U.S. patent application number 12/585398 was filed with the patent office on 2010-01-14 for resin cross-linking.
This patent application is currently assigned to THE UNIVERSITY OF MANCHESTER. Invention is credited to David J. Berrisford, Peter A. Lovell, Andrew Whiting.
Application Number | 20100010266 12/585398 |
Document ID | / |
Family ID | 9948567 |
Filed Date | 2010-01-14 |
United States Patent
Application |
20100010266 |
Kind Code |
A1 |
Lovell; Peter A. ; et
al. |
January 14, 2010 |
Resin cross-linking
Abstract
A method of effecting cross-linking of a resin comprises
generating vinyl sulfonyl moieties in situ with the resin, said
sulfonyl moieties then undergoing a reaction which effects
cross-linking of the resin. The vinyl sulfonyl moieties may be
generated as a result of a loss of a liquid carrier for the resin
to be cross-linked. The cross-linking reaction may result from
reaction of the vinyl sulfonyl moieties with nucleophilic groups in
the resin composition. The resin may be a co-polymer of a compound
of formula (IV) with other olefinically unsaturated monomers.
Inventors: |
Lovell; Peter A.; (Appleton,
GB) ; Berrisford; David J.; (Levenshuime, GB)
; Whiting; Andrew; (Nevilles Cross, GB) |
Correspondence
Address: |
NIXON & VANDERHYE, PC
901 NORTH GLEBE ROAD, 11TH FLOOR
ARLINGTON
VA
22203
US
|
Assignee: |
THE UNIVERSITY OF
MANCHESTER
Manchester
GB
|
Family ID: |
9948567 |
Appl. No.: |
12/585398 |
Filed: |
September 14, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10535333 |
Aug 9, 2005 |
7598323 |
|
|
PCT/GB2003/005240 |
Nov 27, 2003 |
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12585398 |
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Current U.S.
Class: |
568/32 ;
568/28 |
Current CPC
Class: |
C08J 3/24 20130101 |
Class at
Publication: |
568/32 ;
568/28 |
International
Class: |
C07C 317/22 20060101
C07C317/22; C07C 317/18 20060101 C07C317/18 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 27, 2002 |
GB |
0227608.7 |
Claims
1-36. (canceled)
37. The compound of formula (IV) ##STR00010##
38. The compound of formula (V) ##STR00011## in which
R.sup.1-R.sup.3 are as defined in claim 3, R.sup.4 is as defined in
claim 7, R.sup.5, R.sup.6 and R.sup.7 are independently hydrogen or
methyl, and n is a positive integer.
Description
[0001] The present invention relates to a method of cross-linking
resins and also to a cross-linkable resin composition.
[0002] There is a general need for improved storage-stable resin
compositions which incorporate a resin to be cross-linked and all
agents required to initiate cross-linking at the time required.
Such compositions avoid the need for admixing a resin and a
cross-linking agent shortly before cross-linking is to be
effected.
[0003] The need exists, for example, in the field of cross-linkable
latexes which are useful for coating, e.g. in the form of emulsion
paint, and also in the field of high solids coatings.
[0004] Environmental pressures have forced the coatings industry to
seek alternatives to the conventional solvent-borne coating systems
that are used, for example, as paints and adhesives. The pressures
have led to growth in the development and use of high-solids and
water-borne coating systems. However, in many cases, this has
brought with it significant technical difficulties, one of which is
the need to match the performance characteristics of solvent-borne
coatings by crosslinking of the coatings. A very large number of
different chemistries have been investigated for this purpose,
including the use of functional monomers such as N-methylol
acrylamide and its alkyl ethers, acrylamidobutyraldehyde dialkyl
acetals, glycidyl (meth)acrylate, (meth)acrylic acid, hydroxyethyl
methacrylate, hydroxypropyl methacrylate, aminoethyl methacrylate,
2-acetoacetoxyethyl (meth)acrylate, trichlorophenyl acrylate, vinyl
and acryloxy silanes, methyl acrylamidoglycolate methyl ether,
1,1-dimethyl m-isopropenylbenzyl isocyanate, N-acryl-3,5 dimethyl
pyrazole, 2-alkenyl-2oxazolines and 2-(1-aziridinyl)ethyl acrylate.
