Note: Descriptions are shown in the official language in which they were submitted.
59 6~ 0
The present invention relates to the polymeri~ation of
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vinyl halides, particularly vinyl chloride, and to a method and
: means for reducing the content of unreacted vinyl halide in the
polymer.
The polymerization of vinyl halides, such as vinyl
chloride, to form a homopolymer of the vinyl halide or a
copolymer thereof ~ith a copolymerizable monomer,such as a vinyl
ester, an ol~fin, etc., is well Icnown. TD prepare polymers that
are readily recoverable in particle form, as contrasted to latex
form, suspension, solution or bulk polymerization techniques
employing a catalyst or initiator are used. The polymerization
is effected under pressure and elevated temperatures, e.g.
120-140F., are developed. At the end of the reaction, the
pressure vessel used as the reactor is vented and the pressure
is rapidly lowered to sub-atmospheric pressure to recover `
unreacted vinyl halide, and then the slurry of polymer is
': ~ nl-ri f~ .or1 ~nr~ ~r; .o~ :
These techniques have been quite effective in the past,
` but as of Januar~ 1, 1975 very stringent Federal regulations will
impose very low levels o~ airborne vinyl chloride monomer that
are permissible. Polyvinylchloride (PVC) containing large amounts
o~ unreacted vinyl chloride i~ thus undesirable, since it ~ay ;
act to increase the airborne vinyl chloride content in areas
where the PVC is stored or processed, thus necessitating costly
measures to make those areas conf~rm to the Federal standards.
It is thus an object of this invention to provide a
methocl for reducing the content of unreacted vinyl halide monomer
in a polymer of a vinyl halide.
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Thls ob~ect ~ accomplished by th~ presen~ inventlon
by polymerizing the vinyl halide in the presence of an alkane D
and heating the polymer thus obtained to remove unr~acted vinyl -~
halide and copolymerizable monomer,
It has been found that the pre~ence of the alkane
during the polymerization allows removal of ~reater quantities
of unreacted vinyl h~lide and othe~ monomer. It is believed that
the alkane enters the oily phase containing the vinyl halide and
~hu~ is phy~ically trapped inside the vinyl halide polymer,
Removal of the alkane from ~he polymer also resul~ in stripping
additional amounts of unreacted vinyl halide therefr~m~ perhap~
due to an inereased porosity of the polymer ari~ing from ~he use
of the alkane.
Quite surprisingly, two further i~po~tant effect~
have been noted. Firs~, the polymer re~ulting from the stripping
has enhanced dry blending properties, i.e. it will blend more
rapidly with monomeric and polymeric plasticizers, pig~ents and
other additives in conventional dry blending equipment, such ~s
Banb.ury mix~rs, etc. In addition, it is posæible to carry the .
~0 polymerization ~o h~gher yields while still retaining the dry
blending properties. Thus; in prior art polymerizations of vinyl
halide~, the reac~ion is terminated shortly ~fter the pressure in
~he reactor ~tarts to drop, and a pre~ure drop of S psi is
conventionally employed to maximize the dry blendin~ properties
o~ the polymer. I larger pressure drops are used, the try
blending properties of the polymer ~re adversely affected. By
~he use of the alkane in the polymeriza~ion, prxssure drops a3
much as 40 p8i can be accepted whlle still obtaining a polymer
with good dry b~nding properties,
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The present invention i~ operable in any vinyl halidepolymerization technique that i8 employed to give recovery of
polymer a~ particulate solids, namely su~pension, solution or bulk
polymeri8ation~ In all of these teehniques, elevated pressure
and an initiator are employed. The ~details of these polymerization
techni~ues will not be set forth here~n as they are well known
and form no part of the present invention. Furthermore, the vinyl
halide may be polymer~zed alone to form a homopolymer, or may be
polymerized with up to 100% of a copolymerizable monomer, ba~ed
on the vinyl halide, containing an ethylenically unsaturated double
bond, e g. vinyl e~tar~, vinylidene halides, acry~onitrile, or
olefins.
