CATIONIC POLYMER

POLYMERE CATIONIQUE

English Abstract

The invention provides a water swellable, water-insoluble polymer comprising
units derived from a diallylic quaternary ammonium salt monomer cross-linked
by a suitable polyfunctional vinyl compound, at least a substantial proportion
of the function groups being in basic form. The invention also provides a
process for the production of a water-swellable, water-insoluble polymer which
comprises polymerising a diallylic quaternary ammonium salt monomer and a
suitable polyfunctional vinyl compound as cross-linking agent by cationic
polymerisation in an aqueous phase using a free radical catalyst and polymers
obtainable thereby. The water absorbent polymers are superabsorbents having
improved water absorption properties particularly in respect of saliva
solution.

French Abstract

L'invention porte sur des polymères gonflant au contact de l'eau et insolubles dans l'eau comportant des unités dérivées d'un monomère du type sel diallylique d'ammonium quaternaire réticulé par un composé polyfonctionnel vinylique, une partie au moins substantielle des groupes fonctionnels se présentant sous une forme basique. L'invention porte également sur le procédé de production des susdits polymères consistant à polymériser un monomère du type sel diallylique d'ammonium quaternaire avec un composé vinylique polyfonctionnel adéquat utilisé comme agent de réticulation, par polymérisation cationique en phase aqueuse à l'aide d'un catalyseur à radicaux libres et les polymères ainsi obtenus. Les polymères absorbant l'eau sont des polymères superabsorbants présentant des propriétés d'absorption de l'eau accrues, en particulier pour ce qui est de la salive.

Claims

14
Claims
1. A water-swellable, water-insoluble polymer
comprising units derived from a diallylic
quaternary ammonium salt monomer, cross-linked by
a suitable polyfunctional vinyl compound,
characterised in that the polymer has been
produced by cationic polymerisation in an aqueous
phase using a free radical catalyst.
2. A water-swellable, water-insoluble polymer
comprising units derived from a diallylic
quaternary ammonium salt monomer cross-linked by
a suitable polyfunctional vinyl compound,
characterised in that at least a substantial
proportion of the functional groups are in basic
form.
3. A water swellable, water insoluble polymer as
claimed in claim 1 or 2 wherein the monomer has
the formula
<IMG>
wherein R1 and R2, which may be the same or
different, are each organic radicals which do not
adversely affect the properties of the polymer and
X is a suitable anion.
4. A water swellable, water insoluble polymer as
claimed in claim 3 wherein R1 and R2 are each
independently an optionally substituted saturated
hydrocarbon group or aryl group.

5. A water swellable, water insoluble polymer as
claimed in claim 4 wherein the saturated
hydrocarbon group or the aryl group may be
substituted by one or more suitable substituents
selected from carboxyl, ester, hydroxyl, ether,
sulphate, sulphonate, primary, secondary or
tertiary amines or quaternary ammonium groups.
6. A water swellable, water insoluble polymer as
claimed in any of claims 3 to 5 wherein the groups
R1 and R2 and the R groups in the ester and ether
substituents have from 1 to 20 carbon atoms, more
preferably from 1 to 6 carbon atoms.
7. A water swellable, water insoluble polymer as
claimed in claim 6 wherein the R1, R2 and R groups
are methyl.
8. A water swellable, water insoluble polymer as
claimed in any of claims 3 to 7 wherein X is a
halide, nitrate, phosphate, nitrite, carbonate,
bicarbonate, borate, sulphate or a carboxylate
anion.
9. A water swellable, water insoluble polymer as
claimed in claim 8 wherein X is a chloride or
hydroxide anion.
10. A water swellable, water insoluble polymer as
claimed in any of claims 3 to 9 wherein the
monomer is dimethyl diallyl ammonium chloride or
dimethyl diallyl ammonium hydroxide.
11. A water swellable, water insoluble polymer as
claimed in claim 10 wherein the monomer is
dimethyl diallyl ammonium chloride.

