Solutions of polymers of aspartic acid or its amine copolymers prepared by thermal condensation are reacted with a decolorizing agent selected from the group consisting of hypochlorfte, chlorine, chlorine dioxide, hydrogen peroxide, a peroxycarboxylate or ozone, sufficient in strength to effect the desired decolorization.

FIELD OF THE INVENTION 
This invention relates to methods for the reduction of color obtained in 
the thermal polymerize on of aspartic acid or the ammonium salts of maleic 
acid or fumaric acid to produce polysuccinimide which is then hydrolyzed 
to obtain polyaspartic acid or of copolymers of aspartic acid obtained by 
the thermal polymerization of these materials with polyamines. 
DESCRIPTION OF RELATED ART 
Sodium polyaspartate and copolymers of polyaspartate find application as 
adjuvants in cosmetics and in hair-treatment compositions such as 
shampoos, hair wave setting lotion or hair brushing lotion. Preparation of 
such polymers, however, is associated with the generation of highly 
colored products which interfere with cosmetic and hair treatment 
applications. 
Previous methods for the reduction of color in the thermal polymerization 
to obtain less colored polyaspartic acid from its precursor compounds have 
centered on the reaction conditions and catalysts used in the thermal 
polymerization. 
In U.S. Pat. No. 4,363,797, a superior method of forming reduced color 
polysuccinimide is disclosed in which the polymerization is carried out in 
the presence of a solvent of high boiling point in conjunction with a 
solid acid catalyst, yielding a polysuccinimide which is only slightly 
colored. Also disclosed is the use of 85% ortho-phosphoric acid as a 
catalyst for the production of a white polysuccinimide; however, the use 
of this reagent is said to require unusual apparatus, delicate separation 
and large volumes of solvent. Polysuccinimide may be converted to 
polyaspartic acid by treatment with hydroxide. 
U.S. Pat. No. 5,057,597 discloses the thermal condensation of aspartic acid 
in a nitrogen atmosphere to form polysuccinimide which may then be 
hydrolyzed to give polyaspartic acid. No decolorization is disclosed. 
These disclosures do not meet the requirement of an inexpensive, effective 
environmentally benign process for the decolorization of polyaspartate and 
its amine copolymers. 
SUMMARY OF THE INVENTION 
A method for decolorizing polyaspartic acid prepared by thermal 
condensation is disclosed wherein a solution of polyaspartic acid is 
reacted with a decolorizing agent selected from the group consisting of 
hypochlorite, chlorine dioxide, ozone, hydrogen peroxide, a 
peroxydicarbonate or chlorine sufficient in strength to effect the desired 
decolorization. 
One objective of this invention is to provide processes for decolorization 
of polyaspartate and its amine copolymers. 
Another objective is to provide processes which produce polyaspartate and 
its amine copolymers having reduced color which is suitable for cosmetic 
and hair-treatment applications. 
A final objective is to provide processes for decolorizing polyaspartate 
and ks amine copolymers which are inexpensive, effective, safe and without 
adverse environmental effects.

DETAILED DESCRIPTION OF THE EMBODIMENTS. 
Polyaspartate may be formed by the thermal polymerization of L-aspartic 
acid followed by the alkaline hydrolysis of the resulting polysuccinimide. 
Another approach is through alkaline hydrolysis of polysuccinimide which 
has been formed by the thermal polymerization of ammonium maleate or 
ammonium fumarate. Amine copolymers of polyaspartate may be formed by 
copolymerization of ammonium maleate with polyamines as disclosed in U.S. 
Pat. Applic. "Copolymers of Polyaspartic Acid," Louis L. Wood, filed 
herewith and incorporated herein by reference. 
Preparations of polyaspartate and of amine copolymers may be decolorized by 
treating water solutions of the polymers with a sodium hypochlorite, 
hydrogen peroxide, peroxydicarbonate, chlorine dioxide, chlorine, or 
ozone. 
The above treatments as well as their effects on the polymer's activity in 
inhibiting calcium carbonate precipitation and their polymer molecular 
weights are described in Examples 1-9. Examples 10 and 11 show the failure 
of treatment with hydrogen or sodium formaldehyde sulfoxylate to 
decolorize. 
Treatment with sodium hypochlorite, hydrogen peroxide, a peroxydicarbonate, 
or chlorine dioxide were without effect on the calcium carbonate 
precipitation inhibition properties of the polymers. Such treatments also 
did not effect the molecular weights of the polymers. 
Treatment with sodium hypochlorite peroxide, a peroxydicarbonate, hydrogen 
peroxide, chlorine dioxide, chlorine, or ozone had the unexpected effects 
of effectively decolorizing the polymers without adversely effecting the 
properties of inhibiting calcium carbonate precipitation in the calcium 
carbonate drift assay as well a having no effect or the molecular weight 
of the polymers. 
