An improved greener process for the direct C[sbnd]H:C[sbnd]H arylation polymerization of 3,4-Propylenedioxythiophene derivatives

In this manuscript, we report an improved method for the direct C[sbnd]H:C[sbnd]H arylation process for the polymerization of 3,4-propylenedioxythiophene (Pro-DOT) derivatives. As an alternative to traditional oxidative direct arylation (DAH) polymerization process, the direct C[sbnd]H:C[sbnd]H arylation method has emerged as promising method to polymerize activated aromatic systems. Herein, we report a significant improvement to existing C[sbnd]H:C[sbnd]H arylation polymerization of Pro-DOT derivatives wherein molecular oxygen was used as oxidizing agent to replace the commonly used inorganic oxidants. Furthermore, use of molecular oxygen enabled us to carry out the polymerization without any ancillary ligands. This makes the whole process greener and economically more attractable. The process was optimized by measuring the rate of conversion of monomer using HPLC. It was surprising to note that there is a trade-off between the rate of polymerization and percentage conversion. The final optimum temperature was found to be 70 °C. Therefore, the polymerization was initially carried out at 70 °C till the complete conversion of monomer followed by at higher temperature to build the molecular weight. This stepwise ramping of temperature allowed us to get polymer with 72 % yield and a weight average molecular weight of 44 kDa. The final purified polymers were characterized by GPC, 1H NMR and UV–vis studies.