Tetraalkylpiperidinyl substituted uracil derivatives and their use as ultraviolet light stabilizers

Tetraalkylpiperidinyl substituted uracil derivatives are disclosed which can be represented by the formula ##STR1## wherein each R' is independently an alkyl radical, n is 1 or 2 and R is a substituted or unsubstituted aliphatic radical, cycloaliphatic radical, aromatic radical or aromatic-aliphatic radical. These derivatives are useful as UV light stabilizers in synthetic resins.

This invention relates to certain uracil derivatives and their use as 
ultraviolet light stabilizers. 
It is well known that the physical properties of various synthetic resins 
deteriorate as a result of extended exposure to ultraviolet (UV) light. 
This deterioration, which varies in degree and nature depending on the 
particular polymer structure and on the location and duration of the 
exposure, has been attributed at least in part to a free radical 
generating photooxidation reaction. The free radicals so formed will 
attack the polymer chain to form additional free radicals by a 
self-propagating mechanism. Manifestations of the degradative effect of UV 
light on such polymers as polyethylene, polypropylene, and polyvinyl 
chloride include loss of mechanical strength (e.g., reduced tensile 
strength and flexibility), discoloration, cracking, and dimensional or 
surface change. 
Over the years, substantial research and development work has been carried 
out in search of additives which, when incorporated in the resin, would 
have the effect of preventing, or stabilizing the resin against, 
photodegradation. As a result, numerous materials have been developed or 
identified for use as UV stabilizer additives. 
Depending on the chemistry of the particular additive, its function as a UV 
stabilizer may fall in one of several categories. For example, the 
additive may serve as a screener, preventing the light from impacting on 
the plastic's molecular structure, or as a preferential absorber of UV 
light. A third category of UV light stabilizers is that of the so-called 
"scavengers". The hindered amines (e.g., tetramethyl piperidine) are 
generally known to serve that function. They trap and transform to a 
harmless species the free radicals formed as a result of the initial 
photo-oxidation of the plastic thus interrupting the propagation stage of 
the photodegradation process. The uracil compounds of this invention fall 
in this category of UV light stabilizers. 
It is also generally well-known in the art that UV stabilizers must meet 
certain criteria if they are to be useful as additives in plastics. 
Compatability with, and retention in, the resin or plastic in which the 
additive is to be used are among the more important requirements. The 
stabilizer also should impart little or no color to the resin. 
Considering the high temperatures at which plastics are processed, it is 
also important in certain applications that the UV stabilizer be 
non-volatile and thermally stable at high temperatures. For the most part, 
only prior art UV stabilizers of the polymeric type can meet this 
requirement. 
Now, in accordance with the invention, new, non-polymeric uracil 
derivatives have been found which meet the foregoing criteria. Further 
according to the invention, synthetic resin compositions are stabilized 
against photodegradation by the inclusion therein of the novel uracil 
derivatives disclosed herein. 
The uracil derivatives of the invention are pyrimidinediones which can be 
represented by the formula 
##STR2## 
wherein each R' is independently an alkyl radical, n is 1 or 2, and R is a 
substituted or unsubstituted aliphatic radical, cycloaliphatic radical, 
aromatic radical or aromatic-aliphatic radical. 
The preferred uracil compounds of the invention are the 
tetramethylpiperidinyl substituted uracil derivatives which can be 
represented by formula II as follows 
##STR3## 
wherein n and R are as defined above. Particularly preferred are compounds 
of Formula II in which n is 2. These compounds have been found to have 
surprisingly high thermal stability. Also particularly preferred are those 
compounds of formula II in which R is an unsubstituted radical selected 
from the group consisting of alkylene having 1 to 12, more preferably 3 to 
10, carbon atoms, cycloalkylene having 5 to 20, more preferably 6 to 15, 
carbon atoms, arylene having 6 or 12 ring carbon atoms, aralkylene having 
7 to 20, more preferably 7 to 16, carbon atoms, and alkarylene having 7 to 
20, more preferably 7 to 16, carbon atoms. 
The uracil derivatives represented by formula II above can be prepared by a 
multi-step process using readily available raw materials. The first step 
involves the reaction of 4-amino-2,2,6,6-tetra methylpiperidine with 
methyl acrylate to form 
N-(2,2,6,6-tetramethylpiperidin-4-yl)-amino-3-propionic acid methyl ester. 