However there still is no crosslinking system that satisfies all
the desired criteria for water-borne coatings.
[0005] In its broadest (first) aspect, the invention provides a
method of effecting cross-linking of a resin comprising generating
vinyl sulfonyl moieties in situ with the resin, said vinyl sulfonyl
moieties then undergoing a reaction which effects cross-linking of
the resin.
[0006] As explained more fully below, the vinyl sulfonyl moieties
may be generated as a result of loss of a liquid carrier (e.g. by
evaporation) for the resin to be cross-linked.
[0007] The cross-linking of the resin may result from reaction of
the vinyl sulfonyl moieties with nucleophilic groups in the resin
composition.
[0008] According to a second aspect of the present invention there
is provided a cross-linkable resin composition comprising [0009]
(i) a polymer to be cross-linked; [0010] (ii) a liquid carrier for
the polymer; [0011] (iii) nucleophilic groups; and [0012] (iv)
vinyl sulfonyl precursor groups capable of generating vinyl
sulfonyl moieties on loss of liquid carrier from the composition at
least one of the groups (iii) and (iv) being attached to the
polymer to be cross-linked whereby loss of the liquid carrier
results in generation of a vinyl sulfonyl moiety to effect
cross-linking of the polymer.
[0013] Thus, the resin compositions of the invention incorporate,
in addition to the polymer to be cross-linked and the liquid
carrier, both (iii) nucleophilic groups and (iv) vinyl sulfone
precursor groups capable of generating vinyl sulfonyl moieties on
loss of liquid carrier (particularly by evaporation) from the
composition, at least one of these types of groups (iii) and (iv)
being attached to the polymer backbone. The vinyl sulfonyl moieties
generated may be of the formula (I)
##STR00001##
(in which represents a chemical bond to carbon or a heteroatom) or
a substituted version thereof in which one, two to three of the
hydrogen atoms bonded to the olefinic carbon atoms are replaced by
appropriate substituents. If the sulfur atom is bonded to a
heteroatom then the latter may be nitrogen. Thus, the vinyl
sulfonyl group may be a vinyl sulfonamide.
[0014] The vinyl sulfonyl groups (I) are then capable of reacting
with the nucleophilic groups, e.g. in a Michael-type reaction,
resulting in the formation of a chemical bond between a carbon atom
of the vinyl sulfonyl component (I) and a residue of the
nucleophile as represented by the following equation
##STR00002##
[0015] The composition of the invention is storage-stable and only
becomes cross-linked when steps are taken to ensure loss of liquid
carrier, e.g. by evaporation.
[0016] In the composition of the invention, it is preferred that
both the nucleophilic groups (iii) and the vinyl sulfonyl precursor
groups (iv) are attached to polymer chains to be cross-linked so
that a nucleophilic group on one polymer chain may react with a
vinyl sulfonyl moiety formed on another chain to provide
cross-linking. We do not however preclude the possibility that,
say, the vinyl sulfonyl precursor groups are bonded to the
polymeric chains whereas the nucleophilic groups are provided on a
cross-linking species having two or more such nucleophilic groups.
Similarly we do not preclude the possibility that the nucleophilic
groups are bonded to the polymer chains and the vinyl sulfonyl
precursor groups are provided on a cross-linking species having two
or more such groups.
[0017] Preferably the generation on the vinyl sulfonyl moiety
results from loss of HX from the vinyl sulfonyl precursor groups,
where X is a leaving group.
[0018] Preferably the vinyl sulfonyl precursor groups are of the
formula (II)
##STR00003##
where X is a leaving group, and R.sup.1, R.sup.2 and R.sup.3 are
independently selected from a hydrogen atom, a substituted or
unsubstituted alkyl group, and a substituted or unsubstituted aryl
group.
