METHODS FOR INHIBITING THE POLYMERIZATION OF ETHYLENICALLY UNSATURATED MONOMERS

PROCEDES DESTINES A EMPECHER LA POLYMERISATION DE MONOMERES ALCENIQUES

English Abstract

The polymerization of an ethylenically unsaturated monomer such as isoprene
and butadiene is inhibited during storage or handling
thereof by the addition of a dihydroxycinnamic acid or derivative thereof.

French Abstract

On empêche la polymérisation d'un monomère alcénique, tel qu'un isoprène ou un butadiène, lors du stockage ou de la manutention de celui-ci, en lui ajoutant un acide dihydroxycinnamique ou un dérivé de cet acide.

Claims

7
CLAIMS:
1. A method for inhibiting the polymerization of isoprene comprising adding to
the isoprene an effective polymerization inhibiting amount of a
dihydroxydihydrocinnamic acid or a dihydroxycinnamic acid or derivative
thereof
having the formula
<IMG>
wherein R is H, CH3 or C2H5; R1 is H, CH3 or C2H5 with the proviso that at
least
one of R1 is H.
2. The method as claimed in claim 1, wherein said dihydroxydihydrocinnamic
acid or said dihydroxycinnamic acid or derivative thereof is selected from the
group consisting of dihydroxycinnamic acid and dihydroxydihydrocinnamic acid.
3. The method as claimed in claim 1 or 2, wherein said
dihydroxydihydrocinnamic acid or said dihydroxycinnamic acid or derivative
thereof is added to said isoprene in an amount ranging from 1 part to 1000
parts
per million parts of isoprene.
4. The method as claimed in claim 1, 2 or 3, wherein said isoprene is exposed
to oxygen.
5. The method as claimed in any one of claims 1 to 4, wherein said isoprene
has a temperature ranging from ambient to 100°C.
6. A composition comprising isoprene and a dihydroxydihydrocinnamic acid or
a dihydroxycinnamic acid or derivative thereof having the formula

8
<IMG>
wherein R is H, CH3 or C2H5; R1 is H, CH3 or C2H5 with the proviso that at
least
one of R1 is H.
7. The composition as claimed in claim 6, wherein said
dihydroxydihydrocinnamic acid or said dihydroxycinnamic acid or derivative
thereof is selected from the group consisting of dihydroxycinnamic acid and
dihydroxydihydrocinnamic acid.

Description

CA 02236526 1998-OS-22
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METHODS FOR INHIBITING THE POLYMERIZATION OF
ETHYLENICALLY UNSATURATED MONOMERS
TECHNICAL FIELD
This invention relates to methods for inhibiting polymerization of
ethyfenicaliy unsaturated monomers. The methods are particularly effec-
tive at inhibiting polymerization of these monomers during storage condi-
tions in the presence of oxygen.
BACKGROUND ART
it is well known that ethylenically unsaturated monomers readily
polymerize when heated and that the polymerization rate increases with
increasing temperature. For this reason, the monomers are stabilized by
the addition of substances which act as inhibitors or retarders of polym-
erization, or which block the initiation mechanism leading to the formation
of radicals.
Certain ethylenicalfy unsaturated (diolefin) monomers such as
butadiene and isoprene polymerize when left in storage tanks and during
transportation at temperatures as low as room temperature. This polym-
erization is initiated by reaction of the diolefin monomer with oxygen
present in the monomer containing system. This reaction forms perox-
ides and free radical species which can further react with the diolefin
monomer.

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To prevent this polymerization from taking place, diolefin monomer
manufacturers frequently add tert-butyl catechol (TBC) as a polymeriza-
tion inhibitor. However, TBC is a toxic compound and can cause tissue
damage when it contacts skin. These characteristics make it desirable to
utilize an inhibitor compound that avoids these difFiculties as well as
being water and caustic extractable so that it could be easily removed
from the finished product before use or additional processing.
The present inventor has discovered that dihydroxycinnamic acid
and its derivatives effectively inhibit the polymerization of ethylenically
unsaturated monomers during storage and transportation. These com-
pounds prove particularly effective in the presence of oxygen and at
temperatures up to 100°C.
EP 89-402156 discloses a cosmetic preparation containing an anti-
oxidant system based on a stabilized ascorbic acid ester. The antioxidant
system also contains tocopherol or mixtures of tocopherol, caffeic acid or
its derivatives, a complexing agent and a non-thiol polypeptide.
JP Kokai JP 59015477 teaches a food antioxidant composition
effective for oils and fats which comprises 3,4-dihydroxycinnamic acid
esters and one or more of ascorbic acid-stearic acid ester, citric acid,
malic acid, and ascorbic acid.
DISCLOSURE OF lNVENT10N
The present invention relates to methods far inhibiting the polym- .,
erization of ethyfenically unsaturated monomers comprising adding an
effective inhibiting amount of a dihydroxydihydrocinnamic acid or a
d.ihydroxycinnamic acid or derivative thereof.
r

