Note: Descriptions are shown in the official language in which they were submitted.
This invention relates to the cross-linking of halogen-containing
polymers. More particularly, this invention relates to a method of cross-
linking saturated, halogen-containing polymers with 2,5-dimercapto-1,3,4-
thiadiazole and certain basic organic material.
2,5-Dimercapto-1,3,4-thiadiazole is a known compound and has been
reported in British Patent No. 974,915 as a curing agent for certain unsatu-
rated, halogen-containing polymers (i.e., chlorobutyl rubber and polychloro-
prene elastomers). However, British Patent No. 974,915 does not suggest the
cross-linking of saturated, halogen-containing polymers.
It has now been discovered that saturated, halogen-containing
polymers can be cross-linked to yield stable vulcanizates with good aging,
coppression set resistance, and insolubility in organic solvents using 2,5-
dimercapto-1,3,4-thiadiazole, or a concentrate thereof in a binder material,
in the presence of certain basic organic materials in normal vulcanization
procedures. For purposes of this invention the term "basic material" is
meant to include both bases and materials which become basic on heating to
the cross-linking temperature. Accordingly, this invention relates to a pro-
cess of cross-linking saturated, halogen-containing polymers with 2,5-dimer-
capto-1,3,4-thiadiazole in the presence of a basic organic material to acti-
vate cure.
The saturated, halogen-containing polymers of this invention con-
tain at least about 2%, most preferably about 5%, by weight of halogen. Typi-
cal of the saturated, halogen-containing polymers are homopolymers of epi-
chlorohydrin, copolymers of epichlorohydrin and ethylene oxide or propylene
oxide, chlorinated high-density polyethylene, chlorosulfonated polyethylene,
poly(vinyl chloride), polytvinyl fluoride), poly(chloroalkylacrylates), poly
(vinylidene chloride), and copolymers of vinylidene fluoride and hexafluoro-
propylene.
` In addi~ion, the process of this invention may be used to cross-
link blends of saturated, halogen-containing polymers or saturated, halogen-
containing polymers blended with other polymers. The only requirement is
- 2 -
that there be sufficient saturated, halogen-containing polymer present in
the blend to effect cross-linking.
According to the present invention there is provided the process
of cross-linking a saturated, halogen-containing polymer which comprises
heating said polymer in the presence of an organic basic material and 2,5-
dimercapto-1,3,4-thiadiazole.
In a preferred aspect the invention provides the process of cross-
linking a saturated, halogen-containing polymer which comprises heating said
an C~l~go-n,c~ ba~jIc
~ polymer in the presence of 2,5-dimercapto-1,3,4-thiadiazole and a basic
material selected from the group consisting of (1) tributylamine (2) dicyclo-
hexylamine (3) hexamethylenediamine carbamate (4) hexamethylene tetramine (5)
N,N'-dicinnamylidine 1,6-hexanediamine (6) salts formed by condensation of
2,5-dimercapto-1,3,4-thiadiazole with organic amines (7) quaternary ammonium
~; hydroxides and their salts with acids having a PKa above about 2.0, (8) di-
phenyl guanidine (9) ditolyl guanidine and (10) the condensation product of
- aniline with a lower aliphatic monoaldehyde in admixture with at least an
equal amount of an inorganic base.
As stated above, various bases or materials which will become
basic on heating to the cross-linking temperature, i.e., basic materials, may
be employed as cure activators. Certain organic basic materials may be used
either in place of, or in combination with, inorganic basic materials. Typi-
cal organic basic materials are various primary, secondary and tertiary
amines, amine salts and quaternary ammonium compounds. Preferred organic
basic materials include tributylamine, tetramethylammonium bromide, tetra-
butylammonium bromide, tetraethylammonium benzoate, tetraethyl ammonium ace-
tate, tetraethylammonium nitrate, benzyltrimethylammonium bromideJ 2-amino-2-
.,.~. ~
thiazoline, diazabicyclo-octane, hexamethylenetetramine, hexamethylenediam1ne
carbamate, and N,N'-dicinnamylidine-1,6-hexanediamine, dicyclohexylamine, di-
orthotolylguanidine, diphenylguanidine and the reaction product of butyralde-
hyde and aniline. There may also be used basic inorganic materials together
with the basic organic material. Typical inorganic basic materials are basic
- 3 -
s
metal oxides, hydroxides and their salts with weak acids, for example, lead
oxides, zinc oxide, magnesium oxide, calcium oxide, calcium hydroxide, barium
oxide, zinc carbonate, lead acetatc, barium carbonate, strontium carbonate,
sodium phenoxide and sodium acetate. The preferred inorganic basic materials
are calcium oxide, calcium hydroxide, magnesium oxide and barium carbonate.