U.S. Patent 3,324,097 d~scribes an emulsion polymer-
ization of ~inyl chloride to obtain vinyl chloride latices, and
propo~es the use of hydrocarbon~ of at least 8 carbon atoms to
prevent wet polymer build-up in the reaction vessel. In such a
process, the polymer is recovered as a latex, which is not
amenable to heating under reduced pre~sure for removal of
unreacted monomerO
The alkane is used in an amount s~fficient to reduce
the conten~ of unreacted vinyl halide monomer in the polymer,
e.g. rom 0.1 to 10% by ~eight, based on the weight of the ` :
vinyl halide an~ copolymerizable monomer, preferably from 0.5 to
3% by weight. Since the alkane i8 ~tripped off after ~he
polymerization, there is actually no upper limit on the amount
to be employed, except that quite large amounts, e.g. more than
15%, may give ri~e to odors in the resin. Since there is no
point in using more of the alkane than i8 necessary, eeonomics
will dictate the use of smaller amounts where possible. : :
The alkane is pr~ferably added along with the reactants
charged ~o ~he pol~merization vessel. If desired, however, the
alkane may be added in a manner known per ~ during the cour~e
of the polymerizationO
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Suitable alkanes for u~e in the invention are straight,
branched chain or cyclic alkane~, and ~he term "~lkane" as used
herein and in the appended claims includes straight, branched and
cyelic ~tructures. Any alkane may be u~ed, prefer~bly those that
can be removed from the polymer at the stripping conditions,
such as alkanes of 1 to 20 carbon a~oms, preferably 1 to 15 carbon
atoms, and most preferably 5 to 10 carbon atoms. While straight,
branched or cyclic alkanes may be employed, it i~ presently pre-
ferred to use normal or secondary alkanes, such as n~pentane~
i-hexane, n-heptane and ~-octane.
The alkane is removed from the polymer at the end of
~he reaction by heating the polymer containing the alkane and
unreacted monomer at a tempe~a ture of at least about 160F. at
reduced pre~sure for a suitable period of time to ensure maximum
removal of the alkane and unreacted monomer from the slurry
obtained from the polymerization, e.g. 15 to 180 minutes. Here
again, economic~ will dictate the ultimate selection of operating
parameters.
For example, the polymer is usually at an elevated
temperature a~ the end of the reaction~ say abou~ 110 to about
155F., and hence a s~ripping temperature of at least about 160~F~
will be used. Temperatures closely approaching 230F. tend to
adversely affect the dry blending proper~ies of the polymer and
would not normally be employed. However, if the advantages of
using temperatures higher than 230F. were justified from the
overall economics, then such temperatures could be used. Normally,
ho~ever,a ~ripping temperature of at least about 160~.
preferably ~o provide an increase in temperature of at least about
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15 F., such as about 160F. to abou~ 200~F., e.g. 160F. to
180F., may be employed to advantage.
Generally~ the efficienc:y of the stripping is an r
inverse function o the pressure, and hence it ls preferred to
u6e reduced pressure. Here again,, the degree of vacuum used
depends on a trade~off of increa~ed ~tripping efficiency versus
the cost of vacuum equipment. A suitable range of pressure is
from about 50 to about 200 ~n Hg, and most preferably 75 to
150 mm Hg.
After s~cripping the alkane and unreacted vinyl halide
from the slurry, ~he pressure is brough~ back to atmo~pheric and
the slurry i~ centrifuged to remove water from ~he slurry9 and
then the polymer is dried in a conventional mannerg e.g. at a
tempera~ure of 125F. to 350F. and atmo3pher~c pre~ure.
In ~he most preferred embodiment of the invention, the
reaction maS8 obtained from the polymerlzation i~ sub~ected to
reduced pre~sure to recover unreacted vinyl h~lide monome~ and to
remove ~ater vapor (where present) and then the p~lymer i~ heated
~o a temperature of at least about 160F.~ preferably about 160
to about 200F., at a pre~sure o~ from 50 to 200 mm Hg, for s~ch
time as ~o effect significant removal of unreacted vinyL halide
from the polymer, such a~ from about 15 minutes to 180 minute~.
After the stripping, the pre~ure i~ brought back to a~mospher~c
and the polymer i8 sent to c~ntrifugation and dryin~.
