Aqueous dispersions of new amphiphilic co-oligomers for the washing- and cleaning-resistant oiling of leather and skins and their use

The invention is a process for oiling of leather and skins which imparts washing and dry-cleaning resistance to the treated leather and skins and a composition useful in the process. The washing and dry-cleaning resistance of leather is improved by impregnating the leather with an aqueous dispersion of a co-oligomer containing residues of a partial ester of maleic acid and acrylic acid and/or methacrylic acid and optionally up to 45% by weight of residues of ether hydmphilic and oleophilic monomers. The composition can contain semiesters of sulfosuccinic acid as additional oiling agents.

This application is a 371 of PCT/EP92/01938 filed Aug. 8, 1992. 
FIELD OF THE INVENTION 
The oiling of vegetable- and/or mineral-tanned leathers and skins is an 
essential process step in the treatment cycle leading to the ready-to-use 
leather- or skin-based useful material. The manner in which the oil is 
distributed in the skin and the extent to which the oil components are 
bound into the skin critically determine the properties and usefulness of 
the end products. Extensive specialist knowledge exists on possible 
interactions between the oil components on the one hand and the tanned 
skin containing residual tanning agents on the other hand. The particular 
composition of the oiling preparations, for example the number of 
lipophilic groups and any reactive groups present for reaction with 
suitable reactive constituents in the tanned leather, determines inter 
alia the durability and effectiveness of the oiling treatment in the 
practical use of the leather and hide goods. 
One aspect which is still important in practice is the provision of oiling 
preparations which can be bound in the tanned skin so reliably that the 
leather and hide goods are sufficiently resistant to washing and cleaning 
for practical requirements. High-quality leather goods, for example in the 
clothing industry, are supposed to lend themselves both to washing with 
detergents and even to dry cleaning without any significant loss of 
quality. The further requirement of adequate water tightness of the oiled 
leather is required in special cases. 
BACKGROUND OF THE INVENTION 
Basically, there are three known processes for the waterproofing of leather 
and skins, namely: 
1. impregnation by incorporation of water-insoluble substances, for example 
solid fats, waxes or special polymers, 
2. impregnation by incorporation of water-swelling substances which form 
high-viscosity emulsions on taking up water and which block the 
interstices between the leather fibers, for example special emulsifiers of 
the w/o type, 
3. treatment with hydrophobicizing substances, for example aluminium, 
chromium and/or zirconium complexes, silicones or organic fluorine 
compounds. 
RELATED ART 
DE 1 669 347 describes the use of water-emulsifiable sulfosuccinic acid 
semiesters for oiling leather, although no waterproofing effects are 
obtained. EP 193 832 describes a process for the production of waterproof 
leathers and skins using sulfosuccinic acid monoesters in combination with 
impregnating and/or hydrophobicizing oiling preparations which is 
characterized in that, after retanning, the leathers or skins are treated 
in aqueous solution with impregnating and/or hydrophobicizing oiling 
preparations containing sulfosuccinic acid monoester salts with 
C.sub.12-24 fatty residues and, after acidification, are fixed by addition 
of a chromium, zirconium and/or aluminium salt. The sulfosuccinic acid 
monoester salts are preferably used with impregnating oiling preparations 
from the group consisting of oxidized or oxidized and partly sulfonated 
C.sub.18-26 hydrocarbons or C.sub.32-40 waxes, phosphoric acid 
mono-C.sub.12-24 -alkyl esters, citric acid mono-C.sub.16-24 -alkyl 
esters, sorbitan, glycerol and/or pentaerythritol-C.sub.16-24 -fatty acid 
esters. 
Amphiphilic preparations in the form of selected co-oligomers of, on the 
one hand, hydrophilic or oleophilic monomers and, on the other hand, 
hydrophilic monomer constituents have recently been described and 
recommended for the wet end treatment of, in particular, mineral-tanned 
leathers and skins. Amphiphilic preparations of this type may be 
incorporated, for example by milling, in the leathers or skins to be 
treated in the form of aqueous dispersions, emulsions and/or solutions on 
completion of the primary tanning stage. In the particular case of 
mineral-tanned leathers or skins, these amphiphilic preparations may also 
perform the retanning function. Finally, the amphiphilic preparations may 
be fixed in a final step, more particularly with mineral tanning agents. 
