High Pressure Polymerization of 2,6-Diethynylpyridine

Pressure induced polymerization (PIP) of unsaturated molecules like aromatics is highly focused on its production of novel carbon materials like diamond nanothread and graphane. However, the high stability of the aromatic molecules results in a high polymerization pressure at room temperature. To reduce the reaction pressure of the aromatic ring, here we introduced conjugated alkynyl, investigated the PIP of 2,6-diethynylpyridine (2,6-DEP) up to 30.7 GPa, and successfully obtained one-dimensional (1-D) ordered polymers below 10 GPa. In situ Raman and IR spectra show that the alkynyl starts to react at 4–5 GPa. At 5.4 GPa, the critical crystal structure of 2,6-DEP was investigated by in situ X-ray diffraction, and the shortest intermolecular distance was determined as 2.90 Å, between the pyridine ring. The product recovered from 10 GPa shows clearly a 1-D structure via transmission electron microscopy (TEM), and strong diffractions at d = 7.5 and 5.2 Å, corresponding to the interplane distance of the stacked 1-D polymer. Theoretical simulations show that the reaction starts between the alkynyl groups, after which the aromatic rings are drawn close to each other and react. Combining the predicted reaction and the experimental result, we concluded possible models of the product. Our study shows that alkynyl is a good initiator for reducing the polymerization pressure of the aromatics and therefore allows the synthesis of ordered 1-D carbon materials in large scale