The photochemical behavior of polyhydroxy styrene with azofragments containing free methacrylic double bounds

Article abstract of DOI:10.1080/15421406.2016.1257329

Polymer material which combines advantages of photoaligning azo-compounds with thermal stability of the induced anisotropy provided by free methacryloyl groups was synthesised. FTIR spectroscopy was employed for clarification its photochemical behavior. T

Full text of DOI:10.1080/15421406.2016.1257329

Molecular Crystals and Liquid Crystals
ISSN: 1542-1406 (Print) 1563-5287 (Online) Journal homepage: http://www.tandfonline.com/loi/gmcl20
The photochemical behavior of polyhydroxy
styrene with azofragments containing free
methacrylic double bounds
Oksana Nadtoka, Lyudmyla Vretik, Tetiana Gavrylko & Volodymyr
Syromyatnikov
To cite this article: Oksana Nadtoka, Lyudmyla Vretik, Tetiana Gavrylko & Volodymyr
Syromyatnikov (2017) The photochemical behavior of polyhydroxy styrene with azofragments
containing free methacrylic double bounds, Molecular Crystals and Liquid Crystals, 642:1, 115-123,
DOI: 10.1080/15421406.2016.1257329
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Date: 12 March 2017, At: 06:45

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
, VOL. , –
http://dx.doi.org/./..
The photochemical behavior of polyhydroxy styrene with
azofragments containing free methacrylic double bounds
Oksana Nadtokaa, Lyudmyla Vretika, Tetiana Gavrylkob, and Volodymyr Syromyatnikova
aTaras Shevchenko National University of Kyiv, Kyiv, Ukraine; bInstitute of Physics, NASU, Kyiv, Ukraine
ABSTRACT
KEYWORDS
Azopolymer; FTIR
spectroscopy;
photopolymerization
Polymer material which combines advantages of photoaligning azo-
compounds with thermal stability of the induced anisotropy provided
by free methacryloyl groups was synthesised. FTIR spectroscopy was
employed for clarification its photochemical behavior. Two Fries rear-
rangements in arylester groups and photoinitiated cross-linking in
methacryloyl functional groups were established after the action of UV-
irradiation.
1. Introduction
Azobenzene derivatives have attracted interest of a large number of researches in the field
of photonic materials. A polarized light-induced anisotropy has been observed in polymer
films; since the 1980, this type of anisotropy has been studied in polymers doped with azo
dyes for transient polarization holography [1]. It has also been utilized as new optical switch-
ing materials in the liquid crystal systems, because the photoinduced orientation of azo dyes
by irradiation with a polarized light can be a driving force for the alignment of the liquid crys-
tals [2–3]. It has been demonstrated that photoinduced orientation of dye-containing liquid
crystalline polymers can be used for reversible optical data storage [4].
Recently we developed a new class of photoaligning polymers: methacryloylaminoaryl
methacrylates having free methacryloyl groups [5–8]. The materials of this class provide
excellent LC alignment with variable pretilt angle, rather high anchoring energy and extraor-
dinary high thermal and photo-stability. It was established that polarized UV light illumina-
tion results in photoinduced ordering of side polymer chains due to photoselection mecha-
nism. It has been proven that photochemical transformations theoretically expected in such
kind of materials, namely Fries rearrangements and photopolymerization of free methacrylic
groups, participate in orientational ordering and LC alignment.
Our intention was to create a polymer material which would combines such advantages of
azo containing photoaligning materials as a requirement of very low recording powers, large
photoinduced birefringence, high resolution, and high efficiency with thermal stability of the
induced anisotropy what could be provided by free methacryloyl groups.
CONTACT Oksana Nadtoka
oksananadtoka@ukr.net
This paper was originally submitted to Molecular Crystals and Liquid Crystals, Volumes –, Proceedings of the th
International Conference on Electronic Processes in Organic and Inorganic Materials (ICEPOM-).
Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/gmcl.
©  Taylor & Francis Group, LLC

