Note: Descriptions are shown in the official language in which they were submitted.
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C-9433
SUBSTITUTED 5-AMIDOTETRAZOLES AS BLOWING AGENTS
IN THE PRODUCTION OF CELLULAR THERMOPLASTIC
OR RUBBER MATERIALS
This invention is related to blowing agents
for cellular or plastic foams. More particularly, the
invention is related to selected tetrazole compounds
used as blowing agents in the production of foamed
plastics.
The use of blowing agents in the manufacture
of cellular or foamed synthetic plastic products is
well established. A blowing agent is a chemical
compound which decomposes on heating to a specific
temperature, to yield a vapor or gas or mixture of
l; vapors and gases. In use, the blowing agent is
incorporated in the thermoplastic material at a
temperature below the decomposition temperature of the
blowing agent and the mixture subsequently heated to a
temperature above the decomposition temperature of the
blowing agent whereupon the blowing agent decomposes to
liberate a gas or vapor which forms small voidQ within
the thermoplastic material. It is, of course, of
importance that the blowing agent be finely and
homogeneously dispersed within the thermoplastic
material.
An important characteristic of a blowing
agent i8 the temperature at which it decomposes to
liberate gas or vapor ~ince this temperature limits the
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temperature at which other operations may be performed
on the thermoplastic material after incorporation of
the blowing agent but before actual formation of the
cellular product. It is, therefore, often of
convenience to employ a blowing agent having a
relatively high temperature of decomposition, this
being especially the case when forming cellular
products of thermoplastic material having relatively
high fusion temperatures.
Tetrazole compounds have been previously
employed as blowing agents for plastic materials. For
example, 5-cyanovinyltetrazoles are described as being
suitable for blowing agents in U.S. Patent 3,338,915
issued August 29, 1967 to M. Brown.
lS U.S. Patent No. 3,366,581, issued January 30,
1968 to R. A. Reed et al teaches the use of
5-hydroxytetrazole as a high temperature blowing agent
for thermoplastic resins including polyolefins,
polyamides, acrylonitrile-butadiene-styrene resins, and
high temperature silicone rubbers.
The ammonium salt of 5-azidotetrazole is
useful as a blowing agent for producing any of the
polymeric materials conventionally used in forming
cellular products according to U.S. Patent No.
3,374,188, issued March 19, 1968 to F. D. Marsh et al.
Aliphatic or aromatic substituents on the
5-position of the tetrazole rings are taught in U.S.
Patent 3,442,829, issued May 6, 1969 to L. D. Moore et
al as suitable blowing agents for a wide variety of
rubbers and thermoplastic materials. Commercially
5-phenyltetrazole has been employed extensively in
producing cellular thermoplastic materials.
In addition, tetrazole metallic salts of Zn,
Ba, Ca, Pb, and Al have been described as suitable
blowing agents for polymers such as polycarbonates and
polysulfone in U.S. 3,873,477, issued March 25, 1975 to
1 337868
W. Beck et al; as well as the 5-sulfonylalkylene
substituted tetrazoles taught in U.S. Patent No.
4,126,590 issued November 21, 1978 to H. Illy.
Now it has been found that selected
substituted 5-amidotetrazoles are highly effective
blowing agents for use at high temperatures in the
production of cellular thermoplastic materials from
resins such as polycarbonates. The novel blowing
agents of the present invention are compounds of the
formula:
N N \ ~ G
~ ~ C A (I)
N N~
wherein A represents NHX, NRR' or OR
X represents H or a lower alkyl group,
R represents a lower alkyl group, and
R' represents a lower alkyl group.
More in detail, the novel blowing agents of
~0 the present invention are substituted 5-amido
tetrazoles having thermal decomposition temperatures
above about 250C which provide copious amounts of
gas without the formation of ammonia as an undesired
contaminant.
Novel blowing agents of formula I include
5-amidotetrazole compounds in which A represents NHX
where X can be H or a lower alkyl group. In these
compounds which are also known as N'-alkyl-N-(tetrazol-
5-yl) ureas, the lower alkyl groups have from 1 to
about 6 carbon atoms. Suitable as blowing agents are
5-amidotetrazole compounds in which A is, for example,
an amino, methylamino, ethylamino, propylamino,
isopropylamino, butylamino, isobutylamino,
secbutylamino, tertbutylamino, pentylamino,
neopentylamino, or hexylamino group.
