Restricted Dynamics in Poly(ether ether ketone) As Revealed by Incoherent Quasielastic Neutron Scattering and Broad-Band Dielectric Spectroscopy

Abstract

The molecular dynamics of semicrystalline poly(ether ether ketone) (PEEK) was studied over a broad dynamic range from 10-1 to 109 Hz by combining dielectric spectroscopy (DS) and incoherent quasielastic neutron scattering (IQNS). This allowed us to characterize the polymer dynamics in the glassy, semicrystalline, and molten states. By performing dielectric and neutron-scattering measurements in a comparable frequency range, we proved that the quasielastic broadening observed in IQNS experiments corresponds to the dielectric α relaxation without invoking any kind of low-frequency dielectric data extrapolation. IQNS measurements indicate that the segmental chain motion observed at temperatures higher than the glass transition temperature possesses an elastic and a quasielastic contribution. A model which considers a confined-jump diffusive motion allows a quantitative description of the IQNS spectra. This model provides dimensions of jump length, residence time, available space, and number of scatterers involved in the process. Results indicate that both the size of the restricted volume and the amount of protons involved in the α process increase with temperature and are smaller than the calculated values based on the crystallinity estimates from calorimetric and X-ray diffraction experiments. Both effects indicate for semicrystalline PEEK the existence of a confined amorphous phase with regions of different degrees of mobility. The present experiments provide a quantitative dynamical and spatial description of the heterogeneous amorphous phase of semicrystalline PEEK.