Mercaptides formed by reaction of the 2,5-dimercapto-1,3,4-
thiadiazole with a basic inorganic oxide or hydroxide may also be used as
cross-linking agents alone or in combination with additional basic material.
Also, reaction products of organic amines with the 2,5,dimercapto-1,3,4-
thiadiazole can be used as cross-linking agents either alone or in combination
with an inorganic basic material.
In the case of many of the saturated, halogen-containing polymers
in which the 2,5-dimercapto-1,3,4-thiadiazole or its above-mentioned reaction
products with basic materials are relatively insoluble, such as poly(vinyl
chloride), poly~vinyl fluoride), poly~chloroalkylacrylates), chlorinated
polyethylene, homopolymers of epichlorohydrin, poly(vinylidene fluoride), co-
; polymers of vinylidene fluoride and hexafluoropropylene, chlorosulfonated
polyethylene and poly(vinylidene chloride), it may be desirable to use a com-
bination of inorganic and organic basic materials. Dicyclohexylamine, di-ortho-
` 20 tolylguanidine, diphenylguanidine or their salts, and the reaction product of
butyraldehyde and aniline are particularly preferable organic basic materials
for use in combination with inorganic basic materials.
It may be undesirable to use zinc oxide or zinc salts as the basic
.;~
material in certain cases such as with chlorosulfonated polyethylene, chlori-
nated polyethylene, poly(vinyl chloride) or poly~vinylidene chloride), because
zinc chloride formed in situ during the vulcanization process may cause unde-
; sirable degradation by breaking of the polymer chains.
~'aried amounts of the cross-linking agent and basic material can be
added, and the optimum amount will depend upon the degree of cross-linking
` 30 desired. Generally, the amounts added (based on the weight of the polymer)
will be within the following ranges: 2,5-dimercapto-1,3,4-thiadiazole, from
-- 4 --
about 0.1% to about 20%, preferably from about 0.25% to about 5.0%, basic
material from about 0.25% to about 50%, more preferably from about 0.5% to
about 50%, most preferably from about 1.0% to about 20%; and, if inorganic
basic material is used in combination with organic basic material, the amount
of organic basic material may be from about 0.01% to about 5% more preferably
from about 0.05% to about 5%, most preferably from about 0.1% to about 2%.
. In addition to the cross-linking agent and basic material, other
ingredients can also be incorporated. The types of additives commonly used
in rubber vulcanization can be used, as, for example, extenders, fillers,
pigments, plastici~ers, softeners,
. .
~ .
'
..~
,
- 4a -
, ,
~L ~i .5 ir~ ~t~
etc. The presence of a filler and, in particular, carbon black,
is beneficial and, as in hydrocarbon rubber compounding, gives
very advantageous results. There are many cases, however, in
which a filler is not required or desired and excellent results
- are achieved when only the cross-linking agent and basic materials
are added. Also, most of the saturated, halogen-containing poly-
mers contain a small amount (i.e., from about 0.1% to about 2% by
weight) of antioxidant, added at the time of their preparation.
It may be desirable in some cases to add a small additional amount
of antioxidant before or at the time of cross-linking the polymer.
Exemplary of the preferable antioxidants are phenyl-~-naphthyl-
amine, di-~-naphthyl-p-phenylenediamine, sym-di-~-naphthyl-p-
phenylenediamine, N-isooctyl-p-aminophenol, the reaction product
of diphenylamine and acetone, polymerized trimethyldihydroquino-
line, 4,4'-thio-bis(6-tert-butyl-m-cresol), the reaction product
of crotonaldehyde and 3-methyl-6-tert-butyl-phenol, nickel di-
butyldithiocarbamate, the zinc salt of 2-mercapto-benzimidazole,
!~ and nickel dimethyldithiocarbamate.
