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- W2070291888 abstract "Nonexponential recovery curves have been obtained for anisotropic deuteron spin lattice relaxation of deuterated polyamidoammonium chloride salts for integer generations G = 1, 2, 3, 5, 7, and 9, at room temperature. The temperature dependence of the relaxation of generations 2, 3, and 9 is reported. Multiple exponential relaxation behavior is ascribed to a sum of single exponential, anisotropic contributions from overlapping quadrupole echo powder patterns. These are assigned to interior secondary amide, R2ND, deuterated tertiary amine, R3ND+, and terminal ammonium, RND3+, deuterons in the glassy polymer. Additional temperature dependent features in the middle of the spectra arise from mobile phases. For each type of deuteron the best fit of the relaxation data is achieved by numerically solving the stochastic Liouville equation for the relevant motional model. Planar libration of R2ND and R3ND+ deuterons is simulated by jumps along an arc. Motion of RND3+ groups is modeled as a two-frame process in which ND3+ rotation proceeds at by jumps about the pseudo 3-fold R−N bond axis, which in turn jumps at among sites in a cone. Low, intermediate and high generation subclasses of solid dendrimers are defined on the basis of rates and activation energies for libration and rotation of their spacer groups, branch points, and termini. There are two superimposed powder patterns for terminal ammonium deuterons, distinguished only by their different relaxation behavior. These arise from fast (1010 s-1) and slow (109 s-1) ammonium rotors. For low and high generations, the fast rotors represent a small fraction (<30% at ambient temperature) of less constrained ammonium groups. With increasing temperature, the fraction of fast rotors decreases for G2 and G9, but increases for G3. Data reported here quantify a model in which dendrimer arms of G3 are neither extensively interpenetrated (as for G2) nor backfolded (as for G9)." @default.
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- W2070291888 date "2000-09-13" @default.
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- W2070291888 title "Solid State Deuteron NMR Studies of Polyamidoamine Dendrimer Salts. 2. Relaxation and Molecular Motion" @default.
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- W2070291888 doi "https://doi.org/10.1021/ma000921u" @default.
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