The present invention finds particular utility in a
~uspension polymerization, since this is normally used to
prepare re~in~ that are suitable for dry blending. A150, su~pen-
~ion polymerization accounts for the large~t p~sduction of vinyl
res~ns. In a ~uepen~ion polym~rization, a pres~ure vessel 1~
charged with w~ter and the monomer or monomer mixture, c~talyst,
protective colloid and other ingredlents are added to the water
and the polymerization reaction is allowed to proceed ~t the
desired tempera~u~e9 with cooling if necessary to main~ain the
temperature. The degree of completion i~ determined by the amount
of pre~ure drop béfore the reaction i~ terminated, as described
above.
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Charged to the reactor is a mixture generally comprising:
Parts
Vinyl halide and copolymerizable monomer 100
Water 100-400
Dispersing agent (protective colloid) 0.03-0.3
Catalyst 0.01-0.15
Other recipes may be used, as described in the art. Suitable
dispersing agents include the water soluble pro~ective colloids
such as gelatin~ partially or completely hydrolyzed polyvinyl
acetate, polyalkylene oxides such as polyethylene oxide9 methyl
cellulose or hydroxyethyl cellulose. Suitable catalysts include
diacyl peroxides such as iauroyl and benzoyl peroxide; peroxy-
dicarbonates such as diisopropyl peroxydicarbonate; acyl cyclo-
alkyl sulphonyl peroxides such as acetyl cyclohexyl sulphonyl
peroxide; and azo compounds such as a,a'-azodiisobutyronitrile.
. . .
A~ter the reaction has proceeded to the desired degree,
the reactor is vented to remove water vapor and unreacted vinyl
halide and other monomer, and the pressure is reduced to the
desired degree of vacuum. To heat the polymer, a
heated jacket or introduc~ion of steam into the reactor or any
other sui~able heating may be used. When the stripping of the
alkane and unreacted monomer is completed, the vessel is brought ~ ;
back to atmospheric pressure and the stripped slurry is sent ~o 'r
drying storage, blendin~, etc. just as in the case o~ convention~l
vinyl polymers.
The Examples that ~ollow also illustrate the invention
in terms o~ a suspension polymerization, bu~ the scope o~ ~he
invention is not to be limited thereto.
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In the specification and appended claims, all parts
and proportions referred to are by weight, unless othe~ise
noted. Further3 the percentage of alkane in Examples I V is
based on the weight of vinyl halide and copolymerizable monomer~ -
and the vinyl chloride content in ppm is based on dry solids.
Example I
Several production runs in a commercial PVC reactor
were made by charging to the reactor for each run the following
mixture:
Demineralized water 1100 gallons
Vinyl chloride 760 gallons
IPP * 1 pound `~
* Methocel 60 HG 50 * 3.5 pounds
Sodium bicarbonate (buffer) 1.0 pound
* IPP is diisopropvl peroxy dicarbonate
* Methocel 60 ~G $0 is a me~hyl cellulose derivative manufactured
by Dow Chemical Company
These runs served as controls. Additional runs were made using
the same mixture but including 57.5 pounds of Soltrol 10, a
mixture of 90-95~/O isooctanes and the remainder other isoparaf~ins.
Tne runs were carried out by heating the reaction mass to 131F,
and the pressure rose to about 115 psig. After 8-9 hiours, the
pressure fell to l:L0 psig. and the reaction was terminated by
venting the reac~or. After ventin~, the pressure was reduced to
-10 inches Hg and s~eam was admitted to the reactor to heat the
polymer mass to 180F. During steam addition, the vacuum was
increased to -25 inches Hg, and the polymer mass held at
175-180F. at this pressure for 30 minutes, a~ter ~hich time the
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vacuum was broken and the slurry ~ent to centrifuga~cion and
drying. Samples of the wet cake atld fully dried resin for each
run were obtained for each run, and the resul~ are rsported in
Table I below. The results are re~ported as an av~rage of several
runs o each ~ype.
