Scaling Analysis and Distribution of the Rotational Correlation Times of a Tracer in Rubbery and Glassy Poly(vinyl acetate):  An Electron Spin Resonance Investigation

We studied by ESR the rotational motion of a paramagnetic tracer (a deuterated 15 N-enriched nitroxide) in poly(vinyl acetate) (PVAc). The reorientation of the tracer occurs via jumps of about 50° with a heterogeneous distribution of correlation times. Depending on the temperature range, the average correlation time 〈 τ 〉 scales as the α, β, and γ relaxation times of PVAc, i.e., 〈 τ 〉 = C i 〈 τ 〉 i, i = α, β, γ. On cooling, 〈 τ 〉 tracks the α relaxation to about the α−β bifurcation temperature and then the β relaxation down to the glass transition. In glassy PVAc 〈 τ 〉/〈 τ 〉 γ = C γ ≈ 1.