Adamantane as a Probe for Studies of Spin Clustering with Multiple Quantum NMR

Abstract

Time domain 1H multiple quantum NMR (MQ NMR) was applied to study binary guest/host systems. We investigated protonated adamantane-h16 (A-h16) molecules in deuterated crystalline adamantane-d16 (A-d16) and in glassy polystyrene-d8 (PS) for various guest concentrations and coupling times τ/τc. For pure A-h16 crystals spin clusters of more than 1000 connected spins were observed. We observed the evolution of the multiple quantum connectivities as a function of the coupling time. In all cases the growth curves of the multiple quantum orders can be described by a master curve, showing the validity of a scaling law. For the diluted systems the master curve is obtained by multiplying the time axis with the square root of the dipolar line width (Δν)1/2. The different local structure of the systems leads to characteristic growth curves, in particular to a quadratic function for the crystalline and to a linear function for the glassy material. For short coupling times these differences can be attributed to geometrical constraints caused by the polymer chains while for longer coupling times geometrical constraints and dynamics of the polymer chains can both be responsible for the different growth curves. The technique was applied to study slow phase separation processes in a solution of A-h16 in PS.