Synthesis of chiral-photochromic dopant l-menthyl 4ยข-(4-(1-decyloxy)phenylazo)benzoate (Azo) was carried out according to the following method. To a solution of 4.31 mmol of l-menthol, 5.6 mmol of triethylamine, and 0.56 mmol of N,Nยข-dimethylaminopyridine in 2 mL of purified tetrahydrofuran (THF) 4.31 mmol of 4ยข-(4-(1-decyloxy)phenylazo)benzoic acid chloranhydrite, synthesized using a procedure similar to that described in the literature [18], was slowly added under cooling. The resulting mixture was stirred for 3 days. Then chloroform (50 mL) was added to a filtrate. The solution was washed successively with water, a 5 % solution of acetic acid, and finally with water until pH 7 was achieved. The chloroform extract was dried with anhydrous MgSO 4 . After removal of solvent the red crude product was purified by column chromatography (eluent chloroform). Yield: 39 % of red powder, m.p. 78ยฑ79 C. IR [cm ยฑ1 ]: 2920, 2888, 2856 (CH 2 ), 1710 (CO), 1600, 1588 (CยฑC in Ar), 1256 (COC).
The blend was prepared by dissolving copolymer and dopant in dichloroethane followed by solvent evaporation at 60 C. Then the mixture was dried in vacuum at 120 C for 2 h.
The copolymer PAzo was synthesized by radical copolymerization of monomers in benzene solution at 60 C; 2,2ยข-azobisisobutyronitrile (AIBN) was used as an initiating agent. The synthesized copolymer was purified by repeated precipitation with methanol and dried in vacuum.
Characterization: IR spectra were recorded on a Bruker IFS-88 spectrophotometer using KBr pellets. The relative molecular mass of copolymer was determined by gel permeation chromatography (GPC). GPC analyses were carried out with a GPC-2 Waters instrument equipped with an LC-100 column oven and a Data Modul-370 data station. Measurements were made by using a UV detector, THF as solvent (1 mL/min, 40 C), a set of PL columns of 100, 500 and 10 3 , and a calibration plot constructed with polystyrene standards. The copolymer obtained has the following molecular mass characteristics: M n = 15 000, M w /M n = 2.1.
Investigations of Phase Behavior and Optical Properties: Phase transitions of the mixture and copolymers were studied by differential scanning calorimetry (DSC) with a scanning rate of 10 C/min. All experiments were performed using a Mettler TA-400 thermal analyzer and a LOMO P-112 polarization microscope. Selective light reflection of copolymer and mixture films was studied with a Hitachi U-3400 UV-vis-IR spectrometer equipped with a Mettler FP-80 hot stage. The 20 mm thick samples were sandwiched between the two flat glass plates. The thickness of the test samples was preset by Teflon spacers. Planar texture was obtained by shear deformation of the samples, which were heated to temperatures above the glass transition temperature. Prior to tests, the test samples were annealed for 20ยฑ40 min.
Photo-optical Investigations: Photochemical investigations were performed using a special instrument [10] equipped with a DRSh-250 ultra-high pressure mercury lamp. Using a filter, light with maximum wavelength 366 nm was selected. To prevent heating of the samples due to IR irradiation of the lamp, a water filter was used. To obtain a plane-parallel light beam, a quartz lens was used. During irradiation, the constant temperature of the test samples was maintained using a Mettler FP-80 heating unit. The intensity of UV radiation was equal to 1.9 ยด10 ยฑ8 Es s ยฑ1 cm ยฑ2 (as measured actinometrically [19]).
Photochemical properties of the mixture and copolymers were studied by illuminating the 20 mm thick films or thin films obtained by casting of solution in dichloroethane followed by evaporation at 60 C. Immediately after irradiation, absorbance or transmittance spectra were recorded using a Hitachi U-3400 UVvis-IR spectrometer.