RUPTEURS DE CHAINE POUR LA POLYMERISATION DU CHLORURE DE VINYLE

CHAIN TERMINATORS FOR POLYVINYL CHLORIDE POLYMERIZATION

Abrégé anglais

CHAIN TERMINATORS FOR POLYVINYL CHLORIDE POLYMERIZATION
Abstract of the Disclosure
An improved process for terminating the suspension polymerization
reaction of vinyl chloride monomer into polyvinyl chloride which
comprises adding hindered phenols of the structure presented
hereinafter to the polymerization reaction at a point in time when
a predetermined amount of monomer conversion has occured.

Revendications

- 15 -
WHAT IS CLAIMED IS:
1. In the process for the suspension polymerization of vinyl chloride
monomer which comprises adding the monomer to an aqueous reaction
system containing effective amounts of a suspending agent and a
polymerization initiator, terminating the polymerization reaction
and isolating the polyvinyl chloride, the improvement which
comprises terminating the polymerization reaction by the addition
to the reaction system at a point within the range of 0 to 95 %
monomer conversion of 25-5000 ppm by weight of the vinyl chloride
monomer, of a compound corresponding to the formulae
(I) RX-(CaH2a)-Q
wherein R is
< IMG >
X is oxygen or sulfur,
a is an integer from 6 to 30,
x is an integer from 0 to 6,
R1 is alkyl from 1 to 8 carbon atoms,
Q is hydrogen or -A-(CyH2y)-R2,
A is oxygen, sulfur, ? or<IMG>
y is an integer from 0 to 20,
B is alkyl of from 1 to 6 carbon atoms or alkanoyl of from 1 to
6 carbon atoms,
R2 is hydrogen, hydroxy, alkanoyloxy of from 1 to 6 carbon atoms or

- 16 -
<IMG> , and
R3, R4, R5 and R6 independently are alkyl from 1 to 8 carbon atoms;
(II) RX--[(CbH2b)--Y]d-7
wherein
R and X are as previously defined,
b is an integer from 2 to 6
d is an integer from 3 to 40
Y is oxygen or sulfur, and
R7 is hydrogen, alkyl of from 1 to 6 carbon atoms or
<IMG>
with R5, R6 and x being as previously defined;
(III) 1,1,3-tris-(2-methyl-4-hydroxy-5-tert.-butylphenyl)-butane
or
(IV) 1,3,5-tris-(2,6-dimethyl-3-hydroxy-4-tert.-butylbenzyl)-
isocyanurate.

- 17 -
2. The process of claim l, wherein said compound corresponds to
formula I and wherein X is oxygen, x is 0 to 2, R1 is alkyl of
from 1 to 4 carbon atoms, A is oxygen, y is 0 to 2, R2 is hydrogen or
<IMG>
and R5 and R6 are alkyl of from 1 to 4 carbon atoms.
3. The process of claim 2, wherein R1 and R6 are tert.-butyl
positioned in the ortho-position, R5 is methyl and x is 2.
4. The process of claim 3, wherein said compound is octadecyl
3-(3-tert.-butyl-4-hydroxy-5-methylphenyl)-propionate.
5. The process of claim 3, wherein said compound is 1,6-hexane diol
bis-3-(3-tert.-butyl-4-hydroxy-5-methylphenyl)-propionate.
6. The process of claim l, wherein said compound corresponds to
formula II and wherein X and Y are oxygen, x is 0 to 2, R1 is
alkyl from 1 to 4 carbon atoms, b is 2, d is 3 to 20, R7 is
<IMG>
and R5 and R6 are alkyl of from 1 to 4 carbon atoms.
7. The process of claims 6, wherein R1 and R6 are tert.-butyl
positioned in the ortho-position and R5 is methyl.

- 18 -
8. The process of claim 7, wherein said compound is triethylene
glycol bis-3-(3-tert.-butyl-4-hydroxy-5-methylphenyl)-propionate.
9. The process of claim 1, wherein said compound corresponds to
1,1,3-tris-(2-methyl-4-hydroxy-5-tert.butyl-phenyl)-butane.
10. The process of claim 1, wherein said compound corresponds to
1,3,5-tris-(2,6-dimethyl-3-hydroxy-4-tert.-butylbenzyl)-isocyanurate.
11. The process of claim 1, wherein said addition occurs within
the range of 70 - 90 % monomer conversion.
12. The process of claim 11, wherein said addition occurs at about
70 % monomer conversion.
13. The process of claim 12, wherein 50 - 1000 ppm of said
compound are added to the reaction system.
14. The process of claim 13, wherein 50 - 500 ppm of said
compound are added to the reaction system.
15. The process of claim 1, wherein 100 - 250 ppm of triethylene
glycol bis-3-(3-tert.-butyl-4-hydroxy-5-methylphenyl)-propionate
are added to the reaction system at about 70 % monomer conversion.

