Buy this Article
The influence of xanthene-type dyes, rhodamines 6G (Rh6G) and B (RhB), on the chemical structure and dynamic characteristics of the polyurethane based on oligo-oxypropylene glycol, toluene diisocyanate and trimethylolpropane was investigated by various methods: infrared (IR)-spectroscopy, dynamic mechanical analysis (DMA) and electron paramagnetic resonance (EPR). This polyurethane is intended for use as gain media in solid-state dye lasers. Analysis of a complex band, assigned to the C=O group stretching vibrations in the IR-spectra of such polyurethane showed that the introduction of dyes caused changes in the integral intensities of both low-frequency (it determined the urethane-urethane intermolecular interactions) and high-frequency (it characterized the interactions of the urethane NH-group with the oligoether oxygen) spectral components. In the presence of dyes, the self-association of urethane groups inside the rigid segment prevails, and the interactions between the urethane groups and flexible oligoether parts decrease. This contributes to the mobility growth of the latter. These data are consistent with the observed reduction of Tg and storage modulus E` values for colored polyurethanes, determined by the DMA method. Both methods demonstrate a greater effect of the RhB dye on the mobility of the elastic fragment, since this dye is covalently bonded to the polyurethane chain. Data from the EPR method with the use of a nitroxyl paramagnetic probe showed that the introduction of dyes into polyurethane increased the permeability to vapors of a low molecular compound. EPR and DMA data agree; moreover, the Rh6G dye has a greater effect on the system permeability growth. The obtained results indicate the importance of intermolecular interactions in the formation of the polymer structure in the presence of a dye. The introduction of a reactive or complexing dye can significantly affect the structuring of the system, in particular, the defectiveness of cross-linking and segregation of flexible and rigid blocks, which is a crucial factor, when evaluating the radiation resistance of the matrix in the laser element.