United States Patent Office 2,703,794

Patented Mar. 8, 1955

2
The composite reduction-oxidation catalyst employed
2,703,794 in the reaction constitutes a mixture of organic and/or
ETHYLENE/WNYL ACETATE POLYMERIZATION inorganic compounds that produce a free radical as need
PROCESS ed to copolymerize the ethylene and the vinyl acetate.
The free radical produced by the reduction-oxidation re
Milton J. Roedel, Wilmington, Del, assignor to E. I. du action, which occurs along with the copolymerization
Pont de Nemours and Company, Wilmington, Del, a reaction, may be formed from a peroxygen compound
corporation of Delaware including those well known to the art as Suitable for poly
merizing ethylene and for producing copolymers of
No Drawing. Application September 4, 1951, 0 ethylene/vinyl acetate, while the reducing agent may be
Serial No. 245,079 a metal salt of groups I-B and VIII of the periodic table,
or heavy metal ions generally which exist in more than
4 Claims. (C. 260-87.3) one valence state. Contrariwise, the reducing agent
may be an organic compound Such, for example, as so
This invention relates to a process of preparing copoly 5 dium formaldehyde sulfoxylate, ascorbic acid or the like.
mers of ethylene and vinyl acetate and more particu In addition to the use of a reduction-oxidation catalyst,
larly is directed to a low temperature, highly efficient efficient production of the copolymer necessitates con
process for emulsion copolymerization of ethylene and ducting the copolymerization while the reactants are in
vinyl acetate that yields ethylene/vinyl acetate copolymer an emulsified or disposed phase. When the copolymer
latices that can be hydrolyzed to high molecular weight 20 ization is conducted in this manner the conversion of
ethylene/vinyl alcohol copolymers. This application is a ethylene and vinyl acetate to copolymers is increased
continuation-in-part of my copending application S. N. several fold over that obtained without an emulsified or
199,143, filed December 4, 1950, which in turn is a coll dispersed state being present.
tinuation-in-part of my copending application S. N. An additional feature of the invention, the use of which
98,197, filed June 10, 1949. 25 provides optimum operation of the process resulting in
The copolymerization of ethylene with vinyl acetate increased introduction of ethylene into the copolymer at
was first described by M. W. Perrin and was covered in a given pressure, involves a reaction in which the copoly
the United States by his U. S. Patent 2,200,429. A num merization, in addition to being conducted in a redox
ber of contemporary investigators have described the co catalyst system and in the presence of an aqueous emul
polymers and provided new catalysts, reaction media and 30 sion or dispersion, is likewise carried out in the presence
methods of forming the polymers and improving their of tertiary butyl alcohol.
properties. The hydrolysis or partial hydrolysis of said The examples illustrate preferred embodiments of the
polymers to ethylene/vinyl alcohol compolymers is invention in which parts are by weight unless otherwise
covered in U. S. Patents 2,386,347 and 2,399,653. How described.
ever, in spite of the extensive art, no commercially fea 35 Example I.-The following materials were added to a
sible process has been developed for ethylene/vinyl ace on liter stainless steel rocker tube at 0° C. under a stream
tate copolymers because the high polymerization temper of nitrogen:
atures required by the prior art to introduce ethylene, at 280 ml. deoxygenated water--3 gm. Na2HPO4-10 gm.
commercially feasible rates, on a continuous process basis "Duponol' ME (the sodium salt of sulfated lauryl
lead to extensive branching of the copolymer, which is 40 alcohol).
particularly reflected by marked degradation in molecular 20 ml. deoxygenated water containing dissolved thereil
weight on hydrolysis, giving low molecular weight ethyl 0.14 gm. FeSO4.7H2O.--O.23 gm. Na4P2O7.10H2O.
ene/vinyl alcohol copolymers of insufficient toughness for 0.54 gm. K2S2O8 in a small unstoppered vial.
wide utility in the plastics field. 0.21 gm. NaHSO3 in a small unstoppered vial.
