Applicability of photochemically generated pendant benzoyl peroxides in both grafting from and grafting to techniques

Article abstract of DOI:10.2478/s11696-012-0250-3

Methyl methacrylate and styrene copolymers containing pendant benzil groups, such as 1-[4-(2-methacroyloxyethoxy)phenyl]-2-phenyl-1,2-ethanedione-co- methyl metacrylate (BzMA/MMA), 1-[4-(2-methacroyloxyethoxy)phenyl]-2-phenyl-1,2- ethanedione-co-styrene (

Full text of DOI:10.2478/s11696-012-0250-3

Chemical Papers 67 (1) 9–17 (2013)
DOI: 10.2478/s11696-012-0250-3
ORIGINAL PAPER
Applicability of photochemically generated pendant benzoyl
peroxides in both “grafting from” and “grafting to” techniques
a
b
b
aJaroslav Mosnáček*, Ivan Lukáč, Monica Bertoldo, Francesco Ciardelli
aPolymer Institute, Slovak Academy of Sciences, Dúbravská cesta 9, 845 41 Bratislava, Slovakia
bIstituto per i Processi Chimico Fisici, Consiglio Nazionale delle Ricerche (IPCF-CNR), via G. Moruzzi 1, 56124 Pisa, Italy
Received 30 March 2012; Revised 3 July 2012; Accepted 11 July 2012
Dedicated to Professor Štefan Toma on the occasion of his 75th birthday
Methyl methacrylate and styrene copolymers containing pendant benzil groups, such as 1-[4-
(2-methacroyloxyethoxy)phenyl]-2-phenyl-1,2-ethanedione-co-methyl metacrylate (BzMA/MMA),
1-[4-(2-methacroyloxyethoxy)phenyl]-2-phenyl-1,2-ethanedione-co-styrene (BzMA/S), and 1-phenyl-
2-(4-propenoylphenyl)-1,2-ethanedione-co-styrene (PCOCO/S), were prepared and used as precur-
sors for photochemically generated pendant benzoyl peroxides. Decomposition of the pendant ben-
zoyl peroxides was subsequently used in grafting processes. Either irradiation or a combination of
irradiation with subsequent thermal treatment was adopted for grafting a thin layer of BzMA/MMA
copolymer onto the surface of LDPE films. The grafting resulted in a significant decrease in contact
angle of the film surface. The same activation strategy was successfully adopted to initiate the poly-
merisation of acrylic or methacrylic acids from the surface of styrene copolymer films containing
the initiator precursor in the polymer side chains (BzMA/S and PCOCO/S). The successful surface
grafting was proved by contact angles measurement as well as by infrared spectroscopic analysis.
c
ꢀ 2012 Institute of Chemistry, Slovak Academy of Sciences
Keywords: photografting, surface modification, photo-initiator, cross-linking, increased hy-
drophilicity
Introduction
(Hoffman, 1984), electron and ion beams (Lunkwitz
et al., 1995), and UV sources (Yang & R˚anby, 1999;
Mosnáček et al., 2007; Novák et al., 2007). Various
polar groups are introduced onto the polymer surface
as a result of these treatments. However, the large
quantity of free radicals generated by these meth-
ods imposes several disadvantages, principally those
of low specificity, degradation, and cross-linking of the
macromolecules.
Two main strategies exist for modification of the
polymeric or inorganic surfaces by polymers: the
“grafting onto” technique, representing grafting of the
polymer chains onto the surface, and the “grafting
from” technique, representing the polymerisation of
monomers from initiating sites covalently anchoring
The surface properties of polymers frequently
equal their bulk properties in importance. The sur-
faces of most engineered polymers in use today are
all somewhat hydrophobic; hence it is difficult to
bond these hydrophobic polymer surfaces directly
with other substances, such as adhesives, printing
inks, and paints, which generally consist of polar
groups or components. Methods investigated for the
modification of polymer surfaces without altering the
bulk properties include plasma treatment (Chan et
al., 1996), corona discharge treatment (Catoire et al.,
1984), flame treatment (Briggs et al., 1979), and ex-
posure to high-energy radiation, such as gamma rays
*Corresponding author, e-mail: jaroslav.mosnacek@savba.sk

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J. Mosnáček et al./Chemical Papers 67 (1) 9–17 (2013)
Fig. 1. Synthesis of BzMA monomer. Reaction conditions and yields: i) AlCl3, CS2, 18 %; ii) NaOH, H2O, EtOH, heating, 85 %;
iii) SeO2, H2O, dioxane, heating, 42 %; iv) methacrylic acid, H2SO4, CuCl, heating, 79 %.
