Controlled synthesis of semiconducting polymers in droplet flow microreactors

This thesis reports the development of droplet flow reactors for the preparation of semiconducting polymers, focussing specifically on poly(3-hexylthiophene) (P3HT) pre- pared by Grignard metathesis polymerisation, and random copolymers of P3HT with poly(3-hexylselenophene) (P3HS). In contrast to conventional continuous flow reactors (where the flow consists of a single solvent phase), droplet reactors incorporate an immiscible ’carrier fluid’ that divides the solvent phase into a stream of near-identical microlitre-sized droplets which then pass through the reactor sequentially. In this way, the solvent phase is confined to a well-defined volume that no longer makes contact with the surrounding reactor architecture, and thereby overcomes blockage problems associated with preparation of polymers in continuous flow reactors. To overcome the limited solubility of the Ni(dppp)Cl2 catalyst widely used in Grignard metathesis polymerisation, a more soluble derivative, Ni(dppp)Br2, has been prepared. This catalyst allows P3HT to be synthesised with accurate control over a wide range of molecular weights, even at high throughput (up to 1 kg/day). A scalable ’tube-in-shell’ reactor was developed to provide improved thermal uniformity along the flow reac- tor, enabling the preparation of high molecular weight P3HT with Mw up to 190 kg/mol (PDI 1.5) and lower weight polymers with narrow polydispersity (PDI 1.1). To facilitate multistep chemistries in droplets, a new three-phase methodology is presented that enables the controlled addition of reagents downstream of the original droplet gener- ation. With a view to applying P3HT in electronic devices, an investigation into the influ- ence of polymer purity on the efficiency of P3HT:fullerene bulk heterojunction devices is reported. Polymer purity is shown to have a strong influence over polymer solubility and final device efficiency. With the purest polymers, efficiencies of up to 5.0 % and 7.0 % were obtained with PC60BM and IC60BA, respectively (PC60BM: phenyl-C61-butyric acid methyl ester, IC60BA: indene-C60 bis-adduct). The thesis finishes with the development of a new style of liquid-liquid separator, a key tool for post-processing droplet flows and enabling sequential operations.Open Acces