Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
5~7
This invention relates to novel high-molecular-weight
polymeric amines that have light-stabilizing properties for
alpha-olefins.
One of the greatest problems in the commercial use of
polyolefins such as polyethylene, polypropylene and related
olefin copolymers has been their poor light stability. In
sunlight or any other light containing a significant amount
of ultraviolet radiation, fibers, films and molded objects of
polyolefin degrade to the point of being totally useless
unless the polymer is protected by an effective stabilizer
system.
Among the most successful light stabilizers presently in
use are the "hindered" amine compounds, i.e., compounds con-
taining secondary amine groups having two alkyl substituents
on each of the carbon atoms attached to an amine group.
Examples of a hindered amine compounds which function well as
light stabilizers are 2,2,6,6-tetramethyl piperidine (TMP)
and certain synthetic compounds of medium molecular weight of
similar conEiguration. Commercially available examples of
such synthetic compounds include
a) O O
HN ~-O-C-(CH2)8-C-O- ~ NH
I
- 2 ~ L~ 7
and b) H H
l l
5- ~ N ~ r N--(CH2)6-
t--C8--H17--NH II
10 It has been theorized that the tetramethyl piperidine
acts as a free radical scavenger in effecting light stabili-
zation. The hindered amine moiety is readily converted to an
oxygenated free radical form, N-0-, which, in turn, reacts
with the free radical polyolefin degradation products. This
reaction product is then oxidized to polyolefin nonradical
products and the hindered amine product reverts to the oxy-
genated free radical form whereupon the process starts over.
The hindered amine moiety is sufficiently activated by the
methyl groups on the adjacent carbons that a free radical can
form on the substituent attached to the nitrogen atom where
R' is any of the nonfree radical substituents specified.
Thus, each is capable of participating in the light stabili-
zation in the manner explained.
The stabilizing effect of such amines is discussed in an
article by V. Ya. Shlyapintokh and V. B. Ivanov in
Developments in Polymer Stabilization-5, Applied Science
Publishers, (1982).
~ hese materials function well but have several
disadvantages. a) their relatively high cost per equivalent
of hindered amine group provided to the polymer; b3 since
their unsu~stituted ~ydrocarbon c~ains are relatively short,
they are ~ ~ y with the longer chain polyolefins
and tend to exude from the polymer matrix; c) in textile
~x~
-3- 2212~-1644
applications, they are subject to being ext:racted during
launderlng and dry cleaning; and d) they may cause dermatitis
and therefore are too toxic to be used in film or molded
containers that will be used for packaging :Eood~
According to the invention, a modified olefin polymer
containing a 2,2,6,6-tetramethylpiperidine substituent, that
has light stabilizing properties for alpha-olefins and tends
to avoidthose disadvantages, is characterized in that it has
one of the general formulas III or IV
_ _ l
R-- HC-C
N--~R' III
H C- C
_ X
or
R- --HC-C--O ~R'
I ~
H2C-C - o~R~ y IV
.
in which R represents the residue of an alpha-olefin polymer or
copolymer; and R' represents -H, -OH', ~ or -O-R", where R"
represents a lower alkyl and x and y are integers of a size
relative to the molecular weight of R such that the total
substitution of tetramethylpiperidine residue is between about
pr~
5~17
-3a- 22124-1644
0,2 and 6% by weight~ based on the total weight of the modified
olefin polymer.
The novel polymeric hindered amine compounds of this
invention are highly useful as light stabilizers for polyolefins.
The incorporation of the2,~,6,6~etramethylpiperidine structure
into a maleic anhydride-modified polyolefin molecule provides
substantially improved light stabilizing abil.ity thereto; the
polyolefin backbone is more compatible with the polyolefin matrix
to which it is to be added, there is little or no tendency
toward exudation or rejection of the
D
~2~5~7
stabilizer molecules by the matrix, and there is a signifi~
cant reduction in extractability as compared to lower
molecular weight hindered amines.
Another advantage of the polymeric hindered amine light
stabilizers of the invention is improved reduced toxicity.
Some conventional hindered amine light stabilizers have been
found to cause irreversible eye irritation in rabbits. As a
result, operators working with these materials are required
to take elaborate precautions against inhalation and against
eye exposure to the dust.
The materials of this invention, when tested with
laboratory rabbits, did not present the same irritation
problems.
The residue R- in the above formula can represent any
olefin polymer residue that is based on a preponderance o~
ethylene, propylene, or butene-l, and having a valence of x
or y. Such residue can be either crystalline (stereoregular)
or amorphous (random)~ Thus, it can be either a high or low
density polyethylene residue, a polypropylene residue or a
residue of a copolymer of ethylene with butene 1, a residue
of a copolymer of ethylene and propylene, a residue of a
propylene--butene copolymer or a residue of such a propylene
copolymer with an olefin having up to about six carbon atoms.
