Abstract
The order-disorder phenomenon of local packing structures, space heterogeneity, and molecular dynamics and average lamellar thickness, < l >, of the alpha form of isotactic polypropylene (iPP) crystallized at various supercooling temperatures, Delta T, are investigated by solid-state (SS) NMR and SAXS, respectively. < l > increases with lowering Delta T, and extrapolations of < l >(-1) versus averaged melting point, < T-m >, gives an equilibrium melting temperature, T-m(0) = 457 +/- 4 K. High-power TPPM decoupling with a field strength of 110 kHz extremely improves C-13 high-resolution SS-NMR spectral resolution of the ordered crystalline signals at various Delta T. A high-resolution C-13 SS-NMR spectrum combined with a conventional spin-lattice relaxation time in the rotating frame (T-l rho H) filter easily accessess an order-disorder phenomenon for upward and downward orientations of stems and their packing in the crystalline region. It is found that ordered packing fraction, f(order), increases with lowering Delta T and reaches a maximum value of 62% at Delta T = 34 K. The ordering phenomenon of stem packing indicates that chain-folding direction changes from random ill the disordered packing to order in the ordered packing along the a sin theta axis under a hypothesis of adjacent re-entry structures. It is also found that f(order) significantly increases prior to enhancement of lamellar thickness. Additionally, annealing experiments indicate that < l > is significantly enhanced after a simultaneous process of partial melting and recrystallization/reorganization into the ordered packing at annealing temperature >= 423 K. Furthermore, the center-bands only detection of exchange (CODEX) NMR method demonstrates that time-kinetic parameters of helical jump motions are highly influenced by Delta T These dynamic constraints are interpreted in terms of increment of < l > and packing ordering. Through these new results related to molecular Structures and dynamics, roles of polymer chain trajectory and molecular dynamics for the lamellar thickening process are discussed.