Polymeric materials that are stable enough to use outdoors without changes in excess of 20 years are investigated. Ultraviolet stabilizers or plastic materials were synthesized, polymerizable ultraviolet stabilizers, particularly of the 2(2-hydroxyphenyl)2H-benzotriazole family were prepared their polymerization, copolymerization and grafting onto other polymers were demonstrated, and ultraviolet stabilizing systems were devised. These materials were evaluated from the photophysical point of view

Vogl, O.

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https://ntrs.nasa.gov/search.jsp?R=19830010947 2020-03-21T03:59:17+00:00Z
ffsD 1A
(111S1-CR-169925) ( POLTHERIZi1BLE ULTRAVIOLET
STABILIZERS ?OR OUTDOOR US?] final Report
(Bassachusetts Univ.) 7 p HC 102/NP 1101
CSCL 101
FINAL REPORT^ !l^^►
O
from the University of Massachusetts f, 	 n
JPL CONTRACT NO. 955531
0. yogi
Polymer Science and Engineering Department
University of Massachusetts
Amherst, Massachusetts 01003
December 20 9 1982
it was the objective of this work to assist the Encapsulation Task Force of
the Flat-Plate Solar Array project at the Jet Propulsion Laboratory (JPL) to
devise polymeric materials that are stable enough to use outdoors without
changes in excess of 20 years. Our particular objective was to synthesize new
and effective ultraviolet stabilizers for plastic materials, to prepare poly-
merizabie ultraviolet stabilizers, particularly of the 2(2-hydroxyphenyl)2H-
benzotriazole family, to demonstrate their polymerization, copolymerization and
grafting onto other polymers, to devise new effective ultraviolet stabilizing
systems and to assist JPL in their evaluation of these materials from the pho-
tophysical point of view.
This work has been carried out since September, 1979 9 and was principally
done by the following coworkers: Witold Pradellok, Zohar Nir, Eberhard Borsig
and Shen-Jun Li. Benefits for the project supported by JPL were obz,41ned from
work that has been going on for many years and concurrently in our research
group on polymerizable ultraviolet stabilizers and polymerizable antioxidants
(D. Tirreli, 0. Bailey, M. Kitayama, Y. Sumida, S. Yoshida, and P. Grosso).
083-19218
UQClas
G3/44 02831
-2-
The first successfully concluded project for JPL was the preparation of
2(2-hydroxy-5-vinylphanyl)2H-banzotriazole (2H5V) and 2(2-hydroxy-5-isopro-
penylphenyl)2H-benzotriazole (2H5P). 2H5V had been synthesized before by S.
Yoshida in a six-step reaction consisting of the condensation of o-nitrobenzene-
diazonium chloride with p-ethylphenol; this reaction gave an azo compound which
was reduced by zinc and sodium hydroxide to 2(2-hydroxy-5-ethylphenol)2H-
benzotriazole and was acetylated, braminated, dehydrobrominated and finally
hydrolyzed to 2H5V.
The achievement in the first six months of the contract was to prepare
about 350 grams of 2H5V for the use of JPL. This material has been sent, in
stabilized form (with picric acid to avoid polymerization) to JPL. 2H5V readily
homopolymerized and also copolymerized with normal resonance stabilized monomers
such as styrene, methyl methacrylate and.n-butyl scrylate.
2H5V was then synthesized and a new synthesis of 2H5V was devised by con-
densation of 4-hydroxybenzophenone with o-nitrobenzenediazonium chloride. The
key intermediate for the final synthetic steps is 2(2-scetoxy- 5-acetyiphenyl)
2H-benzotriazole which could be reduced with sodium borohydride, dehydrated and
hydrolyzed to 2H5V or allowed to react with methyl Grignard reagent, dehydrated
and hydrolyzed to 2H5P. Adequate amounts of this compound (over 50 grams) were
prepared for various hone- and copolymerization grafting studies and a portion
was sent to JPL for evaluation. 2H5V is quite different in reactivity as com-
pared to 2H5P; it does not homopolymerize and is stable without additional sta-
bilizer added to prevent polymerization. It is (because of it's tertiary
* 9
A
carbon atom in the polymeric form) also expected to be more photostable.
Many routes (at least 10) were evaluated for the most efficient or more
direct route to 21151 1p none of which resulted in the synthesis of 2M5P.
2115V and 2H5P copolymerized with such monomers as styrene, methyl methecry-
late, and n-butyl methacrylate. The reactivity ratios of these copolymerize-
tions were determined and it was shown that 2145V is very readily incorporated
into all of these copolymers. The 2115P r value is near 0 indicating alternating
tendency for this comonomer; not surprising since this is an eE-methylstyrene
derivative.
2H5V and 2H5P were also incorporated into other polymer systems. 2115V very
readily grafted in solution in chlorobenzene at about 15000 with di-tertiary
butyl peroxide to form graft polymers with stactic polypropylene, ethylene/
vinyl acetate copolymers, ethylene/propylens copolymer, poly(methyl methecryi-
ate) and poly(n-butyl acrylate). It was also sl:awn that 2115V is readily grafted
under much milder conditions onto cis-1,4 polybutadiene and 1 9 2-polybutadiene at
good grafting efficiency and without crosslinking. 2115V and 2115P were also
Incorporated Into ethylene/vinyl acetate copolymers under grafting/crosslinking
conditions.
Unsaturated polyesters were copolymerized in the presence of 2H5V and 2115P
In styrene solution to form unsaturated polyester resins now photostabilized
with our polymerizable UV absorbers. This work is done in cooperation with
Professor Ranby in Sweden; by ESCA measurements, he is determining the actual
placements of the stabilizer on the surface of the stabilized film. He is also
studying the effect of singlet oxygen ( 102) and various accelerated aging
t 4
MA-
conditions on such permanently photostabilized unsaturated polyester resins.
In our early work on polymerizable stabilizers of the benzotriaiole family
we had also been trying to synthesize 2(2-hydroxy-4-vinyiphenyl)2H-benzotria-
zole and 2(2-hydroxy-3-vinylphenyl)2H-benzotriezole. All our efforts to date
failed and we have abandoned these objectives. In all cases peresubstitution,
rather than orthosubstitution occurred which gave the wrong (4-) isomer, non-
effective as UV stabilizer. Dr. S. Yoshida, however, was successful in synthe-
sizing the 2(2-hydroxy-5-methylphenyl)2H-5 1 -vinyl-benzotriazole. It behaves
similarly to 2H5V, can be polymerized and copolymerized with the standard mono-
mers but does not seem to offer any advantages over 2115V or 2H5P-
On a separate project, not supported by JPL, we hove also studied the
synthesis of polymerizable antioxidants particularly 4-vinyl-2,6-tertiary
butylphenol and 4-isopropenyl-2,6-tertiary butylphenol. They can be readily
polymerized directly with styrene and methyl methacrylate in bulk and in solu-
tion but more importantly they could be copolymerized in emulsion with butadiene
and isoprene. These two polymerizable antioxidants could be available whenever
needed for our project of long-term stabilization of polymeric materials, long-
term stabilizations using non-leachable, non-volatilizable stabilizers.
More recently we have emphasized our thrust d n the synthesis of new and
much more effective stabilizing systems. These systems are still based on the
2(2-hydroxyphenyl)2H-benzotriazole and 2-hydroxybenzophenone chromophors.
We have synthesized three new systems of UV absorbing chromophors some of
which we have started to convert into polymerizabla monomers. The objective of
the initial work, however, was to synthesize and identify these new systems in
s
-5-
order to slake them availabl e
 for JPL to study their effecti veness
 to improve the
aging of polymeric material and to evaluate their photophysical behavior.
We have found that resorcinol, 10-d1hydroxybenzene, not only forms a mono-
substitution product, when allowed to react with o-nitrobenzenedlazonium
chloride followed by reductive cyciization (called benzotri awl last ton), but
more importantly a disubstituted product was readily obtained. With phloroglu-
cinol, o-nitrobenzenedlazontum chloride, after condensation and reductive cyelt-
zation, not only gave a disubstituted product but also a tribenzotriazolized
material. These three now compounds straw surprisingly high extinction coef-
ficients, three times as high as the normal monosubstituted benzotriazole dert-
vatives but also a broad absorption from 250 rss to 360 ca.
2,4-01hydroxybenzophenone and 29 4-dihydroxyacetophenone (which are them-
selves effective ultraviolet stabilizers) have been used as starting material
for benzotriazolization and indeed dibenzotriazolized products have been
obtained in both uses. The absorption spectrum of these compounds show extinc-
tion coefficients lower than those of the di- and tribenzotriazolized resor-
cinols and benzophenones (only two-thirds of the extinction coefficient)
however, they show an additional strong band between 260 and 300 nm- It is
Interesting that in the case of the dibenzotriazolized 2,4-dihydroxybenzophenons
we have now a system which has both of the most important ultraviolet stabl-
e
1lzing groups in one molecule, the 2(2-hydroxyphenyl)214- benzotriazole and the
2-hydroxybenzophonone chromophor.
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1
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The product from the acetophenone deri vative is also pf fAkned to be used ss
a starting material for the synthesis of styrene and S&mathyistyrene derivatives
	
