Photodegradable polymer compositions comprising blends of polymers with ketone-containing block or graft copolymers

Polymer compositions which have accelerated rates of degradation on exposure to ultraviolet radiation, e.g. direct sunlight in an outdoor environment, comprise a blend of a major proportion of a normal, standard synthetic polymer, e.g. polyethylene, and a minor proportion of a graft or block copolymer of a ketone group containing monomer, e.g. methyl vinyl ketone, graft or block copolymerized onto a backbone polymer e.g. of polyethylene. The composition can be molded, extruded and otherwise fabricated in the normal way to produce disposable, photodegradable plastic articles such as containers, wrapping films and the like.

FIELD OF THE INVENTION 
This invention relates to synthetic polymer compositions, and more 
particularly to polymer compositions which will degrade upon exposure to 
ultraviolet radiation, for example direct sunlight, over a period of time. 
BACKGROUND OF THE INVENTION 
Polymer compositions in the form of plastic wrapping films, containers and 
other disposable items constitute a significant amount of waste garbage 
and litter, contaminating the environment as such unless disposed of in a 
proper manner. They pose a particular problem in that they are normally 
unaffected by natural erosive forces encountered in outdoor environments, 
over very extended periods of time. Indeed, at least until recently, the 
emphasis of plastics producers has been to stabilize polymer compositions 
against degradation so as to extend their useful shelf or service life. 
The discarding of synthetic polymer articles such as plastic wrapping 
films and containers as litter in remote outdoor areas where they cannot 
economically be collected for proper disposal is a particular problem. The 
present invention has as one of its objects the provision of a polymer 
composition which will photodegrade outdoors over a relatively short 
period of time, but which is nevertheless economical to produce and to 
fabricate into plastic articles. 
BRIEF DESCRIPTION OF THE PRIOR ART 
Proposals have been made in the past for polymer compositions of controlled 
lifetimes which will degrade over a period of time on exposure to 
ultraviolet radiation such as direct sunlight. These previous proposals 
have included the addition of photosensitizing agents to the polymers, and 
the introduction of photosensitizing chemical groups into the polymer 
structure, the objective being to produce a polymeric composition which is 
stable when exposed to visible light and photodegradable only in response 
to the incidence of ultraviolet radiation thereon. Such compositions are 
thus stable under artificial light and behind window glass, which filters 
out almost all the ultraviolet components of sunlight, so that the 
compositions have indefinite shelf life. 
An example of a polymer composition having ultraviolet sensitizers added 
thereto is described in U.S. Pat. No. 3,830,764 Hudgin et al. An example 
of a polymer composition having photosensitizing chemical groups in its 
structure is described in U.S. Pat. No. 3,853,814 Guillet. 
A problem encountered with polymer compositions containing added 
sensitizers of low molecular weight, as in U.S. Pat. No. 3,830,764, is the 
tendency of the additive to migrate out of the composition over a period 
of time, thereby reducing its effect as a photosensitizer and possibly 
contaminating substances with which the composition is in contact, such as 
food-stuffs wrapped in a film of the polymeric composition. Chemically 
modified polymers on the other hand have the chemical photosensitizing 
groups chemically bound therein, but tend to be expensive to make 
commercially, necessitating the modification of large scale and well 
established commercial polymerization facilities. A modified and more 
commercially attractive approach is described in U.S. Pat. No. 3,860,538 
Guillet et al, where a small quantity of polymer containing 
photosensitizing ketone groups distributed throughout its polymer 
structure, is used as a masterbatch and mixed with a normal polymer to 
form a photodegradable polymer blend. This polymeric photosensitizer does 
not migrate out of the composition. 