The more recent patent literature describes auxiliaries of the type in 
question. For example, EP 372 746 describes corresponding preparations and 
their use, the amphiphilic copolymers consisting predominantly of at least 
one hydrophobic monomer and, to a minor extent, of at least one 
copolymerizable hydrophilic monomer. The hydrophobic monomers mentioned 
include long-chain alkyl (meth)acrylates, long-chain alkoxy or 
alkylphenoxy(polyethyleneoxide) (meth)acrylates, primary alkenes, vinyl 
esters of long-chain alkyl carboxylic acids and mixtures thereof. The 
hydrophilic comonomers present to a minor extent are ethylenically 
unsaturated water-soluble acids or hydrophilic basic comonomers. The 
molecular weight (weight average) of the copolymers is in the range from 
2,000 to 100,000. 
EP 412 389 describes the use of copolymers which have been prepared by 
radical copolymerization of (a) C.sub.8-40 monoolefins with (b) 
ethylenically unsaturated C.sub.4-8 dicarboxylic anhydrides along the 
lines of bulk polymerization at temperatures of 80.degree.to 300.degree. 
C. to form copolymers having molecular weights of 500 to 20,000 g/mole, 
subsequent solvolysis of the anhydride groups of the copolymers and at 
least partial neutralization of the carboxyl groups formed during the 
solvolysis step in aqueous medium with bases and which are present in the 
form of aqueous dispersions or solutions as preparations for 
hydrophobicizing leathers and skins. Finally, EP 418 661 describes the use 
for the same purpose of copolymers which contain (a) 50 to 90% by weight 
of C.sub.8-40 alkyl (meth)acrylates, vinyl esters of C.sub.8-40 carboxylic 
acids or mixtures thereof and (b) 10 to 50% by weight of monoethylenically 
unsaturated C.sub.3-12 carboxylic acids, monoethylenically unsaturated 
dicarboxylic anhydrides, semiesters or semiamides of monoethylenically 
unsaturated C.sub.4-12 dicarboxylic acids, amides of C.sub.3-12 
monocarboxylic acids or mixtures thereof in copolymerized form and which 
have molecular weights of 500 to 30,000 g/mole. The copolymers are used 
for the stated purpose in at least partly neutralized form either in 
aqueous solution or in aqueous dispersion. 
Extensive work carried out by applicants has shown that the wide variety of 
materials used in practice in the wet end treatment of leather and skins 
on the one hand and the highly individual and variously pronounced form of 
the intermediate stages in the production of leather and skins make it 
desirable to broaden the possibilities available for the oiling and, 
optionally, retanning treatment of wet end leathers. Accordingly, the 
problem addressed by the present invention was to provide a new class of 
amphiphilic co-oligomers which could be used in an improved manner in the 
above-described treatment of pretanned leathers and skins and which, in 
particular, would be capable of thoroughly impregnating the skin and, on 
the one hand, of achieving the required oiling and, optionally, even 
certain hydrophobicizing effects while, on the other hand, replacing the 
otherwise standard retanning treatment. More particularly, the invention 
set out to enable an at least substantially cleaning-resistant oiling 
effect to be obtained so leathers and skins treated in this way would lend 
themselves to washing with detergents and/or to dry cleaning without 
suffering significant losses of value. 
To solve the problem stated above, the invention uses the class of 
co-oligomers described hereinafter, if desired even in the form of a 
mixture with other oiling and/or hydrophobicizing, more particularly known 
mixture components. In one embodiment, both the class of amphiphilic 
co-oligomers selected in accordance with the invention and the 
above-described auxiliaries optionally used can be fixed in the skin by an 
aftertreatment, more particularly with mineral tanning agents. 
BRIEF SUMMARY OF THE INVENTION 
In a first embodiment, therefore, the present invention relates to the use 
of aqueous dispersions of co-oligomers from the radical-initiated aqueous 
emulsion copolymerization at a pH in the mildly acidic to neutral range of 
(a) semiesters of maleic acid with oleophilic alcohols and/or lower 
alkylene oxide adducts thereof and 
(b) acrylic acid and/or methacrylic acid as principal components which may 
additionally contain 
(c) small quantities of other hydrophilic and/or oleophilic comonomers in 
the oligomer molecule, 
as an amphiphilic preparation for the oiling, washing-resistant and 
dry-cleaning-resistant treatment of leather and skins. 
In this embodiment, the invention relates to the use of the aqueous 
dispersions of these amphiphilic preparations above all for the treatment 
of mineral-tanned leather and/or skins. In this treatment, the 
above-described amphiphilic preparations according to the invention may 
also assume or perform a retanning function. 
