A study on pyrolysis and cross-link formation of poly(p-phenylene butadiyne) by thermoanalysis and spectroscopy

In this study, we prepared a type of arylacetylene, poly(p-phenylene butadiynylene), PPPB, and studied its pyrolysis behavior. A pellet of PPPB maintained its shape and provided a carbonization yield of 94% by heat-treatment at 1000 °C, although it experienced exothermal reaction and partial fusion at approximately 200 °C. It was also found that PPPB did not show graphitization even when it was heat-treated at 3000 °C. X-ray diffraction (XRD) study revealed the breakdown of the initial crystal structure of PPPB at 200 °C and a formation of the carbon structure at above 650 °C. By combining the results of TG–MS, FT-IR, and 13C NMR, a mechanism for pyrolysis of PPPB including the cross-link formation was proposed, which included a Diels–Alder type reaction between the terminal acetylene and the diene structure comprising of diacetylene and phenyl groups, which is facilitated by increased mobility due to the partial fusion and the presence of the terminal acetylene groups.