116
O. NADTOKA ET AL.
Figure . Scheme of synthesisof azopolymer Azo1.
For these reasons polymer Azo1 containing in the same side chain azo and phenyl-
methacrylate groups (Fig. 1) was synthesised. It is well established that photochromic
transformations in azo compounds are related to the induced trans-cis isomerisation of their
azo-containing core. However, for more complicated molecules such as proposed Azo1 the
photochemical behaviour is not so clear. In addition to cis-trans isomerisation also two Fries
rearrangements in arylester groups and photoinitiated cross-linking in methacryloyl func-
tional groups are possible. Thus, FTIR spectroscopy was employed for clarification of photo-
chemical behavior of Azo1 and results obtained are discussed in the presented paper.
2. Experimental section
2.1. Synthesis and characterization of materials
˚
All solvents of p.a. quality (Aldrich) were stored over molecular sieves of 3 or 4 A. Other
chemicals were purchased from Aldrich and used without further purification. Intermediate
(4-methacryloyloxy)-benzoic acid was prepared in accordance with standard procedure by
acylation of starting compound with methacryloyl chloride. Syntheses of intermediates 4-(4-
hidroxyphenylazo)-benzoic acid (Ia, see Sheme 1), 4-(4-dimethylaminophenylazo)-benzoic
acid (Ib) and 4-(4-methacryloxyphenylazo)-benzoic acid (II) for polymers Azo1 and Azo2
was done as described below.
Thin layer chromatography was performed on Merck Kieselgel plates 60-F254. 1H NMR
spectra were recorded with a Varian 400 NMR spectrometer with tetramethylsilane as internal
standard in DMSO-d6 or CDCl3 as solvents.
Synthesis of 4-(4-hidroxyphenylazo)-benzoic acid (Ia). 4-aminobenzoic acid was selected
for preparing diazonium salt. 0.05 mol 4-aminobenzoic acid, 2 g (0.05 mol) sodium hydroxide
and 25 ml water was mixed with stirring. Keeping the temperature at 0–5°C and the solution
of sodium nitrite (3.5 g, 0.05 mol) in 20 ml water was added dropwise with stirring. After
stirring for further 10 min 25 ml of 8 wt.% solution of hydrochloric acid (0.05 mol) was added.
Then put it into an ice-salt bath and stirred rapidly about 20 min. Then the diazonium salt
as paste was obtained. Phenol (4.9 g, 0.05 mol) was dissolved in a 10 wt. % solution of NaOH
(4 g, 0.05 mol). The mixture was cooled to lower than 10°C with an ice bath and 10 g ice
was added. Then the diazonium salt was slowly added at the low temperature. The resultant
mixture was vigorously stirred for one hour, and then the saturated solution of sodium acetate
was added to the adjust pH value at 6–7. The obtained mixture was filtered and washed with
a large excess of water and dried at room temperature.
Ia: orange crystals; yield 69 wt.%, 1H NMR (400 MHz, CDCl3, ppm): δ = 8.09 (d, 2H, Ar),
7.85 (d, 2H, Ar), 7.81 (d, 2H, Ar), 6.91 (d, 2H, Ar). Elem. Anal. Calcd for C13H10O3N2: C,
64.46%; H, 4.13%; N, 11.57%. Found: C, 64.56%; H, 4.16%; N, 11.52%.

