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Photosensitive poly(urethane acylsemicarbazide)s with azobenzene chromophores in the main chain

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Abstract

Poly(urethane acylsemicarbazide)s were synthesized with a two-step process: (1) the in situ generation of diisocyanate through the thermal decomposition of an azobenzene-containing precursor diazide and a reaction with ester/ether polyols to form an isocyanate-terminated prepolymer and (2) chain extension in N,N-dimethylacetamide with aliphatic or aromatic dihydrazides. Films cast from N,N-dimethylacetamide solutions were characterized with attenuated total reflection/Fourier transform infrared spectroscopy, and the thermal properties were studied with thermogravimetric analysis and differential scanning calorimetry. The effects of the hard-segment content and chain extenders on the static and dynamic mechanical properties were investigated. The photoresponsive behavior of the polymers and the effects of variations in the chromophore concentration and chemical composition on the kinetics of photoisomerization were investigated with ultraviolet–visible spectroscopy, which revealed that the rates were independent of the chromophore concentration. The photomechanical behavior, assessed with creep-recovery measurements, proved that the systems underwent photochemical isomerization upon irradiation with ultraviolet light. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 444–454, 2004

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