Synthesis of a conjugated polymer film via interfacial Knoevenagel polymerization and conversion to covalent triazine polymer for photocatalysis

The Knoevenagel condensation was applied to the interfacial polymerization of difunctional aldehyde and trifunctional acetonitrile monomers for the first time. The polymerization was conducted at the interface between water containing a base and an organic phase containing the monomers at room temperature for periods ranging from a day to several weeks. The structural and morphological changes of the polymer were investigated to complete the Knoevenagel condensation and, interestingly, the morphological shape of the polymer was significantly changed from particles to film. Specifically, the polymer showed a particle-type product (about 400 nm) at the early stage of polymerization and was transformed to a film-like structure after a prolonged polymerization time. Scanning electron microscope images revealed that the polymer particles were aggregated and connected to each other to form a film, in which each particle was linked by covalent self-assembly. As one of the proofs of the covalent self-assembly, as a result of the increase in the conjugation length, the polymer's fluorescence wavelength was red-shifted after the film formation. Such a red-shift was also observed across the polymer film from the edge (particle) to the central region (film). To improve the photocatalytic performance under visible light irradiation, a triazine group was introduced using the vinylic nitrile group. Using the triazine-containing polymer, almost 100% photodegradation of rhodamine B dye was attained within 30 min.