What Limits the Molecular Weight and Controlled Synthesis of Poly(3-alkyltellurophene)s?

Polytellurophenes are an emerging class of conjugated polymers; however, their controlled polymerization leading to high molecular weight materials has been a major challenge. Here we present a systematic investigation of the synthesis of poly­(3-alkyltellurophene)­s using the catalyst transfer polycondensation methodology. Learning that previous syntheses were limited by both polymerization reaction kinetics and polymer solubility, we design new tellurophene monomers to overcome these limitations. Controlled polymerization behavior up to M_n = 25 kDa, chain extension, block copolymerization, external initiation, and well-defined end groups are demonstrated for poly­(3-alkyl­tellurophene)­s with appropriately designed side chains. We clarify the role that side-chain branching point plays on polymerization kinetics and optical properties for these prototypical regioregular polymers. In addition, the effect that monomer addition sequence has on well-defined tellurophene–thiophene block copolymers was studied. The controlled polymerization of tellurophene should provide access to more complex polymeric architectures involving these and other conjugated monomers. The methods used to optimize the polymerization of alkyltellurophenes should be applicable to other monomers that have been challenging to synthesize in a controlled manner.