In a first embodiment, the present invention relates to aqueous dispersions 
of the amphiphilic co-oligomers of the above-defined components (a) and 
(b) and optionally (c), the molar ratios of (a) to (b) in these 
co-oligomers being in the range from about 1:1 to 2:1. The optional 
component(s) (c) are present in smaller quantities by weight, based on the 
sum total of (a)+(b). The aqueous dispersions are adjusted to pH values in 
the neutral to mildly basic range and are present in particular as a 
water-dilutable water-containing paste with useful-material contents of 
the co-oligomer of the order of 30 to 50% by weight. 
DETAILED DESCRIPTION OF THE INVENTION 
The key element of the invention is the use of the co-oligomers of 
semiesters of maleic acid with selected oleophilic alcohols--component 
(a)--and acrylic acid and/or methacrylic acid--component (b), hereinafter 
also referred to in the interests of simplicity as (meth)acrylic acid--as 
principal components. These co-oligomers may additionally contain small 
quantities of either hydrophilic comonomers and/or oleophilic comonomers. 
These optionally additional components of the co-oligomer molecule are 
collectively referred to as components of type (c). 
It is crucial to the function of the co-oligomers in accordance with the 
invention that a lipophilic part of the co-oligomer molecule--the 
semiester function of maleic acid with oleophilic alcohols--should be 
attached to the carboxyl groups both from the monomer constituents of (a) 
and from those of (b). 
In preferred embodiments of co-oligomers corresponding to the definition 
according to the invention, at least substantially equal quantities of (a) 
to (b) are used in the synthesis of the co-oligomer molecule, although 
component (a) is preferably used in a molar excess over component (b). 
This ensures that a large percentage of oiling and/or hydrophobicizing 
lipophilic molecular constituents is introduced into the wet end leather 
to be treated, although on the other hand the co-oligomer molecule 
contains a sufficiently large number of free carboxyl groups emanating 
both from constituents (a) and from constituents (b). According to the 
invention, therefore, oiling effects can be selectively obtained in the 
fiber structure of the leather or skin, although at the same time a large 
number of free reactive carboxyl groups is available for interaction with 
the skin and/or auxiliaries already present or subsequently introduced, 
more particularly mineral tanning agents. The desired combination of the 
plurality of treatment effects is thus selectively obtainable in a 
controllable manner. More particularly, the auxiliary can be fixed in the 
skin structure in such a way that cleaning by washing and/or dry cleaning 
is possible without any effect on the soft, oiled leather structure. 
It has been found that preferred molar ratios of (a) to (b) are in the 
range from about 1:1 to about 2:1. 
The following observations apply to the comonomer component (a): 
This component is formed by semiesters of maleic acid with lipophilic or 
oleophilic alcohols. Instead of or in addition to the alcohols, alkylene 
oxide adducts thereof with a limited number of alkylene oxide groups 
adapted in known manner to the chain length of the alcohols may also be 
used. Relevant particulars can be found, for example, in EP 193 832 cited 
at the beginning. Accordingly, in the case of the semiesters of maleic 
acid with lower alkylene oxide adducts of oleophilic alcohols which are 
optionally used in component (a), it is preferred to derivatize the 
last-mentioned components with at most 6 alkylene oxide groups and 
preferably with up to 4 alkylene oxide groups. Relatively low degrees of 
alkoxylation are preferably assigned to relatively short chain lengths 
while relatively high degrees of alkoxylation within the relatively low 
range mentioned may be assigned to relatively long chain lengths. 
Particularly suitable alkylene oxide groups are corresponding EO groups. 
However, one important embodiment of the invention uses oleophilic maleic 
acid semiesters with no such alkylene oxide derivatization as component 
(a). In this case, semiesters of maleic acid with linear and/or branched 
oleophilic alcohols containing at least predominantly 8 to 10 or more 
carbon atoms in the molecule are particularly suitable. The use of 
corresponding maleic acid semiesters of which the alcohol radicals contain 
12 to 24 carbon atoms and are generally saturated or, if desired, may even 
be at least partly monoolefinically and/or polyolefinically unsaturated 
can be preferred. Particularly important ester-forming fatty alcohols are 
corresponding components of natural origin which are obtained in known 
manner, for example by reduction, from fatty acids of natural origin. 
Saturated C.sub.12-18 fatty alcohols can be particularly important for the 
formation of the monomeric components (a). Optimized oiling and, at the 
same time, water-repellent effects are obtained using these components on 
their own or in combination with other components. 
