A triple hydrogen-bond dominated fluorescent probe for monitoring the melting transition of polyurethane

Abstract

Accurately characterizing the phase transition temperatures of polyurethanes (PU) is indispensable for controlling material processing and usage conditions yet challenging. Herein, a DDA–AAD-type triple hydrogen-bonded luminescent complex was developed based on 7-methyl-1,8-naphthyridin-2-amine (D-Ny) and 1,3-dipyridin-2-ylurea (A-Py) to serve as a novel fluorescent probe for monitoring the melting transition of PU. This complex exhibited thermoresponsive luminescence in THF, with a change in the fluorescence intensity at the melting temperature of the solvent. Taking advantage of the specific luminescence response to the phase transition of the matrix, the triple H-bonding groups were chemically bonded to a polyurethane (PU) backbone as dynamic chain extenders. The melting transitions of the soft and hard segments were demonstrated respectively in real time in the temperature-dependent PL spectra of the fluorescent probe, offering higher sensitivity than the signal in the DSC curve in determining the melting temperature of the hard segment. This study provides a prospective approach for monitoring the melting transition of PU using a dynamic temperature-sensitive fluorescent probe.