[0019] In the case of the groups of formula (II) there is, on loss
of the liquid carrier for the polymer (e.g. by evaporation) a
facile elimination of HX from the groups (II) leading to the
production of a vinyl sulfonyl moiety (III) as depicted by the
following equation:
##STR00004##
[0020] Where appropriate, it will generally be preferred that the
liquid carrier for the resin is HX so that the above reaction is
given to the left (resulting from excess of liquid carrier) so that
the vinyl sulfonyl moieties are only generated on substantial loss
of the liquid carrier HX.
[0021] For preference, R.sup.1 (in formula II) is hydrogen.
Optionally or additionally at least one (and preferably both) of
R.sup.2 and R.sup.3 is/are hydrogen.
[0022] The leaving group X may be selected from groups of the
formula --OR.sup.4, --OC(O)R.sup.4, --NR.sub.2.sup.4, --SR.sup.4,
--NCOOR.sup.4 or --OSO.sub.3R.sup.4 where R.sup.4 is hydrogen, a
substituted or unsubstituted alkyl group, or a substituted or
unsubstituted aryl group, or X is F, Cl or Br.
[0023] It is generally preferred that X is of the formula
--OR.sup.4. Preferably also R.sup.4 is hydrogen although other
R.sup.4 groups which are particularly useful are Me and Et since
the eliminated alcohols are of high volatility and low
toxicity.
[0024] For various resin compositions in accordance with the
invention it may be necessary to ensure that the pH of the
composition allows the above reaction to proceed. Thus for example,
is the case where X is --OH and HX (provided also as the liquid
carrier) is H.sub.2O, the pH of the composition should be acidic or
alkaline rather than neutral.
[0025] For preferred embodiments of the invention in which the
groups of formula (II) are attached to the polymer, they may be
attached either directly to the polymer backbone or via a linker
group which may for example be of an aliphatic or aromatic nature.
The nature of the linker group may be selected having regard to the
desired final properties of the cross-linked resin since these will
be influenced by the nature of the linker group.
[0026] By way of example, a polymer incorporating groups of formula
(II) bonded to the polymer chain by a linker incorporating an
aromatic group may be prepared by co-polymerisation of a compound
of formula (IV)
##STR00005##
[0027] with other olefinically unsaturated monomers to produce the
desired polymer.
[0028] Compound (IV) is 4-hydroxyethylsulfonyl styrene and is also
referred to herein as HESS. Modifications of compound (IV) may also
be used. For example the aromatic ring may have one or more
substituents and/or the terminal --OH group may be replaced by any
other --OR group defined above. Alternatively or additionally, the
sulfone group may be ortho or meta position of the benzene
ring.
[0029] Alternatively a compound of formula (V) may be used for
providing the groups (I)
##STR00006##
[0030] in which R.sup.1-R.sup.4 are as defined above, R.sup.5,
R.sup.6 and R.sup.7 are independently hydrogen or methyl, and n is
a positive integer, most preferably at least 2 and ideally having a
value of 2-6. As a modification of formula (V), the sulfone group
may be bonded to the (meth)acrylate residue via a linker
incorporating --(CH.sub.2CH.sub.2--O)-- groups.
[0031] The nucleophilic groups present in the composition, and
provided for reaction with the vinyl sulfonyl groups, may for
example be of the formula --OH, --SH, NHR.sup.8 where R.sup.8 is
selected from the same groups as R.sup.4 above. Alternatively, the
nucleophic group may be provided by a species having a nucleophilic
carbon atom, e.g. an acetoacetoxy group. In this latter case, the
acetoacetoxy group may react in either a keto and enol form as
depicted by the following equation:
##STR00007##
[0032] where P and P.sup.1 represent different polymer chains.
[0033] For the preferred embodiment of the invention in which both
the groups of formula (II) and the nucleophilic groups are bonded
to the polymer chains, it is preferred that the resin to be
cross-linked comprises 0.5% to 25%, more typically 1% to 10% (e.g.
3% to 7%) by mole of the groups of formula (II). The nucleophilic
groups may be present in the resin to be cross-linked in an amount
of 0.5% to 25% more preferably 1% to 10%, and usually 3% to 7% by
mole.
[0034] Compositions in accordance with the invention may be in the
form of solutions with the polymer to be cross-linked being
dissolved in the carrier liquid therefor.