1
of these highly substituted benzotriazole containing systems therefore giving
new polymerizable ultraviolet stabilizer systems.
The benzotriazolization of phloroglucinol had initially yielded only the
di- and trisubstituted product as the condensation of o-nitrobenzenedlezoniun
chloride with phloroglucinol were always carried out in strongly basic solar
tions. it is known that phloroglucinol is very reactive and the reason for it
Is that it exists, as we have shown very recently, to a substantial amount in
the keto form which is apparently undergoing the condensation reaction. By
carrying out the condensation in near neutral aqueous/alcoholic solutions we
were able to prepare the azo compound which, after reductive cyciization, pro-
duced monosubstituted phloroglucinol, namely 2(2,4,6-trihydroxyphenyl)2H-
benzotriazole.
Some initial work has been done to react these new stshilizers with more
than one benzotriazyl units in the molecule with acryl and methac ryi chloride in
order to provide polymerizable methacrylic and acrylic esters of ultraviolet
absorbers. Some of the materials will also be used either directly or in the
appropriately modified form for incorporation in polyesters and polycarbonates.
L-
-In conclusion, we have successfully prepared polgoerizable ultraviolet sta-
biiizars which can be incorporated into polymers by copolymerization and
grafting. We have also prepared new classes of ultraviolet stabilizers which
have high extinction coefficient and are effective over a broad spectrum of
ultraviolet absorption. This work will produce new and more efficient stabili-
zers which could be used either by themselves or when transformed into polymeri-
zable ultraviolet stabilizer would be incorporated into polymers by copolywl-
zation or grafting. We are convinced that these new discoveries and develop-
ments on ultraviolet absorbers will provide further advances in extending the
lifetime of polymeric materials.
The research described in this report was performed for the Jet Propulsion
Laboratory, California Institute of Technology through an agreement with the
National Aeronautics and Space Administration
8.


Polymerizable ultraviolet stabilizers for outdoor use

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