Photochemical modification of polyethylene surface with aryl azides

Article abstract of DOI:10.1134/S0018143913050020

It has been shown that the formation of a covalently grafted modifying layer takes place during the photolysis of polycrystalline layers of 2-azidoanthraquinone and 4-azidobenzoyl azide on the surface of polyethylene. Its thickness is determined by the amount of the azide applied, and phenyl isocyanate groups formed by the photolysis of 4-azidobenzoyl azide are prone to further functionalization of the modified surface with primary amines.

Full text of DOI:10.1134/S0018143913050020

ISSN 0018ꢀ1439, High Energy Chemistry, 2013, Vol. 47, No. 5, pp. 237–241. © Pleiades Publishing, Ltd., 2013.
Original Russian Text © A.V. Budruev, D.Yu. Sinjagina, 2013, published in Khimiya Vysokikh Energii, 2013, Vol. 47, No. 5, pp. 365–369.
PHOTOCHEMISTRY
Photochemical Modification of Polyethylene Surface
with Aryl Azides
A. V. Budruev and D. Yu. Sinjagina
Nizhni Novgorod State University, pr. Gagarina 23, Nizhni Novgorod, 603950 Russia
eꢀmail: budruev@gmail.com
Received April 17, 2013; in final form, April 30, 2013
Abstract—It has been shown that the formation of a covalently grafted modifying layer takes place during the
photolysis of polycrystalline layers of 2ꢀazidoanthraquinone and 4ꢀazidobenzoyl azide on the surface of polyꢀ
ethylene. Its thickness is determined by the amount of the azide applied, and phenyl isocyanate groups
formed by the photolysis of 4ꢀazidobenzoyl azide are prone to further functionalization of the modified surꢀ
face with primary amines.
DOI: 10.1134/S0018143913050020
Photodissociation of aryl azides yields singlet and reactions are insertion into multiple or C–H and
triplet nitrenes, as well as 1,2ꢀdidehydroazepines [1–
N
⎯
H bonds for nitrenes [9, 10] and addition to
8
]. The reactivity of these shortꢀlived intermediates is nucleophilic groups for 1,2ꢀdidehydroazepines [11–
determined by the molecular structure, and their basic 14].
N3
NO2
NH2
X
X
X
•
RH –R
•
h
ν
–N2
O2
isc
RH
•
+
R
X
X
•
•
R
•
N
•
N
•
NH
N
N
X
X
X
X
H
HNu
–N /CO ArN /ArNCO
2 3
X
N
N
X
N
Nu
RH
Scheme. Main photochemical reactions of aryl azides.
The ability of the intermediates to form covalent a process that reduces the efficiency of the insertion
bonds with substrate molecules found practical appliꢀ reaction [20, 21].
cation in works related to investigation into the strucꢀ
One of the challenges in the formation of the covaꢀ
ture and behavior of complex biomolecules [15–17]
lent crosslinks" is the surface modification of polyethꢀ
and in photolithography for creating covalently
ylene (PE). A low reactivity of the methylene groups of
crosslinked polymer layers [18, 19].
the polymer and the uniformity of the surface properꢀ
The efficiency of the formation of the covalent ties make it an interesting object for photochemical
crosslinks” is often not high and is determined not modification with aryl azides. In this study, 2ꢀazidoanꢀ
“
only by the activity of intermediates, but also by the thraquinone (2AA), 4ꢀazidobenzoic acid (4ABK) and
nature of the substrate. In the presence of air oxygen, 4ꢀazidobenzoyl azide (4ABA) were used as photosenꢀ
nitrenes are oxidized to nitro and nitroso compounds, sitive agents for modifying the PE surface.
