Note: Descriptions are shown in the official language in which they were submitted.
2 ~ 3
A PROCESS FOR THE PRODUCTION OF_POLYCHLOROPRENE OF MODERATE
VISCOSITY
This invention relates to a process for the production
of polychloroprene (CR) of moderate viscosity and, hence,
good processability by $hermo-oxidative degradation of CR
of relatively high viscosity.
By virtue of their balanced properties, particularly
their temperature, ozone and oil resistance, CR vulcan-
izates are outstanding rubbers which are superior to many
other materials. They are widely used in the adhesives,
cable and automotive industries. CR is available as a
solid rubber with Mooney viscosities of from about 35 to
about 120 (ML 1+4) 100~C.
Low-viscosity CR types are reguired as solid rubbers
for certain applications. They may be produced using large
quantities of regulators by bulk polymerization (JP-A
72/8608), by emulsion pol~merization with subsequent
working up (GB-PSS 905,971 and 963,075) or by solution
polymerization with subsequent removal of the solvent (DE-
OSS 2 423 7~4 and 2 444 565). On account of their high
content of chemically incorporated fragments emanating from
the regulators, these low-viscosity CR types are not
entirely satisfactory in their vulcanization activity.
It is known that synthetic rubbers are not as easy to
masticate as natural rubber, particularly when the rubbers
have electron-attracting substituents (such as CN, Cl); cf.
H. Fries and R.R. Pandit, Rubber Chem. Technol. 55, 309 et
g. Whereas attempts to degrade CR in decalin solution at
150C led within a few hours to a CR having 1/20th of its
original molecular weight, it was reported that a gel was
formed in the attempted thermo-oxidative degradation of CR;
cf. K. Itoyama, 122nd Meeting of the Rubber Division of the
Amer. Chem. Soc., Chicago/Ill., 04.07.10.1982.
A process has now been found in which a low-viscosity
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CR of low gel content is obtained by thermo-oxidative
degradation of CR.
The present invention relates ~o a process for the
production of polychloroprene having a Mooney viscosity of
5 to 30 and preferably 10 to 25 (ML 1+4) 100C by thermo-
oxidative degradation of a polychloroprene having a Mooney
viscosity of 35 to 120 and preferably 45 to 100 (ML 1+4)
100C at a melt temperature of 40C to 200C and prefer-
ably 70C to 185C by shearing at a shear rate of 30 to
5000 sec~1 and preferably 50 to 1000 sec~l until the desired
Mooney viscosity is reached.
Polychloroprenes suitable as starting products for the
process according to the invention are chloroprene polymers
which, in addition to polymerized 2-chloroprene units, may
contain 0.05 to 30% by weight and preferably 0.1 to 20% by
weight, based on chloroprene polymer of copolymerized units
of other ethylenically unsaturated monomers or sulfur, i.e.
polychloroprenes of the type described, for example, in
"Methoden der organischen Chemie" (Houben-Weyl), Vol.
E20/2, 842-859, Georg Thieme Verlag, Stuttgart - New York
1987.
Preferred ethylenically unsaturated "other monomers"
copolymerizable with chloroprene are, essentially, 2,3-
dichlorobutadiene and l-chlorobutadiene. Sulfur-modified
polychloroprenes are preferred.
The quantity of elemental sulfur used for the
production of sulfur-modified polychloroprene is 0.05 to
1.5% by weight and preferably 0.1 to 1% by weight, based
on the monomers used. Where sulfur donors are used, the
quantity in which they are used should be gauged in such a
way that the sulfur released corresponds to the quantities
mentioned above.
The Mooney viscosity is determined in accordance with
DIN 53 523.
Suitable machines for carrying out the process
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according to the invention include preferably heatable
single-screw and multiple-screw extruders, more particular-
ly twin-screw extruders, having length-to-diameter ratios
of 10 to 100, aeration and vent openings and, optionally,
other feed openings for masticating aids. The screw used
for the following Examples was a twin-screw extruder with
contra-rotating screws having a length of 120 cm, a cylind-
er diameter of 3 cm and the following construction:
Feed zone 1 (length 10 cm) with feed opening,
Heating zone 2 (length 10 cm),
Metering zone 3 (length 10 cm) with aeration opening,
Reaction zone 4 (length 60 cm~ with feed openings in
the middle and at the end of the zone,
Venting zone 5 (length 20 cm) with vent opening,
Extrusion zone 6 (length 10 cm) with extrusion head.
