Free volume and chain constraints in cis-1,4-polybutadiene as observed by high resolution NMR linewidth

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Abstract
High resolution proton magnetic spectroscopy of cis‐1,4‐polybutadiene is used to identify properties observed by NMR on molten polymers. It is shown that temporary constraints exerted on chains and due to entanglements can be qualitatively observed from low speed sample rotation. Also, resonance lines of the two types of protons of the monomer unit are shown to be well shaped according to the same function A|1+[(ω‐ωo)/Δ]3/2|−1; this line shape holds whatever the dilution and the temperature above the melting point of the solvent‐polymer system. Interpretation of the concentration and temperature dependence of the linewidth is shown to be compatible with a free volume description. Several values of free volume parameters are given. It is concluded that NMR spectra are sensitive not only to the chemical structure of monomer units but also to segmental chain motions.