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
117
Synthesis of 4-(4-dimethylaminophenylazo)-benzoic acid (Ib). The diazonium salt of 4-
aminobenzoic acid was obtained the same way as Ia. Dimethyl(phenyl)amine was dissolved
in a 10 wt. % solution of HCl (0.05 mol). The mixture was cooled to lower than 10°C with an
ice. Then the diazonium salt was slowly added at the low temperature. The resultant mixture
was vigorously stirred for further an hour, and then the saturated solution of sodium acetate
was added to the adjust pH value at 6–7. The obtained mixture was filtered and washed with
a large excess of water and dried at room temperature.
Ib: red crystals; yield 71%, 1H NMR (400 MHz, CDCl3, ppm): δ = 8.06 (d, 2H, Ar), 7.8 (dd,
4H, Ar), 6.79 (d, 2H, Ar), 3.12 (s, 6H, 2CH3). Elem. Anal. Calcd for C15H15O2N3: C, 71.66%;
H, 4.78%; N, 13.38%. Found: C, 71.58%; H, 4.76%; N, 13.32%.
Synthesis of 4-(4-methacryloxyphenylazo)-benzoic acid (II). The azocompound Ia (9.7 g,
0.05 mol) and N,N,N-triethylamine (0.05 mol, 7 ml) were dissolved in THF (50 ml). The solu-
tion was kept in an ice bath for 10 min. A solution of distilled methacryloyl chloride (6.0 ml,
0.05 mol) was added slowly to the above mixture. After the addition was completed, the result-
ing mixture was stirred at room temperature overnight. Then the solution was poured into
distilled water (1 L) and the obtained residue was filtered and air-dried. Recrystallization of
II was carried out in ethanol.
II: yellow crystals; yield 60 wt.%. 1H NMR (400 MHz, CDCl3, ppm): δ = 8.17 (d, 2H, Ar),
8.08 (d, 2H, Ar), 8.04 (d, 2H, Ar), 7.5 (d, 2H, Ar), 6.34 (s, 1H, =CH2), 5.88 (s, 1H, =CH2), 2.06
(s, 3H, -CH3). Elem. Anal. Calcd for C17H16O4N2: C, 65.38%, H, 5.13%; N, 8.97%. Found: C,
65.40%, H, 5.19%; N, 9.01%.
Synthetic root for preparation of azopolymers Azo1 and Azo2 is shown on Scheme
(Figure 1).
Synthesis and characterization of azopolymer Azo1. To the solution of 1.20 g (0.01 mol) of
poly(4-hydroxystyrene) (Mw = 8000) in 10 ml of dry THF was added 10 ml dry THF solution
of 3.11g (0.01 mol) of 4-(4-methacryloxyphenylazo)-benzoic acid (II), 2.06 g (0.01 mol) of
N,N’-dicyclohexylcarbodiimide (DCC) and 0.3 g of 4-dimethylaminopyridine (DMAP). The
reaction mixture was stirred at 20°C during 4 days. A residue was formed and filtered off, the
filtrate was poured into 400 ml of distilled water and 2.9 g of polymer Azo1 was obtained. The
obtained polymer was dissolved in 4 ml of DMF and precipitated into 100 ml of methanol.
The mass of the formed polymer was 2.52 g (yield 58 wt.%). 1H NMR (400 MHz, DMSO-d6,
ppm): 8.75 (broad, Ar), 7.8 (broad, Ar), 6.9 (broad, Ar), 6.27 (broad, = CH2), 5.87 (broad, =
CH2), 1.98, 1.62, 1.25 (broad, CH3, CH2, CH). The relative molar ratio of n:m was evaluated
by comparison of 1H NMR integrals for the signals at 7.19 and 5.84 ppm and calculated as
about 25:75.
Synthesis and characterization of azopolymer Azo2. Polymer Azo2 was prepared by
the same polymer analogues reaction of poly(4-hydroxystyrene) (Mw = 8000) with 4-(4-
dimethylaminophenylazo)-benzoic acid (Ib). Yield 42 wt.%. 1H NMR (400 MHz, DMSO-d6,
ppm): δ = 8.75 (broad, Ar), 7.8 (broad, Ar), 7.5 (broad, Ar) 1.98, 1.62, 1.25 (broad, CH3, CH2,
CH). The relative molar ratio of n:m was evaluated by comparison of 1H NMR integrals for
the signals at 6.8 and 6.3 ppm and calculated as about 24:76.
Model polymer Mod1 was prepared by polymer analogues reaction of poly(4-
hydroxystyrene) (Mw = 8000) with methacryloyl chloride. The relative molar ratio of n:m
was evaluated by comparison of 1H NMR integrals for the signals at 6.82 and 5.77 ppm and cal-
culated as about 35:65. Model polymer Mod2 was prepared by polymer analogues reaction of
poly(4-hydroxystyrene) (Mw = 8000) with intermediate (4-methacryloyloxy)-benzoic acid.
Synthesis and characterization of Mod2. To the solution of 1.20 g (0.01 mol) of poly(4-
hydroxystyrene) (Mw = 8000) in 10 ml of dry THF was added 10 ml THF solution of 2.06 g