The masterbatch process described in U.S. Pat. No. 3,860,538 requires the 
production, by copolymerization, of a photodegradable random copolymer of 
a vinyl or vinylidene monomer and a vinyl or vinylidene ketone monomer 
such as methyl vinyl ketone. Then the copolymer is blended with a regular 
vinyl or vinylidene polymer, normally a polymer of the same monomer from 
which the photodegradable polymer is formed, to prepare a compatible 
blended polymeric composition. It is difficult to prepare random 
copolymers of monomers such as ethylene with vinyl or vinylidene ketone 
monomers, economically on a commercial scale. There are in fact only a 
very restricted number of monomers which will copolymerize with ethylene 
to form random copolymers therewith in standard, commercial ethylene 
polymerization processes and facilities, at an acceptable rate. 
BRIEF SUMMARY OF THE INVENTION 
An object of the present invention is to provide a novel polymer 
composition having an accelerated rate of photodegradation on exposure to 
ultraviolet radiation. 
Another object is to provide a process for the production of 
photodegradable polymer compositions which can be operated economically on 
a large commercial scale. 
A further and more specific object is to provide novel photodegradable 
polyethylene compositions and economic commercial processes for their 
production. 
A further object of the invention is to provide a novel graft or block 
copolymer containing ketone groups which can be blended with regular 
polymers to induce photodegradability into the resultant polymeric 
composition. 
According to one aspect of the present invention, therefore, there is 
provided a synthetic polymer composition having accelerated degradation on 
exposure to ultraviolet radiation, comprising an intimate mixture of: 
(a) a major proportion of a normally solid synthetic polymer of at least 
one polymerizable monomer having the general formula 
EQU CH.sub.2 .dbd.CR.sub.1 R.sub.2 
where R.sub.1 represents a hydrogen atom or an alkyl group of from 1 to 6 
carbon atoms, and R.sub.2 is selected from the group consisting of a 
hydrogen atom, an alkyl group of from 1 to 6 carbon atoms, an aryl group, 
an aryl group substituted with one or two halogen or lower alkyl groups, a 
carboxylic acid group, a carboxylic acid lower alkyl ester group, a lower 
acyloxy group, a cyano group, an alicyclic group of not more than 8 carbon 
atoms, an alkoxy group of from 1 to 6 carbon atoms, an amido group and an 
alkenyl group of not more than 6 carbon atoms; and 
(b) a minor proportion of a compatible polymeric product of graft or block 
copolymerization of a grafting monomer onto a polymeric backbone, said 
polymeric backbone being a polymer of a first monomer of general formula 
EQU CH.sub.2 .dbd.CR.sub.3 R.sub.4 
wherein R.sub.3 represents a hydrogen atom or an alkyl group of from 1 to 6 
carbon atoms, and R.sub.4 is selected from the same groups from which 
R.sub.2 above is selected, and said grafting monomer having the general 
formula 
##STR1## 
wherein R.sub.5 represents a hydrogen atom or an alkyl group of from 1 to 
6 carbon atoms, and R.sub.6 is selected from the group consisting of alkyl 
groups having 1 to 6 carbon atoms, aryl groups, alkaryl groups having up 
to 9 carbon atoms and alkenyl groups having up to 6 carbon atoms, said 
product of graft or block copolymerization containing from about 0.2 to 
about 20 weight percent of ketone carbonyl groups. 
It has been found that, in a masterbatch composition of a normal, 
synthetic, non-photodegradable polymer and a photodegradable copolymer 
having keto carbonyl groups at a location adjacent to its polymeric chain, 
it is not necessary that the ketone groups be randomly distributed along 
and among the polymeric chains of the copolymer, in order to confer 
ultraviolet photodegradability upon the composition as a whole. The ketone 
groups can be concentrated at a specific location in the polymer, for 
example concentrated in a side, branch chain or in an end segment or a 
middle segment of a linear polymer chain. Thus the ketone copolymer can be 
a graft copolymer of ketone group containing monomer, optionally with 
another monomer, grafted onto a backbone chain of a normal polymer for 
example a hydrocarbon polymer, or a block copolymer having discrete 
polymeric segments of polymerized ketone monomer, optionally with another 
monomer, and discrete segments of a normal polymer. 
