Note: Descriptions are shown in the official language in which they were submitted.
v~
BACKGROUN~ OF THE INVENTION
1. Field of the Invention
The present invention relates to stable graft
polymer dispersions having low viscosity and containing less
toxic by-products than found in commercially available gxaft
polymer dispersions~ More particularly, the inventlon
relates to graft polymer dispersions prepared by the ln SltU
polymerization of an ethylenically unsaturated monolner or
mixture of monomers in a polyol in the presence of certain
l.iquid free radical azo catalysts.
2. Prior Art
Graft polymer dispersions prepared by the ln situ
polymerization of an ethylenically unsatura-ted monomer or
mi.xture of monomers in a polyol in the presence of a free
radical catalyst and the use thereof in the preparation of
polyurethanes are weIl known in the art as evidenced by U.S.
Patent Nos. 3,652,659; 3,875,258; 3,950,317, and Reissue .
Patent Nos. 28,715 and 29,014. While these patents disclose
various methods of preparing graft polymer dispersions, the
; most preferred mèthod involves the simultaneous addition at :
a steady rate of a stream of monomer and a stream of catalyst
dispersed in a portion of polyol to a reactor containing the
remaining portion of the polyol. Numerous free radical ~.
catalysts are taught to be useful in the process described
in the above patents with azobis(isQbutyronitrile) generally
.
2 ~
described as the catalyst of preference. While azobis-
(isobutyronitrile) is a most suitable catalyst for the
polymerization reaction, it is a solid at room temperature
and only slightly soluble in the polyol and as a result
thereof requires that it be continually stirred with the
polyol so that it may be introduced into the reaction system
in equally measured amounts. Moreover, when azobis(iso-
butyronitrile) decomposes during the reaction, one of its
decomposition products, namely tetramethylsuccinonitrile, is
an extremely toxic substance which is exceptionally difficult
if not impossible to remove in toto from the graft polymer
dispersion. The present invention relates to an improved
process for the preparation of graft polymer dispersions
comprising employing as the free radical catalyst certain
liquid azo compounds.
SUMMARY OF THE INVENTION
The present invention relates to the preparation
of graft polymer dispersions by the ln situ polymerization
in the presence of a free radical catalyst of an ethyl-
enically unsaturated monomer or mixture of monomers in aliquid polyol employing as the free radical catalyst a
liquid unsymmetrically-substi-tuted azo compound having a
ten hour half-life between 55C and 100C and represented by
the formula:
Rl .
R-N=N-C-R2
z
wherein
R is a lower alkyl of 1-6 carbon atoms and
--3--
46~
Rl is selected from alkyl of 1-20 carbon atoms, phenalkyl
of 7-12 carbon atoms, cycloalkyl of 3-12 carbon atoms,
a heterocyclo radical wherein the hetero atoms is 0, S
or N and together with R2 can form an alkylene biradical
o from 2 to 16 carbon atoms, and can be substituted by
Z, R2 is R, or phenyl and Z is H, CN, S-R2 or O-R2.
The resulting dispersions have viscosities generally equal
to or better than those attained employing azobis(iso-
butyronitrile), are more easily prepared since the catalysts
are liquid and do not contain toxic decomposition products.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In accordance with the process of the subject
invention, an ethylenically unsaturated monomer or mixture
of monomers is polymerized in a polyol in the presence of a
liquid free radical catalyst having the formula:
Rl1
R-N=N- f -R2
z
wherein
R is a lower alkyl of 1-6 carbon atoms and
Rl is selected from alkyl of 1~20 carbon atoms, phenalkyl
of 7-12 carbon atoms, cycloalkyl of 3-12 carbon atoms,
a heterocyclo radical wherein the hetero atoms is 0, S
or N and together wi-th R2 can form an alkylene biradical
of from 2 to 16 carbon atoms, and can be substituted by
Z, R2 is R, or phenyl and Z is H, CN, S-R2 or O-R2.
