Abstract:
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 π″(ωτ s) are constructed by employing frequency-temperature superposition with τ s 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/τ s) 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. © 2012 American Chemical Society.
