Self-assembly and optical property of triblock copolymers made of polystyrene and oligo(p-phenyleneethynylene) in different mixtures of toluene and hexane

Using a combination of laser light scattering (LLS), UV-vis, and fluorescence spectrometry methods, we comparatively examined the self-assembly and optical property of two triblock copolymers made of polystyrene (PS, coillike) and oligo(p-phenyleneethynylene) (OPE, rodlike) in different mixtures of toluene and hexane. For the coil-rod-coil (PS-OPE-PS) triblock copolymer, intrachain wrapping of the two soluble PS coil blocks on the insoluble middle OPE rod block in the solvent mixture reduces the π-π stacking of OPE and makes it more planar, resulting in a red shift in its UV-vis and fluorescence spectra, presumably, due to the J-type aggregation. While for the rod-coil-rod (OPE-PS-OPE) triblock copolymer, two intrachain stacked insoluble OPE blocks are wrapped and stabilized by the soluble middle PS block in toluene. The addition of hexane, a nonsolvent of PS, leads to further interchain aggregation of OPE, resulting in large polymeric micelles with an insoluble OPE core and a soluble PS shell. The blue shift in its UV-vis and fluorescence spectra reflects that intrachain stacking and interchain packing of OPE in the core are mainly H-type; i.e., they are parallel to each other, which increases the π-π interaction of OPE.