Mixtures of protonated and deuterated polybutadiene and polydimethylsiloxane are studied by means of field-cycling (FC) 1H NMR relaxometry in order to analyze the intra- and intermolecular contributions to spin–lattice relaxation. They reflect reorientational and translational dynamics, respectively. Master curves in the susceptibility representation χ″(ωτs) are constructed by employing frequency–temperature superposition with τs denoting the segmental correlation time. The intermolecular contribution is dominating at low frequencies and allows extracting the segmental mean square displacement ⟨R 2(t)⟩, which reveals two power-law regimes. The one at short times agrees with t 0.5 predicted for the free Rouse regime and at long times a lower exponent is observed in fair agreement with t 0.25 expected for the constrained Rouse regime of the tube-reptation model. Concomitantly the reorientational rank-two correlation function C 2(t/τs) is obtained from the intramolecular part. Again two power-law regimes t –ε are identified for polybutadiene. The first agrees with t –1 of free Rouse dynamics whereas at long times ε = 0.49 is obtained. The latter is corroborated by the 2H relaxation of deuterated polybutadiene, yet, it does not agree with ε = 0.25 predicted for constrained Rouse dynamics. Thus, the relation C 2(t) ∝ ⟨R 2(t)⟩–1 as assumed by the tube-reptation model is not confirmed.
Poly(propylene glycol), poly(isoprene), and poly(dimethlyl siloxane) (PDMS) of different molecular masses M are investigated by field-cycling 1H NMR relaxometry to monitor the crossover from segmental dynamics, to Rouse and entanglement dynamics. The spin–lattice relaxation dispersions T 1(ω) obtained at different temperatures (160 K – 400 K) are converted to the susceptibility representation χ″ DD (ω) = ω/T 1(ω). Applying frequency–temperature superposition, the data are merged to provide master curves χ″ DD (ωτ s ) with τ s = τ s (T) being the segmental correlation times. Combining them with those from dielectric spectroscopy about 12 decades in time are covered. A similar M dependence of χ″ DD (ωτ s ) is observed for all polymers (t ≫ τ s ) and comparison with dielectric normal mode spectra is carried out. In the case of PDMS showing particularities at t ≈ τ s we attempt to separate intra- and intermolecular relaxation contributions. Transformation into time domain yields the dipolar correlation function C DD (t/τ s ) which covers up to six decades in amplitude and eight decades in time. Whereas glassy dynamics is observed at shortest times, the correlation function closely follows C DD (t) ∝ t –1 at intermediate times as predicted by the Rouse theory. For longer times and high M entanglement sets in yielding C DD (t) ∝ t –ε with ε (<1) being M-dependent. As for the previously studied poly(butadiene), a highly protracted transition to full reptation is observed.
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