However, it has been found that other important properties for the use of 
the co-oligomers in accordance with the invention can be controlled by 
slight variations even in the alcohol radicals of the monomer component 
(a). The use of branched alcohols to a limited extent is particularly 
mentioned in this regard. The use of limited quantities of branched 
alcohols clearly promotes the ability of the co-oligomer to penetrate into 
the fiber structure of the skin to be treated, small quantities of 
branched alcohols being sufficient to initiate the desired effects. 
Branched alcohols may even contain less than 12 carbon atoms in the 
molecule, corresponding components containing at least 6 carbon atoms and 
preferably at least 8 carbon atoms being suitable. One important branched 
alcohol which may be used in the preparation of the maleic acid semiesters 
(a) is 2-ethylhexanol. However, the quantity in which the branched and, in 
particular, relatively short-chain alcohols are used will always be 
comparatively limited. Thus, generally no more than 20% by weight and 
preferably no more than 15% by weight or even 10% by weight of the alcohol 
components present in (a) are formed by lower branched-chain alcohols. 
Quantities of the order of 95% by weight of strongly oleophilic long-chain 
fatty alcohols, more particularly in the C.sub.12-18 range, with around 5% 
by weight of a branched-chain alcohol of the 2-ethylhexanol type have 
proved to be adequate for practical purposes. 
The components (a) are obtained in known manner from maleic anhydride by 
alcoholysis with the particular hydrophobic fatty alcohol or alcohol 
mixture selected. 
The preferred monomer component (b) is acrylic acid, although mixtures of 
acrylic acid and methacrylic acid with, in particular, predominant 
quantities of acrylic acid may also be used. 
The co-oligomerization, which will be described in more detail hereinafter, 
is best carried out in such a way that the co-oligomers formed have 
average molecular weights (weight averages) of around 500 to 20,000. 
Particularly suitable co-oligomers of the type mentioned have 
corresponding average molecular weights in the range from about 1,000 to 
10,000. 
If desired, additional oleophilicizing monomer components (c) and/or 
additional hydrophilicizing monomer components (c) may be used in the 
synthesis of the co-oligomer molecule. If, for example, the 
water-repellent effect is to be intensified, copolymerizable oleophilic 
monomer compounds, for example the (meth)acrylates of long-chain alcohols 
known from the prior art, may be additionally used. On the other hand, the 
character of fixability or retannability can be strengthened by the 
incorporation of further acid groups, for example vinylsulfonic acid and 
the like. In the preferred embodiment, however, the amphiphilic 
preparations according to the invention contain the optional component(s) 
(c) in comparatively small quantities by weight, based on the sum of 
(a)+(b). This applies in particular to co-oligomers of the described type 
which additionally contain oleophilic components (c). In important 
embodiments, their content amounts to no more than 45% by weight and, more 
particularly, to less than 30% by weight of the co-oligomer. One 
particularly important embodiment is characterized by the use of 
co-oligomers which have been prepared without the addition of oleophilic 
components (c). According to the invention, additional oiling and/or 
hydrophobicizing effects can be obtained by using other mixture components 
which will be separately discussed hereinafter. 
The Production Of The Co-Oligomers To Be Used In Accordance With The 
Invention 
According to the invention, the co-oligomers of (a), (b) and optionally (c) 
are produced by aqueous emulsion copolymerization. To this end, the 
following procedure may usefully be adopted: 
The separately prepared maleic acid semiester is very finely emulsified in 
lightly preheated water, if necessary after melting. A preferably mildly 
acidic to neutral pH value is established by alkalization, more 
particularly with NaOH. Preferred pH values are in the range from about 
4.5 to 7 and, more particularly, in the range from 6 to 7. At temperatures 
near the boiling point of water, typically above 90.degree. C., an aqueous 
solution of component(s) (b), more particularly acrylic acid, is added and 
the preferably mildly acidic pH value established in advance is maintained 
by simultaneous pH regulation. At the same time, an initiator for the 
radical reaction, more particularly hydrogen peroxide, is added. On 
completion of the reaction, which normally lasts several hours, including 
an after-reaction phase, a neutral to mildly alkaline pH value is adjusted 
in the aqueous reaction medium. It is possible in this way to prepare 
pastes of which the co-oligomer useful-material content is in the range 
from about 30 to 45% by weight, for example, and which contain unreacted 
constituents only in quantities of well below 1% by weight and preferably 
below 0.5% by weight. Preferred pH values for the storable product are in 
the range from pH 7 to 8. The pastes may be mixed at any time with water 
and/or aqueous active-substance mixtures of the type described in the 
following and used in the form of the resulting mixtures. 