Description

3~
-- 2 --
The basic process of vinyl polymerization involves the addition of a
vinyl monomer to a growing polymer chain. The polymerization is
conducted at the proper temperature under pressure in the presence
of an initiator. The polymer chain continues to grow in length until
it is terminated by some means.
With regard to vinyl chloride polymerization, the overwhelming
amount of polyvinyl chloride is prepared by suspension polymerization.
In this process, the vinyl chloride monomer and an initiator are
dispersed by agitation into a water phase at proper temperature and
pressure. Suspending agents such as methyl or ethyl cellulose,
gelatin, polyvinyl alcohol or other water-soluble polymers are
utilized to stabilize the suspension during the polymerization
reaction. The fine granules of polymer in the form of a slurry are
discharged from the reactor and centrifuged or filtered to
remove the water. Thorough washing and drying of the polymer to
remove traces of the suspension stabilizer and the reaction medium
conclude the procedure.
Toward the end of the polymerization cycle the pressure in the
system begins to drop, followed very shortly by a peak in the
polymerization rate. Beyond the peak, the rate begins to drop
sharply and the polymer beads become less porous as the free
monomer is absorbed into the polymer. Such change in the
particle character, both in terms of porosity and particle size
distribution, is disadvantageous to the manufacturer in terms of
reduced performance and economy of production. Thus the crenulated
porous surface is desired for enhanced plasticizer uptake to form
dry blends for various extnlding or calendaring operations. In order
to avoid such adverse effects, the manufacturer will terminate the
polymerization reaction prior to complete monomer conversion. The

:~2~
- 3
experience of the manufacturer will best determine the point at
which polymerization is terminated to give high quality polymer,
although 70 to 90% conversion reflects a general termination point.
Various techniques have been adopted for terminating polymerization.
A purely mechanical approach has involved discharging the polymer
slurry into an evacuated stripper tank and quickly reducing the
temperature and pressure to effectively stop polymerization.
Various chemical approaches have also been adopted. The numerous
conventional chemical means for terminating vinyl polymerization re-
actions are detailed in chemical texts and publications. More recent
approaches have involved adding terminating agents or chain
terminators to halt free radical propagation, removing unreactecl
monomer and processing the converted slurry to obtain the dry poly-
vinyl chloride. Thus, compounds such as methyl styrene, bisphenol A
and various hindered phenol antioxidants have been added to the
reactant mix at a pre-determined point for purposes of chain ter-
mination. Among these compounds, 2,6-di-tert-butyl-4-methylphenol,
i.e. BHT, has been most frequently utilized as a chain terminator by
addition to the polymerization system at the desired termination
point. Various other hindered phenols having tertiary butyl sub-
stituents in the 2- and 6-positions on the benzene ring have also
been used for this purpose. The performance results have, however,
been less than desirable with these hindered phenols, these
materials having little effect when added in concentrations up to
about 250 ppm. BHT has also exhibited this limitation in being unable
to provide effective chain termination at the lower, more desirable
concentration ranges.
A further PVC chain termination composition based on hindered
phenols is disclosed in U.S. 4,229,598. This composition is pre-
pared by the alkylation of a fractionation cut from the product of

3~
vapvr phase methylation of phenol. The fraction that is alkylated
is a specific mixture of cresylic acids resulting in a corresponding
mixture of simple methyl-t-butyl phenols. These mixtures are
necessarily prepared, however, by rather complex and demanding
procedures.
It is thereEore the primary object oE this invention to modify
vinyl chloride suspension polymerization reactions so as to increase
the efficiency of the chain termination step.
It is another object to define a class of additives which when
added to the polymerization system provides the above noted increased
effectiveness.
It is still another object to define the parameters of this improved
polymerization procedure.
Various other objects and advantages of this invention will be
readily apparent from the following detailed description thereof.
It has been surprisingly found that effectiveness of chain termina-
tion in vinyl chloride suspension polymerizations can be signifi-
cantly increased by the addition of a class of hindered phenols
having a methyl group on or associated with the phenyl ring, and
preferably in the ortho or meta-position on the ring, to the poly-
merization reaction system at a point in time when a designated
amount of monomer has been converted. Thus, the presence of the
methyl group, preferably as a substitute for one of the tertiary
butyl groups generally shielding the phenolic group in the prior art
materials, results in an immediate termination of the polymerization
reaction. In this manner, rapid chain termination is effected
thereby facilitating the porduction of high quality polyvinyl

