The temperature-dependent behavior of individual components within metallocene-catalyzed semisyndiotactic polypropylenes (semi-sPP) with a wide range of stereoregular content (26 to 96% rr) is studied using Fourier transform infrared (FTIR) spectroscopy and temperature-modulated differential scanning calorimetry (DSC). Changes in sensitive, high-resolution absorbance spectra are observed as melt-slow-cooled thin films are subjected to stepwise temperature increases. In general, spectral bands previously identified as being sensitive to ordered structures (e.g., conformed chains, crystal morphs) appear to follow overall trends of shifting to lower wavenumbers (energies), broadening, and decreasing in peak area intensity as temperature increases. Peaks that appear due to "splitting" (observed in more stereoregular materials) show a trend toward coalescence as temperature increases; this corresponds to a gradual loss of chain conformational order. Gauche-gauche-trans-trans (ggtt)(n) helical and all-trans (tttt)(n) planar zigzag-conformed chains that participate in the crystalline-amorphous interfacial region ("mesophase") appear to be more stable (i.e., they do not lose their conformational order as easily) with increasing temperature in materials with a greater degree of syndiotacticity. Moreover, IR data correspond well with modulated DSC endotherms located near 50 degreesC and 70 degreesC. At each transition temperature-thought to represent, respectively, a thermally driven chain conformation from planar zigzags to helices, and a dynamic disorder of helices marked by rapid gauche <----> trans isomerization-the IR absorbance ratio, A(978)/A(963), which represents the relative population of helical chains, undergoes an accelerated decrease. (C) 2005 Wiley Periodicals, Inc.