This has very significant practical, commercial consequences, especially in 
respect of polyethylene compositions. Instead of having to prepare random 
copolymers of ethylene and a ketone by copolymerization of a mixture of 
these monomers, which as noted above is difficult and expensive on a 
commercial scale, one can according to the present invention prepare 
polyethylene, in the normal way, and then graft copolymerize the ketone 
containing monomer onto the preformed polyethylene.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Since the invention shows its greatest advantages in respect of ethylene 
and propylene polymer compositions, it will be further described with 
specific reference thereto, especially polyethylene. However, it should 
not be construed as being limited to blends thereof, with ethylene-ketone 
graft or block copolymers. It is similarly applicable to other synthetic 
vinyl or vinylidene polymers such as polymers and copolymers of styrene, 
butene, isobutylene, pentene, hexene, .alpha.-methylstyrene, methyl 
acrylate, methyl methacrylate, acrylonitrile, acrylic acid, vinyl acetate, 
acrylamide, butadiene, isoprene, chloroprene and the like. 
The graft copolymer or block copolymer can be produced by any of the 
standard methods of graft or block copolymerization known in the art. In 
general, these processes include mixing the preformed polyethylene with 
the monomer or monomers to be grafted thereon, and then generating free 
radicals in the mixture so as to initiate the graft copolymerization, e.g. 
by subjecting the mixture to irradiation, the action of light, or 
including suitable chemical initiators of free radical polymerization, 
such as redox systems, azo compounds, peroxy compounds or the like, and 
then subjecting the mixture to known polymerization conditions. Suitably, 
the initiator is a peroxide compound, for example lauroyl peroxide, 
decanoyl peroxide, dicumyl peroxide or the like. Grafting occurs by free 
radical abstraction of a hydrogen atom from the polyethylene. 
It is preferred according to the present invention to graft a mixture of 
the ketone monomer with another monomer onto the polyethylene. If ketone 
monomer is used alone, to produce homopolymer grafted polymer side chains, 
discolouration and cyclization may occur on account of continuous 
sequences of adjacent ketone groups in the polymer side chain. Copolymeric 
side chains reduce the risk of this occurring, since the copolymers 
provide "spacers" between the ketone groups in the side chains. 
Substantially any comonomer which is copolymerizable with the ketone 
monomer under the same polymerization conditions and at substantially the 
same rate as the ketone monomer can be used. Specific suitable monomers 
include styrene, .alpha.-methylstyrene, diethyl fumarate, methyl acrylate, 
methyl methacrylate, vinyl acetate, acrylic and ethyl acrylate and the 
like. 
One specific preferred graft copolymerization process is a melt process, in 
which a polyethylene, preferably a relatively low molecular weight 
polyethylene, is melted and a mixture of grafting monomers and catalyst is 
added to it. The mixture is stirred for a time of about 5-6 half-lives of 
the catalyst. Then excess monomer is removed by application of a vacuum, 
and the grafted copolymer is poured out of the reaction vessel and allowed 
to cool. 
In another process, polyethylene is mixed with water and the monomers and 
catalyst added. The mixture is stirred and the temperature is raised to 
initiate polymerization. After a suitable time, the solid product is 
separated and dried. Alternatively, the catalyst may be dissolved in an 
organic solvent and added to the polyethylene, the monomers added and the 
mixture heated to effect the polymerization. 
The product which is formed as a result of the graft copolymerization step 
inevitably contains some homopolymer or copolymer formed from the 
polymerization or copolymerization of the grafting monomers alone. If 
desired, the graft copolymer can be separated from the other polymeric 
components so formed, e.g. by extraction with a suitable solvent. It is 
not necessary to separate this polymerized material from the graft 
copolymer, however, since it is molecularly dispersed therewith to form a 
compatible, homogeneous mixture which behaves as if it were totally graft 
copolymer. 