This reaction, which is carried out at ambient or higher temperatures and 
in the presence of an appropriate solvent, takes about 2 to 48 hours to be 
complete depending on the temperature. It is illustrated by equation A 
below 
##STR4## 
The resulting N-(2,2,6,6-tetramethylpiperidin-4-yl)-amino-3-propionic acid 
methyl ester, compound III, is then recovered by distilling off the 
solvent. 
The next step in the preparation of the uracil derivatives of the invention 
is the reaction of compound III with an organic mono- or diisocyanate as 
depicted by the following equation B in which R and n are as defined above 
##STR5## 
In carrying out the reaction, a solution of the organic isocyanate, in an 
inert solvent such as an appropriate ether or methylene chloride, is added 
slowly to a continuously agitated solution of compound III. The reaction 
being exothermic, the temperature of the reaction mixture is maintained at 
about 25.degree. C. by means of an ice bath. After the addition is 
completed, stirring of the reaction mixture is continued for some time, 
i.e., about 1-2 hours, while maintaining the temperature at 25.degree. C. 
Then the mixture is refluxed. The resulting urea product, compound IV, is 
then separated by filtration, washed with solvent and dried in a vacuum 
oven. 
The final step in the preparation of the uracil compounds of the invention 
is the cyclization of the urea, compound IV, as illustrated in equation C 
below 
##STR6## 
The urea is dissolved in a solvent, such as dimethylformamide, containing a 
small proportion of an alkaline compound such as sodium methylate, and the 
solution is refluxed for several hours, Thereafter, the solution is 
cooled, causing precipitation of the pyrimidinedione product, compound II. 
The precipitated solids are then separated by vacuum filtration, washed 
with solvent and air dried to yield a crude product. 
The crude product so obtained, although it may be used as such, is 
preferably concentrated and purified. This can be normally achieved by 
recrystallization, using an appropriate solvent. 
For practical reasons, the most preferred uracil derivatives of the 
invention are those which are derived from the reaction of 
N-(2,2,6,6-tetramethylpiperidin-4-yl)-amino-3-propionic acid methyl ester 
with a commercially available organic diisocyanate, R(NCO).sub.2, as 
illustrated in equation B above. The commercially available organic 
diisocyanates, and the commercially available organic diisocyanates, and 
the corresponding identity of the R radical in the uracil compounds of the 
invention (formula II) are listed below 
__________________________________________________________________________ 
Organic Diisocyanate R Radical 
__________________________________________________________________________ 
(1) 
##STR7## tolylene 
(2) 
##STR8## 4,4'-diphenylmethane 
(3) 
##STR9## 1,5-naphthalene 
(4) 
OCNCH.sub.2CH.sub.2CH.sub.2CH.sub.2CH.sub.2CH.sub.2NCO 
1,6-hexamethylene 
(5) 
##STR10## 4,4'-dicyclohexylmethane 
(6) 
##STR11## 4,6-xylylene 
(7) 
##STR12## isophorone 
(8) 
##STR13## 2,2,4-trimethylhexamethylene 
(9) 
##STR14## phenylene 
(10) 
##STR15## cyclohexylene 
(11) 
##STR16## 3,3'-dimethyldiphenylene 
(12) 
##STR17## 3,3'-dimethyldiphenylmethane 
__________________________________________________________________________ 
The uracil derivatives of the invention, although non-polymeric, exhibit 
surprisingly high thermal stability. This is particularly the case with 
the preferred compounds of formula I in which n is 2. They are 
substantially inert, crystalline solids, light in color (i.e., white or 
near white) and compatible with various plastic media. 
In accordance with the invention, it has been found that the uracil 
derivatives of the invention are effective as UV stabilizers in synthetic 
resins. By virtue of their surprisingly high thermal stability, they are 
particularly suited for use in those applications wherein a plastic 
material, be it thermoplastic or thermosetting, is subjected, during 
processing or use, to substantially elevated temperatures. Thus they can 
be used with all types of synthetic resins, illustrative of which are the 
polyolefins, polyamides, polyvinyl chloride, polyvinylidene chloride, 
polycarbonates, epoxy resins, ABS resins, polyaramides, polyhalcarbons, 
polyurethanes, etc. They are especially adapted for use as UV stabilizer 
additives in polyolefins, e.g. polypropylene and polyethylene. 
