Electrolytic initiation of polymerization in aqueous two-phase systems

Ethylenically unsaturated monomers are polymerized by an indirect process which electrolytically initiates the polymerization. The indirect electrolytic polymerization process utilizes a free radical initiator and an electron transfer agent in a two-phase system capable of carrying an electric current.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an indirect process for electrolytically 
initiating the polymerization of ethylenically unsaturated monomers. More 
specifically, the present invention provides an indirect electrolytic 
polymerization process utilizing a free radical initiator and an electron 
transfer agent in a two-phase system capable of carrying an electric 
current. 
2. Description of Art 
Direct electrolytic polymerization processes are well known. For example, 
it is known that polymerization can be initiated electrolytically by 
passing an electric current between an anode and a cathode contained in a 
suitable mixture. Such mixtures are generally one phase and include 
monomers and electrolytes. However, such polymerizations have not been 
entirely satisfactory in that they require high amounts of energy to 
initiate polymerization and have limited utility in that polymerization 
occurs at the surface of an electrode eventually coating the electrode and 
blocking the current passage through the system. Further, many of these 
electrochemical polymerization processes have been used only with monomers 
present in concentrations which are completely soluble in the 
electrochemical mixture. 
Indirect electrolytic polymerization processes, those which do not directly 
utilize electrode reactions for generating the active initiating species, 
have been more recently developed. Typically, these polymerizations 
utilize an electron transfer which allows polymerization to occur in the 
medium and not at an electrode surface. However, present indirect 
electrolytic polymerizations are restricted by the solubility limits of 
the monomers employed and require high concentrations of the electron 
transferrer. 
The general object of this invention is to provide an electrolytically 
initiated polymerization process for polymerizing ethylenically 
unsaturated monomers. Another object of the invention is to provide an 
electrolytically initiated polymerization process capable of polymerizing 
ethylenically unsaturated monomers in concentration above their solubility 
limits. A further object of the invention is to provide an electrolytic 
initiated polymerization process utilizing a two-phase system capable of 
carrying an electric current and containing low concentrations of electron 
transfer agents and polymerization initiator sources. A still further 
object of the present invention is to provide an electrolytic initiated 
polymerization process which utilizes a recycleable electron transfer 
agent. 
SUMMARY OF THE INVENTION 
The present invention provides an indirect process for electrolytically 
initiating the polymerization of ethylenically unsaturated monomer(s) by 
passing an electric current through a two-phase system comprising: (a) an 
organic phase, (b) a continuous aqueous phase capable of carrying an 
electric current, (c) a free radical source capable of forming a 
polymerization initiator, and (d) an electron transfer agent. 
The present invention further provides an electrolytic initiated 
polymerization process which exhibits high polymerization rates and 
yields. This process can be regulated by controlling the electric current 
flow through the electrochemical system and is highly economical since it 
employs low amounts of energy. 
DETAILED DESCRIPTION OF THE INVENTION 
The two-phase system through which the electric current is passed is 
comprised of a discontinuous organic phase and a continuous aqueous phase. 
The organic phase is comprised of the ethylenically unsaturated monomer(s) 
and/or the product polymer. The continuous aqueous phase is comprised of 
an electron transfer agent, an aqueous medium and optionally an 
emulsifying or dispersing agent. The free radical polymerization initiator 
source may be present in either phase. 
Any ethylenically unsaturated polymerizable monomer can be used in the 
process of the present invention. These monomers are generally known to 
those skilled in the art of polymerization as vinyl monomers. Most 
importantly, the process of the present invention is specifically adapted 
to polymerize monomers in aqueous systems in concentrations above the 
solubility limits of the monomer. Illustrative of the polymerizable 
monomer or monomers used are acrylic compounds, substituted acrylic 
compounds, conjugated diene compounds and aromatic unsaturated compounds. 
Examples of these monomers include but are not limited to vinyl acetate, 
vinyl chloride, vinyl toluene, vinyl naphthalene, vinyl diphenyl, 
acrylonitrile, methacrylonitrile, methyl acrylate, methyl methacrylate, 
styrene, alpha-methyl styrene, acrylamide, N-N'-methylene bisacrylamide, 
N-vinyl-2-pyrrolidone, butadiene-1,3, isoprene, chloroprene, bromoprene, 
cyanoprene, 2,3,-dimethyl butadiene-1,3, 2-ethyl butadiene-1,3 and the 
like. The monomers can be used individually, such as in the production of 
homopolymers, or can be used in various combinations, such as in the 
production of copolymers or multipolymers. Further, insoluble monomers or 
monomers with low solubility can be used in combination with highly 
soluble monomers. 
