Thermooxidative stabilization of polymers with a N4-alkylated oxo-piperazinyl-triazine

An oxo-piperazinyl triazine with three piperazinone substituents, each of which has an alkylated N.sup.4 atom ("MPIP-T"), used in an amount no more than 0.2 phr, and without any secondary stabilizer (hence referred to as a "virgin MPIP-T"), and in particular, without any hindered phenol antioxidant, or phosphorous acid ester, simultaneously provides thermooxidative stability and stability against degradation by UV light along with acceptable melt processability. Further, the virgin MPIP-T allows (i) uninterrupted operation of a die or mold while maintaining the surfaces of the cavities essentially contaminant-free; and, (ii) excellent AO stabilization which is equivalent to that obtained with a premier hindered phenol AO, and superior to that obtained with the premier oligomeric piperidinyl-triazine compound, when each stabilizer is used in the same amounts by weight in a thermoplastic synthetic resinous substrate.

BACKGROUND OF THE INVENTION 
Antioxidants ("AO"s) are used to protect hydrocarbon polymers against 
thermal oxidative ("thermooxidative") degradation caused by reaction with 
atmospheric oxygen, usually at, or above ambient temperature. Oxidation 
causes undesirable changes in mechanical, aesthetic, and electrical 
properties of the polymer. Some polymers degrade more readily than others, 
depending upon their structure. The high order of effectiveness of several 
tetramethylpiperidinyl benzoate derivatives in inhibiting the thermal 
oxidation of lauryl aldehyde was measured and the data reported in an 
article titled "Stabilization Mechanisms of Hindered Amines" by Peter M. 
Klemchuk and Matthew E. Gande in Makromol. Chem., Makromol. Symp. 28, 
117-144 (May 1989). The rate of oxygen uptake with no stabilizer was 3.6 
mmol/hr; with BHT was 1.9 mmol/hr; and with tetramethylpiperidin-1-oxyl 
was 0.08 mmol/hr. The rate of oxygen uptake was comparably low (that is 
&lt;0.1 mmol/hr) for tetramethylpiperidinyl compounds with &gt;N-H; &gt;N-OH; and 
&gt;N--O.degree. groups in the tetramethylpiperidinyl moiety, indicating that 
stabilizers containing a tetramethylpiperidinyl moiety and known to be 
good light stabilizers, have good thermooxidative properties. 
Despite the piperidinyl derivatives being generally regarded as ultraviolet 
light stabilizers, such known, good thermooxidative stabilization obtained 
with the piperidinyl derivatives, led to the statement: "In recent years, 
interest in the use of antioxidants to give protection against the effects 
of light has considerably increased. There are a number of reasons for 
this, but the main ones appear to be advances in the understanding of 
mechanisms of photo transformations of polymers of different kinds, which 
demonstrate the key role of free radicals and photochemically active 
molecular intermediate products with which antioxidants are likely to 
interact. From the practical viewpoint a significant incentive proved to 
be the development of new high-efficiency light stabilizers, especially 
the sterically hindered amines, which act predominantly as antioxidants. 
Interest in the use of antioxidants for light stabilization is also 
associated with the fact that they happen, at the present time, to be the 
principal class of thermostabilizers of polymers. Consequently, their 
choice makes it possible to achieve complex protection of the polymeric 
material. See "Stabilization of Polymers Against the Effect of Light by 
Means of Antioxidants" by V.B. Ivanov and V. Ya. Shlyapintokh Polymer 
Deoradation and Stability 28 (1990) 249-273. 
The foregoing statement, despite the fact that hindered amines are usually 
classified as light stabilizers rather than AOs (since they are extremely 
effective in protecting polyolefins and other polymeric materials against 
photodegradation) underlines the intense search in the marketplace for a 
hindered amine which is both an AO and a UV stabilizer. 
Though the piperidyl compounds are stated to be effective antioxidants, 
they are not effective enough (as an antioxidant) in polyolefins, and in 
particular, homopolymers of propylene, or copolymers of propylene and 
ethylene in which the latter is present in a minor amount by weight (such 
homopolymers and copolymers are collectively referred to herein as "PP" 
for brevity), to warrant their use, without the use of a secondary 
stabilizer, for such duty. When piperidinyls are used as stabilizers, they 
are used as light stabilizers to protect against ultraviolet radiation, 
and, in practical applications, only in combination with a phosphorous 
acid ester, hindered phenol or other antioxidant. 
The foregoing is equally true for piperazin-2-one-containing compounds used 
as hindered amine light stabilizers ("HALS" for brevity). Evidence of the 
foregoing is provided in an article titled "Hindered Diazacycloalkanones 
as Ultraviolet Stabilizers and Antioxidants" by J.T. Lai, P.N. Son and E. 