1999). It was also shown that pendant benzil moi-
eties were converted almost quantitatively to pen-
dant BP in aerated polymer films upon irradiation at
λ > 400 nm (i.e., the region where BP does not ab-
sorb) (Kósa et al., 2000; Mosnáček et al., 2002, 2004a,
2004b). Thus, photochemical generation of pendant
BP is a safe and convenient method for the prepa-
ration of polymers with pendant initiators, such as
diacyl peroxides.
In the present work, we demonstrate the applicabil-
ity of photochemically generated pendant benzoyl per-
oxide groups to both the “grafting onto” and “graft-
ing from” processes. Styrene and methyl methacry-
late copolymers with pendant benzoyl peroxide groups
were used successfully either for “grafting onto” the
surface of low density polyethylene film or for “graft-
ing from” the polymerisation of (meth)acrylic acids.
onto the surface (Zampano et al., 2009). Both tech-
niques incur advantages and disadvantages. While
the “grafting from” technique, mainly in combina-
tion with controlled polymerisation techniques, can
result in more uniform and substantially higher graft-
ing density, access to different polymer architectures
is limited. On the other hand, the “grafting onto”
technique makes it possible to first prepare the poly-
mers with a variety of architectures and subsequently
to graft the surface with different polymer structures
possessing the appropriate properties. Moreover, the
procedure of “grafting onto” can be conducted un-
der mild conditions, whereas most of the “grafting
from” approaches require strict reaction conditions
and also, in some cases, complex surface modifica-
tion.
In the “grafting from” method, the radicals on the
polymer surface may readily be formed by irradia-
tion with, for example, γ-rays or an electron beam,
or by radicals abstracting hydrogen from the poly-
mer substrate. For more specific grafting, the radicals
may be formed on the polymer surface by decompo-
sition of the present pendant initiator functionality
(an azo or peroxide linkage) bound to the polymer
chains, or by transformation of other polymer func-
tionalities (Nuyken & Voit, 1994). Various polymers
containing pendant initiators containing either azo or
peroxy moieties as precursors of radicals were used
in the “grafting from” technique (Nuyken & Weidner,
1986; Gupta et al., 1982). While pendant hydroper-
oxides and dialkyl peroxides are commonly used for
grafting, to the best of our knowledge, diacyl perox-
ides have not been described to date. Since radical
initiators are sensitive and decompose readily under
heat and/or light exposure, care is required and mild
conditions must be maintained throughout the pro-
cesses in the preparation of polymers with pendant
initiators to prevent decomposition.
Experimental
Materials
Monomers 1-[4-(2-methacroyloxyethoxy)phenyl]-2-
phenyl-1,2-ethanedione (BzMA) and 1-phenyl-2-(4-
propenoylphenyl)-1,2-ethanedione (PCOCO) were
synthesised as shown in Fig. 1 (Lukáč et al., 1980,
1982) and Fig. 2 (Lukáč & Das Mohapatra, 1992;
Lukáč et al., 1994), respectively. Copolymers 1-[4-(2-
methacroyloxyethoxy)phenyl]-2-phenyl-1,2-ethanedio-
ne-co-methyl metacrylate (BzMA/MMA; Mn
=
403000 g mol−1, Mw = 1250000 g mol−1 based on
PMMA calibration in THF; 1,2-dicarbonyl content
approximately 6.4 mass %) and 1-[4-(2-methacroyl-
oxyethoxy)phenyl]-2-phenyl-1,2-ethanedione-co-styr-
ene (BzMA/S; Mn = 90500 g mol−1, Mw = 192000
g mol−1 based on PS calibration in THF; 1,2-
dicarbonyl content approximately 11 mass %) were
prepared by free radical polymerisation with 0.1
mass % of AIBN as described previously (Lukáč et al.,
1982). 1-Phenyl-2-(4-propenoylphenyl)-1,2-ethanedio-
We recently demonstrated that benzil (1,2-di-
phenylethane-1,2-dione) could serve as a precursor of
benzoyl peroxides (BP) when irradiated in aerated
solid polymer films (Lukáč & Kósa, 1994; Kósa et al.,
ne-co-styrene (PCOCO/S; Mn
= 481000 g mol−1, Mw
= 981000 g mol−1 based on PS calibration in THF;

J. Mosnáček et al./Chemical Papers 67 (1) 9–17 (2013)
11
Fig. 2. Synthesis of PCOCO monomer. Reaction conditions and yields: i) AlCl3, CCl4, 94 %; ii) SeO2, 70 % AcOH, heating, 89 %;
iii) N-bromosuccinimide, 40 %; iv) AcOK, 99 % AcOH, heating; v) NaOH, MeOH, 90 %; vi) pyridinium chlorochromate,
CH2Cl2, 38 %; vii) acetonitrile, sodium acetate, 60 %.
