Unexpected fluorescence emission of poly(α,β-L-malic acid) in aqueous medium

Unexpected fluorescence of poly(α,β-L-malic acid) (α,β-PMA) without traditional fluorophore was observed firstly. This fluorescent polymer was synthesized via melt polycondensation of L-malic acid. The polymer was characterized by gel permeation chromatography (GPC), nuclear magnetic resonance (NMR), differential scanning calorimetry (DSC), thermogravimetry (TG), Fourier transform infrared spectroscopy (IR), Fourier transform Raman spectroscopy (Raman), and X-ray powder diffractometry (XRD). The high molecular weight α,β-PMA was synthesized by the optimum polycondensation at 130°C for 15 h, followed by fractional precipitation with diethyl ether and petroleum ether. The degree of branching of α,β-PMA was from 10% to 20% according to the reaction condition. Terminal group of α,β-PMA was mainly hydroxycarboxylic group companied with a few ---CH==CHCOOH groups owing to dehydration of a normal terminal during the melt polycondensation. A fluorescence emission maximum of α,β-PMA in water appeared at 420 nm when it was excited at 340 nm. Further study indicated that the fluorescence intensity was concentration-dependent, pH-dependent, and molecular-weight-dependent. The fluorescence formation may result from multichain aggregations, which was formed readily in aqueous solution due to intermolecular hydrogen bonds between branched α,β-PMA. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007