The relationship between the morphology and the mechanical properties of copolymer ethylene-methyl methacrylate (EMMA) was estimated as a function of temperature by using polarized light scattering, X-ray diffraction and C-13 solid-state NMR. All of these measurements revealed unstable crystallites within the EMMA films having a MMA content >14 mol %, crystallinity less than 10%, and crystal size of about 3 nm. On the other hand, the ethylene sequences in the amorphous phase had an ordered arrangement rather than a random orientation. It is evident that these characteristics are due to the strong repulsion between MMA and ethylene. Namely, MMA side groups suppress the crystallization as an essential property of ethylene sequences; consequently, the difficulty of accelerating the self-arrangement of ethylene sequences as crystallites leads to a local ordered arrangement of long ethylene sequences in the amorphous phase. The maximum draw ratio of the EMMA film reached 10 times at room temperature. A specimen with a draw ratio <2 showed a reversible change of stress-strain curves up to 40 repetitions at room temperature. This behavior appears to be within the framework of ideal rubber elasticity. However, the stress at a fixed strain decreased with passing time as well as with increasing temperature. This behavior is completely out of the framework. Such inconsistency is due to the fact that small crystallites playing a cross-linking role became disrupted by chain slippage at a constant strain and at elevated temperature.