The ketone monomer which is graft copolymerized onto the polyethylene or 
other polymeric backbone has the general formula 
##STR2## 
wherein R.sub.5 represents a hydrogen atom or a C.sub.1 -C.sub.6 alkyl 
group, and R.sub.6 represents a hydrogen atom, a C.sub.1 -C.sub.6 alkyl 
group, an aryl group, an alkaryl group having up to 9 carbon atoms, or an 
alkenyl group having up to 6 carbon atoms. Specific preferred examples of 
suitable such ketone monomers include methyl vinyl ketone, ethyl vinyl 
ketone, methyl isopropenyl ketone, tertiary-butyl vinyl ketone, isobutyl 
vinyl ketone, isopropyl vinyl ketone, tertiary amyl ketone, isoamyl vinyl 
ketone and the like. 
The amount of ketone monomer which is graft copolymerized onto the 
polyethylene depends to some extent upon the proportion in which the graft 
copolymer is to be mixed with the normal polyethylene, to form the final 
photodegradable composition. It should be sufficient to incorporate into 
the graft copolymer from about 0.2 to about 20 weight percent, and 
preferably from about 0.5 to about 7 weight percent, of ketone carbonyl 
groups derived from the ketone group containing monomer. When the chosen 
ketone monomer is methyl vinyl ketone, this corresponds to a copolymer 
containing from about 0.5 to about 50 weight percent, and preferably from 
about 2.5 to about 17.5 weight percent, of methyl vinyl ketone. The graft 
copolymer is blended with the normal synthetic polymer in amounts suitably 
in a weight ratio of from about 1.2 to about 1.50 and preferably from 
about 1:4 to about 1:50 and preferably from about 1:4 to about 1:24. These 
proportions are chosen in individual cases on the basis of the desired 
rate of photodegradation of the final blended polymer compositions, the 
amount of ketone carbonyl in the graft copolymer, and the relative costs 
of the polymeric components of the composition. 
The method of mixing the polymeric components to form the polymer 
composition according to the invention is not critical, provided that an 
intimate dispersion of the components in the blend is formed. Methods of 
polymer blending known in the art can be used. These methods include dry 
mixing in a mixer, on a mill, on a Banbury mixer, or solution blending, or 
hot melt blending. 
The ethylene-ketone graft copolymers of the invention show good 
compatibility with commercial polyethylenes, both high density and low 
density, which are currently available on the market. As noted previously, 
polyethylene normally presents considerable problems in the preparation of 
polymer blend compositions including it. As is known in the art, very few 
other polymers are sufficiently compatible with polyethylene to allow 
blends thereof to be prepared which have physical properties permitting 
them to be used for the preparation of plastic articles. This is probably 
a consequence of the chemical structure of the polyethylene molecules. The 
graft copolymers of ketone monomers on polyethylene described herein do, 
however, exhibit satisfactory compatibility with normal polyethylenes to 
allow preparation of useful blends therewith, in the proportion desired in 
the present invention. 
Another specific example of a photodegradable composition according to the 
present invention is a blend of polypropylene and a graft copolymer of 
polyethylene with a ketone monomer graft copolymerized thereon, the ranges 
of polymers and monomers in the blend being as previously described. 
Propylene is a particularly difficult monomer to copolymerize with 
monomers containing polar groups, such as unsaturated ketones, since 
propylene will only polymerize to high molecular weight polymers under the 
action of catalyst systems which are generally deactivated by polar 
monomers such as unsaturated ketones. It is not therefore practical to 
make photodegradable polypropylenes by copolymerization of propylene. 
The graft copolymers of ethylene and unsaturated ketones according to the 
present invention are, however, compatible with polypropylene, at least in 
the small amounts necessary to produce photodegradable polypropylene 
blends. Thus, the present invention provides useful photodegradable 
polypropylene compositions. 
