CC BY
22
УДК54.057, 66.095.26-922
O. Krupka, V. Smokal, T. Deberdeev,
A. Kolendo
SYNTHESIS OF BENZYLIDENE AND AZO CONTAINING POLYMERS FOR PHOTOPHISICAL APPLICATION
Ключевые слова: полимеризация, бензолиденовые фрагменты, 1НЯМР, фотохимическая и оптическая активности.
В работе были синтезированы полимеры полученные методом радикальной полимеризации метакриловых мономеров с боковыми азобензеновыми группами и мономеров с бензолиденовыми фрагментами. Полимеризация проводилась в среде ДМФ в качестве инициатора использовался АИБН. Продукты реакции полимеризации характеризовались по оценке спектров 1Н ЯМР. Представлены данные о фотохимической и оптической активности полученных полимеров.
Keywords: polymerization, benzylidene fragments, HNMR, photochemical and optical activities.
In the present work, the polymers built with the use of the free radical polymerization of methacrylic monomers incorporating an azobenzene side-group and monomers with benzylidene fragments have been synthesized. The polymerization was carried out in DMF with AIBN as initiator. The products of polymerization were characterized by HNMR. The results ofphotochemical and optical activities of the corresponding polymers are presented.
Introduction
The development of modern technologies enables us to create polymer materials with a number of properties, which would be impossible to realize in a single polymer. Designing the structure of modified polymer chain with various photoactivatable groups is one of the issues of current importance in present day polymer chemistry. In this work, our investigation concentrates on synthesis of new oxazolone, thiazolidenone, thiohydantoin, hydantoine and azo- derivatives (Fig. 1), radical thermoinitiated copolymeriza-tion of new methacrylic monomers with methylmetacrylate (MMA) and investigation of the resulting polymers. The spectral characteristics of similar compounds were investigated previously [1]. Also it should be noted, that in the last few years there has been a growing research interest in developing materials which exhibit nonlinear optical (NLO) properties for applications such as optical signal processing and information storage [2-8]. Therefore the polymers containing azobenzene chromophore molecules have been extensively studied by many research groups due to their promising features for all-optical devices [9-17].
Besides organic materials might provide the systems developed with unique possibilities and higher flexibilities in comparison with inorganic materials because of the relatively easy way to process organic polymeric materials into practical devices. The main objective of this work is to realize and characterize from optical and physical-chemical point of view new polymers with benzyliden and azobenzene fragments in the side chain in order to find the correlation between the chemical structure of the polymers and its properties (switching etc.).
The aims of our work were synthesized polymers with photochemical properties typical for single molecules. Polar substituents in azobenzene compounds and nature of heterocyclic fragments in benzyliden containing derivatives lead to the change of electronic density during the photoisomerisation. This fact opens the
possibility of creation polymer materials with predicted properties.
CH3
CH3
CH3
CH2=C—^ OR
-pch2—c^—tch^c-я-
I- 2 I -I m L 2 I _ln
4 H
OCH3 OR
where n/m =1:3
M
HN NH hN NH
Y Y
(3) S O
(3) (4)
H3C
H3C
H3C
(5)
(6)
N^^j)-N= N^^^)— NO2
(7)
Fig. 1 - The chemical structure of synthesized benzylidene and azo- containing monomers and co-polymers.
p
Experimental part
Oxazolone containing monomer Ml was prepared as describe previously [23].
2-phenyl-4-[(4-methacryloyloxyphenyl) meth-ylene]-5(4H)-oxazolone (Ml): yield 55%. 1H NMR (400 MHz, DMSO-d6), d (ppm): 5.89 (s, 1H, CH2), 6.34 (s, 1H, CH2), 2.06 (s, 3H, CH3), 7.28-8.18 (m, 4H, Ar), 7.70-8.35 (m, 5H, Ar).
4-(methacryloyloxyphenyl)methylene-2-thioxo-4-thiazolidinone (M2): (2g) 4-
(methacryloyloxy)benzaldehyde, 2-thioxo-4-
thiazolidinone (2.5 g), anhydrous sodium acetate (0.3 g; 0.2 mol) in 50 ml isopraponol was heated on a steam bath 80-90°C. After 2 h, the mixture was cooled and then was poured on ice. The resultant solid product that formed were filtered off, washed with water and dried. Recrystallization from ethanol alcohol gave yellow crystals, yield 65%. 1H NMR (400 MHz, DMSO-d6), d (ppm): 5.86 (s, 1H, CH2), 6.31 (s, 1H, CH2), 2.03 (s, 3H, CH3), 7.28-7.66 (m, 4H, Ar), 7.62 (s, 1H, CH), 13.69 (s, 1H, NH).
