Molecular relaxations in ester-terminated, amide-based dendrimers

This study utilized Matrix Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry, Thermogravimetric Analysis, Differential Scanning Calorimetry, X-Ray Diffraction, and Dielectric Analysis to assess the viscoelastic and structural properties of three generations of tert-butyl and methyl ester, amide-based dendrimers. The effect of generation number and functionality on glass-transition temperatures and corresponding apparent activation energies, obtained via adherence to WLF behavior, were determined. Both were found to increase with increasing generation number and bulkiness of terminal functionalities. WLF constants, C-1 and C-2, allowed the determination of free volume, and thermal expansion coefficients, respectively. Secondary transitions, conforming to Arrhenius behavior, were also characterized and increased in temperature with generation number. The apparent activation energy was greater when the matrix was crystalline. Dielectric relaxation responses were analyzed to yield dielectric strengths of the molecular relaxations which increased with generation number and were comparable for both tert-butyl and methyl esters in the glass-transition region. Electrical properties of the dendrimers were dominated by ionic conductivity in the high temperature region. In order to unmask the glass transition, the data were treated in terms of the electric modulus. (C) 1999 John Wiley & Sons, Inc.