Low-bandgap conjugated copolymers based on a donor-acceptor structure have been synthesised via palladium-complex catalysed direct arylation polymerisation. Initially, we report the optimisation of the synthesis of poly(cyclopentadithiophene-alt-benzothiadiazole) (PCPDTBT) formed between cyclopentadithiophene and dibromobenzothiadiazole units. The polymerisation condition has been optimised, which affords high-molecular-weight polymers of up to M(n) = 70 k using N-methylpyrrolidone as a solvent. The polymers are used to fabricate organic photovoltaic devices and the best performing PCPDTBT device exhibits a moderate improvement over devices fabricated using the related polymer via Suzuki coupling. Similar polymerisation conditions have also been applied for other monomer units.

Soluble semiconducting polymers are attractive synthetic targets as they can be deposited from solution using low-cost processing routes to fabricate organic electronic devices such as light-emitting diodes, photovoltaics, and field-effect transistors.[1] One of the most widely studied systems are the poly(p-phenylenevinylene)s (PPVs), first reported by Burroughes et al. to show electroluminescence in polymeric lightemitting diodes.[2] The parent unsubstituted PPV is insoluble, and substituents are appended to the phenylene groups to produce soluble PPVs. A number of synthetic routes to these polymers has been described, [3] but all of these routes lead to polydispersities consistent with termination processes and consequently these are not living polymerizations.Ring-opening metathesis polymerization (ROMP) offers the opportunity for precise control of the conjugated-polymer molecular weight, low polydispersities, and the preparation of block copolymers. This method has been applied to the synthesis of polyacetylene by Feast et al. [4] and has been exploited in the synthesis of PPV polymers and copolymers. [5,6] Initial reports focused on the preparation of precursors that can be converted into insoluble PPV homopolymer. ROMP of [2.2]paracyclophane-1,9-diene gives PPV directly as an insoluble yellow fluorescent powder. Soluble copolymers of PPV have been prepared by ROMP with cyclopentene, cyclooctene, and cyclocta-1,5-diene comonomers. However, incorporation of more than 5 % of PPV units gives insoluble polymers.[6] Herein we report the first polymerization of substituted [2.2]paracyclophanedienes using ruthenium-based metathesis catalysts to give monodisperse, soluble phenylenevinylene homopolymers. The ROMP of the tetra-alkoxy-substituted [2.2]paracyclophanediene derivative 1, dissolved in THF, was initiated by addition of a THF solution of the second-generation Grubbs catalyst 2 (Scheme 1).[7] The reaction mixture was heated at reflux and then quenched by addition of ethyl vinyl ether. The resulting polymers 3 were purified by filtering through silica gel and isolated by evaporation of the solvent. Polymers with a range of molecular weights were prepared by varying the monomer-to-catalyst ratio. An extended reaction time (36 h) was necessary to achieve complete conversion of monomer, indicating a slow rate of polymerization. [5b, 8] The molecular weights of the polymers were determined by gel permeation chromatography (GPC) in THF solution. The number-average molecular weight (M n ) increased monotonically with the initial monomer-to-catalyst ratio (Figure 1) with a correlation coefficient of 0.999, and the polydispersities were all close to 1.2. The apparent discrepancy between the expected and the observed molecular weights (Figure 1) is due to the difference in the hydrodynamic radii of PPV and polystyrene.[9] From the linear relationship between the monomer-to-catalyst ratio and the degree of polymerization, the low polydispersities, and the complete consumption of monomer, we conclude that chain tra...

A fractal nanostructure having a high surface area is potentially useful in sensors, catalysts, functional coatings, and biomedical and electronic applications. Preparation of fractal nanostructures on solid substrates has been reported using various inorganic or organic compounds. However, achieving such a process using polymers in solution has been extremely challenging. Here, we report a simple one-shot preparation of polymer fractal nanostructures in solution via an unprecedented assembly mechanism controlled by polymerization and self-assembly kinetics. This was possible only because one monomer was significantly more reactive than the other, thereby easily forming a diblock copolymer microstructure. Then, the second insoluble block containing poly(p-phenylenevinylene) (PPV) without any side chains spontaneously underwent self-assembly during polymerization by an in situ nanoparticlization of conjugated polymers (INCP) method. The formation of fractal structures in solution was confirmed by various imaging techniques such as atomic force microscopy, transmission electron microscopy (TEM), and cryogenic TEM. The diffusion-limited aggregation theory was adopted to explain the branching patterns of the fractal nanostructures according to the changes in polymerization conditions such as the monomer concentration and the presence of additives. Finally, after detailed kinetic analyses, we proposed a plausible mechanism for the formation of unique fractal nanostructures, where the gradual formation and continuous growth of micelles in a chain-growth-like manner were accounted for.

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