Synthesis of transparent covalently self-colored polyurethane based on anthraquinone chromophore chain extenders

The hydroxyl terminated polyurethanes covalently bonded anthraquinone chromophores into skeleton were successfully synthesized based on 1-amino-4-hydroxy-2-(6-hydroxy-hexyloxy) anthraquinone (AHHA) and dimethylolpropionic acid (DMPA) as chain extenders. The UV–visible spectroscopy of polyurethane solution revealed that the conjugated structure of chromophore was not affected after bonding into polyurethane. Owing to the absorption of chromophore in the range of 360–630 nm, the polyurethane with 0.12 wt% AHHA in backbone possessed high transmittance of 94.6% in the range of 630–800 nm and that of polyurethane with 0.89, 1.32, 2.13 wt% AHHA were 87.9%, 82.5%, 78.6%, respectively. Interestingly, the optical transmittance of corresponding polyurethane was 80.5% in the range of 630–800 nm. Transparency was strongly related to the phase separation and crystallization behavior. The DSC curve revealed no endothermic peak and XRD showed a broad diffraction peak, demonstrating that chromophore-incorporated polyurethane with different AHHA amounts had no distinct phase separation and crystallization that accounted for good transparency.