Another important embodiment is characterized by the use of amphiphilic 
preparations of the described type which have been produced, particularly 
at the aqueous co-oligomerization stage, using emulsifiers which, on 
introduction into leathers and/or skins, particularly mineral-tanned 
leathers and/or skins, develop an additional oiling or hydrophobicizing 
effect and which, preferably at the same time, can be fixed in the tanned 
leather or skin via acidic groups. One important example of compounds this 
type are the water-emulsifiable sulfosuccinic acid semiesters mentioned at 
the beginning which emanate from long-chain fatty alcohols and/or alkylene 
oxide adducts thereof. The foregoing observations on the semiesters of the 
maleic acid component (a) apply equally to the particular character of the 
alcohols. One important example of emulsifiers of this class are C.sub.18 
sulfosuccinate semiesters which may be used, for example, in quantities of 
5 to 10% by weight (water-free basis) in the co-oligomerization reaction. 
It has been found that advantageous effects can be obtained by using such 
emulsifier-like auxiliary components (which basically are already known as 
finishing agents for the oiling of leather) in the co-oligomerization 
reaction carried out in accordance with the invention. For example, 
particularly fine-particle, water-containing paste-like reaction products 
with high useful-material contents of co-oligomers are formed. 
However, auxiliaries of this type need not necessarily have been used as 
mixture components in the course of the co-oligomerization reaction, 
instead they may also be subsequently added as mixture components to the 
aqueous useful-material mixture used in accordance with the invention. The 
following are mentioned as examples of compounds of this type: 
sulfosuccinic acid semiesters of long-chain fatty alcohols containing in 
particular 12 to 24 carbon atoms and/or alkylene oxide adducts thereof, 
preferably containing up to 6 alkylene oxide groups, corresponding 
sulfosuccinic acid semiesters of fatty acid mono- and/or diglycerides and 
alkylene oxide adducts thereof preferably containing up to 6 alkylene 
oxide groups, the fatty acid(s) again preferably containing 12 to 24 
carbon atoms, long-chain sulfofatty acids, more particularly corresponding 
.alpha.-sulfofatty acids preferably containing 12 to 24 carbon atoms and, 
more preferably, 16 to 18 carbon atoms; in the case of these 
.alpha.-substituted sulfofatty acids, the hydrocarbon radicals are 
typically saturated, and internal sulfofatty acids of monoolefinically 
and/or polyolefinically unsaturated carboxylic acids, such as oleic acid, 
linoleic acid, linolenic acid and the like. 
However, oiling or hydrophobicizing agents in the form of the 
useful-material mixtures known from EP 193 832 cited at the beginning may 
also be used together with the co-oligomers in the composition according 
to the invention. In this embodiment of the process according to the 
invention, therefore, the co-oligomers of (a), (b) and optionally (c) 
defined in accordance with the invention are combined with impregnating 
and/or hydrophobicizing oiling agents containing sulfosuccinic acid 
monoester salts with C.sub.12-24 fatty residues in combination with other 
impregnating oiling agents selected in particular from the group of 
oxidized or oxidized and partly sulfonated C.sub.18-26 hydrocarbons or 
C.sub.32-40 waxes. Other examples of these additional impregnating oiling 
agents are phosphoric acid mono-C.sub.12-24 -alkyl esters, partial esters 
of polycarboxylic acids, such as citric acid mono-C.sub.16-24 -alkyl 
esters, partial esters of polyalcohols, such as sorbitan, glycerol or 
pentaerythritol C.sub.16-24 fatty acid esters. 
Where useful-material mixtures such as these are used, the quantity of 
co-oligomers of (a), (b) and optionally (c) defined in accordance with the 
invention is preferably at least about 35% by weight, based on the 
useful-material mixture and, more particularly, at least about 50% by 
weight. It may be advisable to use at least about 70 to 80% by weight of 
the total useful-material mixture based on the co-oligomers according to 
the invention to be introduced into the wet end leather to be oiled. 
The introduction of the co-oligomers in the form of an aqueous dispersion 
or in the form of mixtures with the other components mentioned is carried 
out by methods known per se, cf. in particular the observations on 
comparable products in the documents cited at the beginning. Accordingly, 
only a brief summary need be given at this juncture: 
The co-oligomer dispersions according to the invention are suitable for the 
treatment of typical tanned skins, more particularly corresponding 
material which has been tanned with mineral tanning agents. The tanned 
skins are normally deacidified before the treatment. They may already have 
been dyed before the treatment. However, dyeing may also be carried out 
after the treatment according to the invention. 
