Decoupled Dynamics and Quasi-Logarithmic Relaxation in the Polymer−Plasticizer System Poly(methyl methacrylate)/Tri-m-cresyl Phosphate Studied with 2D NMR

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Studying the dynamics of the polymer−plasticizer system poly(methyl methacrylate) (PMMA)/tri- m -cresyl phosphate (TCP), we find pronounced dynamic heterogeneities for the additive TCP with one- and two-dimensional 31 P NMR spectroscopy, whereas the dispersion of the dynamics of the polymer PMMA, studied simultaneously with 2 H NMR, remains essentially unchanged upon addition of the plasticizer TCP, despite a large decrease in the correlation time. TCP molecules reorient isotropically even in a rigid polymer matrix at temperatures well below the glass transition of the plasticized PMMA. Taking advantage of the very large time window accessible with the stimulated echo technique for the 31 P nucleus, we show that the orientational correlation functions of TCP change from Kohlrausch decays for pure TCP to quasi-logarithmic decays in the mixture, which resemble those from recent simulations with a bead-and-spring model [Moreno, A. J.; Colmenero, J. J. Chem. Phys. 2006, 124, 184906]. Two-dimensional spectra for TCP show that the dynamic heterogeneities of the plasticizer are transient in nature.