Dynamical analysis of low-frequency depolarized Raman spectra of a neat monodisperse hyperbranched polymer between 333 and 123 K: Poly(propylene imine) DAB- dendr-(CN) 64

Abstract

VH-polarized Raman spectra of the title system between 4 – 250 cm −1 and at 333, 300, 273, 243, 173, 150, and 123 K show varying dynamical aspects depending on temperature and frequency range. At 123 K and between 10 – 50 cm −1 the system shows phonon motions, with a crossover at frequency ν C ∼ 25 cm −1 from a Debye to a fraction regime of spectral dimension d ∼ 1.1 and a correlation length which decreases with increasing temperatures. This implies that the open branching pattern of the molecules assumes, on the average, a more compact configuration with rising kinetic energies. Above 123 K, increasing temperatures cause increasing excess intensity from intramolecular relaxation mechanisms involving the motions of the molecule's terminal (CH 2) 2CN groups, with zero-frequency rates extrapolating to a critical temperature of T C ∼ 213 K, a value which is close to the thermodynamic glass transition point T G = 233 K of the system.