The leather to be impregnated is wet-treated with the dispersions in an 
aqueous liquor over a period of up to a few hours, optionally in several 
stages, at temperatures in the range from about 20.degree.to 60.degree. C. 
and preferably at temperatures in the range from 30.degree.to 50.degree. 
C., best at pH values in the range from about 4 to 10 and preferably at pH 
values of 5 to 8. The treatment is carried out, for example, by milling in 
a drum. The quantity of co-oligomer dispersion required is normally from 
0.1 to 30% by weight and more particularly from 1 to 20% by weight, based 
on the pared weight of the leather or the wet weight of the skins. The 
liquor length is normally from 10 to 1,000% and preferably from 30 to 
150%; in the case of skins, it is from 50 to 500%. 
On completion of the treatment with the aqueous liquor, the pH value of the 
treatment liquor is displaced into the mildly acidic range by addition of 
acids. The addition of organic acids, preferably formic acid, is 
particularly suitable. Preferred pH values are in the range from 3 to 5 
and preferably in the range from about 3.5 to 4. If desired, fixing may 
subsequently be carried out with, in particular, mineral tanning agents, 
the use of aluminium salts being particularly preferred.

The following Examples describe first the production of co-oligomers 
suitable in accordance with the invention and then their use for the 
treatment of wet end leather in accordance with the invention. 
EXAMPLES 
A general procedure for the production of the oligomers according to 
Examples 1 to 6 based on acrylic acid and maleic acid/fatty alcohol 
semiester and optionally maleic acid is first described in the following. 
The molar ratio of acrylic acid to maleic acid derivative is 1:1.44. 
A mixture of maleic acid semiester and optionally maleic anhydride and 
water in a quantity sufficient to give an approximately 44% by weight 
reaction mixture is introduced into a reaction vessel equipped with a 
stirrer, heating system, cooling system, reflux condenser, temperature 
gauge and three feed vessels. To this end, the following procedure is 
adopted: 
The water is introduced first into the thoroughly stirred reaction vessel 
and heated to around 35.degree. C. Where maleic anhydride is used 
(Examples 1 and 2), this component is first added in portions at such a 
rate that the internal temperature of the reaction mixture remains below 
about 55.degree. C. (time required around 20 minutes, possibly with gentle 
external cooling). After the maleic anhydride has completely dissolved, 
the maleic acid semiester, if necessary melted, is added. The solution is 
then neutralized to a pH value of approximately 7.0 by the addition in 
portions of NaOH pellets. The internal temperature rises to at most 
80.degree. C. 
The contents of the reactor are then heated to 90.degree. C. 
Three feed solutions are prepared in advance of and separately from the 
mixture described above, namely: feed solution 1--acrylic acid/water 
(demineralized); feed solution 2--ammonium peroxydisulfate/water 
(demineraiized); feed solution 3--35% by weight hydrogen peroxide. 
After the temperature in the reactor has reached 90.degree. C., addition of 
the feed solutions and the initiator is commenced. The following starting 
formulation is used: 
Initial mixture: 1.44 moles (maleic acid semiester and optionally maleic 
anhydride) + water in a quantity sufficient to form a 44% by weight 
mixture 2 moles of sodium hydroxide pellets 
Feed solution 1: 72 parts by weight of acrylic acid (AA), approximately 1 
mole, 32 parts by weight of water (demineralized) 
Feed solution 2: 8 parts by weight of ammonium peroxydisulfate dissolved in 
32 parts by weight of water (demineralized) 
Feed solution 3: 28 parts by weight of 35% hydrogen peroxide 
Feed solution 1 is uniformly added over a period of 5 hours. At the same 
time, feed solutions 2 and 3 are uniformly introduced over a period of 6 
hours at an internal temperature of 100.degree. C. (a gentle reflux may 
occur). 
The reaction mixture is then heated for 1 hour at 100.degree. C. 
After cooling to around 80.degree. C., a pH value of approximately 7 is 
adjusted by careful addition of an aqueous 20% sodium hydroxide solution. 
The end products obtained in the form of beige-colored pastes of which the 
dry residue (IR drying balance, 150.degree. C.) is determined. 
