Two-dimensional infrared correlation spectroscopic study on thermal polymerization of diphenylbutadiyne

Thermal polymerization of diphenylbutadiyne at atmospheric pressure was investigated by differential scanning calorimetry, thermogravimetric analysis and two-dimensional infrared (2D-IR) correlation spectroscopy. Temperature induced spectral changes from 25 to 250 °C were monitored in the whole region 3200-400 cm−1. The spectral region 2300-2000 cm−1 of the triple bond stretching was thoroughly analyzed because it contains two bands in melt or solution of diphenylbutadiyne, at 2210 cm−1 (IR forbidden) and 2148 cm−1 (IR allowed). The two bands share a synchronous negative cross peak indicating opposite temperature-induced intensity changes in the molten state. At higher temperatures the symmetric CC stretching band at 2210 cm−1 is in fact superposition of close acetylenic bands of different oligomers. The oligomers most probably have cyclic structure since the 2210 cm−1 band persists at the highest temperatures where the monomer band at 2148 cm−1 no more exists. The new ascending band at 700 cm−1 shows the strongest synchronous autopeak and is clearly associated with simultaneous decreasing of the 687 cm−1 intensity associated with phenyl ring out-of-plane deformations. In the temperature interval 90-180 °C the so-called induction period is observed consistent with the onset of the bimolecular mechanism that is most probable for the DPB polymerization at temperatures above 200 °C.