Monomer combinations which work particularly well in the process of the 
present invention comprise a major portion of an ethylenically unsaturated 
nitrile, such as acrylonitrile, and a minor portion of a monomer capable 
of forming a copolymer therewith, such as an ester of an ethylenically 
unsaturated carboxylic acid, optionally polymerized in the presence of a 
rubbery polymer. The rubbery polymer is typically composed of a major 
portion of a conjugated diene monomer, such as butadiene, and optionally a 
minor portion of a monomer capable of forming a copolymer therewith, such 
as an ethylenically unsaturated monomer or another conjugated diene 
monomer. 
Any material capable of generating free radical intermediates through 
reduction/oxidation reactions can be utilized as a polymerization 
initiator in the process of the present invention. Generally, the 
polymerization initiators are free radical intermediates which are formed 
by the reduction of oxidizing agents which require two or more electrons 
to reach a new stable state. When the initiators accept only one electron, 
they become unstable free radical intermediates which initiate 
polymerization. Typically, peroxides, persulfates, perborates, 
perphosphates and hydroperoxides have been found to be suitable 
polymerization initiator sources. Preferred are the peroxide and the 
persulfate salts and most preferred are hydrogen peroxide, potassium 
persulfate and para-menthane hydroperoxide. 
The electron transfer agents used are generally those that remain soluble 
in aqueous systems in at least two valence states. Typically they are 
reducing metals having at least three valence states. As used herein, 
valence states include the 0 valence metallic state. By utilizing reducing 
metals having at least three valence states, electrons can be transferred 
between the electrode, electron transfer agent and polymerization 
initiator without exhausting the electron transferring system. Typical 
metal electron transfer agents include iron, cobalt, nickel, copper, 
ruthenium, rhodium, palladium, iridium, platinum, gold, rhenium and the 
like. Preferred are iron, cobalt and copper and most preferred is iron. 
Unlike other electrochemically initiated polymerization systems, both the 
cathode and the anode are inert with respect to the monomer system. 
Suitable cathodes and anodes are well known in the art. Typically, 
suitable anodes include but are not limited to platinum, carbon, lead, 
dimensionally stable anodes and various semi-conductors. Suitable cathodes 
include but are not limited to iron, platinum, copper, graphite, mercury, 
lead, tin, aluminum and nickel. 
In order to retain a dispersed two-phase system throughout polymerization, 
a suitable emulsifying or dispersing agent is preferably employed. 
Depending upon the specific electrochemical system employed, the 
emulsifying or dispersing agent may also function as an electrolyte. 
Various emulsifying or dispersing agents can be used in the process of the 
present invention and are well known to those skilled in the art. 
Typically, suitable emulsifying or dispersing agents may be ionic or 
non-ionic and include alkyl or aryl sulfates, sulfonates, phosphates, 
carboxylates and the like. 
The volume ratio of continuous to discontinuous phase in the 
electrochemical system can vary widely. For example, in the process of the 
present invention, the discontinuous phase can surprisingly comprise up to 
about 70%, preferably 50% and most preferably 40% by volume of the overall 
system. This high volume of monomer-containing discontinuous phase gives 
the process of the present invention greater flexibility than other 
electrolytically initiated polymerization systems by providing for a high 
capacity of polymer production while utilizing monomers with various 
solubilities. 
The process parameters of the present invention can also vary widely. Any 
temperature can be employed, although it is preferred to use temperatures 
below the thermal activation temperature of the free radical source and 
above the freezing point of the electrochemical medium. Depending upon the 
particular system chosen, the temperature will typically range from 
0.degree. C. to about 75.degree. C., preferably 20.degree. C. to 
60.degree. C. Any pressure can be employed which allows the reactants and 
the medium to remain in a liquid state throughout the reaction. The 
atmosphere is essentially oxygen free and preferably inert. Any inert 
atmosphere can be employed and typically inert gases include nitrogen, 
helium, argon, krypton and the like. Further, the indirect electrolytic 
polymerization can be performed via either controlled current or constant 
potential. 
Although not intending to be bound to theory, it is believed that the 
process of the present invention utilizes a reaction at the electrode 
which generates an electron transfer agent capable of activating a free 
radical generating source and producing a free radical intermediate. The 
free radical intermediate subsequently initiates the polymerization. More 
particularly, it is believed that the electron transfer agent accepts an 
electron from the cathode and transfers the electron to the free radical 
generating source. The free radical generating source accepts the electron 
becoming a free radical intermediate and initiates polymerization. Thus, 
this indirect electrolytically initiated polymerization is activated only 
in the presence of an electric current. Further, the amount of the 
electric current will control the extent of the electrochemical reaction 
and, therefore, the rate of polymerization. The reaction can be stopped by 
discontinuing the electric current although the reaction will continue for 
a short period until the activated electron transfer agents and free 
radical initiators are exhausted. Thus, a batch mode operation can be 
employed. 