[0035] It is however particularly preferred that compositions in
accordance with the invention are in the form of latexes in which
the resin to be cross-linked (incorporating both the groups of
formula II and the nucleophilic groups) is in the form of particles
in a continuous aqueous phase which provides a reservoir of water
effective to prevent loss of HX from the groups of formula (II) and
thus their conversion to vinyl sulfonyl moieties. Thus, the groups
of formula (II) remain unchanged during storage of the latex and
all functional groups necessary for cross-linking can be
incorporated uniformly throughout each latex particle without
compromising latex shelf life.
[0036] Such latexes are useful for forming coatings on surfaces. On
application of the latex to a surface, the loss of the water
reservoir (by evaporation) results in generation of the vinyl
sulfonyl group for cross-linking of the resin as described more
fully above. The elimination of water to form vinyl sulfonyl groups
will become more favourable as film formation proceeds, especially
in the later stages of film formation. This is important because
premature cross-linking would provide a barrier to film
integration. Also, the water-sensitivity of the films will be
reduced not only by the cross-links introduced but also by the
reduction in hydrophilicity associated with the cross-linking
chemistry.
[0037] Polymer latexes in accordance with the invention may be
produced by copolymerising conventional monomers with (a)
comonomers including groups of the formula (II) and (b) further
comonomers including nucleophilic groups using conventional
techniques of emulsion polymerisation, e.g. using monomer-starved
conditions to ensure control and uniformity of copolymer
composition.
[0038] Examples of conventional monomers which may be used include
(meth)acrylic acid, itaconic acid, C.sub.1-20 (e.g. C.sub.1-8)
alkyl esters of these acids, vinyl acetate, vinyl versatate,
styrene, butadiene, and combinations of the aforesaid monomers.
Specific examples of such monomers include vinyl acetate, butyl
acrylate, 2-ethylexyl acetate and/or butyl methacrylate since
copolymers comprising such monomer units are particularly suitable
for water borne paint coatings.
[0039] The comonomers for incorporating groups of formula (II) may
for example be compounds of formula (IV) and/or (V) as described
above. These compounds are particularly suitable because they have
the limited water solubility necessary for emulsion
polymerisation.
[0040] Generally the total amount of the compound of formula (IV)
and/or (V) incorporated in the final polymer will be in the range
0.5% to 25% by mole but more preferably 1% to 10%, e.g. 3% to 7% on
the same basis.
[0041] Examples of comonomers capable of providing nucleophilic
groups for cross-linking with the vinyl sulfonyl groups include
hydroxyalkyl (meth)acrylates (e.g. hydroxyethyl acrylate,
hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl
methacrylate), 2-acetoacetoxyethyl acrylate and 2-acetoacetoxyethyl
methacrylate.
[0042] The latex particles may for example have an average size in
the range 50nm-2 .mu.m but more typically 100-500 nm. The particles
may be of the core-shell type.
[0043] Generally, the latex will have a solids content of 20-80%.
but more usually 40-60% by weight.
[0044] Latexes in accordance with the invention may for example be
formulated with pigments and other conventional ingredients of
coating materials.
[0045] Whilst the invention is particularly applicable to latexes.
it may also be employed in the formulation of high solid coatings
where the polymer content is above 80% of the coating
formulation.
[0046] The compounds R.sup.1-R.sup.3.dbd.H and X.dbd.OH formula II
(see above) for which X.dbd.H may be produced in accordance with
the following reaction scheme (sequence
VI.fwdarw.VII.fwdarw.VIII.fwdarw.IX).
##STR00008##
[0047] More particularly, the sulfonic acid (VI) is easily
converted into the corresponding sulfonyl chloride under a variety
of conditions (e.g. using thionyl chloride or phosphorus
trichloride) which are then readily reduced to the sulfinate salt
(VIII) under dissolving metal or sulfite reduction conditions.
Sulfinate salts are good nucleophiles and react under mild
conditions with ethylene oxide to provide the corresponding
hydroxyethylsulfones.
[0048] An alternative direct route from (VII) to (IX) is the
reaction of a vinyl organometallic compound directly with (VII)
followed by hydration of the double bond.