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N'-alkyl-N-(tetrazol-5-yl) ureas can be
prepared by any suitable method including the reaction
of 5-aminotetrazole with an alkylisocyanate. The
reaction preferably employs a solvent such as
dimethylformamide or acetonitrile.
Novel compounds which are employed as blowing
agents for thermoplastic materials are those of formula
I in which A represents NRR' where R and R' are
individually selected alkyl radicals. Suitably
represented by R and R' are alkyl radicals having from
1 to about 6 carbon atoms. The novel compounds include
those in which A represents, for example, a
dimethylamino, ethylmethylamino, diethylamino,
diisopropylamino, ethylbutylamino, dibutylamino,
disecbutylamino, ditertbutylamino, dipentylamino,
dineopentylamino, hexylmethylamino, or dihexylamino
group.
The novel dialkyl amino derivatives are
prepared by the reaction of 5-aminotetrazole with a
dialkylcarbamoyl halide. The reaction is preferably
carried out under reflux in a solvent such as
dimethylformamide or acetonitrile and the like. In
addition, the reaction mixture may include a halogen
acid scavenger, for example, a trialkylamine or an
inorganic base such as an alkali metal hydroxide or
carbonate compound.
Blowing agents of formula 1 in which A
represents the group OR are tetrazol-5-yl carbamic acid
esters in which R is a lower alkyl radical having from
1 to about 6 carbon atoms. Suitable ester groups
include those in which R is a methyl, ethyl, propyl,
isopropyl, butyl, or secbutyl tertbutyl, pentyl,
neopentyl or hexyl radical.
The novel blowing agents of the present
invention are used in the production of cellular
products of thermoplastic or rubber materials which
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allow processing at elevated temperatures. For
example, they may be used with polyolefins;
acrylonitrile - butadiene - styrene resins; polyvinyl
halides; polyacrylates; polyamides; polyetherimides;
polycarbonates; polyphenylene oxides; polybutylene
terphthalate; polyphenylene sulfides; polysulfones;
polysulfonates; rubbers including silicone rubbers,
polybutadiene and polyisoprene, and the like, as well
as copolymers and graft polymers. The blowing agents
of this invention are especially useful, as indicated,
with polymers and copolymers that have high processing
temperatures such as polycarbonates, polyphenylene
sulfides and polybutylene phthalate.
The substituted 5-amidotetrazole blowing
agents may be employed by incorporating a small, but
effective, blowing amount of the material into a
gas-expandable polymer. The amount of such material
will vary, depending on the polymer foam density
desired and other processing and temperature factors
which are well known. However, typically, the
compounds may be employed by incorporating, for
example, from about 0.10 to about 15 percent by weight
of the compound as a blowing agent; preferably, from
about 0.15 to 5.0 percent, in preparing rigid or
structural foam products such as those of polycarbonate
resins. The blowing agents may be employed in various
particle sizes, and alone or in combination with other
blowing agents, stabilizers, antioxidants, fillers,
plasticizers, cross-linXing agents, dyes, pigments,
carbon and other additives employed in polymeric
compositions.
The novel blowing agents of the present
invention may be admixed, for example, with a
polycarbonate homopolymer in a Banbury mixer, and the
mixed mass milled into a large sheet or other form and
subsequently processed into pellets. The polycarbonate
homopolymer containing the blowing agent may then be
placed or extruded into a multicavity mold and
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preheated to a temperature above the blowing
temperature of the blowing agent for a period of time
to produce a rigid structural foam polycarbonate
product. Since only inert gases such as nitrogen gas
S are produced in the process, no detrimental effects on
the polycarbonate foam product result.
High temperature processing polymer foam
products are also prepared by casting, molding or
injection molding, such as, for example, by preparing
the products by heating the gas-expandable polymer
during the injection-molding of the polymer with an
injection machine at a temperature above the
compounding temperature of the product.
To further illustrate the present invention,
the following examples are given with no intention of
being limited thereby. All parts and percentages are
by weight unless otherwise stated.
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EXAMPLE 1
N-(Tetrazol-5-yl) urea
5-Aminotetrazole hydrate (10.3 g, 0.1 mole)
was slurried into 150 ml of water containing 10 ml of
37 percent HCl. A solution of potassium cyanate (10 g,
0.12 mole) was added at ambient temperature over the
course of one hour. When a slight exotherm began, the
solution was cooled to 10C. The mixture was stirred
two hours, filtered and recrystallized from ethanol.
