Water-soluble (meth)acrylic acid/methallysulfonate copolymers, containing less than 20% by weight of the methallylsulfonate comonomer, are well suited as scale inhibitors for aqueous environments, especially those comprising essentially equal amounts by weight of both acrylic and methacrylic acids.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to novel water-soluble (meth)acrylic 
acid/methallylsulfonate copolymers, and to the use thereof as scale 
inhibitors for aqueous environments. 
2. Description of the Prior Art 
It is known to this art that the breakdown of the calcium carbonate 
equilibrium in water by heating, degassing or increasing the pH thereof 
gives rise to the formation of encrusting deposits of alkaline earth metal 
carbonates on the walls of water-confining vessels, or in the piping 
comprising the various cooling circuits or boilers. As the thermal 
conductivity of these deposits is incomparably lower than that of metals, 
there is a marked loss in the heat exchange capacities of such systems 
with concomitant loss or waste of energy. It is, therefore, obviously 
necessary to prevent the formation of the aforesaid encrusting deposits, 
commonly referred to as scale. 
And to date numerous means have been proposed for preventing scaling, for 
example: 
(i) Partial or total removal of the calcium and magnesium in the water, 
before use, by means of ion exchange or decarbonation with lime; or 
(ii) Addition of an acid agent to the water in the circuit; or also 
(iii) Addition of agents which sequester the calcium and magnesium ions. 
However, these processes are expensive and can also themselves present 
disadvantages, such as corrosion. Therefore, preference is frequently 
given to a more economical and well-known process which consists in adding 
water-soluble chemical additives, in proportions which are typically 
between 0.2 and several tens of mg/liter, to the hard water; these 
additives which are more commonly referred to as scale inhibitors, exert 
their influence on the formation of crystals. They disturb or disrupt 
their growth such that precipitation is retarded and the encrustation, if 
any indeed be produced, is rendered brittle. 
Stated differently, by adding homeopathic amounts of chemical additives to 
the water, the scaling of the heat exchangers is retarded. 
Some of these adjuvants, such as (1) the alkali metal polyphosphates, have 
been known for such purpose for a very long time; but same exhibit the 
disadvantage of hydrolyzing to orthophosphates, whereupon their 
scale-inhibiting attributes vanish, and precipitation of alkaline earth 
metal orthophosphates also takes place, which leads to a result 
diametrically opposed to that desired. 
Other additives have also been similarly employed, such as: 
(2) Phosphonic and polyphosphonic acids, which may or may not contain 
nitrogen, and their alkali metal salts; 
(3) Low molecular weight homopolymers of acrylic acid or methacrylic acid 
and the corresponding alkali metal salts thereof; 
(4) Low molecular weight copolymers of acrylic acid and methacrylic acid 
and the corresponding alkali metal salts thereof; 
(5) Very low molecular weight homopolymers of maleic acid and its salts, 
and copolymers thereof; and 
(6) 1000 to 25,000 molecular weight water-soluble copolymers of a monovinyl 
comonomer, e.g., (meth)acrylic acid, and a major amount of a vinyl 
sulfonate comonomer (as "below 25 mol percent the copolymer is no longer 
suitably effective in acid conditions of pH 3 or in the presence of useful 
amounts of zinc"), or salt form thereof; see U.S. Pat. No. 3,706,717. 
Moreover, it too will be appreciated that the aforesaid list is by no means 
exhaustive. 
It has also been determined, in particular, that polymers of ethylenic 
diacids, such as maleic acid, are better inhibitors of the precipitation 
of calcium and magnesium scales than are the homopolymers or copolymers of 
ethylenic monoacids, such as acrylic or methacrylic acids. 
Admittedly, the scale-inhibiting attributes of polymers of ethylenic 
monoacids are quite good, as are those of the alkali metal polyphosphates. 
However, when the temperature of the water and also the residence or dwell 
time of the water in the particular circuit increase greatly, alkali metal 
polyphosphates lose much of their scale-inhibiting efficacy and it has 
been ascertained that polymers of ethylenic monoacids become poorer scale 
inhibitors than polymers of ethylenic diacids. 
And whatever the procedure employed for the polymerization of ethylenic 
monoacids, whatever the transfer agents used and whatever the catalyst 
selected for the formation of free radicals, polymers are obtained, the 
scale-inhibiting properties of which are essentially equivalent in each 
case, but are demonstrably poorer than those of very low molecular weight 
polymaleic acid. 
