Synthesis of Polyphthalaldehyde-Based Block Copolymers: Utilization of a Thermo-Sacrificial Segment for an Easy Access to Fine-Tuned Poly(3-hexylthiophene) Nanostructured Films

This work deals with the synthesis and characterization of new diblock copolymers based on π-conjugated and depolymerizable units. These diblock copolymers are based on a regioregular poly­(3-hexylthiophene) sequence associated with a sacrificial block, namely polyphthalaldehyde. The conjugated polymer was obtained by Grignard metathesis polymerization and end-capped by an alkynyl group while the depolymerizable segment was synthesized by an anionic cyclopolymerization from an azide moiety. Diblock copolymers with different molecular weights were then successfully synthesized via an alkyne–azide coupling reaction. Under specific conditions, these copolymers self-assemble into fibrillar nanostructures in thin films. The elimination of polyphthalaldehyde was carried out by thermal treatment, generating nanoporous poly­(3-hexylthiophene) films. The use of a dry treatment to remove the polyphthalaldehyde block strongly reduces the morphological damages that would occur with a “wet” processing route. These nanoporous poly­(3-hexylthiophene) films could be useful for controlling the morphology of the heterojunction in organic photovoltaic devices after successful filling with an electron-acceptor material.