Self-assembly of oligo(p-phenylenevinylene)-block-poly(ethylene oxide) in polar media and solubilization of an oligo(p-phenylenevinylene) homooligomer inside the assembly

Rod-coil amphiphilic diblock copolymers, consisting of oligo(p-phenylene- vinylene) (OPV) as a rod and hydrophobic block and poly(ethylene oxide) (PEO) as a coil and hydrophilic block, were synthesized by a convergent method. The aggregation behavior of the block copolymers in a selective solvent (tetrahydrofuran/H₂O) was probed with the absorption and emission of the OPV block. With increasing H₂O concentration, the absorption maximum was blueshifted, the emission from the molecularly dissolved OPV decreased, and that from the aggregated OPV increased. This indicated that the OPV blocks formed H-type aggregates in which the OPV blocks aligned in a parallel orientation with one another. The transmission electron microscopy observation revealed that the block copolymers with PEO weight fractions of 41 and 62 wt% formed cylindrical aggregates with a diameter of 6-8 nm and a length of several hundreds nanometers, whereas the block copolymer with 79 wt% PEO formed distorted spherical aggregates with an average diameter of 13 nm. Furthermore, the solubilization of an OPV homooligomer with the block copolymer was studied. When the total polymer concentration was less than 0.1 wt%, the block copolymer solubilized OPV with a 50 mol% concentration. The structure of the aggregates was a cylinder with a relatively large diameter distribution.