Implementation of Sustainable Solvents in Green Polymerization Approaches

In modern polymer chemistry directed toward the synthesis of conjugated materials, the synthetic routes devised to achieve the process sustainability are based on C-H bond activation. This prerequisite distinguishes both the tandem Suzuki−Heck as well as the direct arylation polymerizations (DArP); however, their compatibility with environmentally benign solvents still represents a challenge. In this paper, the implementation of sustainable solvents for the synthesis of poly(9,9-dioctylfluorenylene-vinylene) by using the traditional Pd(AcO)2/P(o-Tol)3/NEt3 catalytic system is described. It is assessed that selected green solvents (i.e., anisole and propylene carbonate) constitute the ideal media for the tandem Suzuki–Heck polymerization. Furthermore, by modulating medium polarity using mixtures of these green solvents and changing the reaction temperature, a suitable compromise between high molecular weights and regioregularity of the resulting polymers is reached. Conversely, the presence of propylene carbonate is deleterious for the DArP of 2-bromo-3-hexylthiophene, while it is found that catalyst performances in anisole strictly depend on the palladium source used. The best conditions are obtained using PdCl2(PPh3)2 as the precatalyst, affording a highly regioregular (93%) poly(3-hexylthiophene) in quantitative yields and high molecular weights (26.7 kg mol−1).