6~
Representative catalysts used in the subject invention
include
2-t-butylazo-2~cyano-4-methoxy-4-methylpentane
2-t-butylazo-2-cyano-4-methylpentane
2-t-amylazo~2-cyano-4-methylpentane
1-t-butylazo-1-cyanocyclohexane
2-t-butylaæo-2-cyanobutane
1-t-amylazo-1-cyanocyclohexane
2-t-butylazoisobutyronitrile
1-t-butylazo-1-methoxycyclohexane
4-t-butylazo-2,4-dimethoxyoctane
1-t-butylazo-1-phenylcyclohexane
2-isopropylazo-2-cyanopropane
1-sec-butylazo-1-cyanocyclohexane
The preparation of many of these catalys-ts is described in
U.S. Patent No. 4,007,165. In the process of the subject
invention, there is generally employed from about 1% to 10%
by weight of the catalyst based on the weight of the
monomer(s).
The polyols which may be employed in the present
invention are well known in the art. Both conventional
polyols essentially free from ethylenic unsaturation such as
those described in U.S. Reissue Patent No. 28,715 and un
saturated polyols such as those discribed in U.S. Patent
No. 3,652,659 and ~eissue 29,014 may be employed in the
invention. Representative polyols essentially free from
ethylenic unsaturation which may be employed in the present
invention are well known in the art. They are often prepared
6~
by the catalytic condensation of an alkylene oxide or mixture
of alkylene oxides either simultaneously or sequentially
with an organic compound having at least two active hydrogen
atoms such as evidenced by U.S. Patent Nos. 1,922,459;
3,190,927, and 3,346,557.
Representative polyols include polyhydroxyl-
containing polyesters, polyalkylene polyether polyols,
polyhydroxy-terminated polyuxethane polymers, polyhydroxyl-
containing phosphorus compounds, and alkylene oxide adducts
of polyhydric polythioesters, polyacetals, aliphatic polyols
and thiols, ammonia, and amines including aromatic, aliphatic,
and heterocyclic amines, as well as mixtures thereof.
Alkylene oxide adducts of compounds which contain two or
more different groups within the above-defined classes may
also be used such as amino alcohols which contain an amino
group and a hydroxyl group. Also alkylene oxide adducts of
compounds which contain one -SH group and one -OH group as
well as those which contain an amino group and a -SH group
may be used. Generally, the equivalent weight of the polyols
will vary from 100 to 10,000, preferably from 1000 to 3000.
Any suitable hydroxy-terminated polyester may be
used such as are obtained, for example, from polycarboxylic
acids and polyhydric alcohols. Any suitable polycarboxylic
acid may be used such as oxalic acid, malonic acid, succinic
acid, glutaric acid, adipic acid, pimelic acid, suberic
acid, azelaic acid, sebacic acid, brassylic acid, thapsic
acid, maleic acid, fumaric acid, glutaconic acid, ~-hydro-
muconic acid, ~-hydromuconic acid, ~-butyl-a-ethyl-glutaric
~ ~ .
4~
acid, ~ diethylsuccinic acid, isophthalic acid, tere-
phthalic acid, hemimellitic acid, and 1,4-cyclohexane-
dicarboxylic acid. Any suitable polyhydric alcohol, in-
cluding both aliphatic and aromatic, may be used such as
ethylene glycol, 1,3-propylene glycol, 1,2-propylene glycol,
1,4-butanediol, 1,3-butanediol, 1,2-butylene glycol, 1,5-
pentanediol, 1,4-pentanediol, 1,3-pentanediol, 1,6-hexane-
diol, 1,7-heptanediol, glycerol, l,l,l-trimethylolpropane,
l,l,l-trimethylolethane, hexane-1,2,6 triol, ~-methyl
glucoside, pentaerythritol, and sorbitol. Also included
within the term "polyhydric alcohol" are compounds derived
from phenol such as 2,2-bis(4-hydroxyphenyl)propane, com-
monly known as Bisphenol A.
Any suitable polyalkylene polyether polyol may be
used such as the polymeri2ation product of an alkylene oxide
or of an alkylene oxide with a polyhydric alcohol. Any
suitable polyhydric alcohol may be used such as those
disclosed above for use in the preparation of the hydroxy-
terminated polyesters. Any suitable alkylene oxide may be
used such as ethylene oxide, propylene oxide, butylene
oxide, amylene oxide, and mix-tures of these oxides. The
polyalkylene polyether polyols may be prepared from other
starting materials such as tetrahydrofuran and alkylene
oxide-tetrahydrofuran mixtures; epihalohydrins such as
epichlorohydrin; as well as aralkylene oxides such as styrene
oxide. The polyalkylene polyether polyols may have ei-ther
primary or secondary hydroxyl groups and, preferably, are
polyethers prepared from alkylenè oxides having from two to
6~
six carbon atoms such as polyethylene ether glycols, poly-
propylene ether glycols, and polybutylene ether glycols.
