Polyurethane-oligo(phenylenevinylene) random copolymers: pi-conjugated pores, vesicles, and nanospheres via solvent-induced self-organization

Abstract

We report a new series of polyurethane-oligo(phenylenevinylene) (OPV) random copolymers and their self-assembled nanomaterials such as pores, vesicles, and luminescent spheres. The polymers were synthesized through melt transurethane process by reacting a hydroxyl-functionalized OPV with diurethane monomer and diol under solvent-free and nonisocyanate conditions. The amount of OPV was varied up to 50 mol % in the feed to incorporate various amounts of pi-conjugated segments in the polyurethane backbone. The pi-conjugated segmented Polymers were subjected to solvent induced self-organization in THF or THF+water to produce variety of morphologies ranging from pores (500 nm to 1 mu m) to spheres (1.00 nm to 2 mu m). Upon shining 370-nm light, the dark solid nanospheres of the copolymers transformed into blue luminescent nanoballs under fluorescence microscope. The mechanistic aspects of the self-organization process were studied using solution FTIR and photophysical techniques such as absorption and emission to trace the factors which control the morphology. FTIR studies revealed that the hydrogen bonding plays a significant role in the copolymers with lower amount of OPV units. Time resolved fluorescent decay measurements of copolymers revealed that molecular aggregation via pi-conjugated segments play a major role in the samples with higher OPV content in the random block polymers.