A further specific example of a graft copolymer according to the invention, 
useful for blending with polymers such as polyethylene or polypropylene 
for forming photodegradable polymeric compositions, is a graft copolymer 
comprising a substrate or backbone of ethylene-propylene copolymer, having 
graft copolymerized thereon ketone group containing polymeric or 
copolymeric side chains, as previously described. Such ethylene-propylene 
copolymers provide good grafting substrates, since they have substantial 
amorphous polymeric regions, and can be of low or high molecular weight as 
desired. The resulting graft copolymers are compatible in the ranges 
necessary to produce photodegradable polymer blends, with both 
polyethylene and polypropylene in accordance with the invention as well as 
with other polymers. 
The polymer composition according to the present invention can be 
fabricated into plastic articles by fabrication techniques known in the 
art as useful for the corresponding synthetic polymers. No special 
modifications of normal molding, extruding, etc. procedures appear to be 
necessary. They behave essentially as known polymers from the same 
predominant monomers, and can be used in similar known applications, e.g. 
for making films, sheets, molded articles such as trays, bottles, cups, 
containers, cigar tips, blow molded articles, coatings, foams, fibres, 
ropes, etc., where the corresponding regular polymers are commonly used. A 
particularly useful application of the polymer compositions of the 
invention, especially the polyethylene composition, is in agricultural 
mulch film, for the temporary covering of agricultural crops in an outdoor 
environment. 
The invention is further illustrated in the following specific examples. 
EXAMPLE 1 
A series of graft copolymers of ketone monomers and other co-grafting 
monomers, graft copolymerized onto polyethylene, were prepared, blended 
with commercially available normal polyethylenes and the resulting 
compositions tested for photodegradability on exposure to ultraviolet 
radiation. 
The graft copolymers were prepared by a melt process. Commercially 
available branched polyethylene of relatively low molecular weight was 
melted in a flask at 130.degree. C. Monomers and catalyst were added. The 
mixture was maintained at this temperature and stirred, for a period of 
time corresponding to 5-6 half-lives of the chosen peroxide graft 
copolymerization catalyst. This time of reaction varied from about 20 
hours, when di-tertiary-butyl peroxide was used as catalyst, to about 5 
hours when tertiary-butyl perbenzoate was used as catalyst. Then, any 
excess monomer was removed by the application of a vacuum to the reaction 
flask for a period of about 1 hour. The resultant grafted copolymer 
product was then poured out of the reaction flask and allowed to cool. 
Details of the various graft copolymers and their preparation are given in 
Table I. 
In preparing graft copolymers 5, 6 and 7, attempts were made to destroy 
residual catalyst at the end of the polymerization by maintaining elevated 
temperatures for several half-lives of the catalyst after completion of 
the normal reaction period. Sample 7 as a result underwent a degree of 
cross linking, substantially increasing its molecular weight. 
In Table I, the figures are weight percentages based upon the weight of 
backbone, substrate polymer used. 
Table I 
__________________________________________________________________________ 
Weight % 
Ketone 
Graft Catalyst 
Grafting 
Monomer 
Copolymer 
Substrate and Monomers 
Incorpora- 
Numbers 
Polymer Amount and Amounts 
ed 
__________________________________________________________________________ 
1 Polyethylene 
Tertiary-butyl 
Methyl iso- 
1.5 
molecular weight 
perbenzoate 2% 
propenyl 
c 4,000 ketone 10% 
2 Polyethylene 
Di-tert-butyl 
Methyl iso- 
1 
molecular weight 
peroxide 2% 
propenyl 
c 8,000 ketone 10% 
Diethyl 
fumarate 10% 
3 Polyethylene 
Di-tert-butyl 
Methyl iso- 
3.5 
molecular weight 
peroxide 2% 
propenyl 
c 8,000 ketone 10% 
methyl- 
styrene 10% 
4 Polyethylene 
Di-tert-butyl 
Methyl vinyl 
9 
molecular weight 
peroxide 2% 
ketone 10% 
c 8,000 .alpha.-methyl- 
styrene 10% 
5 Polyethylene 
Tertiary-butyl 
Methyl-iso- 
1 
molecular weight 
perbenzoate 1% 
propenyl 
c 8,000 ketone 5% 
6 Polyethylene 
Tertiary-butyl 
Methyl vinyl 
3 
molecular weight 
perbenzoate 1% 
ketone 5% 
c 8,000 .alpha.-methyl- 
styrene 5% 
7 Polyethylene 
Tertiary-butyl 
Methyl vinyl 
3 
molecular weight 
perbenzoate 1% 
ketone 5% 
c 8,000 .alpha.-methyl- 
styrene 5% 
__________________________________________________________________________ 
In experiments to produce graft copolymers 6, 7, 8 and 9, heating was 
continued after completion of the normal reaction period, in an attempt to 
destroy residual catalyst. 