The olefin polymer residue can also contain some unreacted or
partially reacted maleic anhydride residue as it is not
always required that all of the maleic anhydride modifier be
reacted with the hindered amine containing residue. For
example, Compound III may contain some groups of the
structure.
H O
~ 11 , ~
-C-C-NH- ~ N-R'
H2C-C-OH 7~
Il
o
The olefin polymer-based hindered amines of the inven-
tion represented by formula III, in which R' is hydro~en, are
prepared by graft-modifying the appropriate polymer backbone
~ ~J~ ~5
-- 5
with maleic anhydride, and thereafter reacting said maleic an-
hydride modified olefin polymer with 4-amino 2,2,6,6-tetra-
~ethyl piperidine. To prepare the compounds of formula IV,
in which R' is hydrogen, the maleic anhydride modified olefin
polymer is reacted with 4-hydroxy-2,2,6,6-tetramethyl piper-
idine.
The maleic anhydride-modified polyolefins that form the
substrate or carrier for the piperidine residue are known
materials containing about 0.2 to 9~ by weight of combined
maleic anhydride, preferably about 2 to 5~. In fact, one
embodiment of these materials in which the polyolefin is
either amorphous or crystalline polypropylene is a commer-
cially available product, sold under the trademark "Herco
prime( )" by Hercules Incorporated, Wilmington, Delaware.
Polyethylene modified with maleic anhydride is available
commercially from Chemplex Company of Rolling Meadows,
Illinois, under the trademark "Plexar(R)". Any polymer or
copolymer of ethylene, propylene, or butene-l can be modiiied
via the maleic anhydride moiety to form the substrate mole-
cule, including polyethylene, polypropylene, ethylene--propy-
lene copolymer, propylene--butene-l copolymer, or butene-l--
ethylene copolymer. The most frequently encountered and the
preferred maleic anhydride modified polyolefin is that based
on crystalline or s-tereoregular polypropylene.
The preparation of maleic modified polypropylene is de-
scribed in, inter alia, ~.S. Patent 3,483,276. Briefly, the
preparation consists of treating the olefin polymer with a
material or by a means that will induce the formation of
active, free radical sites thereon with which maleic anhy-
dride can react. Active centers can be induced, e.g., by
subjecting the polymer to the action of high energy ionizing
radiation such as gamma rays, x-rays, or high speed electrons;
by contacting it, either as a solid or a solution in a sol-
vent, with a free radical producing material such as dibenzoyl
peroxide, dilaurylperoxide, dicumyl peroxide or t-butyl per-
benzoate; or by simply milling it in the presence of air.
The preferred method i9 the reaction of the polyolefin with
maleic anhydride in solvent solution in the presence of a
free radical initiator.
Preparation of the novel polymeric compounds of the in-
vention i,5 accomplished via relatively simple, known chemical
reactions. In the case of the compound
__
R - - HC - C r ~
¦ N--~ NH
H2C _ C ~
_ O I x
reaction of the maleic-modified polyolefin with 4-amino-
2,216,6-tetramethyl piperidine is effected by refluxing in
the presence of an aromatic solvent, such as, e.g., toluene,
chlorobenzene, or xylene and removing water as it is formed.
The compound
_ O
R ~ HC - C O - ~ N~
H2C - C-O - ~ NH
_ O Y
is prepared by refluxing the maleic-modified polyolefin with
4 hydroxy-2,2,6,6-tetramethyl piperidine in aromatic solvent
under catalytic acid conditions and removing water as it is
formed. The acid condition can be created by any acid that
is compatible with the aromatic solvent and does not partici-
pate in the reaction. Para-toluene sulfonic acid is a pre-
ferred acid.
Where the composition comprises a mixture of an olefin
polymer and a modified olefin polymer, as above described9 it
is found useful to utili~e modified olefin polymer in an
amount sufEicient to provide a concentration of tetramethyl
piperidine residue between 0~2 and 1.0% by weight.
Preparation of the compounds of the invention is illus-
trated in the following examples.
"
~ 7 --
Example 1
_
2-[N-(2,2,6,6-Tetramethyl 4~piperidinyl)Succinimidyl]
_ Polyp~opylene
A commerciaLly available maleic anhydride modified
stereoregular polypropylene (Hercorprime G( ) Hercules In-
corporated) was purified by refluxing in xylene and recrystal-
lizing to remove water and free maleic anhydride. Combined
maleic anhydride content of the purified material was about
~.6%.
