Macromolecules, Vol.46, No.19, 7818-7825, 2013
Dynamics in Crystallites of Poly(epsilon-caprolactone) As Investigated by Solid-State NMR
We investigate the molecular dynamics within the crystallites of poly(epsilon-caprolactone), PCL, crystallized from the melt by means of high-field C-13 and low-field H-1 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 C-13 DIPSHIFT and CODEX MAS experiments as well as low-resolution static H-1 FID and MSE measurements over a range of temperatures. The DIPSHIFT data provide information on motionally averaged C-13-H-1 dipole-dipole couplings and indicate the presence of fast (<= 1 mu s) 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. H-1 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.