The polyalkylene polyether polyols may be pxepared by any
known process such as, for example, the process disclosed by
Wurt~ in 1859 and Encyclopedia Of Chemical Technology, Vol.
7, pp. 257-262, published by Interscience Publishers, Inc.
(1951) or in U.S. Patent No. 1,922,459. Polyethers which
are preferred include the alkylene oxide adclition products
of trimethylolpropane, glycerine, pentaerythritol, sucrose,
sorbitol, propylene glycol, and 2,2-(4,4'-hydroxyphenyl3-
propane and blends thereof having equivalent weights of from
100 to 5000.
Suitable polyhydric polythioethers which may be
condensed with alkylene oxides include the condensation
product of thiodiglycol or the reaction product of a dihydric
alcohol such as is disclosed above for the preparation of
the hydroxyl-containing polyesters with any other suitable
thioether glycol.
The hydroxyl-containing polyester may also be a
polyester amide such as is obtained by including some amine
or amino alcohol in the reactants for the preparation of the
polyesters. Thus, polyester amides may be obtained by
condensing an amino alcohol such as ethanolamine with the
polycarboxylic acids set forth above or they may be made
using the same components that make up the hydroxyl~
containing polyester with only a portion of the components
being a diamine such as ethylene diamine.
Polyhydroxyl-containing phosphorus compounds which
may be used include those compounds disclosed in U.S. Patent
69
No. 3,639,542. Preferred polyhydroxyl-containing phosphorus
compounds are prepared frorn alkylene oxides and acids of
phosphorus having a P2O5 equivalency of from about 72% to
about 95%.
Suitable polyacetals which may be condensed with
alkylene oxides include the reaction product of formaldehyde
or other suitable aldehyde with a dihydric alcohol or an
alkylene oxide such as those disclosed above.
Suitable aliphatic thiols which may be condensed
wi-th alkylene oxides include alkanethiols containing at
least two -SH groups such as 1,2-ethanedi-thiol, 1,2-propane
dithiol, 1,3-propanedithiol, and 1,6-hexanedithiol; alkene
thiols such as 2-butene-1,4-dithiol; and alkyne thiols such
as 3-hexyne-1,6-dithiol.
Suitable amines which may be condensed with
a}kylene oxides include aromatic amines such as aniline,
o-chloroaniline, p-aminoaniline, 1,5-diaminonaphthalene,
methylene dianiline, the condensation products of aniline
and formaldehyde, and 2,4-diaminotoluene; aliphatic amines
such as methylamine, triisopropanolamine, ethylenediamine,
1,3-propylenediamine, 1,4-butylenediamine, and 1,3-~utylene-
diamine.
Also, polyols containing ester groups can be
employed in the subject invention. These polyols are
prepared by the reaction of an alkylene oxide with an
organic dicarboxylic acid anhydride and a compound containing
reactive hydrogen atoms. A more comprehensive discussion of
-these polyols and their method of preparation can be found
in U.S. Patents Nos. 3,585,185; 3,639,541 and 3,639,542.
_g_
~.~a~
The unsaturated polyols which may be employed in
the present invention may be prepared by the reaction of any
conventional polyol such as those described above with an
organic compound having both ethylenic unsaturation and a
hydroxyl, carboxyl, anhydride, or epoxy group or they may be
prepared by employing an organic compound having both
ethylenic unsaturation and a hydroxyl, carboxyl, anhydride,
or epoxy group as a reactant in the preparation of the
conventional polyol. Representative of such organic com
pounds include unsaturated mono- and polycarboxylic acids
and anhydrides such as maleic acid and anhydride, fumaric
acid and anhydride, crotonic acid and anhydride, propenyl
su,ccinic anhydride, and halogenated maleic acids and
anhydrides, unsaturated polyhydric alcohols such as 2-butene
1,4-diol, glycerol allyl ether, trimethylolpropane allyl
ether, pentaerythritol allyl ether, pentaerythritol vinyl
ether, pentaery-thritol diallyl ether, and l-butene-3,4-diol,
unsaturated epoxides such as l-vinylcyclohexane-3,4-epoxide,
butadiene monoxide, vinyl glycidyl ether(l-vinyloxy-2,3-epoxy
propane), glycidyl methacrylate and 3-allyloxypropylene
oxide (allyl glycidyl ether). If a polycarboxylic acid or
anhydride is employed to incorporate unsaturation into the
polyols, it is then necessary to react the unsaturated
polyol with an alkylene oxide preferably ethylene or
propylene oxide, to replace the carboxyl groups with hydroxyl
groups prior to employment in the present invention. The
amount of alkylene oxide employed is such to reduce the acid
number of the unsaturated polyol to about one or less.