Next, the graft copolymers so formed were blended with various amounts of a 
low density polyethylene which is commercially available, specifically 
that designated CIL560, available from Canadian Industries Ltd., Montreal 
Canada. These blends were prepared on a two-roll mill. 
Films of approximate thickness 0.07 mm. were compression molded at 40,000 
psi pressure and 140.degree. C. temperature from certain of these 
compositions, and subjected to weathering tests. To perform this test, the 
sample was mounted in a UV Accelerometer, in which the sample is mounted 
on a drum which rotates around an ultraviolet emitting, mercury arc lamp, 
and thus treated with ultraviolet radiation for various periods of time. A 
control film of polyethylene, CIL560, of similar thickness was also used. 
The photodegradable breakdown of the films on exposure was monitored by 
following the increase in carbonyl absorbance in the infra red spectrum of 
the sample, and by detecting the onset of brittleness as determined by the 
"crease-bend" test. The carbonyl absorbance is expressed as a carbonyl 
index Z, which is the ratio of absorbance at 1715 cm..sup.-1 to the 
absorbance at 1375 cm..sup.-1 (which latter is the absorbance of the 
CH.sub.2 mode). When the carbonyl absorbance had reached a certain value, 
the crease-bend test was also carried out. In this test, the film is bent 
through to 180.degree. and creased. If, on opening out the film following 
this operation, it breaks along the crease, the film is said to be 
brittle. The results are reported in Table II. 
TABLE II 
__________________________________________________________________________ 
Weight Ratio 
Graft Co- 
graft copoly- 
Hours in Hours in 
polymer 
mer: Accelero- 
Carbonyl 
Accelero- 
Carbonyl 
number polyethylene 
meter Index Z 
meter Index Z 
__________________________________________________________________________ 
Control 
0 0 -- 220 0.373 
40 0.058 280 0.600 
80 0.112 340 0.929 
160 0.232 420 1.265 
1 1:9 0 0.118 160 0.541 
40 0.178 220 0.882 
80 0.261 280 1.171 
2 1:9 0 0.194 160 0.546 
40 0.375 220 0.979 
80 0.451 280 1.330 
3 1:9 0 0.296 220 1.352 
40 0.316 280 1.690 
80 0.482 340 2.289 
160 0.819 420 2.956 
4 1:9 0 0.856 220 1.149 
40 0.352 280 1.508 
80 0.497 340 1.851 
160 0.794 420 2.298 
4 1:9 0 0.471 280 1.850 
80 0.377 360 2.788 
160 0.844 400 2.973 
__________________________________________________________________________ 
Similar tests were carried out with blends prepared from graft copolymers 
5, 6 and 7 from Table I again using the polyethylene CIL 560, in a weight 
ratio of 1:19. In this case the Accelerometer was fitted with a UV lamp of 
higher intensity, with the result that the films became brittle more 
quickly. A control film of CIL 560 polyethylene was similarly run. The 
results are given in Table III. 
