Optimization of the Reaction Conditions for Direct Arylation Polymerizations in a Sustainable Solvent

摘要

Direct arylation polymerization (DArP) relieves the synthesis of conjugated polymers from the use of hazardous and toxic reagents typical of the traditional protocols. However, the compatibility with environmentally benign, nonhazardous, and low-cost solvents still represents the critical aspect for projecting DArP as an industrial-scale method for the preparation of conjugated polymers. In this study, a "green" solvent (i.e., cyclopentyl methyl ether) is implemented for the obtainment of poly(3-hexylthiophene) by DArP reaction, in order to explore sustainable reaction conditions also regarding the catalytic system and the base quantity, which equally undermine the sustainability of the DArP protocol. Considering the molecular weights as the indicator of precatalyst performance in determined conditions, it is established that the cheapest palladium source (i.e., PdCl_2) combined with two equivalents of (o-anisyl)_3P is able to yield the best results in the green ethereal solvent. Furthermore, it is found how, with respect to the common DArP protocols, the quantity of the expensive base (i.e., Cs_2CO_3) can be reduced in these reaction conditions without compromising molecular weights and regioregularity of the resulting polymer. These optimized reaction conditions can be extended to the copolymerization of other monomer units with satisfactory results in terms of molecular weights.