Synthesis of Reactive Water-Soluble Narrow-Band-Gap Polymers for Post-Crosslinking

Abstract

In this study, water-soluble, narrow-band-gap polymers containing reactive groups were prepared by the addition-condensation of pyrrole (Pyr), benzaldehyde-2-sulfonic acid sodium salt (BS), and terephthalaldehydic acid (TPA) or p-hydroxybenzaldehyde (p-HB). TPA and p-HB were used for the post-crosslinking reaction between polymers. The polymers were characterized by employing various analyses such as 1H-NMR, thermal gravimetric analysis (TGA), and UV-Vis-NIR. The Eg values of polymers estimated from the absorption edges were 0.55 and 0.62 eV. The post-crosslinking reaction is important for preventing resolubilization and for developing an electron conducting route between the polymer chains. Herein, the post-crosslinked polymer was observed to maintain its narrow-band-gap and conductivity was increased 46 times compared to that observed before crosslinking.

Electrical Conductivities of Narrow-Bandgap Polymers with Two Types of π-Conjugated Post-Crosslinking

“…A comparison of all the pressed polymer samples (Table 2) reveals that the postcrosslinked polymers show a higher electrical conductivity than those without crosslinking. The conductivity of P6 and P7 is 124 and 203 times higher than that of P4 and P5, and significantly higher than the conductivity of our previously studied ester-crosslinked polymers [45]. The improved electrical conductivity occurs due to an improvement in the electron-conducting routes (π-conjugated) between the polymer chains via postcrosslinking (imine-crosslinking and quaternization of pyridine-crosslinking).…”

“…where ρ V is the volume resistivity (Ω cm), R is resistance (Ω), RCF is resistivity correction factor, t is thickness (cm), and σ is conductivity (S/cm) [45].…”

“…The TMDA, pyridine, and aldehyde protons are detected at the same ppm (Figure 1). [45] 0.139 36,000 0.55 P(hydroxy) [45] 0.082 20,000 0.62…”

“…Ref. [45], P(carboxyl): π-conjugated polymer having a carboxyl group; P(hydroxy): π-conjugated polymer having a hydroxy group.…”

“…However, their electrical conductivities were low because of the negligible amount of charge carriers in undoped polymers and the inability of charge carriers conducting between the polymer chains. Recently, we used a post-crosslinking reaction (ester crosslinking) to reduce the distance between the polymer chains, which led to increased electrical conductivity [45]. To further increase their electrical conductivity, we focused on π-conjugated post-crosslinking between the polymer chains, which can provide electron conducting routes between them [46][47][48].…”