16
12. A process for the production of a water-swellable,
water-insoluble polymer which comprises
polymerising a diallylic quaternary ammonium salt
monomer and a suitable polyfunctional vinyl
compound as cross-linking agent by cationic
polymerisation in an aqueous phase using a free
radical catalyst.
13. A process as claimed in claim 12 wherein the
crosslinking agent is a vinyl compound having two
or more polymerizable bonds in the molecule.
14. A process as claimed in claim 13 wherein the
crosslinking agent is divinyl benzyl or N,N-methyl
bisacrylamide.
15. A process as claimed in any of claims 12 to 14
wherein the quantity of crosslinker in mole %
relative to the number of moles of monomer is in
the range of from 0.01 to 20%, preferably from
0.05 to 5%.
16. A process as claimed in any of claims 12 to 15
wherein the free radical initiator is an organic
peroxide, a persulphate or an azo compound.
17. A process as claimed in claim 16 wherein the free
radical initiator is hydrogen peroxide, ammonium
persulphate or 2,2-azo (2-methyl propionamidine)
dihydrochloride.
18. A process as claimed in claim 17 wherein the free
radical initiator is 2,2-azo (2-rnethyl
propionamidine) dihydrochloride.

17
19. Use of a polymer as claimed in any of claims 1 to
12 for the absorption of electrolyte containing
aqeuous liquids.
20. Use as claimed in claim 19 wherein the liquid is
menses or urine.
21. Use as claimed in claim 19 or 20 wherein the
polymer is in base form and is used in conjunction
with an anionic superabsorbent in free acid form
or a cation exchanger in acid form.

Description

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CATIONIC POLYMER
The present invention relates to a cationic
polymer more particularly a water absorbent polymer of
the type commoniy referred to as a "superabsorbent".
The substances currently termed ''superabsorbentsll
are typically slightly cross-linked hydrophillic
polymers. The polymers may differ in their chemical
nature but they share the property of being capable of
absorbing and retaining even under moderate pressure
amounts of aqueous fluids equivalent to many times
their own weight. For example superabsorbents can
typically absorb up to 100 times their own weight or
even more of distilled water.
Superabsorbents have been suggested for use in
many different industrial applications where advantage
can be taken of their water absorbing and/or retaining
properties and examples include agriculture, the
building industry, the production of alkaline batteries
and filters. However the primary field of application
for superabsorbents is in the production of hygienic
and/or sanitary products such as disposable sanitary
n~k; n.~ and disposable diapers either for children or
for incontinent adults. In such hygienic and/or
sanitary products, superabsorbents are used, generally
in combination with cellulose fibres, to absorb body
fluids such as menses or urine. However, the absorbent
capacity of superabsorbents for body fluids is
dramatically lower than for deionised water. It is
generally believed that this effect results from the
electrolyte content of body fluids and the effect is
often referred to as "salt poisoning".

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The water absorption and water retention
characteristics of superabsorbents are due to the
presence in the polymer structure of ionisable
functional groups. These groups may be carboxyl
groups, a high proportion of which are in the salt form
when the polymer is dry but which undergo dissociation
and solvation upon contact with water. In the
dissociated state, the polymer chain will have a series
of functional groups attached to it which groups have
the same electric charge and thus repel one another.
This leads to expansion of the polymer structure which,
in turn, permits further absorption of water molecules
although this expansion is subject to the constraints
provided by the cross-links in the polymer structure
which must be sufficient to prevent dissolution of the
polymer. It is assumed that the presence of a
significant concentration of electrolytes in the water
interferes with dissociation of the functional groups
and leads to the "salt poisoning" effect. Although most
commercial superabsorbents are anionic, it is equally
possible to make cationic superabsorbents with the
functional groups being, for example, quaternary
ammonium groups. Such materials also need to be in
salt form to act as superabsorbents and their
performance is also affected by the salt-poisoning
effect.
EP-A-0161762 relates to partially cross-linked
copolymers of at least one diallylic quaternary
~mmQn;um salt, preferably a diallyldialkylammonium
halide. The polymers are prepared by inverse
suspension polymerisation with an oil phase as the
continuous phase anà an aqueous phase as the
discontinuous phase. The polymers which are produced
directly in salt form are said to be water-swellable
polymers whose water absorbtion properties are not
significantly diminished when used to absorb saline