The thermo-oxidative degradation reguires the presence
of a medium which is capable of stabilizing the fragments
terminated by free radicals which are formed under the
effect of the chemical energy applied. Media such as these
include oxygen itself, gas mixtures containing free oxygen,
such as air for example, and oxygen donors which release
chemically bound oxygen under reaction conditions, such as
for example peroxides, nitrates and chlorates. For reasons
of cost, air is the preferred medium.
The process ac¢ording to the invention is preferably
carried out using radical transfer agents, agents having
radical transfer constants of
50 104 to 20,000 104, preferably
80 104 to 180 104 and, more preferably
110 104 to 150 10~
being particularly effective. The above figures are based
on the polymerization of ethy}ene at 130C as described in
Polymer Handbook, Ed.: J. Brandrup, E.H. Immergut, 2nd
Edition, Wiley, New York 1975. Chain transfer agents of
the type in question include mercaptans, such as the iso-
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meric xylyl mercaptans, thiophenols and zinc salts thereof,
such as pentachlorothiophenol, zinc pentachlorothiophenol,
~-thionaphthol and zinc-o-benzamidothiophenol; aromatic
disulfides, such as o,o'-dibenzamidodiphenyl disulfide:
salts of saturated fatty acids, benzene, toluene, acetone,
tetrachloromethane, iodoform and cumene.
The necessary quantites are mainly determined by the
desired degree of degradation and may be reliably deter-
mined by a few preliminary tests.
In the case of sulfur-modified polychloroprenes, the
desired degradation may be accelerated by the use of
typical peptizing agents of the type described, for ex-
ample, in DE-OS 1 911 439, 2 018 736, 2 755 074 and 3 246
748, in DE-PS 2 645 920, in EP-A 21 212 and 200 857, in FR-
PS 1 457 004 and in US-PSS 2,264,713, 3,378,538, 3,397,173
and 3,507,825.
By virtue of their functional groups which are formed
by the degradation reaction, the low-viscosity polychloro-
prenes produced in accordance with the invention may be
vulcanized solely with metal oxides, such as magnesium
oxide and/or zinc oxide, as vulcanizing agents. The
quantities in which the vulcanizing agents are used are
generally from 2 to 10% by weight, based on polychloro-
prene.
The vulcanization may be carried out at temperatures
of 100 to 200C and preferably at temperatures of 130 to
180C, optionally under a preissure of 10 to 200 bar.
The outstanding properties of the vulcanizates are
generally obtained without conditioning, although they can
often be improved by conditioning.
The polychloroprenes produced in accordance with the
invention may be used with advantage for the production of
drive belts, air springs, conveyor belts and other in-
dustria} rubber articles.
The parts mentioned in the following Examples are
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parts by weight.
Examples
General description of the process:
~he rotational speed of the screw varies between 40
and 60 min~l for a product throughput of 1.5 to 2.5 kg/h.
The product is heated in the heating zone (2) and mixed
with 200 to 700 normal liters air under pressure (2 to 40
bar) in zone (3). The product is then transported through
the reaction zone (4) at a predetermined melt temperature.
In the process according to the invention, other auxiliar-
ies may be added to the polymer either in the middle or at
the end of the reaction zone (4) (see individual Examples).
In the venting zone (5), unreacted air and unreacted
volatile auxiliaries are removed from the product under a
pressure of 10 to 500 mbar. The product is then discharged
from the twin-screw extruder via an extrusion head.
The gel content of the polymers is determined by means
of an ultracentrifuge (5% concentration in tetrahydrofuran,
60 minutes' centrifugation at 20,000 rpm).
Example 1
A mercaptan-regulated polychloroprene having a Mooney
viscosity of 40 (ML 1~4) 100C is degraded to a polychloro-
prene having a Mooney viscosity of 18 (ML 1+4) lOO-C. -~
To-this end, 2.3 kg/h polychloroprene are transported
through the twin-screw extruder at a rotational speed of
the screws of 40 min~l. The product is heated to 60C in
the heating zone (2). Air (1500 l/h) is introduced in zone
(3) and the product is transported into the reaction zone
(4) at 80C. In the reaction zone (4) toluene is intro-
duced in a quantity of 800 ml/h. Toluene and unreacted air
are removed in the venting zone (5) under a pressure of 40
to 50 mbar, the polychloroprene being heated to 140C.