When used to stabilize a plastic material against photodegradation, the 
uracil derivatives of the invention can be incorporated into the plastic 
in an amount or proportion which is effective for that purpose. Thus as 
used herein, the terms "effective amount" and "stabilizing amount" are 
intended to mean and include any such amount. Generally speaking, amounts 
varying from about 0.05 to about 2 percent by weight, based on the weight 
of the plastic, are sufficient, and in most instances a preferred range of 
about 0.1 to about 1 percent by weight is used. 
The uracil compounds of the invention are incorporated into the synthetic 
resin by any suitable procedure. For example, conventional mixing 
equipment, such as a mill or Banbury mixer, may be used to blend the 
powdered uracil compound into the resin. If the resin has a melt viscosity 
which is too high for the desired use, the resin should be worked until 
its melt viscosity is brought down to the desired level before the 
addition of the uracil compound. Mixing is continued until the mixture is 
substantially uniform. It is preferable to also include in the resin mix 
an antioxidant such as 
octadecyl-3,5-ditertiarybutyl-4-hydroxyhydrocinnamate or 
2,2'-methylene-bis(4-methyl-6-tertiarybutylphenol)terephthalate, both of 
which are commercially available materials. If desired, other additives 
may be incorporated into the resin which serve different functions. 
Illustrative are calcium stearate, which serves as a processing aid, 
sodium benzoate, which acts as nucleating or clarifying agent, pigments to 
add the desired color, and so forth. 
The stabilized resin or polymer can be worked or processed into the desired 
shape by conventional methods such as milling, extruding, calendering, 
injection molding and the like. 
The following examples are provided to illustrate the invention. In these 
examples, the test used to measure the thermal stability of various 
compounds is the so-called Thermo Gravimetric Analysis (hereinafter 
referred to as "TGA"). Briefly, a standard-size sample is heated at a 
pre-determined heating rate and its weight and rising temperature are 
constantly monitored during the heating process. A temperature vs weight 
graph is plotted, and for purposes of the examples, the temperature at 
which a 10% weight loss occurs (signifying initial break-down or loss of 
stability) is noted for each compound tested. 
Further in the examples, the effectiveness of an additive as UV stabilizer 
is determined using a commercial accelerated weathering apparatus known as 
the Q(UV) panel in accordance with ASTM-G53-77 procedures. Briefly, a 
plastic specimen, in this case a 15 mil extruded film, is exposed to both 
UV radiation from fluorescent bulbs (16 hours at 60.degree. C.) as well as 
water condensation (8 hours at 40.degree. C.) from a heated reservoir. 
Subjective judgments on the progression of embrittlement, crazing, cracks, 
surface erosion and blooming are recorded and Hunter color measurements 
are taken. Failure occurs when a combination of these factors becomes 
excessive, and at this point, the number of days to failure is recorded. 
Finally all parts and percentages given in the examples are by weight 
unless otherwise specified.

EXAMPLE 1 
Preparation of 
1,6-Hexamethylenebis-[3-(5,6-dihydro-2,4-pyrimidinedione-1-yl)-4-(2,2,6,6- 
tetramethyl-piperidine)] 
A solution composed of 250.0 g of 4-amino-2,2,6,6-tetramethylpiperidine and 
138.0 g of methyl acrylate in 1300 ml methanol was prepared then allowed 
to stand at room temperature (25.degree. C.) for 48 hrs. The methanol was 
then removed by flash distillation on a rotary evaporator leaving a 383.0 
g residue. This residue was identified by NMR and GC as being N-(2,2,6,6 
tetramethylpiperidin-4-yl)-amino-3-propionic acid methyl ester of 92.6% 
purity. This product is of sufficient purity to use for further reactions. 
Distillation of this product at reduced pressure through an 8" Vigreux 
column and collecting the fraction boiling from 98.degree. to 105.degree. 
C. at 0.3 mm Hg gave 300.0 g of product having the following elemental 
analysis: 
Carbon: 64.38% found (versus 64.47% calculated) 
Hydrogen: 10.77% found (versus 10.74% calculated) 
Nitrogen: 11.22% found (versus 11.57% calculated) 
A gas chromatograph of the distillate found it to be of 99.1% purity. 