PCOCO content approximately 24 mass %) was pre-
pared by free radical polymerisation at ambient tem-
perature without any initiator (Lukáč et al., 1994).
Chloroform, acrylic acid, and methacrylic acid (all
from Aldrich) were used as received. As a low density
polyethylene (LDPE), a blown-LDPE film obtained
from low density polyethylene pellets (Exxon Chemi-
cal LD 158 JD; density 0.925 g cm−3, vicat softening
point 98◦C; thickness 50 µm) with one side of the film
corona pre-treated was used.
self-supporting polymer films were separated from the
glass plates by immersing the assemblies into distilled
water. The residual solvent was removed by drying
the films in a vacuum to constant mass at ambient
temperature.
For grafting experiments, the pendant benzoyl per-
oxide structures were generated from pendant benzil
structures by irradiation at λ > 400 nm for 3 h in air
atmosphere in a Spectramat (Ivoclar, Schaan, Liecht-
enstein) apparatus (350–530 nm) using a UV CL SR
HPR plastic film filter (LLumar, USA).
Sample preparation and grafting procedures
Photochemical grafting was performed by immers-
ing the PCOCO/S film pre-irradiated at λ > 400 nm
into a glass tube containing acrylic acid and irradi-
ating with monochromatic light of λ = 366 nm in a
“merry-go-round” apparatus at ambient temperature
using a 125 W medium pressure mercury lamp in com-
bination with a 4 mm Corning 5860 glass filter (USA).
The distance of the films from the axis of the cylin-
drical lamp was 8 cm.
Thermal grafting was performed by immersing the
BzMA/S film pre-irradiated at λ > 400 nm into a
glass tube containing a boiling solution of 15 mole % of
acrylic acid in water for 10 min. In both grafting cases,
the monomer and non-bonded polymer were extracted
3 times with distilled water for 24 h. Any additional
time of extraction afforded no change in either FTIR
spectra or contact angle or decrease in mass of the
film.
Grafting of BzMA/MMA copolymer on surface of
LDPE films
The LDPE films used in the study were non-
corona-treated on one side of the film and corona-
treated on the other side. BzMA/MMA copolymer
was deposited onto the LDPE film by spraying a so-
lution consisting of 10 mg of copolymer in 100 mL
of CHCl3. Irradiation of the samples for various
time periods was performed with a medium pres-
sure mercury lamp Helios Italquartz GR.E. 400 W,
type “P” emitting light of λ > 240 nm (distance
of the polymer surface from the light source was
27 cm). The non-bonded copolymer was removed by
rinsing with CHCl3. The rinsing time was 15 min
in all cases. Any additional rinsing time afforded
no change in either FTIR spectra or contact an-
gle.
Measurements
Grafting from surface of styrene copolymers
A KSV, CAM 200, Optical Angle Meter goniom-
etry was used to measure water static contact an-
gle on various sites of the studied films by forming
5 µL droplets at a rate of 0.2 µL s−1 and two differ-
ent images were recorded for each drop. An average
value was obtained from 3 to 5 measurements for each
sample (maximal deviation was 3◦). FTIR spectra
were recorded on Nicolet FTIR 400 and Perkin–Elmer
Spectrum One spectrometers.
