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Patented July 11,1950
Fred W. Banesand Erving Arundale, Westiield,
NHL, assignors to Standard Oil Development
Company, a corporation of Delaware
No Drawing. Application October 31, 1945,
Serial No. 625,965
14 Claims- (Cl. 260-833)
This invention pertains to improvements in
latex short-stop because of its water insolubility
synthetic rubber latices such as are obtained by
polymerization of conjugated diole?ns or mix
tures of coniugated diole?ns with other copoly
and general lack of activity under the conditions
existent in emulsion polymer latices. It is there
fore necessary to protect the latex rubber from
merizable materials and particularly to short 5 deterioration during the stripping, handling and
stopping the emulsion polymerization reaction
storage by the use of other materials. Substances
and stabilizing the resultant latices against de
which have been used in the past for this purpose
gradation during the stripping and/or storage of
have generally been of the reducing agent type
which possess at least some solubility in water.
said latices.
In the so-called Buna manufacture or emulsion 10 Examples of this class of short-stops are hydro
polymerization, conjugated diole?ns with or with
quinone, hydroxylamine, sodium sul?de, sodium
out other comonomers such as styrene, acryloni
sul?te and sodium hyposul?te (Na2SzO4). How
trile, methyl vinyl ketone and the like which are
ever, most of these compounds possess marked
copolymerizable with conjugated diole?ns in
disadvantages of one type or another. For ex
aqueous emulsion are emulsi?ed in an aqueous 15 ample, hydroquinone is quite effective as a short
medium, the necessary catalysts, polymerization
stop but it discolors the latex and the recovered
modi?ers, etc., added and the mixture heated with
gum rubber very badly. Sodium sul?de, on the
rapid agitation under pressure in suitable reac
other hand, does not discolor the latex or the
tors to effect polymerization to the desired de
gum rubber but does give rise to traces of hy
gree. The rubbery polymer is obtained in the 20 drogen sul?de which are stripped out with the un
form of a latex which may be used as such, con
reacted monomers thereby poisoning them for
centrated by creaming or subjected to coagula
subsequent polymerizations. The inorganic re
tion in order to recover the polymer in solid or
ducing agents have the further disadvantage that
dry form.
they fail, in general, to inhibit cross-linking of
In actual operation it is found that rubber of 25 polymer chains and therefore yield products of
optimum quality is obtained if the polymerization
high gel content.
is not allowed to exceed 70 to 80% conversion
It is the object of this invention to provide the
of the monomers. Above this range the rubber
art with a novel short-stop for emulsion poly
loses its ease of processing, becomes insoluble in
merization reaction systems.
its raw state and yields vulcanizates of inferior 30 It is also the object of this invention to provide
short-stops for emulsion polymerization reaction
properties. In order to avoid the effects of the
monomers themselves or low polymers thereof
systems which do not discolor the polymer latices
such as dimers and trimers on the ?nal product
or‘the polymer, itself and which effectively inhibit
and also for reasons of economy, it is necessary
the cross-linking of the polymer chains.
to remove unreacted monomers from the latex. 35
These and other objects will appear more
This is usually done by stripping the latex under
clearly from the detailed speci?cation and claims
reduced pressure with or without the aid of heat
which follow.
and/or a stripping agent such as steam or inert
gas. Inasmuch as the stripping conditions are
usually as severe as or perhaps more severe than
the actual polymerization conditions it is neces
sary to “short-stop” the system so as to prevent
further polymerization of the monomers and to
prevent inter-polymer reaction, 1. e. cross-linking
of polymer chains to produce insolubility and a
general deterioration of rubber quality.
While it is customary in the rubber industry to
stabilize gum rubber by milling anti-oxidants or
age resisters, such as phenyl-beta naphthylamine
into it, this type of material will not serve as a 50
We have now found that the combined use of
hydroxylamine and dialkylated 0- or p-cresols /
show good short-stopping and stabilization be
havior, that results are obtained with this com
bination which are not obtainable with the in
dividual agents and that the results obtained
with the combination are more than the mere
sum of the effects of the individual'agents. This
combination 'of agents is particularly desirable
since it is not only effective in short-stopping and
stabilizing the latex but also it accomplishes this
result without appreciably discoloring the latex
after passing through such finishing operations
the present invention- is‘ applicable to synthetic
as stripping and prolonged storage.