Table I_
Control I v_ntion
Isooctane (70 of vinyl chloride) O
Stripping Temp, (F~) 180 180
Stripping Pressure (in. Hg)-25 -25
St~ipping Time (rnin.) 30 30
Vinyl Chloride (ppm)
wet cake 224 28
dry cake 50 2 . 7
DOP dry-up time (min . )4 . 0 3 .1
TOTM dry-up time (lliin.) 706 4.1
The DOP and T~TM dryoup tlmes are a measure of the dry blend~ng .
propertie~ of the polymer and are dete~ined as iEollow~. In
both tests~ a charge compri~ing the resin, stabili~er and filler
i~ mixed in a sigma head miKer of 650 ml eapaei~y t 87Co + 0.1C.
for 5 minutes, after which ~ime dioctylphthalate (DOP) or
trioctyl-tr~mellltate (TOlM~ is added over a period of 1 minute.
The mixer is conr;ected ~o a Brsbender pla~tico~der and ~he
transition point ~om a werc lumpy mixture to a dry-free flowing
mixture i3 read from the plasticord~r chart. The DOP or T~TM
dry-up time is r~ported a~ the time in minutes from the addition
of the DOP or TOT~I to the tran~itlon point.
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The charge used for the DOP dry-up time i~
210 gr~m~ resin
21 grams basic whiLte lead carbonate
15 grams No. 33
109 ~rams DOP,
The charge :for the TOTM dry-up time is:
200 gramæ re~in
8 gram~ epoxidized soybean oil
18 grams diba~ic lead ph~halate
1 gram~risto wax 165
20 gram~ clay No. 33
96 gram~ TOl'M
A~ can be seen from Example I, there is a remarkable
reduction in t&e ~mount of unreacted vinyl ch1oride when the
alkane is u~ed, a~ well a~ an in~prov~ment in dry~blending
propertie~. Sa[~ple~ of the con'cro1 and lnveneion run were
pl~ced in gla8~ stoppered Erlenmeyer 1a~k~ and heated at
65C. for one hour. On opening the flasks9 no odor was
de~ected.
Ei~h~ceen tho~sand po~md~ of the polymer prepared using
the alkane were dry-blended with a commercial blend of pigmenk~,
etc. using production techn~ques, and a commerc~ally acc~ptable
dry blend wa3 pr~pared,
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E~LE I~
Following the pro~edure of E~c~mple I, ~ix addi~lonal
runs were made, Runs 1 and 2 emp~oying no isooctane and hen~
being con~rol run~" and Runs 3-6 using 1% i!~ooctane and hence
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illustrating the invention. Runs 1 through 3 employed a 5 psi
pressure dropg which is the pressurle drop most commonly used in
the production o~ dry blending vinyl chloride homopolymers.
Runs 4, 5 and 6 employed pressure drops of 10, 15 and 20 psi,
respectively, and thus resulted in subs~antially greater yield
of polymer. The polymer obtained fxom the six runs ~as analyze~
~or unreacted ~inyl chloride in the wet calce and the dry blending
properties. The results are reported in Table II below.
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- Table II
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Run 1 2 3 4 5 6
Pressure Drop - `
(psi) 5 5 5 10 15 20
Vacuum Strip
Temp. (F.) 180 180 180 180 180 180
Vacuum Strip
Time (min.) 30 30 30 30 30 30
Iso-octane (%) 0 0
Vinyl chloride
(ppm)
~et cake 245 289 37 164 75 232
DOP dry-up time 1 1 2 2 2 2
(min.) 3.7 4.0 2.3 2.6 2.5 2.7
TOTM dry-up
time (min.) - 6.7 4.2 5.8 5.5 4.5
1 - Standard _ 3.3 min.
2 - S~-ndard 2.6 min.
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It can be seen ~rom the data in Table II that the strlp~
ping tempera~u~e D~ 180 ad~ersely a~fected the dry blending
properties of Runs 1 and 2, which represented the control runs,
since these runs had a longer DOP dry-up time than the standard
of 3.3 minu~es established for the polymer made under the ambient
conditions of that day. All of Runs 3 through 6 resulted in PVC
that had substantially better dry blending properties than the
standard used for the specific conditions of runs being made in
the period of Runs 3 through 6. This is true even for Runs 4 ;
through 6, which carried the reaction toward the higher yields
represented by the large pressure drops. This is contrary to
expectations, since normally the combination of higher drying
temperatures and higher yie7d is accompanied by a loss of dry
blending proper~ies.