Jennings, Polymer Stabilization and Degradation 91-99, ACS Symposium 
Series, American Chemical Society, Washington, D.C. (1985). Slit tapes of 
PP (2 .times. 100 mil) containing a combination of 0.1 phr (parts per 100 
parts of substrate) of HALS, aged in the Arizona sun, even the polymeric 
piperidine did not fare very well (pg 92). 
Unique among the HALS disclosed in the aforesaid article was a 
decahydroquinoxaline which provided both AO and light stabilization. It 
was determined that the most important features for its AO activity were 
(i) the fused bicyclodiazacycloalkane ring, (ii) dialkyl substituents at 
the C.sup.3 position, and (iii) alkyl, instead of acyl substituents at the 
N.sup.1 position. 
We have now provided a monomeric N.sup.4 -methylated oxopiperazinyl 
triazine (MPIP-T) which, by itself, gives protection against 
thermooxidative degradation when essentially homogeneously distributed in 
a wide array of synthetic resinous materials. In addition, it is an 
excellent stabilizer against degradation by UV light, and provides 
adequate stability during melt processing. No known HALS stabilizer 
provides this combination of properties. 
The conventional view of the HALS in general, and the polysubstituted 
piperazinone-containing ("PSP") HALS in particular, was that such 
contribution to thermooxidative stabilization as they made in combination 
with a hindered phenol AO or other secondary stabilizer, was eschewed in 
favor of leaving out the AO for the specific purpose of obtaining better 
gas fade stabilization and stabilization against gamma-radiation. U.S. 
Pat. No. 4,797,438 patent teaches the gamma-stabilizing activity of 
PSP-containing HALS in the absence of an antioxidant; and U.S. Pat. No. 
4,929,653 teaches the ability of PSP-containing HALS to improve gas fade 
resistance in the absence of an antioxidant. 
A recent article titled "New Developments in Polymer Stabilization" by 
Motonobu Minagawa Polymer Degradation and Stability 25 (1989) 121-141 
provides an up-to-date appraisal of the field as viewed by one skilled in 
the art. At the outset it points out that, since chemical reactions of 
stabilizers contribute to stabilization, these reactions proceed in the 
molten highly viscous state or in the amorphous solid phase. Additives 
should, therefore, possess adequate mobility to react in plastics. This is 
probably the reason why the molecular weights (MW) of commercial 
stabilizers are almost always in the range of 200-2000, although there are 
some exceptions. But to prevent loss of stabilizer from the polymer in 
increasingly severe conditions of application, the tendency is to increase 
MW. 
Among the low MW HALS in the range from about 400-1000 are Tinuvin 144 
(Ciba-Geigy), Sanol LS 2626 (Sankyo), Mark LA-57, Mark LA-52 and Mark 
LA-62 (Adeka Argus), and Sumisorb TM-061 (Sumitomo Chem). But such low MW 
HALS result in loss or decomposition during the period from processing to 
end use. For the high retention which is necessary, high MW HALS are used. 
Among the high MW HALS in the range above about 2000 are Tinuvin 622 LD, 
Chimassorb 119 and Chimassorb 944 (Ciba-Geigy); Mark LA-63 and Mark LA-68 
(Adeka Argus); Spinuvex A-36 (Montedison) and Cyasorb UV-3346 (American 
Cyanamid). 
But all HALS tend to form salts with acids and the salts adversely affect 
weather resistance, hence greatly reduce the performance of the 
stabilizer. Moreover, the salts contribute to contamination of the 
surfaces of molds or dies used to mold or extrude, or otherwise 
thermoform, the articles to be stabilized. Such problems associated with 
the alkalinity of the piperidinyl-containing HALS have been substantially 
negated by the use of a HALS with one or more piperazin-2-one moieties. 
Especially desirable stability is obtained with piperidyl moieties 
connected to a triazine ring, such as Chimassorb 944 and Chimassorb 119 
commercially available from Ciba-Geigy. Comparable or better stability is 
obtained with piperazin-2-one moieties distally connected to a triazine 
ring in the stabilizers disclosed in U.S. Pat. Nos. 4,480,092 to Lai et 
al., and 4,629,752 to Layer et al, both in class 544/subclass 113. 
We have now provided a method for molding or extruding articles melt, and 
thermooxidatively stabilized with only a low MW HALS, specifically a 
MPIP-T, while maintaining the surfaces of the mold or die essentially free 
of contaminants during operation. 
