Polymerization of Diamines with Sulfur Monochloride To Yield Bright, Conjugated Polymers

Highly conjugated polymers possessing the NSS functional group were synthesized to investigate the colors obtained from polymers with this understudied functional group. Five aromatic diamines were polymerized with sulfur monochloride (S2Cl2) to yield high molecular weight cross-linked polymers. The polymerizations were completed with ratios of amine to sulfur monochloride of 1.5:1, 1:1, 1:1.5, and 1:2 to yield polymers with different levels of cross-linking and molecular weights from 15 to 5100 kg mol–1. The compositions were investigated by elemental analysis to confirm that the amount of sulfur within the polymers agreed with predictions based on the ratio of monomers used in their synthesis. These polymers were brightly colored with colors from yellow, red, brown, green, and blue, and their UV–vis spectra were measured to determine the absorption maxima. Several control experiments were completed that demonstrated that the reactions between monomers occurred between the amines and S2Cl2 rather than electrophilic aromatic substitution reactions. The polymers were air stable but completely degraded in the presence of 2-mercaptoethanol. In each of these degradations, the diamine monomer was isolated without any evidence of a thiol on the ring, as would be expected for electrophilic aromatic substitution. These polymers were investigated for their ability to act as sensors for 2-mercaptoethanol by exposing them to 2-mercaptoethanol and measuring the change in the color. The reactions between the amines and S2Cl2 were rapid and used to print 2D objects with a variety of colors.