[0049] To produce groups of formula (I) in which R is an alkyl
group (e.g. methyl or ethyl), a modification of the abovedescribed
reaction scheme may be used in which an alkyl halide (e.g. methyl
or ethyl iodide) may be reacted with (VIII) in place of
H.sub.3O.sup.+.
[0050] To produce a compound of formula (V) in which n=1 and
R.sup.4=H the following reaction scheme may be used.
##STR00009##
[0051] In the above scheme, R.sup.9 may be methyl, ethyl or acetyl.
Conveniently the scheme is used to produce compounds (V) in which
R.sup.2=H and R.sup.3=methyl.
[0052] The invention will be illustrated with reference to the
following non-limiting Examples.
EXAMPLE 1
Preparation of HESS
[0053] Preparation of p-Styrene Sodium Sulfonylchloride
[0054] p-Styrene sodium sulfinate (10.0 g) and phosphorous
oxychloride (35.0 g) were placed in a 250 ml flask equipped with a
magnetic stirrer bar, a condenser and a drying tube. The reaction
mixture was refluxed at 105.degree. C. After 1 hour the flask was
cooled to room temperature and excess phosphorous oxychloride was
distilled off. The product was extracted with diethyl ether, which
was removed on a rotary evaporator.
[0055] A thick brown oil was obtained (7.64 G, 77%), the purity of
which was proven by .sup.1H and .sup.13C NMR.
Preparation of p-Styrene Sodium Sulfinate
[0056] p-Styrene sodium sulfonylchloride (12.5 g) was added
dropwise to a 1000 ml flask equipped with a magnetic stirrer bar,
which contained 150 ml of distilled water at 70.degree. C. and zinc
powder (10.0 g), with continuous stirring. After 20 minutes, 6 ml
of 12.5 M sodium hydroxide solution was added, raising the
temperature of the mixture to 90.degree. C. Finely powdered sodium
carbonate was then added in portions until the mixture was strongly
alkaline. The mixture was stirred for a further 10 minutes. The
zinc was removed by filtration and the sulfinate salt was
crystallised out of solution (7.20 g, 61%), the purity of which was
proven by .sup.1H, .sup.13C NMR and mass spectrometry.
Reaction of p-Styrene Sodium Sulfinate with Ethylene Oxide
[0057] p-Styrene sodium sulfinate (7.8 g) was dissolved in 25 ml of
distilled water in a 150 ml flask equipped with a magnetic stirrer
bar, to which 15 ml of acetone was added. The mixture was stirred
for 10 minutes. The pH of the solution was brought to 7.5 with
dilute hydrochloric acid. The flask contents were cooled to
-10.degree. C. with a dry ice/acetone bath. Ethylene oxide (1.25
g), diluted with 2.5 ml of diethyl ether (also similarly cooled)
was transferred to the flask, which was then sealed. The reaction
mixture was stirred at room temperature for 30 hours. The product
was extracted with diethyl ether and dried with magnesium sulfate.
The product was identified as HESS (3.72 g, 62%), the purity of
which was proven by .sup.1H, .sup.13C NMR and mass
spectrometry.
EXAMPLE 2
[0058] Latexes were prepared at 30% solids content by
semi-continuous emulsion polymerisations involving two sequential
stages, all polymerisation being carried out under a swept nitrogen
atmosphere at 75.degree. C. The first stage involved the formation
of seed particles of 89-118 nm diameter. This was followed by a
growth stage, which took the final diameter to 184-243 nm. The
particles produced can be considered to be of the core-shell type
in which the core is formed from the seed stage and the shell is
formed in the growth stage. Two types of latex were prepared in
this way:- [0059] (i) poly[(n-butyl (meth)acrylate)] core and a
poly[(n-butyl (meth)acrylate)-co-(hydroxypropyl
(meth)acrylate)-co-styrene] shell. (Comparative). [0060] (ii)
poly[(n-butyl (meth)acrylate)] core and a poly[(n-butyl
(meth)acrylate)-co-(hydroxypropyl
(meth)acrylate)-co-(4-hydroxyethylsulfone styrene)] shell.