The use of a combination of hydroxylamine and
dialkylated 0- or p-cresol in accordance with the
known by the polymerization in aqueous emulsion. ,
present invention is especially useful in produc
ing creamed latex of light color and good storage
pentadiene and the like taken singly or in com- .
rubber latices, which are ‘prepared, as is well
of conjugated diole?ns such as butadiene-LS,
isoprene, piperylene, dimethyl butadiene, methyl
bination and. in admixture with other polymer
stability. In this case any residual water-soluble
izable compounds such as styrene, alpha methyl
short-stopper would be transferred to the serum
styrene, para methyl styrene, alpha methyl para
(the low solids component of the crearning mix
ture which constitutes about three fourths of the 10 methyl styrene, halogenated styrenes such as
chioro- or bromo-styrenes, acrylonitrile, meth
volume of the original latex) and hence would
acrylonitrile, acrylic- and methacrylic acid esters
not offer any resistance to further polymeriza
such. as methyl. acrylate and methyl meth
tion of the latex by active polymer segments or
acrylate, fumaric acid esters such as ethyl
by oxidation. Howeve'rhthe presence ‘of an oil
fumarate and unsaturated ketones such as methyl
soluble stabilizer, although of less short-stopping
vinyl ketone and methyl isopropenyl ketone and
also to resin latices prepared by polymerizing.
monoole?nic materials such as styrene, methyl
methacrylate, methyl isopropenyl ketone and the
potency than the hydroxylamine, would continue
to offer a stabilizing effect on the creamed latex,
since it would separate for the most part into that
phase during the creaming operations. This pro
cedure not only permits production of a light 20 like in aqueous emulsion alone or in admixture
with minor amounts of conjugated diole?ns of
colored creamed latex but also one of sufficient
4 to 6 carbon atoms per molecule. This inven
stability to permit long storage even in the ab
tion is also applicable to these latices before,
sence of antioxidants without serious degrada
during or after creaming thereof as described in
tion in product quality.
The speci?c combination of short-stopping
agents contemplated consists of hydroxylamine
application Serial Ila-555,659 ?led September
30, 1944, now U. S. Patent 2,444,801, by E.
Arundale. These latices will be referred to here
inafter as synthetic latices or synthetic rubber
latices and are not to be confused with any
and acid addition salts thereof such as hydroxyl
amine hydrochloride and dialkyl derivatives of o
and p-cresols corresponding to the general for
30 arti?cial latices prepared by dispersing solid
polymerizates whether of natural or arti?cial
origin in water.
The synthetic latices which are stabilized in
accordance with the present invention are pre
pared by emulsifying the monomers or mixtures
of monomers in from about an equal to about a
.twofold quantity of water using, as the emulsi?er,
water-soluble soaps such as alkali metal or am.
monium salts of oleic, stearic or p'almitic acids or
wherein each R stands for an alkyl group of from 40 mixtures of fatty acids such as are obtained by
1 to 5 carbon atoms and R1 stands for methyl
selective hydrogenation of the mixture of fatty
when R: stands for hydrogen and R1 stands for
acids obtained from ,tallow. Other emulsifying
hydrogen when R: stands for methyl. Speci?c
compounds contemplated include materials such
as ditertiary butyl cresols, di-tertiary amyl cresol,
2,4,6 trimethyl phenol, 2,3-dimethyl-6-tertiary
butyl phenol, 2,6 diethyl-4-methyl phenol and the
like. The ditertiary butyl cresol may be readily
prepared for example, by bubbling isobutylene
through para cresol containing a trace (0.1 to
2%) of an acid type catalyst such as sulfuric
cresol-sulfonic acid, etc., or other suitable type of
alkylation catalyst at a temperature of about
50-60° C., until about two molar equivalents of
isobutylene have been absorbed. To this mixture
is then added sufficient base such as Ba(OH)z,
CaCOa, NaOH, etc. to neutralize the acid catalyst
and prevent subsequent dealkylatiom. The mix
vture is then subjected to distillation under re-
duced pressure to remove isobutylene, isobutylene
polymers, unreacted cresol, etc. The residue con
taining principally dibutylated cresol can be fur
ther purified by vacuum distillation (about 150°
C. at 25 mm. Hg) or by recrystallization from al
cohol~or other suitable solvent to yield a crystal
agents which may be used include such synthetic
surface active agents as salts of alkylated ben
zene- and naphthalene sulfonic acids, fatty alco
hol sulfates, salts of aliphatic or oleflnic sulfonic
acids and also acid addition salts of high molecu
lar weight alkyl amines such as dodecyl amine
hydrochloride or acetate. The amount of emul
sifier used is ordinarily about 0.5 to about 5
weight per cent based on the reactants. A poly
merization catalyst such as benzoyl peroxide,
hydrogen peroxide and alkali metal or am
monium perborates or persulfates or the like is
provided in the reaction mixture in amounts of
about 0.05 to about 0.6 weight per cent based on
the reactants. It is ordinarily preferred to pro
vide a suitable polymerization modi?er or pro
moter such as dialkyl xanthogen disul?des or
aliphatic mercaptans containing at least six
carbon atoms per molecule such as hexyl, octyl,
decyl, dodecyl, Lorol or benzyl mercaptans in the
reaction mixture in amounts of between about
0.2 to about 1.0 weight per cent based upon the
line material of about Gil-69° C. melting point. ~ reactants present. The reaction mixture is main
tained at vthe desired temperature of between
Instead of using para cresol, one may also use
ortho or meta cresol or other phenols and in
stead of isobutylene one may use other isooleflns .
