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Poly(ethylene- co-vinyl acetate) with 42 wt% of vinyl acetate shows autonomic self-healing at room temperature without macroscopic flow. Intermolecular diffusion of amorphous chains through the jointed boundary, which occurs because of the large amount of amorphous chains with low glass transition temperature, is responsible for the healing phenomenon. Furthermore, the healing efficiency is found to be enhanced when the separated pieces are recombined immediately after cutting. This result indicates that the cut surface has marked molecular mobility owing to the destruction of crystallites during the cutting process, which is supported by differential scanning calorimetry (DSC) measurements. The marked molecular mobility at the surface is, however, observed only for a short period after cutting, because further crystallization after cutting restricts the molecular motion. [ABSTRACT FROM AUTHOR]