Using time-domain spectroscopy (TDS), we performed high-precision spectroscopic measurements of polydimethylsiloxane (PDMS) in the terahertz domain. We investigated the influence of crosslinking on the terahertz absorption and refractive index, and modeled the data with vibrational density of states and coupling between photons and vibrational modes of the polymer molecules. We also investigated the influence of the temperature on PDMS, and observed the glass transition temperature, as well as the cold crystallization peak and the melting zone. (C) 2010 Elsevier B.V. All rights reserved.