Determination of relaxation temperature of polymer blends, using polymeric luminescent probe

Full text: In this work were studied the photophysical properties of polymeric blends of luminescent conjugated polymer, poly(9,9'-n-dihexyl-2,7-fluorenodiilvinileno-alt-1,4-henylenevinylene) (LAPPS16), and atactic polymers, poly(methyl methacrylate) (PMMA) (75,000 MW), poly (ethyl methacrylate) (PEMA) (MW 350,000), and poly(isopropyl methacrylate) (PiPMA) (MW 100,000). The self-standing blends were obtained by co-precipitation procedure. No structural difference, X-ray diffraction, was observed for the matrices (methacrylate polymers) containing the luminescent polymers LAPPS16. Optical absorbance, photoluminescence (ambient temperature), and photoluminescence excitation showed that the LAPPS16 in atactic matrix is high diluted with low molecular aggregation formation. The relative emission quantum efficiency for dye molecule displays dependence on vitreos transition temperature (Tg) of methacrylate matrix, in crescent order, PEMA, PiPMA, and PMMA polymers. The polarization of emitted light was studied by emission ellipsometry technique. The samples were excited using linear polarization in the range from 400 – 470nm (absorbance spectral range of LAPPS16) and detected at emission peak of LAPPS16 at ∼~520nm. At low wavelengths, the inter- or intra-molecular energy transfer processes is high due to the lower linear polarization emission. The relaxation temperature of atactic polymers were determined calculating the variation of photoluminescence intensity of LAPPS16 in function of the excitation wavelength, 405 or 488nm, and the sample temperature from 35K to 410K. We found that the luminescent efficiency is direct dependent on the chemical ambient and consequently the attic polymer relaxation temperatures α, β, γ and δ. As a result, it is possible to use luminescent polymer, i. e., LAPPS16, to study the dynamics properties in guest-host matrix systems. (author)