Fourier transform infrared (FT-IR) spectrum was recorded by a
Bruker Tensor 27 spectrometer (Germany) in the range of 4000-
400 cm1. Proton nuclear magnetic resonance (1H NMR) spectrum
was obtained in a Bruker Avance DMX400 spectrometer (Germany)
using CDCl3 as solvent and tetramethysilane as internal standard.
Matrix-assisted laser desorption/ionization time-of-flight mass
spectrometry (MALDI-TOF-MS) analysis was performed on a
Bruker-Autoflex III Smartbeam by using polystyrene as the internal
standard, 2,5-dihydroxybenzoic acid as matrix, sodium iodide as
cationizing agent. Thermal gravimetric analysis (TGA) was carried
out on a TG 209 F3 thermogravimeter (Netzsch, Germany) from 30
to 800 C at a heating rate of 20 C min1 under air atmosphere