Determining multiple component glass transition temperatures in miscible polymer blends: Comparison of fluorescence spectroscopy and differential scanning calorimetry

Fluorescence spectroscopy is used to measure component glass transition temperatures (Tgs) in miscible blends of pyrene-labeled poly(methyl methacrylate) (MPy-labeled PMMA) with poly(ethylene oxide) (PEO) or poly(vinyl chloride) (PVC) over a broad composition range. Component Tgs determined for PMMA blended with PEO can be described by the same value of self-concentration (0.60) determined previously (Lodge et al. J Polym Sci Part B: Polym Phys 2006; 44:756–763) using differential scanning calorimetry (DSC), indicating that fluorescence and DSC report a similar strength of component Tg perturbations. Blends of PMMA with PVC are also characterized via MPy-labeled PMMA fluorescence, demonstrating for the first time that both binary blend component Tgs can be determined from the temperature dependence of the fluorescence of a pyrenyl dye attached to a single blend component. This special sensitivity of the pyrenyl dye label to both component Tgs is hypothesized to derive from the solvatochromic nature of the dye, which in turn implies that the dye fluorescence may be sensitive to local stiffness or modulus in the blend. Because of the close proximity of the Tgs of neat PMMA and neat PVC, DSC is unable to clearly resolve the two component Tgs in these blends. Thus, fluorescence provides information unattainable by DSC and is a powerful new tool for investigating component Tgs in miscible blends.