Particularly in the case of epichlorohydrin polymers,
~; 20 it may be advantageous to add at least one carboxylic acid to the
. .~
cross-linkable composition to act as a scorch retarder during the
compounding step when calcium oxide or calcium hydroxide is used
as the basic material. Maleic acid and N-acetylanthranilic acid
are especially useful.
The cross-linking agent, basic material and additives,
if any are used, can be incorporated or admixed with the polymer
` in any desired fashion. For example, they can be uniformly blend-
ed with a polymer by simply milling on a conventional rubber mill
or mixing in a Banbury mixer. By this means, the cross-linking
agent and basic material are uniformly distributed throughout the
polymer and uniform cross-linking is effected when the blend is
subjected to heat. It is generally preferable to mill at tempera-
tures within the range of from about 20C. to about 95C.
However, the blends are generally scorch-resistant below about
-- 5
120C., unless compounded with a large amount of organic basic
material. Other methods of admixing the cross-linking agent with
the polymer will be apparent to those skilled in the art.
The conditions under which the cross-linking is effected
can be varied over a wide range. Cross-linking can be effected
in minutes at elevated temperatures or in days at temperatures
slightly above room temperature. In general, the cross-linking
temperature will be within the range of from about 30C. to
about 280C., more preferably from about 135C. to about
235C., and most preferably from about 150C. to about
205C. The time will vary inversely with the temperature and
will range from about 30 seconds to 70 hours, preferably from
about 30 seconds to about 120 minutes. While the cross-linking
process can be conducted in air at normal atmospheric pressure,
it will generally be conducted in a metal mold under a compres-
sion of at least about 50 p.s.i. or in a steam autoclave at the
` pressure required for the desired temperature.
For ease in incorporating the 2,5-dimercapto-1,3,4-
thiadiazole into the cross-linkable polymer, and to avoid the use
~, 20 of powders in the compounding step, it may be desirable to prepare
the 2,5-dimercapto-1,3,4-thiadiazole as a concentrate in a binder
; or carrier which can be added, along with the basic materials, in
small amounts to the polymer composition without adverse effect
on the properties of the cross-linked composition. Particularly
.~
advantageous binders or carriers are polymers which may or may not
be cross-linkable by the cross-linking agent. Suitable materials,
in addition to the cross-linkable polymers, are, for example,
ethylene-propylene rubber, ethylene-propylene terpolymers,
butadiene-styrene rubber, natural rubber, low-density polyethyl-
ene, amorphous polypropylene and polyisobutylene. Concentrationsof the 2,5-dimercapto-1,3,4-thiadiazole in the binders can vary
from about 15% to about 90%, preferably from about 30% to about
75%. Other materials which can advantageously be incorporated in
- 6 -
. ~
~'P '~ 'J }~
'
the concentrates are scorch retarders, antioxidants and nonbasic
fillers. It is normally undesirable to incorporate the basic
material in the concentrate. These polymer concentrates are
normally stored and used in the form of sheets, extruded pellets
or rods. Other suitable binders or carriers for use in the prep-
aration of such easily handled concentrates are waxes, resins, or
other low-melting solids. Typical useful materials are paraffin
wax, stearic acid, microcrystalline wax, rosin, rosin esters and
hydrocarbon resins.
The cross-linked products of this invention can be util-
ized to make hoses, tubes, etc., for use as fuel lines carrying
hydrocarbon fuels.
Example 1
This example illustrates the preparation of a concen-
trate of 2,5-dimercapto-1,3,4-thiadiazole in stearic acid.
The concentrate is prepared by dry blending the ingredi-
ents tabulated below, warming the concentrate blend to the melting
; point of the stearic acid, extruding the melted concentrate blend
and cutting the extrudate into rods or pellets.
Ingredients Parts
2,5-dimercapto-1,3,4-thiadiazole 66.6
Stearic acid 16.7
Kaolin clay 7.5
Polymeric plasticizer 9.2
Form white soft pellets
Suggested use in cross-linking epichlorohydrin copolymer
In the following examples a Farrel Size "8" Banbury
mixer is used to compound the formulations. Ingredients are added
to the mixer in the order listed in each example.