118
O. NADTOKA ET AL.
(0.01 mol) of (4-methacryloyloxy)-benzoic acid, 2.06 g (0.01 mol) of DCC and 0.3 g of DMAP.
The reaction mixture was stirred at 20°C during 4 days. A residue was formed and filtered
off, the filtrate was poured into 400 ml of distilled water and 1.97 g of polymer Mod2 was
obtained. The obtained polymer was dissolved in 4 ml of ethylacetate and precipitated into
100 ml of hexane. The mass of the formed polymer was 1.37 g (yield 43%). 1H NMR (400 MHz,
DMSO-d6, ppm): 8.01 (broad, Ar), 6.66 (broad, Ar), 6.27 (broad, = CH2), 5.87 (broad, =
CH2), 1.98, 1.62, 1.25 (broad, CH3, CH2, CH). The relative molar ratio of n:m was evaluated
by comparison of 1H NMR integrals for the signals at 7.19 and 5.84 ppm and calculated as
about 25:75.
2.2. Samples and IR measurements
The polymers were dissolved in N,N-dimethylformamide (DMF) at concentration 2 wt. %
and filtered to 0.2 μm by syringe filter. The polymer films were obtained by spin coating of
the polymer solutions on the KBr plates and subsequent backing at 80°C over 30 min for the
solvent evaporation. The films were subsequently exposed to a broad-band unpolarized irra-
diation from a high pressure mercury lamp DRS-500 (Russia) directed normally to the films.
The integral intensity of irradiation was 105 mW/cm2. The room temperature FTIR absorp-
tion spectra of the polymer films were measured in the spectral range 400–4000 cm−1 with a
resolution of 1 cm−1 with Perkin Elmer Spectrum BX FTIR spectrometer. Reproducibility of
peak position measurements in the FTIR spectra is 0.5 cm−1. An error in absorbance mea-
surements is determined by systematic instrumental errors and equals 0.1%. As a reference,
the KBr window was used. All spectral manipulations, such as baseline correction, smoothing
and normalization, were performed using the standard “Spectra” (PE) standard spectroscopy
software package.
3. Results and discussion
While making an assignment of the absorption bands of Azo1, we mainly focused on the
bands related to vibrations of the molecular groups which are sensitive to photochemical
transformations discussed above. We expected that Fries rearrangements do significantly
change the vibration bands of arylester (both benzoate and methacrylate types) groups, while
photopolymerization modifies the vibration bands related to C = CH2 fragments. Finally, it
would be necessary to identify bands useful for monitoring of trans-cis isomerization of azo
group N = N.
– – =
=
–
Thus, characteristic vibrations of Ar O C O (methacrylate), Ar(C O) O (benzoate)
and C = CH2 molecular groups were especially thoroughly identified. For this purpose, first of
all, we used literature data [9–11]. However, because of quite complicated structure of Azo1,
it was difficult to make unequivocal assignment for a number of the absorption bands. To give
unambiguous assignment, a preliminary assignment based on the literature data for related
compounds was defined more exactly by comparing the FTIR spectrum of Azo1 with the
spectra of model polymers Azo2, Mod 1 and Mod 2 for their structures (see Fig. 2).
3.1. IR spectra before irradiation
As an illustrative example, the infrared spectrum in the 500–1600 and 3000–3900 cm−1
regions of Azo1 film is presented in Fig. 3, parts a and b.

