Note: Descriptions are shown in the official language in which they were submitted.
%5
This invention relat~s to a proce~ for the preparation o~
ethylene/vinyl acetate copolymers which have molecular weights o~
between 500 and 10,000.
Processes for the preparatlon of copolymers of ethylene
and vinyl acetate which have molecular weights o~ from 1,000 to
3 9 000 wherein the monomers are polym~rised at temperatures of
about 138 to 171C and pressures of 48 to 136 bars in a b~nzene
polymerisation medium and in the presence of radical polymerisa-
tion initiators have already been disclosed in DT-AS No. 1,147,79
and in U.S. Patent Speci~ications Nos. 3~093,623, 3,126,364,
3,131,168, 3,159~608, 3,254,063 and ~,627,838. These copolymers
are used as addîtives ~or hydrocarbon propellents or fuels which
have boiling ranges between about 120 and 400C to lower their
pour point and make them easier to filter~ The processes described
in the above mentioned Patent Speoification~ have ~umerous disad-
vantages. The copolymeri~ation mw3t be carried out at high tempe-
ratures 9 nam~ly above 100C~ and in the presence o~ a relatively
large quantity o~ polymerisation inlti~tor 9 namely 2 to 5 % by
weight, based on the amount o~ copolymer obtained in order to
obtain sufiiciently low molecular weights.
- The use o~ physiologically harm~ul benzene solvent as poly-
merisation medium requires the use of special protective devices
to remov~ the solvent vapours duri~g isolation o~ the copolymer.
Another disadYantage o~ the processes m~ntioned above is that
they can only be carried out in speclal apparatus and not in the
usual plants used for the manu~acture of high molecular weight
ethylene/vinyl acetate copolymers.
In the German O~fenlegungsschri~t No. 2,102,469 a process
for the preparation o~ low molecular weight ethylene¦vinyl ace-
tate copolymers by a high pressure polymerisation process in
Le A 15 880
~6g~
the presence of regulators which have transfer constant Cs grea-
ter than 10 2, determined ~or ethylena at 130C and 1360 bars,
and in the absence of solvents ha~ been disclosed. This process
requires a polymerisation plant in which polymerisation can be
carried out at pressures above 1000 bars or ther~abouts.
It has also been disclosed in the German Auslegeschrift No.
1,126,613 that high mo~ecular weight copolymers containing up to
~5 % by weight o~ vinyl esters can be obtained by the polymerisa-
tion o~ ethylene and vinyl acetate at presqures above~10 bars and
pre~erably at 100 to 200 bars in a liquid phase which consiæts
predominantly of tertiary butanol and may contain 0 to 20 % by
weight of water. The copolymers obtained by this process have mo-
lecular weights substantially above 10~000 and their ~iscosity
determined in p-xylene is substant:Lally above 0.5 dl/g.
A process has no~ been found ~or tha preparation of ethylene/
vinyl acetate copolymers having mo:Lecular weights of ~rom 500 to
10,000 and intrin~ic viscosities d~termlned in p-xylene at ~5C
o~ ~rom 0.1 to 0,5 dl/g, by polymerisation of ethylene and vinyl
acetate in molar ratios o~ between 20 : 1 and 1 : 1 in the pre-
sence of radical polymerisation initiators at temperatures of
from 10 to 200C, pre~erably 30 to 150C and at pressures of 10
to 700 bar, pre~erably 50 to 5Q0 bar, wherein the polymerisation
of ethylene and vinyl acetate is carried out in a reaction medium
consisting predominantly of tertiary butanol in the presence of
0,2 to 5 % by weight~ pre~erably 0.5 to 4 % by weight of acetalde
hyde, based on the quantity of the monomers.
Ethylene/vinyl acetate copolymers can be obtained having
any desired molecular weight between 500 and 10,000 by the inven-
tive process by the addition o~ relatively small quantities of
acetaldehyde. A considerable proportion o~ the added acetaldehyde
~ L~ 2 -
91Z~
is copolymerised during polymerisation so that the mixture o~ sol
vent and monomer recovered a~ter isolation of the polymer contalns
only small quantities of acetaldehyde. In contra3t to numerous
other kno~n molecular w~ight regulators which might also be used9
the acetaldehyde in the solvent~monomer mixture can, i~ necessary,
be removed to a large extent, for example by ~raotional distilla-
tion. The residual mixture thus obtained may be then used for the
` preparation of high molecular weigh-t ethylene/vinyl acetate co-
polymers.