--10~
6~
To prepare the unsaturated polyols of use in the
present invention, from about 0.05 mole to about 3.0 moles,
preferably from 0.30 mole to 1.50 moles, of said organic
compound per mole of polyol i5 employed. The preparation of
the unsaturated polyols employed in the present invention
follows conventional prior art procedures such as disclosed
in U.S. Patent No. 3,275,606 and U.S. Patent No. 3,280,077.
Generally, this requires a reaction at a temperature be-tween
0C. and 130C. Both acidic catalysts, such as Lewis ac:id
catalysts and basic catalysts such as alkali metal
hydroxides, may be used. In addition, a noncatalyzed re--
action may be used employing temperatures between 50C. and
2~0C
As mentioned above, the graft copolymers of the
invention are prepared by the ln situ polymerization in -the
above-described polyols of an ethylenically unsaturated
monomer or a mixture of ethylenically unsaturated monomers.
Representative ethylenically unsaturated monomers which may
be employed in the present invention include butadiene,
isoprene, l,4~pentadiene, 1,6-hexadiene, 1,7-octaAiene,
styrene, ~-methylstyrene, methylstyrene, 2,4-dimethylstyrene,
e-thylstyrene, isopropylstyrene, butylstyrene, phenylstyrene,
cyclohexylstyrene, benzylstyrene, and the like; substituted
styrenes such as chlorostyrene, 2,5-dichlorostyrene, bromo-
styrene, fluorostyrene, trifluoromethylstyrene, iodostyrene,
cyanostyrene, nitrostyrene, N,N-dimethylaminostyrene~
acetoxylstyrene, methyl 4~vinylbenzoate, pheno~ystyrene,
p-vinyl diphenyl sulfide, p~vinylphenyl oxide, and the like,
the acrylic and substituted acrylic monomers such as
acrylonitrile, acrylic acid, methacrylic acid, methylacrylate,
2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, methyl
methacrylate, cyclohexyl methacrylate, benzyl methac~ylate,
isopropyl methacrylate, octyl methacrylate, methacrylonitrile,
methyl ~-chloroacrylate, ethyl ~-ethoxyacrylate, methyl
~-acekaminoacrylate, butyl acrylate, 2-ethylhexyl acrylate,
phenyl acrylate, phenyl methacrylate, ~-chloroacrylonitrile,
N,N-dimethylacrylamide, N,N-dibenzylacrylamide, N-butyl-
acrylamide, methacrylyl formamide, and the like; the vinyl
~sters, vinyl ethers, vinyl ~etones, etc., such as vinyl
acetate, vinyl chloroacetate, vinyl alcohol, vinyl butyrate
isopropenyl acetate, vinyl formate, vinyl acrylate, vinyl
m~thacrylate, vinyl methoxyacetate, vinyl benzoate, vinyl
iodide, vinyltoluene, vinylnaphthalene, vinyl bromide, vinyl
fluoride, vinylidene bromide, l-chloro-l-fluoro-ethylene,
vinylidene fluoride, vinyl methyl ether, vinyl ethyl ether,
vinyl propyl ethers, vinyl butyl ethers, vinyl 2-ethylhexyl
ether, vinyl phenyl ether, vinyl 2-methoxyethyl ether,
methoxybutadiene, vinyl 2-butoxyethyl ether, 3,4-dihydro-
1,2-pyran, 2-butoxy-2'-vinyloxy diethyl ether, vinyl 2-ethyl-
mercaptoethyl ether, vinyl methyl ketone, vinyl ethyl ketone,
vinyl phosphonates such as bis~-chloroethyl) vinylphosphonate,
vinyl phenyl ketone, vinyl ethyl sulfide, vinyl ethyl sulone,
N-methyl-N-vinyl acetamide, N-vinyl-pyrrolidone, vinyl
imidazole, divinyl sulfide, divinyl sulfoxide, divinyl
sulfone/ sodium vinylsulfonate, methyl vinylsulfonate,
N-vinyl pyrrole, and the like; dimethyl fumarate, dimethyl
maleate, maleic acid, crotonic acid, fumaric acid, itaconic
-12-
acid, monomethyl itaconate, t-butylaminoethyl methacrylate,
dimethylaminoethyl methacrylate, glycidyl acrylate, allyl
alcohol, glycol monoesters of itacon:ic acid, dichloro-
butadiene, vinyl pyridine, and the like. Any o the known
polymerizable monomers can be used and the compounds listed
above are illustrative and not restrictive of the monomers
suitable for use in this invention.