(Invention).
[0061] The formulations used for 500 ml scale preparations of
latexes (i) (Comparative) are shown in Table 1 and those for
latexes (ii) (Invention) are shown in Table 2, which gives the
masses used. The relative proportions of the growth-stage reactant
mixtures were changed in order to produce a range of latexes with
different levels of functional monomers.
TABLE-US-00001 TABLE 1 Formulation Seed Stage Growth Stage
Component mass/grams mass/grams (mole %)* Butyl 12.5 81.6 (90) 73.1
(80) 62.9 (68) methacrylate Butyl Acrylate -- -- -- 10.0 (12)
Hydroxypropyl -- 4.34 (5) 9.27 (10) 9.38 (10) methacrylate Styrene
-- 3.14 (5) 6.69 (10) 6.78 (10) Aerosol MA 0.19 1.8 Deionised 200
37.5 Water Potassium 0.08 0.12 Persulfate *The numbers in
parentheses give the mol % of each monomer in the comonomer
mixture.
TABLE-US-00002 TABLE 2 Formulation Seed Stage Growth Stage
Component mass/grams mass/grams (mole %)* Butyl 12.5 78.7 (90) 67.8
(80) 58.3 (68) methacrylate Butyl Acrylate -- -- -- 9.27 (12)
Hydroxypropyl -- 4.20 (5) 8.59 (10) 8.69 (10) Acrylate HESS -- 6.18
(5) 12.66 (10) 12.80 (10) Aerosol MA 0.19 1.8 Deionised 200 37.5
Water Potassium 0.08 0.12 Persulfate *The numbers in parentheses
give the mol % of each monomer in the comonomer mixture.
[0062] To prepare the various latexes, the seed stage surfactant
(Aerosol MA) and part of the deionised water (175 g) were added to
a 700 ml flanged reaction vessel, equipped with a condenser
nitrogen inlet and mechanical stirrer. A nitrogen atmosphere was
established whilst the surfactant solution attained the reaction
temperature of 75.degree. C.
[0063] The seed stage monomer was added and after the reaction
temperature had again stabilised, a solution of potassium
persulfate (0.08 g) in de-ionised water (25 g) was added, thus
marking the start of the reaction.
[0064] 60 Minutes was allowed for completion of the seed stage,
before addition of the growth stage reactant mixture was started at
approximately 1.35 g min.sup.-1 using a peristaltic pump
(Watson-Marlow 505S Model). Solutions containing potassium
persulfate (0.04 g) in de-lonised water (12.5 g) were added at 80,
100 and 130 minutes. Following completion of the addition of the
second stage reactant mixture, 60 minutes was allowed before
cooling the latex to room temperature and filtering through a 53
.mu.m sieve.
[0065] Samples were taken at regular intervals during the course of
each latex preparation in order to determine overall and
instantaneous monomer conversions (done by gravimetric analysis)
and z-average particle diameter using a Brookhaven photon
correlation spectrometer.
[0066] The latexes thus obtained were designated 1-6 as shown in
Table 3 which, for each such designation, shows the monomer content
of the "shell" layer in moles and the solid content of the latex.
Latexes 2, 4 and 6 illustrate the invention (Iv) whereas latexes 1,
3 and 5 are comparative (Co).
TABLE-US-00003 TABLE 3 Latex 1 2 3 4 5 6 Formulation Component (Co)
(Iv) (Co) (Iv) (Co) (Iv) Butyl Acrylate -- -- -- -- 12 12 Butyl
methacrylate 90 90 80 80 68 68 Styrene 5 -- 10 -- 10 --
Hydroxypropyl methacrylate 5 5 10 10 10 10
4-(2-hydroxy-ethylsulphonyl) -- 5 -- 10 -- 10 styrene (HESS) Solid
(%) 30 30 30 30 30 30
Gel Fraction
[0067] (i) Films (.about.2 mm thickness) were formed from latexes 1
to 6. After defined intervals (2 weeks, 1 month and 3 months) known
weights of the films were extracted at room temperature with
butanone to determine the gel fraction of the films. The gel
fraction in the latexes was determined through coagulation of a
known quantity of the latex by freeze-thaw cycling, followed by
extraction of the coagulum with butanone at room temperature. The
percentage gel fraction was determined by the following
equation:-
gel %=(mass of the gel/total mass of the polymer).times.100
[0068] (ii) The gel fractions of the latex "as prepared" and also
after storage for 3 months were determined by the same freeze-thaw
and extraction procedure as defined under (i).