EXAMPLE 1 
The use of hypochlorite to decolorize an amine copolymer of polyaspartate 
To 2.5 ml of a 30% water solution of a triamine copolymer with sodium 
polyaspartate, pH 10, prepared by the thermal polymerization of ammonium 
maleate with JEFFAMINE T403 at 240.degree.-250.degree. C. for 45 minutes, 
was added 0.5 ml of a 5.25% solution of sodium hypochlorite. The color 
changed f/om an intense reddishbrown to a straw colored liquid. JEFFAMINE 
is a trademark of Texaco Chemical Co. for its amines. 
Both treated and untreated sodium polyaspartate were tested for inhibition 
of calcium carbonate precipitation by the calcium draft assay. In this 
assay a supersaturated solution of calcium carbonate is formed by adding 
0.3 ml of a sodium carbonate solution (0.25 M NaHCO.sub.3 +0.25 M NP.sub.2 
CO.sub.3) to 29.1 ml of 0.55 M NaCl and 0.01 M KCI containing 0.15 ml of 
1.0 M CACU and 1.7 ppm of the material to be tested. The reaction was 
initiated by adjusting the pH to 7.5-8.0 by titration with 1 N NAOH and 
addition of the material to be tested for inhibition of CaCo.sub.3 
precipitation at a level of 1.7 ppm. At three minutes, 10 mg of CACO.sub.3 
was added and the pH was recorded. The decrease in pH is directly 
correlated to the amount of CaCO.sub.3 that precipitates. The effect in 
the calcium carbonate drift assay was not diminished by this 
decolorization treatment. 
Molecular weight determination was made by chromatography on a 1 cm X 18 
cm, Sephadex G-50 column in a mobile phase of 0.02 M sodium phosphate 
buffer, pH 7.0, running at 0.5 ml/min, with detection in the UV at 240 nm. 
The molecular weight of the polyaspartate was unchanged by decolorization. 
EXAMPLE 2 
The use chlorite to decolorize polyaspartate prepared from L-aspartic acid 
To 2.5 ml of a 30% water solution of sodium polyaspartate, pH 10, prepared 
by the thermal polymerization of L-aspartic acid at 
220.degree.-250.degree. C. for 45 minutes, was added 0.5 ml of a 5.25% 
solution of sodium hypochlorfte. The color changed from a light tan to a 
straw colored liquid. 
When assayed for its effect in the calcium carbonate drift assay and for 
molecular weight by the procedures of Example 1, the effect in the calcium 
carbonate drift assay was not diminished by this decolorization treatment 
and the molecular weight was unchanged by decolorization. 
EXAMPLE 3 
The use of chlorine to decolorize polyaspartate prepared from ammonium 
maleate 
A 33% water solution of sodium polyaspartate, 100 g, pH 10, prepared by the 
thermal polymerization of ammonium maleate at 240.degree.-250.degree. C., 
for 45 minutes, was purged with a light stream of chlorine gas for 8 
minutes. The color change-from an intense reddish-brown to a lemon yellow 
colored liquid. The pH of the decolorized solution was lowered to pH 4. 
When assayed for molecular weight by the procedures of Example 1, the 
molecular weight was lowered by decolorizxation. After 24 hours, the 
decolorization was found to be transient. 
EXAMPLE 4 
The use of chlorine to decolorize polyaspartate prepared from L-aspartic 
acid 
A 30% water solution of sodium polyaspartate, 2 ml, pH 7, prepared by the 
thermal polymerization of L-aspartic acid at 240.degree.-246.degree. C., 
for 45 minutes, was purged with a light stream of chlorine gas for 30 
seconds. The color changed from an dark orange to a pale yellow liquid. 
The pH of the decolorized solution was lowered to pH 4. 
When assayed for molecular weight by the procedures of Example 1, the 
molecular weight was lowered by decolorization. After 24 hours, the 
decolorization was found to be transient. 
EXAMPLE 5 
Use of ozone to decolorize an amine copolymer of polyaspartate 
A 33% water solution of an amine copolymer of sodium polyaspartate, 20 g, 
pH 10, prepared by the thermal polymerization of ammonium maleate with 
JEFFAMINE T403, at 240.degree.-250.degree. C., for 45 minutes, was diluted 
with 20 g of water and a stream of ozone was bubbled through the mixture 
for 30 min. The color of the liquid reddish-brown to a light yellow. 
EXAMPLE 6 
Use of chlorine dioxide to decolorize polyaspartate prepared from ammonium 
maleate 
To 4.0 g of a 30% solution of sodium polyaspartate, pH 10, prepared by the 
thermal polymerization of ammonium maleate at 240.degree.-250.degree. C., 
for 45 minutes, was adjusted to pH 3.0 with concentrated HCI followed by 
300 mg of stabilized 5% chlorine dioxide in water. After stirring several 
minutes at 25.degree. C., the solution changed from dark brown to yellow. 
