Synthesis and photochemical properties of spiropyran graft and star polymers obtained by ‘click’ chemistry

The synthesis of photo-responsive polymers with high density of spiropyran (SP) groups has been investigated. Initially the ATRP synthesis of star-shaped polymer using acrylated benzospiropyran (BSP) was attempted but results suggested an incompatibility of ATRP with BSP preventing the formation of polymers or polymer architectures with a higher chain length or density of spiropyran side chains. Alternatively, copper catalyzed cycloaddition (click chemistry) was successfully employed to obtain spiropyran functionalized polymers. Well-defined poly(6-benzospiropyran hexylmethacrylate)s bearing a BSP moiety on the side chain of each unit of the polymer with linear, star-like and molecular brush architectures and narrow molecular weight distributions were successfully synthesized combining ATRP and click chemistry. All polymers exhibited conventional photochromism as confirmed by absorption and emission spectroscopy. The linear and star-like polymers showed similar behavior with comparable ring-closure kinetics and photostability, while the kinetics of the molecular brush architecture was two times slower and its photostability significantly greater.