A solution of 101 g of 1,6 Diisocyanatohexane in 200 ml of ethyl ether was 
added over a period of 30 min. to a stirred solution of 290.4 g 
N-(2,2,6,6-Tetramethylpiperidin-4-yl)-amino-3-propionic acid methyl ester 
in 100 ml ethyl ether. The temperature was maintained at 25.degree. C. 
throughout the addition by means of an ice bath. 
After the addition was complete the mixture was allowed to stir for 1 hr. 
at 25.degree. C. and then refluxed for 11/2 hrs. The white solids which 
formed were separated by filtration, washed with ether and dried in a 
vacuum oven at 60.degree. C. and 15 mm pressure. The yield of this 
intermediate bis urea was 352 g (90%) and its structure was confirmed by 
NMR. Its elemental analysis was as follows: 
Carbon: 62.63% found (versus 62.58% calculated) 
Hydrogen: 9.82% found (versus 9.82% calculated) 
Nitrogen: 12.75% found (versus 12.88% calculated) 
A 62.0 g portion of this intermediate bis urea was dissolved in 90 ml 
dimethylformamide containing 0.47 g sodium methylate and the solution 
refluxed for 3 hrs. Cooling of the solution caused white solids to be 
deposited. These solids were separated by vacuum filtration, washed with 
ether, and air dried to give 41.6 g (74.4%) of crude bis uracil. 
Recrystallization from isopropyl alcohol gave and 33.5 g (60%) of white 
crystals confirmed by NMR as the title product and having a melting point 
of 162.degree. C. 
The elemental analysis was as follows: Calculated (Found): C-65.31(64.84); 
H-9.52(9.27); N-14.28(13.84). 
EXAMPLE 2 
Preparation of 
1,1'-Methylenebis-[4-phenylene-3-(5,6-dihydro-2,4-pyrimidinedione-1-yl)-4- 
(2,2,6,6-tetramethyl-piperidine)] 
A solution of 37.3 g 4,4'diphenyl-methane diisocyanate in 445 ml of 
methylene chloride was added over a 15 min. period at 25.degree. to 
35.degree. C. to a stirred solution of 72.0 g 
N-(2,2,6,6-Tetramethylpiperidin-4-yl)-amino-3-propionic acid methyl ester, 
prepared as shown in Example 1, in 295 ml methylene chloride. After the 
addition was complete the solution was refluxed for 1 hr., cooled to 
25.degree. C. filtered free of solids and the filtrate stripped of 
volatiles on a rotary evaporator. The semi-solid residue was dissolved in 
refluxing isopropyl alcohol and water was added to the refluxing solution 
until a slight turbidity was observed. Continued refluxing over a 15 min. 
period caused the precipitation of white solids which after cooling to 
25.degree. C. were removed by filtration and washed with a 50:50 mixture 
of isopropanol and water. These still damp solids were then recrystallized 
from ethanol to give 60 g (56%) of the title product whose structure was 
confirmed by mass spec. and NMR. m.p. 280.degree. C. 
Elemental analysis Calculated (Found): C-69.82(68.08); H-8.11(7.89); 
N-12.53(11.41). 
Thermal Stability and UV Stabilizer Tests 
The TGA thermal stability of each of the compounds prepared in Examples 1 
and 2 was measured along with those of two commercially available, 
polymeric UV stabilizers. The latter are identified by the trademarks 
Chimassorb-944LD and Cyasorb-UV 3346. The results are shown in Table I 
below. 
The effectiveness of each of the four compounds (i.e., the two compounds 
obtained in Examples 1 and 2, and the two polymeric, commercial products) 
as UV stabilizers in plastics was determined. The plastic used was 
powdered polypropylene. In each case, a sample containing 0.25% of each 
stabilizer and 0.05% of a commercial antioxidant available under the 
trademark Irganox 1076 was extruded at elevated temperature into a 15 mil 
film. A specimen film was then tested using a Q(UV) panel in accordance 
with ASTM-G53-77 as briefly summarized above. A control specimen 
containing no UV stabilizer additive was also tested in the same manner. 
The results are provided in Table I below. 
The data is Table I demonstrates that although color change is negligible 
in the case of each polypropylene sample including the sample containing 
no stabilizer at all, the stabilizing effect of two uracil derivatives of 
the invention (as measured by the number of days to failure) is comparable 
to that of the two prior art stabilizers. Moreover, the data shows that 
although the uracil compounds of the invention are monomeric, they exhibit 
substantially comparable thermal stability attributes as those of the 
polymeric, prior art materials. 