Self-supporting films of 10 cm2 area consisting
of 20 mg of the respective copolymer (BzMA/S or
PCOCO/S) were prepared by casting from chloro-
form solutions (1 mL containing 20 mg of polymer on
2.5 cm × 4 cm glass plates). The plates were covered
with a Petri dish to slow solvent evaporation. This pro-
cedure resulted in films with good optical quality. The

12
J. Mosnáček et al./Chemical Papers 67 (1) 9–17 (2013)
Fig. 3. Grafting of BzMA/MMA copolymer onto surface of LDPE film either by irradiation at λ > 240 nm or at λ > 320 nm, or by
combination of irradiation at λ > 320 nm with subsequent thermal treatment at 95◦C. Reaction conditions: i) irradiation,
O2; ii) LDPE film, irradiation or heating; n = 98.5, m = 1.5.
Results and discussion
Grafting of BzMA/MMA copolymer onto sur-
face of LDPE film
LDPE film with one side non-corona-treated (nct-
LDPE) and the other side corona-treated (ct-LDPE)
surface was used in the grafting experiments. Pho-
tochemical grafting of the BzMA/MMA copolymer
containing pendant benzil groups onto the surface of
LDPE film was first performed by irradiation at λ >
240 nm. Irradiation in this region ensured decompo-
sition of the pendant benzoyl peroxide groups shortly
after their photochemical generation from the pendant
benzil groups in the presence of air (Fig. 3). In or-
der to determine the irradiation time needed for both
complete generation and complete decomposition of
the benzoyl peroxide groups, a self-supporting film of
another polymer with pendant benzil groups, such as
BzMA/S, was prepared and irradiated at the same
conditions. The BzMA/S allowed us to follow the pro-
cess of photochemical transformation of benzil groups
to benzoyl peroxides and their subsequent photochem-
ical decomposition by FTIR spectra in the region of
1650–1800 cm−1. This was not possible in the case of
Fig. 4. FTIR spectra of BzMA/S copolymer film after vari-
ous irradiation times at λ > 240 nm in air. Irradiation
time/min: 0 (1), 10 (2), 25 (3), 45 (4), 90 (5), and 180
(6).
film at λ > 240 nm in air, the vibration signal in
FTIR spectra in the region of 1650–1690 cm−1 dis-
appeared after approximately 45 min, indicating com-
plete photo-conversion of the benzil groups. However,
for complete decomposition of all the benzoyl per-
oxides formed, accompanied by the disappearance of
peaks in the region of 1750–1800 cm−1, irradiation of
the film for at least 3 h was needed (Fig. 4). There-
fore, irradiation for 1 h and 4 h, to ensure complete
photochemical transformation of benzil and complete
—
the BzMA/MMA copolymer, where a strong C O vi-
—
bration signal from the carboxylate groups of MMA
overlapped the vibration signals of the benzil and ben-
zoyl peroxide groups.
During irradiation of the BzMA/S self-supporting

J. Mosnáček et al./Chemical Papers 67 (1) 9–17 (2013)
13
Table 1. Absorbance and contact angle values of LDPE films grafted by BzMA/MMA copolymer
Irradiation time/h
Contact angleb/◦
Entry
Timea/h
Absorbanced/a.u.
> 240 nm
> 320 nm
nctc
ctc
1
2
3
4
5
6
7
–
1
4
–
–
–
–
–
–
–
1
1
4
4
–
–
–
–
1
–
1
76
74
76
77
74
75
72
76
69
66
71
69
72
71
∼ 0.025–0.030e
nd
nd
∼ 0.015
∼ 0.025
∼ 0.025
∼ 0.025
a) Time of thermal treatment at 95◦C; b) contact angle of pure LDPE irradiated at λ > 240 nm for 1 h and washed was 96◦
(for nct-LDPE) and 78◦ (for ct-LDPE); c) nct – non-corona-treated side of LDPE film; ct – corona-treated side of LDPE film; d)
—
absorbance (νmax (C O)) after washing; absorbance before irradiation was in all cases in the range of 0.025–0.030 a.u.; e) not
—
washed; nd – not detectable.
photochemical decomposition of benzoyl peroxides, re-
spectively, was used for the photochemical grafting of
the BzMA/MMA copolymer sprayed onto the LDPE
film surface.
out. Thus, the LDPE film was immersed into a solu-
tion of benzil or BzMA monomer in toluene for 4 h
(concentration of benzil of BzMA in the solution was
three times higher than the concentration of benzil
groups in the copolymer solution) and irradiated for
4 h under the same conditions. No decrease in contact
angle was observed after the irradiation and washing,
indicating that photochemical transformations of ben-
zil and benzoyl peroxides alone did not have any signif-
icant influence on the LDPE surface at the conditions
used in our studies.
