Dielectric and fluorescent probes to investigate glass transition, melt, and crystallization in polyolefins

Investigation of glass transition dynamics in polyolefins by broadband dielectric spectroscopy (DRS) is facilitated by the addition of a novel dielectric probe, (4,4'-(N,N-dibutylamino)-(E)-nitrostilbene (DBANS), which introduces dipoles and made the polymers dielectrically active. For probe concentrations between 0.1% and 1.0% the dielectric strength Deltaepsilon associated with the dynamic glass transition increases proportionally to the probe concentration. This result indicates that the probe exhibits no intramolecular relaxations, and the probe rotational diffusion effectively senses the microviscosity of the probe environment on the length scale of the segmental dynamics. Temperature-dependent fluorescence spectroscopy on doped polymers shows no changes in fluorescence wavelength around the glass transition temperature. Crystallization and melting of the polyolefin matrix results in an increase or decrease of the probe concentration in the amorphous phase, which was clearly detected by real-time fluorescence because the probe emission is sensitive to the probe content, particularly at higher probe concentrations.