Crystallization of Conjugated Polymers during Oxidative Polymerization from Vapor Phase

The structure-to-function relationship in conjugated polymers have been the subject of much scientific research; nonetheless, there are only a few reports on achieving control over the crystallinity of conjugated polymers, and the synthesis of well-defined conjugated polymers is known to be a challenging task. One way to achieve crystalline polymers is to induce crystallization during Polymerization. Here, we demonstrate the growth of crystalline films of conjugated polymers during polymerization using our liquid-free, oxidative chemical vapor deposition (oCVD), pathway. We demonstrate that by adjusting the substrate structure and tailoring the surface chemistry, we can enable the crystallization of poly(3,4-ethyelenedioxythiophene) (PEDOT). We observe a strong surface dependency for the nucleation of these crystalline materials. The X-ray diffraction, grazing incident wide-angle X-ray scattering, and transmission electron microscopy data suggest that the PEDOT chains are orientated in end-on configuration, perpendicular to the surface of the substrate. Large flakes of crystalline PEDOT, in the range of ~ 1 µm × 1 µm were grown, and the crystalline PEDOT showed enhanced properties compared to its amorphous counterpart, including 96% enhanced charge storage for crystalline material. A similar observation was made when we used other fused ring monomers of thiophene, confirming the instantaneous crystallization during growth for these conjugated polymers from the vapor phase.