Melting point: >305C.
Elemental analysis Calc.: C, 18.76; H, 3.15; N, 65.61
Found: C, 18.72; H, 3.35; N, 65.85
EXAMPLE 2
N',N'-Dimethyl-N-(tetrazol-5-yl) urea
Anhydrous 5-aminotetrazole (8.5 g, 0.1 mole)
was slurried in 150 ml of acetonitrile. On the
addition of triethylamine (10 g, 0.1 mole), the solids
dissolved. Dimethylcarbamoyl chloride (13 g, 0.12
mole) was added at once with no exotherm. The mixture
was refluxed two hours with the formation of white
solids. After cooling, the material was added to cold
water to remove by-product triethylamine
hydrochloride. The water insoluble material was
collected.
Melting point: 294-300C.
Elemental analysis Calc.: C, 30.76; H, 5.17; N, 53.82
Found: C, 30.44; H, 5.05; N, 52.13
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EXAMPLE 3
N'-Methyl-N-(Tetrazol-5-yl) Urea
5-Aminotetrazole (5.5 g, 0.065 mole) was
dissolved in 75 ml of DMF. On the addition of
methylisocyanate (5 g) the temperature began to slowly
rise to 40C with the formation of a white solid.
The solution was heated for 90 minutes at 100C and
on cooling, poured into cold water. The resulting
white solid was filtered, water washed and dried to
give 8.3 g of product which softened at 264-267C but
was not melted completely at 305C.
Analysis for C3H6N6O: Calc.: C, 25.35; H, 4.25; N, 59.14
Found: C, 25.55: H, 4.20; N, 59.59
EXAMPLE 4
N-(Tetrazol-5-yl) ethyl carbamate
5-Aminotetrazole (42.5 g, 0.5 mole) was
slurried in 700 ml of acetonitrile. On addition of
triethylamine (70 ml, 0.5 mole), most of the tetrazole
dissolved. Ethylchloroformate (60 ml, 0.61 mole) was
slowly added as the mixture exothermed to 65C. The
resulting thick, white slurry was refluxed two hours,
cooled and poured into 900 ml of cold water. The
insoluble product was filtered off and washed with water
and ether. On drying, 71.2 g of product (91 percent)
was obtained with a melting point of 259-263C.
Elemental analysis Calc.: C, 30.58: H, 4.49; N, 44.58
Found: C, 30.33: H, 4.34: N, 44.45
EXAMPLES 5-8
The decomposition temperatures of the novel
30 blowing agents prepared in EXAMPLES 1-4 were determined
by differential scanning colorimetry. The results are
recorded in TABLE I below.
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Comparative Example A
The decomposition temperature of 5-phenyl
tetrazole (Expandex~ 5PT, a product of Olin Corporation)
a commercial blowing agent, was determined by the same
procedure as used in EXAMPLES 5-8. The results are
given in TABLE I below.
TABLE I
Decomposition
Example Compound Temperature C
N-(Tetrazol-5-yl) urea >315
6 N',N'-Dimethyl-N-
(tetrazol-5-yl) urea 295
7 N'Methyl-N-(Tetrazol-5-yl) 264
Urea
8 N-(Tetrazol-5-yl) ethyl
carbamate 259
Comp. A 5-Phenyltetrazole 218
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EXAMPLES 9-12
The tetrazole compounds (ea 0.25 g) of
EXAMPLES 1, 2, 3land 4 were each separately blended
with 4-6 grams of dioctylphthalate and placed in a test
tube connected to a gas buret. The test tube was
heated in a sand bath until decomposition occurred.
The gas yields are given in TABLE II below. Nitrogen
compounds in the decomposition gases for EXAMPLES 9 and
12 were identified by gas chromatography.
Comparative Example B
The procedure of EXAMPLES 9-12 was carried
out exactly using 5-phenyltetrazole as the blowing
agent. The results are give in TABLE II below.
TABLE II
Gas Yields and Compositions
Gas
Yield N-containing
Example Blowing Agent (ml/g) gases
9 N-(Tetrazol-5-yl) urea 361 N2
~0 10 N',N'-Dimethyl-N-
(tetrazol-5-yl) urea 215
11 N'-Methyl-N-(Tetrazol 183
-5-yl) Urea
12 N-(Tetrazol-5-yl) ethyl
carbamate 191 N2
Comp. B 5-Phenyltetrazole 175 N2