- 7 -
~L~ 2 ~ 5
Examples 2-3
Ingredients Parts
Example 2 Example 3
Epichlorohydrin homopolymer (38% Cl) 100 100
: DS-207 (Trademark for a mixture
of dibasic lead salts of
C -C fatty acids sold by
N~ional Lead Co.) (process aid)
Carbon black (reinforcing filler) 50 50
Nickel dimethyldithiocarbamate
: (antioxidant)
Calcium oxide 3 3
Tetramethylammonium bromide 2.0
Tetrabutylammonium bromide - 0.1
2,5-Dimercapto-1,3,4-thiadiazole 1.0 1.0
The above formulations are cross-linked by heating for 30 minutes
r` at a temperature of 160C. in a compression mold. The cross-linked products
' have the following physical properties:
;
,:
~ .
. ~
.;
'`'
D - 8 -
3 -
Example ~ Example ~
Air Oven Air Oven
Aged Aged
- 70 hrs.@ 70 hrs.@
Original 150C. Original 150C.
Tensile strength 1850 2125 1540 1900
(p s i )
% Elongation 290 200 300 200
100% Modulus 900 1385 700 1175
10 (p.s.i.)
: Shore A Hardness 77 83 72 81
% Compression Set - 70 - 58
~ (ASTM D-395,
! Method B)
Mooney scorch (at 121C.)
(ASTM D-1646-68)
Minimum visc~osity38 34
Time in minutes for 3
point rise in viscosity5.3 4.5
Time in minutes for 5
point rise in viscosity6.1 5.2
Time in minutes for 10
point rise in viscosity7.2 6.2
Examples~
Ingredients ~ Parts
Example~ Example ;~
Chlorinated polyethylene
(36% chlorine by weight) 100
Chlorinated polyethylene
30 (48% chlorine by weight) - 100
Carbon black (reinforcing filler) 85 85
Magnesium oxide 4 4
Dioctyl adipate (plasticizer and 15 15
softener)
Polymerized 1,2-dihydro-2,2,4-
trimethylquinoline (antioxidant) 0.1 0.1
Di-ortho-tolylguanidine
2,5-Dimercapto-1,3,4-thiadiazole1.25 1.25
The above formulations are cross-linked by heating for
30 minutes at a temperature of 160C. in a steam autoclave. The
cross-linked products have the following physical properties:
_ ~_
Example{~ Example ;'
Tensile strength (p.s.i.) 2010 2475
% Elongation 200 170
100% Modulus (p.s.i.) 1635 2315
Shore A Bardness 86 91
% Compression Set (ASTM D-395,66 82
Method B)
Mooney scorch tat 121C.)
(ASTM D 1646-68)
Minimum viscosity 69 56
Time in minutes for 3 point
~; rise in viscosity 14.0 12.3
;, Time in minutes for 5 point
rise in viscosity 20.0 15.2
Time in minutes for 10 point
rise in viscosity 25.0 21.0
Example ~
Ingredients Parts
Epichlorohydrin homopolymer 50
Hycar 1053 (low molecular weight medium
acrylonitrile-butadiene copolymer
manufactured by B. F. Goodrich) 50
DS-207 (Trademark for a mixture of dibasic
lead salts of C16-Cl fatty acids sold
by National Lead Co.~ (process aid) 0.5
Zinc stearate (process aid) 0.5
Carbon black (reinforcing filler) 45
Magnesium oxide 1.5
Zinc oxide* 5
Octylated diphenylamine (antioxidant)
Benzothiazyl disulfide* 0.5
Sulfur* 1.25
2,5-dimercapto-1,3,4-thiadiazole 0.625
Tetramethylammonium bromide 1.0
*Curing agents for Hycar 1053
The formulation is cross-linked by heating for 30
minutes at a temperature of 160C. in a compression mold. The
cross-linked product has the following physical properties:
Tensile strength (p.s.i.) 3150
% Elongation 400
- 100% Modulus (p.s.i.) 585
Shore A Hardness 67
:'
g 7
, Example ~}
Ingredients Parts
Epichlorohydrin-ethylene oxide copolymer
(26% Cl) 100
Stearic acid (process aid)
10 2,5-Dimercapto-1,3,4-thiadiazole 1.5
Tributylamine 5
The above formulation is cross-linked by heating at
160C. for thirty minutes in an oscillating disc Rheometer