An object of this invention is to provide a process by 45 100 ml. vinyl acetate.
which improved copolymers of ethylene and vinyl acetate
can be produced. Another object is to provide an effi The rocker tube was then evacuated and pressured to 400
cient low temperature process for the emulsion copoly atmospheres with ethylene containing less than 10 p. p. m.
merization of ethylene and vinyl acetate by use of a re oxygen. The rocker was then started, mixing the con
duction-oxidation catalyst. Another object is to provide tents of the vials and emulsifying the monomer and the
a versatile low temperature emulsion process by means temperature brought to 30° C. and the pressure to 1000
of which the combining ratio of ethylene and vinyl ace atmospheres with ethylene. After two hours' reaction
tate can be varied widely by choice of reaction conditions. time and a pressure drop of 120 atmospheres, the rocker
Another object is to provide a medium in which im contents were discharged in the form of a latex which
proved copolymers of ethylene and vinyl acetate can be 55 was coagulated with brine solution. The ethylene/vinyl
produced. A still further object is to provide a process. acetate copolymer was washed with water and dried on
for the production of high molecular weight copolymers hot mill rolls. There was thus obtained 66 gm. of tough,
of ethylene and vinyl acetate in the form of a latex for high molecular weight, colorless polymer which analyzed
use as such or which can be hydrolyzed to high molec 1.2 moles of combined ethylene per mole of combined
ular weight ethylene/vinyl alcohol copolymers. Other 60 vinyl acetate and possessed a melt flow point of 165 C.
objects and advantages of the invention will appear here on a melting point determination block.
inafter. Example 2-The following materials were added to a
High molecular weight ethylene/vinyl acetate co one liter stainless steel rocker tube at 0° C. under a
polymers, having desirable molecular structures and hy: stream of nitrogen:
drolyzable to high molecular weight orientable ethylene/ 65 200 ml. deoxidized water--10 gm. "Duponol' Me--0.31
vinyl alcohol copolymers, are produced in accord with gm. sodium formaldehyde sulfoxylate dihydrate.
the process of this invention by polymerizing ethylene 100 ml. vinyl acetate--0.26 gm, cyclohexanone peroxide.
and vinyl acetate together in the presence of a reducing The rocker tube was then evacuated and pressured to 400
agent and an oxidizing agent capable of generating a free atmospheres with ethylene containing less than 10 p.p.m.
radical by a reduction-oxidation process known as a 70
redox process. This copolymerization reaction is con oxygen. The rocker was then started and the tempera
ducted in an aqueous emulsion of the reactants to give ture brought to 30° C. and the pressure to 1000 atmos
an aqueous dispersion of the copolymer. The redox pheres with ethylene. After two hours' reaction time the
emulsion copolymerization process may be conducted product was recovered as a latex containing 67 gm. of
75 ethylene/vinyl acetate copolymer containing 7.2 moles of
attemperatures from as low as -50° C. up to 125 C., at combined ethylene per mole of combined vinyl acetate
pressures ranging from 10 to 3000 atmospheres or higher. or six times as much combined ethylene per mole of com
For optimum operation, however, and for the production bined vinyl acetate as Example 1.
of superior copolymers, temperatures between 30 and Example 3.-Same charge and procedure as Example
90° C. should be employed and pressures between 50 and 80 2 except run at 400 atmospheres instead of 1000 atmos
i500 atmospheres. pheres pressure. Yield equaled 41 gm. of ethylene/vinyl
 3,708,794
3 4.
acetate copolymer containing 3.2 moles of combined period, sufficient to approach an equilibrium condition
ethylene per mole of combined vinyl acetate. Despite of reactants and products inside the autoclave plus an
the relatively low pressure used, this product was tough interval of time sufficient to sweep the reactor of 90% of
in film form and possessed the high melt flow tempera the initial copolymer formed under non-steady state con
ture of 150° C. ditions, the copolymer was continuously collected in the
Example 4-Same procedure as Example 2 with 15 ml. form of a latex containing 11.5% total solids. This latex
of "Alkanol' WXN (a sodium sulfonate of white oil) was coagulated with brine solution and the ethylene/vinyl
replacing the "Duponol' ME. In this case 64 gm. of acetate copolymer was washed with water and dried on
ethylene/vinyl acetate copolymer was obtained which 10 hot mill rolls. There was thus obtained a tough, color
contained 1.45 moles of combined ethylene per mole of less polymer which analyzed 2.46 moles of combined
combined vinyl acetate, which is /$ as much combined ethylene per mole of combined vinyl acetate.