It is surprising to find that acetaldeh~de is a suitable mo-
lecular weight regulator ~or the preparation of the copolymers
; according to the invention sincè it is known ~rom ~erman Auslege-
schrift No. 17745~570 (= British patent ~pecification No. 1,226,167)
that the addition of acetaldehyde to the copolymerisation of ethy-
lene and vinyl acetate results in cross-linked and there~ore in-
completely soluble productR~ Moreover9 it has been disclosed in
German Auslege~chri~t NoO 1,955,471 (= US-patent pecification No.
3,506,630) that acetaldehyde is unsuitabl~ ~or use as polymerisa-
tion regulator on account of its tendency to ~orm paraldehyde.
Additionally the u~e o~ tertiary butanol as preferred poly-
~; merisation medium, which has a v~ry ~eak regulating action, and
acetaldehyde, which is a power~ul regulator and easily removed,
;~ enables the production o~ ethylene/vinyl acetate copolymers with
very varying degrees o~ polymerisation in one and the same poly-
merisation plant while the residual monomer/solvent mixture con
tinuously obtained from i olatlon o~ the product can be retùrned
to the polymerisation proress.
Although vinyl acetate may be partly or completely rsplaced
by vinyl esters of other aliphatic or aromatic carboxylic acids
having 3 to 20 carbon atoms in the proce~s according to the in-
Le A 1~_~80 3 -
ii9~25
vention, e.g. vinyl propionate J vinyl butyrate, vinyl pivalate,
vinyl laurate or vinyl benzoate, vinyl acetate is preferably used.
The ratio of the copol~mers may vary within wide limits. If
a molar ratio of ethylene to vinyl ester of between 20 : 1 and 1 : 1
is used, for example, the quantity of vinyl acetate incorporated in
the ethylene/vinyl acetate copolymer is 13 to 75 % by weight.
The radical polymerisation initiators used may be a~o com-
pounds, e.g. bis-azo-butyric acid nitrile~ or organoperoxides or
hydroperoxides such as lauroyl peroxide, di-tert.-butylperoxide,
benzoyl peroxide or tert.-butylhydroperoxide. They are pre~erably
used in quantities of 0.1 to 1 % by weight, based on the quantity
o~ monomers used.
By carrying out the polymerisation in tertiary butanol as
the pre~erred polymerisation medium7 it is possible to use rela-
ti~ely low pressures of from 10 to 500 bars. The polymerisation
temperature employed is preferably betw~en 30 and 150C, accordlng
to the decomposition point o~ the polymerisation initiator usedO
The polymerisation proces~ may be carried out either discontinuous~
ly or continuously in several polymerisation autoclaves arranged
in series or in a tubular reactor. The quantity of acetaldehydeused QS regulator is adju~ted to the desired molecular weight. In
order to obtain molecular weights in the region of ~rom 500 to
10,000, for example, it ls ne~essary to use 0~2 to 5 % by weight,
preferably 0.5 to 4 % by weight of acetaldehyde, based on the
quantity of monomers used The molecular weight Mn is d~termined in
a Meckrolab apparatus (see HG. Elias~ Makromolekule, 2nd Edition,
1972, page 237), pre~erably by the vapour pressure osmometric
method of the polymer solution in toluene~
The low molecu~ar weight ethylene/vinyl acetate copolymers
prepared according to the lnventIon may be used as adhesives or
Le A 15 880 - 4 -
~t6g~25 `
adhesive components. Copolymers which contain ethylene and
vinyl ace~ate in molar ratios of from 10 : 1 to 5 : 1 and
which have molecular weights in the range of 500 to 300,
respectively intrinsic ~iscosities in the range of from
0.1 to 0.25 dl/g are added in amoun~s of from 0.01 to 0.5 %
~y~ weight to various mineral oil ractions, particularly
to the so-called middle distillates which have boiling points
of from 120 to 400C, to lower their pour point and/or im- ;
prove their ability to be filtered. To prepare these co- ^
polymers, 1 to 4 % by weight acetaldehyde, based on the
quantity of monomers used, is preferably added to the
monomers. Another wide field of application which is
available to these copolymers is their use as plasticizers ~;
~or various polymers, particularly for polymers which ha~e
a high chlorine content such as polyvinyl chloride, re-
; chlorinated polyethylene and chlorine rubber as well as
~ cellulose esters, polymethacrylic acid esters. The
; saponification products of these copolymers as well astheir reaction products with compounds which are capable
o~ reacting wlth hydroxyl groups, such as isocyanates,
acid anhydrides, acid chlorides, aldehydes~ ketones or
epoxides, ma~ also be used in various fields, for example
for the production of lacquers or adhesives and as plasti-
cizers.