Photochemical grafting of the BzMA/MMA copoly-
mer sprayed onto the LDPE film surface was also
studied by FTIR. The FTIR spectra were measured
through the LDPE film, hence the spectra are the
sum of the carbonyl signals from the nct-LDPE and
ct-LDPE sides. Prior to irradiation, in all cases ab-
The LDPE film surface before and after photo-
chemical grafting was characterised by contact an-
gle measurements and FTIR spectra. The contact an-
gles of pure LDPE films, irradiated and washed un-
der the same conditions as the grafted samples, were
96◦ and 78◦ for the nct-LDPE and ct-LDPE surfaces,
respectively. The contact angle of the BzMA/MMA
copolymer deposited onto the LDPE film surface prior
to the irradiation experiments was 76◦ for both nct-
LDPE and ct-LDPE (Table 1, entry 1), indicating the
expected value of the contact angle of LDPE film
after successful grafting of the copolymer onto the
LDPE surface. After photochemical grafting of the
BzMA/MMA copolymer onto the nct-LDPE side of
the film and subsequent washing out of the free copoly-
mer, the contact angles were 74◦ and 76◦ for 1 h and
4 h of irradiation, respectively (Table 1, entries 2 and
3). These values are comparable with the contact angle
of the BzMA/MMA copolymer layer prior to irradi-
ation, thus indicating modification of the nct-LDPE
surface by the BzMA/MMA copolymer.
—
sorbance of the vibration signals of C O of the MMA
—
copolymer in the region of 1700–1760 cm−1 was in the
range of 0.025–0.030 a.u. During irradiation at λ >
240 nm, a slight decrease and broadening of the vi-
—
bration bands of the C O groups was observed. This
—
could be due to degradation of the copolymer by UV
light. After irradiation and washing of the samples in
—
chloroform, the signal of C O vibration in the FTIR
—
Photochemical grafting of the BzMA/MMA copo-
lymer onto the ct-LDPE sides resulted in the contact
angle values decreasing to 69◦ and 66◦ for 1 h and
4 h of irradiation, respectively (Table 1, entries 2 and
3). These contact angle values are even lower than the
contact angle of the BzMA/MMA copolymer. This in-
dicates some further structural changes either in the
BzMA/MMA copolymer or on the LDPE surface dur-
ing irradiation, due to the presence of various groups,
such as hydroperoxides, carbonyls, etc. on the corona-
treated LDPE surface. To exclude the possibility that
the decrease in contact angle was caused only by ox-
idation of LDPE during photochemical transforma-
tion of the benzil groups present in the BzMA/MMA
copolymer or during decomposition of the photochem-
ically generated benzoyl peroxide groups, control ex-
periments with low molecular mass benzil was carried
spectra decreased dramatically and in most cases no
detectable signal was obtained. This could be due to
the presence of non-grafted polymer chains due to the
degradation of the MMA copolymer referred to above.
In any case, the decrease in contact angles confirmed
that a thin layer of MMA copolymer was grafted onto
the LDPE surface, thus increasing its hydrophilicity.