such as isoamylene and the like. The preparation
of alkylated phenols is described in some detail in
the article entitled “Alkylated Cresols from Re
about 15° C. and about 65° C. for a length of time
sufficient to convert a major proportion, generally
about 75% of the monomers to a solid, high
molecular weight polymerizate of the desired
properties. Ordinarily about 12 to about 18
?nery Gases" by Menerich in Industrial and En- I hours are required to reach this conversion. The
proportions of materials used, temperature, time
gineering Chemistry, vol. 35, page 265- (1943).
The mixture of short-stoppers contemplated by 76 of ‘reaction, etc, are well known or understood by
' 2,514,808
tures after the desired conversion had‘ been at
the art and form no part of the present invention.
When the desired conversion level is reached.
tained, as water or benzene solutions or as dis-_
persions. These additions’ were made by a
technique involving the use of a hypodermic
a polymer stabilizer or short-stop mixture of the
type described above is added to the latex. The
amount of stabilizer added is ordinarily about
0.1% to about 1% although larger amounts such
syringe and needle. In this case a 10 ml. B-D ‘
Yale-Lek syringe ?tted with a 1 inch, 20 gauge
as up to about 6-7 % may be used. The latex
may then be stripped of unreacted monomers by
stainless steel needle was used. In all cases the
concentration of short stop was adjusted so that
subjecting it ‘to steam distillation, preferably
5 ml. of solution could be added to the reaction
under reduced'pressure whereupon the latex may 10
be stored as such or subjected to creaming or
Monomer conversions were determined by a
hypodermic sampling technique. In this case a
5 ml. syringe ?tted with stops for the plunger was
The particular advantages of the mixtures of
used to withdraw samples of latex from the re
hydroxylamine and dialkyl derivatives of o- and
p-cresols as short-stops for synthetic latices is 15 actors just after short-stop addition and again
after the short-stopped reaction mixture had
illustrated by the following examples:
been returned to the vat for an additional 17
hours at 50° C. (total of 24 hours’ reaction time)
or 24 hours at 40° C. (total of 40 hours’ reaction
Quart size King No. 1 siphon bottles were used 20 time.) In both instances the reactors were
shaken vigorously before sampling in order to
as the reactors for the preparation 01' butadiene
obtain homogeneous portions of latex. The
styrene copolymers. The materials charged to
the reactors were as follows:
that the latex could be transferred to .a tared
Grams 25 vessel (containing approximately 0.002 gm. of
hydroquinone) for weighing and subsequent
__________________________ __ 144
Styrene _____________________________ __
syringe was ?tted with a one way stopcock so
__________________ .. ,
Potassium persulfate ________________ __
Tallow acid soap ________________ _--___'..
evaporation to dryness for solids and conversion
determination. A per cent solids-per cent con
version relation was established by sampling re
30 actions in the above manner and coagulating and
The polymerizations were carried out at 40 or
50° C. in a constant temperature vat where the
bottles were rotated on a 36" diameter wheel at 35
a rate of 16 R. P. M.
drying the remaining latex for dry rubber con
tent. By this technique solids from a single re
actor were reproducible to at least :0.2% and
v the conversions to -_'-1.0%.
The results obtained are tabulated in'Table I
set out below:
Short stops were added to the reaction mix
Table I
Test Material
Cone. (per-
cent on
Temp, cm“ at
' -'
Hydroxylamine _______________________ _
e4. 5
Hydroxylamine _______________ __
2,3 dimetliyM-t-butyl phenol. ..