As stated hereinabove, HALS protect polymers by functioning as light-stable 
antioxidants. Their antioxidant activity is explained by a reaction 
sequence in which hindered amines terminate propagating reactions by 
trapping both alkyl and peroxy radicals. But oligomeric HALS are highly 
effective against oxidation when exposed at 120.degree. C. in a forced-air 
oven. (see "Antioxidants" Vol 2, Encyclopedia of Polymer Science and 
Engineering, 2d edition, John Wiley & Sons). A piperazinone-containing 
HALS which we use, by itself without a secondary stabilizer (hence 
referred to as a "virgin MPIP-T"), has unsubstituted N.sup.4 atoms, is not 
oligomeric and has a MW &lt; 1000. Yet the MPIP-T has a very low rate of 
migration. The rate of migration is so slow that the stabilizer does not 
cause significant contamination of a mold--a problem which must be 
addressed when the stabilizer is combined with a hindered phenol. Neither 
is the stabilizer readily extractable with ethanol in which the stabilizer 
is typically soluble. Such low extractability makes the MPIP-T stabilizer 
acceptable for use in containers for comestible foods. This MPIP-T is also 
relatively non-toxic having a toxicity far less than that of the 
commercially used hindered phenols, and comparable to that of a 
piperidnyl-triazine containing HALS. 
Compounds referred to as oxo-piperazinyl triazines in this specification 
are those which contain a triazine ring with three piperazinone 
substituents, each of which has a alkyl-substituted N.sup.4 atom, and each 
of which is substituted with two substitutents, or, substituted with a 
spiro substituent, (referred to as being "polysubstituted"), at both the 3 
and 5 positions of the piperazinone ring. Compounds referred to as 
piperidinyls are those which contain at least one piperidinyl ring which 
is either disubstituted, or substituted with a spiro substituent at the 2 
and/or 4 positions. When substituted as described, such compounds, whether 
piperazinones or piperidines, are referred to as being polysubstituted. 
Compounds referred to as MPIP-Ts are those which contain only a single 
triazine ring having a substituent at each C atom of the ring, each 
substituent containing a polysubstituted piperazinone ring. 
A monomolecular virgin MPIP-T having a single triazine ring, has been found 
to be a better AO in polyolefins, particularly in PP, than an oligomeric 
stabilizer having a triazine ring connected to plural polysubstituted 
piperidyl moieties. The emphatic interest in using a virgin PIP-T is to 
avoid the complicating side-effects which attend the use of secondary 
stabilizers, and to lower cost. 
The PSP moieties of the MPIP-T are connected to the triazine ring through 
an alkyleneamino chain. In prior art oxo-piperazinly triazines (PIP-Ts) 
disclosed in the '092 patent, the chain is unbranched; and in the '752 
patent, the chain is branched. Details of the structures of the MPIP-T are 
set forth hereafter. 
We have now found (as will be evident from the data set forth hereunder) 
that the virgin MPIP-T which we knew provided excellent stabilization 
against degradation by light (that is, had excellent u-v light 
stabilization properties), also functions as an excellent AO when used in 
a concentration no more than 0.2 phr, without any secondary stabilizer. As 
an AO, the virgin MPIP-T is a more effective AO than not only the 
conventional hindered phenols which dominate the market-place, but also 
more effective than the dominant HALS oligomeric stabilizer Chimassorb 944 
which is a compound having a repeating unit consisting essentially of a 
triazine ring and two polysubstituted piperidine rings. 
Because there is so small a concentration of virgin MPIP-T in a stabilized 
polyolefin the MPIP-T is far less prone to migration to the surface of the 
article, particularly during molding or extruding the polyolefin, thus 
minimizes the contaminant effect of the MPIP-T on the surfaces of the mold 
or die. Such a low concentration also makes it difficult to extract the 
MPIP-T with a solvent, thus permits using the MPIP-T in polyolefins for 
making containers for comestible foods, because such very small amount of 
MPIP-T as may be extracted into the food, renders de minimis the slight 
toxicity of the MPIP-T. 
The unexpected properties of the virgin MPIP-T deriving from its use as an 
AO in synthetic resinous materials are attributable to the presence of the 
PSP moiety, and the fact it is distally connected to the triazine ring by 
an alkyleneamino chain. We have now found that this structure accounts for 
the easily distinguishable AO activity of a monomeric virgin MPIP-T 
compared with that of a piperidyl-triazine oligomer. 
In addition to the surprising effectiveness of a MPIP-T when it is used as 
the only stabilizer in any synthetic resinous material, whether in fiber 
or any other shaped article, the MPIP-T is extremely persistent--that is, 
it does not degrade thermally. Nor is a MPIP-T volatilized during the 
manufacture of an article despite its essentially similar volatilization 
temperature compared with that of Chimassorb 944. Nor is the MPIP-T 
volatilized during the useful life of the article at relatively high 
temperature, which, if the article is made from PP, is a temperature in 
the range from about 120.degree. C. to about 145.degree. C., or below the 
heat distortion temperature (HDT) of the PP. 
This resistance to migration at elevated temperature makes a MPIP-T the 
stabilizer of choice for impellers for washing machines for clothes, and 
impellers for dish-washing machines; as an inner liner for automobile 
fenders; for under the hood applications in automobiles; etc. 