ethylene per mole of combined vinyl acetate as Ex The following table demonstrates data obtained in the
ample 2. stirred autoclave by varying the polymerization tempera
Example 5-Same procedure as Example 2 with 10 ml. ture by proper choice of catalyst. The reaction is exo
5 thermic and the temperature was maintained constant by
of "Triton" N-100, a nonionic dispersing agent derived
from ethylene oxide and a substituted phenol, replacing introduction of the feed streams at room temperature
the "Duponol' ME. Yield equaled 14 gm. of ethyl and measuring the temperature achieved under steady
ene/vinyl acetate copolymer containing 1.28 moles of state conditions. It will be noted that not until the
combined ethylene per mole of combined vinyl acetate. polymerization temperature was lowered below 107 C.
Example 6.-The following materials were added to a 20 was high molecular product obtained on hydrolysis with
one liter stainless steel rocker tube at 0° C. under a an inherent viscosity greater than 0.70, which is required
stream of nitrogen: for orientability and hence adequate toughness properties.
220 ml. deoxygenated water--10gm. "Duponol" ME--20 This is thought to be due to the marked chain transfer
ml. deoxidized water containing 0.14 gm. 25 properties of vinyl acetate monomer as well as the vinyl
acetate polymer unit. Hence it is essential to work at
FeSO4.7H2O-0.23 gm. Na4P2O7.10H2O temperatures below 100° C. in order to achieve a high
60 ml. deoxidized tertiary butyl alcohol. molecular weight ethylene/vinyl acetate copolymer which
0.31 gm. 1-ascorbic acid in small unstoppered vial. will yield a tough, orientable ethylene/vinyl alcohol co
0.26 im. cyclohexanone peroxide in small unstoppered polymer on hydrolysis. Heretofore no effective catalyst
Wa. 30 systems were known which could be operated at low
50 ml. vinyl acetate. temperatures, at appreciable polymerization rates in a
The rocker tube was then evacuated and pressured to 400 continuous system when sufficient ethylene was present
atmospheres with ethylene. The rocker was then started to give products containing at least 50 mole percent
and the temperature brought to 30° C. and the pressure 35 ethylene. Hence the present invention permits the ready
to 1000 atmospheres for a two hour period. There was synthesis, under economic conditions, of high molecular
obtained 43 gm. of tough copolymer containing 14.2 weight ethylene/vinyl acetate copolymers and the corre
moles of combined ethylene per mole of combined vinyl sponding hydrolyzed high molecular weight, orientable
acetate, which demonstrates the marked effect that ter ethylene/vinyl alcohol copolymers for use as fibers, films,
tiary butyl alcohol has on the combining power of the molded articles, safety glass interlayers and like plastic
monomers. The use of other water soluble solvents such 40 outlets.
as acetone, methanol, ethanol, isopropyl alcohol and iso Table II
propyl acetate were not effective adjuvants since they
reduced the molecular weight of the copolymer. This Inherent
effect is shown in the following table. Eel 109Eyed
Yis:
Pressure Orient
Table I Temp. (°?o C.) (Atms.) Aggie E.g. ability
Ratio tate
Copolymer
M Ethylylene Egleef Yield
M. Tert-butyl alcohol. 1 Pressure Acetate 50 139 3: 900 3.6 0.25 None
Water Atins' ratio in (gm.) 129 (a)- 600 3.1 0.44 None
Copolymer 107 (b) 900 2.75 0, 62 Poor.
82 (c).--- 600 2.46 0.87 Excel
77 3 a a na a a we 900 2.50 0.94 Excel
None.... 280 1,000 i4.5 3.0 60 (c)---------------- 400 1,70 0.85 Exce
230 1,000 32, 4 27.0 55
280 600 9, 2 15,0
230 600 16.0 27.0 All runs carried out in gall, stainless steel autoclave under constant
environment conditions.