[0069] (iii) Films (.about.2 mm thickness) were prepared from latex
6 (pH=2.4) and also for further latexes obtained therefrom by
adjusting the pH to (a) 5.5-6.2, (b) 7.0 to 7.8, and (c) 8.5 to
9.0. The gel fraction of the films was determined I week after
formation using the procedure described in (i).
[0070] The results of the gel fraction tests are shown in Table
4.
TABLE-US-00004 TABLE 4 (iii) Gel Fractions of films after 1 week
(ii) Gel Effect of latex pH (i) Gel Fractions - "Aged Films"
Fractions - Latexes pH = 2.4 Latex No 2 Weeks 1 Month 3 Months (as
prepared) 3 months (as prepared) pH = 5.5-6.2 pH = 7.0-7.8 pH =
8.5-9.0 1 (Co) 1-2 0 0 0 0 -- -- -- -- 2 (Iv) 10 25 28 0 0 -- -- --
-- 3 (Co) 6-8 0 0 0 0 -- -- -- -- 4 (Iv) 20 35 43 0 0 -- -- -- -- 5
(Co) 1-3 <1 0 0 0 -- -- -- -- 6 (Iv) 72-75 77-82 80-82 0 0 72-80
76-78 0 70-78
[0071] The gel % data for films formed from the latexes show that
crosslinking only occurs for the latex copolymers prepared using
HESS and that the level of crosslinking in the films increases with
time. The comparison latexes prepared using styrene in place of
HESS give films that do not crosslink, even after long periods.
This shows that the repeat units derived from HESS are responsible
for the cross linking.
[0072] The shelf-life of a latex is an important factor for
commercial applications. The gel % data for all the latexes is
zero, even 3 months after preparation. This shows that crosslinking
does not take place during storage of the latex, confirming that
the HESS repeat units do not generate the vinyl sulfone groups
whilst in the latex form due to the excess of water present.
[0073] A series of films were formed from samples of latex 6 (Iv)
that were pH-adjusted just prior to coating. The gel % results for
the films one week after coating show that the crosslinking
reaction proceeds at a wide range of latex pHs except in the range
7.0 to 7.8. This demonstrates that, for this particular
cross-linking system, acidic or alkaline (rather then neutral) pH
is required to effect cross-linking.
Glass Transition Temperature (T.sub.g)
[0074] Latexes 1-6 were tested to find their glass transition
temperature (T.sub.g). All of the latexes were found to have
T.sub.g values in the range 23 to 36.degree. C. thus indicating
that the latexes are film forming.
Tensile Testing
[0075] Films from latexes 5 and 6 were subjected to tensile testing
on an Instron 4301 tensile testing machine to determine their
mechanical properties. The test was carried out on dumbbell
specimens 4.2 mm.times.1.8 mm cross-section with a gauge length of
40 mm using a crosshead speed of 20 mm min.sup.-1. The results of
the test are shown in Table 5.
TABLE-US-00005 TABLE 5 Latex E/MPa .epsilon..sub.y/%
.sigma..sub.y/MPa .epsilon..sub.u/% .sigma..sub.u/MPa 5 (Co) 188
10.9 4.35 280 7.2 6 (Iv) 336 7.1 8.14 210 7.5 Where E = tensile
modulus .epsilon..sub.y = yield strain .sigma..sub.y = yield stress
.epsilon..sub.u = ultimate tensile strain .sigma..sub.u = ultimate
tensile stress
[0076] Thus latex 6 (Iv) prepared according to the invention gave
films with a higher modulus and yield stress but lower ultimate
elongation than the comparative latex 5 (Co) consistent with the
presence of cross-links in the films from latex 6 (Iv).
* * * * *