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solutions. However, the specific example in EP-A-
0161762 relates to a material wnich has, on the basis
of the results reported in the specification, a water
absorption capacity in 0.9~ by weight NaCl solution
only about 20~ of its absorption capacity in deionised
water.
It is an object of the present invention to
provide a cationic water absorbent polymer with
improved water absorption properties and in particular
water absorption properties in respect of saline
solution.
According to one aspect, the present invention
provides a water-swellable, water-insoluble polymer
comprising units derived from a diallylic quaternary
ammonium salt monomer, cross-linked by a suitable
polyfunctional vinyl compound, characterised in that
the polymer has been produced by cationic
polymerisation in an aqueous phase using a free radical
catalyst.
According to another aspect, the present invention
provides a wa~er-swellable, water-insoluble polymer
comprising units derived from a diallylic quaternary
ammonium salt monomer cross-linked by a suitable
polyfunctional vinyl compound, characterised in that at
least a substantial proportion of the functional groups
are in basic form.
According to a still further aspect, the present
invention provides a process for the production of a
waterswellable, water-insoluble polymer which comprises
polymerising a diallylic quaternary ammonium salt
~o~o~r and a suitable polyfunctional vinyl compound as
cross-linking agent by cationic polymerisation in an
aqueous phase using a free radical catalyst.

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It has surprisingly been found according to the
present invention that polymerising a diallylic
quaternary ammonium salt monomer together with a
suitable cross-linking agent by cationic polymerisation
in an aqueous phase produces a water-swellable, water-
insoluble polymer having significantly improved
properties as compared to the polymers of EP-A-0161762.
More particularly, the polymer produced by cationic
polymerisation ln the aqueous phase shows improved
water absorption in deionised water and/or in saline
solution.
As already noted, the polymers of EP-A-0161762 are
produced by inverse suspension polymerisation. It is
to be expected that the different polymerisation
methods as between EP-A- 0161762 and the present
invention, i.e. inverse suspension polymerisation as
opposed to cationic polymerisation in the aqueous
phase, will lead to differences in the final product.
20 These differences may reside, for example, in
uniformity of cross-linking and uniformity of molecular
weight. Whilst these differences cannot be
identified and defined, the differences in properties
between the products and in particular the improved
properties of the product according to the present
invention, demonstrate that the products themselves are
different.
The present invention is applicable to any
diallylic quaternary ammonium salt monom~r which is
suitable for the production of water-swellable
polymers. Essentially the monomers have the formula

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CH2 CH Rl CH CH2
., I I I
H2C - N CH2
wherein R1 and R2, which may be the same or
different, are each organic radicals which do not
adversely affect the properties of the polymer and X is
a suitable anion.
Preferably Rl and R2 are each independently an
optionally substituted saturated hydrocarbon group or
aryl group. For example the saturated hydrocarbon group
may be an alkyl group which may be straight or branched
chain or cyclic. The aryl group also includes arylalkyl
groups. Preferably the groups R1 and R2 have from 1 to
20 carbon atoms, more preferably from 1 to 6 carbon
atoms. The saturated hydrocarbon group or the aryl
group may be substituted by one or more suitable
substituents selected from carboxyl, ester, hydroxyl,
ether, sulphate, sulphonate, primary, secondary or
tertiary amines or quaternary ammonium groups. In the
case of ester (-CO2R) and ether (-O-R) the R group is
a hydrocarbon radical having from 1 to 20, preferably
from 1 to 6 carbon atoms, more preferably the R group
is methyl. In the case of aryl groups, suitable
substituents include saturated hydrocarbon groups as
defined above. The preferred groups for Rl and R2
are methyl groups.
X may be any suitable anion which may be inorganic
or organic. Suitable inorganic anions include halide
(in particular fluoride, chloride, bromide and iodide),
nitrate, phosphate, nitrite, carbonate, bicarbonate,

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borate, sulphate and hydroxide. Suitable organic
anions include carboxyiate such as acetate citrate,
salicilate and propionate.
Preferably the anion is a chloride or hydroxide
ion.
Preferred monomers are diallyl dimethyl ammonium
chloride and dimethyl diallyl ammonium hydroxide.
A particularly preferred diallylic quaternary
ammonium salt monomer is dimethyldiallyl ammonium
chloride.
Polymerisation of a diallylic quaternary ammonium
salt monomer in the presence of a free-radical
initiator produces a linear polymer as follows:
CH2 CH Rl CH CH2 _ -
20H2C--N3--CH2 ~CH2 CH--CH--CH2
R2 CH2 CH2
~ \ N /
Rl R2 - n
where n is the number of monomer units. In order
to ensure that the polymer rem~- n.~ insoluble on
swelling with water, it is necessary to introduce a
sufficient degree of crosslinking into the polymer by
including a suitable crosslinking agent in the
polymerisation reaction.
Suitable cross-linking agents are generally vinyl
compounds with two or more polymerisable double bonds
in the molecule. Specific examples of cross-linking

