The vibrational modes and the purity index of chitin and its derivatives as biopolymers are studied by Fourier transform infrared spectroscopy in the wavenumber range from 4000 to 400 cm(-1). The absorption bands of chitin and its derivatives are assigned. New bands appeared at 1419, 1209, 915, and 800 cm(-1) for chitin derivatives due to the change of vibrational modes. The purity indexes are calculated from the ratio of the absorption band of C = 0 at 1662 cm(-1) and OH at 3443 cm(-1). Generally, the purity indexes of chitin derivatives are higher than that of chitin, which is due to the decrease of OH. The dielectric properties such as the real part of the dielectric constant (epsilon') and loss tangent tan (delta) are measured as a function of temperature at different frequencies ranging from 200 to 2000 kHz. The increase of (epsilon') and tan (delta) with increasing temperature is discussed on the basis of increasing polarizability and the decrease with increasing frequency can be attributed to the dielectric dispersion. AC electrical conductivities as a function of the reciprocal of the absolute temperature are also discussed. The mechanism of the charge carrier is discussed as a tunneling model in the temperature range from 300 to 360 K. (c) 2005 Wiley Periodicals, Inc.