Disclosed is a new class of polymeric hindered amine light stabilizers based on maleic anhydride modified polyolefins reacted with tetramethyl piperidine derivatives. These materials are more effective than most of the generally used hindered amine light stabilizers, but due to their higher molecular weights and the polyolefin backbone, they are more compatible with polyolefins.

This invention relates to a novel class of polymeric high-molecular weight 
hindered amines and the use of the same as light stabilizers for 
polyolefins. 
In the commercialization of the polyolefins such as polyethylene, 
polypropylene and the copolymers of ethylene, propylene, and other 
olefins, one of the greatest obstacles to overcome has been their limited 
light stability. In sunlight or any other source of light containing a 
significant amount of ultraviolet light, the polyolefins degrade rapidly, 
becoming brittle and strengthless in relatively short order. Fibers, films 
and molded objects degrade to the point of being totally useless unless 
the polymer is protected by an effective stabilizer system. A great amount 
of effort has been devoted to the light stabilization problem with 
sufficient success that polyolefin films, fibers, and resins are now very 
substantial items of commerce. 
Among the most successful light stabilizers presently in use are the 
hindered amine compounds, i.e., compounds containing 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 
configuration. Commerically available examples of such synthetic compounds 
include 
##STR1## 
These materials function well but for many purposes are not optimum due to 
their relatively high cost per equivalent of hindered amine group provided 
to the polymer. Moreover, since their unsubstituted hydrocarbon chains are 
relatively short, their compatibility with the longer chain polyolefins is 
not sufficient to prevent exudation thereof from the polymer matrix. 
Likewise, in textile applications, these hindered amines are subject to 
being extracted during laundering and dry cleaning. In addition, these 
compounds have been found to cause dermatitis and they are too toxic to be 
used in film or molded containers which will be used for packaging food. 
It is the purpose of this invention to provide a new class of hindered 
amines and analogs or derivatives thereof which are useful as light 
stabilizers for polyolefins but which are less subject to the stated 
shortcomings of the prior art hindered amine light stabilizers. Another 
object is to provide olefin polymers and copolymers stabilized by the said 
high molecular weight hindered amines. 
In accordance with the invention, there is provided a novel class of high 
molecular weight, polymeric hindered amines prepared from maleic 
anhydride-modified polyolefins and having the general formula selected 
from the class consisting of 
##STR2## 
wherein R--represents an olefin polymer residue based on ethylene or 
propylene; R' is H, OH, O.sup..multidot., or O--R"; R" is a lower alkyl or 
substituted lower alkyl group having at least one hydrogen atom on the 
carbon attached to the nitrogen atom; and x and y are integers of a size 
relative to the molecular weight of R such that the total substitution of 
tetramethyl piperidine residues, is between about 0.2 and 10% by weight 
based on the total weight of the compound and preferably between about 0.2 
and 6% inclusive of 0.2-1%. 
It has been theorized that the tetramethyl piperidine acts as a free 
radical scavenger in effecting light stabilization. The hindered amine 
moiety is readily converted to an oxygenated free radical form, 
N-O.sup..multidot., 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 oxygenated 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 stabilization in the manner explained. 
The residue R-- in the above formula can represent any olefin polymer 
residue which is based on a preponderance of ethylene, propylene, or 
butene-1, 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. 
##STR3## 
The olefin polymer based hindered amines of the invention represented by 
formula III, in which R' is hydrogen, are prepared by graft modifying the 
appropriate polymer backbone with maleic anhydride and thereafter reacting 
said maleic anhydride modified olefin polymer with 
4-amino-2,2,6,6-tetramethyl 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 piperidine. 
The maleic anhydride-modified polyolefins which 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 commercially available 
product, sold under the trademark "Hercoprime.RTM." by Hercules 
Incorporated, Wilmington, Delaware. Polyethylene modified with maleic 
anhydride is available commercially from Chemplex Company of Rolling 
Meadows, Ill. under the trademark "Plexar.RTM.". Any polymer or copolymer 
of ethylene, propylene, or butene-1 can be modified via the maleic 
anhydride moiety to form the substrate molecule, including polyethylene, 
polyropylene, ethylene-propylene copolymer, propylene-butene-1 copolymer, 
or butene-1-ethylene copolymer. The most frequently encountered and the 
preferred maleic anhydride modified polyolefin is that based on 
crystalline or steroregular polypropylene. 
