Molecular relaxations in ester-terminated, amide-based dendrimers

This study utilized Matrix Assisted Laser Desorption/Ionization Time-of-Fli ght Mass Spectrometry, Thermogravimetric Analysis, Differential Scanning Ca lorimetry, X-Ray Diffraction, and Dielectric Analysis to assess the viscoel astic and structural properties of three generations of tert-butyl and meth yl ester, amide-based dendrimers. The effect of generation number and funct ionality on glass-transition temperatures and corresponding apparent activa tion energies, obtained via adherence to WLF behavior, were determined. Bot h were found to increase with increasing generation number and bulkiness of terminal functionalities. WLF constants, C-1 and C-2, allowed the determin ation of free volume, and thermal expansion coefficients, respectively. Sec ondary transitions, conforming to Arrhenius behavior, were also characteriz ed and increased in temperature with generation number. The apparent activa tion energy was greater when the matrix was crystalline. Dielectric relaxat ion 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. Electrica l 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.