Comparison of the pressure and temperature dependence of the elastic incoherent scattering for the polymers polybutadiene and polyisobutylene

The pressure and temperature dependence of the elastic scattering of two am orphous polymers, polybutadiene (PB) and polyisobutylene (PIB), is analyzed on the neutron backscattering spectrometer IN 16 and with an energy resolu tion < HWHM = 0.5 mu eV in a Q-range from 0.2 to 1.9 Angstrom(-1), a temper ature range from 2 to 400 K and for pressures between P-atm and P = 300 MPa . The Q-dependence of the scattering is analyzed in terms of the mean-squar ed displacement as a function of temperature and pressure in Gaussian appro ximation. We show that for polybutadiene the pressure dependence of the mea n square displacement can be scaled to a mastercurve taking the thermodynam ic glass transition temperature T-g as a scaling parameter. For polyisobuty lene the application of pressure clearly separates an additional dynamic pr ocess from the fast and alpha-relaxation process. (C) 1999 Elsevier Science B.V. All rights reserved.