Further, a MPIP-T is exceptionally compatible with polymers, and in the low 
concentration used in this invention, behaves as a single phase, for 
example by being substantially soluble in many polymers, particularly PP, 
polyethylene (PE), and copolymers thereof, the solubility being affected 
by the molecular weight of the polymer. This is particularly note-worthy 
because polar UV stabilizers are known to be excluded from the crystalline 
phase of a polyolefin such as PP, preferring to be concentrated in the 
amorphous phase from which the stabilizer can more readily migrate to the 
surface of a mold or die in which an article is being formed. 
Equally noteworthy is that most HALS with a substituent on the N atom, 
result in retarded nitroxide formation. This was studied in piperidyl 
amines and reported in an article titled "Photo-degradation and 
Photo-stabilization in Organic Coatings Containing a Hindered Amine Light 
Stabilizer: Part VI--ESR Measurements of Nitroxide Kinetics and Mechanism 
of Stabilization" by D.R. Bauer et al Polymer Degradation and Stability 
Vol 28, 115-129 (1990. Conversion was fastest for the &gt;N--H group. Also 
fast is that for &gt;N--CH.sub.3, each of which is about an order of 
magnitude faster than the conversion for other substituents. This provides 
an insight into the AO activity of the virgin MPIP-T. 
Moreover, preferred MPIP-Ts are essentially water-white, or only slightly 
colored, crystalline or amorphous solids, or non-viscous liquids, so that 
they are easily homogeneously dispersed in a polymeric substrate and 
impart no color, or only a negligible amount of color to the substrate in 
which they are dispersed or dissolved. Because of its bulky structure 
which is remarkably soluble as long as the concentration is no more than 
0.2 phr, particularly in PP, once compatibilized in the substrate, a 
MPIP-T diffuses ever so slowly. In addition, its relatively lower pH 
compared with piperidinyltriazines, appears to negate the tendency of the 
MPIP-T to contaminate the surface of molds or dies under injection 
molding, blow molding, or other high temperature forming operations. This 
not only avoids marring the surface of the article formed, but avoids 
having to interrupt operation of the molding machine to clean the surfaces 
of the cavities in the mold frequently. 
Perhaps, most important, the properties of a MPIP-T allows it to be used to 
stabilize housings for equipment,; fibers for fabrics for clothing, even 
articles worn next to the skin; receptacles such as garbage cans, and 
containers for foods and beverages for human consumption, because when 
used in the amount of no more than 0.2 phr in polyolefins, this MPIP-T is 
typically not objectionably toxic. 
SUMMARY OF THE INVENTION 
It has been discovered that an oxo-piperazinyl triazine with three 
piperazinone substituents, each of which has an alkylated N.sup.4 atom 
("MPIP-T"), used in an amount no more than 0.2 phr, and without any 
secondary stabilizer (hence referred to as a "virgin MPIP-T"), and in 
particular, without any hindered phenol antioxidant, or phosphorous acid 
ester, simultaneously provides thermooxidative stability and stability 
against degradation by UV light along with acceptable melt processability. 
Further, the virgin MPIP-T allows (i) uninterrupted operation of a die or 
mold while maintaining the surfaces of the cavities essentially 
contaminant-free; and, (ii) excellent AO stabilization which is equivalent 
to that obtained with a premier hindered phenol AO, and superior to that 
obtained with the premier oligomeric piperidinyl-triazine compound, when 
each stabilizer is used in the same amounts by weight in a thermoplastic 
synthetic resinous substrate. 
It is therefore a general object of this invention to provide a process for 
thermoforming a synthetic resinous material to produce an article of 
arbitrary shape, comprising simultaneously maintaining the cavity surfaces 
of a forming die or mold essentially free from contaminants during 
operation continuously to mold articles, and, stabilizing the material 
being molded, such as a polyolefin, against thermooxidative degradation 
with a virgin MPIP-T in an amount in the range from about 0.1 phr to no 
more than 0.2 phr, which MPIP-T is compatible with the material being 
molded. The article is molded, extruded, or otherwise formed, with 
adequate melt processability, at a temperature in the range from about 
160.degree. C. to about 225.degree. C., over a continuous operating period 
of at least 120 hr without objectionable contamination of the surfaces of 
the mold cavity. 
It has also been discovered that no more than 0.2 phr of a MPIP-T, 
homogeneously dispersed within a PP substrate, is so low a concentration 
of MPIP-T as to hinder its extraction with ethanol at 49.degree. C. 
(120.degree. F.) for 240 hr, after an initial 2 hr soak at 65.degree. C. 
(149.degree. F.), yet is sufficient, simultaneously to stabilize the PP 
against thermooxidative degradation, not only during the molding 
operation, but thereafter, over the useful life of the PP article formed. 