To prevent degradation of the MMA copolymer,
the grafting process was performed by irradiation with
lower energy light, using a filter transmitting the light
of λ > 320 nm, for 1 h or 4 h in air. At this wave-
length, the absorption of photochemically generated
pendant benzoyl peroxides is lower, resulting in their
slower photochemical decomposition, so their subse-
quent thermal treatment at 95◦C for 1 h to com-
plete benzoyl peroxide decomposition was also stud-
ied (Table 1, entries 5 and 7). The contact angles

14
J. Mosnáček et al./Chemical Papers 67 (1) 9–17 (2013)
Fig. 5. Photochemical generation of pendant benzoyl peroxides in BzMA/S film and subsequent grafting of methacrylic acid
(MAA) by thermal decomposition of pendant benzoyl peroxide groups. Reaction conditions: i) irradiation (λ > 400 nm),
O2; ii) heating; iii) MAA; n = 96.5, m = 3.5.
were very similar to previous experiments of irradi-
ation at λ > 240 nm. In the nct-LDPE sides, the con-
tact angles were very close to the contact angle of
the non-irradiated BzMA/MMA deposited onto the
LDPE film, and in the ct-LDPE sides the contact an-
gles were even slightly lower. In all cases, a slight de-
crease in contact angles was observed when thermal
treatment was applied after the irradiation to com-
plete the benzoyl peroxides decomposition. It should
be noted that no grafting of BzMA/MMA was ob-
served in the control experiment of thermal treatment
without previous irradiation.
quent irradiation at λ > 240 nm for 1 h and washing,
—
the vibration signal of the C O groups of the MMA
—
copolymer almost disappeared. Measurement of the
contact angle gave the same values as prior to irradia-
tion at λ > 240 nm. These results indicate that also, in
the case of irradiation at λ > 240 nm, despite degra-
dation of the MMA copolymer, some MMA oligomers
probably still remain bonded onto the LDPE film, re-
sulting in an increase in hydrophilicity of the LDPE
surface.
Grafting from surface of styrene copolymers
films
—
No decrease in the intensity of the C O vibration
—
bands of the MMA copolymer in FTIR spectra was ob-
served either during irradiation at λ > 320 nm or after
thermal treatment at 95◦C. Moreover, only a slight de-
crease was observed after washing the treated samples
in solvent, indicating grafting of the copolymer onto
the LDPE surface without significant degradation of
Pendant benzil moieties present in the synthesised
styrene copolymers were investigated for grafting of
(meth)acrylic acids from the surface of the styrene
copolymers films. Both thermal and photochemical
graftings were investigated. For thermal grafting, a
film of the BzMA/S copolymer was first irradiated at
λ > 400 nm for 3 h to generate pendant benzoyl perox-
ide groups as depicted in Fig. 5. In the FTIR spectra,
disappearance of the vibration signal of benzil in the
region of 1650–1700 cm−1 was accompanied by the
formation of two peaks from the vibration signal of
—
the MMA copolymer. On the basis of the C O vibra-
—
tion signals in FTIR spectra, it was determined that
approximately 50 % and more than 80 % of copoly-
mer was grafted under the conditions in entry 4 and
in entries 5–7 (Table 1), respectively.
To confirm degradation of the MMA copolymer
during irradiation at λ > 240 nm, the LDPE film
prepared and characterised as described in entry 7
(Table 1; i.e. irradiation at λ > 320 nm and subse-
quent thermal treatment) was further irradiated at
λ > 240 nm. While the absorbance in FTIR spectra
after grafting by irradiation at λ > 320 nm for 4 h and
subsequent thermal treatment for 1 h was, after wash-
ing in solvent, approximately 0.025 a.u., after subse-
benzoyl peroxides in the region of 1750–1800 cm−1
,
indicating complete conversion of the pendant benzil
groups to benzoyl peroxide groups (Fig. 6). The pre-
pared film of the styrene copolymer containing pen-
dant benzoyl peroxide groups was subsequently used
for grafting of the methacrylic acid.
It is worth noting that previous studies showed
that partial photo-cross-linking of the PS copolymer

J. Mosnáček et al./Chemical Papers 67 (1) 9–17 (2013)
15
poly(methacrylic acid), was observed in the grafted
copolymer film. Contact angle measurements showed
a decrease in contact angle after the grafting proce-
dure from 78◦ to 46◦. Change in the polymer mass af-
ter 10 min of grafting was negligible, due to the min-
imal amount of poly(methacrylic acid) grafted onto
the surface of the film. However, transparency of the
film decreased after grafting, resulting in a slightly
white colour. As seen in Fig. 6, only a negligible por-
tion of the benzoyl peroxide structures was consumed
—
(negligible decrease in the intensity of the C O vi-
—
bration bands from benzoyl peroxides in the region of
1760–1800 cm−1) during the short heating time, thus
showing the high grafting efficiency of this system.