1 All runs carried out in a one liter stainless steel rocker tube at 30° C. (g) gatalyst system: potassium persulfate-no reducing agent.
with the common charge of 20 ml. vinyl acetate, 10 gm, "Duponol'ME, 8 Catalyst system: potassium persulfate-l-ascorbic acid.
c) Catalyst
0.26 g. cyclohexanone peroxide and 0.31 gm, sodium formaldehyde sulf. 60 sulfoxylate system: potassium persulfate-sodium formaldehyde
dihydrate.
oxylate dihydrate. 2 Determined as an 0.50 percent solution in meta cresol at 25 O.
Example 7-Into a one gallon stainless steel auto The heavy metal reducing agents, other than iron of
clave, equipped with a low speed anchor type agitator, the examples, used in conjunction with the free radical
were fed the following feed streams, at approximately
room temperature, at the pumping rates indicated: producing compounds, include the polyvalent heavy metal
65
ions and more especially the ions from the heavy metals
wasFeed streamwhich
pumped, 1-Sixteen pounds per
was composed of: hour of solutionof the third period of the "periodic system,' as arranged
6 parts by weight of the dispersing agent "Alkanol" WXN. in Hackh's "Chemical Dictionary” of 1937, page 695 and
including titanium, vanadium, chromium, manganese,
2 E. by Weight of monobasic potassium hydrogen phos 70 iron,
phate. cobalt, nickel, and copper and combinations thereof.
92 parts by weight of deoxygenated water. Silver is likewise suitable. Silver, while not a polyvalent
334 p. p. m. of potassium persulfate. metal, appears to act like one for it is an effective catalyst
for the reaction when used in the presence of an oxidizing
The pH of this feed stream was adjusted to 4.55 with agent. The preferred heavy metals are iron, silver,
phosphoric acid. 75 nickel and cobalt. The metal ion may be introduced in
Feed stream #2-8.2 pounds per hour of deoxygenated the lower state of oxidation or reduced in situ by a supple
ethylene and 8.8 pounds per hour of inhibitor-free de mentary reducing agent. During the course of the re
oxygenated vinyl acetate. action, the metal ion is oxidized and may be again re
Feed stream is.-206 ml. per hour of a solution of duced by the supplementary reducing agent. In general,
0.00628 gram of sodium formaldehyde sulfoxylate di 80 it is preferred to use the ferrous ions because iron com
hydrate per ml. of aqueous solution. pounds are cheap and readily available. As supple--
The autoclave temperature was adjusted to 82° C. and mentary reducing agents which may be used with, or in
the autoclave pressure adjusted to 900 atmospheres. place of, the heavy metal ions, one may use such com
After the autoclave was operated at the above mentioned 85 pounds as sulfinic acids, benzoin, 1-ascorbic acid, primary,
conditions of temperature and pressure for a two hour Secondary, tertiary and polyamines, sodium or zinc form
 2,70s,794
5 6
aldehyde sulfoxylate and alkanolamines, such as tri 0.05 and 1 part and preferably in amounts between 0.1
ethanolamine and like reducing compounds. and 0.5 part by weight per part of water, markedly in
Examples of suitable oxidizing agents include the per creases the combining power of the ethylene so that much
oxygen compounds for use in forming such active free lower ethylene pressures can be used to obtain a given
radicals, the salts of hydrogen peroxides, perborates, per ratio of combined ethylene to combined vinyl acetate in
carbonates, persulfates, perphosphates, percarboxylates; the copolymer. In general the most useful ratios have
organic hydroperoxides such as methylhydroperoxide, been found to be 1 to 30 moles of combined ethylene per
ethyl hydroperoxide, tertiary butyl hydroperoxide, tetra mole of combined vinyl acetate. In particular the 3/1
lin hydroperoxide, cumene hydroperoxide, cyclohexane mole ratio ethylene/vinyl acetate copolymer on hy
hydroperoxide, cyclohexanone peroxide, diacy peroxides, 10 drolysis yields a hydroxylated polymer possessing an out
such as benzoyl peroxide, acetyl peroxide, acetyl benzoyl standing combination of properties for molded article
peroxide, lauroyl peroxide, crotonyl peroxide, etc.; alkyl usage, such as extreme toughness, clarity and excellent
acyl peroxides such as tertiary butyl perbenzoate, diter outdoor durability properties. Similar properties are ob
tiary butyl perphthalate, tertiary butyl permaleic acid, tainde when other vinyl esters are used in place of vinyl
tertiary butyl perphthalic acid, hydrogen peroxide, per 5 acetate, such as vinyl formate, vinyl propionate and vinyl
acetic acid, perbenzoic acid, diisobutylene ozonide, methyl benzoate.
