Synthesis of Aromatic Conjugated Main Chain Azobenzene Polymers and Their Properties

Abstract

Azobenzene polymers have great potential and impact on fundamental and applied research. However little is known about their thermal stability and degradation behaviours. Herein, nine conjugated main chain azobenzene polymers were synthesized using the nitroamine derivatives of some diphenylene compounds such as 4-amino-4′-nitrobiphenyl 1, 4-amino-4′-nitrobiphenyl ether 2 and 4-amino-4′-nitrobiphenyl sulfide 3, and comonomers triphenylamine A, N-methyldiphenyl amine B and triphenylphosphine C via diazo coupling reaction. These heteroatom containing polymers were characterized by 1H- and 31P-NMR, FTIR, UV–Vis and Raman spectroscopy. The thermal stability and degradation behaviour of these polymers were studied by means of TGA technique. Electronic spectra of the polymers recorded in DMF showed two strong maxima at ca. 280 and 380 nm. They were resistant to heat up to 270 °C and, produced 41-61% char under a nitrogen atmosphere at 800 °C. UL 94 burning tests performed for TPU Ravathane® (TPE-U) with added azobenzene polymer revealed that these polymers could be used as an intumescent reactive flame retardant additive, particularly for polyurethanes and elastomers, due to their high char yield at relatively high temperatures (e.g 800 °C). The carbonized materials were further characterized by XRD and SEM/EDX.