For the photochemical grafting experiments, a film
of the PCOCO/S copolymer was used. The structure
of this copolymer (Fig. 7) facilitates more effective
photodecomposition of the pendant benzoyl peroxides
at λ = 366 nm, due to efficient absorption of the inci-
dent light by the monocarbonyl groups present and the
subsequent photosensitised decomposition of the pen-
dant benzoyl peroxides. Also, in this case, as a first,
the PCOCO/S film was irradiated at λ > 400 nm for
3 h to generate the pendant benzoyl peroxide groups
as depicted in Fig. 7. Grafting by acrylic acid was per-
formed by immersing the copolymer film containing
the pendant benzoyl peroxide groups into the deaer-
ated acrylic acid and irradiation by monochromatic
light of λ = 366 nm was applied for 30 min. After
grafting, any free polymers and monomers were re-
moved by extraction with distilled water for 48 h and
subsequent drying at reduced pressure. An approxi-
mately 50 % copolymer film mass increase was ob-
served after the grafting and purification procedure.
Due to such a high amount of grafted polymer onto
Fig. 6. FTIR spectra of BZMA/S copolymer film prior to ir-
radiation (· · ·) and after photochemical generation of
pendant benzoyl peroxide groups (3 h of irradiation)
(– – –), and after their thermal decomposition in the
presence of methacrylic acid (grafted for 10 min) (—).
films occurred during photochemical transformation
of the pendant benzil groups to benzoyl peroxide
groups (Kósa et al., 2000; Mosnáček et al., 2004b).
This cross-linking of the copolymer film during pho-
togeneration of the pendant benzoyl peroxides and
use of diluted methacrylic acid, as non-solvent for
the BzMA/S copolymer, allow the subsequent graft-
ing of monomers by direct immersion of the poly-
mer film into the monomer solution without destroy-
ing the grafted copolymer film. In this case, the pre-
irradiated BzMA/S film with pendant benzoyl per-
oxy groups was immersed in the boiling 15 mass %
methacrylic acid in water. After 10 min, the PS film
was carefully extracted with distilled water and dried
at reduced pressure to remove both the unreacted
monomer and free homopolymer. In the FTIR spectra,
—
the surface of the PS copolymer film, the C O vibra-
—
a new strong peak in the region of 1670–1720 cm−1
which can be attributed to carboxyl groups of grafted
,
tion signal of carboxylic groups in the FTIR spectra
was outside the spectrum range.
Fig. 7. Photochemical generation of pendant benzoyl peroxides in PCOCO/S film and subsequent grafting of acrylic acid (AA) by
photochemical decomposition of pendant benzoyl peroxide groups. Reaction conditions: i) irradiation (λ > 400 nm), O2;
ii) irradiation (λ = 366 nm); iii) AA; n = 89, m = 11.

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J. Mosnáček et al./Chemical Papers 67 (1) 9–17 (2013)
Conclusions
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1080–1085. DOI: 10.1002/(SICI)1521-3935(19990501)200:5
<1080::AID-MACP1080>3.0.CO;2-7.
Kósa, C., Lukáč, I., & Weiss, R. G. (2000). Photochemical trans-
formation of benzil pendant groups of polystyrene copoly-
mers into benzoyl peroxide moieties and their subsequent
thermal decomposition. Cross-linking or chain scission?
Macromolecules, 33, 4015–4022. DOI: 10.1021/ma991493z.
Lukáč, I., Zvara, I., Kulíčková, M., & Hrdlovič, P. (1980).
Synthesis of acyl 1-acetoxy-2-phenoxyethanes and the cor-
responding hydroxy derivatives. Collection of Czechoslovak
Chemical Communications, 45, 1826–1830. DOI: 10.1135/
cccc19801826.
