ABSTRACT
The concept of a living polymerization is centralized on the idea that no chain-breaking reactions, such as transfer or termination, occur to interfere with the chain-growth process. Living polymerization was first coined by Szwarc in 1956 through his investigations with anionic polymerizations. 1 Since his work, the concept of living polymerizations has extended to encompass a variety of methods that involve cationic, radical, or coordinating organometallic polymerizations. This form of controlled polymer growth allows for precise molecular weights, narrow dispersities, regioregularity, and end-group functionalization, which are desirable properties that can affect the overall performance of π-conjugated polymers in optoelectronic devices. 2 This synthetic method is more advantageous over step-growth mechanisms, which do not share the same control over polymerization. In chain-growth mechanisms, the monomer adds to the same growing chain one at a time. For step-growth polymerizations, the resulting dimers, trimers, tetramers, and oligomers that form can subsequently react with each other or with another monomer. This randomness results in the lack of control in polymerization. Figure 6.1 depicts the difference between chain-growth and step-growth polymerizations. In this chapter, we will review the recent developments in controlled polymerizations on π-conjugated materials, with an emphasis on poly(3-hexylthiophene) (P3HT) following the seminal findings by Yokozawa 3 and McCullough 4 that revolve around the utilization of Ni-mediated catalyst-transfer polycondensations. Scheme 6.1 depicts the synthesis of P3HT using the Kumada–Corriu cross-coupling.240 Depiction of chain-growth and step-growth polymerizations. https://s3-euw1-ap-pe-df-pch-content-public-u.s3.eu-west-1.amazonaws.com/9781315159522/ab60430e-1b37-4c27-9089-7b3e8b4c996e/content/fig6_1_B.tif"/> Synthesis of P3HT. https://s3-euw1-ap-pe-df-pch-content-public-u.s3.eu-west-1.amazonaws.com/9781315159522/ab60430e-1b37-4c27-9089-7b3e8b4c996e/content/fig6_10_B.tif"/>