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agents include divinyl benzene and N,N-methylene
bisacrylamide. The crosslinker should be employed in
a sufficient quantity such that the absorbent gelling
material (AGM) produced is insoluable when it is in
contact with aqueous solutions, however the crosslinker
must not be used in such quantities that it interferes
with the ability of the AGM to absorb aqueous
solutions. The amount of crosslinker used in mole
relative to the number of moles of monomer is in the
range of from 0.01 to 20~ and preferably in the range
of from 0.05 to 5~.
The cationic polymerisation according to the
invention takes place in aqueous medium in the presence
of a suitable free-radical initiator. Any free radical
initiator of the type conventionally used for cationic
polymerisation can be used including organic peroxides,
such as hydrogen peroxide, persulphates, such as
ammonium persulphate and azo compounds, such 2,2-
azobis(2-methyl propionamidine) dihydrochloride.
Preferred free radical initiators include azo compounds
and particularly azobisisobutyronitrile ("AZBN").
The process for polymerization may be conducted as
followR:
The following solutions were prepared:
a) An aqueous 60~ solution of monomer.
b) An approximate 230g/1 solution of crosslinker in
distilled water.
c) An approximate 60g/1 solution of a free radical
initiator in distilled water.
a) was disareated with, for example, a vacuum pump.
Thereafter b) and c) were added to a) with continuous
stirring. The mixture was heating to approximately
60~C. A solid product formed after approximately four

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hours. The product was cut to obtain smaller pieces
and swelled by adding approximately 4 litres of
distilled water thereto. After approximately 2 hours
the swelled gel was filtered using, for example, a
nonwoven fabric tissue filter. The gel was dried, for
example, in a ventilated air oven at approximately 60~C
for approximately l0 hours resulting in approximately
l00g of dried product.
The product formed may be converted into basic
form by swelling the product in distilled water, adding
an alkali solution for example NaOH with continuous
stirring, after approximately l hour the gel was
filtered. Treatment with hydroxide and filtering was
lS repeated until no further chloride ions were present in
the washing waters; this may be measured by
precipitation titration using silver nitrate (AgN03).
The gel was washed with distilled water until the
washing water had a pH of 7. The product is dried, for
example, in a ventilated air oven.
Apart from differences in terms of the nature of
the product, the process according to the present
invention which involves solution polymerisation in
aqueous medium has advantages over the inverse
su~pension polymerisation process of EP-A-0161762 in
terms of the process itself. In particular, solution
polymerisation in aqueous medium requires addition of
fewer components to the reaction medium, for example
emulsifiers are not required, and this leads to less
impurities in the final product. In addition the
polymerisation proceeds better with a product of higher
molecular weight being formed.
The process according to the present invention
leads to a product which can be used as an absorbent
for water or saline in either salt or basic form. The

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basic form of the polymer may be obtained from the salt
form of the polymer by conversion with alkali as
described previously.
In use in absorbing saline, for example in the
form of salt containing liquids such as urine or
menses, there are considerable advantages in using the
polymer according to the invention in basic form. In
this case, at the same time as absorbing the liquid,
the polymer also has a desalting effect on the liquid
by virtue of the con~ersion of the polymer into the
salt form. As the polymer according to the invention is
a strong ion exchanger the polymer will spontaneously
con~ert to the salt form of the polymer when in contact
lS with saline solution.
The absorbent according to the present invention
is particularly suitable for use in applications where
it is desired to absorb salt containing aqueous
liquids. Examples of such liquids include in
particular menses and urine and the absorbent material
can be used as the filling in catemenials and diapers
generally in admixture with a fibrous absorbent such as
cellulose fluff. The absorbent according to the
present invention in base form can also be used in
conjunction with an anionic superabsorbent in free acid
form or a cation Pxch~nger in acid form as described in
our copending patent applications nos ... (internal
reference DR 24) and ... ( internal reference DR 26)
respectively.
The invention is illustrated further by the
following examples.
ExamDle 1
lO g of a 60~ aqueous solution of diallyldimethyl