5. 4
49. O
53. 0
4. 0
51. 2
Hydroxylamine ................ _
2, 3 dimethyl-d-t-butyl phenol.._--
The above results show that hydroxylamine is
highly effective as a short-stop only if used in
amounts of at least 0.2% based upon the mono
A butadiene-acrylonitrile type latex of 75%
monomer conversion was prepared as described
in Example 2. The fresh latex was short-stopped
mers and that dialkyl phenols and alkoxyalkyl >
phenols are substantially ineffective as short
with 0.2% of hydroxylamine-HCl and then
stripped by heating for 3 hours at 60° C. This
stripped latex was divided into four equal por
tions for aging'tests at ‘room temperature and
at about 50° C. but are somewhat more e?ective
at 50° C., the accelerated aging tests being car
as short-stops in higher conversion latices and 10 ried out inclosed pressure-type bottles. Portions
at lower temperatures. Surprisingly, however,
of the above latex were aged without further ad
mixtures of 0.1 to 0.2% of trialkyl phenols and
ditlon of stabilizing agent at room temperature
about 0.1% of hydroxylamine exhibited a con
and at 50° C. The other portions were subjected
siderable activity as short-stopping agents. Ac
to the same aging tests after the addition of
cordingly, by using the trialkylphenols which per 15 0.2%
of 2,6-di-t-butyl-4-methy1 phenol. After
so are not particularly e?ective as short-stops
varying periods of aging, latex samples were
in conjunction with hydroxylamine, the amount
drawn for gel analyses of the isolated dry polymer.
_ of the latter may be reduced to substantially half
In all cases 2% of phenyl beta naphthylamine was
that required when used alone as the short-stop.
added to the latex before coagulation to insure
20 against gel formation during the drying of the
polymer. An increase in the gel content of the
A butadiene-acrylonitrile latex containing
polymer is an indication that cross-linking of
about 25% of rubber solids and 2l/2% of sodium
polymer chains has occurred either by the action
oleate based on the water, was prepared by co
polymerizing butadiene and acrylonitrile in ap 25 of active polymer segments or by oxidative proc
esses. The data obtained are as follows:
proximately a 3 to 1 molar ratio, the polymeri
stops, for emulsion polymer latices whilevthe tri
alkyl phenols are of unsatisfactory activity when
added as shorty-stops to 50% conversion latices
Per Cent Gel in Dry Rubber
Alter Aging at Room Temp. Alter-Aging at 50° C.
0 days
48 days
300 days
0 days
11 days
0%, Hydroxylamine.HCl ...... __
HydroxglaminaHCi ...... __
2,6-di- ‘- utyH-methyl phen
These data show that although the water-solu
ble hydroxylamine-HCI is an eilfective short
zation being carried to approximately a 75% con
version of monomers to polymers. This latex
was divided into several smaller batches. Each
stopping agent it is not e?ective in preventing
gel formation during prolonged storage but that
batch was short-stopped in a diilerent manner,
then stripped of monomers by heating for 2 hours
at 60° C. whereupon 2.0% of phenyl beta naphth-l
ylamine was added to each batch, the latex
coagulated with brine, slurry washed and oven
dried for 10 hours at 175° F. The dry coagulum
was analyzed for gel (the benzene insoluble por
tion of the polymer), a low value for percent gel 50
a 'mixture of hydroxylamine-HCI with a‘ trial
kylated phenol is considerably more effective as
a stabilizer for butadiene-acrylonitrile type latices
during prolonged storage.
up to the point of anti-oxidant addition. Mooney
The foregoing description contains a limited
number of embodiments of the present inven
tion. It will be understood, however, that the
foregoing examples are merely illustrative of
the present invention and that the latter is not
plasticity measurements were also made on the
limited to the speci?c conditions described since
dry polymers, the lower values indicating better
numerous variations are possible without depart
ing from the scope of.our invention as de?ned
signifying e?ective short-stopping and stabilizing
latex stabilization. The data obtained are tabu
lated below:
in the following claims.
What we claim and desire to secure by Letters
Patent is:
Mooney Vis
Short Stop (Per Cent on Polymer)
Per Cent Gel WW1?‘ 212°
In Dry Poly-
None .............................. -.
Hydroxylamine.HCl _________ _.
