The Nature of Secondary Relaxations: The Case of Poly(ethylene-alt-propylene) Studied by Dielectric and Deuteron NMR Spectroscopy

Main (α-) and secondary (β-) relaxation of the linear poly(ethylene-alt-propylene) (PEP) with different molar masses are investigated by dielectric and 2H NMR spectroscopy. Regarding the α-process, time constants in the range 10–11–1 s are reported, and the correlation function is described by a Cole–Davidson function with stretching parameter β ≅ 0.34. Both methods show clear evidence of a pronounced β-process; the latter is thoroughly studied by different NMR techniques. The results are compared to toluene-d3 and toluene-d5, respectively, as reference systems. The solid-echo spectra as well as the spin–lattice relaxation display typical features of spatially highly restricted angular displacements similar to those reported in other glass-formers showing a β-process−like toluene. Above Tg all chain segments participate. As both chain and methyl group were deuterated and as the β-process is rather fast, its angular displacement growing with temperature above Tg is directly reflected in a reduction of the ...