Elastomeric polymers. Part II: NMR and NMR imaging characterization of cross-linked PDMS

Proton NMR relaxometry and imaging have been applied to investigate the molecular properties of silicone rubber networks unfilled, filled with silica, washed from the sol component, and in the presence of a guest polymer. For all the analyzed samples, the decay of the echo magnetization has been discussed on the basis of a single chain model with a distribution of dipolar interactions. The relaxation parameters have been investigated in order to correlate the structural and motional parameters of the elastomeric networks to the macroscopic characteristics of materials, mainly the cross-link density. On test samples a quite good agreement has been found between the calculated cross-link density and the T 2 and the qM 2 residual dipolar coupling parameters, determined by fitting the transverse magnetization decay on the basis of the assumed chain model. The imaging technique has been employed to characterize two networks, endowed with intrinsically different chain mobility and characterized by the presence and the absence of silica filler. An "in situ" polymerization reaction occurring in the silicones has been followed by NMR relaxometry and imaging techniques. The effects of thermal and chemical processes on the two different elastomeric matrices as well as the quality of the distribution of the guest polymer inside the host matrix have been assessed.