Thus, by way of example, the scale-inhibiting effectiveness of polymers 
prepared from ethylenic monoacids is good at moderate temperatures and up 
to 95.degree. C., but upon reaching the boiling point of the water, and 
even 101.5.degree. C. in the case of sea water, such scale-inhibiting 
effectiveness is then poorer than with polymaleic acid. 
This rule applies whatever the polymerization system used, namely, 
persulfate associated with acetic acid, hydrogen peroxide associated with 
acetic acid or with isopropyl alcohol in larger or smaller amounts, or 
hydrogen peroxide associated with hydroxylamine sulfate and with isopropyl 
alcohol. Moreover, in the case of methacrylic acid homopolymer, the 
viscosities of the resultant products are very high and same are totally 
inadequate as regards providing good scale-inhibiting characteristics. 
SUMMARY OF THE INVENTION 
Accordingly, a major object of the present invention is the provision of a 
novel class of water-soluble polymeric scale inhibitors, which novel 
polymers are devoid of those disadvantages and drawbacks to date 
characterizing the state of this art. 
Briefly, the novel water-soluble polymers according to this invention are 
prepared by copolymerizing a minor amount of an alkali metal 
methallylsulfonate, notably sodium methallylsulfonate, with at least one 
monoethylenically unsaturated acid selected from the group comprising 
acrylic acid and methacrylic acid.

DETAILED DESCRIPTION OF THE INVENTION 
More particularly according to the present invention, a spectacular 
improvement in scale-inhibiting efficacy is attained when the subject 
copolymers are comprised of a mixture containing both acrylic acid and 
methacrylic acid. 
In the more specific case of enhancing scale-inhibiting efficacy utilizing 
the subject novel polymers, with respect to calcium and magnesium scales, 
and in the case of both ground water and sea water, it too has been 
determined that, when such mixtures of acrylic and methacrylic acids are 
copolymerized, the introduction/incorporation of sodium methallylsulfonate 
in an amount by weight of less than 20% of the total amount of the acrylic 
and methacrylic acids is sufficient. 
A preferred but non-limiting recipe to prepare a novel water-soluble 
copolymer having admirable scale-inhibiting characteristics per this 
invention, is that comprising a comonomer mixture containing approximately 
equal amounts by weight of acrylic acid and methacrylic acid and from 10 
to 18% by weight of the sodium methallylsulfonate. 
The polymer compositions according to the invention are useful as scale 
inhibitors for any aqueous environment, such as underground water, 
watercourse water or sea water. Typically, a dose or unit amount of 0.2 to 
50 mg/liter, and preferably of 1 to 20 mg/liter, is an effective amount. 
However, as stated above, the present invention is not to be construed as 
being limited either to the said specific polymers, or recipes for the 
preparation thereof, or to the scale-inhibiting characteristics thereof. 
The particular method of (co)polymerization can be of any known 
free-radical type, such as those employing, for example, hydrogen peroxide 
as the catalyst for the formation of free radicals, in association with 
isopropyl alcohol, in the presence of a small amount of a copper salt, it 
also being possible for the latter to be replaced by a given amount of 
hydroxylamine sulfate, or hydrogen peroxide together with an iron salt 
(ferrous sulfate) and hydroxylamine sulfate, or also sodium persulfate or 
ammonium persulfate in the presence of acetic acid. 
In order to further illustrate the present invention and the advantages 
thereof, the following specific examples are given, it being understood 
that same are intended only as illustrative and in nowise limitative. 
In said examples, all of the polymerization recipes were polymerized in 
accordance with the same procedure and differed only in the proportions 
and amounts of the respective comonomers and other ingredients. 
The procedure for the preparation of those polymers noted in Table I was as 
follows: 
A solution of those comonomers/ingredients listed in the first column of 
Table I labelled "reaction flask 1" was placed, under a nitrogen blanket, 
into a 2 liter round-bottomed flask having ground glass necks (the Table I 
reaction flask 1), which was fitted with a stirrer, a heating sleeve, a 
nitrogen inlet tube, a monomer inlet tube and a catalyst inlet tube. The 
deaerated and stirred medium was subsequently heated to reflux temperature 
and 10% of the comonomers/ingredients listed in said first column of Table 
I under the heading "introduction flask 2" was then introduced and 12% of 
the hydrogen peroxide was added. The mixture was again heated to the 
reflux temperature, under stirring, and the remainder of the comonomers 
(noted in Table I under the heading "introduction flask 2") and 68% of the 
hydrogen peroxide were then introduced continuously and concomitantly. 