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After discharge from the twin-screw extruder, the product
was soluble in tetrahydrofuran; the gel content was below
2% by weight.
Example 2 (Comparison)
The polychloroprene having a Mooney viscosity of 40
(ML 1+4) 100C used as starting product for Example 1 is
subjected to hot-air ageing at 70C in a recirculating air
drying cabinet. Its Mooney viscosity increased and measur-
ed 41 (ML 1+4) 100C after 3 days, 43 (ML 1+4) 100C after
5 days and 45 (ML 1+4) 100C after 7 days. The gel content
after 7 days was 3.2% by weight.
Example 3
The procedure is as in Example 1, except that a
solution of 20 g 2,2-diphenyl-1-picrylhydrazyl in 200 ml
toluene was added at the end of reaction zone (4) in a
quantity of 200 ml/h. The end product had a Mooney
viscosity of 19 (ML 1+4) 100C and a gel content below 2
by weight.
,Example 4
A sulfur-modified polychloroprene having a sulfur
content of 0.5% by weight and a Mooney viscosity of 4~ (ML
1+4) 100C is degraded to a polychloroprene having a Mooney
viscosity of 19 (ML 1+4) lOO-C.
To this end, 2.45 kg/h polychloroprene are transported
through the twin-screw extruder at a rotational speed of
,the screws of 60 min~1. The product is heated to 60C in
the heating zone ~2). Air (1650 l/h) is introduced in zone
(3) and the product is transported into the reaction zone
(4) at 130C. In the reaction zone (4) toluene is intro-
duced in a quantity of 900 ml/h. Toluene and unreacted air
are removed in the venting zone (5) under a pressure of 10
to 50 mbar, the polychloroprene being heated to 140C.
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After discharge from the twin-screw extruder, the product
was soluble in tetrahydrofuran; the gel content was below
2% by weight.
Example 5 (Comparison)
The polychloroprene having a Mooney viscosity of 48
used as starting product of Example 4 is subjected to hot-
air ageing at 90C in a recirculating-air drying cabinet.
After 14 hours, the Mooney viscosity measures 26 (ML 1+4)
100C, passes through a minimum of 24 (ML 1+4) 100C after
16 hours and measures 27 (ML 1+4) 100C after 18 hours and
65 (ML 1+4) lOODC after 36 hours. The fall in viscosity
initially observed is presumably attributable to post-
peptization; the viscosity reachable through this degrad-
ation is always higher than the viscosity reachable by
thermo-oxidative degradation.
Example 6
The procedure is as in Example 4, except that a
solution of 20 g tetraethyl thiuram disulfide in 200 ml
; toluene is added at the end of reaction zone (4) in a
quantity of 180 ml per hour. The end product was soluble
in tetrahydrofuran and had a Mooney viscosity of 16 (ML
1+4) 100C and a gel content below 2% by weight.
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Example 7
A xanthogen-disulfide-regulated polychloroprene having
a Mooney viscosity of 58 (ML 1+4) 100C is degraded to a
polychloroprene having a Mooney viscosity of 17 (ML 1+4)
100C.
To this end, 2.2 kg/h polychloroprene are transported
through the twin-screw extruder at a rotational speed of
the screws of 45 min~~. The product is heated to 60C in
the heating zone (2). Air (1600 l/h) is introduced in zone
(3) and the product is transported into the reaction zone
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(4) at 170C. In the reaction zone (4) toluene is intro-
duced in a quantity of 1000 ml/h. Toluene and unreacted
air are removed in the venting zone (5) under a pressure of
40 to 50 mbar, ~he polychloroprene being heated to 170C.
After discharge from the twin-screw extruder, the product
was soluble in tetrahydrofuran: the gel content was below
2% by weight.
Example 8
The procedure is as in Example 7, except that a
solution of 18 g xanthogen disulfide in 200 ml toluene is
added at the end of reaction zone (4) in a quantity of 190
ml per hour. The end product had a Mooney viscosity of 16
(ML 1+4) 100C and a gel content below 2% by weight.
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