Recently, we observed a large-magnitude bending in glassy, crosslinked polyimides functionalized with azobenzene (X-azo-PI). Exposure of these materials to blue-gree irradiation (442 nm) yield nearly identical polarization-directed forward and reverse bending to that observed in glassy azo-liquid-crystalline networks(azo-LCN) with polydomain orientation. Here, we report on the photomechanical response of a series of linear polyimides that contain main-chain azobenzene units and span from amorphous to semi-crystalline, exhibiting a considerable increase in both Tg(>350oC) and storage modulus(>6 GPa) from X-azo-PI and azo-LCN. The photogenerated tensile stress in these materials is as much as an order of magnitude larger than observed in glassy azo-LCN. Through systematic composition variation of the flexible (6FDA) and rigid (PMDA) dianhydrides together with 4,4'-diamino-azobenzene, we note that crystallinity decreases the magnitude of bending as well as tensile stress. The reduction in photomechanical output with crystalline content is attributed to a reduction in the photoresponsivity of the material system, confirmed through spectroscopic examination of the materials before, during and after 442-nm irradiation.

Structural and morphological factors in photomechanical enhancement of polyimides with main-chain azobenzene moieties

244th National Meeting (2012)

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