237

238
BUDRUEV, SINJAGINA
O
O
N3
N3
N3
OH
N3
O
O
2АА
4ABK
4ABA
EXPERIMENTAL
Electronic absorption (UV/Vis) spectra of polymer
layers in the range of 200–800 nm were recorded verꢀ
(
1
ν
ArN3 and Ar(CO)N ); 1698 (ν C=O); 1288.5,
as
249.05 (
3
Ar(CO)N3
ν
ArN3
)
.
s
A solution of the azide in methylene chloride was
sus the irradiated but not modified films on an Analyꢀ applied to have a given mass per unit area on a methꢀ
tik Jena Specord 40 spectrophotometer. The IR specꢀ ylene chlorideꢀdegreased and stretched polyethylene
–1
2
tra were recorded in the range of 4000–400 cm on a film with an area of 24.6 cm . After evaporation of the
Shimadzu IRPrestigeꢀ21 Fourierꢀtransform spectroꢀ solvent, a dense fineꢀgrained layer of the azide was
photometer. To increase sensitivity in recording the IR formed on the film.
spectra, the films were folded 64 times and compressed
The stretched films with the deposited azide layers
into tablets with a hydraulic press (200 MPa).
were irradiated with light of a DRKꢀ120 highꢀpressure
Corresponding amines (0.015 mol) were dissolved
in a mixture of 15 mL of water and 17 mL of HCl conc.
and then diazotized with NaNO2 (1.08 g, 0.015 mol
mercury lamp at a distance of 14 cm. The irradiated
films were washed twice in 20–30 mL of a solvent and
dried. Methylene chloride was used to remove 2AA
and 4ABA, and 4ABK was removed with acetonitrile
as a better solvent for it.
in 10 mL of water) at 0–5°C. On cooling and after
3
0ꢀmin agitation of the solution with a magnetic stirꢀ
rer, the diazonium salts were azidized with sodium
azide (1.3 g, 0.02 mol in 10 mL of water).
RESULTS AND DISCUSSION
4ꢀAzidobenzoic acid (white needleꢀlike crystals)
was reprecipitated from acetone with water and
recrystallized from a boiling mixture of petroleum
ether and benzene in a volume ratio of 5 : 2. IR (KBr
To reduce the translational diffusion of intermediꢀ
ates, increase the probability of their interaction with
the polymer surface, and hinder oxidation with air
oxygen, PE was modified by photolyzing dense polyꢀ
crystalline layers of azides on the polymer surface.
–1
disks, cm ): 2130.07, 2106.68, 2053.01 (
ν
N );
as 3
1
680.67 (
ꢀAzidoanthraquinone (yellow crystals) was
recrystallized from boiling benzene. IR (KBr disks,
ν
C=O); 1287.44 ( s
ν
N3).
2
Photolysis of monoazides under these conditions
may result in the formation of monolayers of the modꢀ
ifying coating, because the insertion of nitrenes in the
aromatic C–H bonds of other azide molecules is
unlikely. However, the insertion of nitrenes into carboꢀ
nyl groups of the azide molecules with the formation
of crosslinked threeꢀdimensional layers is possible in
the case of 2AA or 4ABK photolysis.
–1
cm ): 2116.41, 2031.54 (
ν
N ); 1678.08 ( C=O);
3
ν
as
1302.44 (νs
N3).
4ꢀAminobenzoic acid hydrazide was prepared by
heating 2.5 g (0.015 mol) of ethyl 4ꢀaminobenzoate
with 15 mL of hydrazine monohydrate for 6 h on a
water bath under reflux. Then the crystalline solid
formed by cooling was thoroughly filtered off and
washed with a little quantity of iceꢀcold isopropanol.
The separated hydrazide was used without further
purification for the synthesis of 4ꢀazidobenzoyl azide.
The photolysis of 4ABA (as that of aryl azide or
benzoyl (aroyl) azide)) follows a more complex mechꢀ
anism. Photochemical reactions of the aryl azide moiꢀ
ety of 4ABA are similar to the reactions of other aryl
azides. Photolysis of the aroyl azide moiety leads to the
formation of both aroyl nitrenes, which can insert into
bonds like aryl azides, and isocyanates as a Curtius
rearrangement product [6, 22, 23]. Therefore, nitrenes
formed by the photolysis of 4ABA are capable of
inserting in the multiple bonds of carbonyl and isocyꢀ
anate groups to form “thick” modifier layers.