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
119
Figure . Structures of model polymers Azo2, Mod 1, Mod 2 in comparison with structure of azopolymer
Azo1.
Like other carbonyl compounds, esters are primarily recognized by their strong carbonyl
band at around 1740 cm−1 [9] and corresponds to carbonyl stretching ν(C = O). Because
Azo1, Mod1 and Mod2 have similar structures of arylester fragments, the peak positions of
ν(C = O) vibrations of these fragments in the mentioned polymers are close, namely at 1734,
1734 and 1738 cm−1. In addition, according to [9, 10], the other characteristic bands of the
ester group are two ν(C-O) vibration bands with a peak position at around 1200 cm−1 and
in the range 1150–1100 cm−1. In the IR spectra of Azo1, corresponding bands were found
at 1200 cm−1 for methacrylate fragment and 1264 cm−1 for benzoate. Such assignment was
proven by a comparison of Azo1 spectrum with the spectra of Azo2, Mod1 and Mod2 having
similar arylester structures and thus similar positions of characteristic bands (at 1257 cm−1 in
Azo2 for benzoate, at 1204 cm−1 in Mod1 for methacrylate and at 1202 cm−1 and 1266 cm−1
for methacrylate and benzoate in Mod2).
To identify the absorption bands corresponding to ν(C = C) vibrations of C = CH2 frag-
ment, foreseen in literature in 1680–1620 cm−1 region, we have compared the IR spectra of

120
O. NADTOKA ET AL.
Figure . FTIR spectra of Azo1 before (solid line) and after (dotted line) UV irradiation (I =  mW/cm)
in the – (a), – (b) and – cm− (c) region. The inset in the upper picture shows
changes in the absorption of CH groups. Solid line in the bottom picture represents a difference between
the two depicted spectra.
Azo1 with Mod 1, Mod 2 as well as with data presented in [9]. In accordance with [9], the
band centered at 1628 cm−1 was attributed to the C = C stretching vibration. In the spectrum
of model polymer Mod 1 this band exhibited at 1638 cm−1 while in the spectrum of Mod 2 it
is shifted by 1cm−1 towards higher wave numbers (1639 cm-1). Finally, this band in the Azo1
spectrum was recognized at 1636 cm−1 and no detected in Azo2.
The other band which could be attributed to C = CH2 fragment in the Azo1 spectrum is
centered at 948 cm−1 and appears due to the δ(C-H) vibration. Indeed, according to [9] for
the CH2 = C-С = O conjugated systems this kind of vibration has a band position in the
region 930–945 cm−1. Corresponding band was also found in Mod 1 and Mod 2 at 948 cm−1
and 946 cm−1, respectively. No absorption bands in this region were detected in the spectra of
poly(hydroxystyrene) and poly(acetylhydroxystyrene) and Azo2. The characteristic absorp-
tion bands related to groups mentioned above of Azo1 and Mod 1, Mod2 are summarized in
Table 1.

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
121
Table . Assignment of the IR absorption bands in the IR spectra of Azo1 and Mod1, Mod2 compounds to
the vibrations of the structural elements responsible for photochemical transformations.
Material code
Ester, C = O
Ester, C-O-C
C-H in CH = , cm−
Azo1
, ∗

 (methacrylate),  (benzoate)
 (benzoate), overlapped
 (methacrylate)

Absent

Azo2
Mod1
Mod2
, ∗

 (methacrylate),  (benzoate)