Thiohydantoin containing monomers M3 was synthesized analogously to thiazolidinone containing monomer M2 as describe previously.
(4-methacryloyloxyphenyl)methylene-2,4-imidazolidinedithione (M3): yield 64%. 1H NMR (400 MHz, DMSO-d6), d (ppm): 6.44 (s, 1H, CH), 2.04 (s, 3H, CH3), 5.85 (s, 1H, CH2), 6.3 (s, 1H, CH2), 12.22 (s, 1H, NH), 12.04 (s, 1H, NH), 7.14-7.71 (m, 4H, Ar).
Hydantoin containing monomer M4 synthesized analogously to thiazolidinone containing monomer M2 as describe previously.
(4-methacryloyloxyphenyl)methylene-2,4-imidazolidinedione (M4): yield 55%. :H NMR (400 MHz, DMSO-d6), d (ppm): 7.56 (s, 1H, CH), 2.04 (s, 3H, CH3), 5.8 (s, 1H, CH2), 6.3 (s, 1H, CH2), 8.98 (s, 1H, NH), 9.31 (s, 1H, NH), 7.2-7.6 (m, 4H, Ar).
4'-[(2-ethacryloyloxyethyl)ethylamino]- 4-cyanoazobenzene (M5). A solution of 4'-[(2-hydroxyethyl)ethylamino]-4-cyanoazobenzene (3 g, 0.01 mol) and triethylamine (1.11 g, 0.011 mol) was dissolved in THF (35 mL). The solution was kept in an ice bath for 10 min. A solution of distilled methacryloyl chloride (1.15 g, 0.011 mol) in THF (10 mL) was added slowly to the reaction mixture. After the addition of methacryloyl chloride, solution was stirred for 12 h at ambient temperature. The solvent was removed by rotary evaporation and the residue was washed with a solution of sodium carbonate (0.8 g) in water (40 mL). After removing the solvent, the resulting material was purified by column chromatography (silica gel, ethyl ace-tate/hexane 1/8). Red solid residue, yield: 87%. :H NMR (400 MHz, CDCl3), d (ppm): 7.89, 7.87 (d, 4H, Ar), 7.75, 7.73 (d, 2H, Ar), 6.82, 6.8 (d, 2H, Ar), 6.1 (s, 1H,CH2), 5.6 (s, 1H, CH2), 4.36 (m, 2H, OCH2), 3.7 (m, 2H, NCH2), 3.55 (m, 2H, NCH2), 1.94 (s, 3H, CH3), 1.25 (m, 3H, NCH2CH3).
4'-[(2-Methacryloyloxyethyl)ethylamino] -azobenzene (M6). Azomonomer M6 was synthesized using the above procedure for azomonomer M5. The product was purified by column chromatography (silica gel, ethyl acetate/hexane 1/8). Orange solid residue,
yeld 75 %. 1H NMR (400 MHz, CDCl3), d (ppm): 7.83, 7.85 (d, 4H, Ar), 7.48 (t, 2H, Ar), 7.38 (t, 1H, Ar), 6.8 (d, 2H, Ar), 6.11 (s, 1H, CH2), 5.6 (s, 1H, CH2), 4.36 (m, 2H, OCH2), 3.71 (m, 2H, NCH2), 3.51 (m, 2H, NCH2), 1.95 (s, 3H, CH3), 1.24 (m, 3H, CH3).
4'-[(2-methacryloyloxyethyl)ethylamino] -4-nitroazobenzene (M7). Azomonomer M7 was synthesized in the same way as azomonomer M5. The solid was recrystallized from methanol. Dark red crystals yield 80%. 1H NMR (400 MHz, CDCl3), d (ppm): 8.33, 8.31 (d, 2H, Ar), 7.92 (t, 4H, Ar), 6.83, 6.81 (d, 2H, Ar), 6.1 (s, 1H, CH2), 5.6 (s, 1H, CH2), 4.37 (m, 2H, OCH2), 3.74 (m, 2H, NCH2), 3.56 (m, 2H, NCH2), 1.94 (s, 3H, CH3), 1.24 (m, 3H, CH3).
