Abstract
AbstractThe transition of NMR properties from a solidlike spin system response to a liquidlike one observed on molten polymers or on concentrated solutions is analyzed to characterize the slow diffusion process of long linear polyisobutylene (PIB) chains. It is first shown that the relaxation function of the transverse magnetic component of protons linked to PIB chains obeys a superposition property when the polymer concentration is varied from 0.5 to 1.0g/cm3; this is interpreted as reflecting the applicability of the viscoelastic submolecule concept to the description of NMR properties. The transition in NMR properties is then analyzed numerically, using a model of polymer chain relaxation based on a multiple‐relaxation‐mode process analogous to the Rouse model. The terminal relaxation time τv1 is shown to depend upon the chain molecular weight M as M3; it is found to be equal to 8.3 × 10−2 s for molecular weight M = 2.25 × 105 and concentration c = 0.47 g/cm3 in carbon disulfide at room temperature.
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