∗hydrogen bonded
Band centered at 1222 cm−1 can be assigned to δ (C-O) stretching vibration (theoretically
predicted in the region 1260–1180 cm−1) of the residual phenol Ar-OH structure.
The other set of pronounced bands of the IR spectrum of Azo1 with the peaks at 1598,
1610, 1512 and 1448 cm−1 relate to Q(C· · ·C) vibrations of benzene rings. The correctness of
this assignment is confirmed with a fact that all these bands are present in the IR spectra of
Mod 1 and Mod 2 homologues containing substituted benzene rings.
Such bands of Azo1 FTIR spectrum as 1406, 1376, 1322, 1140 and 1076 and 1012 cm−1
could be only preliminary assigned employing literature data and original IR spectrum of
poly(4-hydroxy styrene). The bands centered at 1376 and 1322 cm−1 could be assigned
to skeleton δ(C-H) vibrations of CH2 groups of the main polymer chain and C-CH3 in
methacrylic groups. In this region could exist also an absorption band associated with a vibra-
tional coupling between the ν(N = N) and Q(C· · ·C) stretching vibration [14]. Finally, the
bands centered at 1076 and 1012 cm−1 could be assigned to δ (C-H) vibrations of aromatic
part of the Azo1 molecules.
The bands observed at 2852 and 2926 cm−1 are assigned to the main chain methylene
symmetric and antisymmetric CH stretching modes, respectively. The bands centered at 3020
and 3067 cm−1 refer to aromatic CH stretching vibrations.
A single broad O-H stretching bands is observed at 3396 cm−1; this band is due to hydrogen
bond formation [15] between the O-H group in the phenol moiety and the C = O group in
the benzoate moiety (O-H· · · O = C). This result is supported by the appearance of C = O
stretching band at 1718 cm−1 being originated by the formation of hydrogen bonds between
the carbonyl and hydroxyl groups. The same signal was detected at 1718 cm−1 for Mod 1.
Theoretically, the azo group shows only weak bands at between 1000–1615 cm−1 [12], and
since a lot of bands generally occur in this region, it is not possible to make definite conclu-
sions more correctly. As reported previously by Buffeteau et al. [15], the band at 1385 cm−1 is
assigned to a vibration coupling of between the ν(N = N) and the ∅-N stretching vibration.
However, in the spectrum of the Azo1 compound, corresponding spectral region is concealed
by the absorption of other functional groups, and therefore it was not possible to identify such
vibration band.
Thus, the comparison of the IR absorption spectra of Azo1 and those of model polymers
Mod1 and Mod2 allowed us to make an assignment for the majority of strong absorption
bands of the Azo1 polymer, Table 2. The assignment of some minor absorption bands remains
unclear and needs additional investigations which are beyond the scope of this paper.
3.2. Changes in IR spectra after UV irradiation
At the next stage, FTIR spectra of Azo1 before and after UV irradiation (I = 105 mW/cm2)
were compared. As was expected, in the spectrum of Azo1 the changes of the vibration bands
attributed to both types of ester fragments were observed, such as lowering the intensity of

122
O. NADTOKA ET AL.
Table . Peak position of main IR absorption bands and their assignment to vibrations of selected structural
elements of Azo1.
Peak position, cm−
Structural element
Experimental
Ref. [, ]
Assignment
Methylene, main chain
2924
2852

–
νas. (CH)
νsym. (CH)
Ester
Aryl
1734
–
– and – (benzoates),
– (acrylates)
 [], – []
–
ν(C = O)
ν (COC)
1264, 1200 and 1168
3022
νar(C-H)
Q(C· · ·C)
1598, 1610
1512
–
–
–
–
Q(C· · ·C)
830
1636, partially overlapped
948
δo.o.p. (C-H), p-substituted
ν(C = C)
C = CH
δ(C-H)
Note: ν, Q - stretching, δ -deformational vibrations
the following bands: ester ν(C = O) stretching band centered at 1734 cm−1 and hydrogen
bonded at 1718 cm−1, ν(C-O) vibration bands centered at 1266 and 1202cm−1 (see Fig. 3, a.,
b.). Such a behavior of the bands attributed to the ester groups was interpreted as the result
of Fries rearrangement (see Fig. 4) described in the literature for aromatic esters [16]. Small
changes observed in the region of OH stretching vibrations (Fig. 3, b), such as insignificant
drop in intensity and broadening at the high-frequency side of the band, can be attributed to
rearrangement of intra-molecular H-bonds.
Photopolymerization of C = CH2 groups is also evident from the IR spectra of irradiated
Azo1: photo-sensitive absorption band centered at 948 cm−1 slightly reduce its intensity after
90 min of irradiation (see an inset in Fig. 3, a).
Insignificant growth and broadening of some absorption bands in 1400–1370 cm−1 regions
is completely understandable taking into account a possibility of the photopolymerization
reaction (Fig. 4, b.) in UV-irradiated film which leads to the formation of new –C(CH3)-CH2-
fragments having δ(C-CH3) bands at 1380–1450 cm−1 [10].
In spite of the reported in [13, 15, 17] and references therein, possible band formation at
∼-1515 cm−1 attributed to the N = N stretching vibration of the cis species, was not detected
in Azo1 spectrum after UV irradiation may be due to its small intensity and overlapping with
strong Q(C· · ·C) band at 1512 cm−1.
Figure . Possible photoshemical transformations of azopolymerAzo1: a - Fries rearrangements and trans-
cis isomerization, b -photopolymerization of free methacrylic groups.

