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Trans → cis photoisomerization of the stilbene residues in the side chains of copolymers from 2‐hydroxyethyl methacrylate and monomer containing stilbene residue

1974; Wiley; Volume: 175; Issue: 8 Linguagem: Inglês

10.1002/macp.1974.021750814

0025-116X

František Mikeš, Petr Štrop, Jaroslav Kálal,

Photopolymerization techniques and applications

Abstract The rate of the trans → cis photoismerization of the stilbene residue was compared in the copolymer 3 from 2‐hydroxyethyl methacrylate ( 1 ) and trans‐N ‐4‐(4‐nitrostyryl)phenylmethacrylamide ( 2a ) with its low molecular weight analogue trans‐N ‐4‐(4‐nitrostyryl)phenylisobutyramide ( 2b ) in methanol, 2‐ethoxyethanol and in the binary solvents propanol/water and tert ‐butyl alcohol/water. It was observed that the trans → cis photoisomerization of the stilbene residues was more rapid at 20°C in the side chains of the copolymer than for 2b in most solvents. This result may be interpreted on the basis of the quantum yield dependence for the trans → cis isomerization on the polarity of the medium where the isomerization takes place. Acceleration of the trans → cis isomerization of the stilbene residues in the side chains of the copolymer results from a decrease in the polymer microenvironment polarity as compared to the polarity of the solvent itself. This interpretation is supported by direct measurement of the polarity of the polymer chain microenvironment, based on the Kosower semi‐empirical polarity scale. The course of the trans → cis isomerization of 2b and 3 does not obey the equilibrium, first‐order reaction for all the solvents mentioned. The effect of preferential sorption of one of the components in binary solvents on the polymer coil and the effect of temperature on the photochemical trans → cis isomerization are discussed in connection with the experimental results.