The following special observations apply where necessary Examples 1 to 6 
summarized hereinafter in tabular form. 
Example 1 
A mixture based on maleic anhydride (MA) and maleic anhydride semiester (MA 
semiester) is used as the reaction component based on maleic acid. The 
semiester is prepared by reaction of the corresponding quantity of MA with 
C.sub.12 fatty alcohol. 
Example 2 
A mixture of MA/MA semiester is used in this case, too. The semiester is 
the reaction product of MA with C.sub.16 fatty alcohol. The oligomer 
formed is initially lumpy, a homogeneous reaction mixture only being 
obtained after standing overnight and heating. 
Example 3 
The MA semiester is a mixed product based on the alcohol components 
C.sub.16/18 fatty alcohol mixture and 2-ethyl hexanol (2-EHOH); for the 
quantity ratio, see the following Table. The reaction mixture is extremely 
lumpy during the reaction and is subsequently diluted with water on 
account of its high viscosity. 
Example 4 
The aqueous maleic acid semiester mixture corresponds to the mixture of 
Example 3, except that C.sub.18 sulfosuccinate semiester is additionally 
added as an emulsifier. A highly viscous but homogeneous reaction mixture 
is formed. 
Example 5 
The semiester with C.sub.12 fatty alcohol--no addition of MA--is used as 
the reaction component based on maleic acid. 
Example 6 
The reaction component based on MA semiester is the mixture identified in 
the following Table of the semiesters based on C.sub.16/18 fatty alcohols 
and 2-ethyl-hexanol (2-EHOH). In contrast to Example 3, however, twice the 
quantity of water is used in the initial mixture from the outset. The 
reaction product obtained separates into two phases after 24 hours at room 
temperature. 
TABLE 1 
__________________________________________________________________________ 
Quantities in moles 
semi- Acrylic 
NaOH (g) 
% Dry 
Appearance 
Example 
MA ester acid (AS) 
33% solution 
residue 
End product 
pH Value 
__________________________________________________________________________ 
1 0.72 
0.72 C.sub.12 
1.0 128 43.2 
Beige, pasty 
7.0 
2 0.72 
0.72 C.sub.16 
1.0 128 38.4 
Light yellow, 
7.5 
pasty 
3 1.20 C.sub.16/18 
0.875 
110.3 25.4 
Beige, creamy 
7.5 
0.06 2-EHOH 
4 1.20 C.sub.16/18 
0.875 
110.3 36.4 
Beige, pasty 
2.4 
0.06 2-EHOH 
5 3.78 C.sub.12 
2.625 
330.9 38.8 
Beige, pasty 
7.3 
6 1.83 C.sub.16/18 
1.34 196 25.0 
after 24 h/RT = 
2 phases 
__________________________________________________________________________ 
Using oligomer compounds corresponding to the definition according to the 
invention, chrome leather samples are treated with the oligomers according 
to the invention under the working conditions of Examples 7 to 11 below. 
Example 7 
Type of leather: upper leather (with fixing) 
Starting material: wet blue 
Percentages based on pared weight 
Initial pH value: 4.0 
______________________________________ 
Run- 
ning 
time 
Step % by wt. Product/remarks 
.degree.C. 
(mins) 
pH 
______________________________________ 
Washing 200 Water 40 15 4.1 
Drain off liquor 
Neutraliza- 
100 Water 40 
tion 0.5 Na formate 4.3 
Drain off liquor 
Treatment 
100 Water 40 
(hydrophobic- 
5.4 Oligomer of 90 
izing + invention 
retanning) 
+ 0.7 Formic acid 30 4.2 
Drain off liquor 
Fixing 100 Water 40 
0.5 Formic acid 10 3.8 
+ 4 33% basic chrome 90 3.5 
tanning agent 
Drain off liquor 
Washing 300 Water 40 15 
Drain off liquor 
Washing 300 Water 25 15 4.2 
______________________________________ 
Hoard up leather overnight, stretch, vacuum dry for 1.5 mins/70.degree. C. 
Example 8 
Type of leather: upper leather (without fixing) 
Starting material: wet blue 
Percentages based on pared weight 
Initial pH value: 4.0 
______________________________________ 
Run- 
ning 
time 
Step % by wt. Product/remarks 
.degree.C. 