The preparation of maleic modified polypropylene is described in, inter 
alia, U.S. Pat. No. 3,483,276. Briefly, the preparation consists of 
treating the olefin polymer with a material or by a means which will 
induce the formation of active, free radical sites thereof with which 
maleic anhydride 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 solvent, with a free radical 
producing material such as dibenzoyl peroxide, dilaurylperoxide, dicumyl 
peroxide or t-butyl perbenzoate; or by simply milling it in the presence 
of air. The preferred method is 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 invention is 
accomplished via relatively simple, known chemical reactions. In the case 
of the compound 
##STR4## 
reaction of the maleic-modified polyolefin with 
4-amino-2,2,6,6-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 
##STR5## 
is prepared by refluxing the maleic-modified polyolefin with 
4hydroxy-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 which is compatible with the aromatic 
solvent and does not participate in the reaction. Para-toluene sulfonic 
acid is a preferred acid. 
Where the composition comprises a mixture of an olefin polymer and a 
modified olefin polymer, as above described, it is found useful to utilize 
modified olefin polymer in an amount sufficient to provide a concentration 
of tetramethyl piperidine residue between 0.2 and 1.0% by weight.

Preparation of the compounds of the invention is illustrated in the 
following examples. 
EXAMPLE 1 
2-[N-(2,2,6,6-Tetramethyl-4-piperidinyl)Succinimidyl] Polypropylene 
A commercially available maleic anhydride modified stereoregular 
polypropylene (Hercoprime G.RTM.-Hercules Incorporated) was purified by 
refluxing in xylene and recrystallizing to remove water and free maleic 
anhydride. Combined maleic anhydride content of the purified material was 
about 2.6%. 
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 distillation 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] Polypropylene 
A mixture of 49 gms maleic anhydride modified polypropylene (Hercoprime 
G.RTM.-Hercules 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 
for 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 which precipitated was isolated from the mass by vacuum filtration 
through sintered glass, pressed dry and washed with acetone. The product 
was dried in air, then in an oven at 50.degree. C. for fifteen minutes. 
Dry weight of the product was 50.5 grams. 
EXAMPLE 3 
Example 2 was repeated using xylene as the solvent and refluxing for five 
hours. About 50.3 grams of product were recovered. IR spectra indicate the 
presence of some free carboxylic acid but showed that the diester was the 
overwhelmingly predominant product. 
EXAMPLE 4 
A mixture of 7 grams of a propylene--butene copolymer (14% C.sub.4) 
containing about 5.1% combined maleic anhydride in 100 ml of xylene was 
agitated and heated at reflux (136.degree. C.) under a Dean-Stark trap for 
about 2 hours until all traces of H.sub.2 O were removed. The reaction 
mixture was cooled to about 100.degree. C. and 0.9 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. 
As stated hereinabove, the novel polymeric hindered amine compounds of this 
invention are highly useful as light stabilizers for polyolefins. While 
other light stabilizers containing the 2,2,6,6,-tetramethyl piperidine 
structure are known, the incorporation of that moiety into a maleic 
anhydride modified polyolefin molecule provides substantially improved 
light stabilizing ability thereto. Also, the polyolefin backbone is more 
compatible with the polyolefin matrix to which it is to be added than are 
many previously known hindered amines. As a result, there is little or no 
tendency toward exudation or rejection of the stabilizer molecules by the 
matrix. This, in turn, leads to a significant 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 safety. Some conventional hindered amine light 
stabilizers have been found to cause irreverible eye irritation in rabbits 
(BNA Occupational Safety and Health Reporter--May 8, 1980). 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. Thus the same safety precautions are 
not so critical. 
In use as light stabilizers for polyolefins, the polymeric 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 conventional 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 
200.degree. C. 
Films of each of the materials, along with a blank containing no light 
stabilizer and controls containing commercially available hindered amine 
light stabilizers, in amount to provide equivalent 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. 
TABLE 1 
______________________________________ 
Specimen 
Additive(1) 
Conc. Average Life (hrs) 
______________________________________ 
Blank -- -- 80 
Control 1 
I 0.025 pph. 
590 
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 
______________________________________ 
(1) I is compound of formula I, hereinabove. 
II is compound of formula II, hereinabove. 
5A Imide is compound of formula III, hereinabove, where R is 
homopolypropylene residue, R' is H, and combined maleic anhydride content 
is 3%. 
5B Diester is compound of formula IV hereinabove, where R is 
homopolypropylene residue, R' is H, and combined maleic anhydride content 
is 3%. 
5C Imide is compound of formula III, hereinabove, where R is 
polypropyleneco-butylene residue, R' is H, and combined maleic anhydride 
content is 5.1%. 
5D Imide is compound of formula III, hereinabove, where R is 
homopolypropylene reside, 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 piperidine when used in tetramethyl pipridine- 
equivalent concentrations.