This addition of the comonomers and the catalyst was continued for 1 hour, 
30 minutes under reflux. 10% of the hydrogen peroxide was subsequently 
added, and the mixture was again maintained under reflux for 30 minutes, 
the final 10% of the hydrogen peroxide was added, and the mixture was then 
maintained under reflux for 1 hour, 30 minutes. Same was subsequently 
distilled in vacuo in order to bring the polymer concentration to about 40 
to 50%. The mixture was cooled and the solids content and, if appropriate, 
the viscosity of the product, were then measured. 
TABLE I 
__________________________________________________________________________ 
EXAMPLE 1 2 3 4 5 6 7 8 9 
__________________________________________________________________________ 
1.circle. Reaction flask 
Demineralized water, 
200 350 350 350 350 350 200 490 225 
Copper acetate, 0.5 0.5 0.5 0.5 0.5 0.5 0.5 1.3 0.5 
Sodium methallyl- 20 10 5 8 8 5 25 0 0 
sulfonate, 
Isopropanol, 50 50 50 50 100 50 0 100 0 
Acetic acid grams of 
0 0 0 0 0 0 100 0 100 
2.circle. Introduction flask 
chemical 
Demineralized water, 
product 
450 450 450 450 450 450 450 160 500 
Acrylic acid, 230 230 230 230 230 0 460 230 460 
Methacrylic acid 230 230 230 230 230 460 0 230 0 
Sodium methallyl- 30 40 50 72 50 50 50 0 0 
sulfonate, 
Copper acetate -- -- -- -- -- -- -- 0.9 -- 
(Methyallylsulfonate/acrylic + 
10.87 
10.87 
11.95 
17.4 
12.6 
11.95 
16.3 
-- -- 
methyacrylic acids .times. 100) % 
3.circle. Graduated introduction flask 
Hydrogen peroxide of 110 volumes 
100 100 100 100 100 100 100 100 100 
strength (number of ml) 
Solids content at 105.degree. C. in % of the final 
48 50 51 50 50 40 51 44 51 
polymer, after concentration 
Brookfield viscosity - 10 rpm (centipoises) 
270 270 1000 320 240 1500 120 -- 150 
of the polymer after concentration - 
No. 1 spindle 
__________________________________________________________________________ 
SCALE-INHIBITING EFFICACY: 
The scale-inhibiting efficacy was determined by one of the following two 
tests: 
Test for the precipitation of calcium carbonate by boiling hard water: 
Procedure: 
The water used was an underground water. Its initial properties and 
characteristics were as follows: 
pH--7.3 
Total hardness (TH)--33 degrees on the French scale (.degree.F.) 
Temporary hardness--21 degrees on the French scale (.degree.F.) 
Permanent hardness--12 degrees on the French scale (.degree.F.) 
Total alkalinity (TAC)--25 degrees on the French scale (.degree.F.) 
Resistivity--1800 ohm. cm 
150 ml of untreated water, or water treated with the polymers noted in 
Table I, in amounts of 6 mg/liter, were introduced into a 500 ml ground 
glass Erlenmeyer flask; three small washed porcelain chips were added 
thereto. The water was brought to a boil under reflux by means of a heated 
sand bath. When the boiling commenced, same was maintained for exactly ten 
minutes. The Erlenmeyer flask containing the water was subsequently cooled 
under a stream of cold water, the water was then filtered through a 0.45 
micron Sartorius filter and the total residual hardness of the water, 
commonly referred to as the permanent hardness when the water does not 
contain scale inhibitor, was measured. 
The nearer the final hardness (TH) of the water is to its initial total 
hardness, the better the inhibitor is with respect to the precipitation of 
calcium carbonate. 
A boiling time of 10 minutes was determined. 
The results obtained are summarized in Table II: 
TABLE II 
______________________________________ 
Final hardness of 
Inhibitor (6 mg/liter) 
the water (.degree.F.) 