TABLE I 
__________________________________________________________________________ 
TGA, Temp, .degree.C. 
Days to 
Hunter color, 
UVLS Additive 
M.P. (.degree.C.) 
@ 10% Wt. Loss 
Failure 
Initial 
Final 
__________________________________________________________________________ 
EXAMPLE 1 170-175 
310 &gt;35 -0.99 
-0.22 
EXAMPLE 2 278-281 
360 28 -0.97 
2.05 
Chimassorb-944LD 
296 375 28 -0.97 
-0.93 
(CIBA GEIGY) 
Cyasorb-UV 3346 
110-130 
340 35 -0.85 
-0.47 
(American Cyanamid) 
Blank -- -- 14 1.07 
0.12 
__________________________________________________________________________ 
EXAMPLES 3-4 
Two other uracil derivatives of the invention were prepared using 
essentially the same procedure as that of Example 2 except for the fact 
that instead of 4,4'-diphenylmethane diisocyanate, other organic 
diisocyanates were used, namely, 2,4-toluene diisocyanate was used in 
Example 3 and p-phenylene diisocyanate was used in Example 4. The melting 
point and TGA thermal stability of the resulting compounds is provided in 
Table II below. 
EXAMPLES 5-9 
To illustrate the preparation of compounds of formula I wherein n is 1, the 
procedure of Example 1 was followed except that in each of Examples 5-9 a 
monoisocyanate was used instead of a diisocyanate. Based on the particular 
isocyanate reactant used in each example, the R radical in the final 
product is identified in Table II together with the melting points and TGA 
thermal stabilities of the resulting compounds. 
TABLE II 
______________________________________ 
EXAMPLE OR M.P. TGA (.degree.C.), 
COMISON R n (.degree.C.) 
@ 10% Wt. Loss 
______________________________________ 
E-3 tolulene 2 267 365 
E-4 phenylene 2 340 320 
E-5 methyl 1 124 210 
E-6 cyclohexyl 1 123 220 
E-7 phenyl 1 209 245 
E-8 p-chlorophenyl 
1 167 270 
E-9 benzyl 1 156 235 
______________________________________ 
EXAMPLE 10 
Preparation and Testing of a Typical Mono-Uracil 
(a) Preparation of 1-(2,2,6,6-Tetramethyl 
piperidin-4-yl)-3-(1-chloro-4-phenylene)-5,6-dihydro-2,4-pyrimidinedione 
A solution of 34.0 g (0.221 m) of p-chlorophenyl isocyanate in 75 ml 
dimethylformamide was added over a 15 minute period to a stirred solution 
of 53.5 g (0.221 m) of 
N-(2,2,6,6-tetramethylpiperidin-4-yl)-amino-3-propionic acid methyl ester 
in 85 ml dimethylformamide maintained at 25.degree. to 30.degree. C. by 
means of an ice bath. The mixture was then heated by an oil bath to 
153.degree. C. and maintained at this temperature for one hour. The 
dimethylformamide was then removed from the mixture by means of a rotary 
evaporator leaving an oil which crystallized on standing. These solids 
were recrystallized from isopropyl alcohol to give 29.5 g (36.7 percent) 
of white solids having a melting point of 167.degree. C. These crystals 
were subject to NMR spectroscopy which confirmed them to be the title 
product. The elemental analysis of the product was as follows: 
Carbon: 62.63% found (versus 67.72 calculated) 
Hydrogen: 7.43% found (versus 7.20 calculated) 
Nitrogen: 11.12% found (versus 11.55 calculated) 
Chlorine: 9.94% found (versus 9.74 calculated) 
(b) Testing the Title Compound 
The TGA at a 10 percent weight loss is noted in Table II above (refer to 
E-8) as being 270.degree. C. When tested for UV stabilizer properties in 
polypropylene using the procedure as described above with respect to 
Examples 1 and 2, the title product failed after 14 days, as compared to a 
blank which failed after 6 days. The title compound exhibited color change 
during this test falling within an acceptable range. 
By analogous testing of the other products referred to as E-3 to E-7 and 
E-9 of Table II, E-6 was determined to be the preferred mono-uracil 
product.