Dynamic mechanical analysis and dynamic infrared linear dichroism study of the frequency-dependent viscoelastic behavior of a poly(ester urethane) Yanqia Wang a , Richard A. Palmer a, * , Jon R. Schoonover b , Steven R. Aubuchon c a Chemistry Department, Duke University, Durham, NC, United States b Materials Science and Technology Division, Los Alamos National Laboratory, Los Alamos, NM 87544, United States c TA Insturments-Waters LLC, 109 Lukens Drive, New Castle, DE 19720, United States Available online 27 June 2006 Abstract Dynamic infrared linear dichroism (DIRLD) data have been collected as a function of strain modulation frequency in a simultaneous DIRLD- dynamic mechanical analysis experiment. The frequency range is limited, but the DIRLD data indicate some similarities to the temperature- dependent data. The frequency-dependent infrared data do not show the direct correlation with the mechanical data that was evident in the temperature-dependent study. However, the frequency-dependent infrared data do provide some molecular insight, with a similarity to the temperature-dependent results in the 1800–1320 cm 1 region, a quadrature signal increasing with increasing frequency in the 1320–1000 cm 1 region, and complex changes in the low wavenumber region that are interpreted as polymer chain responses as a function of frequency. # 2006 Elsevier B.V. All rights reserved. Keywords: Dynamic infrared linear dichroism; Mechanical response; Poly(ester urethane) 1. Introduction Dynamic mechanical analysis (DMA) measures the com- plex modulus in different modes of oscillatory deformation of materials [1,2]. This technique has been widely used to study dynamic mechanical properties of a variety of materials and is particularly useful for polymeric materials. Some polymers exhibit viscoelastic responses during deformation that are both frequency- and temperature-dependent. Dynamic infrared linear dichroism (DIRLD) is another powerful approach capable of studying frequency- and temperature-dependent viscoelastic behavior. Transitions observed in the frequency domain are expected to be related to the free volume or other microscopic properties of materials [3]. The instrument configuration reported previously is capable of carrying out continuous variable DMA–DIRLD experiments in both the temperature and frequency domains [4]. We have previously reported temperature-dependent DMA–DIRLD of this same poly(ester urethane). The current study probes the corresponding viscoelastic spectral response of this polymer in the frequency domain. Results from the two domains can be compared with respect to the concept of the time–temperature superposition principle, which is based on the observation that time–temperature (or frequency–temperature) effects on a polymer’s mechanical responses are largely equivalent. According to this principle, the behavior at higher temperature correlates with lower frequency and vice versa [5]. Over a wide enough frequency range, the plot of storage modulus versus increasing strain modulation frequency should be roughly similar to the inverse of the plot of modulus versus temperature. Due to experimental constraints, the frequency range in the current study is limited, but the DIRLD data in this limited frequency range can nevertheless be analyzed and examined. Multivariate curve resolution with alternating least squares analysis has been applied to the frequency-dependent dynamic infrared data and compared to the previously published temperature-dependent DMA–DIRLD data [6–10]. Multi- variate curve resolution analysis is a chemometric method that is particularly useful in gauging data as a function of a perturbation. The approach utilized in this application relies on www.elsevier.com/locate/vibspec Vibrational Spectroscopy 42 (2006) 74–77 * Corresponding author. E-mail address: richard.a.palmer@duke.edu (R.A. Palmer). 0924-2031/$ – see front matter # 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.vibspec.2006.04.017