Methyl-Group Tunneling in Viscoelastic Relaxation: Experimental Verification

Abstract

A relation between methyl-group tunneling and viscoelastic relaxation has been found in dynamic mechanical studies of the backbone methyl relaxation in polymethyl methacrylate (PMMA). The pronounced curvature found in the plot of $\mathrm{ln}\ensuremath{\nu}$ versus $\frac{1}{T}$ for the methyl relaxations at low temperatures and the observed large isotope effect for fully deuterated PMMA are in qualitative agreement with tunneling theory.