–1
IR (KBr disks, cm ): 3424, 3343 (
C=O)
In a thickꢀwalled 0.5ꢀL beaker, 2 g (0.015 mol) of
dry 4ꢀaminobenzoic acid hydrazide was dissolved in
ν
NH); 1627
(
ν
.
2
0
1
00 mL of 1.0 N hydrochloric acid. To the solution at
–5 , a solution of 2.2 g (0.032 mol) of NaNO2 in
0 mL of water was poured with stirring, and the
°C
resulting mixture was stirred for additional 30 min.
Then, a solution of 1.3 g (0.02 mol) of NaN3 in 10 mL
Thus, photolysis of 2AA or 4ABK on the PE surꢀ
of cold water was added. The reaction takes place face will result in the surface functionalization with
immediately with the formation of fluffy white crysꢀ the “grafting” of 2ꢀaminoanthraquinone or 4ꢀamiꢀ
tals, which were reprecipitated from acetone with nobenzoic acid, respectively, and that of 4ABA will
water and recrystallized from acetone without heating. lead to the “grafting” of fragments of substituted 4ꢀ
IR (solution in CCl4, cm–1): 2176; 2134; 2129; 2092 aminophenyleneizocyanate.
HIGH ENERGY CHEMISTRY
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PHOTOCHEMICAL MODIFICATION OF POLYETHYLENE SURFACE
239
A
A
5
4
3
2
1
0
0
0
0
.0
.8
.6
.4
.2
0
1
0
0
0
.9
2
3
.8
.7
1
2300
2200
2100
2000
cm–1
10
30
50
70
90 110 130 150
Fig. 1. IR spectra of the PE film (
ification with 4ABA in a quantity of 40
for ( ) 1, ( ) 3, ( ) 6, and ( ) 12 min.
1
) before and after modꢀ
µ
g/cm2
2
µ
g/cm irradiated
2
3
4
5
Fig. 2. The change in the optical density of the samples of
the modified PE in the UV and IR spectra, depending on
the amount of 4ABA; irradiation time, 15 min: at (1) a
–1
Since the optical density of the layer is proportional
wavelength of 250 nm, (
2) a wave number of 2262.5 cm ,
–1
and ( ) a wave number of 2135.7 cm
3
.
to the amount of a modifier on it, the degree of surface
modification and the thickness of the layer formed
were estimated by change in the optical density of the
modified films relative to irradiated samples without
azide deposition.
the dependence of the optical density of the films on
the irradiation time must flatten out.
The IR spectra of a series of 4ABAꢀmodified samꢀ
ples were found to exhibit an absorption band due to
asymmetric stretching vibration of the isocyanate
After washing the irradiated 4ABKꢀcoated films, a
layer of photolysis products remained, which had a
low adhesion and could be easily mechanically
removed from the surface. Since the UV/Vis and IR
spectra of the samples after removing the surface layer
of the photolysis products did not differ from those of
the unmodified layers, the PE modification with
–1
group (2261.56 cm ). After 1ꢀmin irradiation of the
–1
sample, the absorption band at 2135.37 cm assigned
to asymmetric stretching vibration of the azide group
was detected (Fig. 1). This seems to be due to the
“
grafting” of aroyl azide or aryl azide group of 4ABA
4ABK was not further studied.
without dissociation of another azide group of the
molecule.
In contrast, irradiated and washed films modified
with 2AA and 4ABA had a dense, flexible and nonreꢀ
movable coating. After photolysis, they took a yellowꢀ
ish tint, which was changed by pressing IR spectrosꢀ
copy disks to a yellow brown color typical of the phoꢀ
tolysis products of organic azides.
The study of a set of samples with the amount of the
2
applied 4ABA varying from 10 to 162
µ
g/cm and irraꢀ
diated for 15 min revealed a fivefold increase in the
absorbance of the modified films in the UV/Vis range
(
Fig. 2, curve 1). The optical density of the asymmetric
To study the effect of the photolysis time on the
degree of modification of the polymer surface with a
constant amount of azide applied on the film, samples
stretching bands of the isocyanate and azide groups in
the IR spectrum also increased with the increasing
amount of the modifier (Fig. 2; curves 2, 3).