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Exam~le III -
Following the procedure of Example I, a vinyl chloride
vinyl acetate copolymer was prepared from the mixture below, using
a polymerization temperature of 150F. and a vent pressure of '-
~0 psig:
Vinyl chloride91 pounds
Vinyl acetate 9 pounds
IPP 4.5 grams
~auroyl peroxide68 grams
Gelatin (100 Bloom)159 grams
Sodium bicarbonate23 grams
~~-c~'u;ueL-,la,le272 grams
Water 160 pounds
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Three runs w~re made. In Runs 1 and 2 the above mixture
~as used, and irl Run 3 the mixture included l7~, of isoostane.
After the reac~ors were ventedJ the polymer mass wa~ kept a~c the
polymerization temperature in the case of Run l~ or heated to
1~5F. in the ca3e of Run6 2 and 3, to ~rip 8a~e$ and unreac~ed
vinyl chloride and vinyl acetate ~rom the polymer. A ~trip ~ime
of 120 minutes wa~ used for all t~ree run~ ~t a pressure of
-25 inehes ~18. The unreacted vin~l chloride ~a~ me~ured in ~he
wet cake and dry eake as de~eribed above, and the re~ults are
10 reported in ~able III belowO
T~ble III
Run~ 2 3
Isooct~ne (~/0) 0 0
Stripping Temp. (F~ 150 165 165
Stripp1ng Pre~s, (inO Hg) -25 -25 -25
Stripping Time (min. ) 120 120 1 20
Vinyl Chloride (ppm)
wet ealce 4204 1284 376
dry cake 330û 1~35 240
Following the procedure of ~xample I~ three b~tche~
of PVC w~re prepared at a polymerization temperature of 145 and
a vent pr~ssure of 120 p~ig. Run l was a con~rol, and Runs 2 and
3 employed 1% n-hep~cane. The unreae'ced vinyl chloride content in
the wet and dry c~ke were determined, and the resu1ts are repor~ed
in Table IV belo~7.
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Table IV
.
Run 1 2 3
- n-heptane (%) O
Stripping Temp. (F.) 145 145 170
S~ripping Press. (in. Hg) -25 -25 -25
Stripping Time (min.) 60 60 60
Vinyl Chloride (ppm) `
wet cake 13816 2651 486
dry cake 7496 946 322
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ExamPle V
Following the procedure of Example 1, two batches of
vinyl chloride homopolymer were prepared using a polymerization
temperature of 131F. and a pressure drop of 30 p5i. Run 1
contained no alkane and Run 2 contained 1% o~ iso-hexane. At
the end of the reaction, the polymer was heated to a tempera~ure
of 160F. pressure of -25 inches Hg for 60 minutes. The
unreacted vinyl chloride content was determined in the wet and
dry cake and the DOP dry-up time was also determined for both
runs. The results are reported in TabLe ~ o^low.
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Table V
Run , 1 2
Iso-hexane ~%) O
Stripping Temp. (F) 160 160
Stripping Press. (in. Hg) -25 -25
Stripping Time (min.) 60 60
Vinyl Chloride (ppm)
wet cake 1350 340
dry cake - 2~4 60
DOP dry-up time (min.) 5.8 4.5
, ~
As can be seen ~rom the above Examples, the use o~
the alkane in reducing the content of unreacted vinyl chloride in
the polymer is not limited to vinyl halide polymers employed for
dry blending only. Thus, the present invention is applicable
to the production o~ vinyl halide homopolymers and copolymers
that are I-ormed into thick sheets or thin ~ilms, that are
injection molded or compression molded or eætruded into articles
of desired shape9 and to such homopolymers and copolymers that
are blended with the usual range of additives by dry blending or
by any other technique. While the use o~ the alkane does
improve the dry blending properties of such resins ~hat are
ultimately dry blended, there is a significant reduction of
unreacted vinyl halide in the vinyl halide homopolymers and
copolymers, xegardless o~ whethex or not such polymers are used
f~r dry bJ~ending.
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