(mins) 
pH 
______________________________________ 
Washing 200 Water 40 15 4.1 
Drain off liquor 
Neutraliza- 
100 Water 40 
tion 0.5 Na formate 4.3 
Drain off liquor 
Treatment 
100 Water 40 
5.4 Oligomer of 90 
invention 
+ 0.7 Formic acid 30 4.2 
+ 0.5 Formic acid 60 3.8 
Drain off liquor 
Washing 300 Water 40 15 
Drain off liquor 
Washing 300 Water 25 15 4.2 
______________________________________ 
Hoard up leather overnight, stretch, vacuum dry for 1.5 mins/70.degree. C. 
Example 9 
Type of leather: upper leather 
Starting material: wet blue 
Percentages based on pared weight 
Initial pH value: 4.0 
______________________________________ 
Run- 
ning 
time 
Step % by wt. Product/remarks 
.degree.C. 
(mins) 
pH 
______________________________________ 
Washing 200 Water 40 15 
Drain off liquor 
Neutraliza- 
100 Water 40 
tion 1 Complex-active 30 4.3 
neutralizing agent 
(Coratyl MK) 
Treatment 
+ 5 Oligomer of 90 5.3 
invention 
+ oiling + 0.7 Formic acid 30 4.2 
Drain off liquor 
Fixing 100 Water 40 
1 Complexing 
dicarboxylic acid 
6 Basic aluminium 60 3.1 
tanning agent 
(Pellutax ALP) 
+ 0.5 NaAl silicate 30 3.6 
(Coratyl G) 
Drain off liquor 
Washing 300 Water 25 15 
Drain off liquor 
Washing 300 Water 25 15 
______________________________________ 
Hoard up leather overnight, vacuum dry at 70.degree. C. 
Example 10 
Type of leather: clothing leather 
Starting material: wet blue 
Percentages based on pared weight 
Initial pH value: 3.9 
______________________________________ 
Run- 
ning 
time 
Step % by wt. Product/remarks 
.degree.C. 
(mins) 
pH 
______________________________________ 
Washing 200 Water 30 
0.3 Formic acid 10 
Drain off liquor 
Neutraliza- 
150 Water 40 
tion 1.5 Na acetate 15 4.8 
+ 2.5 Na bicarbonate 60 6.7 
Drain off liquor 
Dyeing 200 Water 50 
3 Ammonia 5 
+ 4 Dye 60 
Treatment 
+ 6 Oligomer of 60 
invention 
+ 2 Formic acid 15 
+ 2 Formic acid 30 4.0 
Drain off liquor 
Fixing 100 Water 50 
1 Formic acid 5 
+ 4 33% basic chrome 90 3.6 
tanning agent 
Drain off liquor 
Washing 300 Water 25 15 
Drain off liquor 
Washing 300 Water 25 15 3.9 
______________________________________ 
Hoard up leather overnight, wet-tenter, dry-mill, tenter. 
Example 11 
Type of leather: furniture leather 
Starting material: wet blue 
Percentages based on pared weight 
Initial pH value: 4.0 
______________________________________ 
Run- 
ning 
time 
Step % by wt. Product/remarks 
.degree.C. 
(mins) 
pH 
______________________________________ 
Washing 200 Water 35 10 
Drain off liquor 
Neutraliza- 
100 Water 35 
tion 2 Na acetate 30 4.8 
+ 1.5 Na bicarbonate 60 6.0 
Drain off liquor 
300 Water 55 10 
Drain off liquor 
Dyeing 100 Water 55 
1 Ammonia 10 8.5 
+ 3 Dye 45 
Treatment 
+ 6 Oligomer of 90 
invention 
+ retanning 
+ 6 Vegetable-synth. 
tanning agent 30 5.9 
+ 1.5 Formic acid 15 
+ 1.5 Formic acid 30 3.8 
Drain off liquor 
Fixing 200 Water 40 
0.5 Formic acid 10 
+ 4 33% basic chrome 90 3.6 
tanning agent 
Drain off liquor 
Washing 300 Water 30 15 
Drain off liquor 
Washing 300 Water 25 15 
______________________________________ 
Hoard up leather overnight, wet-staple, dry, moisten, mill, tenter. 
The products of Examples 1, 4 and 5 corresponding to the definition 
according to the invention are used as oligomers according to the 
invention in tabulated Examples 7 to 11. Soft, supple and very full 
leathers are obtained in every case, being distinguished by a pleasant 
feel and by high grain stability. 
The samples can be washed in aqueous detergent solutions (30.degree. C.) 
and dry-cleaned without permanent damage to the product properties. Even 
after repeated cleaning steps of the described type, there is no 
indication of permanent stiffening of the leather.