9L~6~
A mixture of 8000 g o~ terti~ry butanol~ 2000 g of
vinyl ace$~te~ 200 g of acetal~ehyde and 40 g o~ bis-azo-
butyric acid nitrile is introduced into an autoclave which
has a capacity of 30 litres. The ~ir is expelled ~om the
autoclave by nitrogenj and 6000 g of ethylene are forced
in under pre~sure ~rom a steel cylinder. The autoclave
is then heated with stirring~ ~ir~t to 650C i~or 3 hours,
then to 70C for 3 hours and finally to 80C for 6 hours. The
pressure -~ir~t rises to 220 ba~ and then drop~ to 8~ bar~
during polymerisationO The autoclave contents are then
cooled to 20C and the pre~sure is released. 12300 g o~
a 34,7~ by weight solution oi th~e polymer are obtained.
The polymer is isolated by removal of the volatile
constituents under vacuum. 4300 g o~ a viscous ma~
which solidi~ied on cooling wa~ obtained. The ~u~nt~ty
of vinyl acetate lncorporated in the copolymer9 whlch wa~
determined by the saponification number~ 28.2~ by weighte
The intrin~ic vi~oosity (~) determined in p-xylene at
25G~ is iound to be 0~17 dl/g.j The molecular weight of
the product9 determined by vapour preæsure osmometry in
toluene, is 2580.
; Other low moIecular weight ethylene/vinyl acetate
copolymer~ having ~arying compo3ition~ and molecular weight~
are prepared with di~erent ~onomer r~tios ~nd di~ferent
additions of acetaldehyde by the proce~s described in
Example 1. The relatiYe dAta o~ these example~ are
given in the enclo~ed Table l. The intrinsic viscoslti,e6
and molecular weights ar~ determi~ed a~ indicated in
Example 1
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Le A 15 8~0 7_
- ~6~9
~a~
A mi~ture of 59.5 kg o~ tert.-but~nol, 26.8 ~g of vinyl
acetate, 0.475 kg oi acetaldehyde and 0.45 kg of bis-azo
isobutyronitrile is introduced into a pressure autoclave
which has a capacity o~ 190 1 and which i~ equipped for stirringO
The air in the autoclave i~ expelled by nitrogen. 32~8 kg
of ethylene are then ~orced into the autoclave under pressure
from steel cylinders~ The autoclave contents are heated to
650C for 3 hours, to 70C for 3 hours and to 80~ ~or 6 hours.
The pressure ri~es $rom 1~0 bars to 310 bar in the course o~
heating and drops to 40 bars in the course o~ polymerisation,
109.3 kg o~ a 45.4~ polymer ~olution were obtained. The
polymer mixture amounts to 83~ based on the qu~ntity of
; monomers put into the process~ The intrinsic viscosit~ `~
:l 15 is 0.38 dl/g and the molecular weight determined by vapour
. pressure osmometry is 7300,
; A mixture oi 1000 g of tert.-butanol~ 300 g oi vinyl
~cetate, 5 g oi acetaldehyde9 5 g of bis-~o isobutyronitrile
and 700 g of ethylene i~ pumped per hour from below upward~
into two 5 1 autoclave~ joined to iorm a ca~cade, which ~re
heated to 65~C ~nd ~O~C~ re~pectively. A~ter pa3 ing through
: the two autoclaves, the polymerisation mixture is periodically
relie~ed of pres~ure by an excess pressure valve which is
ad~u~ted to 20V bars, The average time oi stay o~ the poly-
merisation mi~ture in the autoclave i~ about 3 hours~ The
e~periment i~ stopped a~ter 60 hour~. The polymerisation
~olution obtai~ed in the period betwean the 50th ~nd 60th
hour has a ~olid co~tent oi 29.0% by weight. The volume/time
yield is about 400 g/l. The polymer ~reed ~rom volatile
constituents cont~ined 30.3% by weight o~ polymerised Yinyl
acetate and h~d an intrin~ic visco~ity (~) determined in
-8-
~L069~ZS; ~;
p-xylene as the solvent at 25C oî 0.172 dl/g~ The molecular
weight determined in toluene by v~pour pressure osmometry
is 2550,
:
~' ' ' . .
g_ ,
I