-- 5 --
chloride in high yields. Tlese results are achieved without any
significant modification of the suspension polymerization reaction
and without any concurrent adverse effects. These chain terminators
perform substantially better than the prior art materials in
providing rapid and total chain termination and in providing these
improved performance characteristics at significantly reduced
concentration levels. Since these phenolic materials are recognized
antioxidants and heat stabilizers for polymeric systems, their
addition to the polymerization reaction effectively stops free
radical propagation while correspondingly providing high levels of
stability to the resulting polyvinyl chloride. In addition, approxi-
mately 90-95% of the chain stopper remains in the resin after
stripping and/or drying, thereby effectively eliminating contamina-
tion of the recovered monomer. In contrast, lower molecular weight
materials such as BHT can be expected to come off with the excess
monomer in the gaseous stream so as to contaminate the monomer
and therefore inhibit any polymerization reaction wherein the re-
cycled monomer is utilized.
The chain terminators applicable for use in the process of this
invention correspond to the formulae
(I) RX~(CaH2a)~Q
wherein R is
3\
\ / x 2x
is oxygen or sulfur,
a is an integer from 6 to 30,
x is an integer from O to 6,

~Z2~3~
Rl is alkyl of from l to 8 carbon atoms,
Q is hydrogen or -A-(C H2 )-R2~
A is oxygen, sulfur, -N- or -C-
y is an integer from 0 to 20,
B is alkyl of from 1 to 6 carbon atoms or alkanoyl of from 1 to 6
carbon atoms,
R2 is hydrogen, hydroxy, alkanoyloxy of from l to 6 carbon atoms or
5\ 0
H0- (C H )-C- , and
R3, R4, R5 and R6 independently are alkyl from 1 to 8 carbon atoms;
(II) RX [(CbH2b) Y~d-- 7
wherein R and X are as previously defined,
b is an integer from 2 to 6,
d is an integer from 3 to 40,
Y is oxygen or sulfur, and
R7 is hydrogen, alkyl of from 1 to 6 carbon atoms or
5\
0--\ / (CxH2x
R6
: with R5, R6 and x being as previously defined;
(III) 1,1,3-~ris-(2-methyl-4-hydroxy-5-tert.-butylphenyll)-butane
; or
(IV) 1,3,5-tris-(2,6-dimethyl-3-hydroxy-4-tert.-butylbeenzyl)-
isocyanurate.
!

3~3~
-- 7 --
Compounds of formula I which are preferred exhibit X as oxygen,
x as 0 tc- 2, Rl as alkyl of from 1 to 4 carbon atoms, A as oxygen,
y as 0 to 2, R2 as hydrogen or the indicated phenol and R5 and R6
as alkyl of frc,m 1 to 4 carbon atoms. Particularly preferred are
those compounds wherein Rl and R6 are tert.-butyl positioned in the
ortho-position, R5 is methyl and x is 2.
Specific compounds of preference are octadecyl 3-(3-tert.-butyl-4-
hydroxy-5-methylphenyl)-propionate and 1,6-hexanediol bis-3-~3-tert.-
butyl-4-hydroxy-5-methylphenyl)-propionate.
Compounds of formula II which are preferred exhibit X and Y as
oxygen, x as 0 to 2, Rl as al~yl of from 1 to 4 carbon atoms, b as
2, d as 3 to 20, R7 as the indicated phenol and R5 and R6 as alkyl
of from 1 to 4 carbon atoms Particularly preferred are those com-
pounds wherein Rl and R6 are tert.-butyl positioned in the ortho-
position and R5 is methyl. A specific compound of preference is
triethylene glycol bis-3-(3-tert.-butyl-4-hydroxy-5-methylphenyl)-
prop;onate.
,,

