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Dynamics of Linear Polybutadienes in Solution Studied by Field Cycling 1H NMR.

Field cycling 1H NMR relaxometry is utilized to investigate dynamics in solutions of monodisperse polybutadienes of different molecular mass (M) and deuterated toluene. Broad temperature and polymer mass fraction ranges (c = 5-100%) are studied. By applying frequency-temperature superposition, susceptibility master curves χ″DD(ωτs) are constructed. They cover the segmental relaxation and polymer chain dynamics, and provide the concentration dependence of the segmental time constant τs(T). The relaxation strength of polymer dynamics is reduced similarly for all M with decreasing c; for the lowest c, almost no polymer dynamics shows up, that is, the dipolar correlation function obtained via Fourier transform decays almost completely due to segmental dynamics. The dipolar correlation function is decomposed into contributions of segmental and polymer dynamics. Its long-time power-law exponent associated with entanglement dynamics is increased from its bulk value with reduced c. This is interpreted as a continuous increase of the effective entanglement molecular mass.