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
123
Conclusions
As was expected, Fries rearrangements do significantly changes in the vibration bands of
arylester (both benzoate and methacrylate types) groups at 1734 cm−1, 1718 cm−1, 1264 cm−1
and 1200 cm−1. A photopolymerization related to C = CH2 fragments evident due to decrease
of absorption band centered at 948 cm−1. Thus, both types of photochemical reactions (Fries
rearrangement and photopolymerization) could be recognized in FTIR spectra of the UV-
irradiated Azo1 films.
References
[1] Todorov, T.; Nikolova, L.; Tomova, N. et al. (1981). Opt. Quantum Elektron 13, 209.
[2] Wu, Y., Zhang, Q., Kanazawa, A., Shiono, T., Ikeda T., & Nagase Y. (1999). Macromolecules, 32(12),
3951.
[3] Ichimura K. (2000). Chem. Rev., 100(5), 1847.
[4] Kawata, S., & Kawata, Y. (2000). Chem. Rev., 100(5), 1777.
[5] Vretik, L. O., Syromyatnikov, V. G., Zagniy, V. V., Paskal, L. P., Yaroshchuk, O. V., Dolgov, L. O.,
Kyrychenko, V. I, & Lee, C. D. (2007). Mol.Cryst.Liq.Cryst., 479, 121.
[6] Vretik, L. O., Paskal, L. P., Syromyatnikov, V. G., Zagniy, V. V., Savchuk, O. A., Dolgov, L. O.,
Yaroshchuk, O. V., & Lee, C. D. (2007). Mol.Cryst.Liq.Cryst., 468, 173.
[7] Vretik, L. O., Syromyatnikov, V. G., Zagniy, V. V., Savchuk, E. A., & Yaroshchuk, O. V. (2008).
Mol.Cryst.Liq.Cryst., 486, 7.
[8] Kyrychenko, V., Smolyakov, G., Zagniy, V., Vretik, L., Paskal, L., Syromyatnikov, V., & Yaroshchuk,
O. (2008). Mol.Cryst.Liq.Cryst., 496, 278.
[9] Gunzler H, & Gremlich, H. U. (2002). IR Spectroscopy. An introduction. Wiley-VCH Verlag Gmbh,
Weinheim.
[10] Bellamy, L. J. (1963). The infra-red spectra of complex molecules. John Wiley& Sons, New York.
[11] Kim, S. H., Jang, J., Jeon, H. et al. (2008). Applied Physics letters, 92, 183306.
[12] Vretik, L., Kyrychenko, V., Smolyakov, et al. Photochemical transformations in bis-Methacrylic
polymers for liquid crystal photoalignment: IR spectroscopy studies (2011). Mol.Cryst.Liq.Cryst.,
536, 224.
[13] Biswas, N., & Umapathy, S. (1997). J. Phys. Chem. A, 101(30), 5555.
[14] Zemskov, A. V., Rodionova, G. N., Tuchin, Yu. G. et al. (1987). Zhurnal Prikladnoi Spektroskopii
A, 101 49(4), 581.
[15] Buffeteau, T., Labarthet, F. L., Pezole M. et al. (1998). Macromolecules, 31, 7312.
[16] Bellus, D. (1971). Adv. Photochem., 8, 109.
[17] Buffeteau, T., Labarthet, F. L., Pezole M. et al. (2001). Macromolecules, 34, 7514.