~2639~3
-- 8 --
~lethods for preparing tllese hindered phenols are well known to
those skilled in the art. Specific reference is made to U.S.
Patents 3,2851855, 3,944~594 and 4,032,562 for information re-
garding the phenols of formulae I and II and their methods of
preparation. In general, they are prepared,from the appropriate
acids, acid chlorides or lower alkyl esters and alcohols or thio
alcohols utilizing well-l;nown esterification or transesterification
methods.
As previously noted, these hindered phenols are known for their
antioxidant activity in a variety of polymeric substances including
polyvinyl chloride. When added to such polymers for purposes of this
area of utility, they are generally added to the final polymeric
product.
~Tinyl chloride suspension polymerization techniques are likewise
well-knonw to those skilled in the art. Such techniques are
described in detail in most basic polymer chemistry texts such,
for example, as W. Sorenson, "Preparative Methods of Polymer
Chemistry", Second Ed., Interscience Publishers, N.~. (196S). In
general, the reactor is charged with the appropriate amounts of
suspending agent, initiator and emulsifier in the aqueous reaction
system. Typical suspending agents include methyl or ethyl cellulose,
gelatin, polyvinyl alcohol or other water soluble polymers, while
typical initiators include peroxydicarbonate, benzoyl peroxide,
lauroyl peroxide, t-butylperbenzoate, acetyl peroxide, cumene
hydroperoxide, di-t-butyl peroxide, and the like. The emulsifier is
generally added to enhance the porosity of the polymer particles.
'
I'.' ,',~

9~3
This charge is generally added to the reactor at ambient temperature.
The vinyL chloride monomer is then introduced, agitation is ini-
tiated and the reactor is heated to the polymerization range of from
45 to 60C. The pressure will be in the range of from about 140-150
psi for the 5-7 hour reaction period necessary to achieve about
70% monomer conversion, with the residual monomer being recovered
for possible future use. Filtration washing ancl drying complete
the polymerization procedure.
In addition to the chemical structure of the instant chain
terminators, effective termination is dependent upon the amount of
compound added. or purposes of this invention, 25-5000 ppm of
hindered phenol, based on the weight of the vinyl chloride monomef9
added at the time of 0 to 95% monomer conversion will provide the
desired benefits. Preferred values are 50-1000 ppm of hindered
phenol added at 70 to 90% monomer conversion, while particularly
preferred concentrations are 50-500 ppm of hindered phenol.
It is to be noted that the latter 70-90% range is the desired range
for obtaining commercially acceptable yields of polymer. Howevera
the instant hindered phenols will terminate the polymerization
reaction at any stage thereof. Accordingly, the 0-95% range reflects
the possibility of premature termination where emergency conditions,
power outages, and the like, demand such early termination.
The rate of polymerization can be designated in terms of the time
to the designated amount of conversion of the polymerization reaction
and/or the amount of pressure drop after conversion, the latter
being especially indicative of termination capability. In this
context, "conversion" is designated as the point during polymeri-
zation when vinyl chloride monomer is no longer available as a free
monomer and is absorbed into the polymer.

-- 10 --
The compounds designated herein are secn to provide immediate
termination of vinyl chloride polymerization reactions. This
irnmdediate termination alloys for the production of high yields
of high quality polyvinyl chloride. These compounds are also seen
to provide such rapid termination at concentration levels
substantially below that required for currently utilized materials.
The compounds imultaneously provide antioxidant properties to the
resulting polymeric products. Finally, the residual monomer is
virtually uncontaminated by these compounds.
The following examples illustrate the preferred embodiments of the
invention. In these examples, all parts given are by weight unless
othen~ise specified.
Example 1: This example illustrates a typical suspension polymeriza-
tion procedure.
REAGENT PARTS
Vinyl Chloride Monomer (VC~I) 100.~0
Initiator-Peroxydicarbonate 0.04
Suspending agent - Methocel type 0.03
NaOH 0.10
H20 (Deaereated Distilled) 200.00
Antioxidant varies
Sodium Lauryl Sulfate0.02
A. Filling of Lecture Bottle with 250 g VCM
1. Evacuate air from lecture bottle and weigh.
2. Cool in freezer.
3. Place a 3785 cc stainless steel cylinder filled with VC~ in hot
water bath (hot tap water).
4. Connect a 3785 cc cylinder to 500 ml lecture bottle with flexible
stainless steel hose and connectors.
~-,ji