In particular, poly(methyl methacrylate) copoly-
mers containing benzil side chains were successfully
grafted to the surface of LDPE films by radical graft-
ing initiated by pendant benzoyl peroxides. The initia-
tor moieties were generated in situ by photoxidation
of the pendant benzil groups and decomposed under
UV irradiation or thermally at 95◦C to give radical
species. High grafting with no photodegradation of
the methacrylic polymer was obtained by irradiation
at λ > 320 nm followed by thermal treatment. The
modification resulted in an increase in hydrophilic-
ity of the originally hydrophobic LDPE film surface,
as shown by the contact angle value of the treated
LDPE surface which decreased below 76◦. This value
corresponds to the contact angle of the BzMA/MMA
copolymer. When the LDPE surface was pre-treated
by corona discharge, the contact angle after the graft-
ing process even decreased to below 70◦.
Lukáč, I., Zvara, I.,
& Hrdlovič, P. (1982). Preparation
and emission spectra of polymeric 1,2-diketones. Euro-
pean Polymer Journal, 18, 427–433. DOI: 10.1016/0014-
3057(82)90180-x.
Films of styrene copolymers containing pendant
benzil groups were successfully used as activable
substrates to initiate the grafting polymerisation of
acrylic and methacrylic acids from the surface it-
self. The grafting polymerisation was achieved fol-
lowing photochemical or thermal decomposition of
the benzoyl peroxide groups. These were photochemi-
cally generated in situ from the pendant benzil groups
present in the styrene copolymers films. The per-
formed modification provided increased hydrophilicity
to the film surface, as demonstrated by the decrease
in contact angle value from 78◦ to 46◦ following the
grafting process.
Lukáč, I., & Das Mohapatra, G. K. (1992). Synthesis of 1-[4-
(3-chloropropanoyl)phenyl]-2-phenylethanedione. Collection
of Czechoslovak Chemical Communications, 57, 1085–1091.
DOI: 10.1135/cccc19921085.
Lukáč, I., Hrdlovič, P., & Schnabel, W. (1994). Preparation
and photochemical properties of 4-propenoylbenzil polymers.
Macromolecular Chemistry and Physics, 195, 2233–2245.
DOI: 10.1002/macp.1994.021950629.
Lukáč, I., & Kósa, C. (1994). The formation of dibenzoyl
peroxide by photooxidation of benzil in a polymer film.
Macromolecular Rapid Communications, 15, 929–934. DOI:
10.1002/marc.1994.030151204.
Lunkwitz, K., Bu¨rger, W., Lappan, U., Brink, H. J., & Ferse,
A. (1995). Surface modification of fluoropolymers. Jour-
nal of Adhesion Science and Technology, 9, 297–310. DOI:
10.1163/156856195x00518.
Acknowledgements. The authors are grateful for the finan-
cial support from the Grant Agency VEGA through grant no.
2/0074/10 and Centre of Excellence for Functionalised Mul-
tiphase Materials (FUN-MAT) at the Slovak Academy of Sci-
ences. The authors also wish to thank Ing. Anton Popelka and
Ing Angela Kleinová for the contact angle and FTIR measure-
ments, respectively.
Mosnáček, J., Weiss, R. G., & Lukáč, I. (2002). Photochem-
ical transformation of benzil carbonyl pendant groups in
polystyrene copolymers to benzoyl peroxide carbonyl moi-
eties and the consequences of their thermal and photochem-
ical decomposition. Macromolecules, 35, 3870–3875. DOI:
10.1021/ma0117458.
Mosnáček, J., Lukáč, I., Chromik, Š., Kostič, I., & Hrdlovič, P.
(2004a). Network formation of a phenyl vinyl ketone copoly-
mer with 4-vinylbenzil and its photodecrosslinking in films.
Journal of Polymer Science: Part A: Polymer Chemistry,
42, 765–771. DOI: 10.1002/pola.10860.
Mosnáček, J., Weiss, R. G., & Lukáč, I. (2004b). Preparation of
4-vinylbenzil and photochemical properties of its homopoly-
mer and copolymer with styrene. Macromolecules, 37, 1304–
1311. DOI: 10.1021/ma030213j.
Mosnáček, J., Bertoldo, M., Kósa, C., Cappelli, C., Ruggeri, G.,
Lukáč, I., & Ciardelli, F. (2007). Modification and photosta-
bilization of low density polyethylene film by photodecompo-
sition of various diazo-compounds and methyl azidocarboxy-
late. Polymer Degradation and Stability, 92, 849–858. DOI:
10.1016/j.polymdegradstab.2007.01.025.
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