0. a 2.0-di-t-butyl-4-methyl phenoL-
0.1 2,6-di-t-butyi-4-methyl phenoL. }
0.2 Hydroquinone ...... __
by polymerizing in aqueous emulsion a conjugated
diolefin having from 4 to 6 carbon atoms. which
method comprisesv adding to the latex about 0.1
to 0.2% oi‘ a trialkyl phenol having the formula
100 05
ow?nyqmynmmenci .......... __
These data show that 2,6-di-t-butyl-4-methyl
phenol is inferior as a short-stopper for bu
l. A method of stabilizing against further
polymerization a synthetic rubber latex prepared
tadiene-acrylonitrile type latices but that by mix
ing 0.1% of that phenol with 0.1% oi.’ hydroxyl
amine'HCl it is possible to get the same short
stopping effect as is obtained with 0.2% of hy
droxylamine-HCI or 0.2% of hydroquinone.
wherein each 'R stands for an alkyl group hav
ing from 1 to 5 carbon atoms and R1 stands for
75 methyl when R: stands for hydrogen and R1
stands for ‘hydrogen when R: stands for methyl
polymerization a. synthetic rubber latex prepared
by copolymerizing in aqueous emulsion a major
and, .in combination therewith about 0.10% of a
member of the groupconsisting of hydroxylamine
proportion of butadiene-LS .nd a minor propor- and hydroxylamine ‘hydrochloride, the p*rcen— ‘ ‘ tion of acrylonitrile which comprises dispersing
, tage values being based on the amount of mono
therein 0.1 to 0.2 percent based on monomers of mers.
-2,6-di-t-butyl-4-methyl phenol and 0.1 percent
v2. ‘A method of stabilizing against further
polymerization a synthetic rubber latex prepared
by polymerizing infaqueous emulsion a conjugated
diole?n'having from 4’ to 6 carbon‘ atoms and an.
based on monomers of hydro'xylamine hydro
5. A method according to claim 2 wherein the
unsaturated comonomer is styrene. ‘
ethylenically unsaturated comonomer capable‘of ,
6. The process as de?ned in claim 1 wherein
copolymerizing with the said diole?n, which
method comprises adding to the latex about ’1).1
to 0.2% of a trialkyl phenol having the formula
thetrialkyl phenol is 2,4,6-trimethyl phenol.
7-. The process as de?ned in claim 2 wherein
the trialkyl phenol is 2,4,6-trimethyl phenol.
8. The process as de?ned in claim 3 wherein the
‘ trialkyl phenol is -2,4,6-trimethyl phenol.
9. The process as de?ned in claim 5 wherein
the trialkyl phenol is 2,4,6-trimethyl phenol.
10. The process as de?ned in claim 1 wherein
the trialkyl phenol is 2,4-dimethyl-6-t-butyl
11. The process as de?ned in claim 2 wherein
wherein each R stands for an alkyl group having
the trialkyl phenol is 2,4-dimethy1-6-t-butyl
from 1 to 5 carbon atoms and R1 stands for methyl
phenol. when R: stands for hydrogen and R1 stands for
12. The process, as de?ned in claim 1 wherein
hydrogen when Rs stands for methyl and. about 25
the trialkyl phenol is 2,6-di-t-butyl-4-methyl
0.10% of a member of the gro'up‘consisting of hy
droxylamine and hydroxylamine hydrochloride,
14. The process as de?ned in claim 5 wherein
‘ polymerization a synthetic rubber latex prepared
the trialkyl phenol is 2,6-dl-t-butyl-4-methyl
by copolymerizing butadiene-1,3 and acrylonitrile
in aqueous emulsion, which method comprises
adding to the latex about 0.1vto 0.2% of a tri
alkyl phenol having the formula
The following references are of record in the
the trialkyl phenol -is 2,6-di-t-butyl-4-methyl
- 3. A method of stabilizing against further 30
13. The process as de?ned in claim 2 wherein
thepercentage values being based on the amount
file of this patent:
Hart ____________ __ Aug. 29, 1944
wherein each It stands ‘for an alkyl group having
Arundale ________ -_ July 6, 1948
from 1- to 5 carbon atoms and R1 stands for
methyl when R: stands for hydrogen and R1
stands for hydrogen when R: stands for methyl
‘(Du Ront Rubber Chemicals,” Report No. 43-1
and about 0.10% of hydroxylamine, the percen
page 121 (Feb. 23, 1948).
tage values being based on the amount of
White et al.: Ind. Eng. Chem., 37, 770-775
monomers used for the polymerization.
50 (Aug. 1945).
4. The method of stabilizing against further
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