ethyl ketone peroxide, acetone methyl isobutyl ketone Likewise other polymerizable monomers can be added
peroxide, succinic acid peroxide, methyl isobutyl ketone as third components in minor amounts to the ethylene/
peroxide, polyperoxides, diethyl peroxydicarbonate, pel vinyl acetate systems disclosed herein, such as carbon
argonyl peroxide and like materials. Amounts used are 20 monoxide, maleic anhydride, allyl glycidyl ether, methyl
in the range of 0.005 to 3% by weight based on monomer. hydrogen maleate, maleimide, sulfur dioxide, vinyl chlo
The amount of heavy metalion added to the polymeri ride and acrylate and methacrylate esters.
zation mixture can be markedly lowered by the addition The copolymerization reaction may be carried out
of an organic reducing agent which possesses the ability to batchwise, semi-continuously or continuously. It is par
reduce the -icion to the -ous ion thus renewing the supply 25 ticularly well adapted for continuous polymerization in
of -ous ion when the -ous ion is oxidized to the -icion by either an autoclave or a tubular reactor. Agitation may
the peroxy compound. Under these conditions the be provided by the use of stirring devices in an autoclave,
amount of ferrous ion present, for example, is preferably by jet agitation or by shaking machines (in batchwise re
in the range of 0.1-1000 parts per million based on the actions) or by providing turbulent flow in tubular re
total amount of polymerizable monomer present. The 30 actors having a high ratio of length to cross-section.
heavy metal ion can also be obtained by introduction of Partial or complete hydrolysis of the ethylene/vinyl
a simple or complex salt or compound in which the metal acetate copolymers of this invention can be readily
is present in the -ic state provided that a suitable reducing achieved by methods common to the art, such as dis
agent is present to reduce the -ic to the -ous ion. Exam. closed in U. S. Patents 2,386,347 and 2,399,653. For
ples of Such reducing agents are manifold and include 35 example, the copolymer can be readily transferred from
Such compounds as l-ascorbic acid, d-ascorbic acid, sodi the latex to a water immiscible solvent, such as n-butyl
um formaldehyde sulfoxylate, dihydroxy maleic acid, alcohol, benzene, toluene or xylene, by dispersing the
formamidine sulfinic acid, butyraldehyde, sorbose, fruc latter in the latex and then breaking the emulsion, decant
tose and glucose. These reducing agents are generally ing the organic solution, drying to remove traces of water
used in ammounts of 0.005 to 3% based on the total 40 and carrying out an alcoholysis by addition of sodium
amount of monomers present, preferably 0.01 to 1%. methoxide and an alcohol such as methanol. The ethyl
The outstanding characteristic of the process herein ene/vinyl alcohol copolymer is then isolated by a steam
before described is that it produces copolymers of ethyl strike, the copolymer filtered off, washed, dried and com
ene and vinyl acetate of improved molecular structure by pacted by means of an extruder. Alternatively, the addi
an economical process, which copolymers can be hy 45 tion of excess alkali, such as sodium hydroxide and meth
drolyzed to high molecular weight ethylene/vinyl alcohol anol, to the ethylene/vinyl acetate latex gives a fine solids
copolymers for use in fibers, films and molded articles. dispersion which is readily saponified on heating to ethyl
Moreover, more latitude in the control of operating con ene/vinyl alcohol copolymer, which is filtered off, washed
ditions is permitted when the redox system is used, since well with water to remove sodium acetate, dried and com
varying ratios of ethylene can be readily introduced into pacted. Likewise ethylene/vinyl acetate copolymer in
the copolymer depending upon the choice of redox cata fiber or thin film form can be saponified by alkali in
lyst, emulsifying agent and amount of tertiary butyl alco methanol to give continuous fibers or films of ethylene/
hol used. The properties of the redox-produced ethyl vinyl alclohol copolymers.