;3~
5. Weigh 500 cc cylinder during addition and stop when approximate
weigh VCM registers on balance.
6. Weigh 500 cc cylinder with no connections to determine exact
amount of VCM inside.
Charging of Reactor
1. Carefully put thistle tube into reactor's entry port.
2. Add sodium lauryl sulfate through thistle tube.
3. Wash tube with 50 parts water.
4. Add suspending agent in 1% solution (aqueous).
5. Washitube with 50 parts water.
6. Add NaOH in 1% solution (aqueous).
7. Wash tube with 50 parts water.
8. Add initiator in 7.5% solution (toluene).
9. Wash tube with rest ox water.
10. Turn on pressure and temperature recorders.
C. Charging of Reactor with VCM
1. Heat 500 ml lecture bottle in hot water bath (hot tap water).
2. Connect lecture bottle through quick-connect fittings to reactor.
3. Open valves and VCM will flow in within 60 seconds.
4. Close off valves, start stirring motor at 500 rpm and start pre-
heated (62C) circulating water bath through reactor outer jacket.
D. Reaction No
1. Agitate at 500 rpm and heat to reaction temperature oE 57C
within 30 minutes.
2. Typical reaction with peroxydicarbonate initiator achieved 57C
reaction temperature and 140-150 psi reaction pressure approxi-
mately 30 minutes after initiating heating. The pressure remains
in this range for approximately 5-7 hours or to about 70%
conversion after which the pressure gradually drops.

;~26~g~3
- 12 -
E. Addition of Chain Stopper at 70% Conversion
-
l. Add desired amount chain stopper to a 40 cc lecture bottl,e.
2. Fill 40 cc lecture bottle with 20-30 g VCM as in Procedure A.
3. At 70% conversion connect lecture bottle to addition part of
reactor and heat to 90-100C with electric heat gun (check with
pyrometer).
4. Open valves and VCM/chain stopper solution will flow in.
5. Close valves and reweigh lecture bottle to be sure all V~M/chain
stopper solution went into reactor.
F. PVC Recovery
1. Vent unreacted VCM slowly into hood, opening and closing valve
until no pressure is left in reactor.
2. When all VCM is vented, PVC discharged through bottom port into
collection bottle.
3. Filter, then wash with 1000 ml distilled water.
4. Strip wet cake.
The following compounds were utilized in the polymerization
procedures noted in the Eollowing examples.
Compound
(A) Triethyleneglycol-bis-3-(3-tert.-butyl-4-hydroxy-55-methylphenyl)-
propionate
(~)Octadecyl-3-(3-tert.-butyl-4-hydroxy-5-methylphenyyl)-propionate
(C) 1,6-Hexane diol bis-3-(3-tert.-butyl-4-hydroxy-5-methylphenyl)-
propionate
(D) 1,1,3Tris-(2-methyl-4-hydroxy-5-tert.-butylphenyl)-butaane

~.2~
(E)1,3,5-Tris-(2,6-dimethyl-3-hydroxy-4-tert.-butylbeenzyl)-iso-
cyanurate.
Example 2: This example shows the termination effectiveness of a
compound of the instant invention in polyvinyl chloride suspension
polymerizations
The polyrnerization procedure of Ex2mple 1 was utilized herein. In
each reaction, the pressure after the terminator had been added and
the pressure after a 15 hour reaction sequence were noted. These
values were determined by continuous monitoring of the pressure in
the reactor. Small pressure drops after the addition of the
terminator are indicative of effective termination. The following
results were obtained:
Pressure* Pressure**
Concentration Drop after Drop after 70 %
Compound(ppm)15 hours (psi) Conversion (psi)
- - 45 45
A 100 22 16
h 250 0 0
D 250 8 2
E 250 6 0
* Initial pressure minus the pressure at 15 hours.
** Pressure at 70 % conversion minus the pressure at 15 hours.

l 2~6~
- 14 -
Example 3: The polymerization procedure of Example 1 and the
monitoring procedure of Example 2 were again repeated with the com-
pounds noted hereinbelow with the exception that the compounds were
added at the initiation of the polymerization reaction. Although
this approach does not reflect a commercially desirable procedure,
it is satisfactory as a screening procedure in order to predict chain
termination activity.
Thus, since it can be postulated that the rate of initiation in
the polymerization reaction is related to the rate of termination,
an additive which slows the rate of polymerization also effects the
rate of termination. Accordingly, longer periods to pressure drop
are indicative of more effective chain stoppers. Correspondingly,
since pressure drop after conversion is indicative of continued
reaction and a resultant adverse effect on the po]yvinyl chloride,
lower pressure drops are likewise indicative of more effective chain
stoppers.
The resulting data are noted in the following table.
Concentration Time to Pressure Drop
Compound(ppm) Pressure Drop (min.) after 900min.(psi)
- - 365 60
A 100 540 24
250 900 6
B 100 480 30
C 100 570 22
In summary, this invention provides a novel use of chain terminating
agents in suspension polymerization of vinyl chloride monomer.
Variations may be made in procedures, proportions and materials
without departing from the scope of the invention as defined by
the following claims.