2
2
with 40
µ
g/cm 4ABA and 50 g/cm 2AA coatings
µ
Similar results were obtained in the study of the
effect of the amount of deposited 2AA on the degree of
were irradiated.
Comparison of the absorption spectra of the sets of
samples has shown that the absorbance of the modiꢀ
fied layers increases with the increasing photolysis
time. The increase in the optical density may be
explained by both a growing proportion of the modiꢀ
fied methylene units on the surface layer of PE and an
increase in the thickness of the layer of the azide phoꢀ
tolysis products on the PE surface.
PE modification. A set of samples with a 2AA coating
2
of 9 to 135
µ
g/cm and an irradiation time of 30 min
for each sample was examined. By comparing the
UV/Vis spectra of these samples, it was found that the
optical density of the films increases with an increase
in the amount of the azide irradiated on them. Absorpꢀ
–1
tion bands with the maximum at ~1679 cm assigned
to the stretching vibration of the carbonyl group
If the modification affects only the surface layer of appeared in the IR spectra. That is, the modification
the polymer, it is likely that at long irradiation times of the surface with 2AA resulted in the “grafting” of
when all azide molecules contacting with the surface secondary 2ꢀaminoanthraquinone fragments upon the
enter into the reaction, the absorbance of the modified insertion of aryl nitrenes in the CH bonds of the polyꢀ
samples will not increase. Consequently, the plot of mer methylene groups.
HIGH ENERGY CHEMISTRY
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240
BUDRUEV, SINJAGINA
Since the photolysis of polycrystalline layers of aryl indicating the chemical “grafting” of the modifier
azides may generate sparingly soluble oligoazopolyꢀ layer.
mers covalently not bonded to the polymer surface,
The last step was the study of the reaction of isocyꢀ
dimethylsulfoxide (DMSO) was used as a solvent for anate groups of the modified surface with amines in
washing off the products because of its capability to aqueous solutions. Sulfanilic acid, the sulfonate group
of which has a characteristic absorption in the infrared
range, was used as the amine. An increase in the
absorption of the treated samples in this region of the
solubilize such oligomers.
An analysis of the modified films revealed that the
replacement of methylene chloride by DMSO does spectrum would be evidence for the interaction of sulꢀ
not reduce the optical density of the films (Fig. 3), fanilic acid with the modified polyethylene.
H2N
hν
ABA
SO3H
C, 30 min
4
60
°
n
n
n
HN
HN
HN
SO H
3
O
NCO
N
N
H
H
H O
2
n
n
–CO2
HN
O
N
H
OH
NH2
The isocyanate groups of the modifier will react under similar conditions is more likely than their
hydrolysis [24].
with the amine group of sulfanilic acid to form substiꢀ
tuted diphenylurea. Some of the isocyanate groups can
The modified PE films were incubated in aqueous
be hydrolyzed with water to form carbamic acid and solutions of sulfanilic acid with concentrations of
–
2
–2
–1
1.9
×
10 and 5.6
×
10 mol L at 60°C for 30 min
then a primary amine. However, we have shown previꢀ
ously that the interaction of isocyanates with amines
and then washed in water and methylene chloride.
By comparing the IR spectra of the obtained samꢀ
ples with the spectra of samples with nonꢀmodified
–1
A250
layers, an increase in the absorption at 1255 cm
assigned to the stretching vibration of the sulfonate
group was detected. An increase in the concentration
of sulfanilic acid in the solution resulted in an increase
in the optical density of the absorption bands of these
groups.
1
1
0
0
0
0
.2
.0
.8
.6
.4
.2
0
Therefore, photolysis of polycrystalline layers of
the series of aryl azides on PE resulted in the formation
of bulky, not monomolecular coating covalently linked
to the polymer surface.
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Translated by V. Makhaev
HIGH ENERGY CHEMISTRY
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2013