(American Standard Testing Method D2705-68T). The properties
measured are:
Minimum torque (inch-pounds) 6
Torque after 30 minutes (inch-pounds) 35
Torque after 60 minutes (inch-pounds) 40
Examples ~ r
Parts
lc~}~ x mple
Chlorinated polyethylene (36~
chlorine by weight) 100 100
Carbon black (reinforcing filler) 85 85
Dioctyl phthalate (plasticizer 20 20
and softener)
Magnesium oxide 5 5
2,5-Dimercapto-1,3,4-thiadiazole 1.5 1.5
Diphenylguanidine 1.5
30 Butyraldehyde-aniline reaction
product - 1.5
The above formulations are cross-linked by heating at
160C. for thirty minutes in a compression mold. The physical
properties of the cross-linked products are:
' -- a~--
Example ~ Example
Tensile strength (p.s.i.) 2070 2120
% Elongation 250 240
100% Modulus (p.s.i.) 1100 1250
Shore A ~ardness 80 81
~0
Example ~-
!' Ingredients Parts
Poly(vinyl chloride) 100
Santocizer 160 (phthalate ester
10 plasticizer sold by Monsanto) 40
Ba-Cd 1203 (coprecipitated Ba-Cd
soap stabilizer so]d by Ferro Corp.) 1.2
Calcium carbonate 20
2,5-dimercapto-1,3,4-thiadiazole 1.2
Butyraldehyde-aniline reaction
; product
The above formulation is heated at 135C. for thirty
minutes in an oscillating disc Rheometer (American Standard
Testing Method D2705-68T). Satisfactory cross-linking is obtained
without noticeable discoloration.
Example ~
Ingredients Parts
Copolymers of vinylidene fluoride
and hexafluoropropylene 100
Calcium oxide 5
Di-ortho-tolylguanidine 3
2,5-dimercapto-1,3,4-thiadiazole 2
The above formulation is heated at 160C. for thirty
minutes in an oscillating disc Rheometer (American Standard
Testing Method D2705-68T). Satisfactory cross-linking is obtained.
~-l3
Examples 14 15
These examples illustrate the pre-reaction of 2,5-di-
mercapto-1,3,4-thiadiazole with an organic basic material. The
reaction product is then used to cross-link a saturated, halogen-
containing polymer.
.,~ /~
_ ~_
-L~ L~
A mixture of 15 grams (0.1 mole) 2,5-dimercapto-1,3,4-
thiadiazole and 37 grams (0.2 mole) tributylamine in 200 ml tetra-
hydrofuran is heated at 45C. for 20 minutes. A yellow precipi-
tate results which is separated from the solution by crystalliza-
tion, filtered and washed with methylene chloride. The product
is dried overnight in a vacuum oven at 50C. and a pressure of
about 18 mm mercury. Analysis of the product indicates a bis
salt.
The reaction product obtained above is used to cross-
link an epichlorohydrin-ethylene oxide copolymer by formulating
as follows:
Ingredients Parts
~d ~3
~ Example ~ Example
Epichlorohydrin-ethylene oxide
copolymer(26~ Cl) 100 100
Stearic acid (process aid)
Barium carbonate - 7.5
Reaction product of 2,5-dimercapto-
1,3,4-thiadiazole and tributylamine 5.2 5.2
The above formulations are cross-linked by heating at
160C. for thirty minutes in an oscillating disc Rheometer
(American Standard Testing Method D2705-68T). The properties
measured are:
~ ~3
Example ~ Example ~-
Minimum torque (inch-pounds) 7 10
Torque after 30 minutes tinch-pounds) 48 80
Torque after 60 minutes (inch-pounds) 50 81
445
Example 1~
The concentrate of 2,5-dimercapto-1,3,4-thiadiazole in stearic
acid described in Example l was used in this example. Ingredients were
added to and compounded in a Farrel size "B" Banbury mixer in the order
listed.
