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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.

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The segmental dynamics of 1,4-polybutadiene is investigated by means of electronic field cycling 1H NMR. The frequency dependence (dispersion) of the spin–lattice relaxation time is probed over a broad range of temperature (223–408 K), molecular mass (355 ≤ M (g/mol) ≤ 441 000), and frequency (200 Hz–30 MHz). The extremely low frequencies are accessed by employing a home-built compensation for earth and stray fields extending prior reports about 2 decades to lower frequencies. Applying frequency–temperature superposition yields master curves over 10 decades in frequency (or time), and after Fourier transform the full dipolar correlation function is traced over up to 8 decades in amplitude. Several relaxation regimes can be identified, and their power-law exponents are compared to the predictions of the Doi–Edwards tube-reptation model, namely the free Rouse (I) and the constrained Rouse regime (II). Whereas the predicted value of the power-law exponent of regime II is 0.25, we find that it depends on M and levels off at 0.32 for very high M = 441 000 ≈ 220M e (M e: entanglement molecular mass). This is in good agreement with recent results from double quantum 1H NMR and indicates that the actual onset of full reptation dynamics is strongly protracted.

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