Crystalline-noncrystalline structure and chain diffusion associated with the 180 degrees flip motion for polyethylene single crystals as revealed by solid-state C-13 NMR analyses

The structure of the noncrystalline overlayer and molecular motion in the c rystalline region for polyethylene single crystals have been investigated b y solid-state C-13 NMR spectroscopy and transmission electron microscopy. O ur previous finding that the noncrystalline overlayer is mainly composed of loose loops is confirmed for the single crystals with a typical lozenge sh ape by the line shape analysis of the fully relaxed DD/MAS C-13 NMR spectru m with the aids of C-13 spin-lattice and spin-spin relaxation time measurem ents. The occurrence of the 180 degrees flip motion in the crystalline regi on is clarified by using similar methods performed in the previous work. Mo reover, the chain diffusion associated with the flip motion in the crystall ine region is also observed at 78 degrees C in the 2D C-13 exchange NMR spe ctrum. A one-dimensional random walk simulation is carried out to clarify t he correlation between the 180 degrees flip motion and the chain diffusion. The loose loop structure of the noncrystalline overlayer is still kept eve n after the annealing for 7 days at the temperature where the chain diffusi on occurs. It is suggested that loose loops are probably the quasi-equilibr ium structure for the noncrystalline overlayer of the polyethylene single c rystals.