-
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ammonium chloride was mixed with 0.0172 g of N,N-
methylene-bisacrylamide (cross-linking agent) with
continuous stirring in a 150ml vacuum flask. Nitrogen
gas was bubbled into the reaction vessel for 15
minutes, after which 0.015 g of ammonium persulphate
(free radical initiator) was added and the reaction
mixture heated to 70~C and maintained at that
temperature for 3 hours stirring was continued with a
magnetic bar until the bar is prevented from moving.
As the polymer forms the solution gels and becomes a
- solid.
A large volume of deionised water was then added
to the polymer and the polymer was allowed to swell for
24 hours, creating a swelled gel. The swelled polymer
was then dried in a forced convection oven for 10 hours
at 100~C and the dried polymer mechanically blended to
a powder. The resultant polymer is in salt form. The
base form is obtained by treatment of the polymer in Cl
form with alkali (NaOH 0.01m~ as follows:
20g of polymer were placed in a 10 litre beaker
and 4 litres of distilled water were added thereto.
After the polymer has swelled 500ml of NaOH were added
with continuous stirring. After 1 hour the gel was
filtered with a nonwoven fabric tissue filter. The
NaOH treatment and filtration steps were repeated until
no further chloride ion were present in the washing
waters (by agentometic titration). The gel was then
washed with distilled water until the waters are
neutral (pH 7). The gel was dried in a ventilated oven
at 60~C to obtain the product.
The dried powder was tested for absorption of
deionised water and 0.9~ sodium chloride solution
according to the method described below in Example 2
which is equivalent to that reported in EP-A-0161762.

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11
The results were as follows:
Absorption g/g
(Tea-bag test)
Deionised 0.9~
Water NaCl
Polymer of Example 1 in salt form 320 55
Polymer of Example 1 in base form 350 48
s Polymer of EP-A-0161762 160 31
The above results show that the polymer according
to the invention shows a surprisingly greater
absorption that the polymer of EP-A-0161762 both in the
case of deionised water and 0.9~ NaCl solution. The
polymer according to the invention can absorb liquid
irrespective of whether it is in the salt or base form.
Exam~le 2:
Pre~aration of Fai 7 OH
133g of 60~ aqueous solution of dimethyl diallyl
~m~o~lum chloride ~DMAC available from fluka) were
weighed into a 250ml flask.
0.2g of bisacrylamide (BAC available from fluka)
were weighed separately into a 5ml test tube and were
dissolved using 2ml of distilled water.
0.12g of ammonium persulfate (free radical
initiator) were dissolved in a 5ml test tube using 2ml
of distilled water.
The monomer solution was disareated by vacuum
using a vacuum pump.

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12
Thereafter under continuous stirring the
crosslinker solution and free radical intiator were
added to the monomer solution, the temperature was
adjusted to 60~C by placing the flask in a thermostatic
bath for four hours.
The solid product formed was cut using a spatula
and transferred in 5 litre beaker containing 41 of
distilled water, after two hours the swelled gel was
filtered by a nonwoven tissue fabric filter. The gel
was dried in a ventilated oven at 60~C for 12 hours.
60g of dried polymer was collected and called Fai 7 Cl.
20g of Fai 7 Cl was placed in a 10 litre beaker and
swelled by adding 41 of distilled water, under
contlnuous stirring. When the polymer has swelled
(after 2 hours) 500 ml of 0.01 M NaOH solution was
added and after 30 minutes the gel was filtered using
a nonwoven fabric tissue filter. These operations
(alkalinization and filtration) were repeated until
there were no chloride ions in the washing waters
(chloride ions may be checked by AgN03 reaction). At
this point the gel was washed with distilled water
until there was no further evidence of the basic
reaction of the washing waters.
At the end the gel was dried in an ventilated oven
at 60~C for 12 hours 10g of dried polymer was collected
and was called Fai 7 OH.
The dried powder was tested for absorbence in
deionized water and in a 1% NaCl solution according to
the tea bag test as follows :
0.3g of AGM was weighed into a tea bag envelope and
allowed to swell in a 250ml beaker containing 150ml of
NaCl 1% solution (or deionized water) for 1 hour.
Thereafter the beaker was ~e,--oved and the envelope

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remained suspended for 10 minutes and unabsorbed water
drained therefrom. The envelope containing the swelled
AGM was then weighed and absorbency was calculated as
follows:
A = (Wwet - Wdry)/G
where:
A = absorbency Wwet = envelope containing the wet AGM
in g Wdry = envelope containing the dry AGM in g
G = dry AGM for the test in g.
Absorbence g/g tea bag test
Deionized water NaCl 1
Fai 7 OH 351 s5
Fai 7 Cl 340 54