______________________________________ 
Control without inhibiting 
12.0 
treatment 
Polymer 1 of Table I 
25.2 
Polymer 2 of Table I 
26.7 
Polymer 3 of Table I 
27 
Polymer 4 of Table I 
26.2 
Polymer 5 of Table I 
25.9 
Very low molecular weight 
27.2 
polymaleic acid 
Polymer 6 of Table I 
22.0 
Polymer 7 of Table I 
20.5 
Polymer 8 of Table I 
24.0 
Polymer 9 of Table I 
20.5 
Low molecular weight 
20.0 
polyacrylic acid 
Monomeric sodium 12.0 
methallylsulfonate 
______________________________________ 
The improvement in scale-inhibiting efficacy obtained by using polymers 1, 
2, 3, 4 and 5 (of Examples 1, 2, 3, 4 and 5, respectively) was 
significant, in particular in the case of polymer 3, compared with the use 
of low molecular weight polyacrylic acid (polymer 9) and also compared 
with the use of acrylic acid/methacrylic acid copolymer devoid of sodium 
methallylsulfonate (polymer 8). 
Scaling test by boiling sea water: 
Typically, sea water desalination plants operate by distillation in order 
to separate pure water from the brackish salts. Without an inhibiting 
treatment, scaling then takes place, which comprises precipitation of 
calcium carbonate and a more or less complex carbonate of magnesia or 
magnesia itself. Good operation of sea water desalination plants thus 
largely depends on the scale-inhibiting efficacy of the scale inhibitors 
added. 
Procedure: 
A synthetic sea water corresponding to Brujewicz's formulation was prepared 
in the laboratory from distilled water and, according to the Water Book, 
2nd edition, volume 2, page 249, Cebedoc S.P.R.L. H. Goldstein, 63 Rue 
Hayeneux (Herstal Lez Liege), from: 
______________________________________ 
NaCl 26.518 g/kg 
MgCl.sub.2 2.447 g/kg 
MgSO.sub.4 3.305 g/kg 
CaCl.sub.2 1.141 g/kg 
KCl 0.725 g/kg 
NaHCO.sub.3 0.202 g/kg 
NaBr 0.083 g/kg 
______________________________________ 
300 ml of untreated synthetic sea water (control experiment) or synthetic 
sea water treated with 2 mg/liter of scale inhibitor were introduced into 
a 500 ml ground glass Erlenmeyer flask; 8 small washed porcelain chips 
were added thereto. The Erlenmeyer flask was placed in a waterbath 
regulated at 140.degree. C. in order to accelerate the onset of boiling. 
The sea water was brought to a boil under reflux, namely, at about 
101.5.degree. C. When the boiling commenced, same was maintained for 
exactly 40 minutes. The Erlenmeyer flask was subsequently cooled for 20 
minutes with a stream of cold water. The sea water was filtered through a 
0.45.mu. Sartorius filter under a water pump vacuum. 
The scale in suspension, namely, that scale not adhering to the walls of 
the apparatus, was recovered on the filter; same was rinsed 3 times with 
10 ml of double-distilled water, which was used beforehand to rinse the 
walls of the Erlenmeyer flask in order to remove the traces of sea water 
adhering to the wall. After drying the filter, the calcium and the 
magnesium deposited on the filter were dissolved under boil in 3 N extra 
pure hydrochloric acid, and the calcium and the magnesium therefore 
corresponding to the non-adhering deposit were then determined. 
Concurrently, in order to measure the amount of calcium and magnesium 
adhering to the wall of the Erlenmeyer flask (encrusting scale), the scale 
was dissolved in the same manner in hydrochloric acid, and the calcium and 
the magnesium contents were determined. 
The results are expressed as total mg of calcium and total mg of magnesium, 
i.e., as the sum of the calcium and magnesium in suspension, as well as 
that adhering to th flask walls. 
Very severe scaling conditions were adopted in order to differentiate the 
products more clearly, and an inhibiting amount of 2 mg/liter was used. 
The results obtained are summarized in Table III: 
TABLE III 
______________________________________ 
Total deposit, mg of Ca + 
mg of Mg 
______________________________________ 
Control without inhibitor 
22.7 
Low molecular weight acrylic 
18.0 
acid 
Low molecular weight polymaleic 
8.0 
acid 
Polymer 3 of Table I 
9 
______________________________________ 
Thus, a significant improvement in scale-inhibiting efficacy consistent 
with this invention is clearly apparent. 
While the invention has been described in terms of various preferred 
embodiments, the skilled artisan will appreciate that various 
modifications, substitutions, omissions, and changes may be made without 
departing from the spirit thereof. Accordingly, it is intended that the 
scope of the present invention be limited solely by the scope of the 
following claims.