CONFORMATIONAL AND MOTIONAL CHARACTERIZATION OF ISOLATED POLY(EPSILON-CAPROLACTONE) CHAINS IN THEIR INCLUSION COMPOUND FORMED WITH UREA

The behavior of isolated poly(epsilon-caprolactone) (PEC) chains confi ned to the narrow channels of their crystalline inclusion compound (IC ) with urea is contrasted with the behavior of PEC chains observed in bulk, semicrystalline samples. DSC observations of bulk and IC-recover ed PEC samples revealed that PEC recovered from PEC-U-IC via extractio n with a nonsolvent for PEC produces crystals that melt 6 degrees C hi gher than PEC samples recrystallized from solution or the melt. Presum ably an extended chain morphology results when PEC crystals are obtain ed from the collapse of PEC-U-IC. FTIR and CPMAS/DD C-13 NMR observati ons both point to similar extended, nearly all-trans conformations for PEC chains in PEC-U-IC and in the bulk. Quantitative observations by both techniques yield a molar stoichiometry of U/PEC = 4/1. Solid-stat e C-13 NMR observations show channel-bound PEC chains in PEC-U-IC have spin-lattice relaxation times (T-1) only 20-50% as long as those obse rved for bulk PEC samples. On the other hand, the Tl's observed for th e urea carbonyl carbons in PEC-U-IC and n-hexadecane-U-IC are nearly i dentical, though the included n-hexadecane chains are known to be cons iderably more mobile than the included PEC chains.