The comonomer sequence distributions of a series of ethylene -dimethylamino-ethyl methacrylate copolymers(EDAM) were determined by high-resolution 13C-NMR spectroscopy quantitatively. It was found that the crystallinities and the lamellar thickness of EDAM samples reported by Ohmae et al. vary linearly with the numerical average sequence lengths of ethylene sequence. It was demonstrated that only ethylene chains longer than a critical number (25) can enter the crystalline region.This critical number is found to be independent of the molecular weights and the DAM contents of the copolymers under the same crystallization condition.