TABLE III 
______________________________________ 
Hours in Carbonyl 
Accelerometer 
Index 
______________________________________ 
Control 0 0.038 
40 0.085 
80 0.392 
Blend of Graft 
0 0.042 
Copolymer 5 
40 0.112 
80 0.603 
Blend of Graft 
0 0.067 
Copolymer 6 
40 0.167 
80 1.016 
Blend of Graft 
0 0.070 
Copolymer 7 
40 0.202 
80 1.151 
______________________________________ 
All of the above samples became brittle according to the crease-bend test 
within 120 hours of exposure. 
The above results demonstrate the accelerated photodegradability upon 
exposure to ultraviolet radiation of the compositions of the invention, 
indicated by increasing carbonyl contents. 
In other properties, the blended compositions according to the present 
invention are essentially similar to normally available commercial 
polyethylenes, and can be molded and fabricated in the same general way. 
Their shelf and storage life out of ultraviolet radiation is indefinite, 
as in the case of normal polymers. 
Similar results are obtained by using as the backbone substrate for 
grafting purposes a higher molecular weight polyethylene, provided that 
sufficient shearing agitation is provided during the graft 
copolymerization step. For example, this process can conveniently be 
carried out in an extruder, the polymer being extruded at elevated 
temperature and the monomers and catalyst being added to the extrusion 
apparatus. 
EXAMPLE 2 
In this example, graft copolymer generally as previously described was 
blended with polypropylene and the resulting blends tested for 
photodegradability. 
In a first experiment a commercially available ethylene propylene copolymer 
(NORDEL 1500, from E. I. duPont de Nemours and Company) was used as a 
grafting substrate, and into this was graft copolymerized methyl 
isopropenyl ketone. Pellets of the ethylene propylene copolymer were mixed 
with an approximately equal volume of water and catalyst (2% decanoyl 
peroxide) and monomer (14% methyl isopropenyl ketone) added, with stirring 
for an extended period of time to allow absorption of the monomer. Then 
the temperature was raised to 75.degree.-80.degree. C. to allow 
polymerization. After 5 half-lives of the catalyst, the pellets were 
filtered off, washed with water and dried. The resulting product contained 
8 weight % of methyl isopropenyl ketone. 
The graft copolymer so formed was blended with commercially available 
polypropylene (Shell 5520) on a two-roll mill, in the proportion 1 part by 
weight graft copolymer to 9 parts by weight polypropylene. A compatible 
blend was formed. Films of the blend were made by compression molding at 
180.degree. C. and 25000 psi, to produce films approximately 3/1000 inch 
thick. Samples of these films were exposed in a UV accelerometer as 
described in Example 1, alongside a similar sample film of the 
polypropylene as control. 
After four hours exposure, the film of the blend had become brittle, whilst 
no such change was apparent with the polypropylene control. 
As a further control, a blend of the ethylene-propylene copolymer and the 
polypropylene was prepared, in the same proportions and pressed into a 
similar film and similarly tested. No brittleness of this film was 
apparent after four hours exposure. 
EXAMPLE 3 
The graft copolymer number 4 described in Example 1 was blended with 
polypropylene as described in Example 2, at a weight ratio of 1:9, graft 
copolymer in minor proportion. Films were compression molded from this 
compatible blend, and tested for UV photodegradability, as described in 
Example 2. 
The films were brittle after four hours exposure. 
For comparison purposes, a 1:9 blend of low density polyethylene (CIL 560) 
and the polypropylene was similarly prepared, molded into a film and 
tested. This blend showed no apparent brittleness after four hours 
exposure. 
Similar results are also obtained when using various other polymers as 
previously described, as the substrates onto which the monomers are 
grafted, and then blending the graft copolymers so formed with other 
similar polymers with which the graft copolymer is compatible. 
It will be appreciated that the invention is not limited to the specific 
embodiments described and illustrated herein, but is defined in the 
appended claims.