Supramolecular Photoresponsive Polyurethane with Movable Crosslinks
Based on Photoisomerization of Azobenzene
Abstract
Photoresponsive supramolecular materials have been fabricated by
controlling the density of reversible cross-links or the distribution of
movable cross-links. This study prepared photoresponsive polyurethane
(CD-Azo-PU) based on controlling the crystallization of the hard
segments in polyurethane (PU) by complexation between azobenzene (Azo)
and cyclodextrins (CDs). CD-Azo-PU incorporated polyurethane as the main
chain and a 1:2 inclusion complex between Azo and γCD as a movable
crosslink point. Upon ultraviolet light (UV, λ = 365 nm) irradiation,
the photoresponsiveness of CD-Azo-PU bent toward the light source
(defined as positive), while that of the linear Azo polyurethane
(Azo-LPU) without TAcγCD-diOH as a movable crosslinker bent in the
direction opposite the light source. The bending rates were determined
to be 0.058°/s for CD-Azo-PU and 0.027°/s for Azo-LPU, indicating that
the bending rate for CD-Azo-PU was faster than that for Azo-LPU. By
incorporating movable cross-links into CD-Azo-PU, we successfully
achieved specific photoresponsive actuation with an enhanced rate.