End-linked calibrated polypropylene-oxide chains. NMR approach to segmental fluctuations

End-linked calibrated polypropylene-oxide chains were used to establish quantitative experimental relationships between the magnetic relaxation of protons attached to the polymer and gel properties. Attention was focused on the effect of variations of the polymeric precursor molecular weight, M-n, (from 425 to 4000 g/mol). Considering the transverse magnetisation, it was first shown that the relaxation was governed by the non-zero average of dipole-dipole interactions; then, relaxation curves were characterised by a standard parameter which was shown to vary as a linear function of M-n; the slope depends linearly on the temperature interval defined from the glass transition temperature, T-g(M-n). The longitudinal relaxation rare of protons was represented by a single curve by using the reduced temperature variable [T-T-m(M-n)]/T-g(M-n) where T-m(M-n) corresponds to the temperature at which the maximum of the relaxation rate occurs; its amplitude was shown to be a simple linear function of M-n. (C) 1997 Elsevier Science Limited.