Macromolecules, Vol.34, No.26, 9032-9038, 2001
Azobenzene-containing thermoplastic elastomers: Coupling mechanical and optical
Thermoplastic elastomers of a styrene-butadiene-styrene (SBS) triblock copolymer containing grafts of an azobenzene side-chain liquid crystalline polymer were prepared by polymerization of an azobenzene acrylate monomer in solutions with dissolved SBS. Stretching thin films at room temperature induces long-range orientation of the azobenzene mesogenic groups along the strain direction. Upon irradiation with polarized or unpolarized UV light at 360 rim, the orientation of azobenzene moieties in stretched films is erased as a result of the traps-to-cis photoisomerization, while on subsequent irradiation with polarized or unpolarized visible light at 440 nm, the initial stretching-induced orientation is recovered due to the cis-to-traps back-isomerization. Gratings can be inscribed on stretched films at different alignments with respect to the strain direction, whose fringe spacing can be modified through elastic extension or retraction of the films.