A mixture of 49 grams of the purified maleic modified
polymer in 450 ml of xylene was agitated and heated to reflux
temperature. A solution of 4.69 grams of 4-amino-2,2,6,6-
tetramethyl piperidine in xylene was added dropwise over
about 15 minutes and reflux was maintained for about seven
hours. Water was removed as it formed by azeotropic dis-
tillation using a Dean-Stark trap, draining the water from
the trap as soon as it was collected.
The product was allowed to cool overnight, at which time
a solid, light tan product had precipitated. This product
was separated and dried in a forced draft oven. About 48.9
grams was recovered.
Example 2
2-[Di-(2,2,6,6-Tetramethyl-4-Piperidinyl)Succinate]
Polypropyl_ne
A mixture of 49 gms maleic anhydride modified polypropy-
lene (Hercoprime G( ~ - ~ercules Incorporated - 3% combined
maleic anhydride), 500 ml of chlorobenzene, 7.07 grams of
4-hydroxy-2,2,6,6-tetramethyl piperidine, and 1 gram of
p-toluene sulfonic acid monohydrate was agitated and refluxed
~or seven hours under a Dean-Stark trap. Water was removed
from the trap as the reaction proceeded.
After cooling and sitting overnight, the solid product
that precipitated was isolated from the mass by vacuum fil-
tration through sintered glass, pressed dry and washed with
acetone~ The product was dried in air, then in an oven at
50 C f8r fifteen minutes. Dry weight of the product was
50.5 grams.
~2,~5~7
~e~
Example 2 was repeated using xylene as the solvent and
refluxing for five hours. About 50.3 grams of produ~t were
recovered. IR spectra indicate the presence of some free
carboxylic acid but showed that the diester was the over-
whelmingly predominant product.
A mixture of 7 grams of a propylene--butene copolymer
(14~ C43 containing about 5.1% combined maleic anhydride in
100 ml of xylene was agitated and heated at reflux (136C)
under a Dean-Stark trap for about two hours until all traces
of H2O were removed. The reaction mixture was cooled to
about 100C and 0O9 gram of 4-amino-2,2,6,6-tetramethyl-
piperidine in 15 ml of xylene was added dropwise over 15
minutes. The mixture was then agitated and refluxed for ten
hours, the water being removed from the trap as it was
collected.
The reaction product, a light tan solid, precipitated
upon cooling~ This was worked up as described in Example 1.
In use as Light stabilizers for polyolefins, the poly-
meric hindered amines of the invention are added in amounts
such that the tetramethyl piperidine concentration in the
total system is equivalent to that heretofore used with con-
ventional monomeric tetramethyl piperidines, about 0.1 to 3
by weight.
Example 5
A series of modified polypropylenes prepared as described
in the preceding examples were blended with polypropylene
using a conventional laboratory extruder, then extruded and
cut to molding powder. The molding powder pellets were
pressed into ten mil films in a picture frame mold at 200C.
Films of each of the materials, along with a blank con-
taining no light stabilizer and controls containing commer-
cially available hindered amine light stabilizers, in amounts
to provide e~uivalent amounts of tetramethyl piperidine, were
subjected to accelerated aging in a Fade-O-Meter. Specimens
were tested periodically for flexibility and embrittLement.
Average time to failure is recorded in Table 1.
37
g
Table 1
Specimen Additive(l) _ ConcAveraqe L _e (hrs)
Blank --- - - 80
Control 1 I 0.025 pph. 590
5 5-A Imide 0.355 pph. 700
5-B diester 0.185 650
5-C Imide 0.215 960
Control 2 II 0.031 510
5-D Imide 0.30 840
0 (1~ - I is compound of formula I, hereinaboveO
II is compound of formula II, hereinabove.
5-A Imide is compound of formula III, hereinabove, where R
is homopolypropylene residue, R' is H, and combined
maleic anhydride content is 3%.5 5 B Diester is compound of formula IV, hereinabove, where R
is homopolypropylene residue, R' is H, and combined
maleic anhydride content is 3%.
S-C Imide is compound of formula III, hereinabove, where R
is polypropylene-co-butylene residue, R' is ~, and com-
bined maleic anhydride content is 5.1%.
5-D Imide is compound of formula III, hereinabove, where R
is homopolypropylene residue, R' is H, and combined
maleic anhydride content is 3.6%.
From the data it will be apparent that the stabilizers
of this invention are more effective than the conventional
hindered amine light stabilizers based on tetramethyl piper-
idine when used in tetramethyl piperidine- equivalent concen-
trations.