It has still further been discovered that a virgin MPIP-T present in no 
more than 0.2 phr concentration, allows stabilization of PP while it is 
being molded or otherwise thermoformed at a temperature in the aforesaid 
range, into a container for comestible food, without an objectionable 
amount of MPIP-T being extracted from the container into the food while 
the container is in storage. 
It is therefore a general object of this invention to provide a 
thermoformed article of arbitrary shape, formed from a homopolymer of an 
o-olefin, or a copolymer of an .alpha.-olefin, in which copolymer a 
repeating unit derived from said .alpha.-olefin is present in a major 
molar amount, in which homo-polymer or copolymer is disperse no more than 
0.2 phr of virgin MPIP-T. 
It is a specific object of this invention to provide a PP container for 
comestible foods, the PP being stabilized against thermooxidative 
degradation by homogeneously dispersing within the PP the aforestated 
minimal amount of virgin MPIP-T, which is sufficient, simultaneously to 
essentially negate a toxic amount of MPIP-T to be extracted from the 
substrate while the container is stored, and, to stabilize the substrate 
against thermooxidative degradation.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
Synthetic resinous materials which may be unequally stabilized against 
thermooxidative degradation include polyolefins, whether homo- or 
copolymers, exemplified by polyethylene, polypropylene, propylene-ethylene 
copolymers, ethylene-propylene diene copolymers, ethylene-vinylacetate 
copolymers, and the like; homo- and copolymers of polyvinyl aromatics 
exemplified by polystyrene, acrylonitrile-buta-diene-styrene copolymers, 
styrene-acrylonitrile copolymers and the like; homo- and copolymers of 
polyvinyl halides exemplified by polyvinyl chloride, copolymers of vinyl 
chloride with vinylidene chloride, butadiene styrene, vinyl esters and the 
like; homo- and copolymers of acrylic acid, acrylates and methacrylates, 
exemplified by polyacrylic acid, polyacrylates or methacrylates, 
copolymers with butadiene and the like; condensation homo- and copolymers 
exemplified by polyamides, epoxy resins, polycarbonates, 
phenol-formaldehydes, polyesters, varnish, polyimides, and the like; 
addition polymers and copolymers exemplified by polyurethanes and the 
like; and, blends and alloys, exemplified by blends of ABS resins, PVC and 
polymethacrylate blends, blends of polyolefin homopolymers and copolymers 
such as blends of polypropylene in EPDM polymers, and the like. 
The monomolecular polysubstituted N4-alkylated piper-azinone-triazine 
(MPIP-T) compound having a single triazine ring is represented by the 
structure 
##STR1## 
wherein PSP represents a substituent derived from a cyclic amine 
represented by a structure selected from the group consisting of 
##STR2## 
wherein R.sub.1 represents C.sub.1 -C.sub.24 alkyl, C.sub.5 -C.sub.20 
cycloalkyl, C.sub.7 -C.sub.20 araalkyl or alkaryl, C.sub.1 -C.sub.24 
aminoalkyl, or C.sub.6 -C.sub.20 aminocycloalkyl; 
R.sub.2, R.sub.3, R.sub.4, and R.sub.5 independently represent C.sub.1 
-C.sub.24 alkyl; and, R.sub.2 with R.sub.3, or R.sub.4 with R.sub.5 are 
cyclizable to C.sub.5 -C.sub.12 cycloalkyl including the C.sup.3 and 
C.sup.5 atoms respectively, of the piperazin-2-one ring; 
R.sub.6 and R.sub.7 independently represent C.sub.1 -C.sub.24 alkyl, and 
polymethylene having from 4 to 7 carbon atoms which are cyclizable; 
R.sub.8 represents H, C.sub.1 -C.sub.6 alkyl, and phenyl; 
R.sub.9 represents C.sub.1 -C.sub.3 alkyl; and, 
p represents an integer in the range from 2 to about 10. 
It is this limited class of MPIP-Ts, and particularly those monomolecular 
ones having a relatively low MW in the range from about 850 to less than 
2000, which display the remarkable AO stabilization activity in the 
absence of any secondary stabilizer, along with relatively low toxicity, 
and only a slight proclivity to contaminate the surface of a cavity in a 
mold or die, all of which properties are conspicuously absent from N.sup.1 
-alkylated piperidyl-triazine HALS. 
The particular degree of effectiveness of the virgin MPIP-T as an AO in PP 
is evidenced by improved strength and discoloration resistance, and the 
retention of flexibility of test samples of PP plaques and fibers 
oven-aged by exposure to heat in a convection oven in accordance with the 
procedure for heat aging without load set forth in ASTM D-3045-74. The 
tensile strengths of plaques were measured according to the procedure set 
forth in ASTM D-882-83. Failure is determined either by intense 
discoloration, or brittleness when manually flexed, or when the tensile is 
reduced by 50% from the original. 