EXAMPLE 7 
The use of hydrogen peroxide to decolorize polyaspartate 
To 5.0 g of a 30% water solution of sodium polyaspartate, pH 10, prepared 
by the thermal polymerization of diammonium maleate at 
220.degree.-250.degree. C., for 45 minutes, was added 0. 1 g sodium 
peroxydicarbonate (0.0006 moles). The color changed from a dark red brown 
to a yellow colored liquid after 1 hour at 55.degree. C. with stirring. An 
identical solution stirred 10 hours at 26.degree. C. had the same 
The experiment was repeated with 0.2 g of sodium peroxydicarbonate gave a 
lighter shade of solution than the 0.1 g experiment. 
The experiment was repeated with 1.0 g of 3% hydrogen peroxide (.0009 
moles) and the same shade of yellow was obtained as in the first 
experiment. 
When assayed for fits effect in the calcium carbonate drift assay and for 
molecular weight by the procedures of Example 1, the effect in the calcium 
carbonate drift assay was not diminished by this decolorization treatment 
and the molecular weight was unchanged by decolorization. 
EXAMPLE 8 
The use of hydrogen peroxide to decolorize an amine copolymer of 
polyaspartate 
To 25.0 g of a 30% water solution of an amine copolymer of sodium 
polyaspartate, pH 10, prepared by the thermal polymerization of diammonium 
maleate with 1,6-hexanediamine, at 235.degree.-250.degree. C., for 45 
minutes, was added 1 g sodium peroxydicarbonate (0.0006 moles). The color 
changed from a dark red brown to a light yellow colored liquid after 1 
hour at 55.degree. C. with stirring. 
EXAMPLE 9 
The use of sodium borohydride to decolorize polyaspartate 
To 5.0 g of a 30% water solution of sodium polyaspartate, pH 10, prepared 
by the thermal polymerization of diammonium maleate at 
220.degree.-250.degree. C., for 45 minutes, was added 0.05 g sodium 
borohydride. The color changed from a dark red brown to a yellow colored 
liquid after 1 hour at 56.degree. C. with stirring. 
When assayed for molecular weight by the procedures of Example 1, the 
molecular weight was unchanged by decolorization. 
EXAMPLE 10 
Failure of sodium formaldehyde sulfoxylate to decolorize polyaspartate 
To 5.0 g of a 30% water solution of sodium polyaspartate, pH 10, prepared 
by the thermal polymerization of diammonium maleate at 
220.degree.-250.degree. C., for 45 minutes, was added 0. 1 g sodium 
formaldehyde sulfoxylate. The color changed from a dark red-brown to a 
red-orange colored liquid after 1 hour at 55.degree. C. with stirring. 
EXAMPLE 11 
Failure of hydrogen to decolorize polyaspartate prepared from ammonium 
maleate 
A 33% water solution of sodium polyaspartate, 70 g, pH 10, prepared by the 
thermal polymerization of ammonium maleate at 240.degree.-250.degree. C., 
for 45 minutes, was placed in a hydrogenation apparatus with 0.5 g of 10% 
palladium on charcoal find the air above the sample was replaced with 
hydrogen. The bottle was then shaken for 24 hours. Following removal of 
the hydrogen gas, the contents of the bottle were centrifuged at high 
speed to separate the viscous liquid from the palladium on charcoal. No 
change in the intense reddish-brown color of the liquid was obtained. 
EXAMPLE 12 
Decolorizing acid catalyzed, thermally polymerized, polyaspartic acid with 
peroxides 
A 133 g portion (1.0 moles) of L-aspartic acid was slurried in 125 g of 
water containing 25 g of 85% H.sub.3 PO.sub.4 was tumbles at 
150.degree.-210.degree. C. for 5 hrs to give 118.8 g of light tan 
polysuccinimide. The product was washed twice with 200 ml portions of 
water. A 3.8 g portion of the polysuccinimide was dissolved in 1.6 g NaOH 
in 8.4 g of water to five a clear red-orange solution of sodium 
polyaspartate. To this solution was added with good mixing, 0.55 g of 30% 
H.sub.2 O.sub.2 in water. After standing 12 hrs at 25.degree. C., the 
solution was nearly colorless. 
EXAMPLE 13 
Decolorizing thermally polymerized polyaspartic acid with peroxides 
A 133 g portion (1.0 moles) of L-aspartic was tumbled at 285.degree. C. for 
2 hrs to give 96.7 g of tan polysuccinimide. A 3.8 g portion of the 
polysuccinimide was dissolved in 1.6 g NaOH in 8.4 g of water to give a 
clear, dark brown solution of sodium polyaspartate. To this solution was 
added with good mixing, 0.55 g of 3% H.sub.2 O.sub.2 in water. After 
standing 12 hrs at 25.degree. C., the solution was light yellow in color. 
EXAMPLE 14 
Decolorizing thermally polymerized polyaspartic acid with peroxide salts 
A sample so sodium polyaspartate of the same size and preparation as in 
Example 13 was treated with 0.75 g of sodium peroxydicarbonate to give a 
light orange colored solution. 
It will be apparent to those skilled in the art that the examples and 
embodiments described herein are by way of illustration and not of 
limitation, and that other examples may be utilized without departing from 
the spirit and scope of the present invention, as set forth in the 
appended claims.