Impact of Photoactive Monomer Location in Photo-responsive Block Copolymer/Ionic Liquid Solutions

By incorporating a photoactive moiety into a block polymer, the phase behavior can be controlled with light. Here we study the effect of the positioning of pendant azobenzene groups along the polymer backbone on the lower critical disorder-order transition of poly(methyl methacrylate)-block-poly(benzyl methacrylate) (PMMA-b-PBnMA, or MB) in the ionic liquid 1,3-dimethyl imidazolium bis(trifluoromethylsulfonyl)imide. By using small angle X-ray scattering and UV-irradiated small amplitude oscillatory shear rheology, the placement of azobenzene statistically along the benzyl methacrylate backbone (MBsA) is compared to locating it as a midblock between the PMMA and the PBnMA (MAB) or as an end block after the PBnMA (MBA). Two concentrations of polymer in the ionic solvent were studied, 35 and 50 wt%. MBsA was also the only sample of the three to successfully transition reversibly between order and disorder with light. Adjusting the position of the azobenzene within the thermo- and photo-responsive polymer solution significantly changes the overall behavior of the solutions and the ability to control that behavior with light and temperature.