Since the effectiveness of a HALS is predicated upon destruction of 
hydroperoxide, a piperidyl HALS being more basic would be expected to be 
more effective because it would tend to associate with the weakly acidic 
hydroperoxide forming predominantly in the amorphous phase (see 
"Antioxidant Mechanisms of Hindered Amine Light Stabilizers" by D, J. 
Carlsson, et al Makromol. Chem. Suool. Vol 8, 79-88 (1984) and more 
effectively destroy the hydroperoxide. That the AO additive will be 
largely concentrated in the amorphous zones of the polymer where mobility 
is most favored, is also stated in "Photo-oxidation of Polypropylene 
Films. VI. Possible UV-stabilization Mechanisms" by D. J. Carlsson et al 
in Jour. of Appl. Polvm. Sci. Vol 16, 615-626 (1972), middle of pg 616. 
What actually appears to happen is that, contrary to what one would 
expect, the less basic piperazinone HALS works more effectively. The lower 
basicity of the PIP-T permits this mechanistic quirk to redound to the 
thermo-oxidative stabilizing effect of the virgin PIP-T. The basicity of 
an oligomeric piperidinyl-triazine compound is nearly 40% greater than 
that of a PIP-T. The relative basicities are as follows: 
a piperidyl-based HALS has a basicity of about pK.sub.a = 10.0 
a piperazinone-based HALS has a basicity of about pK.sub.a = 6.2 
where pK.sub.a = pH - log [&gt;NH]/[&gt;NH.sub.2 .sup.+ ] 
A particular MPIP-T has the structure (I) in which PSP is represented by 
##STR3## 
The average results (failure at the end of days) obtained in the standard 
procedure of over aging at 125.degree. C. with each stabilizer identified, 
using a statistically significant number of PP plaques, each plaque 5 cm 
.times. 5 cm .times. 20 mils thick, are set forth in Table 1 herebelow: 
TABLE 1 
______________________________________ 
Identif. Level of 125.degree. C. 
40.degree. C. 
of stabil. stabilizer (days) (days) 
______________________________________ 
Blank PP 0 11 2 
MPIP-T(1) 0.1 &gt;212* 73 
Chimassorb 944 
0.1 89 24 
Irganox 1010 
0.1 137 59 
Irganox 1076 
0.1 56 12 
Irganox 3114 
0.1 65 10 
Ultranox 626 
0.1 32 8 
Ethanox 398 0.1 25 6 
MPIP-T(1) 0.2 &gt;212* 80 
Chimassorb 944 
0.2 150 37 
Irganox 1010 
0.2 &gt;212* 108 
Irganox 1076 
0.2 83 15 
Irganox 3114 
0.2 139 19 
Ultranox 626 
0.2 32 10 
Ethanox 398 0.2 20 14 
______________________________________ 
*the samples have not yet failed September 11, 1990. 
Though the MPIP-T(1) does not provide as good stability as the hindered 
phenol Irganox 1010, the MPIP-T(1) is clearly superior to Chimassorb 944. 
At the 0.1 phr level at 140.degree. C. the MPIP-T is three times better, 
and at the 0.2 phr level, the MPIP-T is more than two and one-half times 
as effective. 
Migration Studies of MPIP-T in PP Discs 
A statistically significant number of PP discs containing 0.6 phr of 
MPIP-T(1) and 0.05 phr calcium stearate were molded to about 2 mm 
thickness and 5 cm in diameter. The blank discs contained no MPIP-T(1). 
Extraction of MPIP-T(1) from the discs was done in 95% ethanol at 
120.degree. C. (49.degree. C.) after initial 2 hr at 149.degree. F. 
(65.degree. C.) for 240 hr according to the procedure indicated in 
"Guidelines for Migration Studies for FDA Acceptance of Indirect Food 
Additives" by William C. Bachtel. Analysis was done by HPLC (high pressure 
liquid chromatography). About 50% of the final concentration of extracted 
material extracts in the first 2 hr. The quantity of extracted material 
after 240 hr is about 2% of the total MPIP-T(1) initially present. 
A comparative weight loss study for the monomeric MPIP-T and the oligomeric 
piperidyl-triazine by thermogravimetric analysis in air (atmospheric purge 
of 180 cc/min) at 100/min showed that a weight loss of 0.1% was measured 
for the MPIP-T at 206.degree. C.; the same weight loss of 0.1% for 
Chimassorb 944 was measured at 238.degree. C. Despite the fact that the 
virgin MPIP-T experienced the weight loss at a lower temperature than the 
virgin Chimassorb 944, it proved to be a more effective AO. 