The amount of ethylenically unsaturated monomer
employed in the polymerization reaction is generally from 1%
to 40%, preferably from 15% to 30~, based on the weight of
the graft polymer dispersion. The polymerization occurs at
a temperature between about 80C. and 170C., preferably
from 105C. to 135C.
In general the process of the subject invention is
carried out by blending the catalysts and a portion of the
polyol to form a homogeneous stream and simultaneously
adding at a steady rate this stream along with a stream of
an ethylenically unsaturated monomer or mixture of monomers
to a reactor containing the remaining portion of polyol. In
a preferred embodiment, the two streams are blended in a
static mixture just prior to being added to the polyols in
-the reactor as described more thorouyhly in U.S. Patent No.
3,950,317. As a general rule, the ca-talyst-polyol stream is
added to the reactor over a period slightly in excess of the
monomer stream. This is to assure more complete polymer-
ization of the monomer.
In the Examples that follow, the following polyols
are employed:
-13-
~ 6 ~
Polyol A - a polyol having a hydroxyl nu~ber of 33
and an oxyethylene content of 15% by
weight prepared by capp:Lng with ethylene
o~ide a propylene oxide,/allylglycidyl
ether heteric adduct of a mixture of
glycerine and propylene glycol
Polyol B - a polyol having a hydroxyl number of 50
and an oxyethylene content of 9% by
weight prepared by capping with ethylene
oxide a propylene oxide/allylglycidyl
ether heteric adduct of glycerine
Polyol C ~ a polyol having a hydroxyl number of 51
and an oxyethylene content of 9% by
weight prepared by capping with ethylene
oxide a propylene oxide adduct of
glycerine
Polyol D - a polyol having a hydroxyl number of 33
and an oxyethylene content of 15% by
weight prepared by capping with ethylene
oxide a propylene oxide adduct of a
mixture of glycerine and propylene
glycol
In the following examples, all parts are by weight
unless otherwise indicated.
-14
_XAMPLE I
A reaction vessel equipped with a thermometer,
stirrer, nitrogen source, inlet means and heat exchange
means was charged with 1655 parts oE Polyol A. Nitrogen was
bubbled through the polyol for about one hour. With stirring
and under a slight nitrogen flow, the charge was heated to
120C. A stream of a mixture of 803.5 parts of acrylonitrile
and 268 parts of styrene and a stream of 10.7 parts of
l-t-amylazo-l-cyanocyclohexane in 840 parts of Polyol A were
fed into a KENICS static mixer and continuously added to the
charge over a period of three hours at 120C. Upon
completion of the addition, the reaction mixture was main-
tained at 120C. for thirty minutes. The reaction mixture
was then stripped for one-half hour at 120C. under less
than ive millimeters of mercury. The stripped reaction
product was a liquid dispersion having a Brookfield
viscosity at 25C. of 3200 cps. and a hydroxyl number of
23.5.
EXAMPLE II
A reaction vessel equipped as described in Example
I was charged with 163.5 parts of Polyol A. Nitrogen was
bubbled through the polyol for about one hour. With stirrlng
and under a slight nitrogen flow, the charye was heated to
120QC. A stream of a mixture of 80.35 parts of acrylonitrile
and~26.8 parts of styrene and a stream of 1.07 parts of
1-t-butylazo-1-cyanocyclohexane in 84 parts of Polyol A were
fed into a KENICS static mixer and continuously added to the
charge over a period of ninety minutes at 120C. Upon
* Trademark
-15-
completion of the addition, the reaction mixture was main-
tained at 120C. for twenty minutes. The reaction mixture
was then stripped for one-half hour at 120C under less than
five millimeters of mercury. The stripped reac-tion product
was a liquid dispersion having a Brookfield viscosity at
25C. of 3100 cps. and a hydroxyl number o~ 23.
