Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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This invention relates to peroxide blends for use in
the crosslinking of polymers such as polyethylene, EPDM and
copolymers of ethylene and vinyl acetate.
The use of peroxides for crosslinking polymers is
facilitated if the crosslinking agents are in the liquid
rather than the solid state. Known crosslinking agents are
either solid crystalline materials having a melting point
above room temperature or have been mixed with non-active
materials that serve to lower the melting point of the agent
to below room temperature. The inclusion of non-active
materials reduces the crosslinking efficiency and it is
therefore desirable to provide liquid crosslinking agents
that are composed entirely of peroxides having crosslinking
activity.
According to the invention there is provided a cross-
linking agent that comprises a solid peroxide crosslinking
agent, namely bis(alpha-t-butyl peroxyisopropyl)benzene,
characterized in that to the said agent is added isopropyl-
cumyl-t-butyl peroxide to provide a blend containing 75% to
90% of the latter, thereby rendering the said agent liquid
at an ambient temperature of 23C.
In this specification and in the claims, all parts and
percentages are by weight unless otherwise specified.
The peroxide blend of this invention consists essenti-
ally of from about 25% to about 10% bis(alpha-t-butylperoxy-
isopropyl) benzene and from about 75% to about 90% iso-
propylcumyl t-butyl peroxide.
Preferably, the peroxide blend consists essentially of
from about 25% to about 20% bis(alpha-t-butylperoxyiso-
propyl) benzene and from about 75% to about 80% isopropyl-
cumyl-t-butyl peroxide.
Bis-(alpha-t-butylperoxyisopropyl) benzene is well known
in the art as are the methods for the preparation thereof.
This bisperoxide has the formula (I) below.
ICH3 CH3 CIH3 CIH3
(I) CH3 - C - O - O - C ~ C - O - O - C - CH3
CH3 CH3 CH3 CH3
Specific examples of the bisperoxide are the meta and para
isomers thereof. Mixtures of the meta and para isomers are
commercially available and are preferred for use in this in-
vention. The meta and para isomers are solid at room tem-
perature as are all mixtures thereof. The meta isomer melts
at about 52C., the para isomer melts at about 79C., and
the eutectic mixture (80~ meta isomer) melts at about 45C.
Bis(alpha-t-butylperoxyisopropyl) benzene is a cross-
linking agent for certain polymers such as polyethylene.
- See U.S. patent Re. 25,941.
Isopropylcumyl t-butyl peroxide is liquid at room tem-
perature and has the formula (II) below.
(II) HC ~ C - O - O - C - CH3
CH3
; Specific examples thereof are meta-isopropylcumyl t-butyl
peroxide and para-isopropylcumyl t-butyl peroxide. Mix-
tures of the meta and para isomer, a mixture of about 2
parts meta isomer and about 1 part para isomer for example,
can be used in carrying out this invention. All meta and
para mixtures are liquid at room temperature.
Example 1
The apparatus used in this example consisted of a 4-
necked round-bottom flask equipped with a thermometer, a
mecha-ical stirrer, and an ice water-cooled Friedrich con-
denser with a Barrett moisture trap. Reduced pressure was
read on a U-tube manometer and controlled with a twenty-turn
needle valve through appropriate hose connections.
To the flask were charged 713 grams (4.0 moles) of a
mixture of the meta and para isomers of
~3~196
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isopropyl-alpha,-alpha-dimethylbenzyl alcohol (ratio of meta
to para is about 2 to 1), 440 grams of 90% aqueous solution
of t-butyl hydroperoxide (4.4 moles of hydroperoxide), and
769 grams of heptane. The resulting mixture was stirred at
30-35C. while refluxing at reduced pressure until essen-
tially all water present in the hydroperoxide solution had
been collected in the Barrett trap. The trap was then
drained of water and p-toluenesulfonic acid monohydrate
(7.6 grams, 0.04 mole) dissolved in 7 ml. water was added
to the mixture in the flask. Stirring at reflux ~30-35C.)
under reduced pressure was continued until no more water
was being collected in the Barrett trap (about 9 hours).
At that point the reaction mixture became darker in
appearance.
250 ml. of a 5% aqueous solution of NaOH was added to
the reaction mixture and the thus diluted reaction mixture
was transferred to a separatory funnel. The aqueous phase
was removed from the funnel and the organic phase was washed
four more times with 5% aqueous solution of NaOH followed by
three washes of 500 ml. of distilled water each. The
organic phase was dried over MgSO4, filtered, and stripped
on a rotary evaporator; first at 50C. with aspirator vacuum
to remove heptane and finally at 65-70C. and 0.1 Torr. The
product consisted essentially of a mixture of the meta and
para isomers of isopropyl cumyl t-butyl peroxide. The prod-
uct weighed 940.8 grams and contained 87.2% peroxide as
determined by the iodine liberation method. This represen-
ted a yield of 82% based on the alcohol used. The product
was a clear light yellow liquid at room temperature.
Example 2
A peroxide blend that is liquid at room temperature was
prepared by dissolving 25 parts bis(alpha-t-butylperoxyiso-
propyl) benzene (essentially a 2 to 1 mixture of the meta
and para isomers) in 75 parts of the product of Example 1.
The isopropylcumyl t-butyl peroxide was a mixture of about
2 parts meta isomer and 1 part para isomer.
Examples 3-4
The following polyethylene compositions were prepared
96
--4--
and cured at 360F.
Composition 3 4
Low density polyethylene - 100 100
parts
Antioxidant (AgeRite 0.5 0.5
Resin D) - parts
bis(alpha-t-Butylperoxy- 1.2
isopropyl)benzene - parts
Example 2 peroxide blend - - 2.03
parts
Cure time (min.) 20 20
Physical properties of the cured compositions are set
forth below in Table I.
TABLE I
Cured Composition _ _
100% Modulus (psi) 1095 1165
Tensile Strength (psi)27952500
Elongation, % 550 550
Shore A Hardness 96 96
Shore D Hardness 47 47
Heat Distortion % 10.6 11.3
(ASTM D2655)
Bis(alpha-t-butylperoxyisopropyl) benzene is a solid at
room temperature. One of the disadvantages of this peroxide
is that it must be melted in order to be uniformly dispersed
in polymers, such as polyethylene, prior to cure. This causes
additional expense to the user and is a source of danger as
there is always the possibility of overheating, particularly
by unskilled personnel, which can result in rapid decomposi-
tion of the peroxide and may even result in explosion.Blending of the solid peroxide with polymers, such as poly-
ethylene, is not satisfactory in that it is difficult, if not
impossible, to obtain uniform dispersion of the peroxide
throughout the polymer. It is essential that the peroxide be
uniformly dispersed in order to provide uniform curing or
crosslinking of the polymer.
. .
113~96
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The peroxide blend of this invention, being liquid at
room temperature, is easily and readily admixed with such
polymers as polyethylene to provide essentially uniform blends
of polymer and peroxide without undesirable effects. The
polymer-peroxide compositions, after curing, have good
physical properties.
