NMR properties of poly(dimethyl siloxane) colloids as new contrast agents for NMR imaging

Abstract

By connecting the field-gradient spin-echo theory to spin–spin relaxation, we have found that the relationship between the tube-reptation model and spin–spin relaxation can be represented by G(t) = exp[−(t/T2) n] in which n = 1 and 0.5 for regimes IV and III, respectively. In our experiments, the spin–spin relaxation of linear poly(dimethyl siloxane) (PDMS) agrees with G(t) = exp[−(t/T2)] while that of crosslinked PDMS coincides with G(t) = exp[−(t/T2)0.5]. These results reflect that in the time interval 8–800 ms the dynamics of linear PDMS are in regime IV (governed by reptation motions) and those of the crosslinked PDMS are in regime III (dominated by wriggling motions). The line-shapes of NMR spectra of crosslinked PDMS are consistent with the Lorentzian rather than the Gaussian model. This can be accounted for by supposing that the PDMS chains between crosslinks have liquid-like motions even though crosslinked PDMS is a solid. The liquid-like motions of crosslinked PDMS could be regarded as wriggling motions described by the tube-reptation model. In addition, the experimental results of diameter distribution, viscosity, NMR image and spin–lattice relaxation are presented in this work. © 2000 Society of Chemical Industry