Color Retention 
Knitted polypropylene yarn formed from PP containing 0.2 phr virgin MPIP-T 
and coated with 1% Napcostat 905M finish was placed in a gas-fade chamber 
exposing the fibers to nitrogen oxides and then placed in an oven aging 
test with 3 cycles each 6 hr, the temperature being .+-.60C. The 
yellowness index remained below 10, and the whiteness index remained above 
40, these being values at which the fiber is deemed to be essentially 
water white. The indices were measured in accordance to standard 
procedures. 
For comparison, knitted yarn formed from polypropylene containing 0.2 phr 
virgin Chimassorb 944 is similarly coated and exposed to the same sequence 
of cycles in the gas-fade chamber and the oven. The yellowness index was 
12 that is, above 10), and the whiteness index was 32 (that is, below 40). 
This comparison provides evidence that the virgin MPIP-T provides better 
retention of color than the virgin Chimassorb 944. 
Comparative tests with Injection Molded Articles 
A first batch of water-white polypropylene which is to be injection molded, 
is stabilized with 0.2 phr of virgin MPIP-T(1); a second batch of PP, also 
water-white, is stabilized with both 0.2 phr MPIP-T(1) and 0.2 phr Irganoz 
1010. A single-cavity mold with a diamond-polished mold cavity, to mold a 
casette box with integral lid (weighing about 1 oz.) with a "live" hinge, 
is placed in an Arburg Model 220-90-350U injection molding machine. The 
machine is operated continuously for 120 hr with each PP batch of powder 
at identical molding conditions, and the surfaces of the cavity are 
examined, as are the surfaces of the casette boxes molded. 
The surfaces of the cavity are much cleaner, and the surfaces of the molded 
casette boxes are smoother with the first batch of PP powder, than they 
are with the second batch. Further, the color of the boxes made from the 
first batch are better, that is, essentially water-white, while the boxes 
from the second batch have a slight tinge. 
The conclusion is that there is a distinct advantage to using the virgin 
MPIP-T. 
28-Day Repeated-Dose Oral Toxicity Test of MPIP-T in Rats 
The remarkable lack of toxicity of the MPIP-T(1) is evidenced by the 
following test results of 28-day repeated-dose oral toxicity tests 
conducted with rats. 
Groups of 5 male and 5 female Sprague-Dawley rats were dosed for 4 weeks 
with MPIP-T(1) at dose levels of 0, 100, and 1000 mg/kg/day via the diet. 
Additional groups of 5 males and 5 females were administered 0, or 1000 
mg/kg/day for 4 weeks and then were observed for 2 weeks post treatment to 
assess the extent of recovery. The "kg" refers to the body weight of the 
rat. Body weights, clinical signs, mortality, food and water consumption 
and selected organ weights were monitored throughout the study. 
Blood samples were taken for hematology and clinical chemistry 
investigations from all main study animals during week 4. After 4 weeks of 
dosing all main study animals were killed and necropsied. For the groups 
designated for assessment of recovery, blood samples for hematology and 
clinical chemistry investigations were taken from these animals during 
week 6. After 6 weeks all the recovery group animals were killed and 
necropsied. Gross pathology examination was conducted on all animals. 
Liver, heart kidneys, spleen, lungs, adrenals, testes and ovaries were 
examined histopathologically from all Control and High dose animals 
including the recovery groups. Subsequently, evaluation was extended to 
liver, spleen, adrenals, and lung from the Low and Intermediate dose 
animals. In addition, Oil Red 0 staining for fat was carried out on 
selected animals. 
Dosing Sprague-Dawley rats for 4 weeks with MPIP-T(1) via the diet produced 
signs of toxicity at 1000 mg/kg/day in both sexes. The most notable 
effects seen included evidence of liver disfunction (increased liver 
enzyme levels and bile duct epithelium hypertrophy) and vacuolated 
macrophages in spleen and lungs. In addition, females receiving 100 
mg/kg/day showed slightly reduced cholesterol levels. There was no effect 
in males receiving 100 mg/kg/day or in either sex receiving 10 mg/kg/day. 
Some of these effects showed partial resolution after the recovery period. 
The results can be summarized as follows: 
Mortality: One High dose male met an unscheduled death. 
Clinical Sions: Several High dose males had a poor general condition (thin, 
hunched posture, eyes encrusted and piloerection) during weeks 2-4. In 
some recovery animals these signs persisted to weeks 5-6. There was no 
notable clinical signs in females. 
Body Weight: After 4 weeks the High dose group of both sexes showed a 
marked reduction in body weight gain. These differences were still 
apparent after the recovery period, but showed some slight resolution. 
Food Consumption: High dose males showed a reduction in food consumption 
after the 4 weeks of administration and after the 2 weeks recovery period. 
There were no notable intergroup differences in females. 
Water Consumption: There were no visual intergroup differences in females. 