The above example was duplicated with the exception
that the catalyst employed was 2~t-butylazo~2-cyano~4-methoxy-
4-methylpentane. Results substantially as indicated above
are obtained.
EXAMPLES III - VIII
A series of graft polymer dispersions was prepared
employing various polyols, ethylenically unsa-turated monomers
and amounts thereof. In each preparation, l-t amylazo-l-
cyanocyclohexane was employed as the free-radical catalyst.
Details of the preparations as well as physical character-
istics of the resulting dispersions are presented as Table I
below.
-16-
9L6~
o ~
.,, ~ I o o o o ~ o
o o ~;o ~ ~ o
U2 ,, ~ ,~ ~ ~ ~ ,~
,~ tn r,~
~ ,,~
rn
rl~ rl
O
P~ o o
u~ t.
td ~ ~ t,~ t~r)
~ .
t t~ ~ t~ O
rtJ h t.~ 0 r~
rJ
V O ~ ~ o ~ .~
~1 ~ ~ d~ ~1 ~ dl ,, ~ 1` 0 0 0 0
a) h o tr) ,~ r~ o ~ ts~
rd P~ ~ t,~ ~ t~ r,~ i t.~l ~ t.~ rr~
E~ ~
~ æ ~ Z ~
~ ~ U~ ~ r~ ~ rJ~ ~ tn ~
r Q~ Ln o o u~ o ;
O ~ tv
1~ t.~1 t.~l tO ~I h
., O ~ tV ~ .
:~ ~ O ~ ON
~ r~ ~
V I I
~V
H H H ~ U~ :
X 1--1 ~ H H H ~K
~: ¦ H H ~ ~ * ~ K
.~ ~
- 1 7-
.
_ MPLE IX
A series of graft polymer dispersions was prepared
in the manner described in Example I. In each preparation
100 parts of Polyol B was employed along with 30 parts of a
3:1 weight mixture of acrylonitrile and sty:rene. The re-
actions were carried out in the presence of two parts of
various catalysts. In each instance, viscous graft polymer
dispersions were prepared.
The catalysts employed were as follows:
2~t-butylazo 2-cyano-4-methoxy~4-methylpentane
2-t-bu-tylazo-2-cyano-4-methylpentane
2-t-butylazoisobutyronitrile and
,.
2-t-butylazo-2-cyanobutane
EXAMPLE X
A reaction vessel equipped with a thermometer,
stirrer, ni-trog~n source, inlet means and heat exchange
means was charged with 65 parts of Polyol A. Nitrogen was
bubbled through the polyol for about one hour. With stirring
and under a slight nitrogen flow, the charge was heated to
120C. A stream of 20 parts of butyl methacrylate and a
stream of 2 parts of l-t-amylazo-l-cyanocyclohexane in 35
parts of Polyol A were fed into a KENICS static mixer and
continuously added to the charge over a period of three
hours at 120C. Upon complation of the addition/ the re-
action mixture was maintained at 120C. for thirty minutes.
The reaction mixture was then stripped for one-half hour at
120C. under less than five millimeters of mercury. The
stripped reac-tion product was a liquid dispersion having a
Brookfield viscosity at 25C. of 17,600 cps. and a hydroxyl
number of 23.5.
-la-
EXAMPLE XI
A series of graft polymer dispersions was prepared
in the manner described in Example I. In each preparation,
100 parts of Polyol B was employed along with 30 parts of a
3:1 weight mixture of acrylonitrile and styrene. The re-
actions were carried out in the presence of two parts of
various catalysts. I~ each instance, the polymers coagulated.
In certain instances, stripping loss indi.cated that a low
order of monomer conversion was obtained. The catalysts
which were not efective in this reaction system all had a
ten hour half-life outside of the range of the subject
invention. The catalysts employed were
2-t-butylazo-2-4-dimetnoxy-4-methylpentane (half
life of 122C)
2-t~butylazo-2-methoxy-4-methyl pentane (half life
of 135C)
2-t-butylazo-2 hydroperoxy-4-methyl pentane (half
life of 36C)
t-butylazoformamide (half life oX 105C)
--19--