Ingredients Parts
Chlorinated polyethylene
(36% chlorine by weight) 100
r Carbon black (reinforcing
filler) 85
Dioctyl adipate (plasticizer and
softener) 15
Polymerized 1,2-dihydro-2,2,4-
trimethylquinoline (antioxidant) 0.1
Di-or~ho-tolylguanidine 4.8
2,5-Dimercapto-1,3,4-thiadiazole 1.25
The above formulation was cross-linked by heating for 30 minutes
at a temperature of 160C. in a steam autoclave. The cross-linked product
had the following physical properties:
Tensile strength ~p.s.i.) 1950
% Elongation 220
100% Modulus ~p.s~i.) 1550
Shore A Hardness 86
% Compression Set (ASTM
D-395, Method B) 72
Mooney scorch (at 121C.)
(ASTM D 1646-68)
Minimum viscosity 70
Time in minutes for 3 point rise
in viscosity 16.0
Time in minutes for 5 point rise
in viscosity 23.0
Time in minutes for 10 point rise
`~ in viscosity 29.0
-~S -
Z~ 5
j5 ~7
pl es ~ r~ ~
These examples illustrate the cross-linking of chlorinated
polyethylene using various amine salts of 2,5-dimercapto-1,3,4-thiadiazole.
Ingredients -t~ r
Chlorinated polyethylene
(36% chlorine by weight) 100100 100
Semi-reinforcing furnace black 80 80 80
Polymeric plasticizer 20 20 20
Dioctyl adipate (plasticizer) 10 10 10
Magnesium oxide 4 4 4
Mono(dicyclohexylammonium)-1,3,4-
thiadiazole-5-thiol-2-thioate 2.64
Bis(dibutylammonium)-1,3,4-thiadiazole-
2,5-dithioatemonohydrate - 3.28
Mono(2,2'-diethyldihexylammonium)-
1,3~4~thiadiazole-2,5-dithioate - - 3.12
The above formulations are cross-linked by heating for twelve
minutes at 166C. in an oscillating disc rheometer.
~ ~ J6
Minimum Torque (inch-lbs.) 12 10 9
Torque after 6 minutes 41 38 40
Torque after 12 minutes 43 40 47
/,p_~l
Examples 2~
These examples illustrate the cross-linking of various saturated
halogenated polymers in accordance with this invention.
R 5
j~ ~q ~o
~Example ~ Example ~ Example ~ Example i!~
~ Ingredients a b ca b c a b a b
_
Chlorinated polyethylene
36% chlorine by weightlO0 100100
Polyvinyl chloride - - -100 lO0 lO0
. Chlorosulfonated
polyethylene - - - - - - lO0 100
Epichlorohydrin
; homopolymer - - - _ _ - - 100 lO0
Alkyl phthalate
plasticizer - - - 40 40 40
Stearic acid
(processing aid) - - - - - - - - 3 3
Semi-reinforcing
furnace black 80 80 80 - - - 40 40
- Fast extruding
furnace black - - - - - - - _ 50 50
Aromatic processing
aid 20 20 20
Polymeric plasticizer lO lO lO
Dioctyl adipate
~plasti¢izer) lO lO lO
Barium-Cadmium Complex
(stabilizer) - - - l l - - - - -
Magnesium oxide 5 5 5
Calciwn hydroxide - - - lO lO - - - 4
Calcium carbonate - - - - - - 10
2,5-Dimercapto-
1,3,4-thiadiazole 2 2 2 - 2 21.5 21.5 2
Dicyclohexylamine
(pl~ 3.1, b.p. 256) - - 2 5 5 5 2 2 l 5
`:: Aniline-butyraldehyde
condensate - 2 - - - -
Aniline-acetaldehyde-
butyraldehyde
condensate 2 - - - - -
The above formulations are heated at the temperature recited be-
low in an oscillating disc rheometer.
. . .
s ~
Example ~r Example ~i- Example-~2~ Example ~~
a b c a b c a b a b
Temperature, C. 182 182 182182 182 160 149160 149 160
Minimum Torque
(inch-lbs.) 11 11 13 6 - 46 50 - 22 15
Maximum Torque
(inch-lbs.) 55 56 73 a 62 92 100 76 136147
Time to 90% cure -
minutes 3 3 6N.C. 1 4 50 0.2 9.51.8
a = no increase in torque over a period of 30 minutes.
~'
