Mendeleev Commun., 2014, 24, 138–139 – 138 – © 2014 Mendeleev Communications. All rights reserved. Mendeleev Communications The development of new nonlinear optical (NLO) polymers for applications in photonics and optoelectronics is of importance for modern materials science. 1–3 To study the quadratic NLO activity formed at the molecular level due to incorporated organic chromophores, polymer materials are transformed into an electret state with frozen-in macroscopic polarization arising as a result of chromophore groups orientation in the applied electric field. 1–3 Methacrylate copolymers with chromophores in the side chain historically were one of the first classes of studied NLO poly- mers. 1,2 However, they attract close attention of the researchers up to now. 4–7 Here, we report the NLO activity of methacrylate polymers and copolymers with 4-amino-4'-nitroazobenzene groups in the side chain synthesized by a two-stage procedure allowing to obtain both copolymers and homopolymers with high chromo- phore concentrations. Two-stage synthesis of NLO oligomers is described in ref. 8, the essence of the approach is the following: at the first stage the aniline-containing oligomer precursor is synthesized, serving as azo component in azo functionalization performed at the second stage. Aniline-containing monomer, N-methylaniline hydroxy- propyl methacrylate (AMA) has been obtained by the reported procedure. 9 This monomer was used in the synthesis of oligo- meric precursor by radical polymerization or its copolymerization with methyl methacrylate (MMA) at equimolar ratio of monomers in DMF solution at 80 °C, azobisisobutyronitrile being used as initiator of polymerization. The second stage of the reaction was azo-coupling with p-nitrobenzene diazonium tetrafluoroborate being used as diazo component. As a result we obtained homo- polymer 4'-[N-methyl-N-(3-methacryloyloxy-2-hydroxypropyl)]- amino-4-nitroazobenzene (PMAZ) (yield, 85.5%; M n = 10 200) and copolymer MMA-co-MAZ (yield, 91.2%; M n = 14 400). The structure of the obtained polymers was confirmed by physico-chemical techniques. Azo-functionalization was con- trolled by UV, IR and 1 H NMR spectroscopy. Analysis of the 1 H NMR spectrum shows that, as a result of azo-functionalization in the aromatic region of the spectrum the following three wide singlets appear instead of two singlets near 7.23 and 7.76 ppm corresponding to (p-H + 2o-H) and 2m-H of the aniline fragment in the initial copolymer: d 8.30 ppm, corresponding to ortho- protons with respect to NO 2 group; d 6.83 ppm with respect to –N=N– group; and d 7.91 ppm with respect to NMe group, an intensity ratio of 2 : 4 : 2. In the IR spectrum of the functionalized (co)polymers, absorp- tion bands were observed at 1339 and 1518 cm –1 , corresponding to symmetric and antisymmetric stretching vibrations of the nitro group, and at 1376 cm –1 attributed to azo group vibrations. According to analysis with respect to nitrogen, the molar con- centration of functionalized AMA in copolymer is 45 mol%; the degree of functionalization is approximately 96% in both cases. Synthesized polymers have been obtained as red powders well- soluble in organic solvents. The azo-functionalization technique used in this work has advantages over the radical copolymerization of individual chromo- phores: copolymers are obtained with high degree of functionaliza- tion (~96%) and in good yield (up to 91%) without preliminary synthesis, isolation and purification of chromophore-monomer; moreover, polymer azo-coupling reaction proceeds under milder reaction conditions, not requiring tight control over medium pH and temperature. Since the obtained polymers contain reactive hydoxy groups, on their basis the cross-linked NLO polymers have been synthesized via hardening by 4,4'-diphenylmethane diisocyanate (MDI). To study the NLO activity of the obtained polymers, thin films were spin-cast from a 7% polymer solution in cyclohexanone by the procedure described elsewhere. 10 Film thickness h (Table 1) was determined by atomic-force microscopy in intermittent-contact mode. Poling procedure was carried out in the corona-discharge field (voltage, 6.5 kV) at a poling temperature of 110–130 °C. The quality of chromophores orientation was controlled by UV-VIS spectroscopy by a change in film absorption intensity before and Nonlinear-optical properties of methacrylic (co)polymers with azo chromophores in the side chain Tatyana A. Vakhonina, a Natalia V. Ivanova, a Nikolai N. Smirnov, b Alexander V. Yakimansky, b Marina Yu. Balakina* a and Oleg G. Sinyashin a a A. E. Arbuzov Institute of Organic and Physical Chemistry, Kazan Scientific Center of the Russian Academy of Sciences, 420088 Kazan, Russian Federation. Fax: +7 843 273 7253; e-mail: mbalakina@yandex.ru b Institute of Macromolecular Compounds, Russian Academy of Sciences, 199004 St. Petersburg, Russian Federation. Fax: +7 812 328 6869; e-mail: yakimansky@yahoo.com 04.002 DOI: 10.1016/j.mencom.2014. The efficiency of a two-stage procedure for the synthesis of methacrylic copolymers with azo chromophores in the side chain exhibiting quadratic nonlinear optical activity was demonstrated. Me O OMe CH 2 CH 2 x Me CH 2 O O OH N Me N N NO 2 Me O O OH N Me y z n MMA-co-MAZ: x = 0.53 y = 0.45 z = 0.02 n = 60 PMAZ: x = 0.00 y = 0.96 z = 0.04 n = 26 Structure of the synthesized methacrylic oligomers. Figure 1