ene/vinyl acetate copolymer latex are also of value alone I claim:
or in conjunction with other polymeric materials, waxes, 55 1. The process of claim 3 in which 0.1 to 1000 parts
pigments, dyes and like adjuvants for impregnating and per million of ferrous ion is present per part of water.
coating uses similar to synthetic rubber latices. In par 2. The process of claim 3 in which there is present from
ticular these latices on evaporation at room temperatures 0.5 to 10 parts of water per part by weight of ethylene
produce a continuous, flexible film of utility for decora 60
and vinyl acetate and from 0.001 to 0.10 part by weight
tive water paints, protective coatings, adhesives, and like of an emulsifying agent per part of water.
ISCS. 3. In a low temperature continuous process for the
The copolymerization is carried out in aqueous emul preparation of copolymers of ethylene and vinyl acetate
sions for in such systems the copolymers of ethylene and containing 1 to 30 moles of ethylene per mole of vinyl
vinyl acetate are produced in superior yields. The re acetate, the steps which comprise continuously introduc
action in such a system is carried out in the presence of ing into a reaction zone ethylene and vinyl acetate in a
from 0.5 to 10 parts of water and preferably in the pres ratio of 1 to 30 moles of ethylene per mole of vinyl ace
ence of from 1 to 5 parts by weight of water per part by tate, 0.5 to 10 parts of water per part by weight of ethyl
weight of ethylene and vinyl acetate present. In this ene and vinyl acetate, from 0.1 to 0.5 part by weight
reaction also there is employed from 0.001 to 0.10 part 70 of tertiary butyl alcohol per part by weight of water, an
of an emulsifying, wetting or dispersing agent per part emulsifying agent and a peroxygen compound acting con
of water present. jointly with a reducing agent capable of generating free
As emulsifying or dispersing agents such materials can radicals in situ, maintaining the reaction conditions in
be used as the potassium or sodium salts of long chain said Zone substantially constant at a temperature between
sulfates or sulfonates, ammonium salts of perfluorocar 5 30° C. and 90° C. and at a pressure between 50 and 1500
boxylates containing 7 to 11 carbon atoms, neutral agents atmospheres and continuously withdrawing the copolymer
such as the polyethylene oxide condensates, quaternary produced from the reaction zone.
ammonium salts, such as cetyl trimethyl ammonium 4. In a low temperature continuous process for the
bromide, as well as other emulsifying and dispersing preparation of copolymers of ethylene and vinyl acetate
agents common to the art. The pH may be varied within SO containing 1 to 30 moles of ethylene per mole of vinyl
wide limits depending upon the systems used although acetate, the steps which comprise continuously introduc
most systems yield the highest conversions when carried ing into a reaction zone ethylene and vinyl acetate in a
out at a pH between 4 and 10. ratio of 1 to 30 moles of ethylene per mole of vinyl ace
The use of the water soluble organic solvent, tertiary tate, 0.5 to 10 parts of water per part by weight of
butyl alcohol, which can be employed in amounts between 85 ethylene and vinyl acetate, from 0.1 to 0.5 part by weight
 2,708,794
7 8
of SE butyl
emulsifying agent,als
sodiumF;formaldehyde
E.it. SEsulfoxylate,
yer,an References Cited in the file of this patent
a peroxygen compound that provides a persulfate ion, UNITED STATES PATENTS
maintaining the reaction conditions in said zone substan- 2,380,473 Stewart ---------------- July 31, 1945
tially constant at a temperature between 30° C. and 90° 5 2,436,256 Hanford et al. ---------- Feb. 17, 1948
C. and at a pressure between 50 and 1500 atmospheres, FOREIGN PATENTS
and withdrawing continuously the copolymer from the
reaction Zone. 582,093 Great Britain ------------ Nov. 5, 1946