A particular advantage of the process of the present invention is that the 
electron transfer agent is recycleable. By recycling the electron transfer 
agent, very small concentrations can be employed. This is a particularly 
important advantage since large concentrations of the electron transfer 
agent, such as reducing metals, can break the emulsion or dispersion, 
promote side chain polymerization reactions and promote discoloration of 
the product polymers. Typically, the grams of electron transfer agent 
source per gram of monomer can be less than about 0.01 and preferably less 
than about 0.001. The free radical polymerization initiator source can 
also be employed in small concentrations; typically, in concentrations of 
less than about 0.02 grams per gram of monomer, preferably less than about 
0.01 grams per gram of monomer. 
Another advantage of the process of the present invention is that 
essentially all of the polymerization occurs in the aqueous emulsion and 
not on the surface of the electrode. Thus, polymerization can occur 
continuously without the need for removing or cleaning the electrodes. 
Hence, the present invention can proceed through a continuous mode 
operation. 
It should be further appreciated that low amounts of energy can be 
employed. Since there is no direct utilization of electrons from an 
electrode source to form the polymerization initiator and it is not 
necessary to employ heat generation to activate polymerization, the 
present invention utilizes low amounts of energy to effect polymerization.

SPECIFIC EMBODIMENTS 
The electrolytic cell used in the examples below consist of a 100 ml. 
titration vessel containing a cylindrical platinum gauze or a heavy 
platinum foil working cathode, a platinum wire counter anode and an SCE 
reference electrode with a double bridge (bridge to cell containing 0.1 
molar sodium acetate which was adjusted to pH 5 with acetic acid and upper 
bridge containing 0.1 molar KCl). All experiments were begun at an ambient 
temperature (approximately 22.degree. C.) and were blanketed with an argon 
atmosphere at atmospheric pressure. The argon gas stream was presaturated 
with monomer(s) and water by passage through a prebubbler containing the 
same amount and type of monomer(s) emulsion as in the polymerization cell. 
Constant electric current was passed through the various aqueous systems 
described below while continually stirring the polymerization cell with a 
magnetic stirrer. All percentages below are by weight unless otherwise 
indicated. 
EXAMPLE 1 
An aqueous emulsion was prepared containing 21.6% methyl methacrylate 
(monomer), 0.72% sodium lauryl sulfate (emulsifier) and 77.68% deionized 
water. To 100 ml. of the above emulsion, 5.0 ml. of a 1.0% solution of 
potassium persulfate (free radical initiator source) and 1.0 ml. of a 1000 
ppm Fe (III) solution as ferric chloride (electron transfer agent) were 
added. Thus, the final emulsion contained 3.3 parts sodium laurel sulfate, 
0.23 parts potassium persulfate and 0.0046 parts Fe (III) per 100 parts of 
monomer. A constant current of -100 microamps were passed through the 
system for 112 minutes with samples being withdrawn in 2 minute intervals 
for 30 minutes and randomly thereafter for conversion tests. The results 
can be found in Table I. 
EXAMPLE 2 
An aqueous emulsion was prepared containing 26.37% of a 5/1 ratio of 
acrylonitrile/methyl acrylate, 0.92% sodium laurel sulfate and 72.71% of 
deionized water. The potassium persulfate and ferric chloride were added 
as above in Example 1 with the final emulsion containing 3.5 parts sodium 
lauryl sulfate, 0.19 parts potassium persulfate and 0.0038 parts Fe (III) 
per 100 parts of monomer. The polymerization was begun using -100 
microamps of constant current. However, when the temperature rose rather 
steeply in the first 15 minutes of the reaction, the power was reduced to 
-50 microamps and at 71 minutes, the power was again reduced to -25 
microamps. After 110 minutes, about 91.05% conversion was observed at a 
final temperature of 56.degree. C. The results can be found in Table I. 
