulting concentrated dispersion had a polymer
content of 40%; a viscosity of approximately 2 poises at
25C.
A portion of the concentrated, fluid dispersion was
poured into a glass mould, which was then slowly heated until
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the temperature of the contents reached approximately 140C.
(i e above the environmental Tg of the poly (methyl
methacrylate)backbone~; the mould and contents were then
allowed to cool to room temperature The mould was found to
contain a translucent, slightly opalescent gelatinous solid
which was immobile and could not be poured. The combined
weight of the mould and its contents was the same before and
after the heat treatment.
Another portion of the concentrated fluid dispersion
10 was treated in the manner just described, except that the
temperature of the contents of the mould was raised to 170C.
before cooling. In this case the mould was found to contain
a clear, wax-like solid. There was again no loss in weight
. of material during the heat treatment.
EX~MPLE 2 .
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In this Example there was employed an amphipathic
graft copolymer, prepared in known manner having a backbone
of poly(methyl methacrylate). and side-chains of poly ~ -
(12-hydroxystearic acid) in a weight ratio of 70:30. The
20 molecular weight of the copolymer was approximately 47,000
(peak, as determined by gel phase chromatography)and that of
the side-chains 2,400. The bulk Tg of the backbone was about
100C. 20 parts of this graft copolymer and 180 parts of
aliphatic hydrocarbon (boiling range 205-215C,) were heated
at reflux temperature for 30 minutes; the temperature was.
then lowered to 80C and aliphatic hydrocarbon removed by ~ :
distillation under reduced pressure until the xesidue had
a pol~mer content of 45%. The concentrated, fluid dispersion . .
so obtained was then heated momentarily to reflux temperature,
30 at which it had the consistency of a mobile syrup; no
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significant evaporation of the hemi-solvent hydxocarbon
occurred during this operation. The hot syrup was then poured
into a mould and allowed to cool. The resulting product was
a clear, rubbery solid which could not be poured and which
was free from voids, bubbles or cracks.
EXAMPLE 3
In this Example, the rubbery solid obtained as
described in Example 2, consisting of 45% graft copolymer and
55% hemi-solvent, was employed as starting material. This
solid was broken up into irregular fragments of about 1 cm.
diameter. .
In a first experiment, a portion of the solid : .
fragments was covered with sufficient hemi-solvent aliphatic
hydrocarbon (boiling range 100-120C.) to give a polymer ~-
concentration in the total mixture of 8.5%. The mixture was
left at room temperature and examined at intervals over a .
period of three years. ~o change in ~he appearance of the ~ :
. ~ . .
material was observed over the whole of this period, the
fragments of solid being unaffected and the hemi-solvent
remaininglas separate, fluid phase.
In a second experiment, a further portion of the
solid fragments was mixed with hemi-solvent as in the first
experiment to give a polymer concentration of 8.5%. The - ~ .
mixture was then heated at 90-95C. for 30 minutes with
stirring and allowed to cool. The product was an opalescent,
fluid and homogeneous dispersion of spherical micro-particles~
of copolymer which were completely stable and showed no
tendency to flocculate or aggregate, either when subjeatad to
high shear or when stored at room temperature for three
years.
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In a third experiment, a portion of the stable
dispersion obtained in the second experiment was concentrated
by removal of the lower boiling hemi-solvent by distillation
at 80C. under sub-atomospheric pressure The product
obtained had a polymer concentration of 45%, but, although
similar to chemical composition to the solid fragments used
in the first experiment, it was a fluid dispersiion, having
a viscosity of 0.8 po~ise at 25C. when measured at a shear
rate of 104 sec. l and showing no tendency to flocculate ~:
l0 or aggregate. When a portion of the dispersion was dilu.ted. : -
with the low boiling aliphatic hydrocarbon to a polymer content
of 8.5%, it resembled in all respects t~e product from the
second experiment described above~
; In a further experiment,a portion of the dispersion
of polymer content 8.5% produced in the second experiment . .
was concentrated by removing hemi-solvent by distillation under
atmospheric pressure until the polymer content was 45%. The
final temperature of the concentrated dispersion was 205C. ~. -
On cooling to room temperature, the product obtained was a -
' 20 clear, rubbery solid which was identical in appearance to
; the product described in Example 2.
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