Dynamics in Crystallites of Poly(ε-caprolactone) As Investigated by Solid-State NMR

We investigate the molecular dynamics within the crystallites of poly(ε-caprolactone), PCL, crystallized from the melt by means of high-field 13C and low-field 1H NMR spectroscopy, addressing the question of whether it can be classified as a "crystal-fixed" polymer without chain motion through the crystallites. We address fast, slow, and intermediate-regime (microseconds to milliseconds time scale) motions by means of high-resolution of 13C DIPSHIFT and CODEX MAS experiments as well as low-resolution static 1H FID and MSE measurements over a range of temperatures. The DIPSHIFT data provide information on motionally averaged 13C–1H dipole–dipole couplings and indicate the presence of fast (≤1 μs) methylene group librational motions within the crystalline phase, where the amplitudes increase with increasing distance from the rather rigid ester groups. The CODEX experiments, addressing slow (≥ms) local rotations of the chemical-shift anisotropy tensors, suggest the absence of slow intracrystallite chain dynamics. 1H second-moment and MSE signal loss data of the crystalline fraction, along with the DIPSHIFT and CODEX data, indicate that intermediate-regime chain motions do not take place in PCL crystallites.