TABLE I 
______________________________________ 
Example 1 Example 2 
Time *% Conversion *% Conversion 
in Min 
at 100 .mu.A 
% Solids at 100 .mu.A 
% Solids 
______________________________________ 
2 5.65 1.22 -- -- 
4 8.19 1.77 -- -- 
5 -- -- -- -- 
10 18.15 3.92 1.04 0.27 
15 -- -- 4.78 1.26 
16 29.44 6.36 Current decreased 
-- 
to 50 MA 
20 38.66 8.35 7.45 1.97 
30 58.66 12.67 13.67 3.60 
40 68.52 14.80 20.66 5.45 
50 74.34 16.06 29.90 7.89 
70 -- -- 55.10 14.53 
71 -- -- Current decreased 
-- 
to 25 MA 
90 -- -- 88.17 23.25 
110 -- -- 91.05 24.01 
112 81.98 17.71 -- -- 
______________________________________ 
##STR1## 
- - 
"--" indicates that no readings were taken at that time. 
EXAMPLE 3 
An aqueous emulsion was prepared containing 29.2% of a 5/1 ratio of 
acrylonitrile/methyl acrylate, 10.52% by weight of the rubber component of 
a rubber latex (containing 70 parts butadiene-1,3, 30 parts acrylonitrile, 
2.4 parts emulsifier-GAFAC RE-610 from General Aniline and Film Corp., 0.3 
parts azo-bis-isobutyronitrile, 0.5 parts t-dodecyl mercaptan and 200 
parts water prepared according to U.S. Pat. No. 3,426,102), 0.29% 
polymerization modifier-Q-43 from Cincinnati Milicron, 0.35% 
emulsifier-monowet 70R from Mona Industrial Inc., 0.088% stabilizer 
polyvinyl pyrrolidone and 59.55% deionized water. To 100 ml. of the above 
emulsion, 5.0 ml. of a 1% solution of potassium persulfate and 1.0 ml. of 
a 1000 ppm Fe (III) solution (as ferric chloride). The final emulsion 
contained 1.02 parts monowet 70R, 0.30 parts polyvinyl pyrrolidone, 0.98 
parts Q-43, 36.0 parts rubber latex, 0.17 parts potassium persulfate and 
0.0034 parts Fe (III). 
Due to sampling difficulties, conversions were not monitored as a function 
of time in this experiment. At a constant current of -100 microamps for 
105 minutes, about 94.0% total conversion was observed at a final 
temperature of 42.degree. C., although a maximum temperature of 58.degree. 
C. was reached at 71.5 minutes. 
EXAMPLE 4 
An aqueous emulsion was prepared by mixing 20.31 gms. of deionized water, 
9.7 gms. of styrene, 0.2 gms. sodium lauryl sulfate, 0.02 gms. of ferric 
sulfate.n H.sub.2 O and 0.02 gms. of EDTA (chelating agent). The mixture 
was placed in the cell and purged with argon for approximately 15 minutes. 
0.02 gms. of para-methane hydroperoxide was mixed in 0.3 ml. of styrene 
(total styrene equals 10.0 gms.) and added to the cell. The final emulsion 
contained 203 parts water, 2.0 parts sodium laurel sulfate, 0.2 parts Fe 
sulfate.n H.sub.2 O, 0.02 parts EDTA and 0.2 parts para-methane 
hydroperoxide per 100 parts monomer. A constant potential of -0.20 volts 
was passed through the cell and after 90 minutes, the cell contained 
10.07% total solids with a 28.2% conversion. Although the power was turned 
off, the polymerization continued and after 180 minutes there was 17.10% 
total solids in the cell with a conversion of 49.7 %. The power was turned 
on to promote continued polymerization and 2.5 ml. of a 1% sodium laurel 
sulfate solution was added to the cell. After a total polymerization time 
of 330 minutes, the cell contained 21.50% total solids with a conversion 
of 68.6%. 
The above examples have demonstrated that indirect electrolytic free 
radical initiation systems can be used to conduct emulsion 
polymerizations, including copolymerization reactions, and to obtain high 
yields and stable emulsions. Further, the process of the present invention 
results in essentially no accumulation of polymer on the electrode 
surfaces. The temperature of the systems can be regulated by controlling 
the exothermic polymerization via regulating the electric current flow 
through the cell. 
Thus it should be apparent to those skilled in the art that the subject 
invention accomplishes the object set forth above. It is to be understood 
that the subject invention is not to be limited by the examples set forth 
herein. These have been provided merely to demonstrate operability and the 
selection of monomers, electron transfer agents, free radical initiators, 
aqueous emulsion systems and reaction conditions can be determined from 
the total specification disclosure provided without departing from the 
spirit of the invention herein disclosed and described. The scope of the 
invention includes equivalent embodiments, modifications and variations 
that fall within the scope of the attached claims.