Polymers with azo fragments were synthesized by free-radical polymerization in toluene. The polymerization was carried out in 10 wt% toluene solution monomers and MMA with initial mole ratios 1:3. The polymerization was conducted using AIBN as a free radical initiator (1 wt% of monomer) at 80°C 35 h in argon atmosphere. Previously initial mixture was degassed with repeated freeze-pump-taw cycles. The polymerization was stopped by pouring the reaction mixture into methanol. This procedure was repeated several times to ensure removal of unreacted methacrylic monomers and finally the polymers P5, P6, P7 dried under vacuum at 50°C overnight. The copolymerization ratios in the corresponding polymers were calculated on the basis of the integrated peak areas of 1H NMR spectra in DMSO-d6. The polymerization ability of the new benzylidene containing monomers was investigated kinetically for radical copolymerization using the dilatometric method. The process was conducted in 10% DMF solution at 80°C (argon atmosphere, initiator -AIBN 1%); contractions were measured by KM-6 cathetometer. The resulting viscous solution was added dropwise into ethanol to precipitate polymeric materials. Polymers were purified from ethanol. The conversion rates were controlled gravimetrically. The conversion rate during the copolymerization processes of Ml with MMA was 67% in 390 minutes, M2 with MMA was 45% in 260 minutes, M3 with MMA was 40% in 260 minutes, M4 with MMA was 32% in 260 minutes. The structures of all copolymers calculated from 1HNMR data are approximately the same in the all case as the structure of the initial mixture 1:3.
Results and discussion
The chemical structure of synthesized benzylidene and azo- containing monomers and copol-ymers are represented below.
The polymers were synthesized by radical polymerization using AIBN as radical initiator. Polar substituents in azobenzene compounds as -CN and -NO2 can act as retarding agents of free radical polymerization reaction. Therefore, long reaction time is needed to syntheses polymers with high yield. In consideration of this singularity, only for new monomers with benzylidene fragment were investigated the kinetic characteristics of polymerization process. The kinetics of the polymerization for Ml, M2, M3, M4 were investigated during radical copolymerization with MMA using the dilatometric method.
It should be note that azobenzenes can function as molecular switches by applying light of different wavelengths to obtain varying amounts of cis and trans isomers, where the excess of one of the two isomers may be detected by a change in UV absorption spectra [18,19].
In the previous work have been detailed describe the common photochemical properties of all azobenzene compounds. The possibility of these compounds for photoisomerization through rotation about N-N bond was retained in the synthesized polymers. As example, changes in the absorption spectra of P5 due to optically induced transition to the cis- isomer and the reverse transition the cis- to the trans- state was described [20]. The results the investigation of photochemical and photophysical properties of benzylidene and azo compounds were described previously [1, 20]. It is well know that the stable state of the molecule with benzylidene fragment is the cis-isomeric configuration [21]. The absorption in the visible range of a photon induces the transition to the trans-isomer. This state is metastable with the reverse transition to the cis state taking place through photo activation. Therefore, a molecule absorbing of a photon undergoes a complete cis-trans-cis isomerization cycle [22]. We can suppose that these properties remaining in benzylidene containing polymers. Whereas previously for some of synthesized polymers were demonstrated NLO activity.
It should be noted that photoisomerisation by trans-cis-trans and cis-trans-cis mechanisms is typical for obtained polymers.
Conclusions
During the work new objects for NLO investigation were synthesized. The polymers with MMA with benzylidene and azo fragments were obtained. The polymerization ability of the new monomers was investigated kinetically for radical copolymerization using the dilatometric method. We suggest that the optical activity is determined by a steric delocalization of the active side chain of azoester and benzylidene and also based on different photoisomerization processes in investigated compounds. The azo polymers have been characterized as compound with repeatable trans-cis-trans isomerisation process, for the benzylidene containing polymers we can observe cis-trans-cis isomeriza-
tion cycle. These polymers can prove to be important candidate for optical signal processing and information storage.
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© O. Krupka - к.х.н., с.н.с. каф. химии высокомолекулярных соединений Киевского национального университета им. Т. Шевченко г. Киев, Украина, V. 8шока1 - к.х.н., н.с. той же кафедры; Т. БеЪеМееу - д. т. н., зав. каф. технологии переработки пластмасс и композитных материалов КНИТУ, [email protected]; А. Ко1еп^ - д.х.н., зав. каф. химии высокомолекулярных соединений Киевского национального университета им. Т. Шевченко г. Киев, Украина.