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The dihydroxycinnamic acid or derivatives thereofi generally have
the formula:
HC = C - COOR
0
O R'
OR'
wherein R is H, CH3 or C2H5; R' is H, CH3 or C2H5 with the proviso that at
least one of R' is H. The preferred compounds for use in the present
invention are dihydroxycinnamic acid and dihydroxydihydrocinnamic acid.
The ethylenically unsaturated monomers are characterized as
polymerizable ethylenically unsaturated hydrocarbons and include oie-
phins such as alpha olephins containing 2 to 20 carbon atoms and
preferably 2 to 8 carbon atoms, and conjugated di-olephins, preferably
those containing 4 to 6 carbon atoms such as isoprene and butadiene.
For purposes of this invention, the term "effective amount" refers to
the amount of dihydroxycinnamic acid or derivative thereof necessary to
inhibit polymerization of ethylenically unsaturated monomers. This amount
will vary according to the conditions under which the ethylenicafly unsatu-
rated monomer is subjected during storage and/or handling thereof. At
higher temperatures and higher monomer contamination, larger amounts
of polymerization inhibiting compound are generally required.

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Preferably the effective amount of dihydroxycinnamic acid or de-
rivative added to the ethylenically unsaturated monomer ranges from
about 1 part to about 1000 parts per million parts of monomer. More pref-
erably, the amount of dihydroxycinnamic acid or derivative thereof added
to the monomer ranges from about 10 parts to about 200 parts per million
parts monomer.
The dihydroxycinnamic acid derivatives may be used in combination
with the dihydroxycinnamic acid or as a mixture of the dihydroxycinnamic
acid derivatives when utilized in the methods of the present invention.
The dihydroxycinnamic acid or derivative thereof may be added
to the ethylenically unsaturated monomer as either a dispersion or as a
solution using a suitable liquid carrier or solvent. Any solvent that is
compatible with the dihydroxycinnamic acid or derivative thereof and the
ethyfenically unsaturated monomer may be employed.
MODES FOR CARRYING OUT THE fNVENTtON
The invention will now be described with reference to a number of
specific examples which are to be regarded solely as illustrative, and not
as restricting the scope of the invention.
EXAMPLES
Testing was performed to determine the effectiveness of the pres-
ent invention at inhibiting the polymerization of ethylenically unsaturated
monomers.

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Tests were run in a stainless steel pressure vessel fitted with a
glass sample container and cover, a stem, a pressure gauge with a con-
tinuous recorder, and the appropriate valves and fittings. A solution of 10
mL of isoprene in 40 mL of heptane and the designated treatment were
5 placed in the glass sample container and inside the pressure vessel. The
vessel was closed, filled with oxygen at 100 psig and heated in a water
bath at 100°C. The pressure was recorded continuously until a break
point in the pressure-time curve (i.e., steepest slope of the curve) was
reached. The induction time was calculated as the time elapsed between
the placing of the vessel in the bath and the breaking point. The results
of this testing are reported in Table I.
TABLE!
Polymerization inhibition Testing
Treatment Dose ppm) Induction Time lmin.)
Blank _____ 25
TBC 10 40
BHT 10 31
40 32
DHHCA 10 85
144
Blank _____ 21
TBC 40 90
DHHCA 40 110
25 DHCA 40 54
Blank ----- 25
DHCA 50 102
100 127
TBC is tert-butyl catechol
BHT is 2,6-di-t-butyl-4-methylphenol
DHCA is 3,5-dihydroxycinnamic acid
DHHCA is 3,4-dihydroxyhydrocinnamic
acid

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These results demonstrate that the compounds of the present
invention are effective at inhibiting the polymerization of ethylenically
unsaturated monomers under conditions approximating storage. The
commercially available inhibitors, TBC and BHT proved less effective
than the inventive compounds.
INDUSTRIAL APPLlCABlLITY
The dihydroxycinnamic acid or derivatives thereof are effective at
inhibiting the polymerization of ethylenically unsaturated monomers dur
ing their storage or under transportation conditions. These conditions are
typically found to have oxygen atmospheres present and monomer tem-
peratures up to about 100°C. The present inventor anticipates that the
methods of the present invention can inhibit the polymerization of ethyl-
enically unsaturated monomers during the processing thereof. These
processing conditions, such as purification and distillation processes,
typically employ heat and will often cause fouling of the monomer.
While this invention has been described with respect to particular
embodiments thereof, it is apparent that numerous other forms and modi-
fications of this invention will be obvious to those skilled in the art. The
appended claims and this invention generally should be construed to
cover ail such obvious forms and modifications which are within the true
spirit and scope of the present invention.
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