NEUTRON-SCATTERING STUDY OF THE PICOSECOND DYNAMICS OF POLYBUTADIENE AND POLYISOPRENE

Neutron time-of-flight data of polybutadiene and polyisoprene in a wid e temperature range around the glass transition are reported. The anha rmonic part of the spectra is evaluated using a recently developed tim e domain Fourier transform technique. The results corroborate the rece nt finding of two different time domains in the dynamics, one above a crossover time of about 2 ps and the other below it. Two different int erpretations of the short time behavior are considered, namely a fast Debye regime of the alpha relaxation and a vibrational softening of th e boson peak.