Achieved Dosages: These were close to nominal. 
Analyses of Formulated Diets: These were within acceptable limits (.+-.10%) 
of accuracy. 
Laboratory Investigations: 
Hematology: Mild changes in red blood cell parameters were seen in the High 
dose group of both sexes after the 4 weeks of treatment and after the 
recovery period. 
Clinical Chemistry: After 4 weeks of treatment the High dose group of both 
sexes showed increases in AST, ALT, and total bilirubin and reductions in 
triglycerides and cholesterol. Intermediate dose group females also showed 
a reduction in cholesterol. High dose males also showed reduced glucose, 
total protein and creatinine levels and the High dose females showed 
increased potassium. 
After the recovery period the increases in AST and ALT were still apparent 
in both sexes, as were the reduced triglycerides and creatinine in males 
and increased potassium in females. 
Organ Weights: Males showed no notable intergroup differences after 4 
weeks. 
In only High dose females, liver, lung and spleen weights were increased at 
week 4. These increases were still apparent after the recovery period. 
Gross Pathology: There were no notable intergroup differences. 
Histopathology: A minimal or slight hypertrophy of the bile duct epithelium 
and infiltration of spleen and lungs by enlarged, foamy or vacuolated 
macrophages, was seen in High dose males and females. A slight hypertrophy 
of the zona fasciculata of the adrenals was present in High dose females 
only. All these findings showed evidence of resolution after the two weeks 
recovery period. 
Subchronic Oral Feeding Studies with Chimassorb 944 
During a 13-week rat feeding study with a chemically identical product, 
lymphoreticular system and liver effects were seen at the higher doses, 
with a no observable effect level (NOEL) of 6.3-6.9 mg/kg/day. 
During a 90-day study, rats were fed diets containing 0, 100, 500, 2000 and 
10,000 ppm chimassorb 944 FL. Additional groups of rats also had a 5-week 
recovery period after treatment where all groups received control diet. 
The primary target effects were blood disorders (anemia at 10,000 ppm and 
leucocytosis increase in white blood cells - at 2000 ppm and 10,000 ppm), 
liver function abnormalities (2000 and 10,000 ppm), and destruction of 
isolated areas of tissue (chronic necrotizing inflammation) of the 
mesenteric lymph node (2000 and 10,000 ppm), spleen, liver and ovary 
(10,000 ppm). These effects persisted to some degree in the 10,000 ppm 
group at the end of the 5-week recovery period. The NOEL for all effects, 
e.g. blood clotting slowing, was 6.7 (males) and 7.0 (females) mg/kg. The 
NOEL for the primary target effects were 33 mg/kg (males) and 35 mg/kg 
(females). 
During a 6-month study, rats received a dietary administration of 0, 5, 30 
and 200 mg/kg/day. The primary target effects were blood disorders (anemia 
and leucocytosis, 200 mg/kg), liver function abnormalities (200 mg/kg) and 
inflammation or destruction of isolated areas of tissue (chronic 
necrotizing inflammation) of the mesenteric lymph nodes (30 and 200 mg/kg) 
and other organs (ovaries, adrenal cortex and spleen, 200 mg/kg). The NOEL 
was 5.04 mg/kg and 5.37 mg/kg for males and females, respectively. 
A range-finding study for a two-generation reproduction study was 
performed. Adult rats received dietary levels of 0, 100, 500, 2000 and 
10,000 ppm for 2 weeks prior to mating and post-mating. The 10,000 ppm 
level was found to produce adult toxicity, decreases in body weight gain 
and food consumption along with gross necropsy changes in the spleen and 
liver were produced. No effects were observed in mating performance and 
fertility. In the 2000 and 10,000 ppm groups, pup loss parameters were 
increased along with decreases in pup weight which apparently caused 
retarded physical development (delayed pinna unfolding, hair growth, eye 
opening and incisor eruption). 
From the foregoing it is evident that a direct comparison of the MPIP-T(1) 
and Chimassorb 944 was not made. However, it is clear that the NOEL for 
each is less than 30 mg/kg/day, and neither stabilizer may be used under 
conditions where it might be ingested at above the 8 mg/kg/day level. 
Because excellent thermooxidative stability is obtained with no more than 
0.2 phr of the MPIP-T, while more Chimassorb 944 is needed, and further, 
because the MPIP-T is difficult to extract, it can be concluded that the 
MPIP-T is safer to use. 
Having thus provided a general discussion of the problems addressed and 
solved in our invention, and a specific illustration of the best mode for 
preparing a thermooxidatively stabilized polymer, and for thermoforming an 
article without substantially contaminating the surfaces of the cavity in 
the mold, and, an article thermoformed from such polymer, it is to be 
understood that no undue restrictions are to be imposed by reason thereof, 
except as provided by the following claims.