Snail shell-shaped chiral substituted helical polyacetylene: preparation, characterization and infrared emissivity performance

The first snail shell-shaped helical polyacetylenes (SHPAs) were synthesized from the copolymerization between l-serine-grafted propargylamine (LSA) and propargylamine (PA). The novel structure was obtained at the monomer input proportion of 50%. The monomer (LSA) and copolymers (poly(LSAm-co-PAn)) were characterized by 1H nuclear magnetic resonance, Fourier transform infrared spectroscopy, ultraviolet visible spectroscopy, circular dichroism and transmission electron microscopy. The infrared emissivity of poly(LSA50-co-PA50) investigated at 8–14 μm was 0.451, which was much lower than the other copolymers. This was because the poly(LSA50-co-PA50) could form the obvious intramolecular interaction and self-assembled to a snail-shell shape by intermolecular hydrogen bonding in MeOH solution. Meanwhile, the conjugation performance of the main chain was enhanced. Consequently, the abundant hydrogen bonds formed through N–H and C=O bonding and the strong conjugate properties both could decrease the unsaturation degree, as well as change the heat conduction mode in the molecules, thereby reducing the infrared emissivity. This strategy provided a new direction to achieve the controllable infrared stealth.